1) An oblique plane is a plane surface that is inclined to one of the principal planes, with one of its sides, diagonals, or diameter parallel to the principal plane and inclined to the other principal plane. 2) There are three steps to drawing projections of oblique planes: initial position, intermediate position, and final position. 3) Three example problems are provided to demonstrate drawing projections of different shapes (rectangle, pentagon, rhombus) placed at various orientations relative to the principal planes.

1. Introduction
• When a plane surface is inclined to one of the
principal plane and a side or a diagonal or diameter
of a plane surface is a parallel to that principal plane
and inclined to other plane surface will be called
oblique plane.
• Projection of oblique planes are drown in three
stages:
1. When a plane surface is inclined to H.P
2. When a plane surface is inclined to V.P

2. When a plane surface is inclined to H.P:-
• When a plane surface is inclined to H.P and a
side or a diagonal or a diameter is parallel to
H.P and inclined to V.P projection of plane will
be obtain in following stage:
1. Initial position
2. Intermediate position
3. Final position

3. X Y
a
b c
d
a’
b’
c’d’
a1
b1 c1
d1
a’b’
d’c’ c’1 d’1
b’1 a’1450
300
Problem 1:
Rectangle 30mm and 50mm sides is resting on HP on one small side which is 300
inclined to V.P, while the surface of the plane makes 450 inclination with HP. Draw
it’s projections.
Surface // to Hp Surface inclined to Hp
Side
Inclined
to V.p

4. Problem 2:
A regular pentagon of 30 mm sides is resting on HP on one of it’s sides with it’s
surface 450 inclined to HP.
Draw it’s projections when the side in HP makes 300 angle with VP
b1
d1
a1
e1
b’1
e’1
c’1 d’1
a’1
X Y
a’b’ d’c’e’
300
b1
c1
d1
a1
e1
a
b
c
d
e
45º
c1

5. Problem 3:
Draw projections of a rhombus having diagonals 125 mm and 50 mm long, the
smaller diagonal of which is parallel to both the principal planes, while the other is
inclined at 30º to the H.P.
X Y
a
b
c
d
125
a’
b’
d’ c’ 30º
a1
b1
c1
d1
a1
b1
c1
d1
a1’
b1’
c1’
d1’
50

6. When a plane surface is inclined to V.P:-
• When a plane surface is inclined to
v.p and side or diagonal and
diameter is parallel to v.p and
inclined to H.P.

7. a’
b’
c’
a.b c
50
70 a.b
c
a1’
b1’
c1’
a1’
b1’
c1’
a1 b1
c1
45º
Problem 1 :
A plate having shape of an isosceles triangle has base 50 mm long and
altitude 70 mm. It is so placed that in the front view it is seen as an
equilateral triangle of 50 mm sides and one side inclined at 45º to xy.
Draw its top view

8. Problem 2:
A semicircular plate of 80mm diameter has its straight edge in the VP and
inclined at 45 to HP. The surface of the plate makes an angle of 30 with the
VP. Draw its projections.
X Y
1’
2’
3’
4’
5’
6’
7’
1
7
2
6
3
5
4 30º
11’
21’
31’
41’
51’
61’71’
45º 11
21
31
41
51
61
71
Ø80

9. Problem 3:
A circular plate of negligible thickness and 50 mm diameter appears as an ellipse in
the front view, having its major axis 50 mm long and minor axis 30 mm long. Draw
its top view when the major axis of the ellipse is horizontal.
X Y
1’
2’
3’
4’
5’
6’
7’
8’
9’
10’
11’
12’
1 2,
12
3,
11
4,
10
5,
9
6,
8
7
50 Ø
30
11’
21’
31’
41’
51’
61’
71’
81’
91’
101’
111’
121’
11’21’
31’
41’
51’
61’
71’81’
91’
101’
111’
121’
11’
21’
31’
41’
51’
61’81’
91’
101’
111’
121’