Chapter11 1

Chapter 11
Engineering Graphics I
Dr Simin Nasseri
Southern Polytechnic
State University
© Copyright 2010

© Dr Simin Nasseri
Southern Polytechnic State University

1
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Objectives:

1. Define axonometric, isometric, dimetric, and trimetric.
2. Explain the difference between an isometric projection
and an isometric drawing.
3. Create an isometric drawing.
4. Use true ellipse, four-center, or an ellipse template to
draw a circle in an isometric drawing.
5. Apply the theory of oblique projection to create oblique
drawings and sketches.

© Dr Simin Nasseri

2

Axonometric and oblique pictorial drawings
use a parallel projection technique and are
frequently used in technical documents, sales
literature, maintenance manuals, and
documentation supplements in engineering
drawings.
The Greek word axon means axis and
metric means to measure.
Axonometric projection is a parallel
projection technique used to create
pictorial drawings of objects by rotating
the object on an axis relative to a
projection plane to create a pictorial
view.

© Dr Simin Nasseri

3

Figure 11.3

Axonometric drawings are classified by the angles between the lines
comprising the axonometric axes.

A#B#C

When all three angles are
unequal the drawing is
classified as a trimetric.

© Dr Simin Nasseri

A=B

When two of the three
angles are equal the
drawing is classified as
a dimetric.

A=B=C=120o

When all three angles
are equal the drawing
is classified as a
isometric.

4

Figure 11.5

An isometric view of an object is created by rotating it 45 degrees about a vertical axis,
then tilted forward until the body diagonal of the cube (A-B) appears as a point in the
front view. The angle the cube is titled forward is 35 degrees 16 minutes. The three
corners meet to form equal angles of 120 degrees and is called the isometric axis.
© Dr Simin Nasseri

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Figure 11.6

All the edges of the cube are parallel to the edges that make up the isometric
axis since projections of parallel lines are parallel.
Any line that is parallel to one of the legs of the isometric axis is called an
isometric line.
The planes of the faces of the cube and all planes parallel to them are called
isometric planes.

The forward tilt of the cube causes the edges and planes of the cube to become foreshortened as it
is projected onto the picture plane. Thus the projected lengths are approximately 80% of the true
lengths and an isometric projection ruler must be used.

If the drawing is drawn at full scale it is called an isometric drawing. Isometric
drawings are almost always preferred over isometric projection for engineering
drawings, because they are easier to produce.
© Dr Simin Nasseri

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Figure 11.7

The development of an isometric scale produced on paper using a regular scale.

© Dr Simin Nasseri

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Figure 11.9

Regular isometric looking down on the top of the object.
Reversed axis isometric is developed by looking up on the bottom of the object.
Long-axis isometric is developed by looking from the right with one axis drawn
at 60 degrees to the horizontal.
© Dr Simin Nasseri

8

Figure 11.10
Figure 11.11

nonisometric
planes

Isometric
planes

Any line that runs parallel to any of the isometric axes is called an isometric line.
Any line that does not run parallel to an isometric axes is called a non-isometric line.
The three faces on the isometric cube are called isometric planes. Isometric planes
are surfaces which are parallel to the isometric surfaces formed by any two adjacent
isometric axes.
Planes which are not parallel to any isometric plane are called non-isometric planes.
© Dr Simin Nasseri

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Figure 11.13

In isometric drawings hidden lines are
omitted unless absolutely necessary to
completely describe the object.
Normally, most isometric drawings
will not have any hidden lines. You
can avoid using hidden lines if the
most descriptive viewpoint is chosen.
However, there are times when the
object has some features which cannot
be described no matter which
isometric viewpoint is taken.

© Dr Simin Nasseri

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Figure 11.14

In isometric drawings center lines are drawn if symmetry must be shown or
for dimensioning. Normally, center lines are not used on isometric drawings.

© Dr Simin Nasseri

11

Figure 11.15

Dimensioned isometric
drawings used for production
purposes must be ANSI
standard, with dimension and
extension lines and lines to be
dimensioned lying in the same
plane
© Dr Simin Nasseri

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Figure 11.16

Dimensioned drawings used for
illustration purposes may use the
aligned method.

© Dr Simin Nasseri

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Figure 11.17

Creating a isometric
drawing using the
boxing-in method.

© Dr Simin Nasseri

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Figure 11.18

Constructing nonisometric lines by locating
points in isometric.

© Dr Simin Nasseri

15

Figure 11.19

Locating points to create an isometric drawing of an irregular object.
© Dr Simin Nasseri

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Figure 11.20

Creating an isometric
view of an object with
an oblique plane.

© Dr Simin Nasseri

17

Figure 11.21

To draw an angle in an
isometric drawing, locate the
endpoints of the lines that
form the angle and draw the
lines between the endpoints.

© Dr Simin Nasseri

18

Figure 11.22

Irregular curves are
drawn in isometric by
constructing points along
the curve in the
multiview drawing
which are then located in
the isometric view.
These points are then
connected with an
irregular curve drawing
instrument.

© Dr Simin Nasseri

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Figure 11.23

Circles that lie on any face of an isometric cube will appear as ellipses.

© Dr Simin Nasseri

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Figure 11.24

The location of center lines and the major and minor
axes of isometric ellipses.

© Dr Simin Nasseri

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Figure 11.25

Constructing a true
isometric ellipse.

© Dr Simin Nasseri

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Figure 11.26

R
D

r

Constructing an ellipse using the four-center ellipse construction method.
© Dr Simin Nasseri

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Figure 11.27

Four-center ellipses drawn on the three faces of an isometric cube.

© Dr Simin Nasseri

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Figure 11.28

The comparison between a true ellipse and one constructed by the four-center method.

© Dr Simin Nasseri

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Figure 11.29

Application for which four-center
technique is not used because of
accuracy concerns.

© Dr Simin Nasseri

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Figure 11.32

An ellipse is drawn on an inclined plane of an isometric drawing
by plotting a points on a grid that is on the non-isometric plane.

© Dr Simin Nasseri

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Figure 11.33

Since arcs are partial circles, they appear in isometric
drawings as partial isometric ellipses.
© Dr Simin Nasseri

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Figure 11.34

Constructing a curved intersection on an isometric drawing.

© Dr Simin Nasseri

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Figure 11.40

Screw threads are represented by a series of equally spaced
isometric ellipses whose major diameter is equal to the
diameter of the screw.

© Dr Simin Nasseri

34

Figure 11.45

An isometric grid is a grid paper set using the
isometric axes with vertical and diagonal lines.

© Dr Simin Nasseri

37

Isometric view of a Frenier
pump, illustrating the operation
of a Frenier pump for lifting
tailings at the standard mill.

Drawing by Dana
Lockett, 2001, courtesy
of Historic American
Engineering Record,
National Park Service.

© Dr Simin Nasseri

40

Sketch the following dimensioned isometric drawing. Dimensions are in inches.

R=0.5

From Southbank International School

© Dr Simin Nasseri

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Angle=60

1.0

Sketch the following dimensioned isometric drawing. Dimensions are in inches.
R=1
R=0.5

1.0
http://www.cadalyst.com

© Dr Simin Nasseri

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