lecture – 6 mukesh/ · why do we need 3-d pictorial drawings? parallel to picture plane (only one...
TRANSCRIPT
Lecture – 6
http://home.iitk.ac.in/~mukesh/
PRACTICE
PRACTICE
3-D to Orthographic Projection
Orthographic Projection – 3D
(i) Axonometric – Isometric(ii) Oblique(iii)Perspective
Why do we need 3-D Pictorial Drawings?
Parallel to Picture plane(only one face seen)
Rotated about vertical axis(two faces seen)
Rotated about vertical & profile Axes (three faces seen)
Can get Infinite 3-d views – needs uniformity and standardization
R,U
R,S
S
T
SR
U
T
First Position – one face seen
Rotate about Vertical axis by 450
Two faces seen
Then Rotate about profile axis by 350
(three faces seen)
Projections are still orthographicWhat these rotations have done?SR, RU, RT all foreshortened but byequal lengths
Three mutually perpendicularEdges, SR, RU and RT now make equal angle of 120o
with each other and are calledISOMETRIC AXES
S
R,U
T
S R
U
T
U
T
Schematic presentation of concept
30o30o
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
IsometricAxes
A B
Quiz:How much AB is foreshortened?
A. Isometric projection: foreshortened (81/100)B. Isometric drawing: No foreshortening (100/100)
No difference in shape - Isometric drawing larger inLinear proportion of 1.23:1.
Most common form is to use isometric drawing
A B
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
Make Isometric scale : foreshortened to 81/100 to Be used in Isometric projection
0
0
1
2
3
4
1
2
3
4 450
300
Regular
Scale
Isometric Scale
ISOMETRIC SCALE
20
12
10
20
10
12
A
B
C
Decide width and depth directions – height direction is fixed.
AB
CD
A
B
C
D
Boxing Method
Now start drawingIsometric
Front
Top
Right Side
Identify hidden lines
Now erase the hidden linesFront
Top
Right Side
300300
Now erase hidden portion of ellipse Front
Top
Right Side
Isometric Front
Top
Right Side
Now start drawingIsometric
Front
Top
Right Side
Identify hidden lines and erase
Draw base as in previous isometric
Now draw the additional surface
Smoothly join both ellipses Front
Top
Right Side
Isometric Front
Top
Right Side
56
20
Ø40
Ø56
49
98
FRONT
TOP
RIGHT SIDE
L3 - 3.1
32
56
20
Ø40
Ø56
49
98
FRONT
TOP
RIGHT SIDE
L3 - 3.1
32
56
20
Ø40
Ø56
49
98
FRONT
TOP
RIGHT SIDE
L3 - 3.1
32