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Lecture 6

http://home.iitk.ac.in/~mukesh/

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PRACTICE

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PRACTICE

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3-D to Orthographic Projection

Orthographic Projection 3D

(i) Axonometric Isometric

(ii) Oblique

(iii)Perspective

Why do we need 3-D Pictorial Drawings?

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Parallel to Picture plane

(only one face seen)Rotated about vertical axis

(two faces seen)

Rotated about vertical & profi le

Axes (three faces seen)

Can get Infinite 3-d views needs uniformity and standardization

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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 bequal lengths

Three mutually perpendicularEdges, SR, RU and RT nowmake equal angle of 120o

with each other and are called

ISOMETRIC AXES

S

R,U

T

S R

U

T

U

T

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Schematic presentation of concept

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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

Isometric

Axes

AB

Quiz:How much AB is foreshortened?

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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

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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

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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

Reg

ular

Scale

Isom

etric

Scale

ISOMETRIC SCALE

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20

12

10

20

10

12

A

B

C

Decide width and depth directions height direction is f ixed.

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AB

C

D

A

B

C

D

Boxing Method

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Now start drawingIsometric

Front

Top

Right Side

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Identify hidden lines

Now erase the hidden linesFront

Top

Right Side

300300

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Now erase hidden portion of ellipse Front

Top

Right Side

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Isometric Front

Top

Right Side

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Now start drawingIsometric

Front

Top

Right Side

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Identify hidden lines and erase

Draw base as in previous isometric

Now draw the additional surface

Smoothly join both ellipses Front

Top

Right Side

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Isometric Front

Top

Right Side

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56

20

40

56

49

98

FRONT

TOP

RIGHT SIDE

L3 - 3.1

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56

20

40

56

49

98

FRONT

TOP

RIGHT SIDE

L3 - 3.1

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56

20

40

56

49

98

FRONT

TOP

RIGHT SIDE

L3 - 3.1

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