1. Orthographic, Oblique & Isometric Projections
Created by
Carpentry & Joinery Section
Granville TAFE.

2. Statement of Objectives
The student will be able to:-
Reproduce oblique, isometric & orthographic representations of objects
Draw the plan view, front and side elevation of a particular object given either the isometric or oblique representation.
Draw an isometric or oblique representations of an object given the plan, front and side elevation.
State the need for using scales when drawing an object.
Draw the plan of an object at a scale of 1:2 and 1:5
Find the measurements from a plan when a scale is given but no measurements are given on the plan.

3. 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.

4. In the building Trade drawings serve two purposes
Cottages can be drawn as a ‘pictorial’ by an architect.
Or drawn by a builder to show what it will look like when finished.

5. In the building Trade drawings serve two purposes

6. Housing joints can be shown the same way for similar reasons.
Through housing joint

7. Cottages can be drawn orthographically
This shows internal details such as:-
Room sizes and spacing.
Orthographic projections is from one aspect only.
This gives the builder the information required to do the job.

8. Cottages can be drawn orthographically

9. This also applies to a simple housing joint for the same reason

10. 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.

11. Pictorial drawings most commonly used in the building trade are either ISOMETRIC OR OBLIQUE PROJECTION

12. 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.

13. Isometric projection is a method used to depict three sides of an object.

14. 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.

15. Oblique projection is another method of showing three sides of an object in one drawing.

16. 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.

17. This can be better illustrated if a cube is drawn in both isometric & oblique projection.

18. 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

19. Orthographic projection is the correct or true shape of an object drawn on a flat surface.

20. 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.

21. The object shown if surrounded by 3 surfaces or planes (vertical, side vertical & horizontal) each of the 3 views is called projection.

22. 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.

23. 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’

24. 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.

25. Drawing paper represents one flat surface, so if the objects drawn were laid out flat then the three views would appear as drawn.

26. 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.

27. Orthographic projection is used for working drawings it is essential that the sizes or dimensions are placed onto the drawing.

28. 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.

29. To keep the drawing in proportion the actual dimensions are reduced in the same ratio. This is called ‘SCALING’

30. 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: :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.

31. Drawing to scale is the reducing or enlarging by ratio of an object from its actual size that can fit onto a working drawing.

32. On a scale of 1:5 the 300 represents 300mm but to a scale of 1:5 in represents 60mm ( 300 = 60 ) 50

33. 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.

34. If measurements are indicated on a drawing they should be used in preference to scaling.

35. At this stage you should be have some knowledge of:-
3 different types of drawings.
How to draw and recognise these types.
The purpose of scales.
How to use scales.

36. 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.