Week 2_MIET2093_Free hand and 2D_Sketching_v2

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MIET2012 
1 
Lecture 2: Technical Drawings & 
Sketching 
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 
www.3ds.com/academia/ 
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Email- Do Not reply to Announcement 
tohyen.pang@rmit.edu.au 
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AMP (Week 10 – Week 11) 
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Course outline 
Teaching 
Week 
Lecture Topics Tutorial topics Assessments/Tasks 
Week 1 
Introduction to 
Engineering 
Design & 
Graphics 
Introduction to 
Enovia and 
Getting Started 
with CATIA 
 
Week 2 
Sketches: 
Freehand and 2D 
sketches 
Introduction to 
Sketcher 
Workbench 
 
Week 3 
Drawing: 2D & 
3D solid 
modeling 
Part Design: Basic 
Features 
 
Week 4 Projections and 
Views 
Part Design: 
Dress up Features 
Quiz 1 
Group Project 
(Max. 5 member 
team) 
!
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Quiz 1 sketch, using CATIA - fully constraint 
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MIET2012 
Revision CATIA v6 
RMIT University©2010 7 
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Connecting to V6 
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Workbench 
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Moving objects with mouse 
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•  The role of technical/engineering sketching in the design 
process 
•  Technical Sketch 
•  Identify and use drawing tools 
•  Describe drawing standards and conventions 
•  Drawing sheet 
•  Scale 
•  Line types 
•  Geometry construction 
Objectives 
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Eng’g Design Process 
Problem 
identification 
Analysis 
Documentation 
Refinement 
Ideation 
Decision process/ 
Design selection 
Implementation 
lack of ergonomics 
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Conceptual 
design 
Details 
design 
Requirement Development 
& 
Production 
Operation 
& Support 
PLM
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Overview (1/2) 
• Regardless of the language they speak, people all over the 
world use technical drawings to communicate their design 
ideas. 
• A new product, machine, structure or system may exist in 
the mind of the engineer or designer, but before it can 
become reality, the idea must be communicate to many 
different people 
• The ability to communicate design concept quickly and 
accurately through technical drawings is key to meeting 
project budgets and time constraints 
Giesecke, F.E, Mitchell, A., Spencer, H.C., et al, 2010, Modern Graphics Communication, Pearson Prentice Hall, Upper Saddle River, New Jersey, Columbus Ohio. 
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• Engineering graphics communication involves the use 
of visual material to convey technical ideas and 
problem solutions.
• Engineering or technical drawing – one of the most 
widely used method.
Overview (2/2) 
•  Definition of drawing:
A graphic representation of an 
idea, concept or an entity 
which actually or potentially 
exists in life.
 
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What is technical sketching? 
Technical sketching is the process of producing a rough 
preliminary drawing representing the main features of a product 
or structure 
Normally done by freehand, generally less finished, less 
structured/ restricted, & take less time to produce 
Example 
Technical sketches are used extensively in the first (ideation) 
stage of the design process 
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Technical sketching process 
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Why sketching in an age of computing? 
• Freehand sketching has a number of important uses:
– Engineers often need to make sketches out in the field
– Sketching is also a just-in-time communication tool used by 
engineers, designers, and craftsperson
– Freehand sketching is used creatively for brainstorming ideas, 
inventing and exploring alternatives
– Sketching is essential in order to practice the language of 
engineering graphics
• It is important not to lose sight of the discipline’s rich 
graphical and creative traditions
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A drawing can be created in 3 ways: 
Ways to Create an 
Engineering Drawing 
1.  Freehand sketch 
2.  Using typical drawing instruments (mechanical) 
3.  Using a computer (digital) 
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Example 
Create a Drawing : Freehand sketch 
The lines are drawn using only pencil and erasers on a 
blank or grid paper. 
Pictorial sketch 
Orthographic sketch 
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Example 
Create a Drawing : Using instruments 
Drawing instruments are used to 
draw straight lines, circles, and 
curves concisely and accurately. 
Drawings are usually made to scale. 
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Example 
Create a Drawing : Using a computer 
Computer-aided design/ drafting (CAD) software is 
used. 
2D drawing Solid modeling 
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Understand the role of 
technical drawings 
Drawings and specifications control the many details 
of product manufacture, assembly and maintenance. 
Technical drawing requires knowledge of the 
standards that allow drawing to concisely 
communicate designs around the world 
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Traditional 
Drawing Tools 
 
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Traditional Tools 
Traditional tools are devices used to assist the 
human hand in making technical drawings 
These should include the following: 
Paper 
A range of pencils 
Ruler 
Set squares 
Compasses 
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Sketch Pad or Graph Paper 
Isometric grids Square grids 
Plain bond papers with no linesà offers the highest degrees of 
flexibility 
Two common grid papers are square grid and isometric grid 
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Scales 
Scales are used to measure distances on technical drawings. 
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Straight line 
Arc, Circle 
4. Circle template 
1. Rulers 
2. Triangles 
3. Compass 
Tools Shape to be drawn 
Function of the tools 
T-square and triangles can be used together to draw 
an inclined line with 15o increment, i.e.15o, 30o, 45o, 
60o, 75o, 90o, 105o, 120o, 135o, 150o, 165o, 180o etc. 
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Drawing Standards 
& Conventions 
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Standards 
Standards are set of rules that govern how technical drawing 
are represented 
 
Drawing standard are used so that drawings convey the same 
meaning to everyone who reads them 
 
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ISO International Standards Organization 
Standard Code 
ANSI American National Standard Institute USA 
JIS Japanese Industrial Standard Japan 
BS British Standard UK 
AS Australian Standard Australia 
Deutsches Institut für Normung DIN Germany 
Country Code Full name 
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Conventions 
Conventions are commonly accepted practices, rules, 
or methods used in technical drawing 
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MIET2012 
Drawing Standard: 
Drawing Sheet & 
Scales 
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Drawing Sheet 
http://en.wikipedia.org/wiki/Engineering_drawing 
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Scales 
•  Before you start any drawing you first decide how large the 
drawings have to be.
•  The object may be much too large for the paper or much too 
small to be drawn clearly. 
•  There are drawing aids called ‘scales’ which are designed to 
help the draughts person to quickly enlarge or reduce the 
drawing measurements 
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Drawing Actual 
Length, size 
: 
Scale is a ratio between the linear dimension of a 
drawn representation of an object and the actual object. 
1 2 
Drawing Scales : Definition 
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Matric Scales 
Designation of a scale consists of the word “SCALE” 
followed by the indication of its ratio, as follows 
SCALE 1:1 for full size 
SCALE X:1 (X > 1) for an enlargement scales 
SCALE 1:X (X > 1) for a reduction scales 
Full size: The 1:1 scale is full size, and each division is 
actually 1mm 
Half size: The 1:2 scale is one half size, and each 
division equals 2mm 
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Dimension numbers shown in the drawing represent 
the “true size” of an object and they are independent of 
the drawing scale used. 
Drawing Scales : Notes 
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3-minute discussion 
Do not dimension 
MIET2012 
Drawing Standard: 
Lines 
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Common types of sketching lines 
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Basic Line Types & Application 
Continuous 
Dash 
Chain 
Style 
Thickness Thick Thin 1. Dimension line 2. Extension line 
3. Leader line 
Center line 
Hidden line 
Visible line 
represent features that can be seen in the current view. 
represent features that can not be seen in the current view. 
represents symmetry, path of motion, centers of circles, axis 
of axisymmetrical parts 
indicate the sizes and location of features. 
1. Visible line 
3. Hidden line 
4. Center line 
2. Dimension line 
 Extension line 
 Leader line 
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Line Styles (1/2) 
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Line Styles (2/2) 
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Complete the given orthographic drawings with a missing 
hidden lines 
Class activity : 
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Complete the center lines to the given view. 
Use a drawing instrument. 
Class activity : 
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Sketch the object on the grid 
Class activity : 
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Good & Poor Technique 
Construction line 
Sharp Corner 
Centre & hidden line 
 
Centre & hidden line 
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Geometry 
Construction 
MIET2012 
Drawing a 
perpendicular line
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r1 
r2 
+ 
C 
r2 
r2 > r1 
A 
B 
D 
Given 
play 
Line perpendicular to a point in a line 
Compass method 
Explanations 
1. Use a given point as center, 
 draw the arc with any radius. 
2. Bisect the distance between the 
 intersection points between an 
 arc and a given line. 
3. Draw a line. 
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Given
Class activity :
Sketch the ridge gasket using the tangent arc technique. 
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Creating a new 
drawing/Sketching 
In order to start a drawing project in a CAD 
environment, there are some important steps to follow: 
1.  Create a new drawing file 
2.  Define the drawing units 
3.  Define the drawing limits 
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Layouts 
When laying out a drawing sheet, you will need to 
consider: 
the size and scale of the object you will show 
the sheet size 
the measurement system (units) for the drawing 
the space necessary for standard note and title block 
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Sketching techniques 
James M.Leake, Jacob L. Borgerson (2013) Engineering Design Graphics: Sketching, Modeling and Visualization, John Wiley & Son, Inc. USA 
Line Techniques
A freehand sketch should begin with proportionally laid out 
construction lines.
Construction lines are thin and drawn lightly; they serve to guide the 
lines to follow
All other lines should be dark, crisp and of uniform thickness; they 
can be sketched directly over the construction lines
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Essential of sketching: Straight line 
Freehand sketches should not be sloppy 
NO! 
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Essential of sketching: Proportioning 
Although freehand sketches are not drawn to scale, it 
is important to maintain the relative proportions 
between the principal dimension of the object 
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Constraint-Based 
Modeling 
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Sketching using constraint-based 
modelers 
Constraint-based modelers involve generating a 3-D model 
by applying 3-D construction operations such as extrude, 
revolve, or sweep to 2-D features. 
Feature tools such as dimensions, constraints, references, 
and relations areused to capture design intent. 
When creating a sketch with a constraint-based modeling 
program, rather than the actual size, the shape and 
proportions are important. 
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Drawing 2D Shape 
Some examples of common shapes are: 
Circles 
Squares/rectangles 
Triangles 
Polygons 
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Dimensioning 
Dimensions provide the description of the size and 
location of entities 
Dimensions also give distances between elements, 
lines and points, circle radii 
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Constraints 
The geometry is ‘‘held together’’ by a set of constraints 
what happens if the top edge is moved without the 
constraints between the end points? 
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Types of Constraints 
•  A list of common (but not all possible) constraints that can 
be found in CAD systems is: 
1.  Vertical 
2.  Horizontal 
3.  Parallel 
4.  Perpendicular 
5.  Bisector 
6.  Midpoint 
7.  Fixed 
8.  Tangency 
9.  Coincidence 
10.  Distance constraints 
11.  Angular constraints 
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Dimension schemes 
Check what happens when the overconstraining 
dimension is added 
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Practice by Yourself 
Sketch the object on the grid without dimensioning 
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•  Define and describe the uses for technical sketching. 
•  What is the difference between conventions and standards? 
•  List the typical hand tools used to create a drawing. 
•  Why is constraint important is sketch model? 
•  Define an ideation sketch and explain how it differs from a 
document sketch 
Self practice exercises 
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References 
•  Giesecke, F.E, Mitchell, A., Spencer, H.C., et al, 2010, Modern 
Graphics Communication, Pearson Prentice Hall, Upper Saddle 
River, New Jersey, Columbus Ohio. 
•  Kevin Henry, (2012) Drawing for Product Designers, Laurence King 
Publishing, London 
•  Ian Stroud, Hildegarde Hagy, Solid Modelling and CAD Systems: 
How to Survive a CAD System, Springer-Verlag London Limited, 
2011