TA 101: Technical Arts2015-16 II

Dr. Prishati Raychowdhury

Department of Civil EngineeringIIT Kanpur

Office: FB 336; Phone: 6692E-mail: prishati@iitk.ac.in

Orthographic Projections with Dimensions

Lecture 5

3

Review

Object in FIRST quadrant Object in THIRD quadrant

(a) (b)

Review

Third Angle Projection First Angle Projection

RIGHT VIEW FRONT VIEW

TOP VIEW

(a) (b)

5

Example: Orthographic Projection

6

Why Projection Method is Important

450

hRaR

dReR

gR

fR

bR

gT

fT

eT

dT

cTbT

aT

cR

hT F

1

1a

2

2a

3

3a5

4a5a

6

6a

7

7a

8a9a10a

1a 2a

3a4a

5a6a

7a8a

9a

10a

2

2a

10

10a

7

Terminology• Convention/Terminology for Civil

Engineering /Infrastructure related drawings:

– Top view: Plan View (or Plan)– Front view: Front Elevation– Side/Profile view: Side Elevation

8

A typical architectural drawing

9

10

11

Dimensioning• To describe various features of an object

– Size (width, height, depth etc.)– Position of features (e.g. holes) with

respect to edges, other holes etc.

12

Purpose of Dimensioning• To make the drawing easier to understand by

the manufacturer or builder• Make the drawing simpler, cleaner and more

legible• Simpler to draw, redraw or reproduce• Appropriate number of dimensions

– Not too many – Not too few

13

Dimensioning• Four aspects of dimensioning

– Lines– Symbols– Figures– Notes

R 250Ø 254, 200 deep

95190

95

320

400 thickUnit?

All dimensions in m/cm/mm/FT/inch

14

Dimensioning• How many dimensions per view?

– The object should be able to be manufactured or built

• Most objects: 3 dimensions• Cylinders: 2 dimensions• Sphere: 1 dimension

15

Dimensioning Basics• Dimension line should not touch the object

Front view

95

Red: Extension lineBlue: Dimension line

Gap between extension line and object: 1-1.5 mm

Letter size: 6 mmPencil: HUnits not written

All dimensions in mm

16

Dimensioning Basics• Which view to dimension?• Show dimensions in the view that shows the most

relevant features

R 250Ø 254

95

190

95

320

140

17

Dimensioning Basics• A dimension should not be repeated [e.g. if a dimension is given in the front view, it is not shown again in

another view]A

C

B

D

E

DE

18

Dimensioning Basics• Place dimensions outside the view, as far as

possible

75

20

50

25

75

20

50

25

R 250

R 250

19

Dimensioning Basics• Take dimensions out from visible outlines than

from hidden lines

20

Dimensioning Basics• Dimensions should be unidirectional as much

as possible

21

Dimensioning Basics• Give dimension from Baseline / finished

surface / centerline of a hole

22

Dimensioning Basics• Give dimension from Baseline /finished surface

/centerline of a hole– Except when centerline (or axis of symmetry) passes

through center of hole

2 holes, Ø 50Ø 150

R 100R 50

250500

100 8030

23

Types of Dimensions• Two types

– Size– Location

C

A

D E

B

F

D

B

24

Types of Dimensions• Two types

– Size– Location

P

A B

C

25

Dimensioning a Length• Depending on available space

2500 250 80 40

800 160

50

Dots

Half ArrowsArrows

500 26090 190

Lines

26

Placing of Dimensioning• Only two sides are preferable

27

Placing of Dimensioning• Arrow and text

A

C

B

D

E E

D

B

C

A

28

Placing of Dimensioning• Orientation of dimensioning text

A

C

B

D

E

B

C

Unidirectional Aligned

D

E

A

29

Placing of Dimensioning• Zones for allowed alignments

– Leader lines, Arrows, text

Avoid

Avoid

12090

15030-45º

30

Placing of Dimensioning• Narrow spaces

C

B

D

E

B

C

Unidirectional Aligned

D

E

AA

31

Arrangement of Dimensions• Two basic styles

– Parallel Dimensions

– Chain Dimensions

32

Arrangement of Dimensions• Combined style

33

Dimensioning Diameters• Most appropriate view

– Ensure clarity– Precede with “” to distinguish from length

34

Dimensioning Radii• Arcs of circles

– Precede with “R” to distinguish from length

250

260

R 100

R 30

35

4.8 22 19

18

22 ø26

21.5 12

3

5

300’ 45”

6

Dimensioning in limited spaces

Dimensioning

36

Example 1: Arrangement of Dimensions

37

Example 2: Over-dimensioning• Do not provide too many dimensions

38

Example 3: Positioning• Choose appropriate location

A

B

C

R 20

E F

Ø G

I

H

J

Ø G

39

First Angle Projection

40

TOP VIEW

FRONT VIEW? VIEW

SCALE 1:2

Thank you..

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