cad_lecture_3_r1.pdf

1

Computer Aided Design

Lecture 3UNIVERSITI TUNKU ABDUL RAHMAN(UTAR)

FACULTY OF ENGINEERING AND SCIENCE

http://upload.wikimedia.org/wikipedia/commons/d/dc/Cad_crank.jpg


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Dimensioning

UNIVERSITI TUNKU ABDUL RAHMAN(UTAR)




DimensioningCommunication

Engineering drawing communicate or

conveys information in:

◦ describing the form/shape of the component,

usually by using orthographic and sometimes

pictorial views

◦ giving actual dimensions of all features of the

geometry

◦ giving information about any special

manufacturing processes and materials required

33



DimensioningGeneral Rules

General rules

◦ Standards and conventions should be followed

◦ Dimensions should be placed on drawings so that they may be easily read

◦ The drawing must include the minimum number ofdimensions required to accurately manufacture the design

◦ A dimension should not be stated more than once, unless it aids communication

◦ If use in manufacturing, it should not be necessary for the machinist to have the calculation on any dimensions

44



DimensioningTypes of Dimension

Dimensioning can be broadly

classified as:

◦ Size dimensions. Used to describe heights, widths,

diameters, etc.

◦ Location dimensions. Used to place various

features of a component relative to each other,

such as a hole centre line to a reference surface

◦ Mating dimensions. Used for parts that fit together

requiring a certain degree of accuracy

55



DimensioningConventions of Dimensioning

General conventions:◦ Parallel dimensions, indicating the

size of the plate

◦ edges A and B are being used as

the reference edges (datum)

◦ minimum number of dimensions

required are specified

◦ use of description of 'plate 3mm

thick', so that no side view is

required

◦ evenly spaced dimension lines

66




General conventions:

◦ Overview

77

Gap

“Break” when

2 projection

line intercept

Short

Extension

Dimension

Thin

projection

line

Arrow

Head

Dimension

Line





◦ Dimensioning Line

Thin lines that show where a measurement

begins and where it ends and the size of an angle

Broken for text, if needed

88

Dimension

Dimension

Line





◦ Extension/Projection Line

Thin lines that extend the lines or edges of the object

DO NOT touch the object – away from the object

Extend past the dimension line

Break the line where appropriate

99

Short

Extension

Thin

projection

line

Gap





◦ Arrow Head Used at the ends of dimension lines

Show where a dimension begins and ends

Also used on leaders

Can be open or solid

Must be uniform through out drawing

1010





◦ Example 1

Parallel Dimensioning – thick dimension line, thin

projection line, well spaced of dimension lines

Superimposed Running Dimensioning – thin origin

circle of min. 3mm, dimensioned in series manner

1111





◦ Example 2

A central line or projection line should never be used as dimension line

Dimension line should be drawn unbroken even in break feature

When space is constrained , an oblique strokes of min. 3mm at 45˚ instead of arrow head can be

acceptable

1212



DimensioningDimensioning Common Features

Radii

◦ All radial dimensions are proceeded by the

capital R

shows a radius dimensioned with the centre of

the radius located on the drawing

shows how to dimension radii which do not need

their centres locating

1313




Diameter◦ Circles on engineering drawings are usually either

spheres, holes or cylinders of some description. The

dimension refers to the diameter, and the diameter symbol

is Ø

1414

The ∅40 dimension can also be

refereed to as the PCD or Pitch

Circle Diameter




Chamfers

1515

Chamfer at angle 45˚

Chamfer at angle other

than 45˚




Countersinks and counterbores:

1616

Counter-sinks

Counter-bores



DimensioningDo & Don’t Do

Do & Don’t do

1717

Right!

Wrong!

Wrong!

Wrong!

Right!

Wrong!

Right!

Right!




Do & Don’t do

1818

Wrong! Right!

Wrong! Right!

Shaded area for

corresponding

dimension

Wrong! Right!




Do & Don’t do

1919

Wrong! Right! Wrong! Right!

Wrong! Right!Wrong!Wrong!But, not

recommended



Dimensioning

Parallel Dimensioning◦ Parallel dimensioning consists of several dimensions

originating from one projection line

2020



Dimensioning

Chain Dimensioning◦ Chains of dimension should only be used if the function of

the object won't be affected by the accumulation of the

tolerances

2121



Dimensioning

Superimposed Running Dimensioning◦ Superimposed running dimensioning simplifies parallel

dimensions in order to reduce the space used on a

drawing. The common origin for the dimension lines is

indicated by a small circle at the intersection of the first

dimension and the projection line.

2222



Dimensioning

Combined Dimensioning◦ A combined dimension uses both chain and parallel

dimensioning

2323



Dimensioning

Dimensioning Small Features◦ When dimensioning small features, placing the

dimension arrow between projection lines may create a

drawing which is difficult to read

2424



Dimensioning

Unidirectional system ◦ all dimension texts are always vertical upright

Aligned system ◦ dimension text ca be placed on or in line with the

dimension lines

2525

Aligned SystemUnidirectional

System



Dimensioning

Can be classified in to:

◦ Justify

◦ Controls justification of the text

Align, fit, centre, middle, right etc.

◦ Style

◦ Specifies the text style, which determines the

appearance of the text characters

Time News Roman, Arial, Rockwell etc.

2626

AutoCADAutoCAD AutoCAD

V

e

r

t

i

c

a

l

S

t

y

l

eH o r i z o n t a l S t y l



Placement of Drawing

How?

2727

Good

Drawing



Placement of Drawing

Or

2828

X XX

Y

Y

Y

Clean,

Neat &

TidyGood

Drawing



292929

Line Convention





•Visible Line

◦ represent features that can be seen in

the current view

◦ lines, edges, corners

30303030

Line ConventionVisible Line



• Centre Line◦ symmetrical parts and features, such as cylinders

and holes (alternating long and short thin dashes)

◦ in circular view, short dash should cross at the intersections of centre line

◦ for small hole, centre line is

presented as thin continuous line

◦ centre line should not extend

between views

31313131

Line ConventionCentre Line



•Hidden Line◦ a dashed line that represents a line,

edge or corner, which exists but cannot

be seen or concealed from view due to

obstructed view by part of the object or

of another object

32323232

Line ConventionHidden Line



Principle of Hidden Line

33333333

Line ConventionPrinciple of Hidden Line



• In summary

34343434

1. Visible

2. Hidden

3. Center

Line ConventionSummary



•Precedence of Line• when 2 or more types of lines are happened to

be in the same location

• order of precedence

• A continuous line takes precedence over a hidden line and a hidden line takes precedence over a centerline

353535

Line ConventionPrecedence of Line



•Precedence of Line• e.g.

363636

Line ConventionPrecedence of Line



•Line TypesTHICK• Visible object line 0.60 to 0.70 mm

• Cutting plane line 0 70 to 0.90 mm

• Border line 0.70 to 0.90 mm

• Break Line 0.45 to 0.70 mm

THIN• Hidden line 0.30 to 0.35 mm

• Section line 0.25 to 0 30 mm

• Centerline 0.30 to 0.35 mm

• Dimension line 0.30 to 0.35 mm

373737

Line ConventionLine Types



•What they look like?

383838




•Example 1

393939




•Example 2

404040




414141

Scale





• Scale drawings allows the engineer and

drafter to create drawings which are

proportionately the same as the product it

represents.

•Using scale, Very large objects or very

small objects can fit on a standard size

paper accurately.

42424242

Scale



Scale representation

◦ Scale 2:1

DOUBLE SIZE :2 millimeters on paper =1

millimeter on the parts

◦ Scale 1:1

FULL SIZE: 1 millimeter on paper =1

millimeter on the parts

Scale

Scale representation

◦ Scale 1:2

HALF SIZE : 1 millimeter on paper =2

millimeters on the parts

◦ Scale 1:4

QUARTER SIZE or 1 millimeter on paper= 4

millimeters on the parts.

Scale

cad_lecture_3_r1.pdf

Documents

size dimensions

parallel dimensions

actual dimensions

location dimensions

ends of dimension lines

dimensioning line

extensionprojection

hole centre line