MACHINE SHOP DRAWINGS
 
 PUBLISHERS OF BOOKS FOR./ 
 
 Coal Age * Electric Railway Journal 
 Electrical \\forld * Engineering News-Record 
 Railway Age Gazette v American Machinist 
 Electrical Merchandising ^ The Contractor 
 Engineering 8 Mining Journal v Power 
 Metallurgical 6 Chemical Engineering
 
 Machine Shop Drawings 
 
 READING DRAWINGS, MAKING SHOP 
 SKETCHES, LAYING OUT WORK 
 
 BY 
 
 FRED H. COLVIN, A.S.M.E., F.I. 
 
 ASSOCIATE EDITOR OF THE AMERICAN MACHINIST, AUTHOR OF " MACHINE SHOP 
 
 CALCULATIONS," "AMERICAN MACHINISTS' HANDBOOK," "HILL 
 
 KINK BOOKS," "RAILROAD POCKETBOOK," 
 
 ETC., ETC. 
 
 FIRST EDITION 
 SECOND IMPRESSION 
 
 McGRAW-HILL BOOK COMPANY, INC. 
 
 239 WEST 39TH STREET, NEW YORK 
 
 LONDON: HILL PUBLISHING CO., LTD. 
 
 6 & 8-BOUVERIE ST., E. C. 
 
 1909
 
 Copyright, 1909, BY THE McGRAW-HiLL BOOK COMPANY 
 
 The Plimpton Press Norwood Mass.
 
 rr 
 
 2.30 
 
 L ! B F? /* ^ V 
 
 STA t? M-hi'/i. 
 ftL Ah IS >l> h;.iMt CCOHOIUfcS 
 ANU BASEARA, CALIFORNIA 
 
 PREFACE 
 
 THIS little book is intended to be a help to those who do 
 not thoroughly understand the reading of drawings rather 
 than an attempt to teach drawing itself. It shows how 
 seen and unseen portions are represented, the use of full 
 and dotted lines, the way in which different views are drawn 
 and how to study them all so as to secure a correct idea of 
 the shape of the piece represented. Many actual examples 
 are given from the drawing-room practice of the leading 
 shops in this country and the meaning of each carefully 
 explained. 
 
 A little attention is given to laying out work such as 
 gearing of different kinds, to laying out angles without the 
 aid of any but the crudest instruments, and a number of 
 things which should be useful in many ways. 
 ~? The few examples and hints in regard to sketching 
 k should also be of value, especially to those of an inventive 
 <> turn of mind or those who must convey ideas to others for 
 J3 any purpose. In short it aims to be of service in enabling 
 ^^any one mechanically inclined to have a better grasp of the 
 ^ meaning of working drawings so that he can read them as 
 CT) he would an open book, 
 cn THE AUTHOR. 
 
 Q- 
 
 UJ 
 
 CO
 
 CONTENTS 
 
 CHAPTER PAGE 
 
 I READING DRAWINGS i 
 
 II DRAWINGS OF A MONKEY-WRENCH 17 
 
 III SOME EXAMPLES OF DRAWINGS . 25 
 
 IV HINTS ON LAYING OUT 50 
 
 V LAYING OUT SPUR GEARS 84 
 
 VI LAYING Our BEVEL GEARS 107 
 
 VII THE WORM AND WORM, WHEEL 113 
 
 VIII SKETCHES ROUGH AND OTHERWISE 124 
 
 vii
 
 MACHINE SHOP DRAWINGS 
 CHAPTER I 
 
 READING DRAWINGS 
 
 IN spite of the fact that the drawing is the universal 
 language of the mechanic, there are sometimes differences 
 of opinions about the translation and so we all have to 
 learn how to read drawings and to know what they mean. 
 
 We are so accustomed to seeing a piece of machinery as 
 a whole that it is not easy to look at just one end or place 
 without regard to the rest. This is why drawings in per- 
 spective are so much easier to understand, and if a drawing 
 of this kind, as Fig. i, was always used it would be perfectly 
 clear that a round bar of the dimensions given, was wanted. 
 
 But the regular mechanical drawing shows each side 
 or view separately and this is why they are not as clear as 
 the sketch in perspective. 
 
 Even if we try to look only at the end of a bar we are very 
 apt to get the idea of length as well as diameter, when we 
 should only see that it was something round 2 inches in 
 diameter, as at A, Fig. 2. It might be either a thin disk 
 or a bar a mile long as far as we know from this view, and 
 it is necessary to look at the side view B, to find that it is 
 6^ inches long. 
 
 Pieces of Uniform Shape 
 
 When a solid piece is uniform iri one direction, as round, 
 square, or other shaped bar, two views will show all that 
 
 i
 
 2 MACHINE SHOP DRAWINGS 
 
 is required, but these two are absolutely necessary unless 
 we make a note on the sketch telling its other dimension. 
 
 If we look at B, Fig. 3, there is no hint as to whether this 
 is a strip of tin of this size or the end of a three-foot bar; 
 but when we look at A we see that B is the side and A the 
 
 
 
 
 - 
 
 
 
 -f- 
 
 B 
 
 FIG. 3 
 
 Awurican AfaeAi.uf , X. K 
 
 end of a rectangular bar i$ inches thick, 2$ inches wide, 
 and 5^ inches long. 
 
 Right here let us understand that on drawings we rely 
 on the figures to tell the story and pay no attention to the 
 actual size of the drawing itself. If the dimensions seem 
 very much out of proportion, and you have your doubts 
 about their accuracy, ask the foreman, but don't attempt
 
 READING DRAWINGS 3 
 
 measuring the drawing; depend on the dimensions. If 
 they are wrong the fault is in the drawing room. 
 
 When Three Views are Needed 
 
 So far we have dealt with pieces of uniform shape and all 
 has been plain sailing for it has not mattered which end we 
 looked at, tmt with odd shapes we must know which end 
 is which. 
 
 In this country we use what is called third-angle projec- 
 tion, but it is harmless in spite of its name and is easily 
 explained by Fig. 4. 
 
 The upper sketch shows two views of the same piece in 
 perspective. If your eye was at A, looking at the end B, 
 and you swung the end to the right, it would appear as at C. 
 The view in the direction of the arrow D would be the front 
 view as seen at D' in the center of the lower views. 
 
 Swinging the end B' around to the right shows it like C', 
 and swinging E to the left gives E f . The line ab shows 
 that there is a change in surface at this point, but without 
 the end views we would not know that it was a large flat 
 surface running back to the raised edge or lip F. In a 
 similar way the dotted lines cd and ef show a change back 
 of the front surface .and not visible from it. The end 
 views show this to be a hole through the piece of the shape 
 indicated by GG. These will be taken up a little later. 
 
 For the present, just fix in your mind that the view given 
 at the right of the front or side of a piece is just what you 
 would see if you looked squarely at that end. The same is 
 true of the other end, and of the top and bottom views 
 when they are necessary. The top view shows just what 
 you would see if you looked down on it, and the bottom
 
 MACHINE SHOP DRAWINGS 
 
 li. 
 
 , 
 
 J 
 
 -o ^. "on 
 
 
 
 
 b 
 
 
 
 ^ 
 
 0- 
 
 FIG. 4. The Way Views are Placed.
 
 READING DRAWINGS 5 
 
 view just as it would appear from underneath. The top 
 view is usually called the "plan" view because in most 
 cases it gives the general plan or idea of a machine or a 
 building. 
 
 Points to Remember 
 
 There are two or three points to fix in your mind that 
 will help in reading any drawing. 
 
 Even' solid line shows a change in the surface you see 
 of the object drawn, and the other views should show what 
 this change is. 
 
 Every dotted line indicates a change in some surface that 
 cannot be seen, and dotted lines are used to show that 
 openings occur beyond the surface seen, or the shape of 
 the back or under side of the piece. The only exception 
 to this is the center line, which is sometimes drawn. This 
 should always be drawn with a long dash and a dot, while 
 the regular dotted line is a broken line with dashes of even 
 lengths. The center line does not indicate a change of 
 shape, but is generally used to measure from or to locate 
 points. 
 
 Shade Lines 
 
 Shade lines, that is, lines made heavier than the rest of 
 the drawing, are used to show at a glance which is the top 
 or bottom of the drawing. The light is always supposed 
 to come down from the upper left-hand corner of the paper. 
 This would throw the bottom and right-hand end in a 
 shadow and these lines are made heavier to show that this 
 is the case. This is not always done, however, and is not 
 really necessary, as there is almost always a title, or letters
 
 6 MACHINE SHOP DRAWINGS 
 
 or figures which show the top and bottom. But if the 
 drawing has heavy shade lines, you can tell at once which is 
 the bottom and which the top. 
 
 Figs. 5 and 6 show this. If either of them were handed 
 you, bottom side up and without any lettering, you would 
 know which way they belonged by these heavy lines. 
 
 The front view of Fig. 5 shows three lines, A, B and C, 
 each indicating some change in the surface at these points. 
 What these changes are must be told by the end views. It 
 may be like D, with even steps cut in the side; or like E, 
 with smaller steps; or even like F, shown at the other end 
 where there are no steps, but inclined surfaces between 
 the top and A, and between B and C, while between A and 
 B there is a groove, as shown, and with different angles. 
 
 The front view of Fig. 6 shows a rectangle with a line 
 across the face at A B. This might mean any one of a dozen 
 shapes, but referring to E shows us that the end C, up to 
 the line AB, is cut away at an angle of 45 degrees, as shown. 
 The view F at the other end shows D to be square and the 
 dotted line in F indicates the cutting away at the other end. 
 
 The line A B across the front shows it to be a square cut, 
 while if it had been rounded out as with a milling cutter 
 there would be no straight line AB, but a solid curved line, 
 as shown dotted on D, and as shown, also dotted, on the 
 small sketch at the right which gives a view of the piece in 
 perspective. 
 
 Where Five Views are Needed 
 
 The next example, Fig. 7, requires five views to show the 
 piece. The central view A is the " plan," or view looking at 
 the top of the piece, and gives very little idea of it, except that
 
 READING DRAWINGS
 
 8 MACHINE SHOP DRAWINGS 
 
 the total length is 3! inches, the width is i inch, that there is 
 some sort of a rib or perhaps a groove, inch wide and f inch 
 from one edge, while lines ab and cd show a change of shape 
 of this rib or groove, whichever it proves to be, but gives 
 no information about it. The dotted lines indicate a de- 
 pression of some kind in the upper side and the dot-and- 
 dash line shows the center line of the piece, showing that the 
 widest part is considered as the main part of the piece. 
 
 Going to the right-hand view B, we find that the base is 
 a flange inch thick, and we know from the first view 
 that the width is i inch. This shows that the two parallel 
 lines indicated a rib inch thick, that the upper side of 
 this is f y inch from upper edge of flange, that the rib pro- 
 jects if inches above the flange at this end, that the total 
 hight is 1 1 inches, and that the depression indicated by 
 dotted lines is W mc ^ deep. 
 
 The other end C is similar except that the total hight is 
 i$ inches, the rest of the dimensions being the same. There 
 is no need of repeating similar dimensions as they are always 
 the same in all views. 
 
 The upper view D means simply that the back edge of 
 the piece, as seen in the plan view A, is raised until it is 
 vertical, and it will then show as in D, with the flange on 
 top. This shows that the top of rib is a plain taper from 
 a hight of 1 1 inches to ij inches above the flange (these 
 dimensions being shown in views B and C), that the left- 
 hand upper edge is VV mcn from this end of the base flange, 
 and the right -ft- inch from the other end, with the top of 
 the rib 3^ inches long measured parallel with the bottom 
 flange (or top in this view). 
 
 This view shows that the depression is in the top of the
 
 READING DRAWINGS 9 
 
 rib, as shown in the plan view A, the full lines showing it 
 to be on this side. The long side of this depression is 
 shown parallel with the flange of the base and ft inch from 
 it. The right-hand end is i inch from the end of the flange, 
 
 /, 
 
 / \ " 
 
 1 
 
 
 1 
 
 
 1 
 
 H J 
 
 
 FIG. 7. A Piece where Five Views are Needed. 
 
 the greatest hight or width being | inch, the other point 
 i inch and the length of the various parts f inch, i inch and 
 inch, as shown. 
 
 The view from the wide side is shown at E, where the 
 back edge is pulled down instead of up. The dotted lines
 
 I0 MACHINE SHOP DRAWINGS 
 
 show that some change takes place in the piece beyond 
 the surface that can be seen, but does not tell whether it 
 is a depression or a projection of this shape. We must 
 depend on the other yiews for this part of the story. 
 
 ,y.r. 
 
 ' FIG. 8. How Pieces Appear in Different Positions. 
 
 The way in which these views are drawn out can perhaps 
 be seen to better advantage in Fig. 8. This shows just why 
 the top view seems to be upside down and why the end 
 views seem to be lying on their sides.
 
 READING DRAWINGS H 
 
 Going back to Fig. 7, and calling E the plan view, the 
 end views would then be as shown at F and G, and the 
 bottom views as at H. But neither A, E, F, G nor H 
 show the depression in solid lines, so that D would be neces- 
 sary in any case. But we would then draw it below H, 
 in just the same way as E is placed below A when that was 
 drawn as the plan or top view. 
 
 Other Examples 
 
 In Figs. 9, 10 and n we have other Wamples which will 
 serve to show a little more what we find in the shop, the 
 first being a common lathe center. The taper is 4 inches 
 long, | inch at the small end and i inch at the large end. 
 Looking at the end view we find that the part marked if 
 inches is square and inch thick. The end view shows 
 the front end to be round and the side view indicates a 
 6o-degree cone, while the dotted circle shows simply the 
 small end of the long taper. 
 
 If it were not for the end view there would be nothing 
 to show what shape the piece was round and it might easily 
 be such a shape as shown at the extreme right. 
 
 Fig. 10 shows a socket or holder for a turret lathe or 
 similar purpose. The side view shows a piece 6 inches 
 long by 1 1 inches diameter. The dotted lines at the left 
 indicate some kind of an opening and the dotted circle 
 in the end view shows this to be a round hole. This has a 
 round hole at right angles with a larger hole on one side 
 than the other, the large hole being next the observer so 
 the small hole shows straight through the large one. 
 
 The other end is broken away, showing the hole in solid 
 lines and the metal around it in section lining. In some
 
 MACHINE SHOP DRAWINGS 
 
 A Few Common Examples from the Shop.
 
 READING DRAWINGS 13 
 
 drawings the kind of lines indicate the metal to be used, 
 while in some cases, as the one shown, the material is 
 shown by its name or by letters, as M.S. for machinery 
 steel. The broken section shows the hole to be if inches 
 in diameter and that both holes are ij inches deep. 
 
 It will be noted that the upper wall is not as thick as 
 the lower one, and while this might mean that the hole 
 was eccentric in the bar, as shown at the extreme right, 
 the end view shows the hole to be central, but that the top 
 of the bar is flattened to allow it to be held by a key. 
 
 Fig. ii takes three views to show, and from the left and 
 center views we find that there is a round shank i inches 
 in diameter and 2\ inches, long. The two end views show 
 the shape of the head and give dimensions of the slope, 
 the lip and the other parts. The center of the shank is 
 | inch from one edge and i| inches from the other edge, 
 although the latter dimension is hardly necessary, as by 
 taking J inch from the total, 2\ inches, we have i inches. 
 
 So far we have not touched on threads or gears, assembly, 
 or real working drawings, but these will come at another 
 time. 
 
 The Nut and Bolt 
 
 One of the most common things in the shop is the nut, 
 either square or hexagon, and it makes a good example of 
 how things are drawn out on paper. We must remember 
 that we look only from one side at a time and must see 
 nothing else, so a square nut will show either one flat side, 
 if we look at it squarely, or parts of two sides if we look 
 toward one corner. This corner could be in any position, 
 but is always taken as being in the center as in B, Fig. i la.
 
 I4 MACHINE SHOP DRAWINGS 
 
 A shows the flat side of a nut without chamfer or bevel, 
 while in B we see the corner in the center and the top views 
 show the position of the nuts. The total distance across 
 the nut in B is the long diameter or diagonal of the square. 
 
 D rrrri rrn 
 
 FIG. ua. Different Views of Nuts. 
 
 In C we have a hexagon nut with one corner toward it so 
 that it looks like the Square nut until we see the top view. 
 D is the proper way to show a hexagon nut, with the two 
 corners to the front. The extreme width is always twice 
 the length of one side, and the middle flat is equal to both 
 the others as they appear in this view. This is shown by
 
 READING DRAWINGS 15 
 
 the dotted lines coming down as in D. In laying out a 
 hexagon nut we divide the whole thing into four parts,, 
 put one part at each side and leave the two parts in the 
 middle. 
 
 A square nut is always represented as having one corner 
 in the center, and in a hexagon we always see two corners. 
 Remembering this we can tell without a top view whether 
 a square or hexagon nut is wanted. 
 
 FIG. nb. Bolts and Broken Sections. 
 
 So far we have shown plain, flat nuts with no bevels or 
 chamfer. This is usually drawn as shown in E and F. 
 The thickness of the nut is usually the same as the bolt 
 diameter and it is customary to lay out the curve showing 
 the bevel as shown. The centers for the curves are shown 
 in both side views. Bolt heads are drawn in a similar 
 way, the size being somewhat smaller as can be seen from 
 any bolt table.
 
 X 6 MACHINE SHOP DRAWINGS 
 
 Broken Sections 
 
 When showing bolts and nuts it often happens that we 
 want to use a fairly large scale, but find this will take up 
 too much room if it is a long bolt. So we show the head 
 and nut ends of the bolt as large as we want to and cut 
 the bolt in two as in G, Fig. nb. By giving the length in 
 the dimension line A the same drawing might answer for any 
 length bolt of this size. The broken ends are usually shown 
 in the style given in G, although sometimes a section of the 
 bolt itself is given, as in H . This is also used where bolts 
 or rods of irregular shape are used as in 7 and /. The first 
 is a flattened section, while the other is sort of an H-section. 
 This is a handy way in many cases and shows the shape 
 better than in almost any other way. It also enables the 
 dimensions of the cross-section to be given if desired, as is 
 usually the case.
 
 CHAPTER II 
 
 DRAWINGS OF A MONKEY-WRENCH 
 
 EVERY tool or piece of machinery having more than one 
 piece requires an assembly and a detail drawing unless it 
 is so simple as to be very clear from the one view. But 
 even in this case it is hard to put dimensions on such a 
 drawing, which is confusing where the whole thing is shown 
 together. 
 
 The assembly drawing shows the whole machine put 
 together with no dimensions except at times the distances 
 from one part to the other. The separate parts are shown 
 in detail on detail drawings and all dimensions given. 
 Fig. 12 is a monkey-wrench in perspective showing all the 
 parts in place, while in Fig. 13 all the parts are shown in 
 three views but without dimensions. A regular working 
 drawing would show all the dimensions as we shall see later. 
 
 Beginning with the main bar of the wrench we find there is 
 a side view as shown at A , giving the shape and proportions 
 of the head, the slide or rectangular portion as shown from 
 B, while C shows the end of the head. Although there is 
 nothing to show that the end handle is round, we know 
 it is from the round hole in the handle M as shown at N 
 and O. The sliding jaw is shown at D, E and F, and study- 
 ing all three we see that it has a rectangular hole through 
 it to fit the bar and that it is threaded for the screw. 
 17
 
 i8 
 
 MACHINE SHOP DRAWINGS 
 
 Although the side view shows the thread in dotted lines, 
 the end view in F also shows this by the two circles, one 
 representing the bottom and the other the top of the threads. 
 
 The thrust piece G shows the holes in dotted lines, but H 
 shows the recess to be rectangular to fit the bar, while the 
 other end of this hole is round. The back end of the screw 
 
 FIG. 12. A Monkey- Wrench in Perspective. 
 
 fits into the small round recess which holds it in place. 
 The nut /, which goes on the end of the handle, is also 
 shown in three views, showing that it is taper, is threaded, 
 and has a slot across the end for a special screw-driver. 
 The handle M in this case is not shown exactly round as 
 can be seen from the end views N and O. The screw 
 needs no explanation as the question of thread will be 
 taken up later.
 
 DRAWINGS OF A MONKEY-WRENCH 19 
 
 ^ 
 
 o
 
 20 MACHINE SHOP DRAWINGS 
 
 The next illustration, Fig. 14, shows a few details of 
 this wrench, such as you would get on a shop "card," 
 made from a blue-print pasted to a piece of cardboard' or 
 sheet metal and probably shellacked or varnished so it will 
 not be soiled and injured. This is not taken from the 
 drawings of any wrench maker and all the dimensions are 
 assumed for the occasion, but they serve to show how such 
 drawings are made. 
 
 This "card" or drawing, should contain all the dimen- 
 sions necessary to go ahead and make these parts of the 
 wrench. Beginning with the main jaw or bar, we find that 
 the head is z\ inches long, i inch wide, \ inch thick and 
 that the point tapers down to \ inch; beginning i inch back 
 from the point. 
 
 The bar is set \ inch from the back of the head and set 
 central to the width of the jaw, leaving \\ inches from 
 the bar to the end of the jaw. The straight or rectangular 
 part of the jaw is i X \ inch, as can be found from the side 
 and left end views, and 6J inches long. The rest is round, 
 \ inch in diameter for 4 inches, J v inch on the end and 
 threaded 14 to the inch, U. S. S. thread. This part is 
 i inch long. Adding up the different parts we find the 
 total length is 12 inches. 
 
 Here is where mistakes are liable to creep in and it is 
 well to look at a drawing carefully to make sure the dimen- 
 sions agree. While it is true that any mistake in the draw- 
 ing is "on" the draftsman and is not your fault, still it is 
 better in every way to avoid spoiling work or getting some 
 one else into trouble. 
 
 The recess for the nurled end of the screw is shown to 
 be ft inch long and -^ inch deep. - This is for the nurled
 
 DRAWINGS OF A MONKEY-WRENCH 
 
 -i.. 
 
 Is 
 
 * 15 
 
 --' '-w > 

 
 22 MACHINE SHOP DRAWINGS 
 
 head to turn in and also prevents the jaw from sliding 
 along the bar. It is to be cut with a milling cutter, 2 inches 
 in diameter, which gives a curve of i inch radius as shown 
 in the end view. 
 
 Coming to the sliding jaw we find dimensions a little 
 more .complicated. The total hight is the same as the 
 length, 2\ inches. The jaw is i inch wide, while the hole 
 is fa by sV inch. Comparing this with the bar we see it 
 allows 3^ inch clearance both ways, ^ inch on all sides. 
 The back end of the jaw is \\ inches high, the hole is 2 
 inches long, tapped with a J-inch, square thread tap, 6 to 
 the inch. The jaw point is \ inch deep, the distance 
 across the center ij inches, with \ inch cut away at the 
 back. The lower view shows the sliding jaw from the 
 back, giving the thickness as \ inch through the middle 
 portion. 
 
 The lettering in the corner varies with the idea of the 
 draftsman, the system of numbering the drawings or 
 "cards" being different in almost every shop. 
 
 Tabulated Drawings 
 
 Another plan used in some shops is to make one drawing 
 answer for several sizes by using a table as shown in Fig. 15 
 in connection with the drawing. All the dimensions are 
 lettered and the size of each part given in the table under 
 its proper letter. Thus M represents the total length of 
 the bar and is 6, 8, 10 and 12 inches long according to the 
 size. If you are working on a 6-inch wrench, all the dimen- 
 sions are given in the upper line, the loinch wrench sizes 
 are in the third line, and so on. 
 
 While this saves a drawing for each of the other three
 
 DRAWINGS OF A MONKEY-WRENCH 
 
 
 [ 
 
 (f_j) 
 
 [? 
 
 
 j 
 
 
 .-. 
 
 1 
 
 I 
 
 .; 
 
 | 
 
 i 
 
 
 
 tx 
 
 -1 
 
 3 
 
 f 
 
 ' 
 
 1 
 
 S 
 
 i 
 
 1 
 
 = * 
 
 
 
 
 
 
 
 
 & 
 
 -', 
 
 
 
 X 
 
 - 
 
 
 
 
 
 
 
 
 
 
 X 
 
 
 
 ^ 
 
 X 
 
 
 
 
 
 ; 
 
 ' 
 
 
 y 
 
 CO 
 
 
 
 2 
 
 2 
 
 S 
 
 1 
 
 
 
 
 
 
 
 
 
 
 i? 
 
 * 
 
 ^ 
 
 C/3 
 
 
 
 
 
 
 
 K 
 
 r 
 
 
 
 $ 
 
 X 
 
 S 
 
 
 ? 
 
 
 
 
 
 S 
 
 (0 
 
 30 
 
 S 
 
 2 
 
 Q 
 
 
 T 
 
 
 
 
 1- 
 
 
 J 
 
 S 
 
 
 n 
 
 ; 
 
 
 
 -A 
 
 _i 
 
 
 
 
 
 id 
 
 ,2 
 
 f 
 
 2 
 
 > s 
 
 a. 
 
 
 
 
 
 
 : 
 
 ^ 
 
 S 
 
 X 
 
 ^ 
 
 5 
 
 
 
 
 
 
 i 
 
 
 
 
 
 1 
 
 - 
 
 S 
 
 5 
 
 Q 
 
 
 
 
 
 
 
 K 
 
 
 
 
 
 
 sr 
 
 1 
 
 
 
 
 
 
 
 O 
 
 X 
 
 ^ 
 
 i? 
 
 
 
 1 
 
 
 
 
 
 , 
 
 
 fc 
 
 X 
 
 X 
 
 X 
 
 - 
 
 H 
 
 
 
 
 
 
 
 M 
 
 S 
 
 - 
 
 5 
 
 5 
 
 1 
 
 in 
 
 
 
 
 
 
 
 Q 
 
 :s 
 
 
 
 X 
 
 * 
 
 H 
 
 
 
 
 
 
 
 U 
 
 x 
 
 sr 
 
 X 
 
 - 
 
 S 
 
 
 
 
 
 
 
 W 
 
 
 
 
 
 
 U g- 
 
 
 _._ 
 
 f>) 
 
 - 
 
 
 < 
 
 
 
 S* 
 
 ^ 
 
 - 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 L>\ 
 
 
 
 
 ! 
 
 r 
 
 . 
 
 
 i 
 
 l 
 
 2 
 
 N 
 
 
 h 3 
 
 r 
 
 
 
 t - 
 
 *i 
 
 
 
 1 
 
 s 
 
 
 ' 
 
 
 
 
 
 
 
 1 
 
 ! 
 
 
 
 
 
 
 

 
 24 MACHINE SHOP DRAWINGS 
 
 sizes, it is considerable work making the table and to get 
 it absolutely correct, and it is much harder to work to than 
 the separate drawings because it is very easy to take a 
 dimension from the wrong line and so make a mistake. 
 
 It is a very convenient way to make reference drawings 
 for the superintendent or chief draftsman, but it is not as 
 easy to work from as the separate working drawing and is 
 not generally used on this account.
 
 CHAPTER III 
 
 SOME EXAMPLES OF DRAWINGS 
 
 As the best way to learn a thing is by doing it, so the best 
 way to read drawings is by taking some actual cases and 
 examine them in detail to find out just what they mean. 
 The examples have been taken from a great variety of 
 sources in order to show the practice in different shops 
 and also to give an idea of the different classes of work. In 
 this way many will find the kind of work that interests 
 them most and perhaps understand the drawings a little 
 easier on that account. These are taken from the draw- 
 ings of some of the best firms in the country and show how 
 ideas are put on paper either for illustration or to work to. 
 
 Details of a Bench Lathe Head 
 
 One of the great satisfactions of knowing how to read 
 drawings is the ability to see just how all kinds of machinery 
 is constructed without ever having seen the machine itself. 
 Of course we do not always get things pictured in our 
 minds in the right proportions even where dimensions are 
 given, unless we are careful to compare different parts with 
 other machines that we are familiar with, but the way any 
 machine is built is always at our disposal if we can see the 
 drawings of it. 
 
 Fig. 1 6 is the head of a Cataract bench lathe and is a 
 good example for study. 
 
 25
 
 26 
 
 MACHINE SHOP DRAWINGS
 
 SOME EXAMPLES OF DRAWINGS 
 
 27 
 
 The spring collet or draw-in chuck is plainly shown at A 
 with its back end threaded inside the draw-in tube C 
 which has the handled fastened to the back end. Both 
 collet and draw-in tube are inside the lathe spindle B. 
 The bearings are not shown in detail but are of the cone 
 type, split on one side so as to take up wear as they are 
 forced into the taper hole on the head, outside the spindle. 
 The threaded caps II force the bearings in and at the same 
 time act as dust guards to keep dirt out of the bearings. 
 These bearings are oiled by the wicks shown, which evi- 
 dently lead up from oil reservoirs to the bearings. Although 
 the one at the back seems to touch the index pin H, common 
 sense tells us this is not the case as the oil would work out 
 around the pin and the index holes do not need lubricating. 
 Although it is not shown, we can feel very sure that the oil 
 wick is about in the center of the head and the index pin 
 at one side, toward the front so as to be convenient to use. 
 
 The cone E is fastened to the hollow spindle by the two 
 conical pointed set screws at opposite side, and it would 
 appear that, by removing these set screws so as to clear 
 the spindle and by taking out the draw-in tube, that the 
 whole spindle could be drawn out through the front bear- 
 ing. The cone has two sets of holes, one in the front and 
 the other in the rear flange. The front holes are for lock- 
 ing the head while unscrewing the collet or taking off 
 chucks, while the rear set are kept for accurate indexing 
 and not used for anything else. 
 
 Instead of having thrust collars on the spindle as in most 
 makes of larger lathes, the thrust is taken up in the cone 
 itself by the ball-thrust bearing shown at G. This is 
 adjusted by the nut F with the pin holes for a wrench
 
 2 8 MACHINE SHOP DRAWINGS 
 
 put in at the angle shown. This allows the ball races 
 to be adjusted so that there will be no shake in the head, 
 and the balls take all the thrust of drilling and boring. 
 
 No' thread is seen on the nose of the spindle and the small 
 cut at J shows how the chucks and face plates are held in. 
 The nose is turned to a taper and has what is practically 
 a double bayonet joint. This slot is milled in from the 
 front and then at the angle shown to each side. The chuck 
 or face plate carries a pin that slips in the slot and is held 
 firmly or\ the taper nose by being drawn in close contact by 
 the incline of the side slots. 
 
 A Large Lathe Head 
 
 A decided contrast with the bench lathe is the large lathe 
 head shown in Fig. 17 where the main bearing is 30 inches 
 in diameter and 24 inches long while the rear bearing is 
 1 6 inches in diameter and 18 inches long. The spindle is 
 hollow and has an 8-inch bar running through it which 
 carries a boring and facing head on the outer end for bor- 
 ing the hole and facing the hub of fly wheels while they are 
 being turned on the large face plate. This allows the bor- 
 ing bar to be run at the proper boring speed independent of 
 the slow speed necessary in facing or turning the rim. 
 
 The motor drive is interesting, coming from the motor 
 with its i6-tooth pinion and driving the ii2-tooth gear 
 below it. This drives out to the right while the i8-tooth 
 pinion here drives the io8-tooth gear driving the ao-tooth 
 pinion at the left. From here a shaft (not shown, but 
 we know the face plate must be driven somehow and that 
 it must come from this) runs to the face plate at the right 
 and meshes in the teeth in its outer edge. The first driven
 
 SOME EXAMPLES OF DRAWINGS 29 
 
 FIG. 17. Head of a Large Lathe.
 
 3 o MACHINE SHOP DRAWINGS 
 
 shaft runs to the left as well as the right and carries a tight 
 and loose pulley for driving the feed of the boring and fac- 
 ing bar inside the spindle. The first pair of gears are next 
 to the pulleys on the upper shaft while the next pair are 
 at the end of the rear bearing, the pinion showing in full, 
 but part of the gear being hidden behind the bar. This 
 drives the shaft running to the left and its gears drive the 
 screw behind the bar, using either set desired and allowing 
 the rear set to be changed at will to secure special feeds. 
 Throwing the belt on the loose pulley allows the feed to be 
 operated by hand, using the handle at the extreme left. 
 
 This is not a regular working drawing as it does not give 
 all dimensions but only the main ones and the general 
 layout scheme for the head. This is the kind of a drawing 
 or sketch (for it would not be made as carefully as is here 
 shown) that would be handed over to the draftsman to 
 have the details worked out, the chief having decided on 
 the speeds and gear ratios of the* different parts as well 
 as the main dimensions such as the swing and the bearings. 
 
 General Locomotive Details 
 
 To show how a few dimensions give a good idea of the 
 main points of a locomotive, we can refer to Fig. 18, show- 
 ing an oil-burning Vauclain compound as built by the 
 Baldwin Locomotive Works. The high-pressure cylinder is 
 17 X 32 inches and the low 28 X 32 inches. The center of 
 boiler is 9 feet 2 inches above the rail and the boiler 6 feet 
 2 inches in diameter. The pilot is 4 feet \ inch long, dis- 
 tance from pilot to center of truck wheel 2 feet 9 inches, and 
 the truck wheel is 3 feet 8 inches in front of center of cylin- 
 der, while the forward driver is 5 feet 6 inches behind this.
 
 SOME EXAMPLES OF DRAWINGS
 
 3 2 MACHINE SHOP DRAWINGS 
 
 The driving-wheel centers are 5 feet i and 5 feet 2 inches, 
 while from center of rear drivers to back end of engine 
 is 8 feet 5^ inches. The driving-wheel base, the distance 
 between centers of rear and forward drivers, is 15 feet 4 
 inches, while the total engine wheel base is 24 feet 6 inches, 
 and the total wheel base for engine and tender is 54 feet 
 2\ inches. The engine truck wheel is 2 feet 6 inches, 
 tender trucks 2 feet ioj inches and the drivers 4 feet 9 
 inches. Tender truck distances are shown as are the oil 
 and water capacities of the tender. 
 
 A little familiarity with reading drawings makes much 
 information of this kind available which is not otherwise 
 understandable. 
 
 A French Drawing 
 
 Just to show that drawings are a universal language, take 
 the one shown in Fig. 19 of a worm shaft fitted with ball 
 bearings. The worm is shown at W, in the center of the 
 shaft. At each end are dust and oil guards A A, which fit 
 into grooves in the case, showing, if we did not know from 
 experience that the case is in two pieces and put together 
 in some way, presumably bolted. 
 
 There are three sets of ball bearings, BBB, the one at 
 the left being a thrust bearing with curved ball races at 
 each side to allow for any movement of the shaft out of 
 center. The balls are held in place by the retaining rings 
 DD while the races CC take all the end thrust of the worm 
 in either direction. The other bearings support the shaft 
 and EE are further oil guards to keep the bearing oil in 
 the cases, and the grease or other lubricant, used for the
 
 SOME EXAMPLES OF DRAWINGS 
 
 33
 
 34 
 
 MACHINE SHOP DRAWINGS 
 
 worm, out of the bearings. The bearings are oiled through 
 the small oil cups at the top. 
 
 The dimensions are in millimeters, which may be con- 
 fusing, but there is no trouble in knowing just what is 
 meant by the drawings even if we do not understand the 
 dimensions. Calling a millimeter .039 of an inch, which 
 is near enough for most cases, all you have to do is to mul- 
 tiply the figures given by .039 and you have the dimensions 
 in inches. 
 
 Grinder Spindle Details 
 
 An example of considerable more detail in a small space 
 is in the internal grinding spindles of the Bath grinder 
 shown in Fig. 20. The middle view is the regular spindle 
 with its main support A having a large and substantial 
 flange for fastening to the head of the machine, the exten- 
 sion support B, which carries the bearings and steadies the 
 spindle clear to the work. The grinding spindle proper is 
 C, having a tapered end for holding the wheel bushing E, 
 carrying the wheel W and held in place by the washer F 
 and the nut G. It will be seen that the spindle is not con- 
 tinuous but is jointed at D, being driven by a tang or 
 tongue on one piece fitting a slot in the other. This makes a 
 positive drive and yet does away with any spring due to 
 heating, as each piece is free to take its own position in its 
 own bearing. The driving spindle is H, while / is the inner 
 bearing, the outer bearing being at the end of the spindle 
 and slightly tapered on the outside to allow taking up for 
 wear. 
 
 In. the lower figure we have the supported spindle of 
 the same grinder driven by pulley C, in bearings B which
 
 SOME EXAMPLES OF DRAWINGS 
 
 35 
 
 l-tr 1
 
 36 MACHINE SHOP DRAWINGS 
 
 are supported from the double cross slides A A. The 
 main spindle has a cross slot for driving the tang of the 
 second spindle E, which in turn drives the third and grind- 
 ing spindle in the same way. This is to avoid heating due to 
 any slight bending of such a long spindle. The last spindle 
 carries a large collar and has a threaded projection H on 
 which the wheel bushing or arbor is screwed. This may 
 carry one, two or three wheels, but in any case has a projec- 
 tion on the end which fits into the supporting spindle /. 
 This is supported in a sleeve or bushing K, very similar to 
 the one on the other end and serving a similar purpose, the 
 support of the wheels against the work in grinding. By 
 driving this supporting spindle as well as the other, and at 
 the same speed, there is no wear on the small projecting end, 
 all wear being transferred to the bearing surfaces which are 
 as large as these of the grinding end. The upper view 
 gives a little more detail of this construction. 
 
 A Boiler Setting 
 
 The leading dimensions of a boiler setting for a 48-inch 
 return tubular boiler is shown in Fig. 21. No length is 
 given as this can vary according to the length of the boiler, 
 but the other proportions should be maintained as shown. 
 The grate is 24 inches below the boiler and is 4 feet 6 
 inches long. The bridge is a long table instead of only a 
 deflecting wall as is often used, and the length of this will 
 vary with the boiler. There is 15 inches between the top 
 of this and the boiler, the boiler itself being 43 inches from 
 the floor line. There are 18 inches clearance between the 
 end of the boiler and the back wall, with a curved arch to 
 carry the heat to the tubes. The dotted line shows the
 
 SOME EXAMPLES OF DRAWINGS 
 
 37 
 
 -Q-O 0~0 0--0-Vo~5"o"'o" 
 
 F 
 
 in
 
 3 8 MACHINE SHOP DRAWINGS 
 
 accumulation of ashes and dust that can be expected over 
 the bridge and in the cleaning chamber in front. 
 
 Details of a Back Rest for Ratchet Drill. 
 
 A somewhat unusual but very plain drawing is shown 
 in Fig. 22 which shows all the details as well as the assembly 
 of a back rest or "old man" for a ratchet drill. Beginning 
 at the upper left-hand corner we find three views of the cast- 
 iron base A, which show the front, side and top view. 
 These show it to be practically an angle plate with a lug 
 or boss to hold the upright rod B, which screws into it. 
 The rod B is shown below it and, though broken, is to be 
 1 8 inches long, exclusive of the thread. This is of cold- 
 rolled steel. 
 
 The lever arm C is of machine steel, round at the end and 
 bored to fit the rod B, but of flat section with the depth ver- 
 tically to resist the thrust of the drill. This is held in 
 position on the rod B by the ring clamp or binding screw 
 7 which fits around the rod B in between the two positions 
 of the bored end of C. Around this goes the screw block D, 
 with the washer E between it and the binding handle F, 
 which is threaded to fit the threaded portion of 7. Tighten- 
 ing F, forces the block D against the ends of C, and pulls 
 the clamp ring 7 against the other side of the rod, so that 
 it is bound at three points and held firmly. 
 
 To guide and support the upper end of the ratchet drill 
 is the screw H, held in the screw holder G, three views being 
 shown. This shows how the screw holder slips on the flat 
 bar C, how it is held in place by the small screw / bearing 
 against C and how it is tapped on the other side for the
 
 SOME EXAMPLES OF DRAWINGS 
 
 39
 
 40 MACHINE SHOP DRAWINGS 
 
 pressure screw H. And finally the pressure screw itself, 
 H, of which only one view is needed. 
 
 The assembly drawing shows everything in place, easily 
 distinguished by letters although these are hardly necessary. 
 While this is a very simple case, almost any drawing can 
 
 FIG. 230. Section of Cylinder. 
 
 be studied out in the same way if we go at it easily and do 
 not get excited. 
 
 A Locomotive Cylinder 
 
 The drawing shown in Fig. 23 a and b is made from a 
 working drawing of the Baldwin Locomotive Works and gives
 
 SOME EXAMPLES OF DRAWINGS 
 
 some idea of the many details that go to make up a cylinder 
 and half saddle for a locomotive, in this case for the Central 
 Railway of Brazil. Many of the minor dimensions have 
 
 1 
 
 Steim Inlet 
 
 
 
 
 
 1 
 
 Steam Port 
 
 
 
 
 
 1 
 
 Exhaust 
 
 I 
 
 
 
 
 1 
 
 Stem Port 
 
 | 
 
 
 
 
 1 
 
 Steam Inlet 
 
 1 
 
 FIG. 236. Showing Section Parts. 
 
 been omitted as being unnecessary for our purpose, but 
 enough have been left to show the general proportions 
 and the way in which it is made. 
 
 The inside diameter of the cylinder is 21 inches, the 
 outside is 24 inches and the inside length 32! inches, which
 
 42 MACHINE SHOP DRAWINGS 
 
 means a 24-inch stroke, after allowing for the thickness of the 
 piston head and the clearance. Steam from the boiler comes 
 down through the steam passage 55 and, as can be seen by 
 the dotted lines, divides and goes around the exhaust passage 
 EE. This can be seen both from the view of the valve seat 
 which has been drawn over the cylinder and also from the 
 other view. On dividing, the steam comes into the steam 
 chest through the passages marked 57 and steam inlet, in 
 the two views. From here the steam admits it to the cylin- 
 der through the long passages and, after it has done its 
 work, the exhaust steam finds its way out the same long 
 crooked ports and goes out the stack through the central 
 passage marked E and exhaust. The shape of the steam 
 pipe joint is shown above the passage and at right angles 
 to its face. 
 
 The frame goes each side of the saddle casting as can be 
 seen at F and is secured by bolts running in both direc- 
 tions as shown. The center of the frame is 25^ inches from 
 the center of the engine and the cylinder center 20^ inches 
 beyond this, while the outside of the cylinder is 12$ inches 
 from the center. 
 
 This is a patternmaker's drawing as it shows the dimen- 
 sions of the curves of the steam and exhaust passages, and 
 the machinist would have no use for these as they are not 
 finished. The location of the various centers is shown 
 and also the length of the different distances to be taken in 
 the dividers in striking these curves. 
 
 The dotted lines outside the cylinder show ribs for 
 assistance in lagging and in making air spaces under it. 
 The widths of steam and exhaust ports are shown. This 
 also shows the width of the exhaust passage to be 6 inches,
 
 SOME EXAMPLES OF DRAWINGS 43 
 
 with the walls i inch thick. It also shows how the steam 
 passage divides around it and conies up on each side. Vari- 
 ous other details can be seen by looking over the drawings 
 carefully. 
 
 Eccentric and Eccentric Strap 
 
 Two other parts of those same Brazilian engines are shown 
 in Fig. 24, and aside from showing all the dimensions it 
 also shows how the directions for working are given in 
 actual practice. For example : " Cast iron, four a set," means 
 that the material is cast iron and that four pieces, or four 
 eccentrics, are needed on each engine. "No holes in out- 
 side for set screw" shows that the set-screw holes must be 
 drilled and tapped at an angle sufficient to clear the outside 
 or rim, or else some device used which will drill them from 
 the inside. The set screw is given as a f-inch screw with 
 square head. Nothing is said about the threads per inch 
 as this is to be standard in all cases unless otherwise 
 stated, which means 9 threads to the inch. 
 
 The eccentric is in two parts, divided on the center line 
 of the axle, and held together by the studs shown. Although 
 the drawing does not show any threads on these, we know 
 there must be to allow the keys to be used across the top, 
 and in the detail of this stud we find the thread to be if 
 inches long on a i^-inch stud, while the hole for the key is 
 ^f wide and i| inches long. The split key is made of two 
 pieces of sheet steel, each a T 3 ^ piece of steel fastened 
 together with a rivet at the head. The points are opened 
 out after they are in place to prevent their backing out. 
 
 As can be seen the axle is g inches, the key ij inches 
 wide, and the radius of the outer curve around the axle
 
 44 
 
 MACHINE SHOP DRAWINGS 
 
 Eccentric Strap No. 1592 
 
 Vic. 24. Eccentric and Eccentric Strap.
 
 SOME EXAMPLES OF DRAWINGS 45 
 
 5j inches. The total width is 4 inches, while the face is 
 3^ with the edges turned down for the side bearings of the 
 eccentric straps shown above. 
 
 The different diameters of the eccentric strap, where it 
 fits the eccentric, is clearly shown as well as the various 
 curves. The extension that fits the eccentric rod is tapered 
 as shown and the taper is met by a 6-inch radius curve 
 coming from the outside of the strap. The rod is flat and 
 fits into a pocket, shown more clearly in the end view and 
 extending about half-way down into the projection. 
 
 The oil pocket at the top is drilled down into the eccentric 
 strap and from here to the eccentric bearing. At the side is 
 another reservoir, cast into the strap and closed by the 
 screwed plug, i \ inch in diameter and a 14 thread, a special 
 tap for such places. The two halves of the strap are held 
 together around the eccentric by the two |-inch bolts, 
 double nutted and having a pin outside the outer nut. In 
 this case, as with the eccentrics, it takes 4 to make a set 
 and it is so marked on the drawing. 
 
 A Chuck Screw Drawing 
 
 Another example from actual practice is the chuck screw 
 from the Carter Chuck Company as seen in Fig. 25. 
 
 This shows at a glance that the finished length of the 
 screw must be 5^ inches and the largest diameter f inch, 
 so we would take an inch bar and cut it off accordingly. 
 The small end is | inch in diameter and is straight on the 
 outside, but the thread is cut on a taper of i inch per foot, 
 as shown by the note. The thread is n per inch, United 
 States standard form and .57 inch in diameter at the bottom. 
 
 The large end of the taper under the thread is .663 and
 
 46 MACHINE SHOP DRAWINGS 
 
 from here it is turned straight for a distance of ij inches. 
 The thread on the large portion is also 1 1 to the inch but is 
 of the Acme standard form. Both threads are right-handed. 
 This threaded portion is 2 inches long and adding up the 
 
 FIG. 25. A Peculiar Chuck Screw. 
 
 three lengths we see they tally with the total dimension 
 given. The bottom of the thread is .764 inch, the slot in 
 the end is J inch wide and ^ inch deep, giving us all dimen- 
 sions needed to cut this screw from the solid bar. 
 
 ( -4X-- 1 
 
 r 
 
 FIG. 26. The Outside Screw. 
 
 The Outside or Main Screw 
 
 This is shown in section in Fig. 26. The outside dimen- 
 sions are if by 4! inches long with a square thread, cut 
 5 to the inch on the outside over the whole length, and an
 
 SOME EXAMPLES OF DRAWINGS 47 
 
 internal thread of the Acme form cut n to the inch and 3! 
 inches long with a diameter of .895 outside or just .02 inch 
 larger than the screw in Fig. 25 which fits inside of it, 
 giving a play of one one-hundreth of an inch on each side 
 of the screw. 
 
 At the end of the internal screw is a chamber or recess 
 of the same diameter as the outside of the thread, for 
 allowing the chasing tool or tap to run into. This recess is 
 | inch long. Leading into this from the other end of the 
 screw is the hole which the end view proves to be square 
 with slightly rounded corners. This is -^ inch square on the 
 sides and had fillets or corners of -^ inch radius. This 
 shows us that this screw fits on the outside of the inner 
 screw or stud shown in Fig. 25, and that this is turnecl by a 
 wrench having a square end which fits into the square hole 
 shown in the end. 
 
 Detail Drawing of a Special Flange 
 A very good example of a detail drawing giving very close 
 limits is shown in Fig. 27. The drawing is used in connec- 
 tion with a table as the most of the dimensions are repre- 
 sented by letter. Beginning with the 12 small holes on the 
 inside of the flange we find these are to be drilled and tapped 
 for a No. 8-32 tap, meaning a No. 8 machine screw size with 
 32 threads per inch. There are 6 sets or pairs of holes. 
 The next row of holes, six in number, are outside of these, 
 tapped to the same size, while the outer holes have a No. 14- 
 20 tap and are countersunk this being shown by the 
 letters C. S. 
 
 Some of the other holes are shown at the right. One with 
 a f drill, f inch deep and tapped with a f-inch tap having
 
 4 8 
 
 MACHINE SHOP DRAWINGS 
 
 3 
 I 
 
 ( Jaja 1 '! 1< .'"JgTro^ g n !!' 
 
 X 3 .^-^ * I I ^*" :j.|i "tff^Z O~ * ~H ' | 
 
 if ?! i,- - -^~ 
 'i '8
 
 SOME EXAMPLES OF DRAWINGS 49 
 
 a standard thread, 16 to the inch. Then there are 4 holes, 
 90 degrees apart, drilled with a No. 23 drill and tapped 
 with a No. 10-32 tap, while down below is a No. 8-32 tap, 
 | inch deep. 
 
 It is needless to follow all the holes and we will now 
 look at some of the limits imposed, which indicates, although 
 it does not prove, that it is a toolmaker's job. In the right- 
 hand piece it will be seen the half-inch reamed hole must 
 be 1.093 inches from the center line within a thousandth of 
 an inch, meaning that it can be either 1.092 or 1.094 or 
 anything in between. 
 
 In the center drawing everything has limits, some of 
 them, it will be noticed, only containing a maximum or 
 minimum limit, but not both. This means that, in the case 
 of the flange thickness for example, the flange can be 
 between .499 and .500, but not over the larger dimension 
 given; some, on the other hand, have minimum limits 
 given. 
 
 This also shows that cross-sections maybe given in various 
 ways. The center view is a clear, straight cross cut through 
 the center on the line AOB of the left-hand view. In the 
 lower view, on the other hand, the cross-section is not a 
 straight line, but from C to O and from here to D. This is 
 to show a section through the bolt lug D and at the same 
 time show the recess at the right which is | inch wide. 
 The small view gives a part section along the line OE.
 
 CHAPTER IV 
 
 HINTS ON LAYING OUT 
 
 EVERY machinist needs a few good tools, such as a steel 
 square, bevel, dividers, calipers and protractor to measure 
 angles, but he can do more laying out with only a pair of 
 dividers, a straight rule and a scriber than many imagine. 
 
 FIGS. 28 and 29. Finding 4 and 8 equal points. 
 
 It is better to have but few tools and know how to use them 
 than to have a whole kit full and not understand all about 
 them. 
 
 Suppose you want to lay out some templets for bolt 
 holes in flanges for pipe or similar work, to have four, 
 six and eight holes each. All you need are the dividers, 
 scale and scriber. 
 
 Draw a line A B, Fig. 28, take any point for the center,
 
 HINTS ON LAYING OUT 51 
 
 and draw a circle for the outside of the flange, and another 
 circle inside this for the location of bolt holes or bolt diam- 
 eters, as it is called. Two of the four holes will be where 
 line AB cuts the circle at a and b. Take any distance in 
 the dividers, more than half of-AB, and draw the arcs 
 shown inside the circles, using a and b as centers, so as to 
 cross at two points, c and d. Draw a line that will cut both 
 c and d, and extend this to the circles, cutting them at e and/. 
 This line ef will be at exactly right angles to the first line, 
 and e and / will be just half-way between a and b. Prove 
 this by taking the distance ae in your dividers and trying it, 
 Always prove any work of this kind to be sure there has 
 been no slip. This will always give you two lines at right 
 angles without using a square of any kind, and will also 
 divide any distance, as ab, exactly in half. 
 
 Locating the Half-way Point 
 
 To lay out a templet with eight holes, it is simply neces- 
 
 \ sary to locate four more holes half-way between the holes 
 
 |p already laid out in Fig. 28. This can be done by the 
 
 v same method of dividing any distance in two equal parts 
 
 (see Fig. 29). With one leg of the dividers on b, and any 
 
 v distance more than half the distance from b to/, make the 
 
 ^curves shown. With the same setting and the point on/, 
 
 ^ make another curve, cutting the first in c and d. A straight 
 
 s; line through these two points, c and d, will show the point 
 
 g to be half-way between b and/. The other end of the 
 
 line will, if extended, cut the other side of the circle at * and 
 
 r- 1 give half the distance from a to e. Take the distance bg 
 
 or gf and, with dividers on /, mark h. Prove this by also 
 
 "Busing a as a center and cutting ^e first mark at h. Do the 
 Q_ 
 
 CO 
 
 STATE NORMAL SCHOOL 
 UAt AUTS *Vf HOME ECOHOIWBS 
 SANTA BARRARA, CALIFORNIA
 
 52 MACHINE SHOP DRAWINGS 
 
 same at e and b, which will locate ;, and the eight holes 
 are all laid out. Prove them all, and if the work has been 
 carefully done they will be laid out as accurately as though 
 you had used very elaborate tools, probably more accurately 
 than you would do it with a protractor to measure the angles. 
 
 Radius gives One Side of Hex 
 
 To lay out six holes requires no measurements whatever 
 for the distance, as the radius or half diameter of the circle 
 
 FIGS. 30 and 31. Laying out a Hexagon. 
 
 is the right setting for one side of a "hex" or hexagon, as a 
 six-sided figure is called (see Fig. 30). With the same 
 setting used in drawing the circle, place one leg on a and 
 step around, marking b, c, d, e,/one after the other. Prove 
 this by going around the other way and cutting the first 
 marks as shown. Fig. 30 shows the marks at top and 
 bottom and Fig. 31 shows them at the side. Sometimes 
 the plans call for one, sometimes for the other. 
 
 To make a i2-holed templet, divide the distance between 
 the holes as in Fig. 29, and the rest is easy.
 
 HINTS ON LAYING OUT 
 
 53 
 
 Six, Eight and Ten Rule 
 
 Fig. 32 shows another and very handy way of laying out 
 a right angle or square corner with only the dividers and 
 rule, as already in use. This is one of the handiest things 
 for any one to remember, as it comes into play whether you 
 are laying out a small tool, making a try square for yourself, 
 laying out a tennis court, or staking out for a house founda- 
 tion. It is called the "6, 8 and 10 rule" and dates way back 
 to the ancient Greeks, but it's one of the things that never 
 
 b a b 
 
 FIGS. 32 and 33. Two Ways of Laying Out. 
 
 get old. This rule or law is that any triangle whose sides 
 are in the proportion of 6, 8 and 10, no matter whether it 
 is inches, feet or miles, is a right angle. Take in your 
 dividers 6 of any units you want inches, eighths o^ 
 sixteenths and, with one point at a, scribe an arc as at b. 
 Then take 8 of the same units and, with one point again on 
 a, scribe above as at c. Then take 10 of these same parts 
 and, with one point on either arcs b or c, scribe a mark 
 cutting the other arc. Draw a triangle from these points 
 as at a, & and c, and you have a right angle every time. If 
 you had taken the point e instead of &, with the 10 units in
 
 54 
 
 MACHINE SHOP DRAWINGS 
 
 the dividers, the other corner would be at d, and the tri- 
 angle as shown by the dotted lines, but the angle is 90 
 degrees, or exactly a right angle. 
 
 Triangular Method 
 
 Another way you can lay off a square corner without 
 measurements of any kind is shown in Fig. 33. With the 
 dividers at a and any distance in the dividers, mark from 
 b to c. Shift the point to b and draw the arc ac. Where 
 these cut each other, in c, again place the point, with the 
 same distance as before, and scribe the arc b. Then take a 
 scale and draw a straight line from b, through point c, and 
 continue to d. From the point d to a, draw another line 
 ad, and this will be at exact right angles to ab. 
 
 Using this as a start, it is easy to lay out a hexagon as the 
 side be is already there and ab extended to i gives the base 
 line. Keep the distance ab in the dividers, and from b 
 mark off h. From this point mark curve ig. From * draw 
 curve hg. Draw hg and you have three sides of the hexagon 
 done, cbhg. Draw straight lines through ig and ac. With 
 dividers on c and g draw e and /; connect e and / and the 
 hexagon is complete, without measuring an angle of any 
 kind. Prove the work by stepping off the various sides. 
 
 Independent of Try Squares 
 
 From these two methods of finding a square corner you 
 will see that even if all the squares in the world should be 
 suddenly lost, we would have a way of making new ones 
 always at hand. 
 
 Fig. 34 shows this same method applied to laying out a 
 square. The side will be ad. Taking this in your dividers
 
 HINTS ON LAYING OUT 
 
 55 
 
 and with the point on a mark /. From / scribe at e and 
 repeat this form from d. Where these marks cross, gives 
 the corner of the square and the sides can be drawn as is 
 shown. 
 
 In Fig. 35 the square corner is found by the dividing 
 method shown in Fig. 28 and the lines of and de are laid off 
 at right angles in this way. With dividers at o mark g and 
 
 FIGS. 34 and 35. Other Methods of Laying Out. 
 
 h. Connecting these points gives a 45-degree angle and 
 one corner of an octagon. From this you can go on and 
 lay out a complete eight-sided figure as shown. 
 
 If you want to make it of some particular size, lay off 
 one side of the desired length such as hi. At i, draw a line 
 at right angles to the base by the method shown in dotted 
 lines. With distances hi in the dividers and one point 
 at i, draw the half-circle hf. Divide // in half the same as
 
 MACHINE SHOP DRAWINGS 
 
 in Fig. 29, and draw ik. With the distance hi or ik (both 
 the same) mark off kl, Im (where it cuts the dotted line 
 marks one corner), mn and so on around the figure. 
 
 Fig. 36 shows another application of the first principle 
 in dividing up a square or any figure with square corners 
 into equal parts. This idea can be applied in many ways 
 and is a good thing to remember, as well as the other two 
 ways of finding a square corner shown in Figs. 32 and 33. 
 They are very handy in many kinds of work. 
 
 FIG. 36. Dividing the Sides of any Figure. 
 
 Square Corner Without Dividers 
 
 There is also a very neat way of laying out a square 
 corner without dividers, and even the scale can be dispensed 
 with if you have a straight-edge to draw by. 
 
 Suppose you want to make a square corner at A, Fig. 37. 
 Take any distance as AC and draw it any old way; this 
 happens to be nearly 45 degrees. Mark the same distance 
 each side of C, in a straight line as DCB. Join BA and 
 AD, and the corner A is exactly square.
 
 HINTS ON LAYING OUT 
 
 57 
 
 The same thing is shown in Fig. 38, but with the first 
 line EG at a very different angle. HG and GF equal EG, 
 and joining FE and EH completes the corner. This can 
 be done with dividers in the same way, but shows that when 
 you have or can get a straight-edge of any kind you can 
 make a square corner while you would be hunting up the 
 regular tools. 
 
 The best way to see all the workings of these methods 
 is to take a sheet of metal of some kind tin, brass, copper, 
 
 FIGS. 37 and 38. 
 
 or iron and lay them out to a good scale. With the 6, 8, 
 and 10 rule take 3, 4 and 5 inches, or 12, 16 and 20 inches, 
 according to the size sheet you are working on. If you get 
 these principles down fine you will never be stuck on an 
 outside job because you have forgotten your square, and 
 it is mighty handy to know even in laying out jig and similar 
 work, right in the shop itself. 
 
 Something About Angles 
 
 Angles play an important part in mechanical drawing, 
 as we shall see. Suppose we look at the end of a square 
 bar, as in Fig. 39, and we have no means of knowing whether
 
 5 8 MACHINE SHOP DRAWINGS 
 
 the end is square across the bar, or is flat or rounded, as the 
 bounding lines will be the same in any case. It takes a 
 side view to show whether the end is slanting, as in B, 
 this being an angular view, or of any other shape, as in C 
 above. The top view would be as in D. 
 
 This brings us to what is called projection, or the throw- 
 ing out of lines to show what shape a piece really is or 
 what it looks like in different views. 
 
 FIG. 39 
 
 Having a bar 4 inches square we cut the end at an angle 
 that makes the short side of the bar 3 inches shorter than 
 the other, as shown in Fig. 40. The end or top view is 
 square, but as we look horizontally at the slanting" side it 
 appears as a rectangle 3X4 inches, as at A, while if we look 
 square at the angular surface it is 4 X 5 inches, as shown 
 in the angular projection B. The side view is at C. 
 
 Fig. 41 shows the effect of a triangular bar being cut at 
 an angle. The change in the shape is shown by comparing
 
 HINTS ON LAYING OUT 
 
 59 
 
 the true section or end view B with the angular view A, 
 which is an elongated triangle. This is at right angles to 
 
 FIG. 41 
 
 the angular surface. The side view C does not show 
 whether the bar is round, square or triangular.
 
 6o 
 
 MACHINE SHOP DRAWINGS 
 
 Curved Surfaces 
 
 Bodies with flat sides or surfaces are comparatively easy 
 to throw in any sort of projection, but when it comes to 
 curved surfaces it is a different matter. Take a round 
 stick and cut the end at a slight bevel. Look at it square 
 with the cut and see that it is not round but elliptical; look 
 
 FIG. 42 
 
 at it sideways and see that this also shows an ellipse, but 
 with the long axis the other way. Cut it at different angles 
 and note how the ellipses change shape with each angle. 
 
 In mechanical drawing it is necessary to know how to 
 draw these ellipses both to show how they will look and 
 for the purpose of laying out sheet metal to fit such a shape, 
 either for an angular cover or for a stove-pipe elbow.
 
 HINTS ON LAYING OUT 
 
 61 
 
 In Fig. 42 the side view does not give any idea as to its 
 shape. But when we project the lines a and b from the 
 top and bottom of the slanting side, we find that the angular 
 end looks like an ellipse if we look at it in the center and in 
 the direction of the arrow. The top view will, of course, be 
 round as in B. 
 
 FIG. 43 
 
 Fig. 43 shows a round bar cut at a more acute angle, and 
 two projections are made to show how it appears when 
 looked at from two views: either square with the cut or 
 square with the side of the bar. Then diameter A remains 
 the same in all cases, but the long diameter of the ellipse is 
 decidedly different, as can be seen.
 
 62 MACHINE SHOP DRAWINGS 
 
 Laying Out Sheet Metal 
 
 If it was necessary to cut a sheet of metal to fit the end 
 of a bar cut at an angle it might be puzzling unless we could 
 put the piece over the bar and mark around it. But there 
 is a way of laying out all such shapes without marking 
 around the bar, and it is a very handy thing to know. 
 
 Suppose we want to make a funnel like Fig. 44, how will 
 we cut out the sheets so as to form the right shape when 
 rolled up ? This is really two partial cones joined together, 
 and in laying them out we consider them as complete cones 
 so as to get a center or starting-point. We can do this either 
 by drawing down the sides until they meet as at a, or we 
 can figure it out in the same way we do tapers. The large 
 cone tapers from 7 inches to 2 inches in a distance of 5 
 inches, or a taper of 5 inches in 5 inches or i inch to each 
 inch. So we know that the point a is 7 inches from the 
 top, as shown. 
 
 Next we figure out the distance around the funnel at 
 each end by multiplying both 7 and 2 by 3}, or 3.1416, 
 which gives 22 inches around the top and 6.28 inches 
 around the bottom. So, taking a point as b, Fig. 46, with 
 2 inches in the compass or dividers if it is done on metal, 
 draw part of a circle. Then with a 7-inch radius draw 
 another part of a circle. Take the dividers and step off 
 22 inches on the large circle, preferably half on each side 
 of a center line, and connect the points and the center by a 
 line at each end of the curved piece. As these lines must 
 be radial from the center, it is only necessary to step off 
 the distance on one circle, and the larger one is best as there 
 is less chance of error. This curved sheet when rolled
 
 HINTS ON LAYING OUT 
 
 PIG. 44 
 
 FIG. 45 
 
 FIG. 46 
 
 Laying Out Curved Surfaces.
 
 64 MACHINE SHOP DRAWINGS 
 
 up will make the upper part of the funnel, as can be tried 
 with a piece of paper. As no allowance has been made 
 for the lapping we will add a piece on one end, shown by 
 dotted lines, which gives room for riveting or soldering. 
 The same process repeated for the lower end of the funnel 
 is shown in Fig. 45 and needs no further explanation. 
 
 What an Elbow Looks Like 
 
 The left view of Fig. 47 shows the side of an elbow, the 
 angle being as indicated. How shall we lay out a sheet that 
 will make an elbow of this angle? 
 
 The laying out is an easy matter if we follow each step 
 in the program. First, find the width of the sheet by mul- 
 tiplying the diameter by 3}, or 3.1416. This is from A 
 to B. Draw a half-circle on the pipe diameter, as shown, 
 and divide this into any number of equal parts; the larger 
 the scale and the greater the number of divisions the more 
 accurate the layout will be. In this case there are 10 divi- 
 sions, and the circle could just as well be above the line 
 as below, anywhere to get a curve the same as the shape 
 of the body of the piece for laying out the divisions. 
 
 From each point on the circle draw lines vertically to the 
 angular line as i-i, 2-2, etc. Divide half the length of AB 
 into the same number of equal parts, as shown by i, 2, 3, 
 etc., and project the lines down to the lower line of the 
 angle. Draw lines horizontally from the angular line to 
 these vertical lines and make the points as a, b, c, etc. 
 Connect these by an easy curve, as shown. This is half 
 the elbow, and the other side is just the same. Allow the 
 space for riveting, as shown by the dotted lines at B, and 
 the elbow sheet is laid out. If the seam is wanted on the
 
 HINTS ON LAYING OUT
 
 66 MACHINE SHOP DRAWINGS 
 
 long side or at any other point, we need only to begin the 
 layout at that point. 
 
 A Side Outlet 
 
 In Fig. 48 we have a pipe 1 2 inches in diameter with a 
 side outlet 10 inches in diameter. The shape of the end 
 of this outlet to fit the large pipe is not easy unless we lay 
 it out in the same way as the elbow. Here it fits on a curved 
 surface so that both the curve of the piece itself and of the 
 large pipe must be considered. Draw the pipe in position 
 as at the left, to show its size and hight. Figure out the 
 length around it as in the other case and we have 10 X 
 3.1416= 31.416 inches. AB is one-half of this, as we 
 have laid out only half the piece. Draw the half-circle to 
 the lo-inch diameter, either below, as shown, or above the 
 side outlet, and divide this into as many parts as seems 
 necessary. In this case there are six divisions to the 
 quarter-circle. Project the lines upward to the large circle. 
 Divide the long strip into the same number of parts and 
 project lines at right angles to cut these, as the points i, 2, 3, 
 4, 5, etc. Through these draw an easy curve, as shown, 
 which gives the outline necessary to fit against the larger pipe 
 in this case. 
 
 Information About the Screw Thread or Helix 
 We sometimes see screw threads drawn with the curved 
 lines as they appear when you look at a screw that has a 
 fast pitch for a small diameter. In actual drawing for 
 practical purposes we do not even draw the threads, only 
 a few lines to indicate where they are, but it is interesting 
 to know how the other is done. The plan is much the same,
 
 HINTS ON LAYING OUT 
 
 67 
 
 as we shall see, and, having fixed the principle of the thing 
 in your mind it can be applied to any form of laying out 
 that is necessary. 
 
 FIG. 49. Method of Laying Out a Screw Thread. 
 Taking the outside of the screw first, we draw the larger 
 half-circle, as in Fig. 49, and divide into six parts. Then 
 lay out the pitch down the sides and divide this into the 
 same number of parts, drawing lines straight across the 
 body of the screw as 0-6, 1-5, 2-4, etc.
 
 68 MACHINE SHOP DRAWINGS 
 
 Draw lines down from the divisions on the half-circle, 
 cutting the cross-lines, and lay off the intersections as a, b, 
 c, d and e. Joining these, give the curve for the outside of 
 the screw, which is not very pronounced. When it comes 
 to the bottom of the thread we have an example of a fast 
 pitch on a small diameter, for, while the pitch is the same, 
 the diameter is much less. In this case we draw the smaller 
 half-circle, representing the bottom of the thread, and divide 
 this in just the same way. Marking off these intersections 
 we get the much more pronounced curve shown. 
 
 The upper part of this shows a F-thread, while the lower 
 part shows a square thread. The intersections of the dif- 
 ferent points are shown by the small crosses. These show 
 plainly how the thread angles change for each diameter 
 and pitch and why the side clearance on thread tools is 
 such an important matter. By keeping in mind the reasons 
 for all these different laying-out or intersection points, any 
 work of this kind can be handled without difficulty, and it 
 often comes in very handy to know about it. 
 
 Curves Cut by an End Mill 
 
 Laying out in this way can also be used to show the curve 
 that will be cut by an end mill if it is tipped from the ver- 
 tical position. This can be laid out in exactly the same way 
 as the curves for the elbows and other sheet metal work. 
 When in a vertical position a flat surface will be cut as at 
 A, Fig. 50, while by inclining the spindle to the work as at B 
 and C the curves shown will be cut in the metal moved 
 across the face of the cutter. There are many times when 
 this can be used to advantage in tool making and other 
 work.
 
 HINTS ON LAYING OUT 
 
 69 
 
 Laying Out Any Angle You Need 
 It sometimes happens that you want to lay out some 
 particular angle and that no protractor is handy. You 
 can get almost any angle you want and with a good degree 
 
 FIG. 50. Curves Secured with one End Mill. 
 
 of accuracy if care is used and you know how to go about 
 it. Draw a straight line, Fig. 51, as a base, and taking any 
 size in the dividers, draw the arcs shown, and by connecting 
 points a b and c we have a 6o-degree angle. 
 
 Dividing the distance be by the well-known method of
 
 7 o 
 
 MACHINE SHOP DRAWINGS 
 
 taking more than half the distance in the dividers and 
 drawing an arc from each point so that they will cross, then 
 drawing a line through the intersections and we have d, so 
 we know cd or db is 30 degrees or half of cb. 
 
 Dividing db in the same way, always working along the 
 arc and not on the straight lines, we get de or eb and know 
 they must be 15 degrees each. This can be carried on 
 until you get to degrees, dividing 15 into three equal parts 
 by stepping off carefully with the dividers. This gives 5 
 degrees and these can be divided on down to the single 
 degree. 
 
 FIGS. 51 and 52. Dividing to Get any Degree you Want. 
 
 Fig. 52 shows a quarter-circle divided up, as can be done 
 with the divider alone and without a protractor or triangle 
 of any kind. The 90 degrees are divided into three 30- 
 degree angles, irfto a 45, 15 and six 5-degree angles, making 
 90 in all, of course, and -one of these 5-degree spaces is di- 
 vided into five making single degrees. 
 
 Suppose you want an angle of 57 degrees or 3 degrees less 
 than 60. You have only to lay out the 60 degrees as we did 
 at first, then take away 3 degrees as found by dividing one of 
 the 5-degree spaces into single degrees. In this way it is easy
 
 HINTS ON LAYING OUT 71 
 
 to get any number of degrees wanted, or the table on page 72 
 may be found handy if it is remembered that the distances 
 are given for a i-inch radius as shown in Fig. 53. To use 
 it, draw part of a circle in some even inches from a base line 
 and lay off from b to c the distance shown in the table, mul- 
 tiplied by the number of inches of radius used. That is, 
 if you have 4 inches in the dividers in drawing the circle, 
 multiply the value by 4. For accurate laying out it is a good 
 plan to use 10 inches and multiply all the values by 10. 
 
 FIG. 53. Laying Out from a Table. 
 
 By doing this the error is very much less than in attempt- 
 ing to measure on a radius of i inch. To lay off an angle 
 of 24 degrees, find in the table .4158, which means that with 
 the distance ab i inch and the distance be .4158, the angle 
 will be 24 degrees. Or with a xo-inch radius ab, the dis- 
 tance be will be 4.158 inches for a 24-degree angle. 
 
 In the same way we can find any angle by laying it off 
 on metal or paper and measuring the distance, be, from the 
 table.
 
 MACHINE SHOP DRAWINGS 
 
 TABLE OF CHORDS FOR FINDING DEGREES AT I-!NCH RADIUS 
 
 I 
 
 .0174 
 
 24 
 
 .4158 
 
 46 
 
 78i5 
 
 69 
 
 1328 
 
 2 
 
 .0349 
 
 25 
 
 4329 
 
 47 
 
 7975 
 
 70 
 
 .1471 
 
 3 
 4 
 
 53 
 
 26 
 27 
 
 4499 
 .4669 
 
 48 
 49 
 
 8135 
 8294 
 
 7' 
 72 
 
 .1614 
 .1756' 
 
 5 
 
 .0872 
 
 28 
 
 .4838 
 
 5 
 
 8452 
 
 73 
 
 .1896 
 
 6 
 
 1047 
 
 29 
 
 .5008 
 
 5i 
 
 .8610 
 
 74 
 
 .2036 
 
 7 
 
 .1221 
 
 3 
 
 .5176 
 
 52 
 
 .8767 
 
 75 
 
 2175 
 
 8 
 
 1395 
 
 3i 
 
 5345 
 
 53 
 
 .8924 
 
 76 
 
 2313 
 
 9 
 
 1569 
 
 32 
 
 5513 
 
 54 
 
 .9080 
 
 77 
 
 245 
 
 10 
 
 1743 
 
 33 
 
 .5680 
 
 55 
 
 9235 
 
 78 
 
 .2586 
 
 ii 
 
 .1917 
 
 34 
 
 .5847 
 
 56 
 
 9389 
 
 79 
 
 .2721 
 
 12 
 
 .2O90 
 
 35 
 
 .6014 
 
 57 
 
 9543 
 
 80 
 
 .2856 
 
 13 
 
 .2264 
 
 36 
 
 .6180 
 
 58 
 
 .9696 
 
 81 
 
 .2989 
 
 14 
 
 11 
 
 2437 
 .26lO 
 
 .2783 
 
 ii 
 
 39 
 
 .6346 
 .6511 
 .6676 
 
 g 
 61 
 
 .9848 
 i. 
 1.0151 
 
 82 
 S 
 
 1.3121 
 1-3252 
 1-3383 
 
 17 
 
 .2956 
 
 40 
 
 ..6840 
 
 62 
 
 1.0301 
 
 85 
 
 J-35I2 
 
 18 
 
 3129 
 
 4i 
 
 .7004 
 
 63 
 
 1.0450 
 
 86 
 
 1.3640 
 
 19 
 
 3301 
 
 42 
 
 .7167 
 
 64 
 
 1.0598 
 
 87 
 
 1-3767 
 
 20 
 
 3473 
 
 43 
 
 733 
 
 65 
 
 1.0746 
 
 88 
 
 I-3893 
 
 21 
 
 3645 
 
 44 
 
 7492 
 
 66 
 
 1.0893 
 
 99 
 
 1.4018 
 
 22 
 
 .3816 
 
 45 
 
 7654 
 
 67 
 
 1.1039 
 
 90 
 
 1.4142 
 
 23 
 
 3987 
 
 
 
 68 
 
 1.1184 
 
 
 
 Laying Out Figures Having Three, Four, Five, Six and 
 Seven Sides 
 
 Here, in Fig. 54, is a handy method of laying out polygons 
 or figures having from three to seven equal sides. They 
 are only half finished, but this shows the method just as well 
 and can be completed by any one who desires. Starting 
 with a side AB, which is the same in them all, we construct 
 the different figures as follows: 
 
 Three Sides or Triangle 
 
 Take the distance AB in the compass, and with center on 
 A draw arc BC, then with center on B draw AC. When
 
 HINTS ON LAYING OUT 
 
 73 
 
 no. 54. Laying Out Three to Seven-Sided Figure.
 
 74 
 
 MACHINE SHOP DRAWINGS 
 
 they cross at C is the upper point, and joining these three 
 points by straight lines gives the triangle. A similar 
 triangle could be formed by connecting A, B and D. 
 
 Four Sides or Square 
 
 Taking C as a center and distance AB in the compass, 
 draw a complete circle. Draw a line through the center 
 from D to T. With center on B, draw arc ACV. Then, 
 with center on E, draw arc GH, cutting the first arc at /. 
 This gives ABJ as one-half the square. Drawing arc BCR, 
 with A as a center, gives the fourth point / and would make 
 the square AIJB. 
 
 Five Sides or Pentagon 
 
 Take the distance FG or FH in the compass, and with 
 the center on A mark off L and M. Then put center on B 
 and mark off L and K. This gives the five points and by 
 joining ABML and K we have the complete pentagon. 
 
 Six Sides or Hexagon 
 
 Having the circle drawn from C as a center, the radius 
 CB is the length of one side and all that is necessary is 
 to step off the six points ABQPO and N. Connecting 
 these gives a complete hexagon. 
 
 Seven Sides or Heptagon 
 
 Take the distance FP in the compass, and with center on 
 A mark off F, cutting the other arc. Then moving the 
 center to B mark off U, to V and mark T, and so on. Com- 
 ing back the other way, mark off R from B, S from A , and 
 check T by marking it from R. Joining ABVUTS and R 
 gives a 7-sided figure or heptagon.
 
 HINTS ON LAYING OUT 
 
 75 
 
 Another Way of Laying Out Polygons 
 Another way of laying out equal-sided figures is shown 
 in Fig. 55, using 12 sides or a duodecagon as an example. 
 Taking one side as AB, from A draw the half -circle 
 shown with a radius AB. Divide this half-circle into 12 
 parts. Draw radial lines through these points, as A i C, 
 
 A B 
 
 FIG. 55. Another Way. 
 
 A 2 D, etc., and with a compass step off the distance AB 
 from B to C, from C to D, etc. This will give the sides of 
 the i2-sided figure as shown in Fig. 55. 
 
 Laying Out Bolt Holes 
 
 There are several ways of laying out bolt holes, one of 
 which is shown in Fig. 56. Draw a circle the size of the
 
 76 MACHINE SHOP DRAWINGS 
 
 bolt circle and draw the center lines crossing at right angles. 
 Divide the distance OE into 4 equal parts and lay off EB 
 equal to 3 of these parts, making OB equal to 7 parts. 
 Divide the diameter CF into as many parts as there are 
 
 FIG. 56. Handy Way to Lay Out Bolt Holes. 
 
 bolt holes in the circle, 9 in this case. Draw a line from 
 B through the second division to D. Then the distance 
 CD is the distance between the bolt hole centers. Space 
 around to see that no mistake has been made. 
 This may be no easier than figuring out the circum-
 
 HINTS ON LAYING OUT 
 
 77 
 
 ference of the bolt circle and dividing by the number of 
 bolts, but some prefer it to doing calculations of any kind. 
 
 If you prefer to figure it out, the little table which follows 
 will help. This gives bolt holes from 3 to 12 in number. 
 Multiplying the number given after the right number of 
 holes by the diameter of the bolt circle will give the 
 center distance between bolt holes. 
 
 No', of 
 Holes 
 
 Distance between Bolt 
 Centers when Diameter of 
 Bolt Circle is i 
 
 No. of 
 Holes 
 
 Distance between Bolt 
 Centers when Diameter of 
 Bolt Circle is i 
 
 3 
 
 .866 
 
 8 
 
 .3827 
 
 4 
 
 .7071 
 
 9 
 
 342 
 
 I 
 
 .5878 
 .5 
 
 10 
 
 ii 
 
 39 
 .2817 
 
 7 
 
 -4338 
 
 13 
 
 .2588 
 
 Multipliers for Bolt Hole Centers 
 
 If the bolt circle is 10 inches in diameter and there are 
 12 bolts, the distance between centers will be 10 X .2588 
 or 2.588 inches. Or if the bolt circle is 6 inches and has 
 9 holes, multiply 6 X .342 and get 2.052 inches as the center 
 distance between bolt holes. 
 
 A Way of Finding Pulley Diameters 
 Here is a short cut pointed out by Prof. John E. Sweet 
 that may come in handy almost any time. 
 
 In changing pulleys on line shafts or other places it may 
 be desirable to know how much to cut out of or add to a 
 belt, and have it come right. That is to say, if a belt runs 
 over two pulleys 30 inches in diameter, and the pulleys were
 
 7 8 MACHINE SHOP DRAWINGS 
 
 to be changed to 36 inches, the belt would need to be as 
 
 much longer as one pulley is larger around 'than the other. 
 
 The ordinary way to determine that would be to measure 
 
 or calculate the distance around each pair and subtract one 
 
 B 
 
 FIG. 57. Finding Pulley Diameters. 
 
 from the other; but that is not at all necessary, for the 
 difference of the distances around two pulleys of unequal 
 size is the same as the distance around a small pulley 
 whose diameter equals the difference between the diameters 
 of the two.
 
 HINTS ON LAYING OUT 
 
 79 
 
 For example: we have a belt running on a pair of i4-inch 
 pulleys and wish to put on 21 -inch pulleys instead, how 
 much longer must the belt be? 
 
 We can say, offhand and without any figuring, that it 
 must be the same as the distance around a pulley as large 
 as the difference between the two diameters or a 7-inch pul- 
 ley. Multiplying 7 inches by 3^ gives 22 inches. Finding 
 the circumference of the 14 and 21 inch pulleys in the same 
 way, we have 44 and 66 inches respectively and the differ- 
 ence is 22 inches, the same as the diameter of the 7-inch 
 pulley. So the belt must be 22 inches longer, half of this 
 being taken up on each pulley. 
 
 In the same way we can find the total circumference 
 of any number of pulleys by adding the diameters and 
 multiplying the sum by 3} or 3.1416 as we prefer. This 
 fact is probably as old as Egypt, and yet it may be new 
 to many, that the circumference A, in Fig. 57, equals the 
 sum of the circumference of the other two pulleys, B and C. 
 
 Laying Out Equal Spaces 
 
 It sometimes happens that it is necessary to divide an 
 odd dimension into equal spaces. In the case shown in 
 Fig. 58 it was necessary to divide i^ inches into n equal 
 parts. So instead of trying to figure this out in decimals 
 the scale was laid on at such an angle that n spaces of 
 some divisions of the scale just fitted the space; in this 
 case 2f l g- is taken as being n X fV = f- In the same 
 way ii X 1 = 2| could have been used, but it is better to 
 get the rule as nearly right angles as possible across the 
 space. 
 
 All that is necessary is to take any divisions you need,
 
 '8o MACHINE SHOP DRAWINGS 
 
 whether 64ths or inches, and work at each division selected. 
 Then drawing lines parallel to the others and through 
 these points gives the equal divisions desired. 
 
 1 
 
 > 
 
 \l 
 
 FIG. 58. Laying Out Equal Spaces. 
 
 Screw Threads 
 
 In the old days the draftsman had to carefully lay out 
 all threads, whether they were 2 or 20 to the inch, and draw 
 them to the right angle shown at A, Fig. 59, or even show 
 the tops and bottoms of the threads curved as was shown 
 in the paper on projection. At B is shown a square thread 
 drawn in a similar way, while C illustrates the much more 
 sensible way of showing threads that is now almost univer- 
 sally used. 
 
 Here no attempt is made to show the right angle or the 
 right pitch, but only to indicate that a thread is wanted, to 
 show how long this is to be made, what kind of a thread
 
 HINTS ON LAYING OUT 
 
 81 
 
 TIG. 59. Different Ways of Showing Screw Threads.
 
 82 MACHINE SHOP DRAWINGS 
 
 is wanted and the pitch. When we consider that a drawing 
 is no longer a picture to please the eye but a guide for the 
 making or putting together of some useful piece of machin- 
 ery, the good sense of this change will be seen at once. 
 This not only saves time in drawing but prevents any 
 attempt to measure the drawing and makes it necessary to 
 put full instructions in plain language, where it can be 
 seen. 
 
 Some make a practice of showing a thread or two on the 
 end of the piece or at some portion of its length to indicate 
 the kind of a thread, but this seems unnecessary and might 
 be misleading. 
 
 Finding the Size of a Broken Ball 
 This shows a way of using some of the things we have 
 learned in laying out work, together with a good deal of 
 thought, to find out the diameter of a broken ball when 
 only a part of the ball could be had to work from. This 
 looks like a sticker, but here is the way a bright apprentice 
 boy found out the full diameter from the broken piece. 
 
 His first step was to take a pair of dividers as at B, and 
 find the largest circle he could draw on the broken part. 
 Then taking his drawing board he laid out three points 
 abc as at C, by using the dividers to measure these points 
 on the circle drawn from the ball itself. The next step 
 was to draw a-circle through these points as shown at C by 
 taking a distance more than half-way from a to b and 
 striking the arcs shown; then doing the same between a 
 and c and drawing straight lines through these arcs until 
 they cross at O as shown. This is the center of the three 
 points ab and c.
 
 HINTS ON LAYING OUT 83 
 
 Then the line db at D drawn to the diameter of the circle 
 laid out at C gave the part represented by the broken piece. 
 Taking the same distance as was used in the dividers to 
 mark the circle on the broken ball, and setting at d and b, 
 
 B D 
 
 FIG. 60. Finding the Size of a Broken Ball. 
 
 strike the arcs eo and we have the arc deb representing the 
 broken piece of the ball. With the three points deb, a new 
 circle was laid out through these three points which gave a 
 circle representing the full size of the ball.
 
 CHAPTER V 
 
 LAYING OUT SPUR GEARS 
 
 GEAR wheels and gear teeth are often puzzling to those 
 who have not had a direct acquaintance with them, espe- 
 cially the questions of pitch diameter, diametral and cir- 
 cular pitch. As with most problems in mechanics, how- 
 ever, there is nothing difficult about it if we go slow on 
 learning the reasons. 
 
 If we have two shafts carrying pulleys, Fig. 61, A and B, 
 with A on the driving shaft, then A will drive B, as shown, 
 as long as the load on B is not too great to be driven by 
 friction. The distance between the shafts C is called the 
 center distance and the diameter of the pulley where they 
 drive is called the pitch line, so the "pitch diameter," or 
 driving diameter, is the diameter at this line. 
 
 But friction is not enough to drive all loads and it is not 
 positive enough in all cases. Some machines must have an 
 exact relation between the speed of different shafts and all 
 slip must be avoided. So we build up projections on the 
 face of A, Fig. 62, and in order to have these projections 
 turn we cut corresponding grooves in B for these to fit into. 
 To make both wheels alike and to have the teeth uniform 
 we also build up on B and cut grooves in A so we have gear 
 teeth in both wheels, with part of the teeth above the pitch 
 and part below it. But we must remember this pitch line, 
 as it is the most important part of the whole gear. 
 84
 
 LAYING OUT SPUR GEARS 85 
 
 The part of the teeth above or outside the pitch line is 
 called the addendum (added to), and the part below the pitch 
 
 FIG. 6 1 . Friction Disk to Show Pitch Lines. 
 
 FIG. 62. Putting Teeth on the Disk. 
 
 line the dedendum (deducted from). In the language of 
 the shop the addendum becomes the point and the dedendum
 
 86 
 
 MACHINE SHOP DRAWINGS
 
 LAYING OUT SPUR GEARS 87 
 
 the flank, but they mean just the same thing. To keep the 
 points of the teeth from rubbing in the bottom of the space 
 an additional depth is cut here which is called clearance. 
 All the parts of the tooth are shown in Fig. 63. 
 
 Shapes of Teeth 
 
 In the old days when the teeth of gears were mostly cast 
 it was necessary for the patternmaker or millwright to know 
 just how to shape the teeth to have them run smoothly. 
 This is not the case now, as the teeth are cut by standard 
 cutters, which are supposed to have the right form. But 
 it is well to have some idea of the way in which these shapes 
 are laid out and it is not hard to understand. 
 
 Formerly it was all the style to use the epicycloidal tooth. 
 This was laid out by rolling a small circle on the pitch line 
 and letting one point on the edge of the small circle draw 
 the curve. In Fig. 64 the laying out of a rack tooth is 
 being accomplished by the pulley resting against the straight 
 edge at the bottom which represents the pitch line of the 
 rack. Tie a pencil to the pulley rim as at A next to the 
 line and roll the pulley carefully to the right. The pencil 
 will make a mark, as shown by the curve AB when it has 
 made a half revolution.. The size of the pulley or rolling 
 circle varied according to the ideas of the designer and 
 changed the shape of the tooth. For gear wheels they 
 rolled the circle around outside the pitch circle for the point 
 of the tooth, and inside the pitch line for the flank of the 
 tooth. 
 
 The Involute Curve 
 
 The old form of tooth curve has given way almost entirely 
 to what is called the involute curve, which seems to give
 
 MACHINE SHOP DRAWINGS
 
 LAYING OUT SPUR GEARS 89 
 
 better satisfaction in every way, although some still use the 
 epicycloidal form. 
 
 The involute curve can be produced by using the same 
 pulley as before and wrapping a string around it as in 
 Fig. 65. A pencil tied to the free end of the string will 
 make the curve shown if it is kept taut and swung out as 
 shown. In the case of a gear with a pitch line of the size 
 shown, this would give the correct curve, and it will be seen 
 that this would vary in direct proportion to the diameter 
 of the pitch line of the gear and does not in any way depend 
 on the size of another circle as in the other. 
 
 With a rack there is nothing to wrap the string around, 
 and so the sides of the teeth are a straight line, as will be 
 seen in all the cuts showing a rack. The angle generally 
 used is 143 degrees, because this was a very easy angle for 
 the patternmaker to lay off in the old days, being the same 
 angle as the worm thread and the Acme thread. 
 
 Drawing the Involute Curve 
 
 In the actual laying out of gear teeth we do not use a 
 string, but draw it out on paper, or on sheet metal, as in 
 Fig. 66. Draw the circle, which is the pitch diameter of 
 the gear wanted; divide part of the circle into a number 
 of equal parts, as shown. Line i i is at right angles to 
 a line drawn from i to the center of the circle, 2 2 is a right 
 angle to a line drawn from 2 to the center, and so on. Now 
 take the distance o i in your dividers and with point on i 
 draw from o up to the line i i. Then set dividers o 2 and 
 with point on 2 draw up from line i i to line 2 2, and so on 
 until you get up to the proper hight of the tooth. The 
 curve is shown drawn through the crosses on each line. It
 
 9 o 
 
 MACHINE SHOP DRAWINGS
 
 LAYING OUT SPUR GEARS 91 
 
 is not difficult to do with care, but is not often needed in the 
 shop, though it is a good thing to know how. 
 
 The hight of the tooth above or outside the pitch line is 
 what determines the outside diameter of the gear or the gear 
 blank, and this is one of the most puzzling parts about the 
 gear question. The pitch diameter is not marked on the 
 gear, and if we attempt to measure the outside of the gear 
 we go astray unless we thoroughly understand the question. 
 As the outside diameter is dependent on the pitch, it is 
 necessary for us to understand this part first. 
 
 The Pitch of Gears 
 
 When we speak of a screw the pitch is the distance from 
 one thread to the other, but this is not the usual way to 
 measure gear teeth, although it is done in some cases. The 
 customary way is to give the number of teeth for every inch 
 in pitch diameter as the pitch. In this way a gear 4 inches 
 in diameter on the pitch line with 48 teeth would be called 
 a i2-pitch gear, because there were 12 teeth for each inch 
 of pitch diameter. If this gear had 40 teeth it would be 
 lo-pitch, if 32 teeth, 8-pitch, and so on. 
 
 Pitch is sometimes measured from tooth to tooth, but 
 should be designated as circular pitch, which means the 
 distance from any point of one tooth to a similar point of 
 the next on the pitch circle. This is the circumference of the 
 pitch circle divided by the number of teeth on the gear. 
 In the case of the 4-inch pitch diameter gear with 40 teeth 
 the circular pitch would be 4 X 3.1416 divided by 40, or 
 12.5664 divided by 40, which gives a circular pitch of 
 0.31416 inch, or a little more than three to the inch. Little 
 confusion is likely because when we talk of circular pitch
 
 9 2 
 
 MACHINE SHOP DRAWINGS 
 
 we give the dimension in inches, while if it is diametral in 
 pitch, no inches are mentioned, simply a number, as 2, or 8, 
 or 1 6 pitch, as the case may be. 
 
 The comparative table shows how the sizes of the 
 different pitches compare with each other and also the re- 
 lation between the diametral- and circular-pitch systems. 
 
 Size of Gear Blanks 
 
 The system of using diametral pitch is very simple in 
 every way, especially in knowing the size of gear blanks, 
 but it has the drawback of not meaning anything to a man 
 unless he is familiar with gears. This is because we think 
 of dimensions in inches or other definite measurements. 
 Ten diametral pitch doesn't mean anything to us until we 
 figure it out in inches, which is easy to do. If there are 10 
 teeth to every inch in diameter and there are 3.1416 inches 
 on the circumference to every inch of diameter, we know 
 that there are 10 teeth for every 3.1416 inches of the cir- 
 cumference. So if we divide 3.1416 by 10, or whatever 
 the pitch may be, we get the circular pitch in inches, which 
 tells us in language we can understand, that the size or 
 spacing of the teeth is 0.314 inch, or a little over 3 to the 
 inch. 
 
 In Fig. 67 we have a sketch which shows how the pitch 
 affects the size of the teeth. The pitch diameter is the same 
 in all these cases, but we see the difference, which is very 
 close to exact size. The greatest difficulty is in getting out 
 of the notion that 6 pitch, for example, has anything to do 
 with 6 inches or $ of an inch. When you want to think 
 of it in inches, don't forget to divide 3.1416 or 3! by the 
 pitch and you have it.
 
 LAYING OUT SPUR GEARS 
 
 93 
 
 The great advantage of the diametral-pitch system is in 
 the sizing of gear blanks, or finding the outside diameter 
 of the gear. The teeth are designed to project beyond 
 the pitch line just one part of the pitch. That is, a ip-pitch 
 
 FIG. 67. Sizes of Teeth. 
 
 gear tooth is T V of an inch above the pitch line, and as there 
 are teeth all around the gear we must add 2 parts to find 
 the total diameter. 
 
 A 60- tooth gear of 10 pitch will be 6 inches pitch diameter, 
 and the outside diameter will be -^ more, or 6fa, or 6.2
 
 94 
 
 MACHINE SHOP DRAWINGS 
 
 inches in diameter. A 6o-tooth gear of. 12 pitch will be 
 5tV outside diameter, and if it was 4 pitch it would be 
 15! inches outside diameter. 
 
 All this can be made into rules, which are put in as easy 
 a form as possible and their uses explained. 
 
 Working these out by a gear having a 4-inch pitch diam- 
 eter and 40 teeth, we find the diametral pitch by dividing 
 40 by 4 and getting 10 as the answer. 
 
 Outside diameter will be pitch diameter, 4 inches, plus 
 2 parts of pitch = 0.2 or 4.2 inches; or, having only dia- 
 metral pitch and number of teeth, we have 
 
 40 + 2 = 42, 
 
 and dividing by pitch, or 10, = 4.2 inches as before. 
 
 With outside diameter 4.2 and 40 teeth we add 2 to num- 
 ber of teeth, making 42, and divide by outside diameter, or 
 
 42 -r- 4.2 = 10 = 
 diametral pitch. 
 
 To find pitch diameter we can divide the number of 
 teeth, 40, by the diametral pitch, or 10, giving 4 inches as 
 pitch diameter. Having outside diameter, 4.2, and num- 
 ber of teeth, 40, we add 2 to the number of teeth, giving 42. 
 Then multiply the number of teeth, 40, by outside diameter, 
 40 X 4.2 = 1 68, and divide by 42, which gives 4 inches as 
 pitch diameter. 
 
 These rules will help you find about anything you want 
 about the sizes of gears or gear blanks. 
 
 For those who prefer to have everything figured out for 
 them, table No. 3, from the practice of the A. S. Cook Com- 
 pany, Hartford, Conn., will be found very useful for 8, 10, 
 12 and 16 pitch, which are very common. For other cases 
 the rules will be found to work very easily.
 
 LAYING OUT SPUR GEARS 
 
 95 
 
 COMPARISON OF PITCHES 
 
 TABLE No. i 
 
 . TABLE No. a 
 
 Diametral 
 Pitch 
 
 Circular Pitch 
 
 Circular 
 Pitch 
 
 Diametral Pitch 
 
 ll 
 
 2.5133* 
 
 2* 
 
 I-57I* 
 
 4 
 
 2.0944 
 
 ij- 
 
 1.676 
 
 if 
 
 1-7952 
 
 if 
 
 1-795 
 
 if 
 
 I-57I 
 1.396 
 
 1-257 
 
 1 
 
 1-933 
 2.094 
 2.185 
 
 2f 
 
 1.142 
 
 if 
 
 2.285 
 
 3 
 
 1.047 
 
 IT^T 
 
 2-394 
 
 3i 
 
 0.898 
 
 ij 
 
 2-513 
 
 4 
 
 0.785 
 
 
 2.646 
 
 5 
 
 0.628 
 
 
 2-793 
 
 6 
 
 0.524 
 
 
 2.9=17 
 
 7 
 
 0.449 
 
 i 
 
 3.142 
 
 8 
 
 0-393 
 
 H 
 
 3-351 
 
 9 
 
 0-349 
 
 j 
 
 3-590 
 
 10 
 
 0.314 
 
 if 
 
 3.867 
 
 IT 
 
 0.286 
 
 | 
 
 4.189 
 
 12 
 
 0.262 
 
 H 
 
 4-570 
 
 14 
 
 0.224 
 
 I 
 
 5.027 
 
 16 
 
 0.196 
 
 A 
 
 5.585 
 
 18 
 
 20 
 
 0-175- 
 o.i57 
 
 I 
 
 6.283 
 7.181 
 
 22 
 
 0.143 
 
 
 8.378 
 
 24 
 
 0.131 
 
 T\ 
 
 10.053 
 
 26 
 
 O.I 21 
 
 1 
 
 12.566 
 
 - 28 
 
 O.I 1 2 
 
 ft 
 
 i6.755 
 
 3 
 
 0.105 
 
 1 
 
 25-I33 
 
 32 
 
 0.098 
 
 A 
 
 50.266 
 
 36 
 
 0.087 
 
 
 
 40 
 
 0.079 
 
 
 
 48 
 
 0.065 
 
 
 
 As the teeth must extend below the pitch line as far as 
 they do above it, to allow for the points of the teeth in the 
 other gear, the length of the tooth will be two parts of the
 
 96 MACHINE SHOP DRAWINGS 
 
 TABLE FOR TURNING AND CUTTING GEAR BLANKS FOR STANDARD 
 LENGTH TOOTH FROM ASA COOK Co. 
 
 16 1 
 
 Outside Diameter 
 
 i i . ;! 
 No. of 
 Teeth 
 
 10 8 
 
 135 | -180 | .216 | .270 
 Outside Diameter 
 
 4TV 
 
 4A 
 
 1 
 
 1 : j 
 
 sA 
 
 5 T* 
 
 STJ 
 
 stl 
 
 sH 
 
 6 
 
 1 
 
 Is 
 iS 
 
 7& 
 7f[i 
 
 7A 
 
 sA 
 
 6A 
 6A 
 
 
 
 fi5 ff 
 
 &A 
 
 6A 
 6A 
 
 7A 
 
 IS 
 
 8A 
 
 I 
 
 8 
 
 i 
 
 8A 
 8A 
 
 S*
 
 LAYING OUT SPUR GEARS 
 
 97 
 
 TABLE FOR TURNING AND CUTTING GEAR BLANKS FOR STANDARD 
 LENGTH TOOTH FROM ASA COOK Co. Continued 
 
 .135 I -180 I .216 I .270 
 
 Depth 
 
 fTooth 
 
 10 8 
 
 Outside Diameter 
 
 |. 
 
 6A 
 
 6* 
 
 
 
 !t 
 a* 
 
 f' : f 
 
 7A 
 
 I 
 
 
 8 
 
 8A 
 
 8A 
 
 9 
 
 9A 
 10 
 
 ioA 
 
 "A 
 
 io A 
 
 nf 
 n| 
 
 12 
 t 
 
 I2| 
 12* 
 
 I 
 
 13! 
 
 14 
 
 i4l 
 
 Hi 
 14* 
 
 a 
 
 No. of 
 Teeth 
 
 133 
 
 134 
 i,35 
 136 
 
 i37 
 138 
 139 
 
 140 
 141 
 
 142 
 
 143 
 
 144 
 
 145 
 
 146 
 
 147 
 148 
 
 149 
 150 
 
 152 
 1 53 
 154 
 
 3 
 
 i57 
 tS8 
 
 Outside Diameter 
 
 lift 
 
 "A 
 
 13 A 
 
 X 3i 
 14 
 
 12 
 
 "A 
 A 
 
 15 
 
 i3A 
 
 14 
 
 X4A 
 
 I41 ? 
 
 ?4$ 
 *4A 
 
 17 A
 
 98 MACHINE SHOP DRAWINGS 
 
 pitch plus the allowance for clearance at the bottom of 
 the space. 
 
 The clearance allowed by Brown & Sharpe is obtained 
 by adding one-eighth of the tooth depth. A lo-pitch tooth 
 will be f^, or 0.20, and one-eighth of this is 0.016, so that 
 the total tooth depth for a lo-pitch gear is 0.216 inch. 
 
 The thickness of the tooth at the pitch line will, of course, 
 be one-half the circular pitch, as the circular pitch includes 
 a tooth and a space. We found the circular pitch of a 
 lo-diametral-pitch tooth to be one-tenth of 3.1416, or 0.314, 
 and half of this is 0.157; we can find this direct by dividing 
 0.157, which is one-half of 0.314, by the pitch. 
 
 French or Metric Gears 
 
 The French speak of "their gears in a different way, and 
 as there are a number of French automobiles in this coun- 
 try, it may come handy to know just what gears you need 
 to replace one of these. Instead of diametral pitch they 
 speak of "module," which is the pitch diameters in milli- 
 meters divided by the number of teeth in a gear; so if the 
 pitch diameter is 100 millimeters and there are 40 teeth the 
 module is 2.5, which is very nearly the same as a jo-diametral 
 pitch. 
 
 Having the number of teeth and the module, we find the 
 outside diameter by adding 2 to the number of teeth and 
 multiplying by the module. Taking the same example 
 we have 
 
 40 + 2 = 42, 
 
 and 
 
 42 X 2.5 = 105 
 
 millimeters as the outside diameter.
 
 LAYING OUT SPUR GEARS 
 
 99 
 
 A FEW GEARING RULES 
 
 Having 
 
 To Find 
 
 Rule 
 
 i Pitch diameter and 
 number of teeth 
 
 Diametral pitch 
 
 Divide number of teeth 
 by pitch diameter 
 
 2 Outside diameter and 
 number of teeth 
 
 Diametral pitch 
 
 Add 2 to number of teeth 
 and divide by outside 
 diameter 
 
 3 Number of teeth and 
 diametral pitch 
 
 Outside diameter 
 
 Add 2 to number of teeth 
 and divide by diam- 
 etral pitch 
 
 4 Pitch diameter and 
 diametral pitch 
 
 Outside diameter 
 
 Add to pitch diameter 2 
 parts of diametral 
 pitch 
 
 5 Number of teeth and 
 diametral pitch 
 
 Pitch diameter 
 
 Divide number of teeth 
 by the diametral pitch 
 
 6 Number of teeth and 
 outside diameter 
 
 Pitch diameter 
 
 Add 2 to number of teeth 
 and divide this into 
 the product of the num- 
 ber of teeth and the 
 outside diameter 
 
 
 Laying Out the Teeth 
 
 While not many outside of the drawing room have to 
 do the laying out of gear teeth, it may not come amiss to 
 know how it is done. Fig. 68 shows the single-curve tooth 
 method. The first thing is to draw the pitch circle. Then 
 draw the smaller half-circle with the compasses set to one- 
 half the pitch radius as at A. Take one-half this, or one- 
 quarter the pitch radius, and with the center on B draw 
 the arc C. Where this cuts the half-circle is the base for 
 the base circle for tooth arcs, as shown. This should then
 
 MACHINE SHOP DRAWINGS 
 
 
 1 
 
 . . 3 
 
 I S ! 
 
 HI!.' 
 
 5 M " K 1
 
 LAYING OUT SPUR GEARS 
 
 101 
 
 be drawn all around inside the pitch circle, and used as a 
 base from which to draw the tooth arcs after the teeth have 
 been spaced properly. 
 
 Pressure Angles 
 
 This term is applied to indicate the angle at which one 
 tooth presses against the other and affects the laying out 
 of the teeth. This can best be shown by showing a gear 
 
 FIG. 69. Standard I4i-Degree Tooth. 
 
 in a rack, as in Fig. 69. This shows a i4^-degree tooth, 
 which means that the rack tooth has sides at 14^ degrees 
 from the perpendicular, or 29 degrees total angle, as 
 shown. The pitch circle of the gear is drawn in contact 
 with the pitch line of the rack. Then draw the line AB, 
 and after this the pressure line CD at 14 \ degrees. Next 
 draw a line from the center to the pressure line and at right 
 angles to it, and where they meet is the right place for the
 
 102 
 
 MACHINE SHOP DRAWINGS 
 
 base circle of the tooth arcs, as shown. Fig. 70 shows the 
 same thing for the ao-degree pressure angle and the stub 
 tooth. 
 
 The Stub Tooth 
 
 There is, of course, a difference of opinion both as to 
 the pressure angle and the length of tooth. Many are now 
 advocating the 2o-degree angle in connection with a shorter 
 
 FIG. 70. Stubbed 2o-Degree Tooth. 
 
 tooth, among the earliest and most persistent being the 
 Fellows Gear Shaper Company, who began working along 
 this line in 1899. This gives a broader base to the tooth 
 and makes a stronger gear, especially on small pinions 
 where it is most needed. 
 
 In the Fellows system there is no fixed relation between 
 the length of the stub tooth and the standard tooth. In- 
 stead the length varies, as shown by the following table, 
 which also gives proportions of parts of the tooth:
 
 LAYING OUT SPUR GEARS 
 
 103 
 
 TOOTH DIMENSIONS OF FELLOWS STUB-TOOTH GEAR 
 
 Mark on 
 
 Stub Tooth 
 
 Has Depth 
 of 
 
 Thickness 
 
 Above Pitch 
 
 Below Pitch 
 
 Cutter 
 
 Pitch 
 
 Standard 
 Tooth 
 
 Pitch D Line 
 
 Line 
 
 Line 
 
 4 
 
 4 
 
 5 
 
 0-3925 
 
 0.200 
 
 0.250 
 
 ^ 
 
 5 
 
 
 0.314 
 
 0.1429 
 
 0.1785 
 
 f 
 
 6 
 
 8 
 
 0.2617 
 
 0.125 
 
 0.1562 
 
 3j 
 
 7 
 
 9 ' 
 
 0.2243 
 
 O.I 1 1 
 
 0.1389 
 
 A 
 
 8 
 
 10 
 
 0.1962 
 
 O.IOO 
 
 0.125 
 
 j8j- 
 
 9 
 
 ii 
 
 0.1744 
 
 0.0909 
 
 0.1137 
 
 T$. 
 
 10 
 
 12 
 
 0.157 
 
 0.0833 
 
 0.1042 
 
 H 
 
 12 
 
 14 
 
 0.1308 
 
 0.0714 
 
 0.0893 
 
 This shows that with the Fellows system a stub tooth 
 of 4-pitch will be only as deep as a standard tooth of 5-pitch, 
 or a Q-stub will be the same depth as an 1 1 standard pitch. 
 
 The Nuttall Company have also been advocates of the 
 short tooth, but they have adopted a fixed depth based 
 on the circular pitch of the gear. In the standard tooth 
 the addendum is 0.3183 times the circular pitch, while 
 Nuttall advises only 0.25. The dedendum is 0.30 instead 
 of 0.3683, and as the clearance is the same, the total depth 
 is 0.55 times the circular pitch instead of 0.6866, so that we 
 can say the Nuttall stub tooth is only 0.8 as long as the 
 standard tooth in all cases. 
 
 Having turned the gear blank according to the table, 
 or by calculation, it only remains to set the cutter and gage 
 the depth of cut. For this purpose the gear-tooth gages 
 are made, and Fig. 71 shows how it is used. A gage is 
 made for every pitch, and usually kept in the tool room 
 unless a man has a set of his own.
 
 104 
 
 MACHINE SHOP DRAWINGS 
 
 Generating Gear Teeth 
 
 We have not gone into the theory of gear-tooth shapes, 
 as this is not necessary in the making of gears, but is a 
 
 FIG. 71. Using Gear Tooth Depth Gage. 
 
 FIG. 72. Generating the Gear on the Fellows Gear Shaper. 
 
 question to be decided by the designer in the drawing room 
 and tool room. The generating of teeth, however, as done 
 on the Fellows gear shaper, is interesting in several ways.
 
 LAYING OUT SPUR GEARS 105 
 
 The cutter is really a steel gear with hardened teeth, as at 
 A, Fig. 72. This moves up and down across the face of the 
 gear and planes the teeth. In starting to cut a gear, the 
 cutter is fed straight into the gear blank to the proper 
 depth, then both the cutter and the -blank are revolved to- 
 gether so that the teeth are cut, one after the other, as the 
 cutter and gear blank roll together. It is a very ingenious 
 process, and one cutter cuts all gears of that pitch regard- 
 less of size. 
 
 Rotary Cutters 
 
 In usual practice a set of eight rotary cutters is used for 
 cutting all gears, and these are standardized to such an 
 extent that all agree on the cutters to be used for different 
 sized gears, a set of eight being required for each pitch. 
 These are divided as follows: 
 
 No. i cutter will cut gears from 135 to a rack. 
 No. 2 cutter will cut gears from 55 to 134. 
 No. 3 cutter will cut gears from 35 to 54. 
 No. 4 cutter will cut gears from 26 to 34. 
 No. 5 cutter will cut gears from 21 to 25. 
 No. 6 cutter will cut gears from 17 to 20. 
 No. 7 cutter will- cut gears from 14 to 16. 
 No. 8 cutter will cut gears from 12 to 13. 
 
 When using these cutters the proper depth and thickness 
 at pitch line are shown by the following table:
 
 io6 
 
 MACHINE SHOP DRAWINGS 
 
 PROPORTIONS OF GEAR TEETH 
 
 2$ 
 
 
 Depth to be 
 Cut in 
 Gear 
 
 Thickness 
 of Tooth 
 
 PitchLine 
 
 1$ 
 $ 
 
 Depth to be 
 Cut in 
 Gear 
 
 Thickness 
 of Tooth 
 
 Pitch at Line 
 
 Jj 
 
 1.7*6* 
 1.438 
 
 i.*57' 
 
 1.047 
 
 II 
 
 12 
 
 0.196* 
 0.180 
 
 0.143* 
 0.131 
 
 if 
 
 1-233 
 
 0.898 
 
 14 
 
 0.154 
 
 O.I I 2 
 
 2 
 
 1.078 
 
 0.785 
 
 16 
 
 0.135 
 
 0:098 
 
 3j 
 
 0.958 
 
 0.697 
 
 18 
 
 O. I 20 
 
 0.087 
 
 2* 
 
 0.863 
 
 0.628 
 
 20 
 
 0.108 
 
 0.079 
 
 2l 
 
 0.784 
 
 0.570 
 
 22 
 
 0.098 
 
 0.071 
 
 3 
 
 0.719 
 
 0.523 
 
 24 
 
 0.090 
 
 0.065 
 
 3i 
 
 0.616 
 
 0.448 
 
 26 
 
 0.083 
 
 0.060 
 
 4 
 
 0.539 
 
 0-393 
 
 28 
 
 0.077 
 
 0.056 
 
 I 
 
 0.431 
 0-359 
 
 0.3H 
 0.262 
 
 30 
 32 
 
 0.072 
 0.067 
 
 0.052 
 0.049 
 
 7 
 
 0.308 
 
 0.224 
 
 36 
 
 0.000 
 
 0.044 
 
 8 
 
 0.270 
 
 0.196 
 
 40 
 
 0.054 
 
 0.039 
 
 9 
 
 0.240 
 
 0.175 
 
 48 
 
 0.054 
 
 0.033 
 
 10 
 
 0.216 
 
 0.157 
 
 

 
 CHAPTER VI 
 
 LAYING OUT BEVEL GEARS 
 
 BEVEL gears are entirely different in many respects from 
 spur gears, and instead of being able to easily figure out 
 the outside diameter of the blanks, as in the case of spur 
 gears, it is necessary to lay them out in each case unless you 
 happen to have them worked out for exactly the conditions 
 you have in hand. , 
 
 Bevel gears which transmit power at right angles and 
 which have the same number of teeth are often called 
 miter gears, but they are simply bevel gears in which both 
 gears are exactly alike and in which the pitch line is 45 
 degrees from the center line of the gear. 
 
 Of course it is better to become entirely familiar with the 
 terms used in connection with bevel gears so that there may 
 be no confusion and that we can readily understand what 
 is being talked about. For this purpose we reproduce 
 Fig. 73 having the various portions named, and an occa- 
 sional reference to this will avoid any mistakes being made. 
 
 Assume that we have a pair of bevel gears to lay out, 
 one having 24 and the other 32 teeth of 8 pitch. We 
 begin exactly as in the case of spur gears, finding our pitch 
 diameters in the same way. Dividing 24 and 32 teeth by the 
 pitch, we find that the pitch diameters are 3 and 4 inches, 
 respectively. 
 
 As these are to be at right angles, draw center lines A A 
 107
 
 io8 
 
 MACHINE SHOP DRAWINGS 
 
 and BB at right angles to each other, crossing at O, as shown 
 in Fig. 74, which becomes the center of our operations. 
 Measure ij inches each side of A A and 2 inches each side 
 of BB, and draw in the pitch diameter lines PP 1 P 2 as a 
 starting-point. 
 
 These lines show the pitch diameter of both gears, and 
 the next step is to draw a line through O connecting P and 
 
 FIG. 73. The Names of Parts and Angles of a Bevel Gear. 
 
 P 2 , and another line from O to P 1 . These are the pitch 
 lines on which the teeth roll together the same as in a spur 
 gear. 
 
 The length of the teeth is found in exactly the same way 
 as for spur gears, but before doing this, draw the line EE 
 at right angles to the pitch center line, as shown, these lines 
 giving what is known as the edge angle, as shown in Fig. 73. 
 As these gears are 8-pitch, take one pitch or J of an inch
 
 LAYING OUT BEVEL GEARS 
 
 ,109 
 
 and lay it off on the line EE, each side of the pitch center 
 line, as F and G. The line OF then gives the outside angle 
 of the gear, and after laying off clearance, as GH, we have the 
 line OH as the cutting angle, or the line on which the mill- 
 
 FIG. 74. Finding the Angles of a Bevel Gear. 
 
 ing cutters must travel to cut the tooth to the right depth 
 along its whole length. 
 
 This shows very clearly how the depth of a tooth in a 
 bevel gear varies all along its length, growing smaller as it 
 approaches the center. To show this, we have drawn the
 
 no MACHINE SHOP DRAWINGS 
 
 teeth in section X and Y to give an idea of the difference 
 in the size of the tooth at these two points and also to show 
 how the clearance acts the same as in a spur gear. 
 
 TIG. 75. Finding the Bevel Gear Cutter. 
 
 Selecting the Culler 
 
 If the gears have been laid out carefully, you will have all 
 the necessary dimensions and angle for turning the blank 
 and cutting teeth, but it will be necessary to do a little
 
 LAYING OUT BEVEL GEARS ill 
 
 more laying out before you can decide on what cutter is 
 to be used, as this is different from spur gear cutting in this 
 respect. This brings us to Fig. 75, which is the same pair 
 of gears laid out to the angles found before, and the lines" 
 OA and OB are right angles to each other and representing 
 the centers of two shafts on which the gears run. Through 
 the edge angle draw the line meeting A and B, as shown, 
 and measure the distance between the point where the pitch 
 line cuts this and A, also from C to B. These distances 
 will be 1 1 and 3 T 5 ff inches, respectively. 
 
 In selecting the cutter, we assume that we are dealing 
 with a spur gear having the same tooth as the outside end 
 of the bevel gear tooth, and a diameter that corresponds 
 to this as found by these lines at right angles of the pitch 
 line OC. 
 
 The distances we have measured thus become one-half 
 the diameter of spur gears having the teeth, and we multiply 
 these distances by 2, securing a pitch diameter of 3! inches 
 for the small gear and 6| inches for the large gear. Mul- 
 tiply these diameters by the pitch to find how many teeth 
 of this pitch would be in a spur gear of the same size, and 
 we have 30 teeth for the small gear and 53 teeth for the large 
 gear. 
 
 Looking up the table of gear cutters, we find that a spur 
 gear of 30 teeth requires a No. 4 cutter and one of 53 teeth 
 a No. 3 cutter, so that we select these as proper cutters to 
 be used in these gears. 
 
 If we had been dealing with spur gears of 3 and 4 inches 
 in diameter and the number of teeth which the gears actu- 
 ally have, we would have used a No. 5 cutter for the small 
 gear and a No. 4 cutter for the larger gear, but for the bevel
 
 112 MACHINE SHOP DRAWINGS 
 
 gears it has been found necessary to select the proper 
 cutter in this way in order to secure smooth running gears. 
 A very little practice in the laying out of bevel gears of 
 various sizes and having shafts at different angles will 
 enable any one to become familiar with this work and to 
 lay them out without making mistakes of any kind. It is 
 well to become thoroughly familiar with the names of the 
 various parts and angles so as to avoid any chance of con- 
 fusion.
 
 CHAPTER VII 
 
 THE WORM AND WORM WHEEL 
 
 THE worm and worm wheel may be called a combina- 
 tion of a screw and a gear, the screw driving the gear by 
 forcing its teeth along in the thread as the screw turns. 
 With very few exceptions the screw turns the worm and 
 cannot be reversed, although, with a sharp enough angle 
 to the thread, the wheel can be made to turn the worm. 
 When this is done, the worm wheel has a straight face 
 and the combination comes under the head of spiral gears, 
 though the principle is the same. 
 
 There are serious differences of opinion about worm 
 wheels, many of our best designers contending that a 
 worm wheel with a straight face is as good as one with a 
 face that is hobbed to fit the worm, but as we are more 
 accustomed to the curved or hollow faced worm, we will 
 consider that first. 
 
 The first thing to do- is to learn the names of the different 
 parts as shown in Fig. 76 so that all terms used will be clearly 
 understood. 
 
 The next thing is to decide on the ratio between the worm 
 and the wheel. Suppose we wish to reduce the speed of 
 a motor from 2,000 to 50. We divide 2,000 by 50 and find 
 that it is a reduction of 40 to i ; that is, the screw or worm must 
 turn 40 times to one turn of the worm wheel, and for a single- 
 113
 
 114 
 
 MACHINE SHOP DRAWINGS 
 
 thread worm the wheel must have 40 teeth as the wheeel 
 will be moved one tooth for every turn of the worm. 
 
 Calling the worm i inch in diameter and a lead of { inch 
 or 4 threads to the inch, the wheel must have 40 teeth, 
 ^ inch apart on the pitch line, or J inch circular or linear 
 pitch. 
 
 This means that the pitch circumference will be 40 X J 
 inch or 10 inches, and this divided by 3.1416 will give the 
 pitch diameter of the worm gear. This is 3.182 inches as 
 the pitch diameter of the worm. The diametrical pitch 
 
 TIG. 76. Terms Used in Worm Gearing. 
 
 is found by multiplying 3.1416 by the threads per inch of 
 the worm as measured along it, without regard to whether 
 it is single, double, triple, or how many threads are cut on 
 it. In this case we have 4 threads to the inch so that the 
 diametrical pitch will be 3.1416 X 4 = 12.5664. 
 
 Looking up a table of tooth parts for gears with cir- 
 cular and diametrical pitch we find that the addition or 
 distance above the pitch line is .0796, the depth of space 
 below the pitch line, including clearance, .0921, making a 
 total of .1717 inches. 
 
 So we lay off .0796 each side of the pitch diameter of 
 3.182, making the thread diameter 3.3412 inches in diameter.
 
 THE WORM AND WORM WHEEL 115 
 
 To find the total or outside diameter of the blank we must 
 measure the corners from the drawing, as they depend on 
 the width of face we allow, and this varies according to the 
 ideas of the designer. 
 
 Acmezq-Degrce Screw Thread 
 
 American Machlnkt. If. g 
 
 FIG. 77. Acme and Brown & Sharpe ag-Degree Worm Thread 
 
 The thread of the worm is deeper than the thread of an 
 ordinary screw and has an angle of 29 degrees as seen in 
 Fig. 77, while the depth and the flats are given in the table. 
 
 There seems to be some confusion among mechanics
 
 n6 
 
 MACHINE SHOP DRAWINGS 
 
 regarding the 29-degree Acme standard screw thread and 
 the Brown & Sharpe zg-degree worm thread. 
 
 Cir c ; e 
 
 FIG. 78. Showing Undercut Teeth. 
 
 In Fig. 77 the difference between the threads of the same 
 pitch in the two systems is plainly shown. These are of 
 threads of one-inch linear pitch drawn to scale to the
 
 THE WORM AND WORM WHEEL 
 
 117 
 
 proportions given by the thread formulas in connection 
 with the complete tables of the two systems of threads as 
 given on pages following. 
 
 pitch Circl e 
 
 Jlmtrican Machinist. N. r. 
 
 FIG. 79. Excessive Undercutting. 
 
 The angle of the teeth depends on the pitch of the worm 
 and its diameter, this being determined by laying out 
 the worm on paper and drawing one thread.
 
 u8 
 
 MACHINE SHOP DRAWINGS 
 
 GEAR WHEELS 
 
 TABLE OF TOOTH PARTS CIRCULAR PITCH IN FIRST COLUMN 
 
 S 
 
 il 
 
 I" 
 
 "3-9 
 
 (A 
 
 1 
 S 
 
 M 
 o. 
 
 J| 
 
 j 
 
 11 
 
 i 
 
 c 
 
 1 
 
 
 Js 
 
 OJJ 
 
 C 3 
 
 ffl 
 
 sg 
 
 ^* 
 
 J3 
 
 ^ 
 
 
 
 ctf u 
 
 fi 
 
 u 2 c 
 
 W "^ 
 
 ^jH 
 
 
 
 si 
 
 J3*3 
 
 xH 
 
 5 
 
 | K 
 
 I 
 
 H 
 
 i 2 
 
 I" 8 
 
 I 2 
 
 i 
 
 I H 
 
 I' 
 
 r 
 
 ? 
 
 P 
 
 / 
 
 S 
 
 jy 
 
 N-, 
 
 ir+f 
 
 PX.3I 
 
 rx* 
 
 2 
 I J 
 
 A 
 
 1.5708 
 I-6755 
 
 I.OOOO 
 
 9375 
 
 .6366 
 .5968 
 
 1.2732 
 1-1937 
 
 .7366 
 .6906 
 
 1-3732 
 1.2874 
 
 .6200 
 5813 
 
 .6700 
 .6281 
 
 i} 
 
 if 
 
 i 
 
 1-7952 
 1-9333 
 
 .8750 
 .8125 
 
 5570 
 5173 
 
 1.1141 
 1.0345 
 
 6445 
 5985 
 
 i. 2016 
 1.1158 
 
 5425 
 5038 
 
 .5863 
 5444 
 
 l| 
 
 i 
 
 2.0944 
 
 .7500 
 
 4775 
 
 9549 
 
 5525 
 
 1.0299 
 
 4650 
 
 5025 
 
 x rV 
 
 
 2-1855 
 
 7187 
 
 4576 
 
 
 5294 
 
 .9870 
 
 4456 
 
 .4816 
 
 i| 
 
 -A- 
 
 2.2848 
 
 6875 
 
 4377 
 
 ^8754 
 
 5064 
 
 9441 
 
 .4262 
 
 .4606 
 
 ii 
 
 i 
 
 2.3562 
 
 .6666 
 
 .4244 
 
 .8488 
 
 .4910 
 
 
 4133 
 
 .4466 
 
 I f 
 
 If 
 
 2.3936 
 
 6562 
 
 .4178 
 
 .8356 
 
 .4834 
 
 .9012 
 
 .4069 
 
 4397 
 
 
 f 
 
 2.5133 
 
 .6250 
 
 3979 
 
 7958 
 
 .4604 
 
 8583 
 
 3875 
 
 .4188 
 
 1 A 
 
 H 
 
 2.6456 
 
 5937 
 
 .3780 
 
 .7560 
 
 4374 
 
 .8156 
 
 .3681 
 
 .3978 
 
 
 i 
 
 2.7925 
 
 5625 
 
 .358i 
 
 .7162 
 
 4143 
 
 7724 
 
 .3488 
 
 .3769 
 
 JA 
 
 
 2.9568 
 
 53" 
 
 3382 
 
 .6764 
 
 3913 
 
 7?95 
 
 3294 
 
 3559 
 
 
 i 
 
 3.1416 
 
 .5000 
 
 3183 
 
 .6366 
 
 3683 
 
 .6866 
 
 .3100 
 
 3350 
 
 'I 
 
 1 
 
 3-35io 
 3-5904 
 3.8666 
 3.9270 
 4.1888 
 
 .4687 
 
 .4062 
 .4000 
 3750 
 
 2984 
 
 .2546 
 2387 
 
 5968 
 5570 
 5173 
 .5092 
 
 4775 
 
 3453 
 3223 
 2993 
 .2946 
 .2762 
 
 6437 
 .6007 
 5579 
 5492 
 5150 
 
 .2906 
 2713 
 2519 
 .2480 
 2325 
 
 -3141 
 2931 
 .2722 
 .2680 
 -2513 
 
 fi 
 
 xA 
 
 4-5696 
 
 3437 
 
 .2189 
 
 4377 
 
 2532 
 
 4720 
 
 .2131 
 
 2303 
 
 i 
 
 
 4.7124 
 
 3333 
 
 .2122 
 
 4244 
 
 2455 
 
 4577 
 
 .2066 
 
 -2233 
 
 1 
 
 i' 
 
 5-0265 
 
 3125 
 
 .1989 
 
 3979 
 
 2301 
 
 .4291 
 
 .1938 
 
 .2094 
 
 1 
 
 i 
 
 5-2360 
 
 .3000 
 
 .1910 
 
 .3820 
 
 .2210 
 
 .4120 
 
 .1860 
 
 .2010 
 
 1 
 
 ij 
 
 5.4978 
 
 2857 
 
 .l8l9 
 
 3638 
 
 .2105 
 
 3923 
 
 .1771 
 
 .I9M 
 
 A 
 
 x| 
 
 5-5851 
 
 .2812 
 
 .1790 
 
 358i 
 
 .2071 
 
 .3862 
 
 1744 
 
 .1884
 
 THE WORM AND WORM WHEEL 119 
 
 GEAR WHEELS Continued. 
 TABLE or TOOTH PARTS CIRCULAR PITCH IN FIRST COLUMN 
 
 
 || 
 
 - 
 
 *! 
 
 1 
 
 ^ 
 
 81' 
 
 8 
 
 \ 
 
 1 
 
 g 
 
 "oja 
 
 S 
 
 Su 
 
 B 
 
 V 
 
 " 
 
 ! 
 
 ll 
 
 1 
 
 a 
 
 
 "8 
 
 
 
 Ili 
 
 || 
 
 ll 
 
 I! 
 
 ^3 
 
 Jr 
 
 J> 
 
 1> 
 
 B 
 
 ] 
 
 sla 
 
 ?S 
 
 "o"o 
 
 E.1J 
 
 "|j3 
 
 Sr* 
 
 5d 
 
 D 
 
 
 s 
 
 H 
 
 < 
 
 * 
 
 Q 
 
 ^ 
 
 5 
 
 5 
 
 P' 
 
 ? 
 
 p 
 
 t 
 
 5 
 
 IT 
 
 H-/ 
 
 D"+f 
 
 P'X, I 
 
 P'X-.sss 
 
 i 
 
 2 
 
 6.2832 
 
 .2500 
 
 .1592 
 
 .3183 
 
 .1842 
 
 3433 
 
 155 
 
 1675 
 
 4 
 
 2\ 
 
 7.0685 
 
 .2222 
 
 .1415 
 
 2830 
 
 1637 
 
 3052 
 
 -1378 
 
 .1489 
 
 3*5 
 
 2\ 
 
 7.1808 
 
 .2187 
 
 1393 
 
 -2785 
 
 .1611 
 
 3003 
 
 1356 
 
 .1466 
 
 f 
 
 3* 
 
 7-3304 
 
 2143 
 
 .1364 
 
 .2728 
 
 1578 
 
 .2942 
 
 .1328 
 
 .1436 
 
 | 
 
 2* 
 
 7.8540 
 
 .2000 
 
 1273 
 
 .2546 
 
 1473 
 
 .2746 
 
 .1240 
 
 1340 
 
 | 
 
 2| 
 
 8-3776 
 
 .1875 
 
 .1194 
 
 2387 
 
 .1381 
 
 2575 
 
 .1163 
 
 .1256 
 
 T 4j- 
 
 2f 
 
 8.6394 
 
 .l8l8 
 
 .1158 
 
 2316 
 
 .1340 
 
 .2498 
 
 .1127 
 
 .1218 
 
 
 
 3 
 
 9.4248 
 
 .1666 
 
 .Io6l 
 
 .2122 
 
 .1228 
 
 .2289 
 
 1033 
 
 .1117 
 
 ! 
 
 
 10.0531 
 
 .1562 
 
 0995 
 
 .1989 
 
 .1151 
 
 .2146 
 
 .0969 
 
 .1047 
 
 
 3* 
 
 10.4719 
 
 .1500 
 
 0955 
 
 .1910 
 
 .1105 
 
 .2060 
 
 0930 
 
 .1005 
 
 
 
 10.9956 
 
 .1429 
 
 .0909 
 
 .1819 
 
 .1052 
 
 .1962 
 
 .0886 
 
 0957 
 
 
 4 
 
 12.5664 
 
 .1250 
 
 .0796 
 
 1591 
 
 .0921 
 
 .1716 
 
 0775 
 
 .0838 
 
 
 4i 
 
 14.1372 
 
 .1111 
 
 .0707 
 
 .1415 
 
 .0818 
 
 .1526 
 
 .0689 
 
 0744 
 
 
 5 
 
 15.7080 
 
 .1000 
 
 .0637 
 
 1273 
 
 737 
 
 1373 
 
 .0620 
 
 .0670 
 
 A 
 
 Si 
 
 16.7552 
 
 0937 
 
 0597 
 
 .1194 
 
 .0690 
 
 .1287 
 
 .0581 
 
 .0628 
 
 A 
 
 5* 
 
 17.2788 
 
 .0909 
 
 0579 
 
 .1158 
 
 .0670 
 
 .1249 
 
 .0564 
 
 .0609 
 
 t 
 
 6 
 
 18.8496 
 20.4203 
 
 0833 
 .0769 
 
 0531 
 .0489 
 
 .I06l 
 .0978 
 
 .0614 
 .0566 
 
 .1144 
 i55 
 
 0517 
 .0477 
 
 -0558 
 0515 
 
 
 7 
 
 21.9911 
 
 .0714 
 
 0455 
 
 .0910 
 
 .0526 
 
 .0981 
 
 -0443 
 
 .0479 
 
 T \ 
 
 71 
 
 23.5619 
 
 .0666 
 
 .0425 
 
 .0850 
 
 .0492 
 
 .0917 
 
 .0414 
 
 .0446 
 
 1 
 
 8 
 
 25-1327 
 
 .0625 
 
 .0398 
 
 .0796 
 
 .0460 
 
 .0858 
 
 .0388 
 
 .0419 
 
 ^ 
 
 9 
 
 28.2743 
 
 0555 
 
 0354 
 
 .0707 
 
 .0409 
 
 .0763 
 
 0344 
 
 .0372 
 
 ^5 
 
 10 
 
 31-4159 
 
 .0500 
 
 .0318 
 
 .0637 
 
 .0368 
 
 .0687 
 
 .0310 
 
 0335 
 
 iV 
 
 2fr 
 
 16 
 
 20 
 
 50.2655 
 62.8318 
 
 .0312 
 .0250 
 
 .0199 
 0159 
 
 .0398 
 
 .0230 
 .0184 
 
 .0429 
 0343 
 
 .0194 
 0155 
 
 .0209 
 .0167
 
 120 MACHINE SHOP DRAWINGS 
 
 On small worm wheels the teeth will be undercut as in 
 Fig. 78, while Fig. 79 shows the effect produced if we 
 
 /pitch | 
 
 FIG. 80. Showing Absence of Undercutting. 
 
 turn the blank small (which has the effect of moving the 
 pitch line out nearer the ends of the teeth) the undercut-
 
 THE WORM AND WORM WHEEL 121 
 
 ting being increased in this case. This gives us a clue 
 toward avoiding this undercutting by turning the blank 
 large as in Fig. 80, which throws the pitch line nearer the 
 base of the tooth. This wheel was sized by the following 
 rule, which is used by the Brown & Sharpe Manufacturing 
 Company for worm gears of less than 30 teeth: 
 
 Multiply the pitch diameter by .937 and add 4 times the 
 addendum. This gives the throat or small diameter of 
 the blank. The large diameter must be laid out as before. 
 Figs. 8 1, 82 and 83 show different types of worm wheels. 
 One hobbed, one cut plain with skew teeth, and the other 
 is used for dividing wheels for indexing. 
 
 A worm can be run in any spur gear by setting the worm 
 at the right angle, although this is not often done. 
 
 There is no fixed relation between the diameter of the 
 worm and the speed of the worm wheel. The diameter 
 of the worm may be of almost any size, but it is not cus- 
 tomary to have the worm less than 4 times the pitch or 
 distance between threads, but it can be as much larger 
 as necessity of design demands. 
 
 The speed ratio between the worm and wheel can be 
 varied by using double, triple, quadruple or sextuple 
 threads as is sometimes done. This means that the wheel 
 will be moved 2, 3, 4, or 6 teeth instead of one, for every 
 turn of the worm. The hob must be of the same pitch 
 and lead as the worm in order to cut the worm teeth at 
 the right angle. 
 
 Small worm wheels that are to be hobbed should be 
 driven by positive gearing at the right speed and not be 
 allowed to depend on the hob to turn them, although this 
 can be safely done on larger wheels, say of 20 or more teeth.
 
 I2 2 MACHINE SHOP DRAWINGS 
 
 Where worm wheels are not hobbed it is better to cut the 
 teeth straight across except for the angle necessary to 
 match the thread. In fact many believe they are just as 
 good when cut in this way. 
 
 FIG. 8 1 FIG. 82 FIG. 83 
 
 Different Types of Worm Wheels. 
 
 As an instance of this we are all familiar with the Sellers 
 method of driving their planers and know that the screw 
 working into a plain rack has given excellent service and 
 has almost never given trouble from excessive wear.
 
 THE WORM AND WORM WHEEL 123 
 
 For dividing or index wheels on all kinds of machinery 
 the form of wheel shown in Fig. 83 is generally preferred. 
 It is a neat looking wheel, and where it has to be turned by 
 hand, as is sometimes the case, it is much more pleasant 
 to handle than either of the other forms. 
 
 The length of the hob for any wheel is not a fixed quan- 
 tity, but it should be at least one thread longer than the worm 
 which is to be run on the wheel. Worms are usually made 
 as long as will bear on any of the teeth of the wheel. 
 This means a worm of say 10 threads for a 5oo-tooth wheel, 
 which should be longer than a worm of perhaps 6 threads 
 on a wheel of 120 teeth or of 3 threads on a 3o-tooth 
 wheel, while it is also possible to use a short worm on a 
 large wheel it is necessary in each case to have the hob one 
 thread longer than the worm to be used.
 
 CHAPTER VIII 
 
 SKETCHES ROUGH AND OTHERWISE 
 
 THE first object of a drawing is to give a clear idea of 
 the shape of the pieces wanted and to show the dimensions. 
 While a finely executed drawing, with smooth lines and nice 
 shading, makes a pleasing picture, it may not be nearly 
 as valuable as a rough sketch that has every dimension 
 correct. The sketch may not show everything in its true 
 proportion, but if the figures are right no one should be 
 misled as there is no excuse for measuring a drawing when 
 all the dimensions are given. One of the best things to 
 do for practice is to sketch any tool or object around the 
 shop, such as the anvil, a lathe dog, pair of calipers, a pulley 
 or a hacksaw frame, so as to be able to make a new one 
 just like the other. This teaches us to be careful to put 
 down all the changes of shape and all the dimensions and 
 to be careful that the figures are right. Suppose a back 
 gear on the lathe breaks and we want a new one made that 
 will be sure to fit. Any good, bright boy can make a sketch 
 that will show all the necessary details, can measure all the 
 dimensions, count the teeth and have a drawing from which 
 any mechanic can make a new gear. It does not matter 
 so much how it looks if the dimensions are right, as they 
 tell the story. If no draftsman is handy the gear can be 
 made from the sketch itself. 
 
 Take a plain bolt or nut, sketch it so that you can put 
 124
 
 SKETCHES ROUGH AND OTHERWISE 125 
 
 the dimensions on the right places and any one can read 
 them. For this purpose some sort of a perspective is best. 
 This cannot be done with complicated pieces, but for 
 simple work it is easy to make something that is often more 
 understandable than the regular drawing. In Fig. 84 no 
 attention is paid to getting circles round or lines straight, 
 only to have it give an idea of the general shape of the 
 piece wanted. Any one who could make a mistake in 
 making bolts from such a sketch has no place in a machine 
 shop. This shows the bolt to be 4 inches long under the 
 head with a i3-pitch United States standard thread cut 
 i inches on the end. The bolt is \ inch rough, hexagon 
 head, inch thick and ij inches across the flats, but not 
 finished. Don't be afraid to put any information necessary 
 on the sketch or on any drawing. It is better than leaving 
 a lot to the imagination as some draftsmen seem to take 
 pride in doing. It 's a good plan not to put the same dimen- 
 sion on twice in different places as there is a chance of 
 getting one of them wrong, which makes confusion. Have 
 the sketch tell all it can either by figures or notes; it can't 
 give too much information. 
 
 Fig. 85 is a steel gage, \ inch thick all over, 2 inches long 
 in the main part, with the end projection \ inch each way, 
 leaving a J-inch corner as shown and the round corner with a 
 f-inch radius. The fillet is not important so long as it 
 is rounded out enough to prevent cracking in hardening. 
 
 Fig. 86 shows a small connecting rod, 24 inches center 
 to center, which is the important dimension. The hole at 
 the left is 2 inches in diameter and at the right it is 3 X 4 
 inches for an adjustable box. This opening is shown 
 divided each side of the center so that the total length of
 
 126 
 
 MACHINE SHOP DRAWINGS 
 
 A... 
 
 Shop Sketches.
 
 SKETCHES ROUGH AND OTHERWISE 127 
 
 the rod will be 24 + 2\ + 3 = 29^ inches. The ends 
 are 2 inches thick and the central portion is round, 2 inches 
 in diameter. 
 
 Making sketches is also splendid training in another way. 
 It teaches us to be observing of little details. Most of us 
 look at a thing without seeing more than the bare outline. 
 To test this, lay twenty common articles on a table or bench, 
 ask a man to look at them for a full minute and then go 
 away and make a list of them. Seems easy, of course, but 
 just try it yourself and see how much easier it is to forget 
 from quarter to one-half of them. But in making a sketch 
 we have to note the details and we remember them. 
 
 Let me again impress the importance of not forgetting 
 any necessary dimension. It may not matter much if 
 you can go and take another look at it, but it's a different 
 proposition when you are sent off a few hundred miles to 
 sketch a broken piece and find some dimension is missing. 
 You'll feel pretty cheap and you can just about imagine 
 the complimentary remarks that the boss is making to him- 
 self even if he refrains from saying them. 
 
 It is not the object of this book to make draftsmen, 
 but to show a boy or man who has never had the chance to 
 study anything about drawings, how they can be used in 
 every-day work and how to read them so that there will be 
 no need to ask the boss or the other fellow anything about 
 the next blue-print that comes along. 
 
 More than that, it is handy and often necessary to be able 
 to put your ideas of a new tool or other device on paper 
 so as to explain it to some one else. It saves lots of talking 
 and it can be understood much more quickly if you can 
 make a few rough sketches.
 
 128 MACHINE SHOP DRAWINGS 
 
 The sketches shown with this are only useful with pieces 
 of a simple nature. When it comes to more complicated 
 work, such as the head of a lathe or any other part of 
 machine, it is necessary to read the regular drawings where 
 only one view of a piece can be seen at once, as in looking 
 at the end of a pipe or bar of steel, or the side of a machine 
 which may have much of its mechansim on the inside. 
 But that has already been learned by a little patience and you 
 will have no trouble in following it up from time to time 
 with practical examples along that line. For a beginning 
 let me suggest that you make sketches of various objects 
 in any kind of perspective that comes easiest to you. 
 
 Different Kinds of Perspective 
 
 It is a great gift to be able to sketch rapidly and correctly 
 in perspective, as you can convey your meaning to any 
 one without much chance of being misunderstood. But 
 though many of us cannot attain to this we can cultivate a 
 little skill in this by paying a little attention to either "iso- 
 metric" or "cavalier" projection, which can be used very 
 readily. In the isometric projection the vertical lines re- 
 main vertical, but the horizontal lines take on an angle of 
 30 degrees from the horizontal as in Fig. 87. The beauty 
 of this kind of projection is that you can draw to scale 
 by measuring along the isometric lines and lay out simple 
 pieces of work without any difficulty. The piece shown 
 in Fig. 88 would be rather difficult to sketch so that a black- 
 smith would understand it, certainly not without two or 
 three views of it, but the sketch given leaves no doubt in the 
 matter at all. 
 Perhaps a still better example is the steam-fitting job
 
 SKETCHES ROUGH AND OTHERWISE 129 
 
 FIG. 87. Isometric Sketching. 
 
 FIG. 88. A Sketch that a Blacksmith Can Understand.
 
 I3 o MACHINE SHOP DRAWINGS 
 
 shown in Fig. 89. Try to show this in the regular way and 
 see how many steam fitters know just what you want with- 
 out a lot of explanation. But the youngest boy in the shop 
 can tell what the sketch means without a chance of making 
 a mistake. 
 
 FIG. 89. A Sketch of Piping that Shows Just What You Want 
 to Know. 
 
 Another kind of perspective is shown in Fig. 90 and is 
 known as the "cavalier." Here the base line remains hori- 
 zontal and the other lines go up at an angle of 45 degrees. 
 Some modify this to 30 degrees and it answers the purpose 
 just as well, the idea being to make it plain and not to have 
 an artistic sketch.
 
 SKETCHES ROUGH AND OTHERWISE 131 
 
 Sketches of this kind are being used in many shops, 
 especially to show the toolmaker just how new jigs and 
 
 FIG. 90. Two Other Kinds of Sketches. 
 
 fixtures are to be made, and it is found that they save much 
 more time in the tool room than they cost to make in the 
 drawing room.
 
 I3 2 MACHINE SHOP DRAWINGS 
 
 Practise a little with either kind, laying off distances by 
 rule if necessary and getting as good an idea as you can of 
 how to make something that looks like the piece you have 
 in mind. You can buy paper all ruled for the isometric 
 perspective and it then becomes a case of following the 
 lines, using a little judgment as to curves and joints. But 
 it is difficult to make a sketch that will not be more clear 
 to the average mechanic than most of the regulation blue- 
 prints, although he must learn to read anything that comes 
 along, and can do so after the many examples shown in this 
 book. 
 
 Handling Drawing Tools 
 
 There is only one way to learn to handle drawing tools 
 and that is to handle them. No instructions will go very 
 far in teaching you much about them. Use ordinary com- 
 mon sense and do not forget that they are rather delicate 
 instruments that should not be abused, and you will have 
 no trouble whatever. 
 
 It isn't necessary to get an expensive set of tools nor 
 even a large .set, as a few fairly good tools are better than 
 a large set that are never satisfactory. For about five 
 dollars you can get a s<et of tools that will answer your pur- 
 pose nicely. It is of course handier to have the dividers 
 and compasses separate as it saves changing them from 
 one to the other, but you can get along very nicely with 
 these and do good work if you are careful. It is far better 
 to get a small set and have them good than a large set of 
 poor instruments. 
 
 Practise making circles with the compasses, both large 
 and small circles, to get used to swinging the compasses
 
 SKETCHES ROUGH AND OTHERWISE 133 
 
 clear round the circle, and spending more time on small 
 circles as they are harder to draw. Practise placing the 
 
 . Ordinary Concrete Coursed Hubble 
 
 FIG. 91. Standard Cross-Sections used by the General Electric Co. 
 
 point where you intend to instead of somewhere near it. 
 You will find this specially useful in drawing in fillets and in 
 laying out work to see where you have sufficient clearances.
 
 134 
 
 MACHINE SHOP DRAWINGS 
 
 Draw curves first and then draw the straight lines to 
 meet them and you will find it much easier to make a neat- 
 looking drawing. 
 
 Draw a center line first and work from this even if the 
 piece is symmetrical and the same shape and size all around. 
 The center line is a necessity when the piece is not uniform 
 and should always be used. 
 
 Standard Cross-Sections 
 
 Although it is customary in most shops to put the names 
 of the material on the drawing, some use a standard of 
 cross-sectioning or cross-hatching to show the kind of 
 material. The one shown is from the drawing room of 
 the General Electric Company and was their standard. 
 They generally use a plain cross-section, however, and 
 name the material to be used on the drawing. There are 
 places, however, as in electrical work, where it makes it 
 much clearer to use a different style of cross-sectioning, as 
 then we can easily pick out the insulating material from 
 the metal. At any rate it is well to know what the different 
 styles mean and Fig. 91 shows us just what it is.
 
 INDEX . 
 
 PAGE 
 
 Addendum 85 
 
 Angles, something about 59 
 
 Angular views of bars 58 
 
 Assembly drawings 17 
 
 Back rest for ratchet drill 38 
 
 Bench lathe head 25 
 
 gears, laying out 107 
 
 Boiler setting 36 
 
 Bolt and nut 13 
 
 hole table 77 
 
 holes, laying out 75 
 
 Broken ball, finding size 82 
 
 sections 16 
 
 Card drawing 20 
 
 Cavalier perspective 1 28 
 
 Center lines 5 
 
 Chuck screws 45 
 
 Circular pitch 9i~95 
 
 Clearance 86 
 
 Cross-sections, standard 133 
 
 Curved surfaces 60 
 
 Curves cut by end mill '. 68 
 
 Cutters for bevel gears *. no 
 
 for spur gears 105 
 
 Cycloidal curve 88 
 
 Cylinder drawing, locomotive 40 
 
 Dedendum 85 
 
 Degrees, table for rinding 72 
 
 135
 
 136 INDEX 
 
 PAGE 
 
 Detail drawings 17 
 
 Diameters of pulley 77 
 
 Diametral pitch 9 I- 95 
 
 Dividing distances equally 51 
 
 Dotted lines 5 
 
 Drawing tools, handling 130 
 
 Eccentric and eccentric strap 43 
 
 Elbow, laying out 64 
 
 End mill, curves cut by 68 
 
 Equal spaces, laying out 78 
 
 Examples from the shop 1 1-25 
 
 Finding any degree 70 
 
 Five sides, or pentagon 74 
 
 Five views, where needed 6 
 
 Flange drawing 47 
 
 Flank of gear tooth 86 
 
 Four sides or square 74 
 
 French drawing of a worm 32 
 
 or metric gears 98 
 
 Funnel, laying out 62 
 
 Gear blanks, size of 92-96 
 
 teeth, generating 104 
 
 laying out 99 
 
 shapes of 87 
 
 sizes of 93 
 
 tooth cutters 105 
 
 gage 104 
 
 proportions 1 06 
 
 wheels, table of tooth parts in 
 
 Gearing, rules for 99 
 
 Gears, pitch of 91 
 
 Generating gear teeth 1 04 
 
 Grinder spindle details 34
 
 INDEX 
 
 137 
 
 PAGE 
 
 Handling drawing tools 130 
 
 Helix, drawing 66 
 
 Heptagon s 74 
 
 Hexagon 74 
 
 Hints on laying out 50 
 
 Involute curve 87 
 
 Isometric perspective 128 
 
 Large lathe head 28 
 
 Lathe center . 1 1 
 
 head, bench 25 
 
 large 28 
 
 Laying out angles 70 
 
 out bevel gears 107 
 
 bolt holes 75 
 
 elbow 64 
 
 equal spaces 78 
 
 gear teeth 99 
 
 polygons 72 
 
 sheet metal 62 
 
 spur gears 84 
 
 square corners 53 
 
 square, hexagons, etc 50 
 
 work 50 
 
 Locomotive cylinder 40 
 
 details 30 
 
 eccentric drawings 43 
 
 Measuring drawings a 
 
 Metric or French gears : 98 
 
 Monkey-wrench, drawings of 17 
 
 Nut and bolt 13
 
 I3 8 INDEX 
 
 PAGE 
 
 Parts, of gear teeth 86 
 
 Pentagon 74 
 
 Perspective 2, 18, 128 
 
 Pieces of uniform shape i 
 
 Pitch diameter 85 
 
 of gears 9 1 
 
 Placing views in a drawing '...... 3 
 
 Plan view 6 
 
 Points to remember 5 
 
 Pressure angles - 101 
 
 Projection, third angle y 
 
 Pulley diameters 77 
 
 Ratchet drill back rest 38 
 
 Reading drawings '. t 
 
 Rules for gearing . . 99 
 
 Screw threads 80 
 
 thread, laying out 66 
 
 Seven sides or heptagon 74 
 
 Shade lines $ 
 
 Shapes of gear teeth 87 
 
 Sheet metal, laying out 62 
 
 Side outlet for pipe 66 
 
 Six sides or hexagon 74 
 
 Size of gear blanks 92-06 
 
 Sketches, rough and otherwise 1 24 
 
 Solid lines $ 
 
 Speed ratio 121 
 
 Spur gears, laying out 84 
 
 Square 74 
 
 corners, laying out 53 
 
 Standard cross-sections 133 
 
 Stub teeth 102 
 
 Table for bolt holes 77 
 
 for finding degrees 72
 
 INDEX 139 
 
 PAGE 
 
 Tabulated drawing 22 
 
 Third-angle projection 3 
 
 Threads, how they are drawn 80 
 
 Three sides or triangle 72 
 
 views, when needed 3 
 
 Triangle 72 
 
 Worm and worm wheels 113 
 
 threads 115
 
 MESA 
 BRANCH 
 
 DATE HOUR 
 
 TJ" 
 
 NAME 
 
 
 
 
 APR 22 68 
 
 I
 
 A 000 588 449 9 
 
 2296 
 
 L