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

PowerPoint to accompany

Krar Gill Smid

Technology of Machine Tools6th Edition

Job Planning

Section 4


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PowerPoint to accompany

Krar Gill Smid

Technology of Machine Tools6th Edition

Engineering Drawings

Unit 5


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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


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5-4

Engineering Drawings

Language draftspersons, tool designers, andengineers indicate to machinist physicalrequirements 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


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Orthographic View

orProjection Method

Shows part from three sides


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5-6

Cylindrical Parts

Shown on prints in two views

Front and right

Interior forms difficult

Sectional view


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5-7

Standard LinesExample Name Description Use

Object lines Thick, black Edge of object

.030 in wide

Hidden lines Medium, black Hidden contours

.125 in dashes

.060 in spacesCenter lines Thin lines Centers of holes

long-short

Dimension Thin double Dimensions

arrowCutting-plane Thick black Show imagined

long, two short section cut

Cross section Fine, parallel Show surfaces

45 degrees exposed (cut)

1


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5-8

Drafting Terms

Limits

Largest and smallest

permissible dimensions


Tolerance

Permissible variation ofsize of the part

largest

smallest

Example: .001+.003=.004


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5-9

Drafting Terms

Allowance

Intentional difference in sizes of mating parts

Shop drawing would show both shaft and holewith 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


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5-10

Scale Size

Indicates scale to which drawing has beenmade

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


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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


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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


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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


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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


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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


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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


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5-17

Common Symbols

angularity countersink

basic dimension depth/deep

between diameter

conical taper perpendicularity

counterbore/spotface radiusR

60


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


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5-22

Dimensioning Systems

Dimensions used on prints to give distancebetween two points, lines, planes

Numerical value gives actual measurement Dimension line indicates direction

Arrowheads indicate points between whichvalue applies

Decimal system uses only decimal fractions

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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 ororigin point

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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 fortechnical drawings

American Society of Mechanical Engineers(ASME) ASME Y14.5-1994 publication on

Dimensioning and Tolerancing lists lateststandards

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5-25

Common Machine Shop

Abbreviations

CBORE Counterbore

CSK Countersink

DIA DiameterDiameter

HDN Harden

L Lead

LH Left hand

mm Millimeter

NC National coarse

NF National fine

P Pitch

R Radius

Rc Rockwell hardness testRH Right hand

THD Thread or threads

TIR Total indicated runout

TPI Threads per inch

UNC Unified national coarse

UNF Unified national form

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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 (in.)

Surface finish mark Indicates which surface of part to finish

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Surface Finish Mark

40

.002

.001

Waviness height in

thousandths of an inch

Machining marks runperpendicular to the

boundary of the surface

indicated

Surface finish

in microinches

Roughness width in

thousandths of an inch

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Surface Symbols

Indicate direction of lay

Marks produced by machining operations onwork surfaces

= Parallel to boundary line of surfaceindicated by symbol

X Angular in both directions on surface

indicated by symbol

M MultidirectionalC Approximately circular to center of

surface indicated by symbol

R Approximately radial to center of

surface indicated by symbol

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Material Surfaces

Cast iron and malleable ironAluminum, magnesium

and their alloys

Copper, brass

bronze, etc.

Steel and wrought iron

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