George Davidson 1 R9 _T Q1 T Pr.ofessor of Geography University of tTafifdrrfia ' - ' "^jS -^ *"1>4 ' IHE STARRETT BOOK for MACHINISTS' APPRENTICES BY HOVARD P. FAIRFIELD i * Assistant Professor Machine Construction, Worcester Polytechnic Institute AND CARL S. DOW, S. B. Editor-in-chief Practical Mechanical Engineering Editor-in-chief Practical Shop Work PRICE, 50 CENTS THE L. S. STARRETT COMPANY The World's Greatest Toolmakers ATHOL, MASSACHUSETTS COPYRIGHT 1917 THE L. S. STARRETT COMPANY INTRODUCTION Laying out work preliminary to machining is trans- ferring blue-print instructions on to the metal. While the blue-print gives dimensions accurately, without any great precision in the drawing itself, lines laid out on the metal are to be worked to and must therefore be accurate. No one can consider himself a skilled machinist unless he can lay out his own work and, when called upon, lay out work for the less experienced. To become skilled in laying out should be the aim of every apprentice. Possessing this skill gives more op- portunity to show ability than the running of a machine. It is a qualification one must have for advanced posi- tions such as toolmaker, foreman, or superintendent. But laying out requires some knowledge of mathe- matics, some skill at mechanical drawing, and an acquaint- ance with machinists' fine tools and shop operations. Attention to details and extreme care are of utmost im- portance. Increased labor cost, as well as material wasted because of errors in laying out, are the penalties of mistakes. The apprentice, then, should lose no opportunity to make himself capable of laying out work. Close observa- tion of pieces laid out by skilled machinists is one way of becoming acquainted with the art. The fortunate apprentice may also have opportunity to observe a skilled machinist while laying out various jobs. The number of measuring and laying out tools or instruments now purchasable is very great and the ap- prentice must become familiar with practically all of them. He must know what he can accomplish with each so that he will instinctively select those best suited to the job in hand. M510983 THE STARRETT BOOK Economy of time in laying out is another element of success. Time-saving tools, such as the dial test indi- cator, quick-acting micrometer, and combination set, should be among those ready for use. The combination set, for instance, combines a rule, square, miter, protrac- tor, center square, depth gage, height gage, and level. The fewer the tools used, provided the ones at hand are really good ones, the less the bench will be littered with tools which may be used only occasionally. The tools in a machinist's tool-box are a sure indica- tion of his ability. A well-fitted kit of fine tools helps him hold a job in hard times and is one of the best assets a man can have when applying for a job. The pos- session of many fine tools indicates a love for accurate work, freedom from the borrowing habit, and a deter- mination to do work which will demand recognition. Next to having a complete outfit of fine tools is the dis- position on the part of the apprentice to add the best tools as rapidly as he can afford them. In preparing this book, the aim has been to select those elementary features most essential to the advance- ment of machinists' apprentices and students in techni- cal and manual training schools. It is intended to give such students a portion of the instruction ordinarily given by the teacher or by more experienced machinists. It will also serve as a reference book for data not to be memorized. THE S T ARRETT BOOK READING WORKING DRAWINGS Drawing is the language of the engineer, designer, and machinist. Unless a machinist can at least read working drawings he cannot be known as a skilled me- chanic. Certain conventions relating to views, lines, scales, sections, and other representations, are what make up the language of drawings, and the correct use of these is readily learned. A set of working drawings consists of GENERAL DRAWING, showing the entire machine with all the parts located in their proper relation to one another. This drawing is usually made to a reduced scale; for example, one-quarter or one-half size; it is often termed the Assembled or Assembly Drawing. DETAIL DRAWINGS show each part of the machine separately; they are often termed "detail," or "details." A detail drawing should be supplied with complete data for constructing the part, such as dimensions, material used, number of pieces, operations to be performed, etc., and should consist of sufficient views to be easily read. In practice some firms group several details upon a single sheet others place a single detail upon a sheet. SECTIONAL DRAWINGS show certain assembled portions, as if a part of the stock had been sliced away to more clearly illustrate the interior construction, often termed "sections." Position of "section" is shown by a full line drawn through a "view" and lettered at each end. BOLT AND SCREW LISTS. On these are tabulated all bolts, screws, etc., which are common to the stock- room, and necessary to the erecting of the machine. MOTION DIAGRAMS. Instruction is sometimes nec- essary concerning the relation of certain centers to the motion of parts, velocity ratios, and direction of motion; therefore where a machine has a number of more or less complicated motions, motion diagrams are provided. THE STARRETT BOOK THE STARRETT BOOK THE STARRETT BOOK VIEWS. All material things have three dimensions; length, breadth, and thickness or height. The draftsman of necessity makes use of some method of projection to get his various views on a flat surface on which only two dimensions can be shown the method of projection in machine-shop use places the front view with the other views grouped around in the order of their names, as top view above, bottom view below, etc.; each view cen- tering on either a horizontal or a vertical center line. FULL LINE DOTTED 1TINE CENTER LINE DIMENSION LINE SHADE LINE LINES. Full lines on a drawing indicate the visible lines or edges of the object. Dotted lines indicate hidden or invisible lines and edges. Broken lines, made up of dots and dashes, indicate center lines. All lay-outs should start from center lines. Dimension lines are usually full lines with a break in the line for dimension figures and an arrow head at each end to indicate the surfaces dimensioned. Section lines are parallel lines drawn across a surface which is represented as being in section; they are usually drawn at an inclination of 45 or 60, and equally spaced. By using for sections various combinations of full and dotted lines and special spacings, different materials of construction, such as cast iron, steel, etc., can be indicated. SCALES. Where convenient, all drawings are made actual size, termed full scale. When the object is too 10 THE STARRETT BOOK large to be conveniently represented full size, the draw- ing is made to a regularly reduced size, called a reduced scale drawing. The usual scales are full-size, half-size, quarter-size, and eighth-size, also known as 12", 6", 3", and IV 2 " to 1 foot. When working from drawings the dimension figures should be invariably followed meas- urements should not be taken from the drawing. BRASS OR BRONZE WHITE ALLOYS ALUMINUM LEAD ZINC 11 THE STARRETT BOOK ABBREVIATIONS. All information on a drawing is, when possible, abbreviated as follows: CONVENTIONAL ABBREVIATIONS Finish: Surface is to be finished Scrape: Surface is to be hand- scraped R. H.: Right Hand Grind: Surface is to be ground ' : Feet L. H.: Left Hand Face : To square up " : Inches W. L: Wrought Iron Bore: Use of bor- ing tools or bars Dia. : Diameter C. I. : Cast Iron Ream : Hole should be reamed Rad. : Radius M. S.: Machine Steel T. S.: Tool Steel C. R. S.: Cold Rolled Steel Tap : Hole is to be tapped Thd.: Thread C. S. : Carbon Steel H. S. S.: High Speed Steel. Drill: Hole is to be drilled U. S. S.: United States Stand- ard Running Fit, Drive Fit, Force Fit, Shrink Fit, Taper Fit: Allowances to be made in size of shaft SCREW THREADS, STRUCTURAL RIVETING, PIPE FITTINGS, LINE SHAFT BEARINGS, etc., are so stand- ardized that conventional representations are always used by the draftsmen. 12 THE STARRETT BOOK MEASURING TOOLS Measurements in general are those of length, area, and volume. In machine-shop practice the measurement of length is the common one. This is of such impor- tance, and many of the measurements are of such exact- ness, that a multitude of measuring tools are being marketed, nearly all of which are for the main purpose of obtaining linear measurements. THE YARD. In the United States the Standard of length is the British yard, of which two copies are owned by the United States Government. THE METER, which is the French standard of length, is also coming into use in the United States, notably in instrument work. The meter equals 39.37 inches. The use of measuring tools in machine work is largely confined to the thirty-sixth subdivision of the yard, or the inch. The inch is subdivided into various lengths, of which the ten-thousandth part is the short- est practical shop measurement. Measurements shorter than this are, however, common enough in scientific laboratory work. The practical machinist and toolmaker divides his work into two classes : (a) Flat Work and (b) Round Work. While it can- not be said that each class has its distinctive line of measuring tools, the workman who handles flat work only will usually have a somewhat different set of meas- uring tools from the workman on round work. FLAT WORK In general the worker on flat work will need to be provided with steel rules, dividers, protractors, straight 13 THE STARRETT BOOK Combination Set Toolmakers' Calipers Micrometer Depth Gage 14 THE STARRETT BOOK edges, steel squares, surface, height, depth, and thickness gages, center punches, parallels, slide calipers, etc. ROUND WORK For round work the measurements are by contact, and the usual tools are those having contact points. Contact measurements are made in two ways: (a) The contact tool is first set to some standard of length, as, for ex- ample, a steel rule, or a standard gage. The "set" dimen- sion may then be used as a standard for testing the work. (b) The reverse of this method may be used for deter- mining sizes, viz.: by first setting the contact points to the surfaces of the work, afterward using the steel rule or standard gage to read the size. "FEEL" The accuracy of all contact measurements is dependent upon the sense of touch (feel). In the case of skilled workmen, as, for example, toolmak- ers, the sense of touch is highly developed. Using suitable contact measur- ing tools, the skilled me- chanic can readily "feel" the difference in contact made by changes of di- mensions as small as 0.00025". In the human hand the sense of touch is most prominent in the finger-tips. Therefore the contact measuring tool should be held by 15 THE STARRETT BOOK the fingers only, and in such a way as to bring it in con- tact with the finger-tips. If the tool is harshly grasped by the fingers, the sense of touch or feel is much re- duced. For this reason the tool should be delicately and lightly held instead of gripped tightly. The more common tools for contact measurements are inside and outside calipers, used in conjunction with steel rules, plug and ring gages, and dimension blocks. While it is possible to transfer by "feel" a length with an error not exceeding one-quarter of one thou- sandth inch, the results are not always easily read; for this reason mechanics prefer to use direct reading tools for the more accurate contact work. Two methods of direct reading are in common use. VERNIER CALIPERS This tool is a combination of contact points and steel rules. One of the contact points is a fixed part of a graduated steel rule, while the other contact point is a part of a graduated slider mounted upon the blade of the first. By combining the use of the separate scales, direct readings of one-thousandth part of an inch are readily made. FRONT 16 THE STARRETT BOOK VERNIER HEIGHT GAGE ^^-*~" '1 Another adaptation of the vernier is the height gage. By means of the vernier it is easy to make readings as minute as one thousandth part of an inch. This instru- ment is used chiefly where close, accurate measurements of height must be obtained; the method of using is clearly shown on page 105 where it is used in finding the center to center distance of a pair of jig buttons. By means of suitable adjustments, one of which is shown on the accompanying illustration, its use is extended to include making accurate measurements of depth. The tool is thus rendered particularly de- sirable for use in jig-making for the depth of a recess inside the jig frame may be read- ily obtained. The removable jaw allows the user to make reverse measurements on the jig frame. 17 THE STARRETT BOOK THE STARRETT BOOK MICROMETER CALIPERS With the invention of the micrometer screw there came into use a new method of direct readings in contact measurements. The great accuracy of the micrometer screw becomes evident when it is realized that threaded spindles with a limit of error of 0.001" in one-foot lengths are commercially possible. In micrometer con- struction with a used length of screw thread of one inch only, the error is negligible. A micrometer head con- sists of a spindle, threaded forty to the inch, fitted through a threaded sleeve, having an enclosing thimble fastened to its outer end. Suitable graduations made axially on the threaded sleeve combined with the grad- uations on the edge of the rotating thimble give direct readings of one-thousandth part of one inch. By means of a vernier scale used on the rear of the sleeve direct contact readings as small as one ten-thousandth part of one inch can be readily made. Micrometer screws are mounted in a frame which may be varied in shape and size to render it convenient for the desired purposes. The contact points are also shaped to the particular use desired, and instruments of this type in a variety of styles and of the highest degree of accuracy, convenience, and finish are purchasable, for either inside or outside measurements. For measurement by thousandths up to one-half inch. 19 THE STARRETT BOOK Micrometer Measurements The limit of accuracy obtained by measuring between contacts depends on the graduations on the instrument. It is evident that as the fineness of the graduation increases, the chances for mistaking one graduation for another also increase so that some other method of determining extremely accurate measure- ments must be devised. The commpn instrument for making such measurements is known as a micrometer-caliper. It combines the double contact of the slide calipers with a screw adjustment which may be read with great accuracy. 20 THE STARRETT BOOK HOW TO READ A MICROMETER The pitch of the screw threads on the concealed part of the spindle is forty to an inch. One complete revolu- tion of the spindle, therefore, moves it lengthwise one fortieth (or twenty-five thousandths) of an inch. The sleeve D is marked with forty lines to the inch, corre- sponding to the number of threads on the spindle. Each vertical line indicates a distance of one-fortieth of an inch. Every fourth line is made longer than the others, and is numbered 0, 1, 2, 3, etc. Each numbered line indicates a distance of four times one-fortieth of an inch, or one tenth. The beveled edge of the thimble is marked in twenty- five divisions, and every fifth line is numbered, from to 25. Rotating the thimble from one of these marks to the next moves the spindle longitudinally one twenty- fifth of twenty-five thousandths, or one thousandth of an inch. Rotating it two divisions indicates two thou- sandths, etc. Twenty-five divisions will indicate a com- plete revolution, .025 or one-fortieth of an inch. To read the micrometer, therefore, multiply the num- ber of vertical divisions visible on the sleeve by twenty- five, and add the number of divisions on the bevel of the thimble, from to the line which coincides with the 21 THE STARRETT BOOK horizontal line on the sleeve. For example, in the en- graving, there are seven divisions visible on the sleeve. Multiply this number by twenty-five, and add the number of divisions shown on the bevel of the thimble, 3. The micrometer is open one hundred and seventy-eight thou- sandths. (7 X 25 = 175 and 175 + 3 = 178.) HOW TO READ A VERNIER Readings in ten thousandths of an inch on caliper squares, micrometers, etc., are obtained by the use of a Vernier, named from Pierre Vernier, who invented the device in 1631. For the Vernier caliper, the scale on the tool is graduated in fortieths of an inch (0.25). On the Vernier plate is a distance divided into twenty-five parts, and these twenty-five divisions occupy the same distance as twenty-four divisions on the scale. The difference between one of the twenty-five spaces and one of the twenty-four spaces is one twenty-fifth of one-fortieth, or one thousandth of an inch. To read the tool, note how many inches, tenths (or .100), and fortieths (or .025) the mark on the Vernier is from the mark on the scale; then note the number of divisions on the Vernier from to a line which exactly coincides with a line on the scale. In the engraving above, the Vernier has been moved to the right one and four-tenths and one-fortieth inches THE STARRETT BOOK (1.425"), as shown on the scale, and the eleventh line on the Vernier coincides with a line on the scale. Eleven thousandths of an inch are, therefore, to be added to the reading on the scale, and the total reading is one and four hundred and thirty-six thousandths inches (1.436"), which is the distance the jaws have been opened. HOW TO READ A VERNIER MICROMETER Readings in ten thousandths of an inch are obtained ON THE MICROMETER by the use of a Vernier, which operates on the same principle as the Vernier on the caliper. In this case, however, ten divisions on the sleeve occupy the distance of nine divisions on the thimble. The difference between the width of one of the ten spaces and one of the nine spaces is one-tenth of a THIMBLE LO O JJ'I J I I I I division on the thimble. Now each division on the thimble represents one-thousandth of an inch, and one- tenth of one-thousandth equals One ten-thousandth. To read a ten-thousandth micrometer, first note the thou- sandths as in the ordinary micrometer. Then observe the line on the sleeve which coincides with a line on the thimble. In the diagram shown above there are nine vertical divisions visible on the sleeve, and 9 X 25 = 225, so that the reading of the ordinary micrometer would be .225. Line marked "7" on the sleeve coincides with a line on the thimble and, therefore, we add seven to the reading of the ordinary micrometer. This seven is seven ten-thousandths (.0007), and the readings will be .2257. THE STARRETT BOOK JHHsflHiE h-r-izsl ta^u.'V' '.062S i 3 .16 \S .312 L/M7S Half-Inch Micrometer For measurement by thousandths up to one-half inch. The anvil is shortened, for use in places where the ordinary anvil is too long to be inserted. Has lock nut and ratchet stop. Quick-Adjusting Micrometer Has ratchet stop and lock nut. Six-Inch Micrometer For measuring round work to 4% inches and flat work to 6 inches. 24 THE STARRETT BOOK OPERATION AND ADJUSTMENT OF MICROMETERS QUICK MEASUREMENTS. A micrometer having the quick-adjusting feature can be instantly opened or closed to any size within its capacity. Pressure of the finger on the end of the plunger allows the spindle to move instantly to the desired size without turning the thimble. When the finger is removed, fine adjustments may be made in the usual way. MICROMETER AS A GAGE. By means of a knurled lock nut the spindle can be firmly fixed in position, making the micrometer a solid gage. Turning the lock nut contracts a split bushing around the spindle, keep- ing it central and true. READJUSTMENT FOR WEAR. When slight wear makes correction necessary, the readjustment is accom- plished by various means depending upon the kind of micrometer. With the Starrett micrometer the anvil is fixed, not movable, and correction is quickly made by inserting a spanner wrench and turning until the line on the sleeve coincides with the zero on the thimble. This feature does away with the frequent use of a test piece. 25 THE STARRETT BOOK TRANSFERRING MEASUREMENTS Transferring a measurement may be a delicate job or not, wholly depending upon the degree of accuracy sought. The most common of all machine-shop tools for transferring measurements are steel rules and spring calipers. With these tools, either in combination or used separately, are made the bulk of common ma- chine-shop measurements, whether those of inside or outside surfaces. STEEL RULES These are thin blades of steel of varying lengths, widths, and thicknesses, usually graduated in inches and various subdivisions of the inch upon each edge of both sides and often at the ends. The makers term the vari- ous subdivisions of the inch by graduation numbers, for example, No. 4 Graduation, 1st. edge 64ths; 2d. edge 32ds; 3d. edge 16ths; 4th. edge 8ths. By means of slid- ing or fixed attachments a great variety of length meas- urements may be made with the ordinary steel rule. SPRING CALIPERS The most commonly used tool for contact measure- ments is the ordinary spring caliper, which is used for measuring over surfaces or between surfaces. In- shop language this is called making-outside-or-inside meas- urements. The legs of the spring caliper are curved down, to make two opposite contact points, the distance between being controlled by a screw which works against a tension spring. For either outside or inside measure- ments they may be set to or they may be read to a graduated steel rule. In this way a workman can trans- fer lengths with an error of less than 0.002". Where THE STARRETT BOOK specially accurate spring caliper measurements are de- sired, fixed gages are used for setting the contact points. The degree of accuracy of contact is dependent upon what the workman terms "feel." To accurately transfer a dimension with spring calipers the sense of "feel" must be well developed by the workman, for the contact points are at the ends of very slender arms. Spring calipers, both for inside and outside work, can be set to dimensions either larger or smaller than the gages used by introducing thickness strips between the contact points and the over or inside surfaces. Hard, thin tissue-paper may be used as thickness strips, or, better still, steel thickness gages or " feelers." Calipering Over a Flange 27 THE STARRETT BOOK SPRING DIVIDERS In this tool the contacts are points at the ends of straight legs. Dividers are used for measuring dimen- sions between lines or points, for transferring lengths taken direct from a graduated steel rule, or for scribing circles or arcs. " Feel " does not enter to such an extent into the transfer of dimensions when using spring dividers as it does with spring calipers; however, a certain delicacy of touch is essential. A magnifying glass is a wonderful help for the accurate transfer of dimension with dividers. If a con- siderable length is to be transferred, it is best to use the type where the points are adjustable along a bar, known as a Universal Divider, for the points do not then incline to the surfaces worked upon. THE STARRETT BOOK FITS AND FITTING In machine construction many of the parts bear such a close and important relation to one another, that a certain amount of hand fitting is essential to make the surface contacts as they should be. If the surfaces in contact are to move on each other the fit is classed as a sliding or running fit. If the surfaces are to make contact with sufficient firmness to hold them together under ordinary use, the fit is classed either as a driving, shrink, or forced fit. SLIDING FIT. Under this head may be classed the litting of cross and traversing slides of lathes, milling machines, drilling machines, boring machines, grinding machines, and planers. In most of these fits the moving and stationary parts are held in contact with each other by means of adjustable contact strips or gibs, sometimes known as packing strips. In some cases, such as the tables of grinding and of planing machines, their weight keeps them in sufficiently close contact. RUNNING FITS. The journal bearings of spindles, crank shafts, line shafting, etc., are classed under this heading. FORGED FITS AND SHRINK FITS. Under this head are classed those fits where the separate parts must become in use as if they were a single piece; as, for example, the crank pins and axles in locomotive driving wheels, the cutter heads and spindles of numerous wood- working machines, as .well as many other cases. LIMITS. In the case of running and of sliding bear- ings a certain amount of hand fitting is necessary to obtain desired results, and in all cases certain limiting requirements obtain. In sliding and running bearings the limits are usually those of alignment and of contact, while in either journal bearings or in flat sliding bear- ings it is essential that certain accurate contact between 29 THE STARRETT BOOK the surfaces shall be made, and there will also be a limit of alignment with other parts of the machine. For ex- ample, in the engine lathe the ways or vees and the cross slide of the tool carriage must be parallel to or at right-angles to the axis of the spindles within set limits. In engine lathe construction the limit set for this is 0.001" in a foot of length. In testing the parts use is made of the Universal Test Indicator with the needle reading on a dial or upon a sector arm. The indicator may be clamped to a test bar, a straight edge, or direct to the lathe spindle; also, if desired, it can be and often is held upon a special slider stand fitted to the vees of the machine. In the making of shrinkage and forced fits the limits are usually those of size. The amount of pressure necessary to place the two parts together is the limiting fact in the case of forced fits. In forcing the axles into locomotive driving wheels, the specifications may limit the pressure to between one hundred to one hundred and fifty tons. However specified, it in fact reduces to limits of size and the use of measuring tools. These can be of the direct reading contact type, as the micrometer and vernier bar, or of the indirect reading contact type, as, for example, the ordinary spring caliper used in con- junction with thickness gages or "feelers." AMOUNTS TO LEAVE. Where pins, spindles, etc., are to be forced irito holes, or where collars, hubs, flanges, and other machine parts are to be shrunk on to spindles, it is customary to make the diameter allow- ance upon the spindle rather than upon the hole. The amount which it is necessary to add to the spindle or shaft diameter must of necessity vary with the length and diameter of the hole, the metals used, and the form of the surrounding hub. The following tables give cer- tain practice. 30 THE STARRETT BOOK Allowances for Different Classes of Fits Table 1 (Newall Engineering Co.) Class Tolerances in Standard Holes* Nominal Diameters Up to W %.M' !Vi6"-2" 2yi"-3" 3*M" 4*"-5 A High Limit Low Limit Tolerance +0.0002 0.0002 0.0004 +0.0005 00002 0.0007 +0.0007 0.0002 0.0009 +0.0010 0.0005 0.0015 +0.0010 0.0005 0.0015 +0.0010 0.0005 0.0015 B High Limit Low Limit Tolerance +0.0005 0.0005 0.0010 +0.0007 0.0005 0.0012 +0.0010 0.0005 0.0015 +0.0012 0.0007 0.0019 +0.0015 0.0007 0.0022 +0.0017 0.0007 0.0024 Allowances for Forced Fits High Limit +0.0010 +0.0020 +0.0040 +0.0060 +0.0080 +0.0100 F Low Limit +0.0005 +0.0015 +0.0030 +0.0045 +0.0060 +0.0080 Tolerance 0.0005 0.0005 0.0010 0.0015 0.0020 0.0020 Allowances for Driving Fits High Limit +0.0005 +0.0010 +0.0015 +0.0025 +0.0030 +0.0035 D Low Limit +0.0002 +0.0007 +0.0010 +0.0015 +0.0020 +0.0025 Tolerance 0.0003 0.0003 0.0005 0.0010 0.0010 0.0010 Allowances for Push Fits High Limit 0.0002 0.0002 0.0002 0.0005 0.0005 0.0005 p Low Limit 0.0007 0.0007 0.0007 0.0010 0.0010 0.0010 Tolerance 0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 Allowances for Running Fits t X High Limit Low Limit Tolerance 0.0010 0.0020 0.0010 0.0012 0.0027 0.0015 0.0017 0.0035 0.0018 0.0020 0.0042 0.0022 0.0025 -0.0050 0.0025 0.0030 00057 0.0027 Y High Limit Low Limit Tolerance 0.0007 0.0012 00005 0.0010 0.0020 0.0010 00012 0.0025 0.0013 0.0015 0.0030 0.0015 0.0020 0.0035 0.0015 -0.0022 0.0040 0.0018 z High Limit Low Limit Tolerance 0.0005 0.0007 0.0002 0.0007 0.0012 0.0005 0.0007 0.0015 0.0008 0.0010 0.0020 0.0010 0.0010 0.0022 0.0012 0.0012 0.0025 0.0013 * Tolerance is provided for holes, which ordinary standard reamers can pro- duce, in tw9 grades, Classes A and B, the selection of which is a question for the user's decision and dependent upon the quality of the work required ; some prefer to use Class A as working limits and Class B as inspection limits. t Running fits, which are the most commonly required, are divided into three grades : Class X for engine and other work where easy fits are wanted ; Class Y for high speeds and good average machine work ; Class Z for fine tool work. 31 THE STARRETT BOOK LIMITS OF TOLERANCE While it is possible to produce machine parts with measurements refined to any degree of accuracy, ex- treme precision may prove too costly for commercial work. To avoid waste of time, lahor, and money, the Taft- Peirce Manufacturing Company has formulated a set of rules which defines the degree of accuracy to be expected in those cases where specifications and drawings do not call for greater precision than the rules provide for. (1) Full information regarding limits of tolerance should be clearly shown by drawings submitted, or be definitely covered by written specifications to which reference must be made by notations on the drawings. (2) Where the customer fails to supply proper data as to limits, this Company's Engineers will use their best judgment in deciding just what limits it may be advisable to work to. The Company will not, in any event, assume responsibility for possible excessive cost brought about through working to closer limits than may be necessary nor for permitting greater latitude than may subsequently be found to be proper. (3) Where dimensions are stated in vulgar frac- tions with no limits of tolerance specified, it will be assumed that a considerable margin for variation from figured dimensions is available; unless otherwise or- dered, the Company's Engineers will proceed according to the dictates of their best judgment as to what limits should be taken. (4) For all important dimensions Decimal figures should be used and limits clearly stated on detail draw- ings. If Decimal figures are not used for such dimen- sions a notation referring to the degree of accuracy required must be placed prominently on the drawing. (5) It is frequently necessary to reduce fractions 32 THE STARRETT BOOK representing fourths, eighths, sixteenths, thirty-seconds, and sixty-fourths to decimal equivalents. When a dimen- sion of this character is expressed in a decimal equivalent and carried out to three, four, or five places and limits are not specified it will be assumed that a limit of plus or minus .0015 is permissible unless otherwise ordered. (6) Where dimensions are stated in decimal figures derived by other processes than those explained in para- graph five, but with limits not specified, the following variations from dimensions stated may be expected: Two place decimals .005 plus or minus Three " " .0015 Four " " .0005 Five " " .0002 (7) Where close dimensions, such as the location of holes from center to center in jigs, fixtures, machine parts, and other exact work of like character are re- quired, detail drawings should be prominently marked "ACCURATE" and clear instructions be given. (8) The dimensions of internal cylindrical gages, external ring gages, snap gages, and similar work speci- fied to be hardened, ground, and lapped, will be obtained as accurately as the best mechanical practice applying to commercial work of the particular grade specified will permit. (9) As drilled holes vary in size from .002" to .015" (and in some cases even more) over the size of the drill used, those which require to be made accurately to defi- nitely specified sizes should be either reamed, ground, or lapped, and detail drawings thereof should bear nota- tions accordingly. (10) U. S. Standard form of thread and pitches will be used for *4 -inch and all sizes above. A. S. M. E. Stand- ard will be used for numbered sizes below ^4 -inch. In the absence of specifications to the contrary, U. S. Stand- ard form of thread will be used for all SPECIAL sizes. 33 THE STARRETT BOOK THE STARRETT BOOK BENCH WORK Bench work includes laying out, chipping, filing, polishing, hand reaming, hand tapping, and all the many shop jobs done at the bench or in a vise. LAYING OUT. This is the shop term which includes the placing of lines, circles, and centers upon curved or flat surfaces for the guidance of the workman. It is some- what analogous to mechanical drawing. It differs in one important respect, however, that while a line drawing is seldom scaled and therefore exact accuracy of spac- ing is not required; in laid out work, the lines, circles, centers, etc., are to be followed exactly. All lines, cen- ters, etc., should therefore be exactly located and placed, and all scriber, divider, and center points should, while in use, be exact and sharp. Particular care must be maintained to insure fine and accurate laying out. PREPARING THE SURFACE. If work of no special accuracy is desired, carefully rubbing chalk, or white lead mixed with turpentine, upon the surface of the work will be sufficient as a coating. For fine exact lay- outs a special marking solution must be used. The one in common shop use is a mixture of one ounce copper sulphate to four ounces water. A little nitric acid may with advantage be added. This solution applied to a cleaned iron or steel surface gives a dull coppered sur- face, and the finest line scribed upon it is brilliantly visible. SCRIBING LINES. The usual scribing points are those common to dividers, hermaphrodite calipers, scratch awls, scratch gages, surface gages, and trammel points. Combined with the scribing points, may be used steel rules, bevel protractors, steel squares, steel straight edges, levels, end measuring rods, micrometer or vernier height and depth gages, and the various center punches. Ability to so combine and make use of the various tools 35 THE STARRETT BOOK THE STARRETT BOOK as to insure accuracy is a considerable asset to the lay- ing-out man. PROTRACTORS As made for machine-shop use the common protrac- tor is provided with attached straight edges, and can be used either to measure or to lay off lines at an angle to each other. Measuring the angularity of two or more lines with a protractor is termed "reading the angles." As oftentimes its use is determining the angle made by two surfaces (a bevel), the tool is usually termed a bevel protractor. Protractors for common shop use are grad- uated to degrees through a length of circumference of one hundred and eighty degrees. An attached vernier enables the user to read angles to one-twelfth of a degree (five minutes). LAYING OUT PLATE. If desirable results are to be 37 THE STARRETT BOOK obtained in laying out flat work, special metal plates upon which to rest the work and the tools must be pro- vided. These are known as leveling, surface, or laying- out plates; they furnish an accurate plane surface upon which work and tools may be placed. The size of these plates varies from those of small areas used in laying out small jigs, etc., to those for large pieces, having sides several feet in length. The work may be laid directly upon the surface of the plate or held upon leveling strips or blocks placed on the plate, and the gages, squares, and other tools used around the work. In other cases it is convenient to clamp the work to knee or angle irons, which are then placed upon the leveling plate. CHIPPING Formerly many of the surfaces of machine parts were hand-chipped and filed to a fit. While the mechanic in the modern shop can usually find methods of machin- ing most of the surfaces he needs to fit up, there are still occasions when the work has to be hand-chipped. TOOLS USED. The common chipping tools are a hand hammer and a hand chisel. The hand hammer should weigh not less than three-quarters of a pound nor over two pounds, and may be either of the ball peen or flat peen type. A chipping hammer should balance well in the hand when fitted to a handle not more than sixteen inches long. The handle near where it enters the hammer should be thinned and worked down to a shank that is somewhat flexible, so that the shock to the arm and hand will be less. The face of a good chipping hammer should crown slightly. Chipping chisels, ordinarily termed cold chisels, are of various sorts, and are often known by the shape of the cutting end; for example, flat, cape, roundnose, dia- mond, and gouge chisels. The steel from which they are THE STARRETT BOOK made should be eighty to ninety point carbon, of octa- gon cross-section, with the cutting end forged to the desired shape, well packed by the forge hammer, hard- ened, and the temper drawn to a medium blue. The hammer end of the chisel should be forged from the octagon to a reduced round but not hardened. Flat- chipping and cape chisels should be ground with straight, symmetrical, cutting edges, at as acute an angle as the nature of the work will permit. 39 THE STARRETT BOOK In hand chipping the hammer handle should be grasped near the end and the hammer swung free from over the shoulder with an easy forearm movement. Hold the chisel loosely in the hand at an angle with the work that permits an even chip of right depth. The vision should be directed to the cutting edge of the chisel, rather than at the end struck by the hammer. Avoid gripping hammer or chisel tightly, as this rapidly tires the hand and arm. In shops which have compressed air, use is made of the modern pneumatic chipping hammer, which does remarkable work of the heavier sorts. FILING The file is essentially a finishing tool, and in skilled hands surfaces may be made very accurate and smooth. Files are designated thus (a) by their length this does not include the tang; (b) by their cross-section, as, for example, square, round, half-round, triangular, flat, knife-edge, etc.; (c) by their cut single or double cut; (d) by the degree of coarseness. Files for some purposes are made tapered in their length, and for other uses have straight sides. The de- grees of coarseness are designated by the following names as rough, coarse, bastard; 2d cut, smooth, and dead smooth; extra fine files are designated by numbers, No. 00, No. 0, No. 1, etc., to No. 8. The degree of coarse- ness varies with the length, for example, an 8-inch file second cut is coarser than a shorter file bastard cut. This confuses the user somewhat, unless he is familiar with practice. Single-cut files are those having teeth made by single parallel cuts across the face at an angle of twenty-five degrees. In double-cut files the teeth are made by break- ing up the single cuts into points by a second cut made at an angle with the first. 40 THE STARRETT BOOK Rasp files are those having teeth made by a punch. Used for hoofs, wood, etc. HEIGHT OF WORK. This must of necessity vary with the height of the worker. A common rule is to have it the height of the worker's elbow as he stands erect. For very light free-hand filing the work may be much higher, in some cases the height of the shoulders. 41 THE STARRETT BOOK POSITION OF THE HANDS. If the worker wishes to avoid tiring, position is very important; position also has direct bearing upon the quality and quantity of the product. The worker should clasp the file handle with the extended thumb on top, grasping the point with the fingers and thumb of the remaining hand with thumb on top. In heavy filing the point of the file may be grasped by the fingers and the palm of the hand with the palm on top. In hand-filing the worker should train his hands, arms, and body to carry the file across the work with regular, even, and controlled strokes. As the file is in no sense self-guided the worker must train his body to regular controlled motions if he is to do effective work. DRAW FILING. Used to set the grain somewhat smoother than regular cross-filing. The worker should clasp the blade of file near its ends in each hand and then draw the file, held crosswise, along the length of the work. A fine grain surface results. TESTING FLAT FILING. Flat work is tested by the use of steel straight edges, steel squares, bevel protrac- tors, etc. THE STARRETT BOOK POLISHING Where a particularly smooth surface is necessary, as, for example, journal bearings, or where brilliancy of finish is desired, the surfaces are polished with some fine abrasive. For ordinary polishing of machine parts, journals, etc., common grain abrasive is used, glued to cloth or leather. Grain abrasives are known by numbers, as, for ex- ample, No. 100, which means that the particles are of a size to readily pass through a sieve having one hundred meshes to the linear inch. The finer sizes are often known as flours. GRADES OF EMERY The numbers representing the grades of emery run from 8 to 120, and the degree of smoothness of surface they leave may be compared to that left by files as follows : 8 and 10 represent the cut of a wood rasp. 16 20 a coarse rough file. 30 40 60 80 100 120F and FF an ordinary rough file, a bastard file, a second cut-file, a smooth file, a superfine file, a dead-smooth file. SEVERING METAL WITH HACK SAWS Hack saws are narrow, thin blades of hardened steel with teeth cut along one edge, and are used for severing metal. They are held in suitable hand or power frames, which have the necessary adjustments for holding the blade in stiff tension. It is obvious that it requires care and good sense in using a hack-saw blade if good results are expected. If the stock to be cut is both hard and thin, particular care is required to avoid injuring the blade. 43 THE STARRETT BOOK CUTTING SPEED. When hack sawing, under aver- age conditions and without a lubricant, a cutting speed of fifty to sixty strokes per minute should be main- tained. If the saw is used in a power machine, and the material is soft steel, a cutting speed of one hundred strokes per minute may be made, using a suitable lubri- cant. Unannealed tool steel should be cut under the above conditions at not to exceed sixty strokes per minute. MOUNTING THE BLADE. The blade when mounted in a hand-frame should have the cutting-teeth rake for- NO.I45 TAKES 8 IN.TOI2 IN. SAWS ward; that is to say, the saw should cut on the for- ward stroke. In machine cutting this is usually so, but not so with some makes of machines. The cutting stroke is always the pressure stroke, and the return stroke is made as light as convenient without actually lifting the blade from its work. The blade should be under considerable tension when in use. It must be held in the plane being cut, and all tendency to bending the blade avoided. Suitable blades and frames may be purchased for almost every service, and the user should consider this fact if com- mercially economical results are desired. 44 THE STARRETT BOOK HACK SAW MACHINE Hack saw blades used in cutting up bar stock or structural shapes are much more efficient in a machine so designed that its several motions and adjustments can be properly controlled. Such a machine is as sensitive to the operator as a hand frame. The machine shown above has been especially de- signed to efficiently operate hack saw blades. The base column carries the working parts and the work-holding vise. By means of suitable weights, the cutting pressure upon the blade may be regulated according to the material being severed, and the stroke length of the blade-carrying frame can be adjusted to use the entire blade length, no matter what diameter of bar is being severed, thus getting the full efficient service from each blade. To avoid blade breakage through careless handling, a safety device in the form of a dash pot is connected with the blade-carrying frame to prevent the blade from being dropped suddenly upon the work. The blade-carry- 45 THE STARRETT BOOK ing frame is raised by a foot lever leaving the hands free for work adjustments and measurements. The cutting lubricant is conveyed to the blade from a tank in the column by means of a small rotary pump. What Hack Saw to Use No. 103 in hand frames, to cut cast steel, cast iron, tool steels and all solid metals. No. 103B in hand frames, to cut cold rolled stock and soft metals. No. 102 in hand frames, to cut sheet metal and tubing 16 to 18 gage. No. 253 in hand frames, to cut sheets and tubing thinner than 18 gage. No. 112 for heavy hand frame work and light power machines, on tool steels. No. 112B for light power machine work on soft steel, and heavy hand frame work. No. 114 for general work in medium weight power machines. No. 115 on electrical conduit, pipe, brass stock, light angle and channel iron. No. 255 on high speed machines cutting tool steels. No. 255B on high speed machines cutting machinery steel, cast iron, etc. No. 262 for cutting angle iron, brass stock and ornamental iron work. No. 254 for heavy high speed machines, to cut tool steel. No. 254B for heavy high speed machines, to cut cold rolled shafting and machinery steel. No. 259 for cutting iron pipe, light structural iron, auto frames, etc. No- 256 for extra heavy power machines, to cut tool steel. No. 256B for extra heavy power machines. 46 THE STARRETT ROOK DRILLING DRILLS. A drill is an end-cutting tool, consisting usually of two cutting edges set at an angle with the axis. The more common types of drills are flat flat- twisted straight-fluted spiral-fluted and gun-barrel. The most common, and for most purposes the most effi- cient, type is the spiral-fluted, known as a twist drill. Twist drills are made with two, three, or four cut- ting lips. The two-lip drill is used when drilling solid stock. The three and four lip drills are used for en- larging holes previously cored or drilled. When drilling solid stock with a two-lipped drill, the point of the drill controls the cutting edges, and if the drill is correctly ground the resulting hole will be reasonably round, straight, and the size of the drill. When a drill is used for enlarging holes already made, either by coring or by previous drilling, the drill is guided by its sides and a three or four fluted drill will give better results. FORM OF POINT. In the types referred to all except gun-barrel drills are cone-pointed on the cutting end. The gun- barrel drill, used when especially straight, round, and true holes are essen- tial, has a blunt end with a single cutting lip. A cone-pointed drill of two or more cutting lips depends for its efficient working upon four factors: (a) All the cutting lips shall have the same inclina- tion to the axis of the drill. (b) Cutting lips should be of exactly equal length. (c) A proper lip clearance of the surface back of the cutting edges. FIG. 1 47 THE STARRETT ROOK FIG. 2 (d) A correct angle of lip clearance. Figs. 1, 2, and 3 show the result of careless free-hand grinding. Figs. 4 and 5 show how to test the length of the cutting lips, also their inclination to the axis. After sharpening a drill free-hand, use the hand-feed at first and ob- serve (a) the chips made by the cutting; (b) the size of the hole. If the cutting lips are shaped to a proper clearance, the chips will curl as they start from the cutting edge; but if the cutting lips lack a proper clearance the resulting chips have the appearance of being ground off rather than freely cut. If the cutting lips are of uneven length the hole will be enlarged over the diameter of the drill. Drillings from cast iron should look as in Fig. 6, and those from steel as in Fig. 7, if the drill is properly sharpened. Free-hand grinding results are usually so dis- appointing that in most machine shops the drills are sharpened in a spe- cial drill-grinding ma- chine. The design of this machine is such, that when it is set for grind- ing any size of drill the cutting lips are made of equal length and of the correct form. Fig. 8 shows how the cutting lip is located to correctly grind the edges. FEEDING THE DRILL. To get the best results from drills and drilling machines, the drill should advance FIG. 3 48 THE STARRETT BOOK into the work a definitely regulated amount for each revolution. The distance which the drill advances per revolution is termed the FEED, and must be adjusted to suit the conditions under which the work is being performed. Table No. 2 gives the feeds per revolution recommended by one manufacturer of drills. They are recommended for average conditions; they can be greatly exceeded under some conditions, but must be reduced for others. FIG. 4 FIG. 5 Feeding the drill freehand, if skilfully done, may answer in certain cases, but is less effective than power feeds, except for small wire drills. DRILL SPEED. This is the surface or peripheral speed of the drill in feet per minute, and is rated at the outer diameter. Under average conditions the peripheral speed recommended for carbon steel drills is thirty feet 49 THE STARRETT BOOK to forty feet, and for high-speed drills seventy feet to one hundred feet. Working conditions may at times cause a change in these figures. When the extreme outer corners of the cutting edges wear rapidly it is evidence of too high a surface speed. FIG. 6 FIG. 7 Table No. 3 gives the revolutions per minute at which to run drills for various cutting or surface speeds. For example, with a 1-inch drill and seventy feet as the selected cutting speed, read across from 1-inch in the left-hand column and under heading 70' find 267, the revolutions per minute. FIG. 8 60 THE STARRETT BOOK Speeds and Feeds for Drilling* Table 2 High-Speed Steel Drills Size of Feed Bronze, Brass, OAA Cast Iron, An- Cast Iron, Mild Steel, Drop Mai. Iron, Tool Steel, Cast Steel, Drill Re C v. 300 Feet nealed, 170 Hard, 80 Feet 120 Feet Feet 90 Feet 60 Feet 40 Feet Feet Inches Inches R.P.M. R.P.M. R.P.M. R.P.M. R.P.M. R.P.M. R.P.M. R.P.M. Vie 0.003 18300 10370 4880 7320 3660 3490 3660 2440 Vs 0.004 9150 5185 2440 3660 1830 2745 1830 1220 %e 0.005 6100 3456 1626 2440 1210 1830 1220 807 Vi 0.006 4575 2593 1220 1830 915 1375 915 610 H 0.007 3660 2074 976 1464 732 1138 732 490 % 0.008 3050 1728 813 1220 610 915 610 407 0.009 2614 1482 698 1046 522 784 522 348 0.010 2287 1296 610 915 458 636 458 305 0.011 1830 1037 488 732 366 569 366 245 0.012 1525 864 407 610 305 458 305 203 % 0.013 1307 741 349 523 261 392 261 174 1 0.014 1143 648 305 458 229 349 - 229 153 0.016 915 519 244 366 183 275 183 122 1V2 0.016 762 432 204 305 153 212 153 102 1% 0.016 654 371 175 262 131 196 131 87 2 0.016 571 323 153 229 115 172 115 77 Carbon Steel Drills Size of Drill Feed JK. Bronze, Brass, 150 Feet Cast Iron, An- nealed, 85 Cast Iron, Hard, 40 Feet Mild Steel, 60 Feet Drop Forg., 30 Feet Mai. Iron, 45 Feet Tool Steel, 30 Feet Cast Steel, 20 Feet Feet Inches Inches R.P.M. R.P.M. R.P.M. R.P.M. R.P.M. R.P.M. R.P.M. R.P.M. We 0.003 9150 5185 2440 3660 1830 2745 1830 1220 0.004 4575 2593 1220 1840 915 1375 915 610 9ie 0.005 3050 1728 813 1220 610 915 610 407 V4 0.006 2287 1296 610 915 458 636 458 305 0.007 1830 1037 488 732 366 569 366 245 % 0.008 1525 864 407 610 305 458 305 203 7 Ae 0.009 1307 741 349 523 261 392 261 174 % 0.010 1143 648 305 458 229 343 229 153 % 0.011 915 519 244 366 183 275 183 122 K 0.012 762 432 204 305 153 212 153 102 % 0.013 654 371 175 262 131 196 131 87 1 0.014 571 323 153 229 115 172 115 77 ttt 0.016 458 260 122 183 92 138 92 61 m 0.016 381 216 102 153 77 106 77 51 1% 0.016 327 186 88 131 66 98 66 44 2 0.016 286 162 77 115 58 86 58 39 * Copyright, 1911, by the Henry & Wright Mfg. Co. 51 THE STARRETT BOOK The Speed of Drills Table 3 A feed per revolution of .004 to .007 for drills M inch and smaller, and from .007 to .015 for larger is about all that should be required. This feed is based on a peripheral speed of a drill equal to : 30 feet per minute for steel ; 35 feet per minute for iron ; 60 feet per minute for brass. It may also be found advisable to vary the speed somewhat according as the material to be drilled is more or less refractory. We believe that these speeds should not be exceeded under ordinary cir- cumstances. Table of Cutting Speeds Ft. per Minute 15' 20' 25' 30' 35' 40' 45' 50' 60' 70' 80' Diam. REVOLUTIONS PER MINUTE ttein. 917. 1223. 1528. 1834. 2140. 2445. 2751. 3057. 3668. 4280. 4891. % 459. 611. 764. 917. 1070. 1222. 1375. 1528. 1834. 2139. 2445. tt 306. 408. 509. 611. 713. 815. 917. 1019. 1222. 1426. 1630. ft 229. 306. 382. 458. 535. 611. 688. 764. 917. 1070. 1222. ttj 183. 245. 306. 367. 428. 489. 550. 611. 733. 856. 978. % 153. 204. 255. 306. 357. 408. 458. 509. 611. 713. 815. 7 Ae 131. 175. 218. 262. 306. 349. 393. 437. 524. 611. 699. M 115. 153. 191. 229. 268. 306. 344. 382. 459. 535. 611. % 91.8 123. 153. 184. 214. 245. 276. 306. 367. 428. 489. % 76.3 102. 127. 153. 178. 203. 229. 254. 306. 357. 408. % 65.5 87.3 109. 131. 153. 175. 196. 219. 262. 306. 349. l 57.3 76.4 95.5 115. 134. 153. 172. 191. 229. 267. 306. H6 51.0 68.0 85.0 102. 119. 136. 153. 170. 204. 238. 272. m 45.8 61.2 76.3 91.8 107. 123. 137. 153. 183. 214. 245. 1% 41.7 55.6 69.5 83.3 97.2 111. 125. 139. 167. 195. 222. 1% 38.2 50.8 63.7 76.3 89.2 102. 115. 127. 153. 178. 204. 1% 35.0 47.0 58.8 ,70.5 82.2 93.9 106. 117. 141. 165. 188. 1% 32.7 43.6 54.5 65.5 76.4 87.3 98.2 109. 131. 153. 175. 1% 30.6 40.7 50.9 61.1 71.3 81.5 91.9 102. 122. 143. 163. 2 28.7 38.2 47.8 57.3 66.9 76.4 86.0 95.5 115. 134. 153. 2K 25.4 34.0 42.4 51.0 59.4 68.0 76.2 85.0 102. 119. 136. 2V 2 22.9 30.6 38.2 45.8 53.5 61.2 68.8 76.3 91.7 107. 122. 2% 20.8 27.8 34.7 41.7 48.6 55.6 62.5 69.5 83.4 97.2 111. 3 19/1 25.5 31.8 38.2 44.6 51.0 57.3 63.7 76.4 89.1 102. 52 THE STARRETT BOOK CUTTING COMPOUNDS. To maintain high cutting speeds, it is necessary to use a lubricant. Those recom- mended have stood the test of service : For hard and refractory steel, turpentine, kerosene, or soda water. For soft steel and wrought iron, lard oil, or soda water. For brass, paraffine oil. For aluminum, turpentine, kerosene, or soda water. For cast iron, a jet of air if anything is used usu- ally worked dry. LAYING OUT. Locating the centers for drilled holes upon the body of the work is termed "laying out." On the smaller jobs, laying out and drilling are usually done by the workman. Larger amounts of work warrant a skilled "layer out." Laying out for drilling comes under two heads, viz. : APPROXIMATE and ACCURATE. Unless the holes when drilled are to match up with other holes or with fixed studs, it is enough if the center is laid off with a chalk pencil and a steel rule. For jig, tool, and experimental work, the centers must be accurately laid out and scribed upon the surface of the work. The practice is to scribe two or more lines which intersect at the exact desired point as shown in Fig. 9. Assume that the link is to FIG. 9 63 THE STARRETT BOOK connect two studs. Proceed to scribe two intersecting lines upon one of the hubs, as shown in Fig. 9, using a combination square fitted with a center head. At the intersection accurately place a light center-punch in- dentation. Place one leg of a spring divider with its point in the center mark and adjust the other leg to have its point touch the edge line of the hub and note the concentricity of the center. If correct, close dividers to scribe a circle the diameter of the required drilled hole, setting the points by the scale graduations upon a steel FIG. 10 rule. Locate light center-punch marks on the scribed circle as shown in Fig. 10. When the work is laid out by another than the FIG. 11 54 THE STARRETT BOOK driller, a second circle, having a slightly greater diameter, should be scribed. This check will show whether the hole was drilled to the original lay out. If no impor- tance is attached to the center to center distance of the holes proceed as before with the second hub. Where the center to center distance is important, set the points of the universal dividers to the center length, and with the point A, Fig. 11, in the previously located center mark scribe on the opposite hub. Scribe a short line across its face afterward, proceeding as before. For all accurate work use the automatic center- punch, Fig. 12, and for heavy work the machinists' center-punch, shown in Fig. 13. PREPARING THE SURFACE. For accurate laying out, clean the machined surfaces and wet the portion to be worked upon with the copper sulphate (blue vitriol) solution., When dry, the surface will distinctly show any lines which are made upon it. Chalk well rubbed into the surface is sufficient for the less accurate jobs. STARTING THE DRILL. After laying out and previous to drilling, greatly enlarge the center holes with a center- punch to assist the starting of SCRIBING CIRCLES WITH DIVIDERS the drill. Start the hole with drill point in the enlarged center, using hand feed until a reasonable dimple is made in the work. Observe if this is central with the scribed circle, and if not central use center gouge, as in Fig. 14, and repeat until accurate. TO DRAW A DRILL. When starting a drill it often has a tendency to slide or crowd off to one side. Where it is essential that the drilled hole coincide or center with some previously scribed circle or layout, the drill 55 THE STARRETT BOOK FIG. 12 must be brought back into the correct posi- tion. This is accomplished by the use of a small gouge-pointed chisel, sometimes called a center chisel, and the process is termed, "drawing the drill." First, note toward which side of the small dimple left by the drill-point it is necessary to shift the drill. Then chisel a small groove in that side of the dimple. If the start is very eccentric, sev- eral chisel grooves may be necessary; whereas, if only slightly eccentric, a mere touch of the chisel will often suffice. It is readily seen that the drill is made to cut more easily where the grooves are, and therefore the natural resistance of the opposite side pushes the drill toward the side cut by the gouge-pointed chisel. Drill drawing can only be done previous to reach- ing the full diameter of cut. HOLDING THE WORK. Careless- ness in holding the work is respon- sible for many drilling accidents. If no special holding device is available, the work should be held in a drilling vise, clamped directly to the drilling- machine table, or clamped to an angle iron. Fig. 15 illustrates a method of holding the work safely. When once the work is clamped in position on the drilling-machine table, adjust the table to center the located hole with the drill rather than reclamp the work. HOLDING THE DRILL. In Fig. 16, at A, the drill is shown held di- FIG. 13 66 THE STARRETT BOOK rectly in the spindle. This is a good method if several holes of the same diameter are to be drilled at a single setting. When frequent changing of the drill is neces- sary, as in drilling holes of numerous sizes, using a single-spindle machine, some form of quick-acting collett chuck should be used. The changes can then be made without stopping the machine. FIG. 14 DRILLING FOR REAMER. When it is essential that the holes be of an exact standard diameter, it is cus- tomary to use a drill somewhat smaller than the given diameter, and afterward ream the holes to standard size. The amount left for reaming depends upon whether one or two reaming operations are necessary, and whether or not the reaming is to be done directly in the drilling machine. If the drilling is done through jig bushings and the holes are short as compared to their diameter, H FIG. 15 57 THE STARRETT BOOK a single reaming operation will often suffice. If the holes are relatively long, the drill should be 1/64" to 1/32" smaller than the finished hole diameter, to allow for passing a machine reamer 0.005" small through the hole which is afterward hand-reamed. This method gives results as accurate as any, except by grinding, and is accepted practice for good work. DRILLING FOR TAPPING. Where a full thread depth is essential the hole to be tapped should be made with a drill of a diameter smaller than the nominal diameter of the bolt by an amount equal to double the depth of the thread. In practice the nearest commercial size of drill is listed for drilling tapped holes. THE STARRETT BOOK Letter Sizes of Drills Table 4 Diameter Decimals Diameter Decimals Inches of 1 Inch Inches of 1 Inch A i% 4 .234 N .302 B .238 % .316 C .242 P 2 V 6 4 ' .323 D .246 Q .332 E M .250 R 1 V32 .339 F .257 s .348 G .261 T 23/ 64 .358 H 17/ 6 4 .266 U .368 I .272 V */8 .377 J .277 W 2 %4 .386 K % 2 .281 X .397 L .290 Y i%2 .404 U 1% 4 .295 Z .413 Sizes of Tap Drills Table 5 Tap Diameter Threads per Inch Drill for V Thread Drill for U. S. Standards Drill for Whitworth M 16, 18, 20 5 /32 %2 M/64 %6 3 /16 %2 16, 18, 20 %6 13 /64 13 /64 5 /16 16, 18 7 /32 15 /64 M 15 /64 *% 16, 18 1 A 17 /64 H 14, 16, 18 M %2 %2 %2 %2 %2- 14', 16, 18 19 /64 2 V 6 4 2 V64 7 /16 14,16 21 /64 ^32 1 VS2 Hb 15 /32 14,16 2 %4 H 1 A 12, 13, 14 Z /8 2 %4 25 /64 13 /32 H 9 /16 12,14 %6 29 /64 7 /16 N 10, 11, 12 15 /32 Y 2 l /2 l /2 y 2 Hie 11,12 O/ Q/ V16 716 K 10, 11, 12 19 /32 ^ 5 /8 % 18 /16 10 2 V32 % 9,10 45 /64 23 /32 28 /32 2 %2 15 Ae 9 49 /64 1 8 13 /1 P 27 /32 27 /32 See also pages 78, 176 and 177. THE STARRETT BOOK Handy Equivalent Tables Made of Spring Steel NO. THE L.S.STARRETT CO. ATHOL. MASS. U.S.A. DECIMAL EQUIVALENTS H 3 590 THE L.S.STARRETT CO. ATHOL. MASS U.S.A. \ TAP DRILLS I; FOR MACHINE SCREW TAPS r OR STEEL WORK USE AP DRILLS ONE OR TWO SIZES LARGER THAN. UST jto V N -(ii) 591 THE L.S. STARRETT CO. ATHOL. MASS. U.S. A. DRILL SIZE f TABLE fP 1 LETTER SIZES 1 yji it 11 1 1 ijj i ~~K j ^r ~* -3p- 290 < -I? 4 295T - : .4)3 22 5 \ ^-:8i5 IS?- -3 i -I 20^ -4 f~Hf~ 2O4 ' 2 1 ' .07 5 It ' |3E1 IS : 1 Pi -4e Zc 1E3 ISP : I 182 5 1 *w ij fr-i MF a 59 za 157 \ .0' It 54 S:^ n r ^ J HE s -hr-- E^s - yt. if: C E : f^ T z 5 ES - 4t t iH ^ s-"^ ffi If -> f-$Hhd IO 7 51 3B JB5 7 2 .02 40 1 fcjjM 1^ - .J-';f- THE STARRETT BOOK SIZES OF TAP DRILLS. Because of the large num- ber of screw thread standards in use, many tables would be required to cover all selections of tap drills. The sizes of tap drill for all pitches of V threads may be found by the following formula. 1.400 Tap drill = D - T in which T = number of threads per inch D = dia. of tap or thread EXAMPLE. What diameter of tap drill should be used for a % X 10 tap? 1.400 Tap drill = .75 - = .75 - 10 .14 NOTE. For U. S. Standard threads use same formula, but 1.3 should be used in place of 1.4. FIG. 17 DRILLING LARGE HOLES. Twist drills are sold, ranging in size from No. 80 wire gage to four inches in diameter. As the drill increases in diameter the web is corre- spondingly thickened, and as the cutting edges at the web do not cut as effectively as they do outside the web thickness, considerable pressure is required to force the larger drills into the work at an efficient cutting feed. For this reason many workmen first drill a lead hole, using a drill whose diameter approximates the web thick- ness of the larger drill, as shown in Fig. 17. A lead hole will also assist in centering the drill upon an inclined surface. However, if the inclination is considerable it is necessary to butt mill or hand chip a spot giving 61 THE STARRETT BOOK sufficient surface to work upon. The practice of some firms is to use in place of a single large drill a relatively smaller one, afterward enlarging the hole by some method of counterboring at a much less expense for tools and at as rapid a production rate as by entire drilling. BOLT HOLES. When the bolts are for holding pur- poses only and are not used for aligning the several pieces, it is customary to drill the holes through which the bolts pass somewhat larger than the bolt diameters. This allows for a variation in the bolt sizes and for in- accuracy in locating the centers. DEEP HOLE DRILLING. Under this name may be classed the drilling of holes through the axes of spindles lathe, milling-machine, and grinder and that special line of drilling known as gun-barrel drilling. While for spindle drilling it is possible to use ordinary twist drills with extended shanks, it is customary in efficient drilling of this sort to use special drills designed for the purpose. Fig. 18 shows a special hollow drill often used for drilling axial holes in lathe spindles, and Fig. 19 shows the machine with the drill guides in working position. FIG. 18 In all cases of deep-hole drilling it is better to rotate the work rather than the drill. The drill must be started exactly concentric with the axis of the machine. For this reason a starting-hole the exact diameter of the drill is first counterbored. COUNTERBORING. There are many cases in which it is desirable to enlarge a hole throughout a portion of THE STARRETT BOOK FIG. 19 its length. If a drill is used for this purpose there is no certainty that the two diameters will be concentric. The practice is to enlarge the already drilled hole by using a cutting tool having a pilot or leader to guide the cutting edges. This tool is known as a counterbore, and its use is termed counterboring. In Fig. 20 are shown the tool in operation and its purpose. THE STARRE T T BOOK THE STARRETT BOOK THE LATHE CARE OF THE LATHE. The engine lathe is capable of producing the largest variety of product of any of the machine-tool family. Especial attention should be given to applying a suitable machine oil to all the bear- ings, for improper lubrication of the wearing surfaces is one of the immediate causes of excessive wear. A medium-size flexible-bottom squirt can is best for this purpose, and oiling should be frequent on those bear- ings which are given the severest service, either from excessive pressure or from high-speed rubbing. All oil holes should be kept free and clean, and where possible should be protected from entering dirt. Those bearings, as, for example, the ways upon which the carriage moves, which by construction are hard to protect "from dirt, should be frequently cleaned and reoiled. At least once a week the lathe should receive an all-over cleaning, and the bearings should be washed out with kerosene. A plugged oil hole prevents the proper lubrication of the bearing. INDICATING AND ADJUSTING. Upon the condi- tion of the centers, rests to a large degree the accuracy of the work produced. After attention to lubrication the competent workman proceeds to prepare and test the centers. Remove both centers and after cleaning them and the tapered holes note whether they return to their places with a successful fit. The "dead" or foot- stock center should have a hardened point to resist wear. The cone-points of the centers should be smooth and an exact sixty degrees. The centers should align with each other in the vertical and horizontal planes, and the "live" or head-stock cone-point should rotate truly concentric with its axis. The trial and error method of adjusting the centers in alignment is to first bring the cone-points nearly into 65 THE STARRETT BOOK contact, and by adjusting the foot-stock frame upon its cricket bring them into as exact truth as is reasonably possible. With the foot-stock clamped in position to receive the work, surface the diameter of a trial piece for a length sufficient to allow testing its diameter at several places. If the diameter increases or decreases as the tool passes along the length of the work, readjust the foot-stock and repeat the test until the required UNIVERSAL DIAL TEST INDICATOR FIG. 21 degree of accuracy is obtained. To test the live center for concentricity, place in the tool-post a universal test- indicator, as shown in Fig. 21, with the feeler in touch with the cone-point. Rotate the head-stock spindle slowly by hand and note the dial. If the dial shows an eccentricity in excess of the allowed limits for the job 66 THE STARRETT BOOK to be done, the cone-point should be machined true. In cases where it is customary to have the live as well as the dead center hardened, the cone-point must be trued by some grinding attachment, as, for example, a tool-post grinding fixture. By many workmen the live center is left unhardened, and can be trued with a square nose- cutting tool, and afterward lightly filed to a smooth sur- FIG. 22 face. To test either center for its proper cone-point angle use is made of a center gage, shown in Fig. 22. TEST INDICATOR. This is a tool for indicating minute contact variations upon a graduated dial or upon 67 THE STARRETT BOOK Truing Work in Chuck Truing Jig on Face Plate Indicator Used with Surface Gage on Bench Plate 68 THE STARRETT BOOK a graduated arc. The graduations are usually one hun- dred in a complete circle with an easily read width of spacing. The instrument is built in such a way that one of these spaces represents a movement of the contact- point of 1/1000 inch. Various mechanisms are employed for multiplying the movement of the contact-point, all of which are based upon a combination of short and long arm levers. USE. The test-indicator may be used with advantage in any of the common machine tools, to in- dicate eccentricity in the lathe, milling ma- chine, or grinding machine; to indicate uni- formity of height in the planer, shaper, boring machine, or milling machine; to indicate par- allelism, and to test for alignment in any_ machine. WORK CENTERS. Most turned work is done upon the lathe centers, and it becomes necessary to provide suitable cavities in the work, coned to- fit the cone-points. This is termed "centering the work," and consists in first locating the position of the cavities and afterward drilling and reaming them to form and size. Best practice in this respect is to use a combination drill and center reamer, as it insures exact concentricity in the drilled and reamed hole. LOCATING THE CENTERS. It is evident that the centers should be so located that the entire diameter of the turned job shall finish to size. Beside this, efficient turning demands HE RMAPHRO- that the chip taken shall be of practically uni- DITE ftfrm depth as the work rotates against the CALIPERS cutting tool. For these reasons some degree of accuracy in centering is necessary. Where the turned job is made from ordinary black bar stock, the centers may be located THE STARRETT BOOK LATHE TOOLS 1 LEFT-HAND SIDE TOOL 2 RIGHT-HAND SIDE TOOL 3 RIGHT-HAND BENT TOOL 4 RIGHT-HAND DIAMOND POINT 5 LEFT-HAND DIAMOND POINT 6 ROUND-NOSE TOOL 7 CUTTING-OFF TOOL 8 THREADING TOOL 9 BENT THREADING TOOL 10 ROUGHING TOOL 11 BORING TOOL 12 INSIDE THREADING TOOL 70 THE STARRETT BOOK by scribing lines at an angle across the ends, using a combination square with a center head and the provided scriber. In place of this tool a hermaphrodite caliper may be used to scribe the ends of the stock. The center is located with a center-punch at the intersection of the scribed lines and the concentricity tested by spinning the bar upon the lathe centers. If necessary, the center- punch marks are shifted. If the piece is bent it must, after centering, be straightened to reasonable truth. For exact turned work the centers should afterward be lightly rereamed to correct the errors in their alignment due to the straightening of the bar. When the' job is to be turned from a forging, it is usual to roll the forging on straight edges and scribe lines across the ends, using a surface or height gage. In such cases the forging is so located with reference to the straight edges as to give a fair average of the surface errors due to forging. It is also usual to leave a greater excess of stock for finishing purposes upon a forging than upon rolled bar stock. When the centers are well located the holes may be drilled under a drill-press or in a hand-lathe, as convenient. Where much bar stock must be centered a special self-locating centering machine is often used. LATHE TOOLS. A set of tools for use in the engine lathe is shown in the chart on page 70. While in com- mon shop language all these are known as cutting tools, technically speaking, many of them separate the stock in a manner that is analogous to crowding off the metal rather than by pure cutting action. Cutting in its proper sense is a splitting action, and a properly ground and properly set cutting tool is a wedge in that it splits off the excess stock. Among the common lathe tools, the side tool and the diamond-point tool are the best exam- ples of wedge or splitting action. The nose of a cutting tool has several sides, two of 71 THE STARRETT BOOK which come together at some angle to form a cutting edge. The angle formed by these surfaces must be suffi- cient for strength, and to furnish enough metal to con- duct away the heat generated by the cutting action. For turning ordinary soft steel and soft gray iron an angle of sixty degrees is good practice. For harder material^ the angle may be increased. In the case of forged lathe tools, the working end of the tool is forged upon the end of a short piece of square or rectangular bar stock. The length and size of the shank of the forged tool depend upon the size of chip and the machine used. RAKE. The angle which the upper side of the tool makes with the horizontal is termed the rake. If the CLEARANCE FIG. 23 SIDE CLEARANCE slant is away from the work it is termed front rake; if in the direction of the axis of the work, it is termed side rake. A cutting tool may have its upper face forged and ground with either a front or a side rake or a combina- tion of both. (See Fig. 23.) CLEARANCE. By clearance is meant the angle which the under side of the tool makes with the vertical. As in the case of "rake" the clearance directly away from the axis of the work or lathe is termed front clearance, 72 THE STARRETT BOOK that along the axis of the work side clearance. With the tool in cutting position the clearances must be in any case not less than three degrees, and in most cases not more than ten degrees. RIGHT-HAND TOOLS. These are tools having the rake, clearances, and cutting edges formed to turn or square from the right towards the left. LEFT-HAND TOOLS. When the rake, clearances, and cutting edges are formed to cut from the left to the right the tool is known as a left-hand tool. SETTING THE LATHE TOOL. It is very important that the lathe tool be properly set in relation to the axis of the work and the direction of the cut. While there are exceptions, notably that of the diamond point, lathe tools are usually set with the cutting point at the exact height of the axis of the lathe. In the case of the dia- mond point, the front clearance is usually forged to fifteen degrees or over. It is necessary, therefore, to set the point above the axis height to obtain a working clear- ance of not to exceed ten degrees'. Unless the cutting tool has a bent shank it is usually set at right-angles to the surface of the work. GRINDING LATHE TOOLS. Lathe tools made from carbon tool steel should be sharpened by grinding upon a wet emery-grinder, or upon an ordinary water-drip grindstone. If made from the newer high-speed steel the grinding should be upon a dry and rather coarse abrasive wheel. The grinder should have a suitable work-rest upon which to support the tool in sharpening the larger tools, or for resting the hands in the case of the smaller tools. For purposes of safety, the work rest should be firmly and securely clamped as close as possible to the used face of the wheel. The grinding may be done upon the pe- riphery of a disk-wheel or upon the sides of a cup-wheel, as desired. In any case the wheel should rotate to force 73 T t H E STARRETT BOOK the tool upon the rest rather than from it, and should run true and in balance. Efficient cutting depends very largely upon the correct sharpening, as well as the cor- rect setting of the cutting tool, and great care should be taken when grinding a lathe tool to have the several faces true and making correct angles with each other. The manner of doing this is a pretty good index of the workman. The usual lathe-cutting tools have well-de- 45V FIG. 24 fined cutting edges, and the angularity of the surfaces which meet to form the cutting edge can often be meas- ured with a bevel protractor, and in the case of a sixty- degree angle the center gage is suitable. This tool is also used to test the angle when grinding a vee-pointed thread tool, as illustrated in Fig. 24. TESTING THE CUTTING ANGLES. As the usual machine construction materials are not excessively hard, a cutting angle of not far from sixty degrees may be maintained on such tools as the side tool and the diamond point. In this case the angle can be tested by use of the usual center gage. Where cutting angles other 74 THE STARRETT BOOK than 60 are used, also for testing clearances, the uni- versal Bevel Protractor is useful. TOOL HOLDERS. The high cost of the materials used for modern cutting tools has resulted in the mar- keting of a variety of holders designed to hold cutting points. In this manner a large number of relatively inexpensive cutting points are made to interchange in a single shank or holder. One form of tool-holder is made to hold points forged in the regular forms shown in the chart, page 70. In some examples, however, the holders are made to carry short bits broken from square bar stock and afterward sharpened into some resem- blance to the true forged shape. (See Fig. 25.) FIG. 25 MATERIALS FOR GUTTING TOOLS. These are known as carbon steel (tool steel), high-speed steel, and a new product of the electric furnace sold under the trade name of "Stellite." Carbon steel, or, as it was formerly termed, "tool steel," is high in carbon, eighty point to one hundred and twenty-five point, and when correctly heated and afterward plunged in cold water, hardens to a very high degree. Unfortunately for high- speed cutting the hardness is drawn at a comparatively low heat, and care must obtain not to overheat or blue it. High-speed steel is a special steel having its com- position alloyed with tungsten and perhaps vanadium or molybdenum. While heat treatment does not give it the exceeding hardness of tool or carbon steel, high- 75 THE STARRETT BOOK speed steel has the peculiar property of retaining its hardness at temperatures considerably in excess of those which readily soften tool steel. Tools made from high- speed steel are used at speeds, feeds, and cuts which heat the tools and chips to a dull red. Stellite is a new cutting material composed of chro- mium, cobalt, and sometimes tungsten. It is cast into form and cannot be forged. Its hardness is equal to the diamond, and under favorable conditions marvelous turn- ing may be done. MANDRELS. Where the work is to be turned true with a hole through it, as, for example, turned pulleys, work-centers must be provided for holding it on the lathe centers. The common way is to force or drive into the work-hole a bar having center holes in its ends. This bar should be classed as a tool-room tool, and is properly known as a mandrel, although often called an arbor. A standard set of mandrels varies in diameter and in length, according to the shop conditions. They are made of either tool steel hardened and ground true with the centers, or from soft machinery steel, case-carbonized and afterward ground. The ends for a short distance are reduced in diameter and provided with flats for clamping on the dog. Mandrels usually taper at the rate of 0.0005" in an inch. The diameter of the hole fitted by the mandrel is stamped upon the larger end. As the quality of the work depends upon the truth of the man- drel it should be tested upon dead centers with a test- indicator before being used. To use, drive or force it into place, using a Mandrel press for forcing or a lead hammer for driving, carefully removing dirt, chips, or pieces of lead from the centers before placing the work in a lathe. Lathe drive with the usual lathe-dog as for any job done on the centers. Avoid forcing or driving the mandrel into a hole that is neither round nor straight. Also avoid scoring the mandrel with the cutting tool. 76 THE STARRETT BOOK SCREW THREAD CUTTING. A screw thread is a helical groove cut or formed into the surface of a bar, rod, or bolt, or inside a nut. For ordinary machine screws, bolts, studs, etc., the threads are made with special tools called threading dies. These are screwed upon the bolt, screw, or stud to be threaded by rotating either the work or the die. Threading dies are used both by hand and in power-driven machines. SCREW THREADS. There are numerous screw- thread standards in more or less general use. The so- called United States standard is in this country the more generally accepted one, and is therefore illustrated in Fig. 26 and Table 6. It will be noted that in addition to a definite form of thread cross-section each diameter has a specified number of threads per inch of length. The United States standard thread, when sectioned, shows a truncated sixty degrees triangle with the space and the land alike. PITCH AND LEAD. Pitch in a thread is the ; j /WIDTH distance measured from the "^ OF FLAT center of one thread to ~T the center of an adjacent DEPTH thread. If the screw thread OF P, is a single helix, the lead is equal to pitch. If the helix is double, the lead is double FlG - 26 the pitch. While strictly speaking pitch is the reciprocal of the number of threads per inch, as, for example, 1/7" pitch for a screw thread 7 per linear inch, shop men speak of it as 7 pitch, written, 7 P. THREADING IN A LATHE. When screw threads are cut in an engine lathe, the point of the cutting tool is shaped to the exact form of the spaces between threads. By means of a lead screw and a train of gearing the tool is compelled to move along the axis of the work at a 77 THE STARRETT BOOK U. S. Standard Screw Threads Table 6 Diameter No. of Threads per Inch | Diameter at Root of Thread Diameter of Tap Drill Area in Sq. Inches , Dimensions of Nuts and Bolt Heads 1 h^ k ->! H a H & Of Bolt At Root of Thread M 20 0.185 13 /64 0.049 0.026 H 0.578 0.707 1 A 1 A H 18 0.240 H 0.076 0.045 19 /32 0.686 0.840 5 A6 19 /64 16 0.294 5 Ae 0.110 0.068 Hie 0.794 0.972 H H'32 7 A 6 14 0.345 2 %4 0.150 0.093 2 %2 0.902 1.105 %e 25 /64 H 13 0.400 27 /64 0.196 0.126 % 1.011 1.237 H 7 Ae %e 12 0.454 15 /32 0.248 0.162 3 V32 1.119 1.370 9 Ae 3 V64 H 11 0.507 17 /32 0.307 0.202 !Vl6 1.227 1.502 5 /8 17 /32 H 10 0.620 4 V 6 4 0.442 0.302 \\i 1.444 1.768 % N 8 9 0.731 % 0.601 0.419 1 7 /16 1.660 2.033 7 /8 23 /32 8 0.838 5 %4 0.785 0.551 1% 1.877 2.298 1%6 V/8 7 0.939 3 V32 0.994 0.694 1 13 /16 2.093 2.563 V/8 29 /32 1M 7 1.064 1%3 1.227 0.893 2 2.310 2.828 1M 1 1H 6 1.158 1%2 1.485 1.057 2 3 /16 2.527 3.093 IN 1%2 1H 6 1.283 1H&2 1.767 1.295 2^ 2.743 3.358 i^ 1 3 /16 iff V/2 1.389 ! 27 /64 2.074 1.515 2% 6 2.960 3.623 1% 1%2 i% 5 1.490 ! 17 /32 2.405 1.746 2M 3.176 3.889 1% 1^ V/8 5 1.615 l%a 2.761 2.051 2 1 % 6 3.393 4.154 IK 1!%2 2 4M 1.711 1 4 %4 3.142 2.302 33^ 3.609 4.419 2 1%6 2M 4X 2 1.961 2V 6 4 3.976 3.023 3^ 4.043 4.949 2M Ik 2^ 4 2.175 2' %4 4.909 3.719 3% 4.476 5.479 2^ 1^46 2% 4 2.425 2%4 5.940 4.620 i 4.909 6.010 2M 2^ 3^ 2.629 2i%e 7.069 5.428 4N 5.342 6.540 3 2% 6 3J 3^ 2.879 2i%e 8.296 6.510 5 5.775 7.070 3M 2^ 33^ 3^ 3.100 3iy 64 9.621 7.548 5^ 6.208 7.600 VA 2^6 3% 3 3.317 3^g 11.045 8.641 5 6.641 8.131 VA 2>i 4 3 3.567 3^ 12.566 9.963 6H 7.074 8.661 4 3Vi6 4^ 2^ 3.798 32% 2 14.186 11.340 6>i 7.508 9.191 4^ VA 4^ VA 4.028 4% 2 15.904 12.750 6K 7.941 9.721 4K 3%6 4% 2 5 /8 4.255 45A 6 17.721 14.215 7M 8.374 10.252 4M 3^ 5 V/2 4.480 49/16 19.635 15.760 7% 8.807 10.782 5 3i 3 Ae 5M 2 l /2 4.730 4*%6 21.648 17.570 8 9.240 11.312 53 4 5^ zy* 4.953 5% a 23.758 19.260 8^ 9.673 11.842 5^ 4%6 5^ 2*/8 5.203 5% 2 25.967 21.250 8^ 10.106 12.373 5^ 4^ 6 2 1 A 5.423 5 J /i 28.274 23.090 9.H 10.539 12.903 6 4%6 COURTESY OF " MACHINERY " See also pages 55, 56, 168 and 78 THE STARRETT BOOK definite rate of advance as the work- rotates. As the train of gears usually furnished with an engine lathe can be changed to give different rates of advance, it is in this manner possible to cut threads of a. large variety of pitches. In practice a set of several gears having dif- ferent numbers of teeth are furnished with each lathe. Those furnished will usually provide for cutting all the threads within the usual range of the lathe with which they come. These are known as "change gears," and their use is obvious. SELECTING CHANGE GEARS. Given the number of threads per linear inch to be cut and the number of threads per linear inch of the lead screw, the problem is to select gears giving the desired ratio of cut to lead screw. For example, it is desired that single seven threads per linear inch shall be cut upon a li/d-inch bolt, and it is found by scaling that the lathe lead screw has single five threads per linear inch. The ratio of cut to lead screw is then that of seven to five (7/5). The change gears selected should, therefore, be as seven is to five. If both members of a fraction are multiplied by the same number, the ratio is not changed. This allows of raising the fraction to suit the gears which are 7 5 35 in the set furnished; for example, - X - = . If gears 5 5 25 having thirty-five teeth and twenty-five teeth, respec- tively, are found in the furnished set, the selection of these gears will give, when rightly placed, the desired tool advance for cutting seven threads per linear inch. The directions above refer to the most simple form of lathe. Various lathe manufacturers have introduced different arrangements of the gearing, but with any lathe the above procedure will give correct results if it is first determined what number of threads per inch will be cut if gears of the same number of teeth are placed on spindle stud and lead screw. This number called the 79 THE STARRETT BOOK Lathe Set Up for Thread Cutting Note Thread Stop at A 80 THE STARRETT BOOK "lathe screw constant" should then be considered as being the number of teeth on the lead screw gear even though it is not the actual number. PLACING THE CHANGE GEARS. The common engine lathe has projecting through its headstock a shaft known as the "stud." This projects a sufficient distance STUD GEAR COMPOUND GEAR OUT OF MESH INTERNED GEAR SIMPLE TRAIN OF GEARS FOR THREAD CUTTING 81 THE STARRETT BOOK to allow of mounting gearing and usually the upper cone for the feed belt. Gears mounted or to be mounted upon this projecting stud are termed "stud gears." Those mounted upon the projecting end of the lead screw are known as lead gears. When the number of threads to be cut is more per linear inch than that of the lead screw, the smaller of the selected gears is placed upon the "STUD" and the larger upon the lead screw. In the example, the 25-tooth gear would be placed on the stud and the 35-tooth gear on the lead screw. Reverse the order if the number of threads per linear inch is less than that of the lead screw. The number of teeth in the large idler gear has no bearing upon the results, as it simply conveys the motion of the upper or stud gear to the lower or lead-screw gear. In the above it is assumed that the stud rotates in unison with the lathe spindle. COMPOUNDING THE GEARS. As a means of en- larging the range of threads per linear inch possible to be cut with any set of change gears, most lathes are provided with an adjustable compound auxiliary stud which is provided with two locked gears having a ratio each to the other of two to one. As an example of their use, assume that a gear having ninety teeth was needed upon the lead screw to cut a given number of threads. If the set of gears furnished failed to provide a ninety gear, but did provide one of forty-five teeth, placing this on the lead screw and meshing the two to one com- pound stud into the train completes the desired ratio, and advances the tool as if the 90-tooth gear had been used. THREAD TOOL. Among the tools listed on page 70 is shown the ordinary threading-tool point. It is obvious that this or any other form of point must be formed and tested to give the correct form of thread. The point shown has sides at an angle with each other of sixty degrees. The point can therefore be tested with a center 82 THE STARRETT BOOK STUD GEAR INTERMEDI GEAR COMPOUND GEARS FOR THREAD CUTTING gage or rule. The same gage may also be used in setting the tool square with the axis of the work (see page 74). GRINDING THREAD TOOLS. It is important that the point of the thread tool shall conform to the outline of the groove between the adjacent threads, and that the surfaces below the cutting edge properly clear the stock being cut. When grinding a thread tool, particu- 83 THE STARRETT BOOK lar care should be given to have the clearances sufficient for the lead of the thread. SETTING THE TOOL. Set the tool point at the exact height of the lathe centers, and at right-angles to the axis of the lathe. USES OF CUTTING LUBRICANT. Use lard oil when threading steel, wrought, and malleable iron. Cut the cast metals dry. THREAD CUTTING TOOL SET AT HEIGHT OF LATHE CENTER RIGHT AND LEFT THREADS. A right-hand thread results when the threading tool is advanced from right to left as it cuts. If the tool when cutting advances from left to right the resulting screw has a left-hand thread. MEASURING AND TESTING SCREW THREADS. For ordinary purposes screw threads when cut are fitted to some threaded hole. This may be a hardened and ground gage, or may be an ordinary threaded nut, depending upon the accuracy of the work. Where the quality of the work demands special- accuracy, or where 84 THE STARRETT BOOK standard threaded gages are not available, the thread is tested by measurements made with calipers. If the point of the thread tool has been carefully and exactly formed and accurately set in place, measuring the diam- eter at the root of the thread may give sufficiently accu- CALDPERS FOR TESTING THREADS rate results, and this may be done with a set of thin point spring calipers. When greater accuracy than this is required, micrometers having special thread-measur- ing points are resorted to x (see Fig. 27). In all this it is assumed that the thread tool is ground, set, and oper- ated to give an exact thread outline. MEASURING LATHE WORK. Work done in the engine lathe is of such a variety that a considerable list of measuring tools may be needed to cover all cases. Ordinarily, however, the diameter measurements can be 85 THESTARRETT BOOK made with spring calipers, micrometers, or some of the usual bar calipers. Cylindrical plug and ring gages, as well as limit snap gages, are also used for diameter measurements, and many of these may be used in meas- uring the shorter lengths. For the longer measurements of length, steel rules are provided with or without sliders. The more accurate measurements are usually made by using a micrometer. FIG. 27 TAPER TURNING. Where two parts are to fit firmly together when in use, as, for example, centers into lathe spindles, and it it desirable to have them easily remov- able, what are known as taper-fits are used. For this purpose several rates of change in diameter have become standards. Pages 87 and 88 give the more common stand- ards. The Brown & Sharpe Standard is in general use for the spindle tapers in milling machines. The Morse taper is the one commonly used for all drills and drill- ing machinery. Either of these may be used for the tapered hole in lathe spindles, while some lathe manu- facturers have established standards of their own. 86 THE STARRETT BOOK T IT T i s ' I 1 i H | ANY * i 1 l^v 1 1 s^ Brown & Sharpe Taper Shanks Table 7 COLLET OR SPINDLE Taper per ft. is Yz in., except for No. 10 shank, where the taper is 0.5161 in. per ft. Number of Taper Diam End o 0.239 0.299 0.375 0.385 0.395 0.402 0.420 0.523 0.533 0.539 0.599 0.635 0.704 0.720 0.725 0.767 0.898 0.917 1.067 1.077 1.260 1.289 1.312 1.498 1.531 1.797 2.073 2.344 2.615 2.885 3.156 3.427 t"0_*i gc f o 11%2 2T/32 2 21%2 1% 2%6 2%2 2i % 2 327/32 3% 4% 4y 4 4iyi6 48 /4 617/32 71%2 9%r 10 8 /8 82 18 2y 8 2% i2y 32 2%2 2 3 /10 2%e 2 7 /8 6 3% 417/32 4% 4% 47/6 615/ie 6*%2 9%2 92y 32 ioy 4 o -o 1 (5 C/5 0.200 0.250 0.312 0.312 0.312 0.350 0.350 0.450 0.450 0.450 0.500 0.500 0.600 0.600 0.600 0.600 0.750 0.750 0.900 0900 1.0446 1.0446 1.0446 1.250 1.250 1.500 1.750 2.000 2.250 2.500 2.750 3.000 il 2 U4. iiyie 1% 2 2% 2% sy 4 27/^ 3 3%6 4y f 6% 2 6/4 9H w 2i %4 3iy 6 4 218/32 517/32 8%2 817/32 Length Keywa H 15 /10 Width of Keyway 0.135 0.166 0.197 0.197 0.197 0.228 0.228 0.260 0.260 0.260 0.291 0.291 0.322 0.322 0.322 0322 0.353 0.353 0.385 0.385 0.447 0.447 0.447 0447 0.447 0.510 0510 0.572 0.572 0.635 gth of ngue 27/So 27/32 83 * o SH M %- & % 8/8 Vl! n 87 THE STARRETT ROOK Morse Standard Taper Shanks Table 8 ANY r 1 i i i K i "> 1 i 1 f ft! SOCKET OR SPINDLE ^ ^ |H !o w "S w P 3 rt I E I 0.252 0.369 0.572 0.778 1.020 1.475 2.116 2.750 Dia. at End of Socket 0.356 0.475 0.700 0.938 1.231 1.748 2.494 3.270 4Vie 5%e U QC ^ 2H32 3Me 3/4 4% 6 4^8 5V4 lOfc K 4i% 7 9% Length o Keyway 2% ou II JH *>* Thickness of Tongue % Width of Keyway W 0.160 0.213 0.260 0.322 0.478 0.635 0.760 1.135 11 2%2 2% .625 .600 .602 .602 .623 .630 .626 .625 Short Shanks 0.271 0.388 0.600 0.816 1062 1.532 2.201 2.857 0.356 0.475 0.700 0.938 1.231 1.748 2.494 3.270 ! 5 /8 1% 2 ? 34* 4^8 5 5 /8 3^8 4Vl6 5Me 7Vie 9^6 2 Vie 5% ! 27/ 32 2 7/ 82 Tfc ! 5 Ae ?'* 2% 3% V4 %6 V2 I 1V4 ! 5 /8 0.195 0.260 0.387 0.514 0.639 1.014 1.266 1.642 1 27 &2 2 6% .625 .600 .602 .602 .623 .630 .626 .625 The dimensions given above for regular (full length) Morse taper shanks are those which have been accepted as standard and are used by most manufacturers. In a recent catalogue of the Morse Twist Drill & Machine Co., however, a table is given in which the length of the tang and, consequently, the whole length of the shank is slightly increased. The increase in length, however, is so slight that it does not prevent the shank from fitting into the ordinary standard taper socket. THE STARRETT BOOK TURNING TAPERS. Ordinary tapers are rated at the amount which the diameter changes in a foot's length; as, for example, the Brown & Sharpe taper of % inch per foot. To turn a taper it is necessary to use a lathe provided with a taper attachment or to adjust the foot- stock of the engine lathe sufficiently off center to give TAPER TURNING IN LATHE 89 THE STARRETT BOOK the required rate of diameter change. As all taper attach- ments are graduated to read direct, they are easily set for the required taper. Adjustment of the foot-stock of an engine lathe is not so simple as the taper attachment. In setting the taper attachment, the axial distance the center points are apart is not important, while this dis- tance must be considered in setting over the foot-stock of the lathe. AMOUNT TO OFFSET CENTERS FOR GIVEN TAPER. If the distance the center points enter the work or the mandrel is ignored, the mandrel length can be considered as the distance apart of the center points. The calculation necessary to determine the distance which the centers shall be offset, is that of multiplying the length of the work or mandrel in feet by one-half of the required taper in inches. To turn a Brown & Sharpe taper on a piece of work nine inches long the problem would work out as follows: .500 9 3 _ x - - = 0.1875 = - 2 12 16 and the foot-stock would be set over 3 Ae inch. In the above illustrative example both length and amount of taper are given, but the amount of taper is not always known. Suppose a piece is 8 inches long and a taper is to be turned on one end, the tapered portion to be 4 inches long. The difference in diameters of these 4 inches is to be % inch. How much must the tail stock be offset? If the taper is % inch in 4 inches it would be 1% inches in a foot and the tail stock would be moved over one-half of 1% inches or % inch, if the piece were a foot long, but as it is only 8 inches or % of a foot long, the tail stock should be moved over % multiplied by % or V 2 inch. Had the piece been 18 inches long, the tail stock should be moved over % multiplied by % or 1% inches. 90 THE STARRETT BOOK It has been assumed for these simple calculations that the lathe centers merely touch the ends of the piece, thus making the length of the piece the same as the dis- tance between centers. But in actual work the distance the centers enter the piece must be considered. The calculation should be as accurate as possible to avoid continually changing the tail stock to get a reasonably good taper fit. The necessity of considering the distance the center enters the piece depends somewhat upon its length. If the piece is very long, the actual taper will differ considerably from the calculated taper. If each center enters the piece one-fourth inch they would enter a total of one-half inch, and the length of the piece should be reduced by one-half inch in the calculation. While turning the taper the calipers should be used fre- quently so that it may be soon determined whether or not the tail stock is correctly placed. For coning pulleys, set the foot-stock away from the operator when adjusting. In most taper work, however, the center is offset towards the operator. SETTING THE TOOL. The tool-point should be set at the exact height of the axis of the lathe. TESTING THE TURNED TAPER. To test the taper as it is turned, ground, or filed, it should be pressed lightly into a standard tapered hole and worked back and forth sufficiently to mark the places where bearing occurs. If the work has been lightly covered with some marking pigment, the bearing points will be more distinct. Care, however, must obtain that the coating is not sufficient to smooch, as it will deceive the workman. Adjust taper- setting until a correct fit is obtained. ECCENTRIC TURNING. While for the most part the lathe is used for work exactly concentric with the axis, it can be used for turning work not concentric with the axis. Work of this sort is termed "eccentric," and an example of such work is seen in the eccentrics which 91 THE STARRETT BOOK Amount of Taper in a Given Length, When the Taper per Foot is Known Table 9 v< Taper per Foot j! Me %2 tt Vi % * 0.600 % M 1 1V4 Hi .0002 .0002 .0003 .0007 .0010 .0013 .0016 .0016 .0020 0.0026 0.0033 T/ 0003 0005 0007 0013 0020 .0026 .0031 0033 0039 00052 00065 % .0007 .0010 .0013 .0026 .0039 .0052 .0062 .0065 .0078 0.0104 0.0130 vie .0010 .0015 .0020 .0039 .0059 .0078 .0094 .0098 .0117 0.0156 0.0195 ^4 .0013 .0020 .0026 .0052 .0078 .0104 .0125 .0130 .0156 0.0208 0.0260 %6 .0016 .0024. .0033 .0065 .0098 .0130 .0156 .0163 .0195 0.0260 0.0326 % .0020 .0029 .0039 .0078 .0117 .0156 .0187 .0195 .0234 0.0312 0.0391 %e .0023 .0034 .0046 .0091 .0137 .0182 .0219 .0228 .0273 0.0365 0.0456 Vz 00?fi 0039 .0052 0104 .0156 .0208 .0250 .0260 .0312 0.0417 00521 %e .0029 .0044 .0059 .0117 .0176 .0234 .0281 .0293 .0352 0.0469 0.0586 .0033 .0049 .0065 .0130 .0195 .0260 .0312 .0326 .0391 0.0521 0.0651 Hie .0036 .0054 .0072 .0143 .0215 .0286 .0344 .0358 .0430 0.0573 0.0716 % .0039 .0059 .0078 .0156 .0234 .0312 .0375 .0391 .0469 0.0625 0.0781 1 %e .0042 .0063 .0085 .0169 .0254 .0339 .0406 .0423 .0508 0.0677 0.0846 % .0046 .0068 .0091 .0182 .0273 .0365 .0437 .0456 .0547 0.0729 0.0911 1 y^e .0049 .0073 .0098 .0195 .0293 .0391 .0469 .0488 .0586 0.0781 0.0977 1 .0052 .0078 .0104 .0208 .0312 .0417 .0500 .0521 .0625 0.0833 0.1042 2 .0104 .0156 .0208 .0417 .0625 .0833 .1000 .1042 .1250 0.1667 0.2083 3 .0156 .0234 .0312 .0625 .0937 .1250 .1500 .1562 .1875 0.2500 0.3125 4 .0208 .0312 .0417 .0833 .1250 .1667 .2000 .2083 .2500 0.3333 0.4167 5 .0260 .0391 .0521 .1042 .1562 .2083 .2500 .2604 .3125 0.4167 0.5208 6 .0312 .0469 .0625 .1250 .1875 .2500 .3000 .3125 .3750 0.5000 0.6250 7 .0365 .0547 .0729 .1458 .2187 .2917 .3500 .3646 .4375 0.5833 0.7292 8 .0417 .0625 .0833 .1667 .2500 .3333 .4000 .4167 .5000 0.6667 0.8333 9 .0469 .0703 .0937 .1875 .2812 .3750 .4500 .4687 .5625 0.7500 0.9375 10 .0521 .0781 .1042 .2083 .3125 .4167 .5000 .5208 .6250 0.8333 1.0417 11 0573 .0859 .1146 .2292 .3437 .4583 .5500 .5729 .6875 0.9167 1.1458 12 .0625 .0937 .1250 .2500 .3750 .5000 .6000 .6250 .7500 1.0000 1.2500 92 THE STARRETT BOOK operate the valves of steam engines. If the work has a hole through it, as in the above example, the hole is first finished to required dimensions. A mandrel is then used for carrying the work on the centers. While the mandrel has been built on one set of centers exactly true with its axis, for eccentric turning it has a second set of centers which are offset the amount required for the eccentricity specified. In the case of eccentrics made solid with the FIG. 28 shaft, the two sets of centers, one t for turning the shaft and the other for finishing the eccentrics, are made side by side in the ends of the shaft, as shown in Fig. 28. When the specified eccentricity is too extreme to allow both pairs of centers coming within the limits of the diameter of the shaft, special ends may be cast or forged on the ends of the work, and can afterward be machined off. In crank-shaft turning, special attach- ments are provided for the ends of the shaft. Special eccentric turning chucks .may be made to hold the work. CHUCKING. Chucking includes, not only the mount- ing of the work in the chuck, but performing the neces- sary operations on it while so held. The name "chuck" is given to a line of tools having a variety of form, all 93 THE S T A R R E T BOOK 94 THE STARR E T T BOOK of which are designed to hold work or tools upon the nose of a spindle. In general the heavier sorts are mounted upon a face-plate which screws upon the end of the spindle, while smaller sizes are fitted with a taper- shank which fits tightly into the tapered hole in the spindle. The smaller sizes are used for carrying tools, such as drills, also screws, studs, wire pins, etc.; and are known as drill-chucks. The larger sizes are widely used for holding work for machine operations, and are sometimes called "work- chucks." On their face they are provided with adjust- ing jaws movable regularly to and from the center; these jaws are so designed that a considerable variety of work may be readily held and successfully worked upon with common cutting tools. The jaws are moved by means of screws or gears, and can be adjusted independently, the chuck being called an independent jaw-chuck; or, all the jaws may be made to move together, in which case it is known as a Universal chuck. HOLDING THE WORK. The work must be clamped firmly in the chuck while being machined. Care must also be taken that the clamping of a slender piece is not so firm as to distort or spring it. If work slips, tools may be broken, and if held too tightly and sprung or crushed, the work is injured and in some cases en- tirely ruined. TRUING THE WORK. Adjusting the chuck-jaws so that the work will run as true as desired is termed, "truing up the work." This is preliminary to any tool- ing which may be done on the job. Often this truing of the work can be accomplished by holding a piece of chalk to just touch the work, leaving a plain mark- ing this method is used when chucking rough pulleys for drilling out the hole in the hub. Where greater accuracy is required, the work is indicated with a Uni- versal dial test indicator. 95 THE STARRETT BOOK CHUCKING TOOLS. With the work located in the chuck it may be tooled with ordinary lathe tools, such as shown in the tool-chart (page 70), or it may be drilled with two, three, or four fluted twist drills, and reamed with machine reamers, or special shell bits and coun- terbores. CHUCKS ON TURRET LATHES. In turret lathe- work, for bar-stock, the chuck is a part of the regular tool equipment; these chucks are often of special design, so made that they open and close by hand-operated levers or automatically-operated cams. KNURLING. The surfaces of adjusting screws and small machine parts are often given a regular rough sur- face for easy gripping. In the machine shop this is done by using a tool known as a "knurl" or "knurling tool," which consists of one or more indented rollers or knurls mounted to rotate in some form of holder. 32nds. I 0312 3 0937 5 .1562 7 .3187 9 .2812 II .3437 I- 1-4- .250 3-8 .375 IBths. .0625 3 .1875 5 .3125 NO 232 7 .4375 15.4687 THELaSTARRETTCD ATHOLMASS.USA FIG. 29 These knurls are forced into and fed along the stock until the indented design has been sufficiently imprinted into the surface. When neatly and effectively done the re- sults give a fine gripping sur- face and a rather pleasing effect to the eye. The knurling tool may be fed along the surface of the work by hand, but usually the power traverse feed is used. The process is repeated if one passage of the tool does not give suffi- cient depth. Fig. 29 shows knurling on a micrometer. 96 THE STARRETT BOOK TOOL-MAKING Under the name "tools" are listed the various small or tool-room tools used either by hand or in various ma- chines. So important has their use become that large industries are devoted to their manufacture, and most machine-building firms now buy their more common tools rather than maintain a tool-making plant of their own. For example, drills, reamers, milling cutters, counterbores, colletts, etc., are usually purchased in the open market. Every skilled machinist, however, should know the principles upon which such tools are made, and should be able to make any or all of them. DRILLS. Drills are now largely of the twist type, and the most efficient are machined and milled from solid bar-stock, and for this purpose both Carbon-tool steel and high-speed steel are being used. The prevailing type has a straight or a tapered holding shank, spiral- milled flutes and a cone-point with effective cutting lips as noted under drill sharpening. The flutes or lands taper slightly from full diameter size at the cone-point to several thousandths inch smaller at or near the hold- ing shank. To prevent rubbing on the sides of a hole, the flutes are also cleared back from the front edge throughout their length. The grooves are milled with cutters having a form that gives the maximum chip capacity, yet leaves the cutting edge of the drill-lip a straight line. Several makers of twist-drills increase the lead of the twist when milling the grooves; such drills are known as "increase twist" drills. The web is as thin as con- sistent with the required strength, and with some makers is thicker near the shank than at the point. Drills are carefully heat-treated, straightened, and ground to diameter. REAMERS. The term "reaming" is given to the proc- 97 THE STARRETT BOOK ess of enlarging a drilled hole. Reamers are of two well- defined types, known as "fluted" reamers and "rose" reamers. The fluted reamer is one having numerous flutes on the circumference of the cutting portion of the tool. In other words, the cutting is done on the cir- cumference instead of at the end, as with a drill. The number of flutes on the surface of a reamer varies with the diameter, and with some makes the num- ber of flutes is greater for a given diameter when the reamer is to be used in a machine instead of for hand reaming. As its name implies, a fluted hand reamer is made for hand use, and is seldom called upon to enlarge a hole more than .007" for any diameter, and not more than .003" in the smaller sizes. In the case of machine or lathe reamers, the length of the flutes for any given diameter is fifty per cent less than the standard length for hand reamers. The depth of flute is usually somewhat in excess of that of hand reamers. In most cases machine reamers are used for enlarging drilled holes to a diameter which only allows sufficient stock for hand reaming. When the holes are not to exceed a diameter in length, machine reamers may be used for finishing the drilled hole to its full diameter; but when straight, round, accurate holes are to be of exact diameter the better practice is to first drill 1/32" to 1/16" under size, enlarge to hand reaming size with a machine reamer, and then carefully hand ream to exact size. ECCENTRIC FLUTES. Formerly fluted reamers had an odd number of flutes, such as nine or eleven. Although this method eliminated chattering to some extent, it had the disadvantage of making it difficult to caliper the diameter of the cutting edges. Eccentric fluting, as it is called, consists in milling the flutes with uneven spac- ing to obviate chattering, but having them exactly oppo- 98 THE STARRETT BOOK site, so that a diameter measurement may be made with a micrometer. A rose-reamer is an end-cutting tool, and is often used in place of a drill in cored holes. It is never made for hand use, and in general practice is seldom used for exact diameter. MILLING CUTTERS. In lathe work the cutting tool is fixed and the work rotates. In a milling machine the cutter rotates and work is fed against it. The rotating cutter, termed a "milling cutter," has an almost unlimited variety of sizes and shapes for milling regular and irreg- ular forms. Milling cutters are made from some of the tool steels, heat-treated to give the right cutting quali- ties, the stock coming to the tool-maker in the form of rough blanks, carefully annealed. Where the cutter has a hole through it this is first drilled, bored, or reamed to a diameter somewhat smaller than that in the finished cutter. The reason for this is that all the exact true sur- faces must be finished after the cutter has been hardened some grinding process being necessary which requires an excess of stock. When the length of the cutter is greater than about one-half inch, it is usual to chamber the hole to a shape that renders it necessary to diameter grind the holes at the ends only. In cutters of considerable length the saving in grinding by this procedure is considerable. The sides of the blanks are usually recessed, giving a hub- and-rim effect at the sides of the cutter. An even num- ber of teeth is preferable, and these are spaced to a cir- cumferential pitch varying from three-eighths to three- quarters inch for ordinary cutter sizes. When the teeth are milled into the solid blank, a cutter giving a space angle of sixty degrees is preferred for cutting the peripheral teeth, while one of seventy degrees is generally used for the side teeth. Where milling cutters are made in quantity, special space cutters 99 THE STARRETT BOOK are worked out to give the maximum chip room con- sistent with tooth strength. After the cutter has been heat-treated to the proper hardness, it is finished to the specific dimensions by grinding. GRINDING THE HOLE. Unless special methods and tools are employed the hole is completely finished as the first operation of grinding. This is accomplished by holding the cutter trued in a chuck screwed on the spindle of a Universal grinder and grinding out the hole to standard size, using an internal grinding attachment. GRINDING THE SIDES. Fig. 30 shows how to grind the sides with the cutter held flat against a face- plate. If the cutter is to be used for deep cuts, the face- plate is set to give a slight concavity to the sides of the cutter. FIG. 30 CLEARANCE OF THE TEETH. The teeth of milling cutters are given a slight clearance back from the cutting edges; five degrees is usually sufficient. 100 THE STARRETT BOOK JIGS AND FIXTURES Jigs and fixtures are special devices designed to put manufacturing upon an efficient basis. Three distinct purposes are served by the use of jigs: (a) Reduction of cost per piece; (&) interchangeability of parts; and (c) accurate production. Jigs and fixtures are usually made from cast iron or steel. Their use practically does away with fitting, as this term is known in shops not using jigs. JIG DESIGN. A jig is a device for holding the work and for locating the tool work to be done upon it. A good example of this is shown in the drill jig, Fig. 31. Jigs are of the plate type which lies upon and is clamped to the surface of the work; of the open-box type; and of the closed-box type. In designing a jig, the piece is first drawn upon a sheet of paper, which is sufficiently large to allow locat- ing the views some distance apart. This permits build- ing the jig in the drawing around the "coupon," as the piece is often called. To start the design, first determine and lay down the locating points or stops, then arrange the clamping device. A jig should be so designed that the work can be put into position in only one way. Provide for supporting the thrust of the cutting tools in such a manner as to avoid springing the work. Make the jig as simple as possible, avoiding every feature in design that complicates the workman's use. While in the larger shops the jigs are designed by the draftsmen, in many shops the tool-maker both de- signs and builds the jigs, and in no other way can a workman so clearly show his ability and ingenuity as in the building of jigs. JIG BODY. The jig body is usually of cast iron, which is first rough planed or milled on all surfaces which are to be finished. These surfaces are then finish 101 THE STARRETT BOOK planed to final dimensions. In some cases jig bodies are finished by grinding in a surface grinder. LOCATING BUSHING HOLES. If no particular accuracy is demanded, the holes for bushings can be located directly by careful attention to ordinary laying- out methods, and the hole drilled and reamed directly. FIG. 31 When the allowable error is very small a more accurate scheme must be followed, and the best of several meth- ods for the average tool-maker is that known as the button method. In this the holes are located by laying out scribed center lines and locating intersections where the holes are to be centered. Instead of drilling and reaming the bushing holes, holes are drilled and tapped to fit the button screws. The jig buttons are small, accurately ground cylinders, as shown in Fig. 32. These are held by means of the screws, lightly clamped in place, 102 THE STARRETT ROOK and exactly located to centers by accurate measurements. The highest possible accuracy in locating holes is secured bv this method. FIG. 32 BORING HOLES. The holes for the hardened bush- ings are usually bored by swinging the jig body upon a face-plate in an engine lathe. The jig body is then shifted upon the face-plate until a button indicates true THE STARRETT BOOK with a Universal Dial Indicator, as shown in Fig. 33. The jig body is then clamped tightly upon the face-plate. After removing the jig button, the hole is first rough- ADJUSTING BUTTONS TO SIDE OF PLATE BUTTONS IN PLACE ADJUSTING BUTTONS WITH MICROMETER 104 THE STARRETT BOOK THE STARRETT BOOK 106 THE STARRETT BOOK drilled approximately to size, and afterwards carefully bored exactly to size. This prepares the hole for hold- ing the hardened steel bushing; the process is repeated for all the previously located buttons. JIG BUSHINGS. If the holes in a cast-iron or soft- steel jig body were left as bored, they would soon lose accuracy by wearing off center; To prevent this wear the holes are lined with hardened and carefully ground bushings, pressed or driven tightly into place. These bushings are made with a hole having a diameter equal to that of the tool which passes through them. The bushings are sufficiently long to support the drill. In case the jig bushings must be removed frequently, they are known as slip bushings, and the hole in which they slip is lined with a steel lining, itself hardened and ground. In some cases the bushing locates the work as well as the tool, and if so the bushing screws through the body of the jig and against some prominent part of the work, as a boss for example. 107 THE STARRETT BOOK TOLERANCES. In all construction work a certain amount of inexactness is allowable. In other words, it is impossible to obtain absolute precision, and the allowable errors in exactness are termed "tolerances." In some cases a tolerance of one-sixteenth inch might be allowed, while in others exactness to the fraction of a thousandth part of an inch may be necessary. See pages 31 and 32. JIG FOR DRILLING BOLT HOLES IN CYLINDER FLANGE AND HEAD The projection on the jig keeps it concentric with the bore of the cylinder, and the recess fits over the pro- jection on the head. 108 THE STARRETT BOOK GRINDING In the machine shop the term "grinding" refers to the producing of finished surfaces by means of rotating grinding wheels, and the process of grinding as used in finishing machine parts is to-day the most efficient method devised for the purpose. With a proper selec- tion of grinding machine and grinding wheel, all of the common machine construction materials may be readily and accurately finished. Grinding machines are classified into two groups, (a) those for curved surfaces; as, for example, cylin- drical work; and (5) those for plane or flat surfaces. The first of these is usually called a cylindrical grinder, and the second is known as a surface grinder. Each group has many designs, made necessary by the varied uses to which grinding is adapting itself. GRINDING WHEELS. These are now known as abrasive wheels, and the material from which they are made is termed an abrasive. The abrasives in common use are the minerals emery and corundum, and the manufactured abrasives, sold under the trade names of Alundum, Aloxite, Carborundum, Crystolon. Owing to the uniformity of the product as it comes from the electric furnace, manufactured abrasives are at present more largely used than natural abrasives. MAKING ABRASIVE WHEELS. An abrasive wheel is made up of one of the above-named ABRASIVES and a BOND. The bond is, as its name indicates, something for holding the abrasive in mixture. Grinding wheels are made by three processes, known as Vitrified, Silicate, and Elastic. VITRIFIED WHEELS. In wheels made by the Vitri- fied process, the bond is of earth or clay which hardens or vitrifies' when subjected to a temperature of about 2500 F. to 2800 F. for a definite period of time. Vari- 109 THE STARRETT BOOK Allowances for Grinding Table 10 Diameter, Inches Length, Inches 3 6 9 12 15 18 24 30 36 42 48 Allowance, Inches X K i 1M U4 2 2K VA 3 3^ 4 V/2 5 6 7 8 9 10 11 12 0.010 0.010 0.010 0.010 0.010 0.015 0.015 0015 0.010 0.010 0.010 0.010 0.015 0.015 0.015 0.015 0.010 0.010 0.010 0.015 0.015 0.015 0.015 0.015 0.010 0.010 0.015 0.015 0.015 0.015 0.015 0.020 0.015 0.015 0.015 0.015 0.015 0.015 0.020 0.020 0.015 0.015 0.015 0.015 0.015 0.020 0.020 0.020 0.015 0.015 0.015 0.015 0.020 0.020 0.020 0020 0.020 0.020 0.020 0.020 0.020 0.020 0.020 0.020 0.020 0.020 0.020 0.020 0.020 0.020 0.020 0.025 0.020 0.020 0.020 0.020 0.020 0.020 0.025 0.025 0.020 0.020 0.020 0.020 0.020 0.025 0.025 0.025 0015 0015 0.020 0.020 0020 0.020 0.020 0.025 0.025 0.025 0.025 0.015 0.020 0.020 0.020 0.020 0.020 0.025 0.025 0.025 0.025 0.030 0.020 0.020 0.020 0.020 0.020 0.025 0.025 0.025 0.025 0.025 0.030 0.020 0.020 0.020 0.020 0.025 0.025 0.025 0.025 0.025 0.030 0.030 0.020 0.020 0.020 0.025 0.025 0.025 0.025 0.025 0.030 0.030 0.030 0.020 0.020 0.025 0.025 0.025 0.025 0.025 0.030 0.030 0.030 0.030 0.020 0.025 0.025 0.025 0.025 0.025 0.030 0.030 0.030 0.030 0.030 0.025 0.025 0.025 0.025 0.025 0.030 0.030 0.030 0.030 0,030 0.030 0.025 0.025 0.025 0.025 0.030 0.030 0.030 0.030 0.030 0.030 0.030 0.025 0.025 0.025 0.030 0.030 0.030 0.300 0.300 0.030 0.030 0.030 0.025 0.025 0.030 0.030 0.030 0.030 0.030 0.030 0.030 0.030 0.030 0.025 0.030 0.030 0.030 0.030 0.030 0.030 0.030 0.030 0.030 0.030 110 THE STARRETT BOOK ous grades of hardness are obtained by using bonds of different tensile strength. The ideal bond is one which retains the grains of abrasive until sufficiently dulled by use, and then allows them to break away, and in this manner bring fresh cutting edges and points into grind- ing contact. SILICATE WHEELS. Silicate of Soda is the bond used in silicate wheels; and wheels made by this proc- ess are most efficient for tool and knife grinding. ELASTIC WHEELS. This process of bonding is generally used for the very thin wheels used for slitting metals. The principal ingredient of the bond is shellac. GRADING THE ABRASIVE. By numerous crushing, grinding, cleansing, and sorting processes, the abrasive is graded into a series of sizes which give the wheel its grain number. This number conforms to the sieve mesh through which the abrasive is passed; for example, grain No. 40 indicates that the abrasive was graded through a sieve having a mesh of forty to the linear inch. COMBINATION WHEELS. For many grinding pur- poses the combination wheel is preferred to a wheel of single grade. Combination wheels are made up of abra- sives of several grain numbers. BONDING. The ideal bond is one which is imper- vious to moisture, does not soften by heat, and which holds firmly the cutting points of the abrasive until they become dulled by use. The bond then releases the dull abrasive and permits fresh, sharp points to begin cutting. With abrasives of equal quality the maker who nearest approaches the ideal bond produces the superior wheel. GRADING THE WHEELS. In grinders' language, abrasive wheels are known as hard wheels and soft wheels. The maker, therefore, lists his wheels as hard or soft by some scale of numbers or by letters. A prom- inent firm uses the letters of the alphabet, as shown in the following list in which "M" is medium. Ill THE STARRETT BOOK Norton Grade List The following grade list is used to designate the degree of hardness of our Vitrified and Silicate Wheels, both Alundum and Crystolon. E Soft F G H I Medium Soft J K L MEDIUM M MEDIUM N O P Medium Hard Q R S T Hard U V W X Extremely Hard Y The intermediate letters between those designated as soft, medium soft, etc., indicate so many degrees harder or softer; e. g., L is one grade or degree softer than me- dium; O, two degrees harder than medium, but not quite medium hard. Elastic Wheels are graded as follows: 1, 1 V 2 , 2, 2^, 3, 4, 5, and 6. Grade 1 is the softest and grade 6 the hardest. 112 THE STARRETT BOOK CYLINDRICAL GRINDING. When the piece being ground is rotated, the process is known as cylindrical grinding, and the development of machines for grind- ing cylinders has given the process a great impetus. While it is possible to grind from the rough stock with- out previous lathe work, the method usually followed is to first rough turn the work. ROUGHING FOR GRINDING. This process includes the work done in removing excess stock previous to finishing to size in the grinding machine. Unless a study is made of the conditions surrounding the whole operations of the lathe and the grinding machine, lack of efficiency may result. In general where the work is to be ground it is best to consider the lathe as a mere roughing machine for removing the excess of stock at as deep a cut and as coarse a feed as is consistent with an efficient cutting speed, leaving the job of finishing to the grinding machine. AMOUNT TO LEAVE FOR GRINDING. If the grind- ing machine is modern in design as much as 1/32 of an inch, or even more may be left on machinery steel parts for removal in the grinder; the amount varying with the size of the work itself. An allowance of 1/64 of an inch is general on the smaller machine parts, but this allowance should be increased on larger sizes. Table 10, page 110, shows allowance for grinding as recommended by one maker of grinding machines, and Table 11 shows grinding wheel speeds. SELECTING THE WHEEL, the selection of the wheel to be used in any grinding operation can, per- haps, best be made by reference to Table 12, page 115, which fairly represents general practice. As the hard- ness of material and the area of contact made by the wheel have a marked influence, no table can entirely solve the problem, but it may be used as a start in the right direction. In general a soft wheel should be used on hardened work and a harder wheel on soft materials. 113 THE STARRETT BOOK Table of Grinding Wheel Speeds Table 11 Diameter Wheel Millimeters Rev. per Minute for Surface Speed of 4.000 Feet, or 1,200 Meters Rev. per Minute for Surface Speed of 5,000 Feet, or 1,500 Meters' Rev. per Minute for Surface Speed of 5,000 Feet, or i, 800 Meters 1 inch about 25 15,279 19,099 22,918 2 " 50 7,639 9,549 11,459 3 " 75 5,093 6,366 7,639 4 ' 100 3,820 4,775 5,730 5 ' 125 3,056 3,820 4,584 6 ' 150 2,546 3,183 3,820 7 ' 175 2,183 2,728 3,274 8 ' 200 1,910 2,387 2,865 10 ' 250 1,528 1,910 2,292 12 f 305 1,273 1,592 1,910 14 ' 355 1,091 1,364 1,637 16 ' 405 955 1,194 1,432 18 ' 455 849 1,061 1,273 20 ' 505 764 955 1,146 22 ' 515 694 868 1,042 24 ' 610 637 796 955 26 ' 660 586 733 879 28 ' 710 546 683 819 30 ' 760 509 637 764 32 ' 810 477 596 716 34 ' 860 449 561 674 36 ' 910 424 531 637 38 ' 965 402 503 603 40 ' ' 1,015 382 478 573 42 ' 1,065 364 455 546 44 ' 1,115 347 434 521 46 ' ' ' 1,165 332 415 498 48 ' ' 1,220 318 397 477 50 ' ' 1,270 306 383 459 52 ' ' 1,320 294 369 441 54 ' ' 1,370 283 354 425 56 ' ' 1,420 273 341 410 58 ' " 1,470 264 330 396 60 " " 1,520 255 319 383 The R. P. M. at which wheels are run is dependent on conditions and style of machine and the work to be ground. Wheels are run in actual practice from 4,000 to 6,000 feet per minute; in some instances as high as 7,500 feet. 114 THE STARRETT BOOK Grade and Grain of Grinding Wheels for Different Materials* Table 12 (The Norton Co.) Class of Work Alundum Crystolon Grain Grade Grain Grade Aluminum castings 36 to 46 3 to 4 Bias. 20 to 24 20 to 24 24 to 36 16 to 24 16 to 24 30 to 46 16 to 30 20 to 30 16 to 24 20 to 30 20 to 30 PtoR QtoR PtoR PtoR OtoQ JtoL JtoL QtoS QtoS Q OtoQ Brass or bronze castings (large) Brass or bronze castings ^small) Car wheels cast iron Car wheels, chilled Cast iron, cylindrical Cast iron, surfacing Cast-iron (small) castings Cast-iron (large) castings Chilled iron castings Dies chilled iron . 20 24 comb. 20 to 46 24 to 30 16 to 20 20 to 30 JtoK HtoK PtoR QtoR PtoU Dies, steel 36 to 60 20 to 30 JtoL PtoR Drop-forgings Internal cylinder grinding . . ., Internal grinding, hardened steel Machine shop use, general Malleable iron castings (large) Malleable iron castings (small) Milling cutters, machine grinding . . Milling cutters, hand grinding Nickel castings Pulleys, surfacing cast iron Reamers, taps, etc., hand grinding. . Reamers, taps, special machines Rolls (cast iron) wet 30 to 60 ItoL 46 to 60 20 to 36 14 to 20 20 to 30 46 to 60 46 to 60 20 to 24 46 to 60 46 to 60 24 to 36 70 JtoM OtoQ PtoU PtoR HtoM JtoM PtoQ KtoO JtoM JtoM !Hto2 Elas. "RtoS QtoS R ' KtoL 16 to 20 20 to 30 20 to 25 30 to 36 24 to 38 70 to 80 30 to 46 30 to 50 jtoM' I^to2 Elas. 2 to 3 Elas. KtoM Rolls (chilled iron), finishing Rubber .' 30 to 50 36 to 50 60 24 comb. 46 to 60 24 to 36 24 comb. 46 to 60 36 to 46 12 to 20 20 to 30 16 to 46 16 to 24 46 to 60 36 to 60 12 to 30 46 to 60 JtoK MtoN OtoQ LtoN LtoN HtoK K JtoL HtoK SSS LtoP PtoR M KtoM PtoU KtoM Saws, gumming and sharpening .... Saws, cold cutting-off Steel (soft), cylindrical grinding. . . j Steel (soft), surface grinding Steel (hardened), cylindrical grind- 5 ing { Steel (hardened), surface grinding . . Steel, large castings : ::::; Steel (manganese), safe work Structural steel Twist drills, special machines Wonrlwnrkincr tnnls . . * The information contained in this table is general and intended only to give an approximate idea of the grade used under ordinary conditions. 116 THE STARRETT BOOK MOUNTING THE WHEEL. The wheel should be so mounted that there are no unequal stresses set up. Suitable guards should be provided to prevent injury to the workmen in case of the wheel bursting. The accompanying illustrations show RIGHT and WRONG methods of mounting wheels carefully study the cuts. MEASURING THE WORK. The use of micrometers for obtaining exact measurements is nowhere better illustrated than in grinding. Fig. 34 shows an oper- ator adjusting his micrometer for obtaining a measure- ment on a cylindrical piece, and Fig. 35 shows the operator as he makes his reading. While in lathe work the position of the operator leads naturally to adjusting the micrometer spindle with the fingers of the right hand, the left hand grasping the frame, in grinder work the reverse is generally true, hence he occupies the position as shown. GRINDING FLAT SURFACES. Flat surface grind- ing may be divided into two general classes : (a) Machine 116 THE STARRETT BOOK FIG. 34 parts, such as boxes, tables, cross-slides, faces of nuts, etc.; and (b) fine tool work, as, for example, steel blades, scales and rulers, straight edges, etc. Until recently the first-named class of work was done by reciprocating the work beneath the circumferential face of an abrasive wheel in a machine which, in principle, is not unlike a small planer. The use of machines with CUP WHEELS has practically revolutionized such grinding, and an exactness of surface is being obtained on fine flat work which leaves little to be desired. LAPPING. In certain lines of work the final grind- ing process is often made, not with abrasive wheels as previously described, but by using metal discs, rings, or cylinders, the surfaces of which have been charged with a fine flour abrasive. Such a tool is called a "lap," and its use "lapping." Laps were first used by lapidaries in finishing the surfaces of mineral specimens, but laps have been in common use for a considerable time on fine work in the machine shop. 117 THE STARRETT BOOK Laps are generally made of some material soft enough so that the abrasive can be readily pressed into the surface; or, as it is correctly termed, the surface is "charged." Soft, close-grained cast iron, copper, brass, or lead may be used for the lap, and any of the flour abrasives may be charged into the surface by roll- ing the abrasive into the lap either with a hardened roll or on a hardened surface. FIG. 35 In some of the finer grinding operations the lap is charged with diamond dust which has been precipitated or settled in a suitable dish of olive oil. The several grades are denoted by the time taken to precipitate; as, for example, fineness No. 5 takes ten hours. Since lapping is a somewhat slow and tedious proc- ess it should be used only for the removal of small amounts of stock. COMMON USES OF LAPPING. The more common uses of lapping are those of finishing micrometer ends, plug and ring gages, holes in jig bushings, and in the finest die and punch work. 118 THE STARRETT BOOK LOCATING AND ALIGNING MACHINERY When the product of the shop is determined, the proper location of the machines may be found by means of a plan or location drawing worked out in the draft- ing room. An easy way to do this is to provide rectangu- lar slips of cardboard, each representing to some definite scale the plan outline of each machine. Placing these upon the floor plan of the room, the better of several arrangements may be found, and by using push pins the cardboard representations may be fixed in position. FIG. 36 Having decided upon the location, the machinery may be aligned in these positions by measurements from some base line made upon the floor or ceiling; or a leveling instrument,* such as shown in Fig. 36, may be used. Ordinarily the machines are aligned by simple meas- * See page 124 for directions for setting up a level. 119 THE STARRETT BOOK urements and the countershafting hung from the ceil- ing vertically over the machine by plumbing up from the previously located machines. In such work thought must always be given to the line shafting and pulleys. Unless care is used, there may be such interferences as to necessitate repeating the work. As the efficiency of the shop depends to a considerable extent on a con- venient arrangement of the machines, all interferences should be taken care of on the ceiling rather than alter- ing the arrangement of the machines. ALIGNING THE SHAFTING. With the locations of the several lines of shafting determined upon, the usual method of alignment is to stretch a wire or cord the length of the room at the desired level of the shaft and at a distance from its location sufficiently great to give easy working room. With the two ends of the wire in position it should be stressed to bring it taut and should be supported at frequent intervals by wire hangers. FIG. 37 With the shafting hangers in approximate position and the shafting in place, the necessary shifts can be made to bring the shaft parallel with the wire. A light stick notched at one end to rest upon the shaft and a wire brad at the other end for a feeler is all that is neces- sary for ordinary alignment. Leveling the shaft is done with special spirit levels having metal frames, the bases of which have been carefully grooved to set upon the shaft. Such a level is shown in Fig. 37. Special level- ing and aligning attachments for setting and lining up 120 THE STARRETT BOOK shafting are sometimes used. Shafting is often lined by plumbing up from a data line on the shop floor with a mercury plumb bob. Mercury Plumb Bobs 121 THE STARRETT BOOK LEVELING INSTRUMENT While the surveyors' transit can be used in shop level- ing and in shaft aligning a much simpler and a more inexpensive instrument termed a leveling instrument is all that is needed. It consists of a table capable of being adjusted in the horizontal plane, which carries a yoke which in turn carries a twelve-inch brass tube. The whole instrument is placed upon a suitable tripod. The tube has no lenses and therefore is not a telescope as in the surveyors' instrument. At one end of the tube are the usual cross hairs which locate the axis and at the opposite end is a peep hole or sight piece for the eye. The yoke which carries the tube is attached to a graduated arc which is let into the upper part of the table; this allows the instrument to swing to read angles in the horizontal plane. ADJUSTING THE INSTRUMENT. In using this in- strument it is important that the table be carefully lev- eled. It is pivoted on the tripod tube by a ball and socket joint. Three knurled-head adjusting screws threaded through the tripod top and resting against the under side of the table furnish a means of adjusting the table. Upon the table carrying the yoke is a bent-tube spirit level with a sensitive air bubble. After the tripod legs have been placed to roughly level the instrument, adjust the knurled leveling screws to give .as correct a centering for the air bubble as is possible. To test this adjustment swing the yoke, which carries the air bubble, to several posi- tions and note any change in the position of the bubble. If there is a change, readjust the leveling screws until the yoke can be swung through its travel with the air bubble maintaining its central position. USING THE LEVELING INSTRUMENT. While it is possible to so mount the leveling instrument upon a plat- 122 THE STARRETT BOOK form that its height will be sufficient for the use of targets mounted upon the shaft, the usual method is to hang targets upon the shaft and adjust them to swing low enough to allow the leveling instrument to be set with its tripod on the floor or on some convenient foundation spot. THE TARGETS. These consist of stirrups which carry a spirit level and block with vertical and horizontal lines crossing each other. A plumb is hung upon the stir- rup in such manner as to be readily raised or lowered. One of the targets may be hung upon the shaft free to swing plumb, the other is used as a fixed wall target. USE. After the shafting has been roughly aligned with the wall of the building or with a line of columns, this being done by measurement, the leveling instrument is placed vertically beneath one end of thfc shaft. To locate the leveling instrument, plumb down from the center of the shaft, using the hanging target plumb bob, and locate a point in the floor or board placed on the foundation. A prick punch mark in the flat head of a wire brad previously driven into the floor provides a permanent point. Set the tripod of the leveling instru- ment directly over this point, using the plumb bob hang- ing from the center of the table. Next carefully level the table as already described. Hang the portable target closely in front of the cross-hair end of the tube and level and adjust its height until the horizontal cross hair of the tube coincides with the horizontal cross line of the target. Remove the target to the far end of the shaft and swing the tube of the leveling instrument until the sight through the tube coincides with the vertical line on the target. With the hanging target displaced, mount a fixed target upon the wall at the far end of the shaft and adjust it until its cross lines coincide with the cross hairs of the tube as sighted. If the instrument is in its 123 THE STARRETT BOOK original position with the plumb bob over the point in the floor, the setting up of the instrument is complete. By reference to the fixed target it can at all times be checked. Replace the hanging target at the far end of the shaft and adjust the adjacent hanger so that the cross lines of the target coincide with the cross hairs when sight- ing through the tube. Repeat for each hanger until the target can be hung upon the shaft adjacent to any hanger and show perfect coincidence of target cross lines and tube cross hairs. Note that after the instrument and target have been set neither should receive further adjustment except in case of accident the shaft itself receives the adjust- ments. HOW TO SET UP THE TRANSIT The Starrett transit or level can be used for the same purposes as any engineer's transit and level, and because of its simplicity and freedom from complications, it can be used by any one in laying out foundations for buildings, aligning machinery, and in building dams and raceways for simple water-power developments. The transit combines in one instrument the facili- ties for measuring both horizontal and vertical angles, and enables the operator to lay out anything that does not require excessive refinement. The level is for meas- uring angles in a horizontal plane only, and it should be borne in mind that the level will do all that the transit will do, except measure vertical angles. The transit, which is furnished either with a telescope or plain-sight tube, is mounted on a tripod, and has a plate carrying a graduated arc. The telescope or sight-tube is connected to a graduated vertical arc so that vertical angles may be measured as well as horizontal. It is provided with 124 THE STARRETT BOOK leveling screws, and with a ground level vial for adjust- ing the level of the graduated plate. To level the instrument, the legs must be firmly set into the ground or floor, so that neither wind nor acci- dental touch will disturb the adjustment. It should then be made as nearly level as possible by adjusting the lower parts of the extension legs. It should then be brought to a perfect level by means of the leveling screws between the plate and tripod head. This is done by bringing the level over any one of the leveling screws and turning one screw in and another out until the bubble appears in the center of the level glass. The sight tube or telescope should then be turned through an angle of about ninety degrees and again the bubble ad- justed to the center of the glass by means of two leveling screws. This operation should be continued until the bubble stands in the center of the glass, no matter in what direction the telescope may be turned. To find differences of level of two places, the instru- ment should be placed in a position about equally dis- tant from the two points. First obtain the height of the target on one of the rods by means of the cross line in telescope or sight tube and make record of the same. Then carry the rod to the other position and find the height of the target at that point. The difference be- tween the two heights, as read on the rod, will be the difference of level of the two places, that place being higher at which the height of the target is less. 125 THE STARRETT BOOK ELEMENTARY ALGEBRA Many engineering and shop problems can be solved more readily with algebra than by means of arithmetic. In fact, some problems cannot be solved by arithmetic; as, for example, when the conditions are not fully and concretely stated. Algebra is applied by expressing the relations in algebraic terms, forming them into an equa- tion, which states the conditions, and then solving the equation. In arithmetic a figure has a definite value, 4 or 20 for instance, and the value remains unchanged; it is always 4 or 20. In algebra letters are used, and as these letters do not always have a definite value, their use adds flexibility to mathematical operations. Some find it easier at the beginning to think of the letters as abbreviations. SYMBOLS Some of the symbols or signs of algebra are the same as those used in arithmetic. THE SYMBOLS OF QUANTITY are the figures used in arithmetic and the letters of the alphabet. THE COMMON SYMBOLS OF OPERATION are the signs used in arithmetic; they are as follows: + is the sign of addition, called plus. If no sign precedes numbers or letters the plus sign is understood; that is, 2abc is + 2abc. is the sign of subtraction, or difference, called minus. X is the sign of multiplication, called times. When there is no sign between letters or between letters and figures, multiplication is understood. Thus Serf means 3 X c X d. But this does not apply to numbers : 328 is not 3 X 2 X 8, but 328, same as in arithmetic. 126 THE STARRETT BOOK * -*- is the sign of division, read " divided by." Divi- sion may also be expressed by a horizontal line between a 16 the quantities, as, a -*- b = or = 16 -*- 4. b 4 COEFFICIENT. The numerical factor or number is generally called the coefficient; in 5abc, 5 is the coeffi- cient; but, strictly speaking, 5a is the coefficient of be, and 5a& is the coefficient of c. Again in the expression 3a (b c), 3a is the coefficient of (b c), or in the ex- pression (a + b) x, (a + b) is the coefficient of x. When no numerical coefficient is expressed, it is always unity or 1. Thus a = la. EXPONENT. The small figure or letter written at the right and a little above a number or letter is called the exponent; it shows how many times the number is to be taken as a factor. Thus 2 2 is read "2 squared" or "2 with the exponent 2." The number 2 is to be used twice as a factor, or mul- tiplied by itself. Similarly a 3 is read "a cubed" or "a with the exponent 3." The letter a is to be taken three times as a factor, or a X a X a. In the same way (m + n) 4 = (m + n) X (m + n) X (m + n) X (m + n). Again a*bc*d*=a X aXbX cX cXcXdXd XdXd. Note this difference m*= m X m X m X m 4m = m + m + m + m SYMBOLS OF RELATION show the relative values of letters. = is the sign of equality, read "equals" or "equal to." a = b means that a is equal to b, or whatever value is given to a, the same value must be given to b. If 4a = 3&, 4 times some quantity represented by a is equal to 3 times some quantity represented by b, but it is evident that a does not equal b. : is read "is to" or "to." It indicates ratio. 127 THE STARRETT BOOK If two ratios are equal, they may, 01 course, be con- nected by the sign of equality, but more often they are connected by this sign : : SYMBOLS OF AGGREGATION ( ) Parentheses. [ ] Brackets. | j Braces. Vinculum. V Radical Sign (square root). Letters or quantities enclosed in parentheses are to be handled as a single quantity. 5 (c + d) means that c + d as one quantity is to be multiplied by 5. Or (a + b) -5- (x + {/) means that a + b taken as a single quantity is to be divided by x + y taken as a sin- gle quantity. Another way of expressing it is, the same operation performed on a must be performed on b also. Again (a + b) means that the sum of a and b taken as a single quantity is to be subtracted. It does not mean that a alone is to be subtracted. THE RADICAL SIGN. This sign is used as in arith- metic; that is, it shows that some root of the quantity is to be found, or expressed. The small number or index used in connection with the radical sign denotes what root is meant. Thus ^/~a is read "the cube root of a." ^/6 is read the fifth root of ft." When no index figure is used the square root is understood. Vx + y = the square root of x + y. When the horizontal line extends over the expression it means that the indicated root is to be found of the entire expression. V m + n = "the square root of m + n." 128 THE STARRETT BOOK Let m = 36 and n = 64. V~m~+ n= V"367F 64 = VIM" = 10 V/n + n=V36+ 64=6 + 64-70 Vm + Vn = V36+ V64=6+ 8 = 14 POSITIVE AND NEGATIVE TERMS A term or quantity preceded by the plus sign, or by no sign at all, is a positive term, and one preceded by the minus sign is a negative term. This applies whether the term is a simple one like 3a (a monomial) or (x + y) (a binomial) or (a 2 + 2ab + b 2 ) (a polynomial). SIMILAR TERMS. When several terms have the same letters, but may differ in numerical coefficients, they are called similar terms. Thus 4ac, 5ac, and 3ac are similar terms. In arithmetic we say that + 5 and 5 cancel; that is, if we have five units and subtract five units we get zero. Similarly in algebra 5a cancels 5a, or Gcfxy cancels Qa 2 xy. ADDITION Addition is finding the sum of two or more quantities. Arithmetic Algebra 4 apples 4ab 3 apples 3a& 10 apples lOafr 17 apples 11 ab When the terms are alike, we add them by adding the coefficients; when they are not alike the addition is expressed. 6ac added to 6ac 129 THE S T A R RETT BOOK If the terms have different signs they can be added by algebra. 6ac added to ISac = 12ac 6ac added to ISxy = I8xy 6ac When there are several quantities which are alike, but the signs unlike, we add them by adding all the posi- tive or plus terms, then subtract the sum of all the nega- tive or minus terms. For instance, 5/nn 2mn 3/nn 6mn 15mn The positive terms in the above equal + 23mn and the negative terms equal 8mn, the result being 23mn 8mn = 15mn. Had all the signs been changed, the answer would have been 15/nn; for the sign prefixed to the answer is that of the greater sum. SUBTRACTION Subtraction in many ways is like addition; that is, like terms can be subtracted in the same way that they can be added, and unlike terms are subtracted by indi- cating the difference. Subtraction is the process of finding the DIFFER- ENCE between two quantities. In arithmetic the larger cannot be subtracted from the smaller, but in algebra this can be done by express- ing the difference. In arithmetic 11 cannot be subtracted from 4, but in algebra 7 11 = 4; that is, 7 lacks 4 of being equal to 11. It is minus 4. 130 THE STARRETT BOOK The difference (in number of units) between 8 and 2 is 6, whether it is 8 2 or 2 8. Whether the differ- ence is 6 or + 6 depends upon which number is being subtracted. These few rules should be remembered. Subtracting a + quantity is the same as adding a minus quantity. Subtracting a quantity is the same as adding a plus quantity. The sum of a minus quantity and a plus quantity is the difference between the quantities, with the prefixed sign of the larger. The difference between a plus quantity and a minus quantity is equal to the sum of the quantities. MULTIPLICATION Multiplication is a short method of addition; that is, if you add 4ac five times, the result is the same as mul- tiplying 4ac by 5. 4ac 4ac 4ac 4ac 5 20ac Multiplication is a process of taking a given quan- tity as many times as indicated by a number or another quantity. Multiplication differs from addition in that unlike quantities can be multiplied. 5abx multiplied by Qaxy = 131 THE STARRETT BOOK This simple example shows that to multiply we first multiply the coefficients, then annex the letters, multi- plying them when alike by adding the exponents; for instance, a X a = a 2 , x X x = x~. SIGNS. If both quantities are plus, the product is plus; if both are minus, the product is plus; if one is plus and the other minus, the product is minus. Multiplying more complicated quantities, those con- sisting of two or more terms each, is illustrated by this example in arithmetic: Multiply 4 + 3 + 2-1 by 6 Instead of adding before multiplying let us multiply each number by 6 : 4+ 3+ 2-1 6 24 + 18 + 12 - 6 = 48 If we use letters also, we proceed in the same way : Multiply 4ac + Sab + 2e c by 6a. 4ac + 3afc + 2c - c 6a 24a 2 c + 18a 2 fc + 12ac - 6ac Combining similar terms, 24o 2 c + 18a 2 + 6ac Multiply 2a + 4b by 3a - 66 6a 2 + Go 2 -24&' 132 THE STARRETT BOOK The above example should be thoroughly understood, for it involves multiplication, addition, and cancellation of like terms. If three quantities are to be multiplied, first multiply two of them, then multiply the product by the third. DIVISION Division is the process of finding how many times one quantity is contained in another. In arithmetic dividing 20 by 4 is finding how many times 4 is contained in 20. In algebra dividing 25a 2 fcc by Sac is finding how many times 5ac will go in 25a 2 c. First divide the coefficient 25 by 5, then divide the letters by subtracting the exponents of the same letter, a 2 -*- a = a because 2 1 = 1. When no similar letter is in the dividend, as in the case of b, there is no exponent to subtract, therefore we put the b in the quotient. In the case of the letter c, c goes in c once or 1. 5ac ) 25a c ab Another way to state this is to divide the terms into factors : 5ac =5ab The 5 cancels 5 in the numerator, a cancels one a in the numerator and c cancels c. These cancel because the exponents become zero; for instance, 1 1 = 0, and c with the exponent zero equals one or unity. 133 THE STARRETT BOOK SIGNS. Since division is the converse of multipli- cation, the rules governing signs are practically the same : When both divisor and dividend are + the quotient is +. When both divisor and dividend are the quotient When the divisor is + and the dividend is the quotient is . When the divisor is and the dividend is + the quotient is . The process of polynomials is merely an extension of the process of dividing monomials. Example: Divide 40a 4 35a 3 & + Sa 2 b lab 2 by 8ut do not know what pulleys to use in place of B and G. Revs, of first driver product of diameters of all drivens Revs, of last driven product of diameters of all drivers Revs, of A diameter of B X diameter of D or Revs, of D diameter of A X diameter of C The two unknown quantities are diameter of B and diameter of G; but the RATIO can be found. Using the data in the above example we have 1200 16 X diameter of B 125 diameter of C X 4 Diameter of B 4 1200 Diameter of G 16 125 - 12 ~!> 169 THE STARRETT ROOK Then the ratio of the diameters is 12 : 5, and any pulleys having diameters in this ratio will give the desired speeds. The pulleys may be 12 and 5 inches, 18 and 7V 2 , or 24 and 10. Example: The shaft of 3-inch pulley D is to make 900 revolutions; what pulleys must be placet as B and C if A is 14 inches in diameter and makes 150 revolutions? The available pulleys have these diameters 8, 9, 10V 2 , 11, 12, 13y 2 inches. The formula to use is Revs, of first driver product of diameters of all drivens Revs, of last driven product of diameters of all drivers 150 diameter of B X 3 900 14 X diameter of C 1 3 diameter of B ^ Tijn _ vv 6 14 diameter of C Diameter of B 1 14 __ vx f _ Diameter of C 6 3 _14_ 7 ~18~ "9" 160 THE STARRETT BOOK Then multiply the ratio 7 : 9 by any number which will make 7 and 9 equal to the diameters of pulleys on hand. Multiplying by 1% gives 10% and 13y 2 . To prove that the calculation is correct, place these values in this expression: The speed of the first driver (150) multiplied by the diameters of all drivers (14) and (13%) is equal to the speed of the last driven (900) multiplied by the diam- eters of all driven pulleys (10%) and (3). 150 X 14 X 13% = 900 X 10% X 3 28,350 = 28,350 LENGTH OF BELTS Open Belt. Pass a tape, preferably a steel tape, around the pulleys. This will give the length direct, if a single belt; but if a double belt is to be used add to the measurement twice the thickness of the belt. The length of small belts may be obtained by passing the belt around the pulleys and straining with hand pull. New belts stretch and become slack after a short time, and the slack should be taken up. With long belts stretching may be anticipated by cutting the belt one inch shorter for every ten feet. Rule for Length of Open Belt Add diameters of pulleys in inches and multiply the sum by 1.57, then add to this product twice the distance between centers in inches. Formula for Length of Open Belt (R-r) 2 L = 3.14 (R+r) +2D + - D R = Radius of large pulley, inches. r = radius of small pulley, inches. D = Distance between centers of shaft, inches. L = Length of belt, inches. 161 THE S-TARRETT BOOK Formula for Length of Crossed Belt (R + r) 2 L = 3.14 (R + r) + 2D + D The letters have the same values as above. Example: Two pulleys are 11 feet apart and are 24 and 16 inches in diameter. Length of belt? Open and crossed. (12- 8)* L = 3.14 X (12 + 8) + (2 X 132) + - 132 16 = 62.8 + 264 + - 132 = 326.8 + .12 = 326.92 inches, open belt. -(12 + 8) 2 L = 3.14 X (12 + 8) + (2 X 132) + - 132 400 = 62.8 + 264 + - 132 = 326.8 + 3 = 329.8 inches, crossed belt. GEARS CONSTANT VELOCITY RATIO. Belts over pulleys and plain rolling cylinders cannot be depended upon to give a constant velocity ratio there is always some loss of speed due to slip. But when two gears are in mesh a point on the pitch circle of one moves at the same linear velocity as a point on the pitch circle of the other, and the number of revolutions is always a constant ratio for these two gears. 162 THE STARRETT BOOK Two gears in mesh have the same pitch; that is, the distance from the center of a tooth to the center of the next tooth, measured along the pitch circle, is the same for both gears. Therefore, two gears of the same pitch, but of different diameters, must have an unequal number of teeth. It may be said that the space occupied by a tooth and the space between two teeth is the same in both gears if they have the same pitch. This fact shows immediately that the linear velocity of the pitch circles must be equal and the rotative speeds can be found in the same way as with belts. The pitch diameter or the num- ber of teeth is substituted for the pulley diameter, for the numbers of teeth are proportional to the pitch diam- eters in the same way that the peripheries of pulleys are proportional to the diameters. A gear having twice as many teeth as the gear mesh- ing with it will make but one-half as many revolutions in a given time. Or, the speeds (rotative) are inversely as the number of teeth; the gear with the smaller number of teeth runs at the higher speed. As in belts and pulleys, one gear of a pair is the driver and the other the driven or follower. The number of revolutions of the driver multiplied by the number of teeth on the driver is equal to the number of revolutions of the follower multiplied by the number of teeth on the follower. Revs, of driver X T = Revs, of follower X t, if T = number of teeth on the driver and t = number of teeth on the follower: "Revs, of follower X / T = and t = Revs, of driver Revs, of driver X T Revs, of follower 163 THE STARRETT BOOK To find the number of teeth (T) on the driver, mul- tiply the revolutions of the follower by its number of teeth and divide the product by the revolutions of the driver. Example: The follower has 64 teeth and makes 30 revolutions per minute. The driver makes 80 revolutions per minute. How many teeth has the driver? 30 X 64 T = - - = 24 80 Example: The driver makes 160 revolutions per minute and has 40 teeth. The follower makes 100 revo- lutions. How many teeth? 160 X 40 / = - - = 64 100 Revs, of follower X / Revs, of driver = - Revs, of follower = T Revs, of driver X T Example: The follower has 90 teeth and makes 110 revolutions per minute. If the driver has 44 teeth, how many revolutions per minute? 110 X 90 Revs, of driver = - = 225 44 Example: A driver having 63 teeth makes 800 revo- lutions per minute. If the follower has 42 teeth, what will be its speed? 800 X 63 Revs, of follower = = 1200 42 164 THE STARRETT BOOK FORMULAS FOR SPEED OF GEARS When three factors are known the fourth can be found by using one of the following formulas: Revs, of follower X teeth on follower Revs, of Driver = Revs, of Follower = teeth on driver Revs, of driver X teeth on driver teeth on follower Revs, of follower X teeth on follower Teeth on Driver = Teeth on Follower = Revs, of driver Revs, of driver X teeth on driver Revs, of follower As in the case of pulleys, great speed changes are made by trains of gears in place of a pair. Examples are found in hoists, clocks, lathes, etc. Each pair in the train has its driver and follower, and if the shafts are parallel it is usual to get the speed change by keying two gears of unequal size on every shaft, except the first and last. The velocity ratio of the first to the last is found as follows: The product of the number of teeth on all the drivers divided by the product of the number of teeth on all the followers is the velocity ratio. Suppose the train has three drivers, A, B, and C and three followers, L, M, and N. A has 14 teeth and drives L having 70 teeth. Pinion B on same shaft with L has 13 teeth and drives M hav- ing 104 teeth. Pinion C has 15 teeth, and is on the same shaft with M; C drives N having 75 teeth. What is the velocity ratio of A to N? 165 THE STARRETT BOOK Velocity ratio = teeth on A X teeth on B X teeth on C teeth on L X teeth on M X teeth on N 14 X 13 X 15 70 X 104 X 75 1 ~ 200 Knowing the velocity ratio of the train, it is easy to find the speed of N if the speed of A is known. If A runs at 1800 revolutions per minute, N will make only 9 revolutions for 1800 4- 200 = 9. When the speed of the first driver or the last fol- lower is also known, the speed may be figured from the following: Multiply the revolutions per minute of the first driver by the continued product of the number of teeth on all drivers, and divide by the continued product of the teeth on all followers. The quotient will be the revolu- tions per minute of the last follower. LATHE GEARING The apprentice who wishes to figure change gears for screw cutting should understand the principles, as 166 THE STARRETT BOOK already explained, rather than be dependent upon formu- las. There is but one statement to be memorized. The continued product of the speed of the first driver and the number of teeth on all drivers, is equal to the speed of the last follower multiplied by the con- tinued product of the teeth on all followers. In figuring change gears, the number of threads per inch to be cut corresponds to the revolutions of the driver, and the number of turns on the lead screw to move the carriage one inch corresponds to the speed of the follower. Then the number of threads to be cut multiplied by the teeth on the spindle stud equals the number of threads on the lead screw multiplied by the teeth on the lead screw gear. Or threads to be cut teeth on lead screw gear threads on lead screw teeth on spindle stud Suppose there are 6 threads on the lead screw and 46 teeth on the lead screw gear how many threads will be cut if a 24-tooth gear is placed on the spindle stud? threads to be cut 40 6 " 24 40 threads to be cut = X 6 24 = 10 The above assumes that the lathe is geared 1:1; that is, the lathe screw constant is equal to the number of threads per inch on the lead screw. If the lathe is not so geared, the lathe screw constant should be used in place of the threads per inch on the lead screw. 167 THE STARRETT BOOK The foregoing example shows how the figuring can be done when the gears are on the spindle stud and lead screw; but the problem is usually one of finding out what gears to use. Suppose seven threads are to be cut, and there are five threads per inch on the lead screw. What gears are to be used? threads to be cut teeth on lead screw gear threads on lead screw teeth on stud gear 7 teeth on lead screw gear 5 teeth on stud gear The ratio of the gears is as 7 : 5. By multiplying both 7 and 5 by any number, such as 6, we get 42 teeth on lead screw gear 30 teeth on stud gear Using the formula as above may aid in disposing of that troublesome question, "Which gear goes on the stud?" In some cases it may seem easier to assume one gear and go through the calculation to find the other, there being then one unknown quantity and three known quantities. 168 THE STARRETT BOOK Table 13 Specific Gravity and Properties of Metals Metal or Composition Specific Gravity Weight per Cubic Inch, Pounds Melting Point. Deg. F. Linear Ex- pansion per Unit Length per Deg. F. Aluminum Antimony Barium Bismuth Boron Brass: 80 C., 20 Z 70 C., 30Z...... 60C..40Z 50C..50Z 2.56 6.71 3.75 9.80 2.60 8.60 8.40 8.36 8.20 885 0.0924 0.2422 0.1354 0.3538 0.0939 0.3105 0.3032 0.3018 0.2960 03195 1200 1150 1560 500 1700-1850 1675 0.00001234 0.00000627 0.00000975 0.00000957 00000986 8 60 03105 610 1 57 0567 1450 Chromium Cobalt Copper Gold Iridium Iron, cast Iron, wrought Lead 6.50 8.65 8.82 19.32 22.42 7.20 7.85 11.37 1 74 0.2347 0.3123 0.3184 0.6975 0.8094 0.2600 0.2834 0.4105 0628 2740 2700 1940 1930 4100 2300 2900 620 1200 0.00000887 0.00000786 0.00000356 0.00000556 0.00000648 0.00001571 Manganese 742 2679 2200 Mercury (60 F ) 13 58 04902 39 Molybdenum Nickel Platinum, rolled Platinum, wire 8.56 8.80 22.67 21.04 87 0.3090 0.3177 0.8184 0.7595 00314 4500 2600 | 3200 144 0.00000695 0.00000479 Silver 1053 3802 1740 00001079 Sodium Steel Tellurium 0.98 7.80 625 0.0354 0.2816 02256 200 2500 840 0.00000636 Tin 729 02'632 446 00001163 Titanium 354 1278 3360 18 77 6776 5400 Vanadium Zinc, cast Zinc, rolled 5.50 6.86 715 0.1986 0.2476 02581 3200 | 785 0.00001407 169 THE STARRETT BOOK Table 14 Average Specific Gravity of Miscellaneous Substances Substance Specific Gravity Asbestos 2.8 Asphaltum 1.4 Borax 1.75 Brick, common 1.8 Brick, fire 2.3 Brick, hard 2.0 Brick, pressed 2.15 Brickwork, in motor 1.6 Brickwork, in cement 1.8 Cement, Portland 3.1 Chalk 2.6 Charcoal 0.4 Coal, anthracite 1.5 Coal, bituminous 1.27 Concrete 2.2 Earth, loose 1.2 Earth, rammed 1.6 Emery 4.0 Glass 2.6 Granite 2.65 Gravel 1.75 Gypsum 2.2 Ice 0.9 Ivory '. 1.85 Limestone 2.6 Marble 2.7 Masonry 2.4 Mica 2.8 Mortar 1.5 Phosphorus ( 1.8 Plaster of Paris 1.8 Quartz 2.6 Salt, common 2.1 Sand, dry 1.6 Sand, wet 2.0 Sandstone 2.3 Slate 2.8 Soapstone 2.7 Soil, common black 2.0 Sulphur 2.0 Trap 3.0 Tile 1.8 170 THE STARRETT BOOK Table 15 Specific Gravity of Gases (At 32 degrees F.) Gas Sp. Gr. Gas .?: Air. 1.000 Hydrogen . . 0.069 Acetylene . 0.910 Illuminating gas . . . 0.040 Alcohol vapor 1.601 Mercury vapor 6.940 Ammonia 0.592 Marsh gas 0.555 Carbon dioxide 1.520 Nitrogen 0.971 Carbon monoxide 0.967 Nitric oxide 1.039 Chlorine 2.423 Nitrous oxide . 1.527 Ether vapor 2.586 Oxygen 1.106 Ethylene Hydrofluoric acid Hydrochloric acid 0.967 2.370 1.261 Sulphur dioxide Water vapor 2.250 0.623 1 cubic foot of air at 32 degrees F. and atmospheric pressure weighs 0.0807 pound Table 16 Specific Gravity of Liquids Liquid fe Liquid Sp. Gr. Acetic acid 1.06 Muriatic acid 1.20 Alcohol, commercial 0.83 Naphtha 0.76 Alcohol, pure . 0.79 Nitric acid . 1.22 Ammonia 0.89 Olive oil 0.92 Benzine Bromine 0.69 2.97 Palm oil Petroleum oil 0.97 0.82 Carbolic acid 096 Phosphoric acid 1.56 Carbon disulphide 1.26 Rape oil 0.92 Cotton-seed oil 0.93 Sulphuric acid 1.84 Ether, sulphuric 0.72 Tar ... 1.00 Fluoric acid Gasoline Kerosene 1.50 0.90 0.80 Turpentine oil Vinegar Water 0.87 1.08 1.00 Linseed oil 0.94 Water, sea 1.03 Mineral oil 0.92 Whale oil 0.92 171 THE STARRETT BOOK Table 17 Composition of Miscellaneous Alloys Alloys Antimony Bismuth 1 | I 1 c H H N Brass, common yellow 61.6 2.9 0.2 35.3 Brass, to be rolled 32 1.5 10 Brass castings, common 20 2.5 1.25 Gun metal 8 1 Copper flanges 9 026 1 Bronze Statuary 91.4 1.37 1.7 5.53 German Silver 2 6.5 7.9 6.3 Britannia metal 50 25 25 Chinese white copper 20.2 15.8 1.3 12.7 Pattern letters 15 15 70 Bell metal 4 1 Chinese gongs 40.5 9.2 White metal, ordinary 28.4 3.7 14.2 3.7 Spelter 1 1 Type metal 1 3-7 172 THE STARR ETT ROOK Table 18 Average Specific Heats of Various Substances Substance Specific Heat Substance Specific Heat Alcohol (absolute) 700 500 Alcohol (density 0.8) 0.622 0214 Lead.... Limestone 0.031 217 Antimony Benzine 0.051 450 Magnesia Marble 0.222 210 Brass 0.094 Masonry, brick 0200 Brickwork 0.200 0057 Mercury Naphtha 0.033 310 Charcoal Chalk 0.200 0215 Nickel Oil machine 0.109 0400 Coal 0.240 Oil, olive 0350 Coke Copper 32 to 212 F 0.203 0094 Phosphorus Platinum 0.189 032 Copper, 32 to 572 F 0.101 Quartz , 188 Corundum 0198 Sand 195 Ether 0503 Silica 191 Fusel oil Glass 0.564 194 Silver Soda 0.056 0231 Gold 0.031 Steel, mild 116 Graphite 0201 Steel high carbon . ... 117 Ice 0504 Stone (generally) 0200 Iron, cast 0.130 Sulphur 178 Iron wrought, 32 to 212 F . 110 Sulphuric acid .... 0330 32 to 392 F 115 Tin 0056 32 to 572 F 0.122 Turpentine 0472 32 to 662 F 126 Water ... 1 000 Iron, at high temperatures : Wood, fir 0650 1382 to 1832 F 1750 to 1840 F 0.213 0218 Wood, oak Wood pine 0.570 0467 1920 to 2190 F 0.199 Zinc 0.095 173 THE STARRETT BOOK Table 19 Templets for Drilling Standard and Low Pressure Flanged Valves and Fittings American Standard V N to *l s= Thickness of Flange Diam. of Bolt Circle "SI2 |2 "S I c^ S| II 5^ Thickness of Flange Diam. of Bolt Circle o l 0.2 Va && 1 4 7 A 3 4 H 42 53 2% 49H 36 VA 1% 4^ H 3H 4 7 /ie 44 55% 2% 51% 40 IX 1H 5 %6 SK 4 *Ji 46 57% 2^6 53% 40 1A 2 6 M 4% 4 M 48 59H 2% 56 44 1 5 A 2H 7 ^6 SM 4 K 50 61% 2% 58% 44 1% 3 7H M 6 4 H 52 64 2K 60H 44 1% 3H 8H 15 ft6 7 4 5^ 54 66% 3 62% 44 1% 4 9 15 Ae 7^ 8 H 56 68% 3 65 48 1% 4^ 9% !%6 7% 8 % 58 71 3H 67% 48 1% 5 10 !%6 8M 8 % 60 73 3K 69% 52 1% 6 11 i 9H 8 % 62 75% 3% 71% 52 IH 7 12 H l^le 10% 8 % 64 78 3% 74 52 IH 8 13 M m 11% 8 % 66 80 m 76 52 1% 9 15 1% 13% 12 % 68 82% VA 78% 56 IK 10 16 1%6 14% 12 K 70 84^ m 80^ 56 IK 12 19 Hi 17 12 J^ 72 86H 3M 82^ 60 IK 14 21 iH 18% 12 l 74 S8 1 A 3H 84^ 60 IK 15 22^ IK 20 16 l 76 90% m 86H 60 IK 16 23^ l%a 21% 16 1 78 93 3% 88% 60 2 18 25 lAe 22% 16 1H 80 95% 3% 91 60 2 20 27H 1^6 25 20 1H 82 97H 3K 93% 60 2 22 293^ l 18 Ae 27% 20 1% 84 99% 3Ji 95H 64 2 24 32 IK 29H 20 1% 86 102 4 97% 64 2 26 34% 2 31% 24 1% 88 104% 4 100 68 2 28 36^ 2^6 34 28 1% 90 106^ 4^ 102% 68 2K 30 38% 2K 36 28 1% 92 108% 4H 104^ 68 2K 32 41% 2% 38>i 28 1H 94 111 4% 106% 68 2K 34 43% 2%6 40^ 32 1H 96 113% 4% 108^ 68 2% 36 46 2K 42% 32 1H 98 115H 4M 110% 68 2% 38 48% 2K 45% 32 1H 100 117% 4M 113 68 2% 4.0 CAS./ ?V4 47 \ 36 154 4U OU/4 ^/2 **( 74 A/ 8 Bolt holes are drilled K inch larger than nominal diameter of bolts. 174 THE STARRETT BOOK Table 20 Templets for Drilling Extra Heavy Flanged Valves and Fittings American Standard Size Diam. of Flange Thickness of Flange Diam. of Bolt Circle No. of Bolts Size of Bolts 1 4^ ># 3K 4 H in 5 % 3% 4 /4 6 13 /16 4 % 2 2 6M I/fa 5 2 4 5 /8 2^ 71^ 1 57^ 4 3 8K 1/^8 6^ 8 % 3/^ 9 1 8 /16 7K 8 % 4 10 IK 7% 8 % 4/^ 103^ 1 5 /16 8 % 5 11 9K 8 % 6 12H 1 7 /1 6 10^ 12 % 7 8 14 15 3H 13 8 12 12 7 /8 7 A 9 16K 14 12 10 17J^ 15K 16 1 12 20^ 2 8 17% 16 l/^ 14 23 2/'8 20K 20 1^8 15 24^ 2%6 21/^ 20 IK 16 25^ 2K 22^ 20 IK 18 28 2^i 24% 24 IK 20 30^ 2^ 27 24 if! 22 33 2/^ 29K 24 24 36 2% 32 24 i/^ 26 38K 34^ 28 i/^ 28 40% 2^5/16 37 28 i/^ 30 43 3 39 K . 28 1% 32 45K 33^8 41^ 28 1/^8 34 47^ 3K 43^ 28 1J/8 36 50 3^g 46 32 IJ/g 38 52K 3^16 48 32 1% 40 54^ 3%6 50K 36 l/^ 42 57 3 1 ^io 52% 36 \1/o 44 59K 3% 55 36 2 46 61^ 3% 57K 40 2 48 65 60% 40 2 Bolt holes are drilled inch larger than nominal diameter of bolts. 175 THE S T A R RETT BOOK Table 21 Tap Drills For A. S. M. E. Standard and .Special Machine Screw Taps The diameter given for each hole to be tapped allows for a practical clearance at the root of the thread of the screw and will not impose undue strain upon the tap in service. Size of Tap No. of Threads Size of Drill Size of Tap No. of Threads Size of Drill 80 .0465 9 32 .1405 1 64 .055 10 24 .140 1 72 .0595 10 30 .152 2 56 .0670 10 32 .154 2 64 .070 12 24 .166 3 48 .076 12 28 .173 3 56 .0785 14 20 .182 4 36 .080 14 24 .1935 4 40 .082 16 20 .209 4 48 .089 16 22 .213 5 36 .0935 18 18 .228 5 40 .098 18 20 .234 5 44 .0995 20 18 .257 6 32 .1015 20 20 .261 6 36 .1065 22 16 .272 .6 40 .110 22 18 .281 7 30 .113 24 16 .295 7 32 .116 24 18 .302 7 36 .120 26 14 .316 8 30 .1285 26 16 .323 8 32 .1285 28 14 .339 8 36 .136 28 16 .348 9 24 .1285 30 14 .368 9 30 .136 30 16 .377 NOTE : Special Taps are in Bold Face Type. 176 THE STARRETT BOOK Table 22 Tap Drills for Machine Screws Size of Tap American Standard Diameter in Inches Size of Drill for Outside Diameter of Screw Size of Drill for Tapping Hole Size of Tap American Standard Diameter in Inches Size of Drill for Outside Diameter of Screw H| 2x48) 50 13x20) 17 2x56 .25763 44 49 13x22 .071961 *%4 17 2x64] 48 13x24] 15 3x40) 49 14x20) 15 3x48 .22942 39 47 14 x 22 .064084 V* 11 3x56] 45 14x24] 10 4x32) 46 15x18) 12 4x36 4x40] .20431 33 44 43 15 x 20 15 x 22 .057068 F 10 8 15x24] 7 5x30) 5x32 5x36 5x40] .18194 tt 43 42 41 38 16x16) 16 x 18 16x20] .05082 I 12 7 6x30) 6 x 32 6 x 36 .16202 28 38 37 36 17x16) 17 x 18 17x20j .045257 L 8 4 3 6x40J 35 18x16) 2 7x28) 7x30 .14428 24 34 33 18 x 18 18x20] .040303 19 /64 2 1 7x32] 32 19x16) 1 8x24) 8x30 .12849 19 31 31 19 x 18 19x20] .03589 *; B 8x32] 30 20x16) c 9x24 9x28 9x30 9x32 .11443 16 30 28 28 26 20 x 18 20x20] 22 x 16 \ 22 x 18 / .031961 .025347 p s E F H 10x24) 26 24 x 14 ) L 10 x 30 10x32] .10189 11 24 24 24 x 16 24x18] .0201 % M N 11x24) 11 x 28 .090742 6 21 20 26 x 14 \ 26 x 16 / .01594 18 /82 p 11x30] 19 ' 12x20 24 28 x 14 \ 28 x 16 / .012641 fti R 12x22 20 12x24 .080808 %2 19 30 x 14 \ u 12x28 18 30 x 16 / .010025 2%4 V 177 INDEX Abbreviations for Drawings 12 Abrasives, Grain . , . . 43 Adjusting Toolmakers' Buttons with Micrometer . . 104 Algebraic Signs 132-136 Aligning Shafting 119 Alloys, Composition of , 172 Angle, Measurement of 140 Bench Work 35 Bolt and Screw Lists . .- 7 Boring Holes in Jig Body 103 Buttons' Toolmakers' 104 Calipering over a Flange 27 Calipers, for Testing Screw Threads 85 Calipers, Hermaphrodite 69 Calipers, Inside and Outside 27 Calipers, Micrometer 19 Calipers, Spring 26 Calipers, Vernier 16 Carbon Steel 75 Carbon Steel Drills, Speed of 51 Center Gage 67 Center Punches 56 Change Gears 79 Chipping 38 Chisels for Chipping 38 Chucking 93 Chucking Tools : 96 Coefficient (Algebra) 127 Composition of Alloys 172 Compound Gears for Thread Cutting 82 Contact Measuring 15 Counterboring : 62 Cup Wheels 117 Cutting Compounds for Drills 53 Cutting Lips of Drills 47 Cutting Screw Threads 77 Deep Hole Drilling . 02 Detail Drawings 7 Dividers, Spring 28 Draw Filing 42 Drawing the Drill 55 Drill Grinding . 48 Drill Speed . 51 Drilling 48 Drilling Deep Holes 62 Drilling, Drawing the Drill . . . . ' 55 Drilling for Reamer "... 57 Drilling for Tapping 58 Drilling, Holding Work 56 Drilling Large Holes 61 Drilling, Starting Drill 55 Drilling, Templets for Extra Heavy Flanged Valves and Fittings . 1J5 178 THE STARRETT BOOK Drilling, Templets for Standard and Low Pressure Flanged Valves and Fittings 174 Drills, Cutting Compounds 53 Drills, Cutting Lips 47 Drills, Kinds 47 Drills, Letter Sizes of 59 Drills, Making ' 97 Drills, Testing Cutting Lips 49 Eccentric Turning 91 Elementary Algebra 126 Emery, Grades of 43 Equations 134 Equivalent Tables 60 Expansion of Metals 169 Exponent 127 Extra Heavy Flanged Valves and Fittings, Templets for Drilling . 175 Files, Kinds . 40 Filing 40 Filing, Testing Surface 42 Fits, Amounts to Leave 30 Flanged Fittings, Templets for Drilling . . . 174 Forced Fits 29 Forces 151 Gear Speeds, Formulas for 165 Gears for Thread Cutting 79 Gears, Speed of 163 Gears, Trains 165 Grades of Emery 43 Grading Grinding Wheels Ill Grinding 109 Grinding, Allowances for 110 Grinding, Amounts to leave 113 Grinding Cylindrical 113 Grinding Flat Surfaces 116 Grinding Wheels, Grade and Grain 115 Grinding, Measuring Work 116 Grinding Milling Cutters 100 Grinding Speeds for 114 Grinding Wheels 109, 111 Grinding Wheels, Grades Ill Grinding Wheels, Mounting 116 Hack Saw Machine 45 Hack Saws 43 Hack Saws, Cutting Speed 44 Hack Saws, What One to Use . 46 Hand Chipping 38 Height Gage 17 High Speed Steel Drills, Speed of 51 Holding Drill in Spindle 56 Holding Work for Drilling 57 Holding Work in Chucks 95 How to Read a Micrometer 21 How to Read a Vernier 22 How to Read a Vernier Micrometer . 23 Involute 146 179 THE STARRETT BOOK Jig Bushings 107 Jig for Drilling Cylinder Flange 108 Jigs and Fixtures 101 Jigs, Locating Bushing Holes 102 Jigs, Types 101 Knurling '..... 96 Lapping 117 Lathe 65 Lathe Centers 65 Lathe Gearing 106 Lathe Tools 70, 75 Lathe Tools, Clearance 72 Lathe Tools, Grinding 73 Lathe Tools, Rake 72 Lathe Tools, Setting 73 Lathe Tools, Testing Cutting Angles 74 Lathe Work, Measuring 85 Laying Out for Drilling 53 Length of Belts, Formulas for 161, 162 Level for Aligning Shafting 119 Leveling Instrument 119 Leveling Instrument, How to Set Up 124 Levels, Finding Difference 125 Levers 153 Limits of Accuracy , 29, 32 Locating Bushing Holes in Jigs 102 Locating Jig on Face Plate 103 Locating Machinery 123 Low Pressure Flanged Fittings 174 Lubricant for Thread Cutting 84 Mandrels, Use of 76 Measuring Lathe Work 85 Measuring Screw Threads 84 Measuring Tools 13 Measuring Work, Grinding 116 Mechanics 151 Melting Point of Metals 169 Mensuration 140 Micrometer, Adjusting Buttons with 104 Micrometer as a Gage 25 Micrometer Calipers 19 Micrometer, for Measuring Screw Threads 86 Micrometer, How to Read 21 Micrometers, Adjustment for Wear 25 Micrometers, Quick Adjustment . . 25 Milling Cutters 99 Milling Cutters, Grinding 100 Plane Figures 142, 146 Plate for Laying Out 37 Plumb Bobs 121 Polishing 43 Preparing Surface for Laying Out 35 Protractors 37 Pulley Diameters and Speeds, Formulas for 157 Pulleys 155 180 THE STARRETT BOOK Pulleys, or Blocks . . 154 Quick Adjustment of Micrometers 25 Radical Sign 128 Reamers, Making 97 Screw Threads 77 Screw Threads, Measuring ." 84 Screw Threads, Pitch 77 Screw Threads, Properties of U. S. Standard 78 Scribing Lines for Laying Out 35 Section Lines 11 Shop and Engineering Formulas 137 Signs (Algebra) 132 Sliding Pit . 29 Solids 146 Specific Gravity of Gases 171 Specific Gravity of Liquids . ' 171 Specific Gravity of Metals 1G9 Specific Gravity of Substances 170 Specific Heat of Substances 173 Speed of Drills 52 Speed of Gears, Formulas for 165 Standard Flanged Fittings 174 Starting Drill 55 Stellite 76 Surface Plates 38- Table 1 Allowances for Different Classes of Fits 31 2 Speeds and Feeds for Drilling 51 3 Speed of Drills 52 4 Letter Sizes of Drills 59 5 Sizes of Tap Drills 59 6 TJ. S. Standard Screw Threads 78 7 Brown & Sharpe Taper Shanks 87 8 Morse Taper Shanks 88 9 Tapers 92 10 Allowances for Grinding . 110 11 Grinding Wheel Speeds 114 12 Grinding Wheels for Different Materials 115 13 Specific Gravity and Properties of Metals 169 14 Specific Gravity of Substances 170 15 Specific Gravity of Gases 171 16 Specific Gravity of Liquids 171 17 Composition of Alloys 172 18 Specific Heat of Substances 173 19 Templets for Drilling Standard and Low Pressure Flanged Valves and Fittings American Standard 174 20 Templets for Drilling Extra Heavy Flanged Valves and Fittings American Standard 175 21 Tap Drills, A.S.M.E. Standard . . . 176 22 Tap Drills for Machine Screws 177 Tap Drills, Sizes of ... t 59, 78, 176, 177 Taper in Given Length 90 Taper Shanks 87, 88 Taper Turning 86 Taper Turning, Offset of Centers, Amount 90 Tapers, Testing 91 181 THE STARRETT BOOK Targets 123 Testing Cutting Lips of Drills 4!) Testing Flat Filing 42 Test Indicator . . . . 67 Testing Turned Taper 91 Thread Tool, Form of 82 Thread Tool, Setting 84 Tolerance, Limits of 32 Tool Holders 75 Tool Making 97 Toolmakers' Buttons 103 Train of Gears 165 Transferring Measurements 26 Truing Work in Chucks 95 Turning, Work Centers 69 Universal Dial Test Indicator 07, 103 Vernier Calipers . . . .- 16 Vernier Height Gage 17. 10r> Vernier, How to Read 22 Vernier Micrometer, How to Read 23 Vitrified Wheels 109 Wear of Micrometers 25 Weight per Cuhic Foot of Substances 170 What Hack Saw to Use Windlass Work Centers Work Centers, Locating , - , Working Drawing Abbreviations Working Drawings 46 154 69 89 12 182 THE STARR E T T BO Q K SETS OF TOOLS FOR APPRENTICES AND STUDENTS SET NO. 900 IN FOLDING LEATHER CASE Size of case folded, 7" x 4%" x l%* Set No. 900 consists of the leather case and the following tools: No. 11, 6" Combination Square, com- No. 390, Center Gage plete No. 241, 4" Caliper No. 117B, Center Punch No. 79, 4" Outside Caliper with solid nut No. 321, 6" Flexible Steel Rule in pocket No. 73, 4" Inside Caliper with solid nut case No. 83, 4" Divider with solid nut PRICE, set complete $6.00 183 THE STARRETT BOOK SETS OF TOOLS FOR APPRENTICES AND STUDENTS SET NO. 901 IN NICELY FINISHED WOODEN CASE Size of case, 12"x7"xl^ Set No. 901 consists of the wooden case and the following tools: No. 11, 6" Combination Square, com- plete No. 321, 6" Flexible Steel Rule in pocket case No. 117B, Center Punch PRICE, set complete No. 390, Center Gage No. 77, 5" Divider with solid nut No. 79, 6" Outside Caliper with solid nut No. 73, 6" Inside Caliper with solid nut $6.15 184 UNIVERSITY OF CALIFORNIA LIBRARY BERKELEY Return to desk from which borrowed. This book is DUE on the last date stamped below. Allgl7'48JL .RY U>E i Due end of WINTER Quarter M AB 1 5 9 flQ 3 * subject to redall after- WR 1 "7' 'IS STACKS REC'OLO 21-100m-9,'47(A5702sl6)476 M51G983