PowerPoint to accompany
Technology of Machine Tools
6th Edition
Krar • Gill • Smid
Job Planning
Section 4
Copyright © The McGraw-Hill Companies, Inc.
Permission required for reproduction or display.
PowerPoint to accompany
Technology of Machine Tools
6th Edition
Krar • Gill • Smid
Engineering Drawings
Unit 5
Copyright © The McGraw-Hill Companies, Inc.
Permission required for reproduction or display.
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
5-4
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
5-5
Orthographic View
or
Projection Method
Shows part from three sides
Copyright © The McGraw-Hill Companies, Inc.
Permission required for reproduction or display.
5-6
Cylindrical Parts
• Shown on prints in two views
– Front and right
• Interior forms difficult
– Sectional view
5-7
Standard Lines
Example
1½
Name
Object lines
Description
Thick, black
.030 in wide
Hidden lines Medium, black
.125 in dashes
.060 in spaces
Center lines Thin lines
long-short
Dimension
Thin double
arrow
Cutting-plane Thick black
long, two short
Cross section Fine, parallel
45 degrees
Use
Edge of object
Hidden contours
Centers of holes
Dimensions
Show imagined
section cut
Show surfaces
exposed (cut)
5-8
Drafting Terms
• Limits
– Largest and smallest
permissible dimensions
largest
smallest
• Tolerance
– Permissible variation of
size of the part
Example: .001+.003=.004
Copyright © The McGraw-Hill Companies, Inc.
Permission required for reproduction or display.
5-9
Drafting Terms
• Allowance
– 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
5-10
Scale Size
• Indicates scale to which drawing has been
made
• Representative measurement
Scale
1:1
1:2
2:1
Definition
Actual size of part
One-half actual size of part
Twice actual size of part
5-11
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
5-12
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
5-13
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
5-14
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
– .6783 indicates tolerance of .0001 in.
• Can show specific limits (high or low) or as
plus or minus tolerancing
5-15
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
5-16
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
5-17
Common Symbols
angularity
60 basic dimension
countersink
depth/deep
between
diameter
conical taper
perpendicularity
counterbore/spotface
R radius
5-18
Symbols
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
5-19
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
5-20
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
5-21
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
5-22
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
5-23
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
5-24
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 Y14.5-1994 publication on
Dimensioning and Tolerancing lists latest
standards
5-25
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
R
Rc
RH
THD
TIR
TPI
UNC
UNF
Pitch
Radius
Rockwell hardness test
Right hand
Thread or threads
Total indicated runout
Threads per inch
Unified national coarse
Unified national form
5-26
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
5-27
Surface Finish Mark
Surface finish
in microinches
.002
40
.001
Waviness height in
thousandths of an inch
Machining marks run
perpendicular to the
boundary of the surface
indicated
Roughness width in
thousandths of an inch
5-28
Surface Symbols
• Indicate direction of lay
– Marks produced by machining operations on
work surfaces
=
X
M
C
R
Parallel to boundary line of surface
indicated by symbol
Angular in both directions on surface
indicated by symbol
Multidirectional
Approximately circular to center of
surface indicated by symbol
Approximately radial to center of
surface indicated by symbol
5-29
Material Surfaces
Copper, brass
bronze, etc.
Aluminum, magnesium
and their alloys
Steel and wrought iron
Cast iron and malleable iron
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.