1. 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

2. Engineering Drawings
The universal language draftspersons, tool designers, and engineers use to indicate to machinist the physical requirements of part
Complete product: Assembly drawing
Each part component: detailed drawing
Reproduced as copies called prints

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

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

5. 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

6. 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.

7. 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

8. 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

9. 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

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

11. 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

12. Metric Dimensions
Zero must be used to left of decimal for sizes less than 1 millimeter
No decimal point or zero follows whole number

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

14. 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

15. Common Machine Shop Abbreviations
CBORE Counterbore
CSK Countersink
DIA Diameter
Diameter
HDN Harden
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 fine

16. 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.