Week 4_MIET2093_Projections and Views

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MIET2012 
1 
Lecture 4: 3D modelling, Projections and 
Views 
MIET 2093 
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 Schedule 
Group Project 
(lab) 
Teaching 
Week 
Lecture Topics Tutorial Topics Assessments/
Tasks 
Week 3 Drawing: 2D (Arc) & 3D Basic, Dress-up 
features
Week 4 3D, Projections and Views Dress-up & 
Transformation 
Features
Quiz 1
Group Project
Week 5 Isometric Views Part Design 
(emphasise on multi-
views and projection)
Week 6 Auxiliary Views 3D modelling 
(emphasise on 
isometric views)
Quiz 2 (labs)
Test 1 (1.5hr)
Saturday, 18th April
10:00-12:30pm
Building 56, level 4 
PC labs
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Group Project 
Form a group of maximum 5 members 
Choose a group leader 
Each member in the group will have a minimum 1 part 
to model 
Report due in Week 12 (Template will be given)-leader 
to submit e-report and CATIA file online 
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1. Fighter rig 2. Rotary 
Engine 3. Shaper 
Tool head 
4. Flash Light 5. Silicon Gun 
6. GPS holder 7. Plummer block 8. Clamp 9. Jack 
10. Nail 
Clipper 
Group Projects 
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Scaling Factor 
If the scaling factor for your group sf=1.01, you are to multiple all 
the dimensions in the drawing by 1.01 before you start your project 
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•  3-D modeling, 
•  Dress-up features 
•  Additional features 
•  Feature order and relationships 
•  Duplicating Part Feature 
•  Geometric Transformations 
Objectives 
MIET2012 
3D Modeling: 
Dress-Up Features 
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Fillets 
A fillet is a curved face of a constant or variable radius that is 
tangent to, and that joins, two surfaces. 
Together, these three surfaces form either an inside corner (fillet) 
or an outside corner (round) 
Example 
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Chamfering 
Chamfering is an operation which replaces sharp edges by small 
planar faces at an angle to the faces adjacent to the original edge. 
Example 
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Draft 
Draft features apply an angle to a part surface relative to some 
reference. 
Example 
Material is added or removed depending on the draft angle & pull 
direction 
What is needed for the basic draft technique? 
1.  Pulling direction 2.  Draft angle 
3.  Neutral element 
1 
3 
2 
3.  Neutral element 
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Shell 
Empty a solid while keeping a given thickness on its sides 
Example 
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MIET2012 
Features order and 
relationships 
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Features created are recorded for a part in a tree 
The order that features and operations appear in the specification 
tree affect the geometry of the part. 
Feature order (1/2) 
Changing the order is sometimes necessary because features 
have been created in the wrong order or perhaps design intent 
has changed. 
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Feature ordering (2/2) 
Example 
Box 
Shell 
Hole 
Box 
Hole 
Shell 
Reordering features give the operator a powerful tool for 
redefining the end resulting geometry of the model 
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Feature interdependencies (1/2) 
When a feature is referenced by another during a design, a 
parent-child relationship is established 
Parent (first feature) 
Child (second feature, dependent) 
A child feature is defined relative 
to a parent feature through 
geometric definitions such as 
constraints, alignment, or 
workplanes. 
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Feature interdependencies (2/2) 
A child feature is placed below the parent feature in the feature 
tree 
Deleting or changing the geometry of parent feature may delete or 
alter the child feature 
MIET2012 
3D Modeling: 
Duplicating Part Features 
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Mirror allows one half of a symmetrical part and duplicate the 
opposite side about some reference. 
Example 
Duplicating Features: Mirror 
What is needed for the mirror modeling technique? 
Design feature Datum plane or planar surface 
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Duplicating Features: Patterns 
Rectangular pattern 
User pattern 
Three different types of patterns within the Part Design 
workbench: 
Circular pattern 
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Patterns: Rectangular 
Rectangular patterns are linear and can be created in two 
directions 
Examples 
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Patterns: Circular 
Circular patterns are radial and are defined about an axis. The 
axis reference can be defined by an edge, a line, or a normal 
vector off a planar surface or datum plane. 
Examples 
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Patterns: User Defined 
User patterns use an existing sketch of points to define the 
location of the instances. 
Examples 
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•  Why would you want to reorder features? 
•  Give an example of a parent–child relationship. How is a feature tree 
used to identify parent–child relationships? 
•  Name two primary types of duplication methods. What input 
parameters are needed to define each one? 
Self practice exercises 
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Objectives 
•  3-D Viewing Techniques
•  Explain orthographic and multiview projection
•  Projection theory
•  Create a multiview drawing by sketching
•  Create an isometric drawing 
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Creating Three-View Drawings 
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Purpose 
To graphically represent a 3-D object on 2-D media 
(paper, screen etc.). 
Object (3D) placing 
on the paper (2D) 
Transparent plate is placed 
between object and 
observer’s eyes. 
Object’s features are transferred 
through projection. 
Inconvenient to 
communicate 
A view of an object on 
2D media 
Convenient to 
communicate 
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What is (Planar) Projection? 
Projections is the process of reproducing a spatial object on a 
plane, curved surface, or line by projecting its points. 
A projection is a mapping of a 3D space onto a 2D subspace, i.e.a plane. 
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Elements of (Planar) Projections 
Every planar projection includes 
the following elements 
The 3D object to be projected. 
Sight lines (called projectors 
or visual rays) passing 
through each point on the 
object 
A 2D projection plane 
The projected 2D image that 
is formed on the projection 
plane 
Projected image 
Plane 
Object 
Projector 
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Projection Methods 
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Multiview Projection 
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Guidance 1 : Examples 
Rectangular prism 
Cylinder Cone 
Sphere 
The readers have a stock of a pair of an orthographic views and a 
simple shape object. 
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Guidance 2 : Examples 
The readers familiar with a generic object, i.e. an object that is 
modified from a simple shape object. 
Simple shape 
object database 
Generic object database 
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3-minute discussion 
Sketch a multiview of the object 
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MIET2012 
Projection 
Theory
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Concept
A projection theory is based on 2 variables:
1) Line of sight
2) Plane of projection (image or picture plane)
Plane of projection
is an imaginary flat plane upon
which the image created by the
LOS is projected.
Line of sight (LOS)
is an imaginary ray of light
between an observer’s eye
and an object. projectionline
LOS
Plane of projection
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Line of sight
Lines of sight can be parallel or perspective. 
Perspective projection Parallel projection 
Infinity distance finite distance 
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Line of sight
The parallel projection lines can be normal (orthogonal)���
or oblique to the plane of projection.
Oblique Orthogonal 
In this course, we consider only a parallel and orthogonal���
projection, i.e. orthographic projection.
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Image on a projection plane. 
Rotate
TiltMultiview drawing
shows a 2D view of an 
object.
���
Axonometric drawing ���
shows a virtual 3D view 
of an object.
View
View depends on a relative orientation between an object and a 
plane.
MIET2012 
Multiview ���
drawing
Contents 
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Multiview drawing is a set of related images that are created by 
viewing the object from a different direction.
Definition
Width Depth 
Height 
Width 
H
ei
gh
t 
Depth 
D
ep
th
 Adjacent view(s) 
is needed to 
fulfill the object 
description. 
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Multiview drawings shows the true size and shape of the various 
features of the object 
Advantages of multiview drawings 
Multiview drawings provide the most accurate description of three-
dimensional objects and structures for engineering 
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The frontal plane (front or back 
view) is typically the first plane 
established and shows the width and 
height dimensions of the object. 
Multiview Projection Planes
The horizontal plane (top or bottom 
view) shows the depth and width 
dimensions. 
The profile plane (side (left or 
right) view) shows the depth and 
height dimensions 
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1. Revolve the object with respect to observer
Methods
Front view Right side view 
Top view 
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Glass box : Revolution of the planes of projection
Bottom view 
Left side view 
Rear view 
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Height 
Width 
D
ep
th
 
Six Principal views
Left side view Right side view 
Bottom view 
Top view 
Rear view 
Front view 
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Summary : Problem solving steps
1 2 
3 
4 
Given 
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Given
Class activity : 
Sketch a multiview set of object 
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Object features
Edge is a line that represent the boundary between two 
faces of an object. 
Surface limit is a line that represents the last visible 
part of the curve surface. 
Prism Cylinder Sphere 
No edges! 
Surface is an area that are bounded by edges or surface 
limit. Surface can be plane or curve. 
These features will appear as lines in a multiview drawing. Note 
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Projection of a curve surface 
Play 
Glass box concept Multiview drawing 
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Projection of an object having 
curved surface and plane 
In the case of intersection, an edge exists and becomes a line 
in a multiview drawing 
Curved surface can either tangent or intersect with an 
adjacent plane or curve surface. 
In the case of tangential, there is no edge and line in a multiview 
drawing 
I 
I 
T 
T 
T 
I 
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Tangent or intersect 
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Examples 
Play 
2 
3 
Play 
Play 
4 
Play 
1 
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Examples 
Play 
5 6 
Play 
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Examples 
Play 
Play 
7 8 
9 
Play No line exists 
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Given
Class activity : 
Sketch a multiview of the given object 
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Projection of an object 
Play 
Glass box concept Multiview drawing 
Do the same procedures for 
all remaining edges (or planes) 
Hidden line is used 
to show existence of 
a hidden edge. 
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Projection of an inclined line 
Play 
Glass box concept Multiview drawing 
AF 
BF 
AF 
B 
A 
BF 
AR 
BR 
AR 
BR 
AT 
BT 
AT 
BT 
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Projection of an inclined plane 
Play 
Glass box concept Multiview drawing 
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Practice yourself : 
Given the isometric pictorial drawingof an object, sketch the missing 
orthographic (multiview) top, front and side views of the given object 
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Practice yourself : 
Given the isometric pictorial drawing of an object, sketch the missing 
orthographic (multiview) top, front and side views of the given object 
School of Aerospace, Mechanical & Manufacturing Engineering 62 RMIT University©2015 
Practice yourself : 
Given the isometric pictorial drawing of an object, sketch the missing 
orthographic (multiview) top, front and side views of the given object 
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School of Aerospace, Mechanical & Manufacturing Engineering 63 RMIT University©2015 
Practice yourself : 
Given the isometric pictorial drawing of an object, sketch the missing 
orthographic (multiview) top, front and side views of the given object