This lecture contains the detail of isometric projections of an object. This will improve your skills to draw isometric views which is the major part of engineering drawings.

1. ISOMETRIC
PROJECTIONS
Ahmad Hassan 2016-Civ-321

2. Types of Pictorial Projections
a
b c2. Dimetric Two angles are equal.
b
a
c3. Trimetric None of angles are
equal.
a
b c
1. Isometric All angles are equal.

3. Introduction
 It is a type of pictorial projection in which three
dimensions of a solid are clearly shown.
 The actual dimensions of the solids can also be
measured directly from such projections.

4. Isometric axes, lines and planes
 DA, DC and DF lines, meeting at
point D and subtending 120 degree
angles with each other are termed
as isometric axes. All the lines
parallel to these axes are known as
isometric lines. The planes
representing the faces of the cubes
shown in fig. 1 as well as other
planes parallel to these planes are
called isometric planes. In fig.1. EF,
FG, EA, GC are examples of
isometric lines, where faces ABCD,
ADFE, DFGC etc. are the examples
of isometric planes.
FIG. 1

5. Isometric scale
 Isometric projection is reduced in a ratio i.e.
isometric lengths are 0.815 of the true length.
 Thus while drawing an isometric projection; it is
essential to convert true lengths into isometric
lengths for measuring and marking the sizes. This
can easily be done by constructing and making
use of an isometric scale.

6. Isometric Drawing or Isometric View
 If the foreshortening of the isometric lines in an
isometric projection is disregarded and instead, the true
lengths are marked, the view obtained will be exactly of
the same shape but larger in proportion (about 22.5%)
than that obtained by the use of isometric scale.
 Due to the ease in construction and the advantage of
measuring the dimensions directly from the drawing, it
has become a general practice to use the true scale
instead of the isometric scale.
 To avoid confusion, the view drawn with the true scale
is called isometric drawing or isometric view, while
that drawn with the use of isometric scale is called
isometric projection.

7. Isometric sketch
Isometric sketch is an isometric view that is drawn
in full size.
Isometric projection
(True projection)
Isometric drawing
(Full size)
Forshorten
Full scale

8. Orientation of Isometric Axes
Isometric axes can be arbitrarily oriented to create
different views of a single object.
Regular
isometric
Reverse axis
isometric
View point is looking
down on the top of
the object.
View point is looking
up on the bottom of
the object.

9. Distance in Isometric Sketch
Isometric line is the line that run parallel to
any of the isometric axes.
Isometric axes
True-length distances show along isometric lines.
Nonisometric lines

10. Isometric Sketching

11. 1. Place the object in the position which its shape
and features are clearly seen.
2. Define an isometric axis
3. Sketch the enclosing box
4. Estimate the size of each detail
5. Darken all visible lines
Sketch from an actual object

12. STEPS
1. Positioning object.
2. Select isometric axis.
3. Sketch enclosing box.
4. Add details.
5. Darken visible lines.
Sketch from an actual object

13. 1. Positioning object.
2. Select isometric axis.
3. Sketch enclosing
box.
4. Add details.
Note In isometric sketch/drawing, hidden lines are omitted
unless they are absolutely necessary.
STEPS
5. Darken visible lines.
Sketch from an actual object

14. Front View
Top View
Side View
Example 1 : Object has only normal surfaces
Bottom View
Bottom
Front
Side
Side
Front
Top
Regular
Reverse
W
D
H
H
DW

15. Example 2 : Object has inclined surfaces
W
HD
y
x Front View
y
x
Nonisometric line

16. A
A
B
B
C D
E
D
EF
F
x
y
Front View
Regular
C
Example 4

17. Circle & Arc in Isometric
In isometric drawing, a circle appears as an ellipse.
2. Construct an isometric square.
3. Sketch arcs that connect the
tangent points.
Sketching Steps
1. Locate the centre of an ellipse.

18. Circle & Arc in Isometric
3. Construct a perpendicular
bisector from each tangent point.
4. Locate the four centres.
5. Draw the arcs with these centres
and tangent to isometric square.
Sketching Steps
Four-centre method is usually used when drawn an
isometric ellipse with drawing instrument.
2. Construct an isometric square.
1. Locate the centre of an ellipse.

19. Example 5

20. Irregular Curve in Isometric
1. Construct points along the
curve in multiview drawing.
2. Locate these points in the
isometric view.
3. Sketch the connecting lines.
Steps