Lecture – 4

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

Above

Front

Front

Above

1 stQuad

3rd Quad

2nd

4th

•Quadrant 1 and Quadrant 3 are Used for Orthographic Projections•In whatever Quadrant the object is in, viewing directions are same•In what quadrant, so far, we have been keeping the object in?

Object - Plane - Observer

Revisit 3rd Angle Projection SchemeThis is Profile Plane

Here too Observer – Plane - Object

RECAP of Concept

See the positions of Front, top, RS, LS Views

3rd Angle Projection Scheme contd..

1st Angle Projection Scheme

Recap the Concept

•See the positions of Front, top, RS, LS Views•Examine how different these are from 3rd angleprojection•And why?

Plane - Object - Observer

RS Front

Top

LS

Hinge

Concept

In 3rd angle ProjectionObserver – Plane - ObjectPosition wrt Front view;top view is above, R-S View on right and L-S view on left

In 1st angle projectionObserver – Object - Plane

Position wrt Front view;top view is below, R-S View on left and L-S view on right

Third angle

Identify the angle of projection

Third angle

First angle

Quiz

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tion.

Theory of Dimensioning -Techniques and Conventions

Object is made of several parts – Need

•Position (P)•Size (S)•Each feature is dimensioned once •For each feature, dimension positioned where its shape shows•No Redundancy

S Drill, 2 holes

S(RAD.)

3mm≥8mm

PS

SS

P

P P

S

S

S

S

Extension Lines Dimension Lines Arc and Circular Features

S: SizeP: Position

x=1mm usually

Arrow DimensionsALL DIMENSIONS IN MM

(Near Title Block)x

3x •Avoid giving any dimensions inside the drawing.•No two dimension lines cross each other.•Center line can be used as extension line.

Extension line

ArrowheadDimension line

Leader 2 Holes, ø12 Note

45

60

45

ø40

4520 60

6020

40

ø20

ø60

40

A B

C D

Ø20 Drill

Aligned System Unidirectional Systemvalues read from bottom only(Preferred when?)

values read from bottom and Right side

16

60

16 1030

50

50

Continuous or Chain Dimensioning

20

Progressive or Parallel Dimensioning- From Common Base (Preferred)

Avoid

Avoid

80100

126

450

Areas to avoid – Place them so to read conveniently

INCORRECT

CORRECT

Dimensioning a circular arc.

16

Omit unnecessary dimensions.

Enlarged View at “A”

Use of enlarged view to clarify dimensions.

Dimensioning of arcs

Single arrow, inclined, show where true shape

Equally spaced holes.

4.8 22 19

18

22 ø26

21.5 12

3

5

300’ 45”

6

Dimensioning in limited spaces