W;^'WWI^Jl^4WWWS^!«yi««l««I«^ Practical Problems in Mechanical Drawing and Blue-Print Reading STURTEVANT gte^feV'ftM^iiraiffr.iifaiiygiysrflliTriltTrilW^ PRACTICAL PROBLEMS In Mechanical Drawing and Blue-Print Reading By WrW. Sturtevant Instructor of Mechanical Drawing , at South High School Minneapolis, Minn. Formerly instructor of Mechanical Drawing at the Jackson Grade School, the Bremer Junior High School and Evening and Part-Time Trade Classes in Minneapolis. Copyright, 1921, by W. W. Sturtevant Published by PRACTICAL PROBLEMS CO. 3332 Forty-fourth Ave. S. Minneapolis, Minn. iMiitrTTnm iiii i ini i i i ifmi ii iMi ii i ii ii TffffTnwMWWHWl^^ TO THE TEACHER Much criticism has been directed at the "copy" method of teaching Mechanical Drawing and undoubtedly some pupils have copied drawings which they did not clearly understand. The attempt, however, to make a problem of every drawing has been' responsible for much poor teaching. Many boys have gained the impression that a third view was always necessary, when as a matter of fact, two views of an object gave all of the information necessary and the drawing of the third view was a waste of time. Similarly if dotted lines on a view <|ive the pupil a clear idea of an object, the drawing of a section is poor practice. It is suggested that the test drawing, the side view or section or sketch be made on a sep- arate sheet in pencil, thus saving time and avoiding the possibility of the pupils receiving the impression that it must be made to complete the drawing. Acknowledgement is here made of the many helpful suggestions of my supervisors and co- workers in the Minneapolis Public Schools in the selection of these plates. W. W. Sturtevant. DEC 16 1921 ,r«.A654285 2 D/?AW l//VeS /N THE P/RECT/OA/ /A/P/CAr£P BY ARf^OWS H££P rOiy/^ F£/^C/L5 S/VARP rOU- /^LfST SE £XACT A / / / / / /,. /^ / 1/' (:^—^^p^-~^ %) W ^''^ ^3 ^^ — / ^ ^^ ^- - / ^ ' ' \u ^ n . n «>. ' 10 ^ \ r / / ^ A // 1 // nb- // ^ 1 c V ^- 1 — /"^ —^^'— ^\x-^ 1 / V / 1 Ar\ / ~- n / / _ 1 1- J X 1 • • H'f— 11 12 7 ^ ^3 A -"i H~ 1 -2i & a 1 ^ _ 1— r- -^ ^- T ^K i: t T^ -: 9- r\^ nf 1 H' 1 y^ \ ^ -5 1 ^ 1 j 1 1 1 \ t / , i| ! ; 1 1 1 \ 1 fr\ f ! II ii i; ! P/\ UW L£Fr END 1 !■ ' CASr/NG 14 TANGENTS In the development of good technic in Me- chanical Drawing there is probably no point that presents greater difficulty than the gain- ing of a smoothness of tangent line's and arcs. The following plates are offered as illustrat- ing the several different problems that confront the pupil. • The two plates showing the eight problems should be drawn by the' pupil, after the usual explanation by the teacher. With these plates at hand the average boy should encounter no great difficulty in drawing any of the other plates. The construction lines on the first two plate's make clear the method of locating the center of the arc by drawing lines parallel to the straight lines and circles concentric with the circles. The point of tange'ncy is on a radial line drawn perpendicular to the straight line and on a line drawn through the center of the circle and the center of the small arc. Each boy is to draw as many of the plates as is necessary in order to de'velop the required skill. No pupil is to be asked to draw all of the plates, but by having at hand a number of plates the teacher may select one that meets the needs of the' pupil and is within the limits of his ability. By giving each boy his own problem much greater interest may be secured th°an by hav- ing the whole class draw the same plate. Also by asking boys to check the drawjngs made by othe'rs in the class they will learn much. The ability to visualize may be developed by asking for the side view or the top view, which may be drawn on the same or a different sheet. If the time ne'cessary to complete the third view is not available a free hand sketch may be substituted for this. 15 16 17 f BOLTS M CAM 3RACKET I Mcu ^ 18 3-OR/LL^ I H/NGE 19 DFiJLL ^ i-COUA/TERSINH O SH/FTfR EYE CATCH 21 5ELL CRANK 23 1 — r '.^i TtTTT Ttrrr r:^ i-r 'nioo i_2i. ©i B£IL CRANK ^RILL 3- ^ H0LE5 24 r^l^ "^lOQ OR/LlfFOf^ OIL HOLE- ^ ^\r^ STEERING GEAR LINK 25 3 / yDRILL^ -* — z ■ 2 L 1 /^ 1 ^^x l/ __^ ^1 --^ 1 4- . ! ^ vi ^ V 1 4- i i \ \ i 'nioa ' n- -i- ^/; / ^ i-^i- t - TT ^ CLl/TCH PEDAL SHAFT BRACKET r r ^^ • kU" t ^ ^ K 1 1 1 I a 1 1 J 1 26 dR:-K^ ^\^ ^j DOG HANDLE DRAW POG ^YANPL5. Af/IR^ /='0//VT3 OF TAA/GFA/CK 0/=iAW 6/P£ //£W. Ofi/LL # ¥C Njp RAD EYE W\ 29 SECTIONAL VIEWS. Frequently drawings are required of objects that because of their construction require a gre'at number of dotted lines to show the loca- tion of hidden parts. Such drawings are usual- ly difficult to understand. Especially is this true if the dotted lines intersect. To add clearness, in such cases sectional views or sections are usually used. The object is drawn as though the' section or part of the object nearest the observer were broken away and the interior exposed to view. The line on which the section, is taken is an imaginary plane, passing through the' object, called a trace. It need not be a straight line. Any line that will show the object to the best advantage may be used. This cutting plane is purely imaginary and any sections may be drawij that in the draftsman's opinion will give' added clearness. Only one view is, as a rule, shown in section the other views of the drawing show the object complete. On the drawing, the surfaces which are as- sumed to be cut are covered with light slanting lines, known as section lines or sometimes as cross-hatching. Section lines are usually drawn at an angle of 45° but in cases where the ap- pearance would be improved the angle may be change'd. These lines should be about one half of the weight of ihe standard line and they should be spaced a uniform distance apart. The spacing varies somewhat, being greater on large surfaces and less on small. Usually 1/16 of an inch apart is about right. On a large surface 1/8 or 3/16 is better. Very large surfaces are frequently lined only around the edge and very small surfaces are filled in solid. On the pencil drawing the surface to be sec- tioned is indicated but the section lines are drawn on the tracing or ink drawing only. Lines are spaced by the eye, no attempt is made to lay them off equal distance by measure. Standard section lining to represent different materials are shown on page 33, but these are not in universal use. Many drafting rooms draw all materials with the same lining use'd for cast iron and designate the material by let- ters, abbreviating the name, placed on the sur- face to be cross-hatched. 30 As a shop note usually specifies the' material the tedious and expensive section lining to show cast steel, wrought iron, etc., is not con- sidered necessary. Some draftsmen fill in sectioned surface's with a soft pencil on the tracing. This shows clearly on the blue print and has the advantage of being very quickly done. Some exceptions to the rules governing draw- ing are' made on sectional views. These con- ventions are listed below. Dotted lines showing invisible lines back of a section may be drawn in or omitted as de- sired. Spokes are never drawn in section. The drawing is made as though the' cutting plane passed in front of the spoke. This makes clea,r the difference between wheels having spokes and those cast solid. Webs are not drawn in section. Webs are sometimes sectioned as in page 39. By omit- ting alternate lines the web is made easy to distinguish. Objects that are symme'trical about an axis are usually drawn one half in section. Unsymmetrical objects, as wheels with 3 or 5 spokes, are drawn as though they were symmetrical. Adjacent surfaces of different pieces are sec- tioned in a different manner or with lines drawn at a different angle. The draftsman must use his judgment as to the number of sectional views that are neces- sary. Sometimes three or four sections are necessary. Again a revolved section of a very small part is all that is nee'ded. Often the shape of a spoke or a web or similar small part of an object may be showh by what is called a revolved se'ction. This sec- tion is placed on the regular view. The pupil should bear in mind the fact that a section takes more time and therefore costs more than the drawing of a side view, and should be used only when the added clearness gained will warrant the -extra time necessary in the drafting room. Solid cylindrical objects, like bolts or shafts, are not drawn in section. Removed sections are sections drawn in some convenient place on ti.e sheet, out of their na- tural position. Partial sections are used when a section of a small part of an object will show all that is nece'ssary. 31 CAST IRON STE5L SPRING VALVE STEM PACKING 32 CAST IRON STEEL WIRE 33 en/WER HEAD ^i-^ 34 h-/i PR/LL^- ] g: Bf^ACKET 7 4 36 m7?w<' PULLEY "^m^^A SECTION THROUGH 3 POKE 37 4- DRILL \—li SECTION THROUGH A RIB f\J SIDE PLATE 38 ROLLER END 4R^ ^m^ \^-'t^ U|. ^ 4^/^y> ^//Zl -/J a 8 £ " 39 9i /| /6 THPS. 5AE. 6TC> VALVE 40 COMMUTATOR CAP 43 HAND W/iEEL & ^ mc 44 /y/^/vz) i4///£-f/. DOTTED SECTION 45 FLY WHEEL 47 WEIGHT 48 CR/\NK SHAFT 49 DRILL § — / ^ h-/i- •1^ COVER 50 / REAM CLUTCH SP/PER 51 FLY WHEEL /4 D 52 ^'O/VE PULLEY ^I^gl5g?^^^^g^^vk!ia j;?| ^^ T^?^ ■^^ ^^?^^te;^^^^;i;^y;k^^l§^^ 'iCQ -100 53 AUXILIARY VIEWS Auxiliary views are used when it is neces- sary to show the true length of a slanting sur- face that would appear fore-shortened in the top or side view. The center line of the auxiliary view is drawn parallel to 'the surface to be shown in this view. DIMENSIONS The dimensions on a drawing are of the utmost importance and the correct selection of the dimensions to be' given and the proper placing of these dimensions requires good judg- me'nt and a considerable knowledge of shop practice. Without the dimensions the drawing is of little or no value. It shows the shape of the object but the exact sizes are necessary before it is of value to the workman. To dimension a' drawing properly the drafts- man should be familiar with the methods and machines used by the mechanic who is to make the object he is drawing, as this knowledge will enable him to give the information in the best way and may save the mechanic much an- noyance. The following are some general rules which it is well to follow, but it must be borne in mind that there are exceptions to all rules and if added clearness or a saving of time will result one should not hesitate to violate any of them. Dimension lines should present a sharp con- trast to the lines of the drawing. They are usually made about one half the weight of the" standard line. Most draftsman use a continu- ous light line with a space left near the center for the figures. Some use a line made up of long dashes about I14 to 1% inches long separ- ated by a small space. Red ink is sometimes used for center lines. This makes a contrast on the blue print as the red lines print very light. If red ink is used the figures and the arrow heads are made in black ink. Sharp arrow heads are placed at the ends of /the dimension lines. Arrow heads should- be about 3/16 of an inch in length and 3/32 of an inch in width at the wide end. In structural work figures are sometimes placed above the dimension lines instead of in a space left for them near the center of the line. Extension lines are the same weight as the dimension lines or about one half the weight of the outline. They should not touch the drawing. A space of about 1/8 of an inch should be left between the end of the exten- sion line and the part of the drawing to be dimensioned. The extension lines should ex- tend about 3/16 of an inch beyond the arrow heads of the dimension lines. The dimensions that appear on a drawing should be those' of the object regardless of the scale of the drawing. Figures should be plain arid not too small. A common mistake of beginners is to confuse minuteness with neatness. Figures should be neat but not smaller than 1/8 of an inch in height. From 3/16 to 1/8 of an inch ^s good size. Do not use fancy figure's. Plain readable figures that allow of no mistake are best. Dimensions should be given in the fractions of an inch that are given on the machinists' scale, halves, fourths, eighths, etc., to sixty fourths. Other fractions should be given in decimals as 1.33" or 2.23". In some drafting rooms decimals are used entirely. It is customary in many drafting rooms to + .003, give a limit of accuracy, as 4. — .0 , meaning that the finished object may exceed 4 inches by not more than 3/1000 of an inch. 4. — .005 means that the object may be 5/1000 smaller, but no larger. 4. + .003 would indicate that the finished piece might be either 3/1000 larger or 3/1000 smaller; but must not exceed that limit. Fractions should be made with the line be- tween the numerator and the denominator horizontal, not slanting. Thus J, not 1/4. The slant line allows the possibility of a mistake, as in 1 5/16 or 15/16. Dimensions should, if possible', be kept off of the drawing and placed at the side or be- tween views. A good drawing should stand out clearly and each dimension line placed on it adds to the confusion. Give the diameters of circles and the' radii of arcs. Diameters should be followed by the abbreviation, Diam., Dia., or D. ; radii, by Rad. or R. Diameters are usually given for circles be- cause a round object is usually turned on the lathe and the workman will measm'e with cali- pers. If the radius is given on the drawing, he must multiply that by two and might make a mistake. Holes are drilled with drills marked accord- ing to their diamete'rs, as %", 1", etc. Arcs are laid out with the compasses or dividers and the workman must use the radius. Never place dimensions on a drawing so that it is necessary for the shop man to make cal- culations. Do not ask him to add several di- mensions in orde'r to get the total. Do not 56 ask him to subtract in order to find the size of a part. The place for calculations is in the drafting room. Give all necessary dimensions. Do not duplicate dimensions. Frequently it is convenient to change one or two dimensions on a drawing and thus save' making a new drawing. In such cases, if dimensions appear in more than one place, one may be changed and the other overlooked. Figures should read at right angle's to dimen- sion lines. Figures should read from the bottom or right of the sheet. Never place figures so that they read from the top or left of the sheet. Dime-nsions on diagonal lines should change at 60°. Dimension from center lines and from finished surfaces. Use notes freely when by so doing you can save time. Dimensions up to two feet should be given in inches; over that distance' in feet and inches. Dimensions for the sheet metal shop are all given in inches. The sizes of wheels, gears, pulleys, and cylin- der bores; the stroke" of pistons and the length of wheel bases are usually given in inches. Keep dimensions off of sections, if possible. Neve^ use center lines as dime'nsion lines. Never place dimensions on lines of a draw- ing. When it is desired to dimension small spaces where figures would appear crowde'd, the figures may be placed outside' of the space. The dimensions of angles are given on a line drawn with the compass set at the vertex of the angle. BLUE-PRINT READING Blue-print reading, properly taught, should give the pupil three things; first the ability to make a free-hand working drawing, second the ability to make perspective sketches and last and most important the ability to visualize. This is more likely to be of value than the ability to make Mechanial Drawings as many more boys will be engaged in work, where they will be required to read drawings, than will go into the drafting room. It is suggested that the pupil be asked . to study the drawing and then, by means of a sketch or a clay model give exp'ression to his idea of the shape of the object. A few lessons in Cabinet and Isometric Drawing should precede the work in Perspec- tive Drawing. 57 45° TOP FITTING 59 GRIND DRILL /y/IA/O WHEEL PR AW HAA/P WHEEL s ^/ZE. A//i^E PRAWJA/G i OF THE P//VEA/S/0/VS BUT RUT JN F/ CURE 5 AS THEY ARE HERE. 64 , 1 i ; ; ; i 1 '; i -A ^ ^\ ^-^ '^ ^ 7^_ r i \ ^ ^ ^--^ >| \) \] U ~T J ! 1 ! 1 1 / 1 1 ! ■- E / o 7 9i 7 ./I 5 ^ai SUPPORT ///V^Z^ 66 DRILL 4- § HOLES ■5 D. HAND RAIL KNOB 68 LEVER ENP ^>- e _L_ A B C D E F G H /r L M BOLTS a /i 7i li d /i li i i /i 7 a i >k 2i 9i 2i vi /i ^i i i £ li i ^i J /S 3i H 2h 3ii / / 5 li *■ 69 STEERING CEAR CONNECT/ON J_ =-_-L.-:. ' ~3\ ■ICQ ;^ic>j la- ONE 50± ON^ 3 2' /^Or^ - /iAH£ ONE 32' CENTERS AS SHOWN BY DOrrEP LINES 70 Tip -Vh'-M BRACKET 71 SPEC /F/CAT/ONS:-.IS T0.2S CARBON -ROUffJ^ TORN TO /.26S" S^AFTEf^ HARDEMA/e Gfi/ND / ^'p/A t ,0006 H -PRILL- WR/3T PIN M/LD sr££L MAKE 4 Tl '^"0 iiiiii!iii'iiiiiii ^^^ llllillllll llllilll ^^ (m > DRAFT CLEV/5 I—/ H W 73 ' y .^2-0/?/LLj 3 3 \ ^^^^ MACH. STE6L ^ ■It) ^^-^ \ ^ J \V \ '^ i t ^ J 1 -2 -3i- o / c / 1 /~i r . FUEL SWITCH LEl/ER * 74 • . LUGS '\\ i ! 1 ! 1 /i -^ 3 WA A/T£P /J L OOP & L 0/^G p 3WAA/r^P /"loop 3" LONG 75 ^i z//v/r MAKE A WORKING DRAW/A/ G 76 >\ M 80 Tf(UCK WHE^L CONSTRUCT A PENTAGON TO LOCATE /iOLES _ _ CM HEX. WASHER ^1 /^ ]e \J O/RAW TOP V/EW 82 e^/^^i /e TEETH f^ATCH^T 3 /SECT 45 ANGLE TO GET /6 TEETH 83 WASHER REVERSE CURVE 84 sz:l A K 10 ^ 86 87 --' 89 90 \ 91 1 ^\^ ^^ :> ' ■ ^ >^^fi^ V i m> N ^ - y^ — — j 1 ■ ' ,„, , , 93 B£V£L ^£A/^ ^£/l/?S /A/ n£SH 94 LIBRARY OF CONGRESS III 019 719 922 2