Week 8_MIET2093_Dimension and Tolerancing_v1

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MIET2012 
1 
Lecture 8: Dimensioning and tolerencing 
MIET2093 
Computer Aided Design 
 
by: 
Dr. Toh Yen Pang 
tohyen.pang@rmit.edu.au 
9925 6128 
B251.3.22 
School of Aerospace, Mechanical & Manufacturing Engineering 2 RMIT University©2015 
Teaching 
Week 
Lecture Topics Tutorial Topics Assessments/
Tasks 
Week 7 Section View 3D modelling 
(emphasise on 
Section views)
Week 8 Dimension & Tolerance Generative Drafting 
Fundamentals 
Week 9 Assembly & Drafting Assembly Design 
workbench 
Week 10 Reverse Engineering 3D scanning (AMP 
building 55, level 4) 
Quiz 4 
Week 11 Rapid Prototyping 3D printing (AMP 
building 55, level 4) 
Teaching Schedule 
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AMP (Week 10 – Week 11) 
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Group Project 
Report due in Week 12 (Template 
given)−leader to submit e-report. pdf 
and CATIA file online 
Problem 
identification 
Analysis 
Documentation 
Refinement 
Ideation 
Decision process/ 
Design selection 
Implementation 
Generate design idea/
possible solution 
Evaluate the ideas 
against the criteria 
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Group Project (2/2) 
Identify the Design 
problem 
Generate design idea/
possible solution 
Evaluate the ideas 
against the criteria 
Document (Written Report) 
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Overview 
•  Dimensioning and Tolerancing 
•  Dimensioning 
•  Symbols, Abbreviations and General notes 
•  Manufacturing features 
•  Placement of dimension 
•  Tolerancing 
•  Apply tolerances to dimensions 
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Dimensioning 
 
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Dimensioning 
•  Before an object can be built, complete information about both the 
size and shape of the object must be available. 
•  The exact shape of an object is communicated through orthographic 
drawings, which are developed following standard drawing 
practices. 
•  The process of adding size information to a drawing is known as 
dimensioning the drawing. 
•  A dimension is a numerical value used to define the size, location, 
geometric characteristics of a part or feature. 
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RMIT Drawing Template 
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3-minute discussion 
Sketch the assigned problems. Each grid square equal
to 2mm. Completely dimension the drawings.
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8
12 
4
8
4
12 
8
 φ4 
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Definition 
Dimensioning is the process of specifying part’ s 
information by using of lines, number, symbols and 
notes. 
Notes 
1. Lines to be used are always thin continuous line. 
2. Symbol or abbreviation commonly found in a drawing are 
 - “diameter” is represented by a symbol “φ ”. 
 - “radius” is represented by a letter “R ”. 
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Unit of measure 
•  Length 
– Drawings are typically dimensioned using either millimeters or 
decimal inches 
– A general note similar to ‘Unless otherwise stated, all dimensions 
are in millimeters (or inches)’ appears. 
•  Angle 
– Degrees, minutes, 
seconds 
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Applying the dimensioning 
components 
Extension line, dimension 
line and dimension number 
Mostly done by using 
Leader line and note 
The appropriate method depends on the object’s features. 
27 φ10 
Notes 
Detail of a local note depends on the object’s features. 
Example Example 
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Arrangement of Dimensions 
•  Keep dimension off of the part where possible 
•  Arrange extension lines so that the large dimension are outside of the 
smaller dimensions. 
•  Stagger the dimension value labels to ensure they are clearly 
defined. 
60 
45 
30 
20 
30 
40 
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Basic concepts of 
dimensioning 
 
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Dimensioning components 
Extension lines 
Dimension lines (with arrowheads) 
Leader lines 
Dimension numbers 
(or dimension figures) 
Notes 
20 
13
 
φ10 
- indicate the location on the 
 object’s features that are dimensioned. 
- indicate the direction and extent of a 
 dimension, and inscribe dimension 
 numbers. 
- indicate details of the feature 
 with a local note. 
- local or general note 
R16 
Example 
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Extension line 
Always leave a visible gap (≈ 1 mm) from a view or center lines 
before start drawing a line. 
Extend the lines beyond the (last) dimension line 2-3 mm. 
Good practice Poor practice 
1 
2 
3 
2 
4 
School of Aerospace, Mechanical & Manufacturing Engineering 20 RMIT University©2015 
Good practice Poor practice 
Dimension lines should be appropriately spaced apart from each 
other and the view. 
25
 34
 
At least 2 times 
of a font size 
30
 
At least 1 time 
of a font size 
25
 34
 
30
 
25
 34
 
30
 
Too close 
Too far 
Dimension line 
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Dimension 
number 
 
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The height of numbers is suggested to be 2.5~3 mm. 
Place the numbers at about 1 mm above and at a middle 
of a dimension line. 
General 
Good practice Poor practice 
25
 34
 
25
 
34
 
30
 
30
 
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Angular dimension is expressed in degree with a symbol 
“o” places behind the number (and if necessary minutes 
and seconds may be used together). 
Length dimension is expressed in millimeters without a 
necessity to specify a unit symbol “mm”. 
25
 
Good practice Poor practice 
25
 m
m
 
Unit 
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16.25 
or 
If there is not enough space for number or arrows, put it 
outside either of the extension lines. 
1 
Not enough 
space for 
number 
Not enough space 
for arrows 
1 1 16.25 16.25 
Good practice Poor practice 
Narrow Space Situation 
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1. Aligned method 
2. Unidirectional method 
The dimension figures are placed 
so that they are readable from the 
bottom or right side of the drawing. 
The dimension figures are placed 
so that they can be read from the 
bottom of the drawing. 
Do not apply both systems on the same drawing or on the same 
series of drawing (JIS Z8317). 
1st 
choice 
2nd 
choice 
Orientation 
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30
 
3030 
30
 
EXAMPLE : Orientation of a length dimension 
30 
30 
30 
30 
30 30 
30 
30 
1. Aligned method 2. Unidirectional method 
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45o 
45
o 
45o 
45
o 
45o 
45o 
45o 
45o 
45o 45o 
45o 
45o 
EXAMPLE : Orientation of an angular dimension 
1. Aligned method 2. Unidirectional method 
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Poor practice 
Place near to the feature which they apply but should be 
placed outside the view. 
Always be lettered horizontally. 
12 Drill 
12 Drill 
≈ 10mm 
Too far 
Must be used in a combination with a leader line. 
Good practice 
12
 D
ril
l 
Placed above the bent portion of a leader line. 
12 Drill 
Local notes 
School of Aerospace, Mechanical & Manufacturing Engineering 29 RMIT University©2015 
3-minute discussion 
Sketch the assigned problems. Each grid square equal
to 2mm. Completely dimension the drawings.
School of Aerospace, Mechanical & Manufacturing Engineering 30 RMIT University©2015 
8
6 6
4
4
4
8
4
4
16 
8
2
5
10 
2 x φ2 
4
12 2 x R2 
4
2 x R1 
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Dimensioning the 
object’s features 
 
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Basic Concepts 
• The term ‘feature’ refers to surfaces, faces, slots, 
corners, bends, arcs and fillets that add up to form 
an engineering part 
• Dimensions defined the size of a feature or its 
location relative to other features or a frames of 
reference, called a datum 
Rxx 
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Dimensioning holes 
φ 50 
Use extension and 
dimension lines 
Use diametral 
dimension line 
Use leader line and 
note 
φ 50 
Rxx 
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Dimensioning 
components 
Information 
to be dimensioned 
Angle 
- Angle between 
 edges. 
A circular dimension line must have its center at the vertex of the angle. 
Poor practice Example 
Extension and circular dimension 
lines, and dimension number 
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The note and the arrowhead should be placed in a concave 
side of an arc, whenever there is a sufficient space. 
R6.5 
Place a note and 
an arrow outside 
Insufficient space 
for both 
Radius of an Arc 
R62.5 
Place a note outside 
Sufficient space 
for arrowhead only 
R62.5 
Sufficient space 
for both. 
Example : Radius of an arc 
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R62.5 R62.5 
Arc : Common mistakes 
R62.5 
R62.5 
R62.5 
62
.5
 
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If the arc has its center lies outside the sheet or interfere 
with other views, use the foreshortened radial 
dimension line. 
Arc 
A drawing sheet 
Method 1 
Example 
Method 2 
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Curve (A combination of arcs) 
Leader line and local note - Radius 
- Location 
 of its center 
Dimensioning 
components 
Information 
to be dimensioned 
Extension and dimension lines, 
and dimension number 
Poor practice 
Example : Radius of the arcs 
R20 
R40 
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Fillets and Rounds 
Dimensioning 
components 
Information 
to be dimensioned 
- Radius 1. Leader line and local note 
2. General note 
3. Combination of both 
NOTE: 
All fillets and round are R6.5 
1. All fillets and rounds 
have an equal radius 
NOTE: 
All fillets and round are R6.5 
unless otherwise specified. 
R12 
2. Most of fillets and rounds 
have an equal radius 
except for some places 
Example 
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Cylinder 
Dimensioning 
components 
Information 
to be dimensioned 
- Diameter 
- Length 
Extension and dimension lines, 
and dimension number 
Diameter should be given in a longitudinal view with the symbol “φ 
” (read phi) placed in front of a number. 
φ 
70
 
150 Example Measurement of object’s diameter 
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External chamfer 
Dimensioning 
components 
Information 
to be dimensioned 
- Linear distance 1. Leader line and local note or 
- Angle 
S θ S S 
S S 
Case of 45 degrees Case of 45 degrees 
S S 
2. Extension and dimension lines, and dimension number 
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Rounded Bars and Slots 
pad pad 
Locate the center of the arc, or the center of the slot. 
Use R to denote the radius, do not dimension it twice. 
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Placement of 
dimensions or 
Dimension guidelines 
 
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Extension lines, leader lines should not cross dimension 
lines. 
Poor practice 
Extension Line Practices 1 
Example 
Place longer dimensions 
outside shorter ones. 
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Extension lines should be drawn from the nearest points 
to be dimensioned. 
Poor practice 
Example 
Extension Line Practices 2 
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Extension lines of an internal feature can cross a visible 
line without leaving a gap at the intersection point. 
Example 
Wrong 
Extension Line Practices 3 
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Do not use visible, center, and dimension lines as an 
extension lines. 
Dimension guidelines (1/5) 
Example 
Poor practice 
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Avoid dimensioning hidden lines. 
Poor practice 
Example 
Dimension guidelines (2/5) 
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Place dimensions outside the view, unless placing them 
inside improve the clarity. 
Example 
1 
2 
Dimension guidelines (3/5) 
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Apply the dimension to the view that clearly represents 
the contour or shape of a feature being dimensioned 
Example 
Poor practice 
Dimension guidelines (4/5) 
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 Avoid repeat a dimension (superfluous dimensions). 
Example 
Poor practice 
Dimension guidelines (5/5) 
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Dimension lines should be lined up and grouped together 
as much as possible. 
Grouping Dimensions 
Example 
Poor practice 
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Good Good Poor Poor 
Poor Poor Good Good 
Practice yourself 
Determine an appropriateness of the given 
dimensions. 
 
Click on the button below to see the answer. 
(Also, try to think about the reason and how to 
 give a better dimension.) 
1 
2 
34 
5 6 
7 
8 
1 2 3 4 
5 6 7 8 
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Put the lesser dimensions closer to the part. 
Staggering Dimensions 
Example 
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Dimensions from common line 
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 Use the symbol ‘x’ to dimension repetitive features. 
Example 
Repetitive Features 
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Poor Poor Poor Poor Poor Poor Poor Poor 
Poor Poor Poor Good Good Good Good 
1 2 3 4 5 6 7 8 
Practice yourself 
Determine an appropriateness of the given dimensions. 
1 
12 
3 
4 
5 
6 
7 
9 
10 
11 
13 14 15 
2 
8 
9 10 11 12 13 14 15 
MIET2012 
Tolerance
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Tolerance is the total amount dimension may vary. 
It is defined as the difference between the upper 
and lower limits. 
TOLERANCE
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TOLERANCE: Purpose
1. To control an interchangeability of parts. 
2. To ensures the mating part will have a 
 desired fit. 
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TOLERANCE Representation
Tolerance can be expressed in several ways: 
Direct limit or as tolerance values applied directly 
to a dimension
Geometric tolerances
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Direct Tolerance
ALL METRIC DIMENSIONS TO BE HELD TO ± 0.05
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Geometric Tolerance
Geometric characteristic symbol
Diameter symbol
Stated tolerance
Datum feature
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Symbols 
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Plus & Minus Tolerance
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Fit
The degree of tightness between mating parts is called the fit. 
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Clearance & Interference Fit
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Fit Type Determination
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Summary 
•  Dimensioning is a method of accurately communicating size 
information for objects and structures so that they can be produced. 
•  There are standards to guide the proper use and placement of 
dimensional information on engineering drawings. 
•  Tolerances allow a dimension to vary within limits. 
•  Toleranced dimensions are useful in the accurate manufacture of 
assembled parts.