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FRIDAY, APRIL 22ND WILL BE USED AS THE BUFFER DAY FOR MEL 110 PRACTICALS. -TIME: 9 AM TO 1 PM. -VENUE: WS 204

LAB 13. WILL BE COMPUTER BASED IN THE CAGIL.

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TV

FV

A flag post is held by 3 wires symmetrically placed around it. They are hooked to the post at a height of 12.5 m. and anchored to the ground at a distance of 2m, 2.5m, and 3 m from the pole axis respectively. Draw their projections and find their true lengths and true inclinations with the horizontal by method of rotation.

•Draw top and front views incorporating given distances.

•Use method of revolution/rotation to obtain true lengths of the wires.

•With o as center and oa, ob, oc as radii, rotate the wires so that they are parallel to frontal plane.

, , and are the true inclinations with the horizontal.

12.5

2

2.53

Flag post

Ground

Wire

o

c’b’a’

a

b

co

An oblique square pyramid of side 4 cm and height 5 cm is placed with its base a, b, c, d horizontal with ab making an angle of 30o to the vertical plane. Draw its projections and find the true lengths and true inclinations with the horizontal plane of its edges ao, bo, co, do meeting at the vertex o. The axis of the pyramid is inclined at 60o to the horizontal and parallel to the frontal plane.

•Draw top view of square with one side having angle 30o with the frontal plane.

•Find the point of intersection of diagonals of the square. This is the lower point of the pyramid axis.

•Project this point in the front view and draw the axis from it, at an angle of 60o to the horizontal up to a vertical height of 5 cm.

•As the axis is parallel to the frontal plane, it can be projected back into the top view.

•Find true lengths by rotation method. In this case o has been taken as center and oa, ob, oc, od as radii, rotate the lines in top view to make them parallel to frontal plane.

•Project true lengths.

a’b’c’ d’

a

b

c

d

o

o’

c1d1 b1a1

T

F

60o

True lengths

30o

5

4

f

f’

Three points A, B, and C represent milestones and are 7.5 m above the ground level, on the ground level, and 9 m below ground level and 9 m below ground level respectively. They are connected with each other by roads and are seen at angles of depression of 10o, 15o and 30o respectively from a point O on a hill 30 m above the ground level. A is due Northeast, B is due North and C is due Southeast of O. Find the lengths of the connecting roads.

A

B

C

A’B’

C’

O

O

30

7.59

10o

15o 30o

T

F

Obtain true lengths in one view by subtending given angles from pt. O to the respective heights

Required distance is True Length of AB + BC + CA

HINT: Rotate AB, BC, CA in any one view and obtain True Lengths in the other view. E.g. AC1 is one such length

Add the distances to get the final answer

C1

N

NE SE

Ground level

To find the piercing point and angle of inclination of a line with a plane

p1

Line

Plane

Edge view of the plane

Principal line

True length of principal line

p’

p

Part of the line hidden by the plane should be shown dotted

TF

p2

Angle between line and plane

True length of line

Edge view of plane

p3

Draw auxiliary views such that you get the TRUE LENGTH of the line and EDGE VIEW of the plane

T A1A2A1

A2

A3

p, p’, p1, p2, p3 are the piercing point of the line with the plane

AB

Q

P

Z Y

XW

S

R

To find the line of intersection of two planes

AB is the line of intersection obtained by getting the piercing point (A) of WZ with plane PQRS and (B) of XY with plane PQRS.

AB

Q

P

Z Y

XW

S

R

To find the line of intersection of two planes

AB is the line of intersection. In this case the piercing point of XY with PQRS (B) and of PS with plane WXYZ (A) is to be obtained.

To find corresponding points on lines appearing vertical in TV and FV and obtaining True Length

a’

b’

c’

a

b

c

d’

d

1. With a’ as center rotate a’d’ and a’b’ and make the line horizontal

2. Project d’ and b’ upto a line that is horizontal and in line with a meeting it at d1 and b1 respectively

3. Join b1 and b. Draw a line parallel to b1b to intersect ab in d

d’b’

b1 d1

e’

e

Principle line

True length

The ratio of corresponding distances in both views should be same

ab

ad

ba

da

ba

da

11

11''

''

T

F

a’

a

b’

b

TF

Horizontal Trace: Projection of point of intersection of extension of AB with the Top plane

Vertical Trace: Projection of point of intersection of extension of AB with the Frontal plane

Definition: The point of intersection of a line-produced with a plane is called its TRACE on that plane.

VT

HT

To find the TRACE of a line: Case I

VT

HT

A

B HV

HV

a’

a

b’

b

TF




VTHT

To find the TRACE of a line: Case II

VT HT A

BH

V H V

a’

a

b’

bTF




VT

HT

To find the TRACE of a line: Case III

VT

HT

A

B

H

TL

TL

a’

a

b’

bTF




VT

HT

To find the TRACE of a line(Trapezoidal method): Case III

HT

A

B

TL

TL

a

b

A

B

AG

FED

CB I

H

A’

H’,G’

I’,F’B’,E’

C’,D’

30o

A

GF

E

D

CB

I

H

Approach I: Use Frontal plane as the wall

Auxiliary view will give edge view and angle with frontal plane

Principal line

AG

FED

CB I

H

A’

H’,G’

I’,F’B’,E’

C’,D’

30o

Approach II: Include a wall at 30o to the edges DC and GH

PAV, in which PAP is the wall

Obtain edge view using principal plane concept in SAV. Angle that it makes with the axis is the angle with the wall

Q. Two regular pentagonal plates ABCDE and AFGHI of equal sizes (side length 30 mm) are joined at A such that the included angle between them is 75o. The edges opposite to corner A are on the ground and make 30o with a vertical wall.a)Draw projections of the plates.b)Find the angle of the plates with the wall.

75o

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