1. Engineering Graphics 2018-19-I
Lecture 6
TA101A
Engineering Graphics I By
Dr. Mukesh Sharma
Professor
DEPARTMENT OF CIVIL ENGINEERING
INDIAN INSTITUTE OF TECHNOLOGY KANPUR
KANPUR , INDIA

2. PRACTICE

3. PRACTICE

4. 3-D to Orthographic Projection
Orthographic Projection – 3D
Axonometric – Isometric
Oblique
Perspective
Why do we need 3-D Pictorial Drawings?

5. Can get Infinite 3-d views – needs uniformity and standardization
Rotated about vertical axis
(two faces seen)
Rotated about vertical & profile
Axes (three faces seen)
Parallel to Picture plane
(only one face seen)
Can get Infinite 3-d views – needs uniformity and standardization

6. First Position – one face seen
R,U T
First Position – one face seen
R,S T U S
R,U T R U
Rotate about Vertical axis by 450
Two faces seen
Then
Rotate about profile axis by 350
(three faces seen) S R U T
Three mutually perpendicular
Edges, SR, RU and RT now
make equal angle of 120o
with each other and are called
ISOMETRIC AXES
Projections are still orthographic
What these rotations have done?
SR, RU, RT all foreshortened but by
equal lengths

7. Schematic presentation of concept

8. Quiz:
How much AB is foreshortened? A
Isometric
Axes B
30o
30o
One Can draw isometric Figure with the help of Isometric box
Two types : (i) Isometric Projection – Take lines as foreshortened
(ii) Isometric drawing - Disregard foreshortening take actual length

9. Isometric projection: foreshortened (81/100) A B
Isometric projection: foreshortened (81/100)
Isometric drawing: No foreshortening (100/100)
No difference in shape - Isometric drawing larger in
Linear proportion of 1.23:1.
Most common form is to use isometric drawing

10. Important All lines parallel to isometric axes – Isometric lines
All isometric lines are foreshortened equally (81/100)
All other non-isometric lines may or may not foreshorten
Foreshortening ratio of such lines may vary disproportionately
Projections of parallel lines are parallel.
All measurements can only be marked on isometric lines

11. ISOMETRIC SCALE 4 3
Regular Scale 2
450 4 1 3
300
Isometric Scale 2 1
Make Isometric scale : foreshortened to 81/100 to
Be used in Isometric projection

12. Decide width and depth directions – height direction is fixed.12 20 12 20 10 B 10 A C
Decide width and depth directions – height direction is fixed.

13. D C B A D C B A
Boxing Method

14. Top
Now start drawing
Isometric
Front
Right Side

15. Now erase the hidden lines
Front
Top
Right Side
300
300
Identify hidden lines
Now erase the hidden lines

16. Front
Top
Right Side
Now erase hidden portion of ellipse

17. Front
Top
Right Side
Isometric

18. Top
Now start drawing
Isometric
Front
Right Side

19. Draw base as in previous isometric
Now draw the additional surface
Front
Top
Right Side
Smoothly join both ellipses
Identify hidden lines and erase

20. Front
Top
Right Side
Isometric