1. Job Planning
Section 4

2. Engineering Drawings
Unit 5

3. Objectives
Understand the meaning of the various lines used on engineering drawings
Recognize the various symbols used to convey information
Read and understand engineering drawings or prints

4. Engineering Drawings
Language draftspersons, tool designers, and engineers indicate to machinist physical requirements of part
Three standards similar
American ANSI Y14.5 (American standard)
ASME Y14.5M-1994
ISO R1 101
Complete product: Assembly drawing
Each part component: detailed drawing
Reproduced as copies called prints

5. Orthographic View or Projection Method
Shows part from three sides
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

6. Cylindrical Parts Shown on prints in two views
Front and right
Interior forms difficult
Sectional view

7. Standard Lines Example Name Description Use
Object lines Thick, black Edge of object in wide
Hidden lines Medium, black Hidden contours
.125 in dashes
.060 in spaces
Center lines Thin lines Centers of holes
long-short
Dimension Thin double Dimensions
arrow
Cutting-plane Thick black Show imagined
long, two short section cut
Cross section Fine, parallel Show surfaces
45 degrees exposed (cut)
1 ½

8. Drafting Terms Limits Tolerance
Largest and smallest permissible dimensions
largest
smallest
Tolerance
Permissible variation of size of the part
Example: =.004
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

9. Drafting Terms Allowance Fit
Intentional difference in sizes of mating parts
Shop drawing would show both shaft and hole with max and min sizes to produce best fit
Fit
Range of tightness between two mating parts
Two general classes
Clearance fits: part revolve or move
Interference fits: two parts forced together as single

10. Scale Size Indicates scale to which drawing has been made
Representative measurement
Scale Definition
1:1 Actual size of part
1:2 One-half actual size of part
2:1 Twice actual size of part

11. Units of Measurement
Metric system of measurement is international standard
Inch system widely used in US and Canada
Note on title block of drawing should identify: inch, metric, or dual

12. Manufacturing Methods
Drawing only defines part
Does not specify how part made
Example: Hole diameter shown
Does not indicate drill, ream, bore
Tolerance or limit should be provided if dimension is critical

13. Basic Dimensioning
Used on working drawings to explain to machinist shapes and sizes required
Title block
Type of material
Number of parts required
Special notes

14. Dimensioning Tolerances
Define accuracy of specific operation or part
Each dimension should have tolerance
Tolerance on dimension as 1 or 2 units of last digit
indicates tolerance of in.
Can show specific limits (high or low) or as plus or minus tolerancing

15. Inch Dimensions
Fractions sizes stated to two decimal places indicates not critical size
Whole dimensions shown with minimum of two zeros to right of decimal point
No zero used to left of decimal for values less than 1 in.
Critical dimensions shown in three or four decimal places and tolerances included

16. Metric Dimensions
Zero must be used to left of decimal for sizes less than 1 millimeter
No decimal point or zero follows whole number
Where dimension larger than whole number by decimal fraction, last digit to right of decimal point is NOT followed by zero

17. Common Symbols R angularity countersink basic dimension depth/deep
between diameter
conical taper perpendicularity
counterbore/spotface radius 60 R

18. Symbols
SYMBOLS
Some of the symbols and abbreviations used on shop drawings indicate the surface finish, type of material, roughness symbols, and common machine shop terms and operations.
A few of the common symbols used in this book are as follows:
   angularity    countersink
60 basic dimension    depth/deep
   between    diameter
   conical taper    perpendicularity
   counterbore/spotface R radius
Countersinks, counterbores, and spotfaces can be shown on drawings by abbreviations or dimension symbols, with the symbols being preferred. Samples of some common symbols in use are shown in Fig. 5-7 on p. 44.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

19. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

20. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

21. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

22. Dimensioning Systems
Dimensions used on prints to give distance between two points, lines, planes
Numerical value gives actual measurement
Dimension line indicates direction
Arrowheads indicate points between which value applies
Decimal system uses only decimal fractions

23. Dimensioning Systems Two types used in computer numerical control work
Incremental system
Dimensions given from previously known point
Absolute system
Dimensions or positions given from fixed zero or origin point

24. Workplace Communication
Manufacturing part of global economy
Standardized symbols and characteristics
International Standards Organization (ISO)
Established in 1946
TC#10 committee to develop standards for technical drawings
American Society of Mechanical Engineers (ASME)
ASME Y publication on Dimensioning and Tolerancing lists latest standards

25. Common Machine Shop Abbreviations
CBORE Counterbore
CSK Countersink
DIA Diameter
Diameter
HDN Harden
L Lead
LH Left hand
mm Millimeter
NC National coarse
NF National fine
P Pitch
R Radius
Rc Rockwell hardness test
RH Right hand
THD Thread or threads
TIR Total indicated runout
TPI Threads per inch
UNC Unified national coarse
UNF Unified national form

26. Surface Symbols
Deviation from nominal surface caused by machining operation
Includes roughness, waviness, lay, and flaws
Measured by surface finish indicator in microinches (µin.)
Surface finish mark
Indicates which surface of part to finish

27. Surface Finish Mark .002 Waviness height in Surface finish40
.002
.001
Waviness height in
thousandths of an inch
Surface finish
in microinches
Roughness width in
thousandths of an inch
Machining marks run perpendicular to the boundary of the surface
indicated

28. Surface Symbols Indicate direction of lay
Marks produced by machining operations on work surfaces
= Parallel to boundary line of surface indicated by symbol
X Angular in both directions on surface indicated by symbol
M Multidirectional
C Approximately circular to center of surface indicated by symbol
R Approximately radial to center of surface indicated by symbol

29. Aluminum, magnesium and their alloys
Material Surfaces
Copper, brass
bronze, etc.
Steel and wrought iron
Aluminum, magnesium and their alloys
Cast iron and malleable iron
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.