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I 




MACHINE DEAWING 



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:PUDLISHERS of »00K.S. FOR^i 

Coal Age ^ Electric Railway Journal 
Electrical WDrld v Engineering News-Record 
American Machinist v Jhe Contractor 
Engineering 8 Mining Journal ^ Po we r 
Metallurgical 6 Chemical Engineering 
Electrical Merchandising 

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INDUSTRIAL EDUCATION SERIES 



MACHINE DRAWING 



PREPARED IN THE 

EXTENSION DIVISION OF 
THE UNIVERSITY OP WISCONSIN 



BY 
RALPH W. HILLS 

IKSTSnCTOB IN MECHANICAL DRAWINQ IN TBI 
UNTVBSaiTV BXTBNSION DIVIUON 



First Edition 
Seconp Impression 



• •. 



^ ■* <* • ■* ^ ^ ■> 









McGRAW-HILL BOOK COMPANY, Inc. 

239 WEST 39TH STREET. NEW YORK 



LONDON: HILL PUBLISHING CO., Ltd. 

6 & 8 BOUVERIE ST., E. C. 
1917 



¥ 
^ 






1^ 



.^/; 



coptright, 1917, by the 
McGbaw-Hill Book Compant, Inc. 



•* • 

,*♦« * * 

• ••-•_•• •« ••* 

^.' : :•: •• : ••• 



THK MAPUE PRESS VORK PA 



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PREFACE 

This book aims to teach the fundamental principles of mechan- 
ical drawing to men who wish to become draftsmen, or who for 
any other reason wish to acquire a working knowledge of the 
subject as practiced in the l;>est drafting offices. The mcUerial in 
this volume is the first half of the instruction papers in Machine 
Drawing y as developed and used by the Extension Division of the 
University of Wisconsin. Part of the material has been taken 
from WooUey and Meredith's "Shop Sketching," of the Univer- 
sity Extension Division series. The second volume, Advanced 
Machine Drawing, will he largely devoted to the applications of 
machine drawing to the more specialized lines of work, such as 
gearing, isometric, cabinet, and other special methods of projection, 
electrical, structural, and piping conventions, and advanced prob^ 
lems in detail and assembly drawings of complete machines, sketch- 
ing, intersections and developments, and sheet metal paitern drawing. 

In order to secure the interest of the student at the outset, 
working drawings are made by the student from the very begin- 
ning. The text and the problems have been carefully prepared 
and arranged so as to develop speed, accuracy, neatness, and a 
knowledge of the best drafting room practice. Believing that 
draftsmen should be able to make neat, clear, comprehensive, 
freehand sketches of machine parts, the author has introduced a 
chapter on technical sketching. In addition to being suitable 
for home study this book is also adapted as a text for trade, 
industrial and continuation schools. 

The author desires to acknowledge his indebtedness to Mr. 
Earle B. Norris, Associate Professor of Mechanical Engineering, 
University of Wisconsin, for a careful reading of the proof, for 
checking the illustrations, and for many valuable criticisms and 
suggestions; and to Mr. Joseph W. L. Hale, of the Department 
of University Extension, Massachusetts Board of Education, for 
valuable suggestions. 

R. W. H. 

Madison, Wis., 
June 16, 1917. 



Vll 



436266 



CONTENTS 

Paqs 

PREFACB Vii 

Instruments and Materials xi 

CHAPTER I 
Principles of Mechanical Drawing 

1. Projections 1 

2. Relations between Views 4 

3. Making the Drawing ; . . . . 5 

4. Dimensioning the Drawing 6 

5. Standard Sizes of Drawings 8 

6. Drawing Board and T-Square 9 

7. Triangles . 10 

8. Pencil 11 

9. Scale 11 

10. Starting the Drawing 12 

11. Broken Lines 17 

12. The Compass 22 

13. Center Lines 23 

14. Arrangement of Dimensions 24 

15. Finish 25 

16. Finish Marks 25 

17. Fillets 27 

18. Notes on Dimensioning 27 

19. Use of Formulas 31 

CHAPTER II 
Screws and Screw Fastenings 

20. Screw Measurements 35 

21. Forms of Threads 35 

22. Pitch 37 

23. Bolts 37 

24. Bolt Heads and Nuts 37 

25. Thread Conventions •. 40 

26. Right-hand and*Left-hand Threads 40 

27. Tapped Holes 41 

28. Other Thread Conventions 43 

29. Cap Screws 43 

30. Machine Screws 45 

31. Set Screws 40 

ix 



X CONTENTS 

Paqb 

32. Multiple Threads 47 

33. Lead 48 

34. Method of Drawing Square Threads 50 

35. Drawing to Scale 51 

CHAPTER III 
Sections 

36. The Use of Sections 65 

37. Half-sections 56 

38. Broken Sections 57 

39. Fillets 58 

40. Partial Sections 61 

41. Revolved Sections 61 

42. Shortened Views 64 

CHAPTER IV 
Technical Sketching 

43. Use of Sketching . 65 

44. Suggestions for Sketching 65 

45. Sketching on Plain Paper 67 

46. Sketching Circles 69 

CHAPTER V 
Tracing 

47. Use of Tracings 71 

48. Aids to Tracing 72 

49. Erasures 72 

50. Removal of Blots 73 

51. Order of Procedure in Tracing . -. 73 

52. Suggestions on Lines 74 

53. Handling the Pens 74 

CHAPTER VI 
Assembly and Detail Drawings 

54. Assembly and Detail Sheets 77 

55. Conventional Forms for Cross-hatching 81 

56. Drafting-room Procedure 85 

Index 91 



INSTRUMENTS AND MATERIALS 

The following equipment of instruments and materials, as shown in the 
frontispiece, is needed for carrying out the course of study outlined in this 
text: 

1 set drawing instruments including: 

6-in. compasses with detachable pencil and pen points and 
lengthening bar. 

6-in. plain or hairspring dividers. 

3i-in. bow dividers. 

3i-in. bow pencil. 

3i-in. bow pen. 

5i-in. ruling pen. 

Box of leads. 

8-in. 46® triangle. 

10-in. 30® X 60® triangle. 

Architect's 12-in. triangular scale. 

Bottle waterproof black ink. 

1 doz. thumb tacks. 

Penholder. 

Ball pointed pens. 

2H drawing pencil. 

4H drawing pencil. 

20-in. X 24}-in. drawing board. 

24-in. T-square. 

Combination pencil-and-ink eraser. 

Smooth file or block of sandpaper. 

18 sheets drawing paper, 12 in. X 18 in. 

6 sheets tracing cloth, 12 in. X 18 in. 



zi 



MACHINE DRAWING 



CHAPTER I 

PRINCIPLES OF MECHANICAL DRAWING 

ASSIGNMENT 1 

1. Projections. — ^The principle of projections is the basis of 
mechanical drawing and must be thoroughly understood in order 
to read a mechanical drawing or to make one. 

In making a mechanical drawing of any object, a draftsman 
deals with one face at a time, and makes separate drawings or 
views showing how the different sides or faces look. Thus we 
sometimes make as many different drawings or views of an object 




Fig. 1. 



as the piece has different sides. Each view is made as if the 
draftsman were looking squarely at the particular side he is 
drawing. In Fig. 1 is shown a picture of an oilstone, such as 
might be made by an artist or a photographer. Looking to- 
ward the comer, as in this figure, we see three faces, the side Aj 
the end C, and the top B. Fig. 2 shows a mechanical drawing 
of this same oilstone. Notice that the stone has its three differ- 
ent faces shown by the three views il, B, and C. In all there are 
six faces but, since the two ends are aUke, and likewise the two 

1 



• _ • • 






; •- ^ ;/• :M4.<}mm\DRAw^ 




Fig. 2. 




FiQ. 3. 



PRINCIPLES OF MECHANICAL DRAWING 3 

sides, and the top and bottom, it is necessary to show only the 
three different faces. £ach view is a picture of ooe side as we 
would see it if the stone were held squarely in front of, and on a 
level with, the eye. 

In making these views showing the different sides of any 
object, they should be placed in such a way as to show how th^ 
are related to each other in their position on the object. This is 
done by the principle of projection as follows: Referring to 
Fig. 2, notice that the top view B is placed directly above the 
side view A, so that the edges of B are on the same line as those 



^ 



\JE.WT EnO 

Wcw 




BoT-ror-1 Vicvu. 



View 



of A, as shown by the dotted lines. Also, end view C is directly 
in line with A. This is the principle of projection. In other 
words, the length of A is "projected" directly upward to form 
the length of B and the height of A is "projected" to the right 
to form the height of C. The dotted lines indicate the position 
of the straight edge in laying out the work, and show the relations 
between the sizes and positions of the views. 

Fig. 3 shows a picture of an anvil. Fig. 4 shows the complete 
mechanical drawing of this anvil with the correct names of the 
different possible views that might be shown. As a general rule, 
we follow this grouping: In the center we place the side view 



* » 

• _ • 



• • • • .• . ► 

' 1 ■ * • • 



» • ..»*•• 



;•- : ;/; :M4x}uwb:drawino 




Fig. 2. 




Fig. 3. 



PRINCIPLES OF MECHANICAL DRAWING 3 

sides, and the top and bottom^ it is necessary to show only the 
three different faces. Each view is a picture of one side as we 
would see it if the Stone were held squarely in front of, and on a 
level with, the eye. 

In making these views showing the different sides of any 
object, they should be placed in such a way as to show how they 
are related to each other in their position on the object. This is 
done by the principle of projection as follows: Referring to 
Fig. 2, notice that the top view B is placed directly above the 
side view A, so that the edges of B are on the same line as those 




Top View 



C 



[ 



2 



X 



1 




Lef^t Eno 
View 



tz 
3(DC View 




Right 



Eno 




View 



View, 



Fig. 4. 

oi A, as shown by the dotted lines. Also, end view C is directly 
in line with A, This is the principle of projection. In other 
words, the length of A is "projected" directly upward to form 
the length of B and the height of A is "projected" to the right 
to form the height of C. The dotted lines indicate the position 
of the straight edge in laying out the work, and show the relations 
between the sizes and positions of the views. 

Fig. 3 shows a picture of an anvil. Fig. 4 shows the complete 
mechanical drawing of this anvil with the correct names of the 
different possible views that might be shown. As a general rule, 
we follow this grouping: In the center we place the side view 



4 MACHINE DRAWING 

which shows the object set up in its natural position before the 
eye, and project the other views from it, placing the top view 
above, the bottom view below, the right-end view at the right, 
and the left-end view at the left. 

The views of an object which show it set up before the eye in 
its natural position are sometimes called elevations and are further 
designated as fronty side, or end elevations* The top view, ob- 
tained by looking down upon an object, is sometimes called 
the plan. The names which we give to the elevation views 
vary with different objects and different people. Usually we 
have two elevations given in a mechanical drawing, but people 
look at things differently and the view that some people would 




Tenon 




MORTISC. 



Fig. 5. 



call a front view others might consider a side view. So we might 
have front and side views, or front SLud end views, or in the case 
of any object that does not have any particular face that could 
be called the front, we might call the views the end and side views. 

Note Carefully. — We seldom need more than two or three 
views of a piece in order to show it. Generally a top, a side, 
and an end view are all that are necessary. It is only with very 
irregular objects like the anvil that we need as many as five views. 

2. Relations Between Views. — ^Fig. 5 shows a sketch in one 
view of two blocks of wood which are formed so that they may 
be joined together with a mortise-and-tenon joint. A mechanical 
drawing of the tenon is shown in Fig. 6. Three views are shown, 



PRINCIPLES OF MECHANICAL DRAWING 5 

namely, the side view AB, the top view CD, and the right-end 
view EF. The right-end view is shown rather than the left-end 
view because the form of the block and also of the tenon are 
shown in the right-end view. The surface A in the side view is 
shown in the other two views by the lines a. The surface B in 
the side view is represented by the lines 6 in the other two views. 
The student should check over the rest of the drawing with the 
aid of the letters so as to see just what each line in one view 
represents in the other views. The capital letters are used to 




Fig. 6. 

mark the surfaces. The corresponding small letters mark the 
lines which m other views represent these same surfaces. These 
letters are shown merely by way of explanation and would not 
appear upon a working drawing. From this drawing it will be 
seen that whenever a surface lies flat and on a level with the eye, it 
is represented by a line. 

3. Making the Drawing. — In making the drawing in Fig. 6, 
we would draw the side view AB first, laying oflf the various 
dimensions with the scale. Then in drawing the top view CD 
we would use the principle of projections to simplify the work 
and to locate the view properly with respect to the side view. 
The vertical (up and down) lines on the side view we would 



6 MACHINE DRAWING 

extend or project upward with a triangle. These lines would 
then show the lengths of the horizontal (crosswise) lines of the 
top view. After deciding how much space to leave between the 
views, we would then draw the horizontal lines of this view, 
spacing them properly with the aid of the scale, to show the de- 
sired width of the object. The right-end view is drawn in a 
similar manner, by extending toward the right the horizontal 
lines of the side view and locating the vertical Unes with the aid 
of the scale. These Unes, which are drawn from the side view 
in determining the other two views, are called projection lines. 
They are usually drawn lightly so that they may be readily 
erased from the finished drawing. The distance to be left be- 
tween the views is largely a matter of choice. The considerations 
which govern it will be developed later. From the preceding 
discussion it will be seen that the following relations exist be- 
tween the different views: 

The horizontal dimensions of the side view and of the top view 
are equal. 

The vertical dimensions of the side and end views are equal. 

The horizontal dimensions of the end view and the vertical 
dimensions of the top view are equal. 

4. Dimensioning the Drawing. — ^After the representation of 
the object is completed, it must be dimensioned for the guidance 
of the mechanics who are to have a part in its manufacture. 
Kg. 7 shows a shop drawing of the tenon shown in Fig. 6. It 
will be noticed that the extension lines and dimension lines have 
been added. 

Dimension lines are light lines broken at the center for the 
insertion of the dimensions, and having arrowheads at their 
ends to show the distances which they measure. The arrowheads 
should be made very sharp. As shown in Fig. 8, they should 
have a sharp wedge shape with a sUght curve to the sides rather 
than a straight V-shape. They should not be blocked in soUdly. 

Extension lines are light lines which show the points on the 
object between which the dimension is measured. Extension 
lines should be drawn up to about iV in. from the object and 
should project about | in. beyond the dimension lines. 

Dimension lines should be placed equally apart and equally 
distant from the object lines. About t\ in. is a good average for 
this spacing. Dimensions should be placed in one or two views 
when possible. Notice in Fig. 7 that all the dimensions arQ 



PRINCIPLES OF MECHANICAL DRAWING 7 

shown in two views. It is bad practice to repeal dimenaiona — that 
is, to pvt the same dimension in more than one of the views. Dimen- 
sions which are closely related should be placed near to each 
other, as shown by the arrangement of dimensions in the right- 



-*f- 



-if— 



-JSftw 



OCTAJI- OPTcNON 
FOR 

Mortise and Tenon Joint 



Fia. 7. 

end view of Fig. 7. The dimension 4f in. is known as the over- 
oU dimension. It is usually given so that the workman may 
know the total length of material required. The overall dimen- 
sion should be placed just outside the dimensions of which it is 



the sum, so that its dimension line will not be cut by any exten- 
sion lines. Be sure that the sum of the small dimensions is the 
same as the overall dimension. 



8 



MACHINE DRAWING 



Dimensions are usually shown by vertical figures about | in. 
high. , Fig. 9 shows the type of numerals generally used. The 
total height of fractions should equal twice the height of the 
whole numbers. The dividing line of a fraction should be oppo- 
site the middle of the whole number and should be on a level 
with the dimension line. The figures of the fraction should not 
touch the dividing line. All horizontal dimensions should read 

Freehand Lettering 



ABCDEFGHIJKLMN0PQR5TUVWXYZ& 
^/${' •'&• ^d, 'j^ V I234567S90 

abcdefghijklHnopqrstuvwxyza 



I234567S90 



4-1 3% 7k 



Fia. 9. 



Jrom the bottom of the' sheet, and all vertical dimensions from the 
right-hand side of the sheet Notice Figs. 7 and 11, in this respect. 
In all of the dimension lines that run up and down the sheet the 
dimensions are placed so that they can be read from the right- 
hand end of the sheet. 
In Fig. 10 is shown a picture of an angle brace. A mechanical 

drawing of the angle is shown in Fig. 11. 
This drawing should be studied care- 
fully, observing the following points: 
Relative positions of the views. 
Relations between lines in the dif- 
ferent views. 

Arrangement and position of dimen- 
sions. 

Extension lines and arrowheads. 
6. Standard Sizes of Drawings. — 
In making the drawing, the first thing 
to do is to determine the proper size of paper to use. In most 
drafting offices a regular system of standard sizes of sheets is 
used. For example, one office will take the standard letter size, 
8^ in. X 11 in. for the smallest size, and base all other sizes on 




Fig. 10. 



PRINCIPLES OF MECHANICAL DRAWING 



9 



this one, as 11 in. X 17 in., 17 in. X 22 in., and 22 in. X 34 in. 
Another office will use 9 in. X 12 in. for the smallest size, the 
others being 12 in. X 18 in., 18 in. X 24 in., and 24 in X 36 in. 
In this course of study two sizes will be used, 9 in. X 12 in. and 
12 in. X 18 m. 





ANGLE BRACE 

4.-RCQUIRCD STEEL 



Fig. 11. 

6. Drawing Board and T-square. — ^First take the drawing 
board. Fig. 12, and the Tnsquare, Fig. 13, and place as in Fig. 
14. This is the working position of the Tnsquare, and the blade 
can be moved up and down over the surface of the board with 
the left hand while holding the head firmly against the working 




FiQ. 12. 



edge of the drawing board. For a left-handed man, the working 
edge of the board would be at the right, and the head of the T- 
square would be held in place with the right hand. 
Drawing boards are made of soft wood, should be free from 



10 



MACHINE DRAWING 



It 



HEAD 



knots and cracks, and should be provided with cleats across the 

back or ends. 
The T-square consists of a head and blade, fastened together 

at right angles. The upper or working edge of the blade must be 

straight, and is used for drawing all 
horizontal lines (lines running the 
long way of the board). 

^^ ^^— The left end of the drawing board 

\ y^^^oc, must also be straight. The student 

can determine for himself whether, 
or not, the working edges of the T- 

square and of the drawing board are straight by holding them 

as shown in Fig. 15. They should be in contact along their 

entire length. 






LOWER EDQE 

Fig. 13. 



] 




Fig. 14. 

AU horizontal lines should be drawn with the T-square, drawing 
from left to right, meanwhile holding the head of the T-square firmly 
against the working edge of the hoard with the left hand. 





Fia. 15. 



4.5' TRIANGLE 

Fig. 16. 



30% 60* TRIANGLE 

Fig. 17. 



7. Triangles. — Triangles are used for drawing lines other than 
horizontal. They are made of hard rubber, celluloid, wood, or 
steel. There are two common shapes, called the 45® triangle 
and the 30® X 60® triangle. These are shown in Figs. 16 and 
17. The 45® triangle, shown in Fig. 16, has one angle a right 



PRINCIPLES OF MECHANICAL DRAWING 11 

angle, or 90?. The other angles are each 45^, just half of a right 
angle. The 30° X 60** triangle shown in Fig. 17 has one angle 
a right angle; another angle is 60° (two-thirds of a right angle); 
and the other is 30° (one-third of a right angle). 

For drawing vertical lines (lines at right angles to the hori- 
zontal lines), the T-square should be placed in its working posi- 
tion and one of the triangles placed against its working edge. 




Fia. 18. 

Fig. 18 shows the correct position of the hands and the method 
of holding the pencil for drawing these lines. 

Always keep the working edge of the triangle toward the head 
of the T^equare and draw from the bottom up, or away from the 
body. 

8. PenciL — The pencil must be properly sharpened and must 
be kept sharp. Good clean-cut lines cannot be made with a 
dull. pencil. Sharpen your pencil as shown in Fig. 19. The 




^^ 



Fig. 19. 

end a shows the chisel point used for drawing lines, while b shows 
the round point used for marking off distances and for putting 
in dimensions, lettering, etc. About f in. of lead should be 
exposed in making the end a, and then it should be sharpened 
flat on two sides by rubbing on a file or piece of sandpaper. 

9. Scale. — If you have the triangular scale called for in the 
list of materials, you will find on it eleven different scales, two 
on each edge, except where the full-size scale is shown. For the 



12 



MACHINE DRAWING 



present we will use only the full-size scale shown on the top edge 
of Fig. 20. This is the same as the scale of an ordinary foot 
rule divided into 16 parts to the inch. The uses of the other 
scales will be explained when we come to use them. 

10. Starting the Drawing. — ^The size of the sheet required for 
the drawing in this assignment is 9 in. X 12 in. As this is one- 
half the size of sheets specified in the list of materials, it is neces- 



w\^^v^v^V\^v^^^^<^\^^^w\^^v^v^^^w\^^^ 





■^^u^%m^^^ 



5 



\ ^ \ V\Av:^ 



Fia. 20. 



sary to cut one of the sheets into two equal parts. Use the back 
of the board and the lower edge of the T-square as a straight edge. 
Cut with a sharp knife. See Fig. 21. Then place a 9-in. X 
12-in. sheet of drawing paper near the center of the working 
surface of the board, with the 12-in. dimension nmning the long 
way of the board. Fasten the sheet to the board by placing a 
thumb tack in the upper UfUhand comer of the sheet. Swing the 




Fig. 21. 

sheet, if necessary, to bring its upper edge in line with the work- 
ing edge of the T-square when held in position. When the top 
of the paper is parallel with the blade of the Tnsquare, put a 
thumb tack in the hwet right-hand comer of the sheet. Then 
put tacks in the other two corners, after stroking the paper gently 
toward the corner in which the tack is to be placed. 

Now, starting } in. from the top and 1 in. from the left end, 
draw horizontal and vertical lines to form a rectangle 8 in. X10§ 



PRINCIPLES OF MECHANICAL DRAWING 13 

in. in size. The sheet should now appear on the drawing board 
as shown in Fig. 22, except that there will be no dimensions or 
lettering on it. This leaves a margin of ^ in. on three sides and 
1 in. on the left end. This wider margin on the one end is for 




Fig. 22. 

the purpose of binding together several drawings, where that is 

desired for any reason. 

Problem 1 

Fig. 23 shows a sketch of a gib key. A working drawing of this key is 
shown in Fig. 24 with an appropriate title. Such a key is used for fastening 




Fig. 23. 



pulleys, couplings, or collars to shafts and is driven into a slot, half of which 
is cut in the shaft and half in the piece to be fastened to the shaft. The 



14 



MACHINE DRAWING 



head is used for pulling the key out of the slot. The slots cut in the shaft 
and pulleys are called "keyways." Fig. 25 shows the same key as in Figs. 
23 and 24, but viewed from a different position. 



rlH 



*Qhf 



ri'H 






4^ 



l-RCQUlReO MACH. 
FihISH ALL OVCR. 



Fig. 24. 

Make a pencil drawing of this gib key, making the views the full size of the 
k^ according to the dimensions given in Fig. 24. Draw the viewi of the 




Fig. 25. 

hey that loovld he obtained by looking along the arrows C, D, and E, in Fig, 25. 
The arrangement of views should be as shown in Fig. 26. 

The first thing to do is to determine the proper location of the views on 
the sheet. They should be placed so that the whole drawing will be cen- 



PRINCIPLES OF MECHANICAL DRAWING 15 

tered on the sheet. Since the key is to be 4} in. long, this will be the length 
of the side view and of the top view. The end view will be f in. wide and, 
if we allow } in. between views, the drawing will take up 4} in. + } in. -f- 
I in. « 5{ in. We will divide the remaining space so as to leave an equal 
amount on each end between the views and the border lines. The length 
between the border lines is 10} in. and the views occupy 5} in. 

10} in. — 5} in. = 4f in. 

4f in. -^ 2 = V in. X i = li in. = 2A in. 

Therefore, we have 2 A in. at each end between the 'views and the border 
line. 



DRAW TOP VIEW HERE. 



DRAW END 
VIEW HERE 



Fig. 26. 

Vertically, the views occupy } in. for the side view, } in. between views, 
and f in.' for the top view, so that i in. + i in. + f in. = 2} in. The 
working space on the sheet is 8 in. high. 

8 in. — 2} in. = 51 in. 

5J in. 4- 2 = V- in. X i - }J in. « 2H in. 

Thus we have a space of 2it in. both above and below the views. By 
referring to Pig. 27, we see that the comer A is thus located 2 Jf in. above 
the lower border line, and 2 A in. from the left border line. 

Through the point A which we have just located, draw a fine horizontal 
line. On this line, lay off from A 4} in. to the right, thus locating the 
point B. Measure to the right from 5 f in. and we have the point C; then 
measure | in. to the right of C and we get point D. Through the points 



16 



MACHINE DRAWING 



Af Bf C, and D draw light vertical lines, using the T-equare and triangle as 
shown in Fig. 18. 

On the vertical line through A lay off AE » } in. On the vertical line 
through B lay off BG » i'; in. Then measure up from ^ } in. for the 
space between the views, and | in. more for the width of the top view. 
Draw a horizontal line through E to the right until it crosses the vertical 
lines drawn through C and D. This gives the height of the side view and 
the end view. Now measure i in. from E to the right, locating the point 
F. Draw a vertical line downward from F and then a horizontal line to 
the left from G until 4t intersects the vertical line. The outline of the side 
view is thus completed. The top and end views are not complete, however, 
and the student should determine for himself what lines are necessary to 
complete these views and should put them in. Now go over all the object 




Pig. 27. 



ines and make them heavier, and with the pencil eraser, erase all other lines 
that have been used in constructing the views. 

The extension lines should be drawn next. These are light, solid lines 
drawn from the ends of the views and between which the dimensions are 
placed. The extension lines should not touch the viewl^ by about -fig in. 
and should be about i in. long. 

Now put in the dimension lines, drawing them about | in. from the 
views. The extension lines and dimension lines should be placed on the 
drawing about as shown in Fig. 24, and should not be as heavy as the out- 
lines of the views. Leave a break near the center of the dimension line for 
the dimension or figures. Now put arrowheads at the ends of the dimen- 
sion lines. They should be drawn as shown in Fig. 8. 

Use vertical figures for dimensions, making them about i in. high. 
Make each figure of a fraction as large as the whole number, and be careful 



^^^P^^^^mmmm::^^m 



PRINCIPLES OF MECHANICAL DRAWING 17 

that they do not touch the dividing line. The dividing line of a fraction 
should be on a level with the dimension line. 

Horizontal dimenaiona should read from the bottom of the sheet, and vertical 
dimeneiona from the right-hand side of the sheet. See Fig. 24. All dimensions 
that do not give the size of the object should be omitted from the drawing, 
aS| for example, those marked (*) in Fig. 27. These are given only to show 
how the views are located on the sheet. 

Fig. 28 shows the arrangement of the title for thb drawing. This ar- 
rangement is used throughout the course, the number of the lines varying 
with the different problems. More can be added, or some omitted. The 
name of the object shown on the plate is the most important part of the 
title, and therefore is put in the first line and in the largest letters. If the 
name of the machine for which the part is used is given, it should be placed 
in the next line, but in smaller lettering. The number of parts required, 
the material, the scale of the drawing, and the date will vary with the differ- 
ent plates, but should be arranged as shown. The number of the plate 
shoidd go in the comer, as indicated in Fig. 28. 



KEY 

l-REQURED rtACH. STECI. 
aCALC: 12 «|k>r 9-4-- 1^* 

OR. m CH, f^^ I 



Fia. 28. 

* 

The items DR., TR., and CH., in the title are to be followed by the initials 
of the persons who have drawnf traced and checked the drawing. It is quite 
common in drafting offices to require that this information be given on every 
drawing so that responsibility can be placed for any errors that may be 
found. 

The item in this title Scale: ITf » y--(f refers to the scale of the draw- 
ing, that is the relation between the size of the drawing and the size of 
the actual object which it represents. 12' "■ I'-O' means that 12 in. 
on the drawing are used to represent 1 ft. of actual object. Therefore, this 
drawing is full size. When the scale of a drawing is 3' » I'-O*, then 3 in. 
on the drawing represents an actual. length of 1 ft., or the drawing is only 
one-fourth the actual size of the object. 

A good, simple type of lettering to use is shown in Fig. 9, which also shows 
the general method of making the letters. The strokes of the pen should 
all, be made either downward or to the right, thus minimizing the danger 
of blotting. Fig. 9 also shows the best forms for the numbers. Consider- 
able practice is necessary to do a good job of lettering, and the student 
should not be discouraged by the results of his first attempt. 

ASSIGNMENT 2 

11. Broken Ljnes. — In drawing any view, if a surface is hidden 
from sight but needs to be shown in some manner, it is customary 



18 



MACHINE DRAWING 



to life a broken line. This line will show the location and extent 
of the hidden surface, but, by being broken, will indicate that 
the surface represented is not on the front but is out of sight. 

Broken lines are drawn with dashes about i in. long with 
spaces about ^ in. long between them. See Fig. 42. In 





• 










« 


















V 






















[".::] 




■■ 








. 




































• 







Fig. 29. 



drawing broken lines, they are usually made just a, little lighter 
than the full object lines of the drawing. 

A judicious selection of the views to be shown will often avoid 
the necessity of using broken lines. For example, the right-end 




Fig. 30. 



view of Fig. 29 shows the end outline of the tenon in full view and 
therefore is preferable to the left-end view. Figs. 30 and 31 
show a case where the broken lines are needed. These figures 
show a picture and a mechanical drawing of a bronze bushing. 



PRINCIPLES OF MECHANICAL DRAWING 19 



3i' 




Bronze Bu9hin3 
finish all over 



FlQ. 3L 





FiQ. 32. 



20 



MACHINE DRAWING 



This is a hollow cylinder, the hole extending clear through from 
end to end. In the side view of Fig. 31 it is necessary to repre- 
sent the hole by two broken lines. These 
lines extend throughout the length of the 
side view and thus indicate that the hole 
extends from one end of the piece to the 
other. Without these lines we could not 
tell how far the hole extended. These 
lines are located by projecting the top 
points of the inner circle of the end view. 
Suppose now that we were to make a 
cylinder like that of Fig. 31 but closed at 
one end so that it would look like a cap 
for a pipe. It might then b^ shown by 
the side viiew and right-end view of Fig. 
32. Notice how the broken outline in the 
side view shows the form of the interior and indicates that the 
hole does not extend all the way through the piece. These two 




Fig. 33. 



























1 


• 






















i 




1 




f 








■ 








1 

1 


\ 

1 










(^ 














/ 
/ 










\ 


^^r 
^^^ 




» 




r ' 




1 - 








1 





Fia. 34. 



views would be sufficient to give a clear idea of the cap. If the 
left-end view were desired, it would appear as shown at the left. 



PRINCIPLES OF MECHANICAL DRAWING 21 



The inner circle of this view is broken because it represents a 
hidden surface. 

Fig. 33 shows a ''stop" such as is commonly used on planer 
beds for bracing castings. It is 
shown by four views in Fig. 34. 
These views are not all needed, 
but are given to show how the stop 
would appear in the different views. 
The left-end view contains a broken 
circle, because the surface which it 
represents is concealed when the 
stop is viewed from the left-end. 
The side view and right-end view 
are all the views needed to give a 
complete idea of the shape of this stop. 

Fig. 35 shows a sketch of a flange bushing. A complete shop 
drawing of this flange bushing is shown in Fig. 36. When the 




Fia. 35. 




r 

M 



2i* 



i 



•f*- 



(Vi 

i 



Fi.AN€e Bushing 

Z, RCQUIRCD BRASS 
FINIStI ALU OVER 



FlQ. 36. 



bushing is viewed from the left end, the 2-in. cylindrical surface 
is concealed from sight by the flange, and is therefore shown by a 
broken line in the left-end view. 



22 



MACHINE DRAWING 



Always end a broken line with a dash running ri^ht up to the 
point where the surface ends which the line represents. Compare 
the ends of the lines in Figs. 37 and 38. Whenever a broken line 
crosses a full line, always make one of the dashes definitely cross 
the full line. The correct method of observing this is also shown 
in Fig. 37, and the improper method is shown in Fig. 38. 

If the bushing is shown on a shaft, the diameter of which is 
the same as that of the hole, then the broken lines will terminate 
as shown in Fig. 39. This explanation applies not only to this 
particular problem, but to all similar cases. 

In all work in drawing, full-line views should be shown, when- 
ever possible, rather than broken-line views. For instance, in 
drawing the cap of Fig. 32, it is better practice to show the side 
view and right-end view rather than the side view and left-end 

' CORR C CT AND INCORRECT MCTMOOQ Of d»1pWIN€ BROKCN UNBS; 





PiQ. 37. 



AVOID 

Fig. 38. 



Fig. 39. 



view, because in the former case all of the lines of the end view 
are full lines, while in the latter case one of the circles is broken. 
12. The Compass. — The compass is an instrument used for 
describing circles. It is provided with a needle point on one 
leg, and a pencil or pen point on the other leg, as shown in Fig. 
40. A lengthening bar is also provided for making large circles. 
In order that all lines on the drawing may be of the same weight 
the student should take sonie lead from his drawing pencil and 
insert it in the pencil section. Fig. 41 shows how the compass is 
used. Note that both the needle and pencil sections are vertical 
to the plane of the paper. This is the proper way to hold the 
compasses, because if the points are not vertical to the paper, a 
slight pressure will cause them to spread apart, thus spoiling 
the circle or curve. Do not bear upon the needle point or it 
will dig large holes in the paper. A slight pressure will be neces- 
sary on the pencil point. The lead should be sharpened from the 
oviside only, using a knife, or better a smooth file, emery cloth, 



PRINCIPLES OF MECHANICAL DRAWINO 23 

or sandpaper. Do not touch the inside. The point will then 

produce sharp lines and stand considerable usage without 

resharpening. 
13. Center LhicB. — It will be seen that light dot-and-dash lines 

are shown through the center of views of Figs. 31, 32, 34 and 36. 

These are known as center lines. Whenever an object is sym- 
metrical about a common center line (that 
is, just alike on both sides of the center 
line) it is ciistomary to show the center 
line on the drawing. The most common 
method is to use a line made up of dashes 
about an inch long with single dots be- 
tween. Center lines should be drawn 
lightly. Both the horizontal and vertical 
center lines of all circular views should be 
shown. In starting a drawing, the center 
lines should always be the first lines drawn. 
In making a drawing like Fig. 31, the 
center lines would be drawn first, and the 
circular end view next. The side view may 
then be constructed with the aid of projec- 
tion lines from the end view. The object 
lines of a drawing, whether full or broken, 




Fia. 41. 



should be heavier than the center, extension, and dimension lines, 
as shown in Fig. 42. To obtain this result, the pencil should be 
sharpened carefully at the beginning of the work. This will 
enable the student to draw fine but distinct center lines. The 
object should then be drawn, making the lines heavier. After 
completing the views, the pencil should be sharpened again 



24 



MACHINE DRAWING 



preparatory to drawing the extension and dimension lines, which 
should also be fine lines. 



Fui-i_ Lines 



Broken Lines 



Extension Lines 



Dimension Lines 



CcNXER Limes 
FiQ. 42. 

14. Arrangement of Dimensions. — Always dimension full-line 
views rather than broken-line views. Dimensions should be 
placed as close as possible to the place which they measure so 




Fig. 43. 



as to avoid the use of unnecessarily long extension lines; for 
example, in Fig. 36 notice how the extension lines for the 2i-in. 
dimension are drawn to the side view rather than to the end view. 



PRINCIPLES OF MECHANICAL DRAWING 25 

Dimensions should always be carried outside of the views of the 
drawing when convenient, so that the drawing may be the more 
easily read. 

In Fig. 36, it will be noticed that the hole is dimensioned on 
the end view, in which it appears as a circle. This is done be- 
cause to dimension it on the other view would necessitate dimen- 
sioning from hidden lines, which is undesirable. Dimensions 
placed in this way should be put on a slant so as to avoid the 
center lines. A single dimension should slope 45® ; that is, half- 
way between the horizontal and vertical center lines. Fig. 43 
shows how a number of dimensions would be arranged on a 
circular end view, the dimension lines being arranged so as to 
divide evenly the spaces between the center lines. 

16. Finish. — In several of the drawings shown, there appear 
in the title the words, "Finish All Over." This indicates that 
all the surfaces are to be machined to the dimensions shown in 
the drawing. The piece must therefore come to the machinist 
with extra stock all over and on the inside so that he can machine 
it to size. If a piece is cast, the pattern-maker must allow for 
this in making the pattern; if forged, the blacksmith must leave 
the extra material in forging. Different shops may use different 
phrases, such as Finish, Finished, Finish All Over, Fin., or the 
letters F. A. 0. 

Problem 2 

Make a fuUnsize pencil drawing of the flange bushing shown in Figs. 35 
and 36, drawing the side elevation and right-end view. Use a 9-in. X 12-in. 
sheet. Careful attention must be given to all directions contained in articles 
11 to 15 inclusive. 

ASSIGNMENT 3 

16. Finish Marks. — Fig. 44 shows a full-size drawing of a 
rocker arm. This drawing illustrates several features that have 
not been explained before. 

This rocker arm is not to be finished all over, but only on the 
faces and through the holes of the head and of the hub. When a 
flat surface, such as the faces of these ends, is to be finished, the 
general practice is to put a letter / across the line representing 
this surface. Some concerns use the capital F, others the ab- 
breviation Fin., while still others put the whole word FINISH 
in capitals just outside of the line. The finish mark / shown in 
Fig. 44 will be used in this course because it is in most general 



26 



MACHINE DRAWING 




iH 



/ 



1" 

8 



.-\. 



1^' 
•8 




^ 



M 




iL' 



l« 



xl^t 



16 



> 



^ 



RocKCR Arm 

1- REQUIRED CAST IRON 
FULL SIZE 



FlQ. 44. 



PRINCIPLES OF MECHANICAL DRAWING 27 

usage. If a student is employed in a shop having different 
standards, it is suggested that he learn them and use them 
throughout his work. Notice particularly that, when a surface 
is to be finished, the finish marks are not placed on the view where 
the surface is shown in plan, but rather on the view where it is 
represented by a line. Wherever these marks appear, the 
pattern-maker or blacksmith allows extra stock. About ^ in. 
is allowed on small parts, so that, if the draftsman leaves off a 
finish mark where there should be one, it is the same as making 
an error of ^ in. The finish marks indicate to the machinist 
what work is to be done by him on the object. 

When a hole in an object is to be machined, it is customary to 
indicate the process to be used by printing the word after the 
dimension of the hole. Thus in Fig. 44 we have |-in. BORE 
and f-in. BORE to indicate that the holes in the ends of the 
rocker arm are to be bored out to the given dimensions. In 
Fig. 45 is shown a hexagonal (six-sided) hole in a wrench. The 
word BROACH indicates that the hole is to be finished by the 
broaching process. The forging for the wrench must therefore 
be made so that this hole will be undersize, leaving material to 
be removed by the broach. Likewise, we find holes marked 
REAM, DRILL, or TAP, according to the operation to be used 
in finishing the hole. In a similar manner cylindrical parts that 
are to be finished by turning in a lathe have the word TURN 
after the dimension. 

17. Fillets. — In the views of Fig. 44 it will be noticed that the 
faces of the arm are rounded into the hub instead of leaving a 
sharp comer. A further examination of the figure shows that 
this is done wherever two surfaces meet, so that there will not 
be any sharp comers on the object when made, except where it 
is to be finished. These small curves or arcs on the drawing 
represent fillets. A Fillet is a small curve used to avoid sharp 
comers where two surfaces come together at abrupt angles. All 
unfinished comers should be rounded by fillets, so as to provide 
for the smooth flow of the metal when casting or forging and also 
for strength, as a crack will generally start in a sharp comer if 
the piece is overstrained. 

These fillets are dimensioned by giving the radius, as is done 
with any curve which is not a complete circle. 

18. Notes on Dimensioning. — ^There are several new features 
in connection with the dimensioning of this drawing in Fig. 44. 



28 



MACHINE DRAWING 



A fillet is dimensioned by a line drawn from the curve to the 
center from which the arc was swung. The arrowhead appears 
only on the one end next to the curve. The note J-in. R is 
put at the other end and in line with the arrow. If the dimension 
line had been long enough it might have been broken and the 
dimension put in the break, as was done in the f-in. 22 on the 
head of the rocker arm. Notice that the distance between the 
center lines of the hub and head is given, rather than the overall 
dimension. This is the important dimension and must be made 
accurate in machining. In the side view at the left, the faces of 
the head and hub must be located accurately with respect to 
each other. It would not do to locate these from the unfinished 
face of the arm, so they are located from the center line of the 
arm. The width of the head is given as iVin. overall, but, since 
it is symmetrical about the center line, it is understood that this 
means j^ in. on each side of the center line. 




i 



T 



^ 



DRAW SIDE ELEVATION MERE. 



■*^ — r 






f 



f 



^3h- 



I n I 
I I I 



t 



^'Mexaqonau Box Wpen^m 

DROP FORGED- MACM. STEEL 



Fig. 45. 



This drawing shows several cases where the space between the 
extension lines is very limited. This is especially true of the 
keyway cut through the hub. In giving the width of the keyway 
there was space enough for the figures but not for the arrows, so 
we put the arrows outside, pointing inward. The depth of the 




PRINCIPLES OF MECHANICAL DRAWING 29 

keyway is still narrower. Here the arrows both point in, and the 
dimension is placed outside and in line with one of the arrows. 

Problem 8 

Make a full-size pencil drawing of the i-in. hexagonal box wrench, shown 
in Fig. 45. Use a 9-in. X 12-in. sheet. In this sketch, only the top and 
right-end views are shown. The student is to show the top, right-end, and 
side views. Draw the top and right-end views first, and from them draw 
the side view by means of the principles of projection. 

Order of Work: Always start by laying out the center lines. Locate 
them so that there will be sufficient room between views and so that the 
three finished views will balance up well on the paper. It is always best 
to draw the circles and the curved surfaces first and then connect them with 
straight lines, as smoother joints will result. However, it is 
not practicable to do this in all cases. In this problem, start 
with the head of the wrench. 

The head of the wrench is formed to fit a hexagonal nut for 
a i'lTL . bolt and is therefore known as a i-in. wrench. The 
size of wrench is always designated by the size of the bolt 
whose nut or head it will span, rather than by the size of 
opening of its jaws. 

The hexagon is a regular six-sided figure. Fig. 46 shows the method of 
constructing the hexagon. Draw the two center lines, and with the point 
where they cross as a center and a radius of -xV ^-t draw a circle (a J-in. 
nut has a short diameter of { in.). Tangent to this circle, draw the hori- 
zontal lines 1-2 and 5-4. Draw the lines 2-3, 3-4, 5-6, and 6-1 tangent to 
this circle and making angles of 60^ with the horizontaL This completes 
the hexagon. 

ASSIGNMENT 4 
Problem 4 

Two views of a stuffing box gland are shown in Fig. 47. As these views 
are not the best combination for giving a clear idea of the object, the student 
should draw in pencil the views shown in outline in Fig. 48, using the full- 
size scale. Use a 9-in. X 12-in. sheet, with the 12-in. dimension vertical 
on the board. 

Draw the center lines first, locating them in such a way that the views 
will be centered on the sheet, at the same time providing sufficient room in 
the lower right-hand comer for the title. Allow about } in. between the 
views. Draw the |-in., li-in., and 2^%'in. diameter circles first. Then 
draw the f-in. radius arcs at the ends, from the centers B and C, as shown 
in Fig. 49. The distance across the middle of the gland is 2} in. Take 
one-half of this, or 1} in., for a radius and with a center at A draw arcs 
above and below the horizontal center line. As yet you have not deter- 
mined the lengths of the arcs, but make them longer than necessary and 
then the excess length can be erased later. 



30 



MACHINE DRAWING 



Now draw straight lines DE and FO tangent to the arcs of |-in. and 1{- 
in. radii. Take your triangles and place them on the drawing with the 
upper edge of the 45** triangle coinciding with line FG that you have just 
drawn. Then holding the 30'' X 60^ triangle securely, slide the 45° triangle 
along it to the right until its left-hand side passes through the point A. 
Draw a fine pencil line AF, Still holding the 30° triangle securely, slide the 



*i 



M 



i 






li- 



T 






2*0P1LL 




H' 



Stuffinq Box Gland 

2-REQUlReD BRASS 



Fig. 47. 



45° triangle further to the right imtil its left-hand edge passes through the 
point C. Draw a fine pencil line CO. The two lines AF and CO are parallel 
(the same distance apart along their whole length). This will give you the 
points where the arcs and the straight line FO meet. Find the other points 
where the arcs and straight lines meet in the same way. These fine pencil 
lines BD, AE, AF, CO, etc., should not be erased until after you have com- 
plete the drawing. 





Fig. 48. 



Fig. 49. 



The stuffing box gland is used on steam engines, pumps, etc., for keeping 
the packing tight around the piston rod so that it will not leak. The diame- 
ter of the piston rod in this case would be li in. Examine a steam engine 
or steam pump and see if you can find a gland similar to this. 



PRINCIPLES OF MECHANICAL DRAWING 31 

ASSIGNMENT 6 

19. Use of Formulas. — It quite frequently happens in practice 
that the draftsman is required to use formulas in determining 
the dimensions of certain pieces. A knowledge of the use of 
formulas is, therefore, essential. When a line of several different 
sizes of a tool or machine part is being designed, the different 
dimensions are sometimes made proportional to some funda- 
mental dimension of each size. For example, Pig. 50 shows 
an open-end hexagon wrench dimensioned in letters. By the use 
of suitable formulas the dimensions represented by these letters 
may be calculated for any size of wrench. The following for- 
mulas, taken from "Machinery" data sheets, will enable the 
student to calculate the dimensions for any size of wrench, or for 




SiNGuc End Hexagon Wrench 

Fig. 50. 

a whole series of sizes. The width of opening, or size of the nut, 
would be the first thing known, so that is taken as the basis for 
all of the other dimensions. 

W = width of opening. 
B =^ 0.8 X TF. 
D = 0.65 X W. 
i? = 0.4 X W. 
F = 0.25 X W. 
L = 7 X TF. 

C = distance from center of hexagon to one 
corner (to be measured on the drawing). 

As an example of the use of these formulas, we will start the 
calculations for the problem of this assignment, which calls 
for the design of a |-in. open-end hexagon wrench, the opening 
(TF) of which would be 1 J in. 

4 



32 MACHINE DRAWING 

We can, therefore, start with the fact that the dimension W of 
our wrench is to be made IJ in. The formula for B, the width 
of the handle next to the head, states that: 

JS = 0.8 X TF. 

Since TF = li in., the above formula means that B = 0.8 X 
1 J in. This may be done either decimally or fractionally. The 
fractional method is better because it is more desirable to obtain 
the answer in fractions than in decimals. Changing 0.8 to 
fractional form we have iV- Changing IJ in. to an improper 
fraction we have | in. 

r^ 8 5 . 40 , . 

Then lO^I'"'- "40"^'''- 

0.8 of W is, therefore, 1 in. Then our wrench of this size would 
have a handle 1 in. wide at the head. If the opening W of the 
wrench were larger, the handle would become correspondingly 
larger. 

Likewise, we get the width at the end of the handle from the 
formula: 

D = 0.66 X W. 

0.65 may be written tVt- 

rru * n 65 ^ 5 . 325 13 . 

Therefore, -^ = ^ X ^m. = ^^^ = j^m. 

The other dimensions are calculated in the same way. 

Problem 6 

Using a O-in. X 12-in. sheet, make a pencil drawing for a J-in. hexagon 
wrench of the type shown m Fig. 50, but miJdng the views shown in Fig. 

51. The width of opening W ia H in. 
From this dimension all of the other 
dimensions for the wrench should be cal- 
culated before trying to start the draw- 
ing. Two of the dimensions have al- 
ready been calculated; the others should 
FiQ. 51. be calculated in a similar manner from 

the formulas given. The views are to 
be made full size. In locating the wrench on the sheet, remember that 
the total length of the wrench is somewhat greater than L, being L plus 
one-half of one side of the hexagon. 

Locate the drawing on the sheet so that there will be about f in. between 
the views. 




PRINCIPLES OF MECHANICAL DRAWING 33 

After looating the center of the hexagon, oonstnict the hexagon for the 
vrench aa explained for Fig. 46. In the drawing of the wrench two sides 
of the hexagon are omitted. To draw the head of the wrench: First, with 
the center of the hexagon as a center, draw an arc of radius W, then, with 
a radius C and a ceater which must be located by trial, draw an arc that 
will be tangent to the are of radius W, and which also will pass through the 
outer comer of the heitagon, as the comer 1, of Fig. 46. Two of these arcs 
roust be drawn, one above, and one below ttie center line of the wrench to 
complete the head. 

The width B of the large end of the handle is drawn by laying off points 
one-half B above and one-half £ below the center line of the wrench. 
Through the points thus found, draw horizontal lines and find the points 
where these lines intersect the curve of radius IF. At the other end of the 
handle draw lightly a circle of diaroeter D. Through the points at the large 



Bracket 

l-REOUtREO CAST IRON 

Fio. 52. 

end and tangent to the circle at the email end of the handle, dr^w lines repre* 
senting the sides of the handle. Instead of a sharp comer where the handle 
joins the head, arcs or fillets of radius C are used, which should now be drawn. 
In the other view the thickness of the head is E and that of the handle F. 
In this view the sides of the handle are parallel or, in other words, the thick- 
ness is the same along its whole length. The distance between the hori- 
zontal lines must be measured, but the position of the vertical lines can be 
found by drawing vertical projection lines with the T-square and triangle, 
through the different points on the top view. Draw the fillets between the 
head and handle with a radius equal to one-half of (£ — F). 

' Put on the dimensions that you have calculated and not the letters shown 
in Fig. 50. 

The drop forging of which this wrench is made differs from the forging 
hammered out by hand in the ordinary blacksmith shop in that, after the. 
steel is heated to the proper temperature, it is placed on a "die" oi ablock 
of steel hollowed out to the exact shape that the wrench ie to be, but only 



34 



MACHINE DRAWING 



half deep enough for it. A second die similar to the first is fastened to the 
bottom of a heavy weight which slides between vertical guides. The weight 
is pulled up and then allowed to drop; this is repeated as many times as is 
necessary until the metal that was placed on the lower die is formed between 
the two dies into the desired shape. Drop forgings are much smoother 
than other forgings and require little finishing, except when pieces go to- 
gether. On this wrench only the opening and 
the faces 'Of the jaw are to be machined or 
finished. 



ASSIGNMENT 6 



Ihroblem 6 

Fig. 52 shows a side and end view of a cast-iron 
bracket such as is used to support the camshaft 
on a horizontal gas engine. It consists of a flat 
rectangular plate with four holes drilled through 
it, an arm strengthened by a deep rib, and a 
hub on the end bored for the camshaft. The 
FiQ. 53. bracket is fastened to a planed spot on the base 

of the engine by four i-in. cap screws through 
the holes in the base of the bracket. 

The views shown here are not the best. The bracket would be shown 
to better advantage if the top view were drawn instead of the end view. 
The student is to make a pencil drawing of this bracket using the side view 
and the top view. In Pig. 53 are shown roughly the views wanted. The 
student should make the drawing full size, using a 9-in. X 12-in. sheet, 
placed with the 12-in. dimension vertical on the board. 




CHAPTER II 

SCREWS AND SCREW FASTENINGS 

ASSIGNMENT 7 

20. Screw Measurements. — The Nominal or Outside Diameter. 

— The nominal diameter of any screw or bolt is the diameter at 

the top or outside of the threads. By nominal diameter we mean 

the diameter by which the bolt is known. This is the diameter 

given in the first column of the bolt table, page 3S. Thus, a 

f-in. bolt measures f in. in diameter at the top or outside of 

the threads. 

The Root or Effective Diameter. — The root diameter of a screw 
is the diameter at the bottom or root of the threads. This is 



Fio. 54. 

the dimension from which the strength of the screw is calculated, 
because it is the smallest diameter and hence the weakest. The 
nominal and root diameters are shown in Fig. 54. 

Depth of Thread. — The depth of the thread is the radial dis- 
tance between the top and bottom of the threads; that is, meas- 
ured in a direction straight outward from the center. 

21. Forms of Threads. — The most common thread forms are 
the V, V. S. standard, Square, Acme, Worm, and Whitworth. 
Other shapes may be designed to meet special conditions. Fig. 
55 shows the outlines of the above-named threads. 

The V Thread.— The V thread has an angle, of 60° between 
the sides and is pointed at the top and bottom. Its use is con- 
fined cliiefly to small screws. 



36 



MACHINE DRAWING 



The V. S. Standard Thread.— The United States standard 
thread vtaa designed by Mr. William Sellers of Philadelphia and 
recommended by the Frankhn Institute of that city in 1864. 
It was later adopted in a modified form by the U. S. Government 
and is now variously known as the Sellers, the Franklin Insti- 
tute, and the U. S. standard thread. It is similar to the V thread 
with the exception that the top and bottom of the thread are 
flat, thus leaving a larger root diameter and therefore making a 
stronger bolt than if the V thread were used. It is used generally 
for bolts, studs and cap screws. The width of the flat surface 
at tiie top and bottom of the threads is one-eighth of the pitch. 




Square Thread 



Worm 1hiicM>(tUS3in) 
Fio. Sfi. 



WNrrvwWTM 'n«w>M>' 



The Square Thread. — The Square thread has not been stand- 
ardized. It is used for heavy work to transmit motion or power, 
as in jack screws and screw presses, but each manufacturer has 
his own standards of pitch. It is quite common practice to use 
a pitch twice as great as on a U. S. standard bolt of the same 
diameter. The Square thread is more difficult to cut than the 
other forms of threads. 

The Acme Thread. — The Acme thread is a compromise between 
the Square and U. S. standard threads. It is as deep as the square 
thread, but is stronger and easier to cut. It is used a great deal 
for feed screws, lead screws, etc., on lathes and other machine 
tools. 

The Worm Thread (Brown and Sharpe Standord).— This is 
used for the threads of worms in worm and wormwheel combi- 
nations. It is really a form of gearii^, but is cut in a lathe and 
is therefore ^ven the name of thread. It is a much deeper 



SCREWS AND SCREW FASTENINGS 37 

thread than the Acme, with the same angle (29°) between the 
sides of the threads. 

The Whitworth Thread.— The Whitworth thread is the stand- 
ard U8ed in England. It was designed by Sir Joseph Whitworth 
in 1S41, but has been slightly modihed since that time. It is 
more difficult to form than either the V or the U. S. standard, 
as the thread tools must be ground so as to make the exact curves 
at the top and bottom. 

22. Pitch. — Usually the threading of a bolt or screw is de- 
scribed by telling the number of threads per 1 in. of length, 
thus — "8 threads per inch," or simply "8 pitch." However, in 
giving the proportions of any given thread, we usually describe 
them in terms of the pitch. This is the distance from any point 
of a thread to the corresi>onding 

point on the next thread, as shown 

in Fig. 54, and is designated by the 

letter P, as shown in Fig. 55. The 

pitch of a single-threaded screw is 

the distance the screw or nut will 

advance in one complete turn. Thus 

a screw having S threads per inch 

has a pitch of \ in. and would ad- ^o< 60. 

vahce } in. in one complete turn. 

23. Bolts. — A bolt is a bar with a head on one end and a thread 
for a nut on the other. It is used to fasten two parts together 
by passing through them and clasping them together between 
the head and nut, as shown in the case of the two angles of Fig. 
56. Unless otherwise stated, it is understood that bolts have the 
U. S. standard thread, as this thread is in common use by bolt 
manufacturers. Bolts are designated by the shape of the head. 
The kinds usually employed in machine work are the square head 
and the hexagon (or "hex") head machine bolts (Figs, 67 and 69). 
The round of bar length of the bolt is called the slock, and 
carries on its end the thread for the nut. There are numerous 
special kinds of bolts used in special industries; for example, there 
are plow bolts, carriage bolts, stove bolts, etc. 

24. Bolt Heads and Nuts. — The heads and nuts of machine 
bolts may be either square or hexagonal, as desired. These 
have the same principal dimensions so that the same wrenches 
can be used on either. Table A shows the dimensions of the 
U. S. standard rough-foiled nuts and heads. Finished heada and 



38 



MACHINE DRAWING 



•f ' ' '— - 

DIMENSIONS OF U.S. STANDARD BOLTS, HEAOS^ NUTS. 




ROUSH. 

• 






0IA.OF 


4tOFMOS SHORT OIA. 

miNoiorHEAosai 

_L NUTS 


LONO OUkMCTER 


THICKNESS 


OIA OF 


ROOT 


0Oi.T 


OP HEADS SiNUTS 


4IXAaON &S9UARe 


TAP ORIU. 

YX 


OlAnKTBM 


HSXA80N 


SQUARE 


HEADS 


NUTS 

4=^ 


A 




1 




^w 


-^ 


W 


m 






^P 


^^ 


DI>TACIIOS>n.«B 


D'STACItOI 


tSCORNCffS 






MeAiiesT64« 


h ■! 




1 

■ * 


20 


1 

1 


E 


H 


1 

4- 


i 


& 


.165 




* 


Id 


i& 


^i 


H 


a 


1 


i 


.240 




^ 


16 


^ 


h 


ii 


k 


1 


^ 


.294 




S 


14- 


H 


H 


•a 


H 


ii 


a 


344 




i 


13 


i 


1^4 


li 


i^ 


i 


H 


.400 




1 


12 


¥^ 


li 


li 


1^ 


1 


Jil 


.454 




f 


II 


Ills 


'il 


li 


H 


1 


& 


.507 




1 


to 


'i 


IE 


m 


1 


i 


li 


j620 




i 


d 


lil 


1^ 


2iz 


II 


i 


k 


.731 




1 


d 


l| 


M 


2a 


rt. 


I 


a 


.837 




li 


7 


'S 


2h 


2S 


H 


li 


li 


.940 


• 


'i 


7 


2 


2h 


2g 


1 


■ i 


lik 


1.065 




•I 


6 


2| 


2& 


3iL 


\k 


i| 


•a 


1.160 




li 


6 


2| 


2k 


3a 


\\ 


li 


iH 


1.284 




'1 


5 


2i 


34 


3a 


If 


•i 


1^2 


1.49 1 




Z 


--^i 


3i 


3ft 


4E 


m 


2 


li 


1.712 




2k 


^i 


3i 


4|^ 


4|i 


ii 


2i 


2^ 


I.d62 




zk 


4. 


H 


4E 


^li 


>» 


2i 


2^ 


2.176 




H 


4. 


4.i 


4H 


6^ 


2i 


2| 


2A 


2.426 




3 


3* 


4| 


5& 


6& 


2| 


3 


2{4 


2.629 




Table ,4 






.' 


- »■ V V 


--».•-.- , 












': ■ 1 


' 



SCREWS AND SCREW FASTENINGS 39 

nnts are iV in- smaller in width than the dimensions given 
here. 

In representing a bolt head or nut on a drawing, we do not go 
to the trouble to lay it out precisely from the dimensions given 
in the table, unless the bolt itself is the main part of the drawing. 
If the bolt is only a detail of the drawing we generally use a simple 
system which represents very nearly the exact sizes and saves 
much time in drawing. In Figs. 57, 5S, 59 and 60 are shown the 
different views of square and hexagon bolt heads as they are 
usually drawn. The views of Figfi. 67 and 69 are usually pre- 
ferred because they indicate more clearly in the elevation that 
the heads are square or hexagonal. Kgs. 58 and 60 both have 



SquARK Head Bolt. 



P? 



e 



[^ 



^ 



^ 



USE M/0>0 

Fig. 57. Fia. 58. 



Hexasonau Head Bolt. 




WW 



use AVOID 

Fio. 59. Fia. 60. 



two faces showing in the elevation and therefore might be 
confused. 

In drawing the square head of Fig. 57 the width of the square 
is made about one and three-fourths times the bolt diameter. 
The draftsman does this by eye. The height of the head in the 
front elevation is made half the width of the bead or a little less 
than the bolt diameter. The height of a nut is made the same 
as the bolt diameter. The champfer (the bevelling of the corners 
on top) is shown by the full circle in the top view. In the front 
view we represent this by an arc, with radius equal to the width 
of the head, drawn tangent to the top of the head. 

Td represent the hexagonal head or nut (Fig. 59) the draftsman 
extends the lines representing the bolt stock. This gives one 
face of the head in the front elevation. One-half this width is 
set out on each side, for the other two visible faces. The top 



40 MACHINE DRAWING 

line is next drawn at a height a little less than the bolt diameter. 
The champfer is then shown. In the front face this is drawn 
with a radius equal to the bolt diameter. On the side faces a 
radius about one-third as great is used. In drawing the top 
view of a hexagon head, we locate the center lines and draw a 
broken circle to represent the stock of the bolt. With the 
diameter of the bolt as a radiits we then draw a light construc- 
tion circle, and in this we draw a hexagon. We then erase the 
construction circle. Within the hexagon and just touching 
each side of it, we draw a circle to represent the champfering or 
bevel on the top comers. 

25. Thread Conventions. — ^Draftsmen usually show threads 
in side view by the conventional straight-line method shown in 
Figs. 61 and 62. The long light lines represent the tops or 
"lands" of the thread while the short heavy lines represent the 
bottoms or "roots" of the thread. These lines should be evenly 




R.H.THr»CAO. t..H.THReXO. 

Fig. 61. Fig. 62. 

spaced and should be given a slight slant. On a single-threaded 
screw, one end of a light line should lie approximately opposite 
the other end of its adjacent heavy line. Ordinarily no attempt 
is made to make the spacing of these lines comply exactly with 
the pitch of the screw. 

The method of representing the end view of a screw is also 
shown in Figs. 61 and 62. The circle representing the "lands" 
of the threads is drawn soUd, while the root circle is broken 
because it represents a hidden surface, namely, the bottom of 
the thread. 

26. Right-hand and Left-hand Threads. — The thread shown 
in Fig. 61 is a right-hand thread; that is, to screw a nut on to 
such a thread it would be necessary to turn it in a right-hand or 
clockwise direction. Compare this with Fig. 62, which shows a 
left-hand thread. Note that the thread lines in this figure are 
given a slant opposite to those shown in Fig. 61. Where the 
stock of the bolt ends, a heavy object line should always be 
shown as in these figures. At the place where the thread termi* 



SCREWS AND SCREW FASTENINGS 



41 



nates a light line should be drawn straight across the bolt. The 
end of the stock should always be rounded, but its length should 
only be dimensioned to the cor- 
ner where the rounded end be- 
gins and not to the extreme tip 
of the bolt. 

Left-hand threads are not 
nearly so common as right-hand 
threads; hence, when a left-hand 
thread is desired it should be 
marked, L. H. Thread. It is 
not generally customary to mark 
right-hand threads as such; if 
marked, we would use the note, 
R. H. Thread. 

27. Tapped Holes. — ^The thread which is cut in any piece of 
metal to receive a screw is said to be "tapped.*' Ordinarily a 
hole is drilled in the piece to the same diameter as the inner 




Fig. 63. 



t-* 



> 



I 



J 









Hex Head Bolt 

I-RCQUIRCD MACHINE 



Fia. 64. 



diameter of the thread. A "tap*' (which is somewhat like a 
hardened bolt, having grooves for the cut metal to escape and 



43 MACHINE DRAWING 

sharp cutting edges on its threads) is then screwed into this 
hole, cutting a thread as it advances. 

In representing a tapped hole in a drawing, the plan view of 
the hole is very simple. As shown in Fig, 63, the plan view 
shows a solid inner circle representing the hole drilled for the tap; 
a broken outer circle surrounds it to represent the hidden threads 
cut by the tap. This outer circle is drawn to the nominal diame- 
ter of the screw. 

The representation of a tapped hole in elevation must naturally 
be all in broken lines, since the hole is hidden from sight in 
this view. Fig. 63 illustrates the most common method of 



Face Plate 
l-requibeo cast iron 

SCALE 3*-l' 



Fio. 65. 

showing this. The threads are represented just as in Fig. 61, 
but with all hroken lines. The hole at the left is drilled and 
tapped clear through the piece; that at the right, only part way 
through. 

Fig. 64 shows a drawing of a IJ-in. X 3|-in. hex. head 
machine bolt with nut, using the conventional methods of showing 
the threads and the head and nut. The actual heights of head 
and nut and the true width {from Table A) are given tor the 
guidance of the blac^mith and machinist in making the bolt. 

Fig. 65 shows a drawing involving several tapped holes. This 



SCREWS AND SCREW FASTENINGS 



43 



is a special face plate for a lathe. It is to be tapped with a )-in. 
standard bolt tap at three points equally spaced on a circle of 
4|-in. diameter. These holes are for studa for attaching a special 
fixture to the face plate. In the center of the plate is an in- 
ternal thread for screwing the face plate onto the spindle. The 
note referring to this hole is marked THREAD instead of TAP, 




Fia. 66. 



FiQ. 67. 



because this is to be cut with a thread tool in a lathe in order to 
make it absolutely true. 

28. Other Thread Conventions. — In Figs. 66 and 67 are shown 
other conventions that are occasionally seen. The conven- 
tion at £ in these figures is especially simple and convenient 
for sketching purposes but has the great disadvantage that 



Fia. 68. 

it bears no resemblance to screw threads and hence is not 
recommended. 

29. Cap Screws. — A cap screw is similar to a bolt, but is used 
without a nut. The head may be either square or hexagonal. 
A cap screw is used by passing it through one of the pieces to be 
fastened together and screwing the threaded part into the other 
piece. Fig. 68 shows the method of using cap screws in fastening 



44 



MACHINE DRAWING 



Dimensions 


OF A.5.M.E. Standard 

• 


Machine 


5CREWS 


Na 


THREADS 
PER INCH 

AAAAAA 


DIAHCIER 
OF BODY 

¥ 

D 


OIAH. OF 
FLAT HEAD 

20 -.008 


DIAM. OF 
ftoUNDHCAO 

l.850.-X)05 


(XAM. OF 
FILLISTER HEAC 

M 

I.64D-.009 


LENGTHS 





60 


• 060 


.112 


.106 


.0894 


k'^i' 


1 


72 


.073 


.136 


.I30 


.1107 


i' - i 


z 


64. 


.086 


.164 


.154 


• 1320 


^ " i 


3 


dS 


•099 


• 190 


• 176 


• I5?0 


• 1" - 1" 


4* 


46 


• 112 


.216 


.202 


.1747 


1' " 1" 


3 


44 


.125 


.242 


.226 


.I960 


1* - i" 


6 


40 


• i36 


.262 


• 250 


.2170 


4" ' •• 


7 


36 


J5I 


• 294 


• 274 


.2366 


i" " 'i* 


8 


36 


• 164 


.320 


.296 


.2599 


i" • ^ 


9 


32 


.177 


.346 


.322 


•2813 


i" - 'i" 


lO 


30 


.190 


.372 


•346 


•3026 


i" - «i" 


12 


28 


.216 


.424 


.394 


•3452 


1" - '1" 


14. 


24 


.242 


•472 


.443 


.3879 


r " 2" 


16 


22 


.266 


• 526 


.49) 


.4305 


r • ^" 


16 


20 


• 294 


• 580 


.539 


•4731 


i" •• ^i" 


20 


20 


• 320 


.632 


.567 


.5158 


i" -^r 


22 


16 


.346 


.682 


• 635 


•5584 


V • 3" 


24. 


16 


.372 

1 


.732 


• 683 


.6010 


i* ■ 3" 


26 


16 


• 398 


•768 


• 731 


.6437 


I' ■ *" 


26 


14 


•424 


.840 


.779 


• 6863 


i* " 3- 


30 


14 


.450 


.692 


.827 


.7270 


\ " 3 



Tablb^. 



SCREWS AND SCREW FASTENINGS 46 

a bracket to a machine. In this figure, the metal aroimd the 
cap screw is broken away to show the cap screw clearly. 

The heads of cap screws are smaller than those of bolts. The 
widths (or the short diameters) of hexagon heads for cap screws 
are standardized as foUows: 

For screws up to and including i\ in., the heads are made 
■^ in. wider than the screw stock. 

For sizes ) in. and larger, the heads are made i in. wider than 
the screw stock. 

For square heads, the width is ^ in. greater than the stock for 
sizes up to and including | in. Above | in. the beads are } in. 



Pig. 69. 

wider than the stock diameter. The height of the bead is equal 
to the diameter of the screw. The top of the head is not flat like 
a bolt head, but is rounded with a radius equal to the long 
diameter of the head. Cap screws can also be obtained with any 
of the other heads shown in Fig. 70. 

30. Machine Scfews. — Machine screws are used for the same 
ptupose as cap screws, but for small work only. Machine 
screws are generaJly used for sizes below } in. They are made in 
screw gage sizes and sold by the gage numbers instead of the 
fractional inch sizes. 

Table B gives the dimensions of standard machine screws. 
The lengths given in the last column are the distances that the 
screws will enter the work, which are the lengths under the head, 
except in the cases of the Flat and French heads, where they are 
the overall dimensions. 

For drawing the heads of machine screws the following dimen- 



«*".. 



46 



MACHINE DRAWING 



sions for Fig. 69 may be used, although they do not check exactly 
with those of Table B: 





FUlister Head 


Flat Head 


Round Head 


D = 


Diameter of body 


Diameter of body 


Diameter of body 


A = 


1.6 D 


2.0 D 


1.75Z) 


B = 


0.75Z) 


0.6 D 


0.6 A 


C - 


0.5 D 


0.3 D 


0.6 D 


E - 


0.25D 


0.25D 


0.25D 


B = 


A 




0.6 A 



Fig. 70 shows some of the different kinds of heads for machine 
screws. The square and hexagonal heads are the only ones on 
which a wrench can be used. These heads are usually thicker 
and of smaller diameter than the U. S. standard bolt heads. 
All of the other heads are provided with slots for a screw driver. 

31. Set Screws. — ^A set screw is used to fasten two machine 
parts together by screwing through one part and pressmg against 
the other. For example, in fastening a wheel to a shaft, the set 



0? 



SQUARE 




Ch pb 4]b d[7 ^ 



MEXAGON OVAL PT-ACT BUTTON 

r/LLI5TER FILLISTER 

Macmimc Screw Heads. 

Fia. 70. 



FLAT FRENCH OR 
OVAL. 
COUNTERSUNJI 



screw passes through the hub of the wheel and presses against 
the shaft. It is a poor fastening for transmitting power, and 
should not be used if a key or square shaft caH be used. 

Fig. 71 shows some of the common forms of heads for set screws. 
The thickness of the head and the width across the flats are ordi- 
narily made equal to the diameter of the screw. The headless 
set screw, in which a screw driver is used to turn it into place 
has the advantage that it can be screwed in so that there are no 
projecting parts to catch the clothijig. It has the objection, 
however^ that one side is apt to break off. To remedy this 
defect, a hollow-head set screw has been designed. This requires 
a special wrench bent from a hexagon steel bar. 

Set screws are sometimes "necked" imder the head. This is 



SCREWS AND SCREW FASTENINGS 



47 



done by cutting them down bo that the diameter is a little less 
than that of the root of the thread. This makes the "neck" the 
weakest part of the screw so that, if the screw should break when 
being tightened, it will break at the neck instead of in the hole. 
The most common forms of set screw points are shown in Fig. 
72. Any of the heads of Fig. 71 can be used with any of these 



SQUARC MEAD 



LOW HEAD 



Sbt Screw HeAD% 
Fig. 71. 

points. In using a set screw on finished work, where the point 
of the screw is liable to burr or roughen the part against which 
it presses, a round brass piece called a "gib" is often dropped 
into the tapped hole so that the screw point presses against the 
gib and the gib against the part to be fastened. Set screws are 
made of steel and are usually case-hardened. 




S»T Screw Bsints. 
Fio. 72. 

S2. Multiple Threads. — In all of the threads that we have 
considered thus far, there has been but a single thread on the 
screw. It is sometimes desirable, however, to have more than 
one. If there are two separate threads on tli,e screw, it is called 
a double thread; if three threads, a triple thread; and if there ar« 
four threads, it is a quadruple thread 



48 



MACHINE DRAWING 



In Fig. 73 is shown a double-thread screw. . Compare it with 
Fig. 64. The outside diameter of the screw, the root diameter, 
the depth of the threads, and the pitch are the same in both oases, 
but the amount that the thread advances in one turn or revolu- 
tion of the screw is twice as great in the double thread as in the 
single thread, and the lines of the threads in the drawings must 
be given a correspondingly greater slant than in the case of single 
threads. _ 

33. Lead. — ^The distance that the thread advances along the 
screw per revolution is called the lead (pronounced as if spelled 
"leed"). For a triple thread, the lead would be three times the 
pitch. Multiple threads are used when it is desired to secure a 
greater advance per revolution, without reducing the root 
diameter of the screw. Any of the threads of Fig. 55 may be 




Fig. 73. 

made multiple. Wherever a multiple thread appears on a draw- 
ing, a note should state the fact, giving complete information. 



Problem 7 

Make a full-size pencil drawing of the details shown in Fig. 74. Use a 
9-in. X 12-in. sheet. First lay out all of the center lines and then draw the 
machine screws. As is noted on the sketch, these are to be No. 24 screws 
with 16 threads per inch. Refer to Table B, which is the table of standards 
adopted by the American Society of Mechanical Engineers, and you will 
find that the diameter of the body of a No. 24 screw is 0.372 in. For draw- 
ing the heads, use the proportions given with Fig. 69, but do not put any 
dimensions on the heads 

The dimensions that you get will be in decimals and, if you have no scale 
divided into hundredths of an inch, you can find the nearest fraction from 
Table C, and use the ordinary scale. For example, the diameter of the body 
of a No. 24 screw is 0.372 in. The decimal in Table C that is nearest to this 
18 0.375 which is the equivalent of I in. Use i in. for the diameter of the 



SCREWS AND SCREW FASTENINGS 



49 



screws when drawing them, but use 0.372 in. when making your calculations. 

The length of each of the screws, exclusive of the head, is 1} in. This 
dimension, together with the number of the screw and the threads per inch, 
is all of the information necessary on the drawing. 

Use the method of Fig. 61 for drawing the threads for all of the details 
on this sheet. 

Next draw the bolt. Obtain the dimensions of the head and nut from 
Table A. Be sure to supply the two dimensions for the nut. 

Finally, draw the square-head cap screw. The head of this screw is 
smaller than that of a bolt but is higher. The dimensions can be obtained 
from the following: 




^•^ 



I 



i'-1 



ljj..jjj.j:l...u...i 



•i--^ 




BUTTON HEAD FILLISTER HEAD FLAT HEAD 

No 24- -16 Machine Screws -Mach. Steel. 





Hex Head Bolt and Nut - Mach. Steel. 



u 3- M 

y\ n - r" 



details of 
Screws 



i* Square HtAo Cap Screw- Mach. Steel 



scale:iz'»i^' 



. DR. TR. 



CH. 



DATE 

No.7 



Fig. 74. 

The short diameter of a square head for a cap screw is i in. greater than 
the diameter of the screw, for sizes of screw up to and including } in. For 
screws } in. and larger, the short diameter of the head is i in. greater 
than the diameter of the screw. The short diameter of a hexagonal head 
for a cap screw is i^ in. greater than the diameter of the screw, for sizes of 
screw up to and including -f^ in. For screws i in. and larger, the short 
diameter of the head is i in. greater than the diameter of the screw. The 
height of either a square or hexagonal head for a cap screw is equal to the 
diameter of the screw. The top of the head, in either case, is rounded with 
a radius equal to the long diameter of the head. . 

Put the title under each of the parts and the general title in the lower 
right-hand comer of the sheet as shown in the figure. 



50 



MACHINE DRAWING 



TABLE OF DECIMAL EQUIVALENTS FROM ^TO \ INCH 



FRACTION 



h 



I 
6^' 



<6 



1^- 



8 



« & 



hi"Z 



&• 



3l- 

16 



ill- 



^- 



64 



i- 



k 






i" «»««« 
.e.... 



4«- 

92 



li- 



a, 
e 



3- 



a 



X 

16 



S- 



DECIMAL 
EQUIVALChCr 



.015625 
•03125 
.046675 
.0625 

..076125 
-.09375 
.. 109375 
-.125 



•. 140625 
...15625 
•.I7ia7& 
.1875 



-.203125 
...2187.5 
...234^75 
-.25 



F-. 265625 
-.28125 
% 296875 
.3125 



I 






-; 328125 
-.•34375 
-.369375 
-. 375 



- . 390625 
.40625 
. 42(875 
.4375 






. 453125 
.46875 
.464375 
.5 



FRACTION 






DECIMAL 
EQUIVALENT 



5. 

16 



i7 



II. 

16 






3l. 

4 






• • •••••• 9 • •• 



^- 



16 



i- 



S" 



32* 



^- 



16. H. 

Sl- 
at 64 

92 
« 6^ 



.515625 
.53125 
.546875 
-.5625 

-.578125 
-.59375 
-. 609375 
-;625 



-.640625 
.. 65625 

.671875 
. 6875 



-. 703125 
.• . 71875 
-. 734375 
.- 75 



•••i-765625 
«... 78125 
-.. 796875 
..% 8125 



'". 828125 
-. 84375 
•. 859375 
-•. 875 



-: 890625 
»-% 9062S 
... 921875 
••. 9375 



-.. 953125 
", 96876 
•n 984375 
•i OOOOO 



Table C. 



ASSIGNMENT 8 

34. Method of Drawing Square Threads. — ^In order to show 
a square thread accurately it would be necessary to show the 
threads curved as in Fig. 76. For shop drawings this is not 
necessary, however, and the straight-line conventional method 
of Fig. 76 may be used. 

To lay out threads by this method, space off points on one 



SCREWS AND SCREW FASTENINGS 



61 



side of the screw so that the thickness of thread and width of 
space are equal; in other words, the points are equally spaced. 
Then space oflE points on the other side of the screw so that they 
are opposite the ones first drawn, as indicated by the dotted lines 
of Fig. 76, which are drawn perpendicular to the center line of 
the screw. For a single thread, the lines drawn across the screw 
should be drawn so that a space on one side comes opposite a 
thread on the other. The threads shown in the figure represent 





Fig. 75. 

a single thread. If the thread were double, a space would come 
opposite a space and the lines would slant still more. 

36. Drawing to Scale. — In representing objects which are 
larger than the allowable drawing space, it is necessary to reduce 
the dimensions proportionately. This is accomplished by the 
use of the architect's scale, shown in Fig. 20. This scale usually 
bears eleven different graduations, as follows: 





Fia. 76. 



Full size 


• 


Scale 3 in. » 1 ft. 


Scale f in. = 1 ft. 


Scale li in. = 1 ft. 


Scale i in. = 1 ft. 


Scale 1 in. » 1 ft. 


Scale A ill' = 1 ft. 


Scale i in. — 1 ft. 


Scale i in. = 1 ft. 


Scale i in. = 1 ft. 


Scale ]/^ in. =1 ft. 



The first reduction in size in common use is half-size, or to the 
scale of 6 in. = 1 ft. This scale is not shown on the architects' 
scale, but is easily taken from the full-size scale. Each dimen- 
sion on a half-size drawing is reduced one-half of full-size. If 
this scale is too large, the next one to use is 3 in. == 1 ft., or 



62 MACHINE DRAWING 

quarter-size. On this scale a distance of 3 in. is divided into 
twelve equal parts, and each of these into eight equal parts. In 




using this scale, the student should think of the distance not as 
3 in., but as a foot divided into inches and eighths of inches. 

In drawing a circle, it is often convenient to lay off the diameter 
on a scale just half the size of the one to which the drawing is 



SCREWS AND SCREW FASTENINGS 63 

made, and use this distance as a radius. For example, to draw 
a circle 1| in. diameter to a scale of 6 in. = 1 ft., lay off 1 J in. 
on the scale of 3 in. = 1 ft., and use this distance as the radius. 

Problem 8 

Make a half-size pencil drawing of the screw and cap of a 12-ton jack 
screw, as shown in Fig. 77, drawing the views indicated in Fig. 78. Use a 
9-in. X 12-in. sheet for this drawing with the long dimension horizontal. 

In drawing the screw, place the horizontal center line 2 in. below the upper 
border line. In the end view, place the vertical center line } in. inside of 
the left vertical border line. Allow f in. between these two views. 

In drawing the cap, place the horizontal center line 4} in. below the upper 
border line. In the end view, place the vertical center line 2} in. to the 
right of the left vertical border line. Allow } in. between the two views 
of the cap. 

Use the Method of Fig. 76 for Showing the Square Threads of 
the Screw instead of the convention shown in the sketches of 
Fig. 77. 

As there are three square threads per inch and as the width 
of space is the same as the thickness of the thread, each inch in 



^ 



&-0- 




FiG. 78. 

the drawing would be divided into six equal parts if the drawing 
were made fulUsize. Since the drawing is to be half^size^ ^ in. 
on the drawing equals 1 in. on the finished object; therefore, 
three complete threads or six equal spaces must be shown in a 
length of § in. on the drawing in order that the threads as well 
as the rest of the drawing will be half-size. The length of each 
of these equal spaces is equal to one-sixth of J in. or ^ in. 
Since the scale is not divided into twelfths of an inch it is neces- 
sary to determine this length, t4 in., in some manner. It might 
be determined by trial with the dividers by setting them to an 
approximate spacing of ^\ in. and then pointing off this distance 
twelve times along a straight line 1 in. long to determine how 
nearly correct the setting is. Another and better way to find 
the length of space without the use of the dividers is as follows: 
Draw a line exactly § in. long, as the line A-B, Fig. 79. From 



54 MACHINE DRAWING 

one end of it, as A, draw the line A-C of indefinite length and 
making an angle of about 30® with A-B. On il-C, starting at 
A, lay off six equal divisions. For these you can take any equal 
divisions, but J in. is a convenient one. Lay ofif il-1, 1-2, 2-3, 
3-4, 4-5, and 6-6, each J in. long. From 6 draw 6-J5. Parallel 
to 6-J5 and through the points 5, 4, 3, 2, and 1, draw the lines 
5-5', 4-4', 3-3', 2-2', and 1-1'. 

The line A-B, i in. long, is thus subdivided into six equal 
parts, each of which is equal to the width of space and the thick- 
ness of thread on the thread of the screw as it will appear upon the 
drawing. Any length of line can be divided into any number of 
equal parts in the same manner. The dividers can now be set 
to this spacing and the threads laid out on the screw. 

The i-in. holes in the largest diameter of the screw are for 
the purpose of inserting a bar to turn the screw. 

Put a title or "legend" under each of the pieces, as shown in 
Fig. 77, in letters | in. high. In the lower right-hand corner 
put the title of the plate, 

DETAILS OP 12-TON JACK SCREW 

as shown in Fig. 77, and make the balance of the title just as in 
the previous assignments. 



CHAPTER III 



SECTIONS 
ASSIGNMENT 9 

36. The Use of Sections. — ^The uses of broken lines to show 
hidden parts were explained in Chapter I, Art. 11. Broken Unes 
are not always satisfactory and are often confusing, especially if 
very numerous. For these reasons, the method of showing 
objects in section is frequently used to show interior construe- 
tions. This method consists in cutting away the parts which 
hide those we want to show, thus allowing the hidden parts to 
stand out in full view. This is called cross-sectioning y or section- 
ing. Such a view is called a cross-section, or more simply, a 
section. As a simple illustration, we have in Fig. 80 two ordinary 
views of a plain cast-iron collar, the hole being indicated in the 





I 



(b 



£ s 



J 



Fig. 80. 



SECTION ON UNC A-e. 

Fig. 81. 



SECTION ON UNC A-0« 

Fig. 82. 



right view by the broken lines. Fig. 81 shows the same collar 
but with the hole shown by a section view. The end view is 
still shown in the usual manner, but, instead of the side view 
being shown by a front elevation, we imagine that the front half 
of the collar in this position has been cut away to show the 
inside. The Ught diagonal lines across the places where the 
metal would be cut form what is called the cross-hatching. 
These lines are drawn lightly about iV in. apart, and usually 
at an inclination of about 45°. If we imagine that the cross- 
hatching lines represent the saw marks, then we can always tell 
what part is to be cross-hatched. When there is a hole or open- 
ing in the object there will, of course, be no saw marks and, 
hence, there is no cross-hatching in thd area representing such 
hole or opening, as is clearly shown in Fig. 81. 
7 55 



56 



MACHINE DRAWING 




Let us suppose that this collar is fastened to a shaft by a set 
screw. In order to show the arrangement of the shaft and screw 
inside of the collar, we can cut the collar in the same way, as 
shown in Fig. 82. To actually cut the collar we would also have 
to saw into the shaft and screw, but it is cuatomary to consider 
them as not being cut, as it would only increase the work of 
making the drawing and would not make the construction of the 
collar any clearer. 

As a general rule it may be stated that: Bolts, screws, shafts, 
keys, arms of pulleys, etc., are not shown in section when cvi along 
the line of their greatest dimension, that is, lengthmse. If the sec- 
tion cuts across a shaft, screw, or 
similar object it might, in such a case, 
be cross-hatched. 

Fig. S3 shows a section of a gland 
for a stuffing box. The flange around 
the top projects all the way around. 
Consequently, in the section elevation, 
the lower edge of the flange might be 
shown by a broken line crossing the 
body from a to b. It is much better, 
however, to keep the section free from 
such complications and only depend 
on it to show the interior of the object. 
If it is necessary to show both the in- 
side and outside of the same view of 
an object, it is better to use the principle of half-sections. 

37. Haif-sections. — When a figure is symmetrical about an 
axis (that is, alike on both sides of its center line), it is a good 
plan to show only one-half in section. Such a drawing is known 
as a "half-section" because we have only sawed halfway through. 
Fig. 84 shows a half-section of the same collar as in Fig, 82. In 
Fig. 84 we really consider that the upper front quarter of the 
collar is removed. The horizontal cut thus produces a surface 
along the horizontal center line, which is indicated by a heavy 
object line on the center line of Fig. 84. Any peculiarities of 
the outside of the object would be shown by one-half of the 
view, while the inside would be shown by the sectioned halt of 
the view. 

If a section passes through the center of a hole that is tapped- 
with a right-handed thread, the thread is shown in the conven- 



FiG. 83. 



SECTIONS 67 

tional straight-line method, but the thread lines slant in a direc- 
tion reverse to those of a right-handed outside thread. The 
threads which appear in the section are those on the far or rear 
side of the tapped hole; see Fig. 85. Fig. 84 shows the collar 
with the set screw in place. Fig. 85 shows the same collar with 
the set screw removed, and the tapped hole which receives it 
exposed to view. 

Half-sections often show the interior construction of an object 
so well that many broken lines may be conveniently omitted 
from the other half of the view. In the view that is half-sec- 
tioned, avoid running dimensions from the sectional part to the 
full part; rather show them in the other view of the object, 
imless the part dimensioned is shown by a full line in both parts 
of the view. Also avoid placing dimensions, or running exten- 
sion or dimension lines across the cross-hatched portion of the 
view, although this is sometimes necessary. 





HALf SBCnON ON UNE A-S.. HAUr OTCTlON OM UNE A-A^) 

Fig. 84. Fia. 85. 

Always put the cross-hatching on after putting on the dimen- 
sions, so that in case it is necessary to put a dimension in the 
cross-hatched area, a break may be made in the cross-hatching. 

It does not make any difference in which direction the cross- 
hatching lines slant, so long as they make an angle of 45° with 
the horizontal, except that on the same piece they should all 
slant in the same direction. You will find it most natural, 
however, to begin in the upper left-hand corner of the view to be 
cross-hatched. The spacing can be judged by the eye, the lines 
being about tV in. apart. 

38. Broken Sections. — Cutting planes need not always be 
continuous; they are very often broken or "zigzagged" so as to 
show the construction of the object in different planes. Fig. 86 
shows a drawing of a bearing block. The cutting plane for the 
half -section is passed along the lines ABODE of the top view so as 
to show the interior construction at the oil hole and also at a bolt 
hole. 



fig MACHINE DRAWING 

Note that the surface CD where the cut is set over is not 
indicated in the section view. Since the bearing block is sym- 
metrical about its axis, the other half may be shown conveniently 
aa a full elevation view. When a section plane follows a devious 
outline as in this case, it is shown in the plan by the usual center- 
line convention. Appropriate letters and notes should show 
where the cutting plane is passed, and the section view should be 
labelled accordingly. It is general practice to omit such notes 
where the cutting plane is passed along the main center line, 
as in Figs. 81, 82, 83, 84, and 85. Notes were used on these 
drawings merely for the information and direction of the student. 
39. Fillets. — The most frequent 
error of the inexperienced drafts- 
man is his habit of showing sharp 
comers on castings, though it k 
very natural that he should if he 
sees no reason for not doing so. 
In all probability such errors on 
the part of the draftsman would 
be taken care of by the pattern- 
maker unless he, too, were inex- 
perienced, when trouble would be 
likely to occur. 

There are three reasons why 
sharp, square comers are objec- 
tionable and why we use rounded 
■MLp sccnoN ON UNC A-B-e-D-c outslde comers and fillets. 

Fig. 86. First. — The rounded comer pre- 

sents a more pleasing appearance. 
Second. — The square comers on the pattern make correspond- 
ing square corners in the sand and these comers in the sand are 
difficult to keep intact, thus causing the molder a lot of trouble. 
Third. — The most important reason, however, for rounding 
the comers is that they give the casting more uniform strength, 
while with square comers the weakest parts of the casting are 
the corners. 

Figure 87 shows the method of crystallization in a casting with 
sharp comers. As the iron hardens, the crystals seem to form 
in lines perpendicular to the faces, as indicated by the hnes in 
Fig. 87, This will leave an open space, or a space of irregular 
crystallization at b, and the casting is liable to break along the 



SECTIONS 



59 



line a-6-c. By rounding ofif the outside corner, and placing on 
the inside corner a fillet (which is the name applied to an inside 
rounded corner), we change conditions to those shown in Fig. 88 
where the lines of crystallization are all perpendicular to the sur- 
faces, and where there are no open spaces or places of irregular 
crystallization. 

In drafting, always show rounded corners, both inside and out- 
side, -on castings which are to have those corners left in the rough, 
that is, not machined. 



Fpg 



=31111111 

^>nniiiiniiiii.l 




Fia. 87. 



Fia. 88. 



Generally a corner of ^in. to |-in. radius is used according 
to the size of the part. The radius to be used is frequently left 
to the judgment of the pattern-maker, in which case it need not 
be noted on the drawing. When larger radii are used there is 
generally a definite reason for the given size, and it should be 
specifically noted. 




Bearing Block 

2-RCQUlReD CAST IRON 

Fig. 89. 



Problem 9 

Fig. 89 shows the side and end views of a plain bearing block. Make a 
full-size pencil drawing of this block showing the views indicated in Fig. 90. 
Use a 9-in. X 12-in. sheet with the 12-in. dimension vertical. 

The views can be arranged to better advantage if the sheet is placed on 



60 



MACHINE DRAWING 



3-9Q- TXIS.Pei^ 



the board with the long dimension vertical. The 1-in. margin should be at 
the top. Place the top view 1 in. from the top border line, and allow } in, 
between the views. This arrangement will allow sufficient space at the 
bottom of the plate for the title. 

In Fig. 90 the sectional view is 
shown cross-hatched all over. This 
was done simply to show which 
view, and which part of the view, is 
to be cross-hatched. It does not 
mean that the whole part is to be 
cross-hatched as shown here. The 
student will need to determine for 
himself just where the cross-hatch- 
ing riiould be placed. This ex- 
planation also applies to pioUema 
which are to follow. 





MAUF SECTION ON LINK A-8. 

FiQ. 90. 



JBpov ran 12 1bN Jack 

l-RCQCMWO CAST IRON 

FiQ. 91. 



ASSIGNMENT 10 

Problem 10 

Make a half-size pencil drawing of the jacknacrew body shown in Pig. 91, 
drawing the views and half-section indicated in Fig. 92. It will be found 
necessary to use one of the 12-in. X IS-in. sheets. The sheet should be 
placed on the board with the 18-in. dimension vertical. Draw the border 




SeCDON ON UW A4. 

Fig. 92. • 




Fig. 93 



lines so that the margin at the top will be 1 in. wide, and on the other three 
sides i in. wide. 

Draw a vertical center line in the middle of the sheet, and, after allowing 
2 in. between views, locate the center of the top view so as to leave an equal 
amount of space between the views and the top and bottom border lines. 



SECTIONS 



61 



In the part of the drawing where the threads are shown in section, it will 
be necessary to show the thread outlines. This can be done as shown in 
Fig. 76, except that in this drawing the threads will slant in the opposite 
direction, as it is the back part of the threaded hole that is being shown here. 
The threads shoidd not be drawn all the way across the hole, but only as 
far as the center line, since this view is a half-section. It will be necessary 
to lay out at least one thread on the opposite side of the hole, however, to 
get the proper slope for the threads. After drawing in one, the others can 
be drawn paraHel by using both triangles. 

The conventional method of representing cast sted in section is shown in 
Fig. 93, being two fine parallel lines close together, then a wider space, then 
two more lines like the first, etc. 

ASSIGNMENT 11 

40. Partial Sections. — When a section is needed to show the 
interior construction of a machine part in only one particular 
place, we can imagine the metal in front of that place broken 
away so as to leave the hidden parts exposed. This is the method 




FiQ. 94. 

that was used to show the cap screws in Fig. 68. To do this, a 
wavy line is drawn free-hand around the part, and the proper 
cross-hatching is placed inside the broken space. This makes 
it appear as if the metal had been broken away roughly. 

41. Revolved Sections. — The necessity of drawing an extra 
view of an object may frequently be avoided by the use of a 
revolved section. For an example of the revolved section see 
Fig. 94. Notice that it consists in drawing a cross-section of the 
handle on the plan view, thus doing away with the necessity of 
making a separate end view in order to show the shape of the 
section of the handle. 

Fig. 95 shows how a piece of an object may be broken out to 
leave room for the revolved section. This is especially desirable 
in this case because the arm tapers, and consequently the lines of 



62 



MACHINE DRAWING 



the lower flange would cross the section if it were drawn on the 
object, as in Fig. 94 without breaking away the arm. 

Fig. 96 illustrates a common method of showing sections where 
the sections are different at diiBferent points along a piece. The 
sections are drawn off the view but the lines at which they are 
taken are located on the drawing of the object. This method 
is frequently used in showing the shape of long parts such as 
lathe legs, connecting rods, etc. 




Fig. 95 

Pulleys, hand wheels, gears, and other such circular objects 
are usually shown by two views, one of which is a section. 

Fig. 97 shows a complete conventional drawing of a six-arm 
pulley. It will be noticed that the section plane is passed along 
the vertical center line, but that the arms which would really be 
cut in making the section are not cross-hatched and, instead, the 
section is shown as if it passed just to one side of the arms. As 
stated in Art. 36, it is. the general practice not to cross-hatch 




SecnON ON Ar6 



secnoNON c-o 
Fig. 96. 

the arms of pulleys, hand wheels, etc., when cut lengthwise. 
Only the hub and rim should be cross-hatched. It should be 
noted that the inside surfaces of the rim should be shown by full 
object lines all the way across, as if the section plane had been 
passed just in front of the arms, thus showing only the rim and 
hub in section. 

For greatest strength, the keyway should always be shown on 
the center line of one of the arms, and not midway between two 



SECTIONS 



63 




Fig 97. 




Hand Wmceu 

HREQUtRCD CAST IRON 



8 



Fig. 98. 



64 



MACHINE DRAWING 



arms. The face of this pulley is 4 in. Instead of being flat or 

straight; it is crowned. Different authorities recommend that 

pulleys should be crowned (or have a rise of) from iV in. to f in. 

per foot of width, but | in. per foot of width is a good average. 

The crown is for the purpose of keeping the belt on the pulley. 

Pulleys for use with shifting belts should be straight or flat, that 

is, without crowning. 

Note that the diameter of the pulley is marked TURN. This 

means that enough stock must be left on the pattern so that the 

pulley can be turned down to the required diameter. 
A revolved section on one of the arms is used to give a clear 

idea of its cross-section. 
42w Shortened Views. — Fig. 96 illustrates a common practice 

in show;ing long slender objects, of breaking and leaving out 

part of the length in order that the piece 
may be shown on the paper without using 
too small a scale. The long arm in Fig. 
95 is broken and the two end pieces placed 
closer together than they would actually 
be if the full arm had been drawn. This 
permits the use of a larger scale on the 
parts shown. The full length of the arm 
should, of course, be given in dimensioning. 




2eCT10N 

ON LiNC A-D. 

Fig. 99. 



Problem 11 

Make a full-size pencil drawing of the hand wheel shown in Fig. 98 
making the views shown in Fig. 99. Use a 9-in. X 12-in. sheet for this plate. 

By referring to Fig. 98 you will note that in the front view there are three 
spokes, while the side view is drawn as if there were two spokes, and these 
directly opposite each other. The left-hand view is depended upon to show 
the number and arrangement of the spokes. If we attempted to show the 
spokes in the side view as they would actually appear when the hand wheel 
is in this position, the two lower spokes woidd appear shortened. It would 
be more difficult to show the spokes in this view as they really are, and 
would make the drawing less easy to read. 

In making the section of the hand wheel, the student should show the 
spokes as if they stood vertically, in the same manner as shown in Fig. 98. 
As explained in Arts. 36 and 41, the spokes should not be cross-hatched. 
The rim and the hub only should be cross-hatched. 

A revolved section of one of the spokes should be shown on the front view. 



CHAPTER IV 

TECHNICAL SKETCHING 
ASSIGNMENT 18 

43. Use of Sketching. — ^The ability to make neat^ clear, 
comprehensive sketches of machine parts is one of the most 
valuable assets a draftsman, designer, or engineer can possess. 
Quite frequently it happens that a repair part, for which there 
may be no regular drawing, is required. The draftsman takes 
a pad of paper, a pencil, a rule, inside and outside calipers, a 
machinist's square, and, in some cases, a protractor, and goes 
direct to the machine in question, where he makes a complete 
sketch of the broken part. This he dimensions fully, adding any 
notes that may be required. The sketch is not made to any 
scale, but is laid out by eye or by some rough measurement to 
secure the right proportions. This sketch is rushed through the 
shop with all possible haste, and the repair part is often completed 
and installed in the machine in less time than it would take to 
make and trace a mechanical drawing of the part required. If it 
is desired to have a permanent drawing of the part, a regular 
mechanical drawing is made from the sketch and filed away in 
the usual manner. 

The designer or engineer uses the sketch as a means of record- 
ing his ideas at once, before he may forget them. The drafts- 
man keeps a sketchbook, the pages of which are made of cross* 
section paper; that is, paper ruled in light horizontal and vertical 
lines spaced i in. to i in. apart. With the aid of these lines 
he is able to make correctly proportioned sketches without the 
use of the scale. Such a book, when filled with sketches, is 
filed away so as to be of use at some future time. 

44. Suggestions for Sketching. — There are many points to 
consider in measuring an object and making a drawing of it, but 
a good mechanic is often better endowed with common sense 
in this respect than is a regular draftsman, because he knows 
better the operations used in making a piece and can see what 
dimensions are most important. A few don^U by way of caution 

05 



66 MACHINE DRAWING 

will point out some of the most common errors in this sort of 
worl^. These are taken from ** Donets for Draftsmen and 
Machinists," published by "Machinery." 

Don't forget fillets. 

Don't repeat dimensions. 

Don't use fancy lettering. 

Don't put unnecessary finish on parts. 

Don't forget clearance for moving parts. 

Don't ever forget to put the scale on a drawing. 

Don't fail to sign all drawings which you make. 

Don't give dimensions in 32ds when 8ths are close enough. 

Don't put important dimensions where they may be over- 
looked. 

Don't omit .minor details; it causes endless confusion and 
delay. 

Don't fail to use stock sizes of drills, reamers, etc., when 
possible. 

Don't make three or four different views of a piece when one 
or two views will do as well. 

Don't forget center lines. A circle without its center lines 
looks like a bald-headed man. 

Don't put a lot of cored work on a "one-casting-only" job, 
A little extra metal is cheaper. 

Don't imagine rough castings come just like the drawing; 
they vary and you must allow for it. 

Don't give the same dimension twice, for it is liable to lead to 
errors when this dimension is changed. 

Don't leave some dimensions to be gotten by adding a lot of 
other dimensions together or by subtracting them. 

Don't forget that the molder despises sharp square corners — 
internal ones more than the external ones. 

Don't, when lines are close together, make arrows so that the 
workmen cannot tell which line they go to. 

Don't put all dimensions on, then all arrowheads; you are 
sure to miss some of the latter by this method. 

The object of this assignment and of the one that follows will 
be to train the student's hand in the making of sketches of 
machine parts. A few exercises in the making of straight hori- 
zontal and vertical lines will be taken up before attempting to 
make any sketches of machine parts. For this piurpose a 2H 
pencil is best fitted. 



TECHNICAL SKETCHING 



67 



To Bketch horizontal lines, hold the pencil about 2 in. from the 
point, as shown in Fig. 100. Swing the forearm from the elbow, 
making the line by a series of connected dashes. For vertical 
lines hold the pencil as shown in Fig. 101. When the views are 
completed go over the lines to make them heavier. After a Uttle 




practice the student will find that it is much easier to sketch 
straight lines by the use of short connected dashes than by 
attempting to make one continuous line. 

Problem 13 

In Fig. 102 is ahown a picture, in one view, of a movable jaw for a planer 
chuck. The atudeat Hhoiild decide for himeelf what views are necessaiy 
to properly ehow this object, and 
should make such a sketch, show- 

ing all necesBary dimeDsions and ^^^/I/^'-n.^ i 

notes. As far as possible, make j--''^^^ ^"""^"^ 

the views of correct proportions. 
Use a 9-in. X 12-in. sheet of 
drawing paper, but do all the 
work free-hand, and lay out the 
drawing by eye, and do not use a 
scale on the drawing. 

ASSIGNMENT 13 

46. Sketching on Plain 
Paper. — ^Free-hand sketch- ^^ jq2 

ing is somewhat difficult to 

the beginner because he must use his judgment and sense of pro- 
portion, while in mechanical drawing the use of the scale does 
away with this necessity. 

As mentioned in the last assignment, cross-section paper is 
often used in free-hand sketching, as it not only makes vertical 




68 



MACHINE DRAWING 



and horizontal lines easy to draw, but it also makes proportion- 
ing easy. 

Plain paper, however, is more frequently used because of the 
fact that cross-section paper is less common and less easily ob- 
tainable. It is desirable, therefore, to adopt some means as an 
aid to the correct proportioning of views on plain paper. The 




FiQ. 103. 



Fig. 104. 



most common aid is the pencil itself. The approximate propor- 
tions of the object are obtained by measuring all dimensions in 
pencil lengths and fractions of such lengths. The outlines of 
the drawing are then blocked out to some desirable size on the 
sheet and the overall dimensions are divided up in the same num- 
ber of equal parts and fractions of parts as there were pencil 




CftANK 

> vmcrmoK nNOcp 
Fig. 105. 

lengths on the actual object. One of these divisions on the out- 
lines of the drawing is then marked off on the pencil and becomes 
the standard unit of proportion for all parts of the drawing. In 
drawing circles it will be found that this method is very helpful 
to beginners. It proves its value on circles and arcs of circles 
much more than on straight lines. 



TECHNICAL SKETCHING 69 

In sketching from pictures it is only necessary to assume some 
convenient length as representing an inch on the drawing, to 
mark it off on the pencil, and to apply it as many times as neces- 
sary to give the approximate required dimensions. By this 
means'it is a simple matter to obtain a drawing that is approxi- 
mately half, double, or, in fact, any other proportion to the size 
of the actual object. 

46. Sketching Circles. — To sketch a circle, draw the horizontal 
and vertical center lines first. Next, from the intersection of 
the two center lines, lay off the radius of the circle on each of the 
four lines, as OA, OB, etc. in Fig. 103. Now connect A and C 
with a smooth curve, as shown in Fig. 104. Sketch this curve in 
lightly, at first, after the manner of sketching straight lines. 
After the circle is completed satisfactorily, make it heavier. 

Problem 13 

fig. 105 shows a fully dimensioned picture of a crank. Make a free- 
hand sketch showing two views of this object. Dimension fully, and add 
all necessary notes. Use a 9-in. X 12-in. sheet with the 12-in. dimension 
vertical 



10 



CHAPTER V 

TRACING 
ASSIGNMENT 14 

47. Use of Tracings. — ^In all up-to-date drafting offices the 
pencil drawings are never allowed to be taken out of the office, 
but are traced on transparent cloth, and from this blue prints are 
made. In the larger drafting offices the work is usually done by 
two different departments; namely, the drawing department 
and the tracing department. In the former, all pencil drawings 
are made. After being carefully checked and approved, they are 
taken to the tracing department to be traced on cloth. The 
tracings are likewise checked and approved before prints are made 
for the shop. 

While tracing is the first step of an apprentice draftsman in 
his profession, the student in mechanical drawing will find that 
considerable care, practice, and skill are required to make a 
satisfactory tracing. 

Tracings are used for the purpose of making duplicate copies 
-of drawings, usually upon blue print paper, and are usually 
made upon a prepared linen cloth called tracing cloth, although 
any thin paper that is transparent may be used. The cloth 
should be used for all permanent drawings as it is tough and 
will outlast any kind of paper that may be used. 

Tracing cloth is a fine-thread fabric which has been sized and 
transparentized with a starch preparation. The smooth, or 
glossy, side was originally intended to be used for the drawing 
as the ink will flow freely on this side without any special prepara- 
tion. It has the disadvantage, however, of reflecting light and 
causing eye-strain. Also, the dull side is preferred by most 
draftsmen because it takes a pencil mark. Tracing cloth, in 
rolls, has a red thread along both edges which protects it in ship- 
ment. These threads should always be torn off before using the 
cloth so that it will lie flat on the drawing board. The cloth 
should be stretched over the drawing and secured to the board 
by means of thumb tacks. 

71 



72 



MACHINE DRAWING 



AojusTiNo aci«ew 



48. Aids to Tracing. — Tracing cloth, as placed upon the mar- 
ket, contains an oily preservative which, unless removed, causes 
'* wire-drawing" of the ink lines, that is, the ink does not flow 
freely and the lines are very irregular. To overcome this effect, 
some gritty substance such as chalk dust, fuller's earth, magnesia, 
talcum powder, or powdered soapstone should be rubbed over 
the surface of the cloth, and the surplus wiped ofif with a cloth. 
The same result may be secured by wiping the surface with a 
cloth dampened with gasoline. This method has the advantage 
that it leaves no grit to catch in the pen and thus smear the ink. 

Since tracing cloth is much more expensive than paper, it 
should be handled carefully. It is very sensitive to atmospheric 

changes and may expand over night so as to re- 
quire restretching. If the complete tracing can- 
not be finished during the day, one or more views 
should be finished, and no view left with only part 
of its lines traced. Water will ruin a tracing, 
and moist hands or arms should not be allowed 
to come into contact with the cloth. Unfinished 
tracings should be covered when not in use. 

Before attempting to trace a drawing the 
student should practice with his ruling and letter- 
ing pens on a separate piece of cloth. Use this 
sheet of cloth for setting the ruling pens for vari- 
ous widths of lines (see Fig. 42, Assignment 2). 
Test both lettering and ruling pens before attempting to put 
any ink on the drawing. Do not dip either lettering or ruling 
pens into the ink. Use the quill dropper in the stopper of the 
bottle. The ink should lie between the nibs of the ruling pens, 
as shown in Fig. 106, and on the under side of the lettering 
pens. Do not use too much ink on the latter as it is liable to 
drop onto the tracing. 

49. Erasures. — The student should practice the erasure and 
subsequent "piecing-in" of ink lines on tracing cloth. Never 
make any erasures with a knife or other sharp instrument, as the 
sharp edge cuts into the strands of the cloth and causes any lines 
which are subsequently drawn upon the erased part to smear and 
spread. If an erasure is necessary, first use the ink eraser 
gently and then the pencil eraser so as to smooth the cloth again. 
Sometimes it is desirable to rub the cloth with the end of the 
handle of a pocketknife or other blunt instrument in order to 









OR TmANQLe 

Fig. 106. 



TRACINO 73 

work the threads of the Unen together. In any event, soapstone 
should be rubbed into the spot and gently brushed away before 
inking upon it again. This may be done merely by rubbing 
the soapstone stick itseU upon the cloth. The student will 
find it to his advantage to sUde his triangle under the part to be 
erased as it gives a smooth hard surface to erase upon. 

When piecing-in a line which has been erased, the pen should 
be set so that it will make a line slightly narrower than the line 
which is being pieced-in, as there is a tendency for the ink to 
spread at the two jimction points, and the junction points will 
be less apparent in the finished tracing, if the pen is given the 
narrower setting. 

60. Removal of Blots. — ^Be careful to let the ink lines dry 
before moving the triangles or the T-square over them; other- 
wise they will be apt to blur. If a blot 

should occur on the tracing from the pen 
being too full, or in any other manner, or 
if an error be made in drawing a line, 
smear it with the thumb or with a blotter 
before it has a chance to soak in. After 
it is thoroTighly dry make the necessary Fiq. 107. 

erasure as before directed. This process 
may spoil some of the work already done, but if the ink is al- 
lowed to soak in, it will be more diflScult to make the erasure. 

In erasing a line or letter, great care must be exercised or the 
surrounding work will also be erased. To avoid this, an erasing 
shield, as shown in Fig. 107, is used. It is made of brass or 
celluloid, and is provided with small slots as shown. The erasing 
is done through the slots and the shield moved about until the 
desired lines have been erased. 

61. Order of Procedure in Tracing. — To get the best results, 
drawings should be traced in the following order, using particular 
care to do all the work requiring a certain weight of line before 
changing the setting of the pen (see Fig. 42, Assignment 2). 

1. AU center lines. 

2. Small circles and fillets. 

3. Large circles. 

4. Straight lines. 

5. Extension and dimension lines. 

Draw top and bottom pencil guide lines for lettering. 



74 MACHINE DRAWING 

When the tracing is completed, wipe the surface with a cloth 
dampened with gasoline. This will remove all dirt and pencil 
lines. 

Problem 14A 

Make a complete tracing of the pencil drawing which you made for Prob- 
lem 1 of this course. 

Be careful to differentiate between the various weights of linds, for this is 
one point that distinguishes a good piece of work from a poor one. Follow 
carefully the instructions given in Art. 51.- 

Problem 14B 

Make a complete tracing of the pencil drawing which you made for Prob- 
lem 2 of this course. 

Follow carefully the instructions given in Art. 51. 

ASSIGNMENT 16 

62. Suggestions on Lines. — Center lines, extension lines, and 
(dimension lines should all be light lines of uniform weight (see 
Fig. 42). The center lines should all be drawn with one setting 
of the pen. The main center lines of an object should project 
about i in. beyond the drawing of the object, while secondary 
center lines should project about i in. beyond the lines which 
they center. 

Extension and dimension lines should be drawn with the same 
weight of line that was used in drawing the center lines. The 
extension lines should fail to touch the object lines by tV in. 
and should extend about | in. beyond their dimension lines. 
The extension and dimension lines should all be drawn with one 
setting of the pen. Always arrange dimensions of circles sym- 
metrically between the center lines as shown in Fig. 43. Nevw 
place dimension lines of circles on the center lines. If the finish 
of a cylindrical hole is shown by a note carried outside of the draw- 
ing by means of an arrow, the arrow should extend clearly within 
the limits of the circle, point toward the center, but should not 
extend clear to the center (notice the f-in. drill in Fig. 47). 

63. Handling the Pens. — Before starting to trace any set of 
lines, the pens should be tried on an extra piece of tracing cloth, 
in order to be sure that they are set to produce lines of the proper 
width before applying them to the tracing. Do not hesitate to 
wipe the pens freely at all times, as the ink dries quite readily 



TRACING 75 

and frequent wiping of the pens is necessary. If the ink dries 
in the pen temporarily, its flow may sometimes be readily re- 
newed by trying it on an extra piece of tracing cloth, on the soft 
wood of the drawing board, on the fingers, or on the finger nails. 
Should any attempt to start the flow of the ink prove unsuccess- 
ful, the pen should be wiped clean and refilled. 

Pens should always be cleaned before putting away, as the 
ink will corrode the steel. 

Problem 16A 

Make a complete tracing of the pencil drawing which you made for Prob- 
lem 10 of this course. 

Problem 15B 

Make a complete tracing of the pencil drawing which you made for Prob- 
lem 11 of this course. 



13 



CHAPTER VI 

ASSEMBLY AND DETAIL DRAWINGS 
ASSIGNMENT 16 

64. Assembly and Detail Sheets. — Every machine or mechan- 
ism containing several parts should be represented by both as- 
sembly and detail drawings. The assembly shows how the 
various parts are related to each other and how they are put 
together; the detail drawings are used by the mechanic in making 
the separate parts. 

If the mechanism involves a large number of parts, there will 
be a single assembly drawing and one or more sheets of details. 
There may be a separate detail drawing of each part, or several 
details may be shown on one sheet. If a mechanism contains 
only a few parts, the assembly and the details may be shown on 
a single sheet. In this case, the usual practice is to place the 
assembly drawing on the upper left-hand corner of the plate, 
the rest of the plate being given over to the drawings of the 
details, as in Fig. 108. The drawing of Fig. 108 shows the assem- 
bly at the left. The front view is shown as a half-section, so 
that both the inside and outside relations of the parts are seen. 
All the principal details of the stuffing box are shown at the right. 
The nuts are not drawn in detail because they are standard hexa- 
gon nuts. 

In making detail sheets, the details are sometimes drawn on 
the plates in the logical order in which they occur in the machine; 
that is, adjacent parts in the machine are drawn adjacent to 
each other on the detail sheets. Sometimes the details of imits 
of the machine which are to be made, and perhaps assembled, 
in one part of the shop, are grouped together on the detail sheets. 
In other cases, it may be convenient to group together the 
details of similar parts which are to be made by the same me- 
chanic or department. For instance, we may place together in 
one group the details of all shafts required; in another group we 
may have all the gears; in another group all the bolts, screws, 
and other parts to be made on screw machines. The choice of 

77 

13 



UACHINE DRAWING 




ASSEMBLY AND DETAIL DRAWINGS 79 

any such methods as above noted will be determined largely 
by the local conditions governing the manufacture of the ma- 
chine and by the number of parts to be shown. 

It is generally necessary to make mechanical drawings to some 
convenient scale. The space allotted to each detail should 
bear some reasonable proportion to the space allotted to other 
details. In other words, a comparatively small and insignificant 
part should not be drawn to a large scale while a larger and much 
more important part is drawn to a much reduced scale. If, 
however, a certain small part is highly important and compli- 
cated in design, it may be advisable to draw it to a large scale in 
order to show it clearly and to emphasize the fact that it should 
be accurately made. Always strive at balance, so thai the space 
given to each detail mil be proportional to its importance and size. 

The detail drawing of each part should be complete and give 
all necessary information. Beneath each detail there should 
appear a title or "legend" giving the name of the part, the 
number required for one machine, the material of which it is to 
be made, whatever finish, if any, is required, and the scale, if 
different scales are used for the details. As a general rule the 
same scale should be used throughout. No title or legend is 
necessary beneath the assembly drawing, except possibly the 
word Assembly. 

The title for the whole plate is usually placed in the lower 
right-hand corner. If the plate contains both assembly and de- 
tails, the title for the plate may appear somewhat as follows: 

STUFFING BOX 

FOR 
4" GATE VALVE 

If the plate contains the assembly drawing only, the title of the 
plate will appear thus: 

STUFFING BOX 

FOR 
4" GATE VALVE 

ASSEMBLY DRAWING 

If the plate contains only the drawings of details^ the title of the 
plate will appear thus: 



MACHINE DRAWING 



CAST IRON WROUSKT IRON MALLEABLE IRON BRASS »* BRONZE 



CAST STEEL 



MACHINE STECL NICKEL STEEL 



LEAD «" BAeeirr 



LEAThtCR CONCRKTE RUBBER «" VULCANITE WOOD 



I Be^M- MACMiNe Steel Hollcw Cylinder -Cast iROrt 



SoUOCn-lNOBR-V/ROUSHT IRON RCCTANQULAR BaR-W»OU0MT IRON 
Fi<3. 109. 



ASSEMBLY AND DETAIL DRAWINGS 81 

DITTAILS OF STUBTING BOX 

FOB 

4" GATE VALVE 

There shotild also appear: the Bcale, the date, the fiUng number, 
and the names of the various draftsmen involved in making the 
drawing. 

In many large offices the various details of a machine are drawn 
on separate sheets, one detail to each sheet. The assembly 
drawing is placed on one sheet by itself and a separate bill of 
material is placed on another sheet. The reason for drawing 
the various details separately is that many of these details might 
be used for other machiiieB as well as for the machine for which 
they were originally intended. In this way the duplication of 
drawings is avoided. 



Fig. 110. 

65. Conventional Forms for Cross-hatching. — In most assem- 
bly drawings, sections are used extensively to show how the 
various parts fit together. Since the various parts of a machine 
are frequently made of different materials, it is quite customary 
to section the various materials differently to distinguish between 
them. Fig. 109 shows the most common forms for cross-hatch- 
ing 16 different matraials; also the conventional forms for repre- 
senting breaks. 

In Fig. 108 it wO be noted that the cross-hatching of one part 
slants in the opposite direction to that of the other part, and 
that the cross-hatching on any one part is always in the same 
direction. This is the universal practice and should be rigidly 
followed. It sometimes happens, however, that three or more 
parts are in direct contact with each other. If the parts are of 
different materials it will not matter if the cross-hatching of 



82 



MACHINE DRAWING 



adjacent parts slants in the same direction; but if all of the parts 
are of the same material the parts can be distinguished by using 
45^, 30^, and 60^ angles for the cross-hatching as in Fig. 110. 



Problem 16 

Fig. Ill shows complete details of a 2}-in. step bearing. This is the lower 
end housing for a vertical shaft, both to give a suitable bearing, and to main- 
tain the position of the shaft. » 




•ff 



;nT 



1 4 



I 
I 
I 



( : ( 



H 



a 



i 



4" 



FT 



fX)0TIN6 -I- QroHUL 
nNISHEO 






1=H» 



U 




ZJ^SrrZ^ BCARINQ 



Housih«-I-Ca5t Iron 



Fig. 111. 



Cast iron is not suitable for a bearing; hence it is not permissible to let the 
shaft rest on cast iron. A piece of bronze bearing metal is fitted into the 
cast-iron housing. This bronze footing is cupped on the upper side to fit 
a 5-in. sphere (2}-in. R). The end of the shaft is turned to a segment of 
a 5-in. sphere; thus the shaft end and the footing form a ball and socket, 
which keeps the shaft centered in the step. The f-in. hole in the base is 



ASSEMBLY AND DETAIL DRAWINGS 83 

provided for the insertion of a bar to drive out the footing when it is to be 
replaced. 

Draw the views and section indicated roughly in Fig. 112, using the full- 
size scale. For this plate use a ^in. X 12-in. sheet with the 12-in. dimen- 
sion vertical. When the two parts are assembled, the footing should rest 
at the bottom of the 2i-in. hole in the housing. The cupped surface of 
the footing should be uppermost. 

Do not dimension assembly drawings in detail but give only the main 
dimensions, showing the relations of the parts to each other, and the main 
dimensions of each part. 

ASSIGNMENT 17 

Problem 17 

In Fig. 113 are given the details of a follow rest for a 12-in. lathe. Make 
a full-size pencil drawing showing the various pieces assembled as in Fig. 
114. Use a 12-in. X 18-in. sheet. 

A follow rest is used on a lathe when turning long slender bars that would 
otherwise spring away from the tool. Where such a bar is to be turned, the 
follow rest is bolted to the carriage of the lathe 
and the guide is adjusted by means of the two 
set screws so that the notch bears on the top and 
back of the bar. This holds the piece rigidly 
against the tool, and, since the follow rest is at- 
tached to the carriage, it moves with the tool 
. and follows it throughout the cut. 

In making the drawing, place the guide so that 
the two faces of the notch are ^ in. from the hmp section on unc a-B. 
center lines of the yoke in the side view. This Fjq, 112. 

is the position for turning apiece f in. in di- 
ameter, since the intersection of these two center lines is in line betwee 
the lathe centers. 

The title of the drawing should contain the words FOLLOW REST FOR 
12" LATHE f in addition to the usual information regarding scale, date, etc. 

When you have completed the pencil drawing, make a tracing of it. 

ASSIGNMENT 18 

Problem 18 

Make a quarter-size assembly of the 12-ton jack screw, the details of 
which have already been drawn in Problems 8 and 10. See Figs. 77 and 91 
for the details. Make a half-section elevation and a top view as shown in 
Fig. 115. Use a 9-in. X 12-in. sheet with the 12-in. dimension vertical 
Assemble the parts so that the total height of the jack is about 16 in. It 
will be noticed in assembling the cap and the screw that the latter would 
project ^ in. through the cap. This extra . length is provided so that the 
end of the screw may be riveted over to prevent the cap from coming off, 
and yet allow it to turn on the screw. In the assembly drawing, this should 




MACHINE DRAWING 



be shown riveted over, aad attention should be called to it by an a 
the word RIVET. 



-1*'- 


1' 


f*-T= 


1 


. _| 


'— n 




1 




1 


T 


^ u.^ 


t 



-^k-*W«>IK(|p 



GuoB-l-Tboi,5Tna,-HApomTO &kRRwae8ou'&N(/T-l-MȣM.5TEci. 



^ia^ 



5CT ScRtws-S- Macm. Stbbl 
t'm. hbads- round points, 

Details of RxjjOw Rest 
TOR 

12' Engine Lathe 



As in the preceding problem, make a complete pencil drawing of the jack 
and then trace it. 



ASSEMBLY AND DETAIL DRAWINGS 



85 



ASSIGNMENT 19 

66. Drafting-room Procedure. — When the design of a machine 
is &*st taken up in a drafting office, the chief engineer or a senior 
draftsman first makes a pencil-sketch assembly. He endeavors 
to provide for all clearances and to proportion the parts correctly. 
When a satisfactory sketch has been obtained, it is turned over 
to a competent draftsman to work up into a finished drawing. 
This finished assembly is often the result of careful and frequent 
consultation with the various other draftsmen and engineers, 
so as to have all the good ideas possible incorporated into the 
design. 

The draftsman who makes the assembly drawing decides what 
materials or metals it will be advisable to use in the several parts, 
what their treatment shall be, what proportions they shall have 






Fia. 114. 



HAtr sccnoN ON unc a- 
FiG. 115. 



in order to give sufficient strength, etc. His drawing should 
show all general and vital dimensions and should be finished in 
such a manner that it may be placed in the hands of a junior 
draftsman or detailer to detail the various parts. Before going 
to the detailer, however, the assembly drawing should be sub- 
mitted to the chief draftsman and chief engineer for their 
approval. 

Under the supervision of the man who made the general 
assembly, the detailer then makes complete detail drawings of 
each piece of the machine. These, in similar manner, should 
also be submitted to the chief draftsman and chief engineer. 

In a large, well-regulated office, all these pencil drawings 
would then be turned over to the "tracer" who would trace them 
on tracing cloth. These tracings should also be approved by the 



86 MACHINE DRAWING 

o£ief draftsman and chief en^neer. In smaller offices all these 
operations might be performed by one man. 

The tracings are next properly indexed for filing away in the 
vaults. Thereafter, they may be issued on a check order system 




whenever it is desired to have blue prints made from them. When- 
ever radical changes are made in the construction of a machine, 
the old tracings are marked "obsolete" or "superseded," and 



ASSSMSLY AND DETAIL DRAWINGS 



88 MACHINE DRAWING 

are replaced in the current files by tracings of the new dedgns. 
If only one or two dimensions are to be altered, the old dimensions 
may be crossed out (not erased) and the new dimensions placed 
above or below the old ones. 

Blue prints are made on paper known as blue-print paper, 
which is sensitive to light. The tracing is placed over a sheet of 
blue-print paper in a printing frame, and then exposed to a 
strong light such as daylight or an electric light. This makes 
an impression on the blue print Hke the drawing on the tracing. 
It usually takes a minute or so to make the print in a fairly good 
light. The blue print is then removed and "fixed" in a water 
bath for a few minutes so that it will be permanent. The lines 



ria. iia 

of the drawing then appear as white lines on a blue background. 
When blue prints are subjected to a great deal of hard usage in 
the shops it is well to moimt them on some stiff cardboard or 
other firm backing and then to shellac or varnish the surface so 

as to protect them. 

Problem 19 

Fig. 116 shows a completely dimensioned assembly of an automatic grease 
cup. Make complete full-size pencil drawings of the various details on a 
12-in, X 18-in. sheet, placed horizontally on the drawing board. The de- 
tails must be arranged on the sheet so they will not be crowded. 

Put the title of each part under the drawing of tt, bother with the num- 
' ber required and the material, for example: 



ASSEMBLY AND DETAIL DRAWINGS 



In the plate title in the lower right-haad Ci 



AUTOUATIC GREASE CUP 

together with the ec&le, date, etc. 

A tracing should be made after the pencil drawing has been checked by 
the instructor. The tracing should also be submitted to the instructor for 
his approval. 

ASSIGNMENT 20 
Problem 20 

Fig. 117 shows a completely dimensioned assembly of a connecting rod 
for a 22-in. X 42-in. X 27-in. engine. Draw fully dimensioned details of 
all parts, using as many 12-in. X 18-in. sheets as are necessary. The stu~ 



Fio. 119 

dent should decide what scale, or scales, to use for these details. Always 
use the largest scale that the working space will permit. If more than one 
scale is used on the same sheet, the scale of each detail should be noted in 
its legend, as stated in Art. 64. 

It will be necessary to break out portions of the rod in order to get the 
complete view on the sheet. In doing this, however, be sure to omit no 
part of the rod which is necessary for complete dimensioning. 

fig. lis shows a picture of the boxes for the cross-head end (small end). 
This will give the student a clearer idea of the shape of these boxes than can 
be shown on an assembly drawing. 

Fig. 119 shows how the rod tapers from the cross-head end of the crank 
end. It also shows a revolved section of the rod. 



/^ 



• • • • • • • 

• •••••• 

• • • ,•> • • » 

• • • • • •> «. 



• • • 
• • •• 
••• • 



••••_• *•- 



• «. •••••...'•i.-. 



INDEX 



Acme threads, 36 
Assembly and detail drawings, 77 
A. S. M. E. standard machine 
screws, 44 

Blots, removal of, 73 
Bolts, 37 

heads and nuts, 37, 38 
Broken lines, 17 

sections, 57 
Brown and Sharpe standard thread, 
36 

Cap screws, 43 

Center lines, 23 

Circles, sketching, 69 

Compass, the, 22 

Conventional forms for cross-hatch- 
ing, 80, 81 

Conventions, thread, 40, 43 

Cross-hatching, conventional forms 
for, 80, 81 

Decimal equivalents, 50 
Depth of thread, 35 
Detail sheets, 77 
Diameters of screws, 35 
Dimensioning, notes on, 27 

the drawing, 6 
Dimension lines, 6 
Dimensions, arrangement of, 24 

of bolts and nuts, 38 

of machine screws, 44 
Drafting-room procedure, 85 
Drawing board, 9 

dimensioning the, 6 

making the, 5 

starting the, 12 

to scale, 51 
Drawings, standard sizes of, 8 

Erasures, 72 
Extension lines, 6 



RlJets, 27, 58 
Finish, 25 

marks, 25 
Forms for cross-hatching, conven- 
tional, 80, 81 

of threads, 35 
Formulas, use of, 31 

Half-sections, 56 

Heads and nuts for bolts, 37, 38 

Lead of threads, 48 
Left-hand threads, 40 
Lettering, 8 
Lines, broken, 17 

center, 23 

dimension, 6 

extension, 6 

suggestion on, 74 

Machine screws, 44, 45 
Making the drawing, 5 
Multiple threads, 47 

Nominal diameter of bolts and 

screws, 35 
Notes on dimensioning, 27 
Nuts for bolts, 37, 38 

Order of procedure in tracing, 73 
of work, 29 

Partial sections, 61 
Pencil, 11 

Pens, handling the, 74 
Pitch of threads, 37 
Projections, 1 

Relations between views, 4 
Revolved sections, 61 
Right-hand threads, 40 
Root diameter of threads, 35 



n 



• • « • 

• • • 

» 1 • » 



• • • • • , • 
• f * • • • • 



• * • • ^ 



« • • 



• • • • . . •, 



92 



INDEX 



Scale, 11 

drawing to, 51 
Screw measurements, 35 
Screws, cap, 43 

machine, 44, 45 

set, 46 
Sections, 55, 56, 57, 61 

broken, 57 

half-, 56 

partial, 61 

revolved, 61 

use of, 55 
Set screws, 46 
Shortened views, 64 
Sizes of drawings, standard, 8 
Sketching, 65, 67, 69 

circles, 69 

on plain paper, 67 

suggestions for, 65 

use of, 65 
Square threads, 36 

method of drawing, 50 



Tapped holes, 41 

Thread conventions, 40, 43 

Threads, depth of, 35 

forms of; 35 

multiple, 47 

right-hand and left-hand, 40 

square, 36, 50 
Titles, arrangement of, 17 
Tracing, 71, 72, 73 

aids to, 72 

order of procedure in, 73 

use of, 71 
Triangles, 10 
T-square, 9 

U. S. Standard threads, 36 

Views, relations between, 4 

shortened, 64 
V threads, 35 

Whitworth threads, 37 
Worm threads, 36 



THIS BOOK IS DT7E ON THE LAST DATE 
STAMPED BELOW 



AN INITIAL FINE OF 26 CENTS 

WILI. BE AS8BS8ED FOR FAILURE TO RETURN 
THIS BOOK ON THE DATE DUE. THE PENALTY 
WILL INCREASE TO SO CENTS ON THE FOURTH 
DAY AND TO tl.OO ON THE SEVENTH DAY 
OVERDUE. 



OCT 331941 



' l" ! ^M *■ » * 






LD 21-100m-7,'40(69S6s) 



yc 12699 



I