Orthographic, Oblique
&
Isometric Projections
Created by
Carpentry & Joinery Section
Granville TAFE.
Statement of Objectives

The student will be able to:-
1.
Reproduce oblique, isometric & orthographic representations of
objects
2.
Draw the plan view, front and side elevation of a particular
object given either the isometric or oblique representation.
3.
Draw an isometric or oblique representations of an object given
the plan, front and side elevation.
4.
State the need for using scales when drawing an object.
5.
Draw the plan of an object at a scale of 1:2 and 1:5
6.
Find the measurements from a plan when a scale is given but no
measurements are given on the plan.
Any object can be drawn.

The purpose of drawing may be to show the object either
as a picture or to show it in a way that would enable
someone to make it.
In the building Trade drawings
serve two purposes
1.
Cottages can be drawn as a ‘pictorial’ by an architect.
2.
Or drawn by a builder to show what it will look like when
finished.
In the building Trade drawings
serve two purposes
Housing joints can be shown the
same way for similar reasons.
Through housing joint
Cottages can be drawn
orthographically

This shows internal details such as:-
1.
Room sizes and spacing.
2.
Orthographic projections is from one aspect only.
3.
This gives the builder the information required to do the
job.
Cottages can be drawn
orthographically
This also applies to a simple
housing joint for the same reason
Pictorial drawings most commonly used in
the building trade are either
ISOMETRIC OR OBLIQUE PROJECTION

They are probably used more in freehand sketches on the
job, than detailed drawings.
Pictorial drawings most commonly used in
the building trade are either
ISOMETRIC OR OBLIQUE PROJECTION
Isometric projection is a method
used to depict three sides of an
object.

( ISO meaning equal, metric meaning measure)

An isometric drawing shows length, width & thickness.



However any lines which are not parallel to the length, width &
thickness are not true measurements.
For example the diagonals of a square or rectangle are equal on
the actual object , but do not appear so in isometric.
The vertical lines are drawn vertically and the angle is 30
degrees.
Isometric projection is a method
used to depict three sides of an
object.
Oblique projection is another
method of showing three sides of
an object in one drawing.



An oblique drawing shows one view in true proportion.
The sides of an object are drawn full size and at a angle of
45 degrees.
To ‘PROPORTION’ the drawing we halve the measurement
of the oblique side.
Oblique projection is another
method of showing three sides of
an object in one drawing.
This can be better illustrated if a
cube is drawn in both
isometric & oblique projection.

The diagonals on the face of the oblique drawing are equal
because this is a true view but not on the isometric.
This can be better illustrated if a
cube is drawn in both
isometric & oblique projection.
Orthographic projection is the
correct or true shape of an object
drawn on a flat surface.

It is the main method used to represent an object in a
drawing.

It gives three views of the object in three separate
drawings.

Gives three basic dimensions, Length, Width & Thickness

Gives three views of the object plan, front, & side elevation
Orthographic projection is the
correct or true shape of an object
drawn on a flat surface.
The object shown if surrounded by 3
surfaces or planes (vertical, side
vertical & horizontal) each of the 3
views is called projection.

The three surfaces or planes are to be represented on
paper as one flat surfaces.
The object shown if surrounded by 3
surfaces or planes (vertical, side
vertical & horizontal) each of the 3
views is called projection.
The 3 views of the object on a
drawing are obtained by projecting
or ‘throwing’ points of the object
onto the drawing.

These projection lines are at 90 degrees to the surface of
the object. Therefore the view obtained will be a true one.
The plan is obtained by looking
‘down on the top’ of the object.
(i.e. projecting onto the horizontal plane.)
The front elevation is projected
onto the vertical plane but
‘looking from the front’.
The side elevation is projected onto the
side vertical plane.
’looking from the side’
Drawing paper represents one flat
surface, so if the objects drawn
were laid out flat then the three
views would appear as drawn.


Projections are made from one view to another.
Projecting from the plan and front elevation will give the
side elevation.
Drawing paper represents one flat
surface, so if the objects drawn
were laid out flat then the three
views would appear as drawn.
Orthographic projection is used for
working drawings it is essential that
the sizes or dimensions are placed
onto the drawing.

Most objects to be drawn are bigger than the drawing
sheet, then it is necessary to fit or ‘scale the object it so it
can be placed onto the paper.
Orthographic projection is used for
working drawings it is essential that
the sizes or dimensions are placed
onto the drawing.
To keep the drawing in proportion
the actual dimensions are reduced
in the same ratio. This is called
‘SCALING’

Although the actual measurements are written on the
drawing they don’t actually measure that amount on a
‘SCALED’ drawing.
To keep the drawing in proportion
the actual dimensions are reduced
in the same ratio. This is called
‘SCALING’
Drawing to scale is the reducing or
enlarging by ratio of an object from
its actual size that can fit onto a
working drawing.

Scaling is a ratio that can be expressed as:
1:2 1:5 1:10 1:50 1:100

The scale chosen depends on the size of the object and the
size of the drawing paper.
Drawing to scale is the reducing or
enlarging by ratio of an object from
its actual size that can fit onto a
working drawing.
On a scale of 1:5 the 300
represents 300mm but to a scale
of 1:5 in represents 60mm
( 300 = 60 )
50
If measurements are indicated on a
drawing they should be used in
preference to scaling.

All dimensions are not shown on a drawing as this would
clutter the working drawing. If this is the case scale
matching the drawing can be done but accuracy can be
compromised.
If measurements are indicated on a
drawing they should be used in
preference to scaling.
At this stage you should be have
some knowledge of:1.
3 different types of drawings.
2.
How to draw and recognise these types.
3.
The purpose of scales.
4.
How to use scales.
Carpenters have to do the actual building which
involves “READING” plans and interpreting
drawings.
Without this knowledge of drawing any carpenter
will find it hard to understand the plans and
therefore hard to build the job.