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NQF Level 3
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Engineering Graphics & Design
Engineering Graphics
& Design
Engineering Graphics
& Design
NQF Level 3
NQF Level 3
Student’s Book
eng graphics-design 3s.indd 1
Sparrow Consulting
STUDENT’S BOOK
TVET FIRST
2015/03/05 12:41 PM
Engineering Graphics &
Design
NQF Level 3
Student’s Book
Sparrow Consulting
Engineering Graphics & Design NQF Level 3
Student’s Book
© Sparrow Consulting, 2011
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First published in 2011 by
Troupant Publishers [Pty] Ltd
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Northcliff
2115
Distributed by Macmillan South Africa [Pty] Ltd
ISBN: 978-1-9203-3493-2
Web PDF ISBN: 978-1-4308-0178-8
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Contents
Topic 1 Isometric Drawing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
Module 1 Construct isometric scales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2
Unit 1.1: What is an isometric scale?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
Unit 1.2: Use an isometric scale to construct isometric drawings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7
Unit 1.3: Plan the drawing to maximise page usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12
Unit 1.4: Produce an isometric scale using engineering drawing instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18
Module 2 Construct an isometric drawing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24
Unit 2.1: First and third angle isometric drawings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24
Unit 2.2: Construct an ellipse using the four-centre method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
31
Unit 2.3: Produce 3-dimensional drawings in first and third angle projection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
37
Topic 2 Assembly Drawing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
45
Module 3 Perform sectioning on engineering drawings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
46
Unit 3.1: What is sectioning? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
46
Unit 3.2: Section engineering drawings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
56
Module 4 Engineering drawing assemblies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
61
Unit 4.1 Label the different parts of the assembly drawing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
66
Unit 4.2: Section the assembly drawing according to the given instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
69
Unit 4.3 Assemble different parts to form one single drawing in third angle orthographic projection . . . . . . . . . . . . . . . . . .
72
Unit 4.4: Assemble different parts to form one single drawing in first angle orthographic projection . . . . . . . . . . . . . . . . . .
75
Topic 3 Detailed drawings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
83
Module 5 Perform dimensioning on a given drawing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
84
Unit 5.1: Dimensioning methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
85
Unit 5.2: Draw and insert dimensions according to a standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
91
Module 6 Produce detailed drawings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
95
Unit 6.1: The parts of an assembly drawing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
96
Unit 6.2: Detailed drawings in first angle orthographic projection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
99
Unit 6.3: Detailed drawings in third angle orthographic projection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
100
Unit 6.4: Dimensioning of the drawings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
101
Unit 6.5: Sectioning the drawing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
102
Topic 4 Development and inter-penetration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
Module 7 Construct a development drawing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
108
Unit 7.1: The parallel line method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
110
Unit 7.2: Drawing equally spaced parallel lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
113
Unit 7.3: Calculate all relevant data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
115
Unit 7.4: Produce the final template . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
117
Module 8 The radial line method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
120
Unit 8.1: The radial line method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
120
Unit 8.2: A basic truncated cone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
122
Unit 8.3: Develop the surface of a truncated cone with a sloping base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
125
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Unit 8.4: Calculate all relevant data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
127
Unit 8.5: Produce the final template . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
129
Module 9 The triangulation method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
134
Unit 9.1: The triangulation method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
135
Unit 9.2: The functions of bend lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
136
Unit 9.3: True length lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
137
Unit 9.4: Transfer top view measurements into true length measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
137
Unit 9.5: Use Pythagoras’ theorem to calculate lengths of bend lines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
139
Unit 9.6: Produce the final template . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
141
Topic 5 Computer-Aided Design (CAD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
Module 10 The computer environment and CAD scale production drawings . . . . . . . . . . . . . . . . . . . . . . . . . . . .
146
Unit 10.1: Selecting a CAD program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
147
Unit 10.2: Learning the basics of CAD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
148
Unit 10.3: Selecting the size, scale and orientation of a drawing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
166
Module 11 Produce scale production drawings using a CAD program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
169
Unit 11.1: Produce scale production drawings to line stage using CAD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
169
Module 12 Complete, verify, save and print CAD scale production drawings . . . . . . . . . . . . . . . . . . . . . . . . . . .
180
Unit 12.1: Title production drawings to meet standard conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
180
Unit 12.2: Production drawings are titled to meet site requirements in terms of typography. . . . . . . . . . . . . . . . . . . . . . . . . .
184
Unit 12.3: Title the production drawing for processing and manufacturing data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
185
Unit 12.4: Drawings are saved according to site procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
193
Unit 12.5: Verify, save and print CAD scale production drawings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
194
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
199
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Topic 1
Isometric Drawing
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Module 1
Construct isometric
scales
Overview
At the end of this module, you should be able to:
• Explainwhatanisometricscaleis.
• Explainhowanisometricscaleisusedtoconstructisometric
drawings.
• Planthedrawingtomaximisepageusage.
• Useengineeringdrawinginstrumentstoproduceanisometric
scale.
Introduction
Imagine you have this great idea on what the next super sports car
should look like, but it is all in your head. How do you explain your
idea to a car manufacturer?
The simplest way is to draw your idea on paper. This drawing should
have all the necessary dimensions to show what your idea looks like
from different angles, showing the top view, front view and side view
of the object. The dimensions give the width, length and height of the
object. By drawing your idea on paper, it is possible to see the correct
shape and the correct size of your super sports car or any other object.
The end result of drawing a technical idea on paper is called an
engineering drawing. Drawing is the universal graphic language of
communication used and understood in engineering. Therefore, it is
very important that you study the techniques, procedures and skills
used to communicate ideas as this will allow you to draw, understand
and interpret engineering drawings.
There are many different types of engineering drawings. In this
module you will learn what an isometric scale is, and how and when
to apply it when constructing an isometric drawing. You will also
learn how to plan an engineering drawing to maximise the page usage.
And to conclude this module, you will learn how to use different
pieces of engineering drawing equipment and instruments.
2
Words &
Terms
engineering draw
ing: a
drawing or pictur
e that
explains a techni
cal idea
graphic: using pi
ctures or
drawings to show
an idea
isometric drawin
g: a
method of 3-dim
ensional
drawing in which
the three
principal dimensio
ns are
represented by th
ree axes
120° apart
principal: main,
most
important
isometric scale:
a scale in
which the true le
ngths of
an object are redu
ced by
a specific amount
so as to
show the foreshor
tening
which occurs wh
en a
surface or line is
seen from
a slanting angle
and not
from right angles
Module 1: Construct isometric scales
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Unit 1.1: What is an isometric
scale?
Words &
Terms
Graphical projections
Before you can explain the concepts of isometric scales and isometric
drawings, you need to know about graphical projections. A projection
is the image you get as a result of looking at an object from a particular
direction. There are two main types of projections used in engineering
drawings, namely: parallel projection and perspective projection.
These differ according to the line of sight and the plane of projection.
In perspective projection, the lines of sight are not parallel to the plane
of projection, as can be seen in Figure 1.1.
perspective: thre
edimensional objec
ts
represented on a
twodimensional surfa
ce so as
to give the impres
sion of
height, width, de
pth, and
distance
projection: the im
age that
you have when yo
u look at a
particular view of
an object
from a particular
direction
line of sight: an
imaginary
straight line betw
een the
observer’s eye an
d the
object being look
ed at
plane of projectio
n: the
plane on which th
e lines of
sight create an im
age; it is
also called the im
age plane
or the picture plan
e
Non-parallel lines
of sight radiating
from a point
View of object projected onto
picture plane
Picture plane (paper or computer
screen)
plane: a flat surfa
ce, which
may be real or im
aginary
Observer (station point) One
viewpoint
Figure 1.1: Perspective projection
In parallel projection, the line of sight is parallel to the plane of
projection, as shown in Figure 1.2. This provides you with the correct
shape and size of the object.
Parallel lines of
sight
View of object projected
onto picture plane
Observer (station point)
Infinite viewpoint
Picture plane (paper or
computer screen)
Figure 1.2: Parallel projection
Module 1: Construct isometric scales
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Did you know?
The different types of engineering drawings are:
Sketches: sketches may be real-life sketches and design sketches, drawn without drawing instruments
Layout drawings: the original design of an object is shown in a layout drawing. This will be used to produce an
assembly or detail drawing
Assembly drawings: drawings which show how the different parts of an object fit together
Detailed drawings: these provide all the information necessary to provide a complete description of an object so that it
can be made, repaired, or changed
Casting drawings: provides all the information needed to cast an object in a mould. This means that it can be made out
of a liquid material (e.g. metal or plastic) poured into the mould and allowed to harden
Fabrication drawings: fabrication drawings are used to show objects that are joined using fasteners (such as bolts and
rivets) or by welding
Views and projections
Words &
Terms
There are two main types of views (projections), namely pictorial
views and orthographic (multiple) views.
In multiple views (or multi-view), the actual shape of an object is seen
from different directions which, (in orthographic projection) are at
right angles to each other. These directions are called views. The object
is drawn such that only two of the three dimensions of the object
are shown in any one view. The three dimensions referred to are the
height, the width and the depth.
The six principal views of an object
are the front view, rear view, top view,
bottom view, right side view and the
left side view. Usually three views are
enough to describe an object, as shown
in Figure 1.3.
Notice that the broken lines in Figure
1.3 show hidden edges or corners. This
is discussed in more detail in Module 2.
Pictorial views provide the overall
shape of the object from only one
direction. The three types of pictorial
views are isometric, oblique and
perspective. For the purposes of
this module you will only deal with
isometric views.
pictorial: like a pi
cture
orthographic proj
ection:
a method of proje
ction in
which an object
is shown
using parallel lin
es to
project its outline
on to a
plane
multi-view projec
tion:
also called multip
le view
projection, show
s several
different views of
an object
Depth
Top view
Width
Height
Front view
Right side view
Figure 1.3: Multiple views of an object
4
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In isometric views, the object is drawn at a 30° angle from a horizontal
surface as shown in Figure 1.4.
Words &
Terms
30˚
30˚
Figure 1.4: Isometric view
You may be wondering by now why so much emphasis is placed on
isometric views. The first reason is that isometric views are the easiest
type of pictorial projection to draw. The second reason is that the
shape of arcs and circles drawn in isometric view is consistent on all
surfaces. This is discussed in Module 2.
Isometric views and scales
The term isometric means equal (iso) measure (metric). In an isometric
drawing, an object is positioned so that its principal axes have the
same angles to each other, i.e. 120°. If this is the case, the principal
axes are called isometric axes. There are three isometric axes, namely a
vertical axis and two inclined axes. The inclined axes are at an angle of
30° to the horizontal as shown in Figure 1.5.
isometric view:
combines
the multi-view of
an object
into only one pict
orial view
in which the two
horizontal
axes are inclined
at 30°
angles to a horiz
ontal
surface
characteristic: th
e main
feature of somet
hing
scale: the ratio of
the size of
a drawing to the
size of the
object being draw
n. A full
scale or a 1:1 ratio
shows
that the drawing
is the same
size as the actual
object.
A 1:2 ratio means
that the
drawing is half th
e size of
the actual object.
A 2:1 ratio
means that the dr
awing is
twice as big as th
e actual
object
The main characteristic of an isometric drawing is that the object is
always placed in such a way that the major vertical edge is drawn
vertically (i.e. 90°) and the major horizontal edges are drawn at 30° to
the horizontal as shown in Figure 1.6.
Inclined axis
Inclined axis
120˚
30˚
30˚
120˚
120˚
Vertical axis
Figure 1.5: Isometric axes
30˚
30˚
Figure 1.6: Isometric drawing
Module 1: Construct isometric scales
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Isometric drawings are made using full scale
measurements. This means that the true lengths of an
object are used along the different axes to make an
isometric drawing of that object. However, it is sometimes
necessary to draw the foreshortened size of an object,
e.g. if the drawing contains other objects that are not
foreshortened, like spheres or surfaces facing the viewer.
In these cases, the dimensions of the foreshortened objects
are reduced according to the isometric scale as shown in
Figure 1.7.
le
ca
s
l
l
Fu
5
4
2
To explain further, look at the cube shown in Figure 1.8. If
you look at the cube directly from the top, the front or the
side, you will see the true size of the object in full scale.
This is because you are viewing the object at a perpendicular angle.
B
D
A
1
C
F
G
3 ic
etr
om
le
sca
30˚
Is
0
C
E
45˚
G
True size orthographic view
Figure 1.7: Isometric scale
Words &
Terms
foreshortened: sh
own
as having less de
pth or
distance than in
reality,
to convey an effe
ct of
perspective
perpendicular: at
90° or at
right angles
F
Figure 1.8: True size orthographic view
If you now view the cube as shown in Figure 1.9, you obtain a
foreshortened view of the object. A foreshortened view means that the
cube appears to be smaller than its true size.
Did you know?
B1
A1
C1
E1
G1
F1
A1
D1
C1
E1
F1
G1
The graphics in computer
games such as SimCity
and the Sims use isometric
projection.
Foreshortened orthographic view
Figure 1.9: Foreshortened orthographic view
When you make a drawing using an isometric scale, it shows the
foreshortening effect due to the parts not being viewed from right
angles, as shown in Figure 1.10(a). Figure 1.10(b) shows the cube
drawn to full size. When you use an isometric scale, the lines drawn
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are approximately 82% of the full scale. This means that the resulting
shapes are approximately 18% smaller than in a full scale isometric
drawing as shown in Figure 1.10. In practice, however, full scale
isometric drawings are usually used so that true lengths can be
measured on the drawing. The only time it is necessary to use the
isometric scale in a drawing is when the drawing contains objects that
are not foreshortened.
(a)
(b)
A: Isometric scale used
B: Full scale used
Figure 1.10: Foreshortened view is 18% smaller than full scale view
Assessment activity 1.1
Group discussion
In small groups, discuss the following questions before answering them in your own words in your
workbook.
1.
2.
3.
4.
5.
What is an isometric scale?
Why is an isometric scale used in isometric drawings?
When should the isometric scale be used in an isometric drawing?
Explain the concept of foreshortening.
Think of an easy experiment that you as a group can do to explain how foreshortening works.
To give you a tip, you can use a pencil or a pen for the experiment.
6. Think of examples in real life where you can see the effect of foreshortening?
7. If you had to draw these objects, why would you need an isometric scale to do it?
Peer assessment: Swap your work with one of your group members and compare the answer
with the given answer sheet. Submit your work to the lecturer as part of your PoE.
Unit 1.2: Use an isometric scale to
construct isometric drawings
Before you can use an isometric scale to construct isometric drawings,
you need to be able to construct an isometric scale.
Construct an isometric scale
To construct an isometric scale, use the following 3-step method.
Step 1: Draw a horizontal line equal to the length of the longest
dimension on your drawing. From the beginning of this horizontal
line, draw two inclined lines at 30° and 45° angle to the horizontal.
Refer to Figure 1.11.
Figure 1.11: Inclined lines drawn
from a horizontal line
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Step 2: Use a ruler to measure and mark lengths of 10 mm multiples
on the full scale (45° inclined line) as shown are Figure 1.12.
low res
Figure 1.12: Marked-off distances on the
45° inclined line
Figure 1.13: Completed isometric scale
Step 3: Draw perpendicular lines from the marked-off points on the
45° inclined line towards the 30° inclined line as shown in Figure 1.13.
low res
Now that you are able to draw an isometric scale, it is time to learn
how to use it to construct an isometric scale drawing.
Construct an isometric scale drawing
Figure 1.14 shows three orthographic views of an object together with
the isometric view.
30
15
20
10
Front view
Left view
20
Top view
Isometric view
Figure 1.14: An object drawn in multi-view orthographic
projection and isometric view
To construct an isometric scale drawing, you can apply the next four
steps.
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Step 1: Construct an isometric scale to measure the longest dimension
on the object. A scale of 30 mm is used for this example as shown in
Figure 1.15. Draw the first line inclined at 30° for the isometric scale.
Draw the second line inclined at 45° for the full scale.
Step 2: Draw the major edge of the object at angles of 30° to the
horizontal. This is shown in Figure 1.16.
Figure 1.15: Draw an isometric scale
Figure 1.16: Create inclined isometric axes
Step 3: Read off the lengths of the object from the given orthographic
drawing and then mark them off using the isometric scale in order
to draw the object. Make sure that vertical lines on the orthographic
projection are vertical on the isometric drawing, and horizontal lines
on the orthographic projection are inclined at 30° to the horizontal on
the isometric drawing. Inclined lines on the orthographic projection
(e.g. at the top right-hand corner of the front view) are drawn on the
isotropic view by marking their end points and joining them. This is
shown in Figure 1.17.
Words &
Terms
isotropic view: a
view of
an object that ha
s equal
physical propertie
s along all
axes
Step 4: Complete the drawing by showing all the necessary lines and
erasing all the unnecessary ones. This is shown is Figure 1.18.
Figure 1.17: Measure off distances
to draw the object
Figure 1.18: Complete the drawing
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Assessment activity 1.2
Working in pairs
The figures below contain the orthographic as well as isometric views of an object. The
orthographic views are labelled with measurements according to the true size of the object. The
dimensions are in centimetres.
1.
2.
Discuss with your partner how you would go about constructing isometric scales for each of
these objects.
Divide the objects between the two of you so that each of you has to construct two isometric
scales.
a)
5
3
6
6
Front view
Left view
5
9
Top view
Isometric view
b)
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c)
d)
3.
4.
5.
Peer assessment: Discuss your scales with each other and make sure that they are drawn
correctly. You can compare your answers with the drawings your lecturer will show you or by
comparing it to other student’s answers.
Using the above isometric scales, discuss how you will construct an isometric scale drawing of
each object.
Swap your scale drawings and draw the two isometric drawing for the scales that your partner
drew.
Peer assessment: Discuss your isometric drawings with each other and make sure that they are
drawn correctly. You can compare your answers with the drawings your lecturer will show to
you.
Discuss how much smaller an isometric scale drawing is than a normal isometric drawing?
Self-assessment: Mark your own answer according to the answer in the given memorandum.
Submit your work to the lecturer as part of your PoE.
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Unit 1.3: Plan the drawing to
maximise page usage
Planning the drawing means making the best use of the provided
space on your drawing sheet.
Plan the drawing for paper size
The sizes of drawing sheets are given in Table 1.1.
Paper designation
A0
A1
A2
A3
A4
Dimensions (mm)
841 × 1 189
594 × 841
420 × 594
297 × 420
210 × 297
Words &
Terms
Table 1.1: Sizes of drawing sheets
After you have selected the size of sheet to use, the drawing layout
must be designed so that the presentation of the drawing meets
professional standards.
It is recommended that you firmly place the drawing sheet on a
drawing board or any table with a smooth surface. The drawing sheet
can be held to the drawing board by using clips or masking tape as
shown in Figure 1.19.
layout: the way in
which
something, espe
cially a
page, is laid out
design: a plan fo
r something
achieved by calcu
lating and
detailing its featur
es to be in
line with its purp
ose
The first step in designing the drawing space is to a draw a borderline
around the edges of the drawing sheet. For A3 paper size, this
borderline should be 10 mm from the drawing sheet’s edge. This is
shown in Figure 1.20.
Figure 1.19: Holding the drawing sheet in place on a
drawing board.
12
Figure 1.20: Drawing of the borderline
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Next, a title block needs to be drawn at the bottom right-hand corner
of the drawing sheet. After this, the remainder of the page is available
to be used for the drawings.
The title block includes information such as the author’s surname and
initials, project name, scale, company name and date. This information
can change according to the purpose of the drawing. For example, for
college purposes, the title block can include information such as the
surname and initials of the author of the drawing, the scale, drawing
number, group number and date. The title block must be placed at the
bottom right-hand corner, the height of the letters being 5 mm. The
height of the title block should be approximately 32 mm depending
on the amount of information put in the title block. This is shown in
Figure 1.21 and Figure 1.22.
Figure 1.21: Drawing of the title block
Figure 1.22: Information found on a professional title block
Isometric drawings are usually drawn together with the orthographic
views on the same drawing sheet. The drawing sheet must therefore
be divided so that the three orthographic drawings are shown together
with the isometric projection. An example is shown in Figure 1.23.
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Top view
Fro
n
297
tv
iew
Top view
R Side
view
ISOMETRIC
Front view
R Side view
ORTHOGRAPHIC PROJECTIONS
420
Figure 1.23: Example of a planned drawing paper
Select a suitable scale and size for your
drawing
The key in planning how best to use the available space is to select a
suitable scale and size for your drawing. This will help you to use the
maximum amount of space on your paper and to make your drawing
as clear as possible. This means that you have to plan the layout of the
three main views of your chosen orthographic projection, including the
isometric drawing.
Remember that an A3 paper has a width of 297 mm and a height
of 420 mm. Drawings made on A3 paper should be placed inside a
10 mm border, with no part of the layout touching the title block. To be
safe, leave a space of 50 × 100 mm for the title block. Also remember
to plan for a space of at least 10 mm between the borders of the paper
and the nearest line of your drawing. Subtracting these values from
the size of the A3 paper gives you the available working space on the
paper.
Two possible layout plans are shown:
• O
ptionAinwhichtheheightofthedrawingismaximised,shown
in Figure 1.24.
• OptionBinwhichthewidthismaximised,showninFigure1.25.
In option A, the available drawing space can be regarded as two
rectangles next to one another. The first rectangle is 257 × 280 mm
and the second rectangle is 100 × 207 mm. This layout maximises the
available height of the drawing space.
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280
297
100
207
257
380
207
297
280
50
420
Figure 1.24: Option A provides maximum height for the
available drawing space on an A3 sheet
420
Figure 1.25: Option B provides maximum length for the
available drawing space on an A3 sheet
In option B, the available drawing space consists of two rectangles, a
large one of 207 × 380 mm above a smaller one of 50 × 280 mm. This
layout maximises the available width of the drawing space.
Words &
Terms
In option B, the larger rectangle is 207 × 380 mm, and the values
should be used to plan a correct scale for the drawing so that you can
be sure all the views will fit in.
sectional view: a
drawing
in which a crosssection of
some part of the
object is
shown by shadin
g
Before you start to plan your drawing, ask yourself the following:
• W
illthedrawingbeinfirstorthirdangleorthographicprojection?
(First and third angle orthographic projections are dealt with in
Module 2.)
• Whatarethelongestandhighestdimensionsofthedrawing?
• Aretheregoingtobeanyextrasectionalviewsinthedrawing?
(Sectional views are dealt with in Module 3.)
Example
Following is an example of how to determine the scale of
your drawing, using the large wooden block shown in
Figure 1.26.
You can assume the following:
• T
hedrawingwillbedoneinfirstangleorthographic
projection, with a front view, a top view and a left view.
(Orthographicprojectionsareusuallychosensothatthe
front and top views will show the most detail.)
• Thelargestverticaldimensionis100mm.
• Thelargesthorizontaldimensionis100mm.
• Nosectionalviewswillbenecessary.
• Assumeadistanceofabout30to50mmbetweenthe
views of the drawing to provide some space for dimensions.
100
20
20
100
100
Figure 1.26: A large wooden block
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From the information provided
above, you already know that you
will need approximately 250 mm in
the vertical direction and 250 mm in
the horizontal direction, as shown in
Figure 1.27.
100
50
100
100
50
100
Figure 1.27: Sizes of the three orthographic views of the part
shown in Figure 1.26
In order to determine the scale, divide the actual size of the part by
the paper size. Scaling is used because it is good practice to create a
drawing that more or less fills the page. If the actual size is larger or
much smaller than the paper, some scaling should be used.
From Figure 1.24, you know that you have 380 mm available in the
horizontal direction and 257 mm available in the vertical direction.
Therefore:
250
Horizontal distance of actual part
= horizontal scale =
= 0.66
380
Horizontal distance of the paper
Vertical distance of actual part
Vertical distance of the paper
= vertical scale =
250
= 0.97
257
It is always important to choose the largest number as your scale, in
this case 0.97. Therefore, an adequate scale will be 1:0.97 where 1 mm
on the paper will be equal to 0.97 mm on the actual part. But this
number would be difficult to work with, so it would be better to round
the number up to 1.0 and make the scale 1:1. This means that 1 mm on
the paper will be equal to 1 mm on the part.
There are three very important rules when it comes to choosing a scale:
• A
lwayschoosethelargestnumberofthecalculatedhorizontaland
vertical scales.
• Ifyouneedtoroundthescaletoamoreworkablenumber,you
must always round up, and never down. In other words, if you
get something like 44.2 you cannot round down to 44; you have to
round up to 45.
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• A
lwaystrytoroundlargerscalefactorsuptothenearestmultiple
of 10. Using the example of 44.2, a good scale would be 1:50.
Examples of good scale are 1:1, 1:2, 1:5, 1:10, 1:20, 1:50, 1:100, 1:200, etc.
As you can see, good numbers to work with are all divisible by 1, 2
and 5.
Assessment activity 1.3
Working in pairs
1. In pairs, discuss how to go about planning for the correct paper size and select the appropriate
scale for your drawing.
Individual activity
2. Using that information, calculate a suitable scale for the following parts to be drawn on an A3
sheet of paper.
You can assume the following:
• Thedrawingwillbedoneinfirstangleorthographicprojection,withafrontview,atop
view and a left view.
• Thereisaborderof20mmfromthepaperedge.(Remembertoallowfora10mmspace
between the border and the nearest line of your drawing.)
• Distancesbetweentheviewsofyourdrawingshouldbe50mm.
a)
b)
1000
200
200
1000
1000
c)
Peer assessment: Swap your work with
your partner and compare the answers
with the given memorandum. Submit
your work to the lecturer as part of your
PoE.
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