1. ENGINEERING GRAPHICS 1E9
Lecture 3: Isometric Projections

2. What is ISOMETRIC?
It is a method of producing pictorial view of an object showing all three faces of the object simultaneously.
It is a type of parallel projection
It is a type of axonometric projection

3. Axonometric Projections
Observer at infinity
Projectors parallel to each other and perpendicular to projection plane
Object is inclined with respect to projection plane

4. Types of Axonometric Projections
Isometric Projection
Dimetric Projection
Trimetric Projection

5. Isometric Projections
All angles between axonometric axes are equal
The three coordinate axes of the object appear equally foreshortened (about 3/4th of true length)
The angles between any two of the three coordinate axes is 120°

6. Isometric Terminology
The three coordinate axes are called isometric axes
Any line parallel to isometric axes is called isometric line
A  non-isometric line is a line not parallel   to   any   one   of   the three isometric axis
In isometric projection of cube, the faces of the cube and any plane parallel to them is called isometric planes

7. Isometric Scale
True lengths of the edges of the object are equally foreshortened
Correct isometric projection can be drawn using an isometric scale (always smaller than ordinary scale)
AEBO is isometric, cube is rotated to obtain AE’BO’ (actual face of cube)

8. Isometric Drawing
Isometric Projection: Drawing prepared with isometric scale on isometric axes
Isometric Drawing:
Drawing prepared
with ordinary scale
on isometric axes
Compared to isometric projection, Isometric drawing has a chunkier overall impression

9. Steps:
Step 1
Isometric sketches begin with defining isometric axes, three lines, one vertical and two drawn at 30° from the horizontal.

10. Steps:
Step 2
Three lines of the isometric axes represent the three primary dimensions of the object: width, height, and depth

11. Steps:
Step 3
Draw the font face of the isometric block.

12. Steps:
Step 4
Draw the rest of the isometric block.

13. Steps:
Step 5
Add details to the block starting from the front face. Then add details to the other faces.

14. Steps:
Step 6
Darken all visible lines to complete the isometric sketch. (make sure that construction lines are light)

15. Axonometric projection shows all 3 dimensions, length, width and height.
The isometric lines are only drawn to scale. Objects composed entirely of isometric lines can be drawn by taking all measurements parallel to main edges of the enclosing box.
Non-isometric lines are drawn by transferring the ordinates (which are on isometric lines) of the end of the lines
Inclined and oblique surfaces are drawn using end coordinates. Box construction and offset measurements are common methods
In  an  isometric  drawing,  an angle never appears in its true size. Angles, irregular curves require special techniques

16. Objects with Normal Surfaces
Make an Isometric Drawing with corner A at the bottom
Hidden detail is omitted unless it is necessary to show shape of object

17. Objects with Normal Surfaces
Hidden detail is omitted unless it is necessary to show shape of object

18. Objects with Oblique Surfaces
Make an Isometric Drawing with corner A at the bottom
NON-ISOMETRIC LINE

19. Objects with Oblique Surfaces
Hidden detail is omitted unless it is necessary to show shape of object

20. Objects with Non-isometric Lines
Make an Isometric Drawing with apex A facing front

21. Objects with Non-isometric Lines
Non-isometric lines are drawn with box construction and offset measurements
Non-isometric lines are not drawn in true length in isometric drawing (BA is shorter than CA in this drawing)
Hidden detail is omitted unless it is necessary to show shape of object

22. Irregular Objects
Make an Isometric Drawing of the following irregular object (pyramid)

23. OA and OB offsets help to locate apex O
Irregular Objects
OA and OB offsets help to locate apex O
Complete box construction may not be needed in each case
Hidden detail is omitted unless it is necessary to show shape of object

24. Objects with Circular Geometry
A circle in a orthographic projection will appear as an ellipse in an isometric drawing.
Instead of actual ellipses often approximate ellipses are drawn for isometric drawing.
Four-centre ellipses are used to approximate ellipses on isometric planes.
How to draw four-centre ellipse???

25. Approximate Ellipse
Draw  the  isometric centre  lines  of  the circle. Using  the  centre  lines,  draw an isometric square with sides equal to the diameter of  the  circle.
From  the  near  corners  of  the  box,  draw two large arcs with radius R, using the two red points as centres.
Draw the two smaller arcs with radius r, using two green points as centres.

26. Cylinder

27. Objects with Circular Geometry
Hidden detail is omitted unless it is necessary to show shape of object

28. Objects with Non-Circular Curved Surfaces
Make an Isometric Drawing of the following curved object

29. Objects with Non-Circular Curved Surfaces
A line that appears as a noncircular curve in a normal orthographic view of an object appears as a non-isometric line in an isometric drawing.
Curves may be drawn using a series of points by measuring along the normal lines in the  orthographic  view  (offset measurements) and  transferring  these points on isometric drawing. Accuracy increases with number of points.
Hidden detail is omitted unless it is necessary to show shape of object