1. TA 101: Technical Arts 2015-16 II Dr. Prishati Raychowdhury
Department of Civil Engineering
IIT Kanpur
Office: FB 336; Phone: 6692

2. Lecture 6
Isometric Projection

3. Review: Dimensioning
Dimensioning is done to describe various features of an object
Show dimensions in the view that shows the most relevant features
Do not repeat a dimension
Place dimensions outside the view, as far as possible
Take dimensions out from visible outlines than from hidden lines
Give dimensions from Baseline /finished surface /centerline of a hole (as far as possible)
Depending on available space, chose wisely among full arrows, half arrows, lines or dots
Depending on available space, choose wisely among parallel, chain or combined dimension style

4. Axonometric Projection
Greek: axon = axis, metric = measure
Axonometric = To measure along axes

5. Axonometric Projection
Axonometric projection is theoretically an orthographic projection in which only one plane is used and the object being turned so that its three faces are visible
Plane of Projection
Plane of Projection
Plane of Projection
Orthographic Projection
Axonometric Projection

6. Axonometric Projection: Overview
In orthographic projection, projections are taken on two or more mutually perpendicular planes
In Axonometric projection, the object is oriented (rotated TWICE) a priori and appropriately, so that all its 3D features are clearly visible on the vertical plane of projection
Axonometric view is one kind of pictorial view

7. Axonometric/Pictorial View: Example
100 80 20 25 60 50 40 12 x z Y

8. Advantages and Limitations
Easier to visualize the design
Relative proportioning of overall size
Relative positioning & sizing of constituent parts
Good for marketing, showing assembly, conceptual ideas
Disadvantage:
Does not show true shapes (shapes distorted)
Does not show details
Not good for dimensioning/manufacturing

9. Axonometric vs. Orthographic Views

10. Axonometric Projection: Basic Concept
One may get several pictorial views depending on the angle of each rotation
Some sort of uniformity and standardization is required

11. Foreshortening When does a line appears in its true length?
The Projection plane is parallel to the object face
Rotate object about vertical axis
Result: Two sides are “foreshortened”
Rotate object about both vertical and profile axes
Result: Three sides are “foreshortened”

12. Foreshortening for a Cube
Top view
No object rotation
Front, Top and Side views
(no foreshortening)
Object rotated about vertical axis (Two sides are foreshortened)
Object rotated about vertical and profile axis
(3 sides are foreshortened)
Square face becomes what?

13. Axonometric Projection: Classification
Axonometric drawings are classified based on how many axes are foreshortened
All three axes are unequally foreshortened: Trimetric projection. [Supposedly the most pleasing to the eye and the most difficult to produce]
Two of the sides equally foreshortened: Dimetric projection. [Supposedly less pleasing to the eye but easier to produce than trimetric drawings]
All three sides equally foreshortened: Isometric projection. [Supposedly least pleasing to the eye but easiest to draw]

14. Axonometric Projection: Classification

15. Isometric Projection Equal foreshortening of all 3 sides
To obtain an isometric view of an object:
Step 1:
Start with the front principal face of the object (cube) parallel to the projection plane

16. Isometric Projection Step 2:
Rotate the object by 45° about its vertical axis

17. Isometric Projection Step 3:
Tilt the object forward by 35°16' (35.27°)
For a cube, this corresponds to a forward tilt till the body diagonal AB appears as a point in the front view
The three axes that meet at A on the projection plane form equal angles of 120°.
They are called the isometric axes.

18. Isometric Projection
The forward tilt of the object causes the edges and planes to become foreshortened as they are projected on the projection plane.
The lengths of the projected lines are equal to the cosine of 35o16’ ( ) times the true lengths.
The projected lengths are approximately 81% of the true lengths.

19. Concept of Isometric ProjectionEH
Concept of Isometric Projection GH FH HH BH DH H AH CH E F AF EF BF FF BP AP FP EP P F A B HP GP CF GF DF HF DP CP H G FH HH C D EH GH BH DH HP
450 DF H AH CH GF FF AF AP BP EP FP FF EF BF P F EF BF AF GF CF HF DF CP DP GP HP FF FP BP EP EF BF AF AP HP
Isometric Projection GF DP GP DF
350 15’ 52’’ CP CF

20. Isometric Axes
Isometric Axis
120
Isometric Box
30
30

21. Important points
• Each edge of the cube is parallel to one of the isometric axes.
• Any line that is parallel to an isometric axis is called an isometric line.
• The planes of the cube faces and all planes parallel to them are called isometric planes.

22. Isometric Projection/Isometric View
A drawing produced using a scale of {1:1.225} is called an Isometric Projection and is a true representation of the object
If everything else is kept same, but we produce the drawing using full scale {1:1}, it is called an Isometric Drawing /View
An isometric drawing has the same proportions as an isometric projection, but is larger by a factor of to 1

23. Remember! Isometric Projections:
Isometric lines drawn using isometric scale
Foreshortened
Isometric Drawing/View:
Isometric lines drawn using 1:1 scale
No foreshortening, take actual lengths

24. Isometric Scale
It is fastest to create an isometric scale for drawing isometric drawings
Position a regular scale at 45° to the horizontal
Project lines vertically to a 30° line as shown
This foreshortens the true distances and creates an isometric scale along the 30° line
This isometric scale can now be used conveniently to mark off appropriate distances in the isometric projection

25. Construction of an Isometric Scale
45o line 10
TRUE SCALE 9 8
30o line 7
ISOMETRIC SCALE 6 5 4 3 2 1
ISOMETRIC PROJECTIONS: Use ISOMETRIC SCALE
ISOMETRIC DRAWING/VIEW/SKETCH: Use REGULAR/TRUE SCALE

26. Isometric Projection Vs Drawing/View/Sketch
Isometric projections are foreshortened because the object is tipped with respect to the viewing plane.
Isometric sketches, or drawings, are usually NOT foreshortened because they still appear proportionate when showing the dimensions full size along isometric axes/lines. It is easier just to sketch the full dimension.

27. Isometric Views Isometric Projection (A): Foreshortened (81/100)B
Isometric Projection (A): Foreshortened (81/100)
Isometric Drawing (B): No foreshortening (100/100)
No difference in shape - Isometric drawing larger in linear proportion by about 1.23:1
Most common form is to use isometric drawing

28. Thank you..