This document discusses sections of solids and how to draw sectional views. It explains that section planes cut through objects and the cross section revealed shows the internal structure. The section line indicates the cut surface. Depending on the position of the section plane relative to the reference planes, the true shape of the section is seen in different views. Several examples are given of drawing sectional views of prisms, pyramids, cylinders and cones cut by variously oriented section planes.

1. SECTIONS OF SOLIDS
By
Venkata Sushma Chinta

2. Invisible features of an object are shown by dotted
lines in their projected views. But when such features
are too many, these lines make the views more
complicated and difficult to interpret.

3. In such cases, it is customary to imagine the object as
being cut through or sectioned by planes. The part of the
object between the cutting plane and the observer is
assumed to be removed and the view is then shown in
section.

4. The imaginary plane is called a section plane or a cutting plane.
The surface produced by cutting the object by the section plane is
called the section. It is indicated by thin section lines uniformly
spaced and inclined at 45°.
The projection of the section along with the remaining
portion of the object is called a sectional view. Sometimes, only
the word section is also used to denote a sectional view.

5. Section plane:
Section planes are generally perpendicular planes.
They may be perpendicular to one of the reference
planes and either perpendicular, parallel or inclined to
the other plane. They are usually described by their
traces. It is important to remember that the projection of
a section plane, on the plane to which it is perpendicular,
is a straight line. This line will be parallel, perpendicular
or inclined to XY, depending upon the section plane
being parallel, perpendicular or inclined respectively to
the other reference plane.

6. (2) Sections: The projection of the section on the reference
plane to which the section plane is perpendicular, will be a
straight line coinciding with the trace of the section plane on
it.
Its projection on the other plane to which it is inclined is
called apparent section.
This is obtained by
(i) projecting on the other plane, the points at which the
trace of the section plane intersects the edges of the solid
and
(ii) drawing lines joining these points in proper sequence.

7. In this chapter sections of different solids are explained in stages as
follows:
1. Sections of prisms
2. Sections of pyramids
3. Sections of cylinders
4. Sections of cones
These are illustrated according to the position of the section plane with
reference to the principal planes as follows:
(1) Section plane parallel to the V.P.
(2) Section plane parallel to the H.P.
(3) Section plane perpendicular to the H.P. and inclined to the V.P.
(4) Section plane perpendicular to the V.P. and inclined to the H.P.

8. Section plane parallel to the H.P.
The projection of the section on a plane parallel to the
section plane will show the true shape of the section. Thus,
when the section plane is parallel to the H.P. or the ground,
the true shape of the section will be seen in sectional top
view.

9. Q1.A pentagonal pyramid with side of base 30 and axis 60 long, is
resting with its base on H.P and one of the edges of its base is
perpendicular to V.P. It is cut by a section plane parallel to the H.P. and
passing through the axis at a point 35 mm above the base. Draw the
projections of the remaining solid.

16. Section plane parallel to the V.P.
The projection of the section on a plane parallel to the section
plane will show the true shape of the section. Thus, when the
section plane is parallel to the V.P. the true shape will be
visible in the sectional front view.

17. Q2.A cube of 35 mm long edges is resting on the H.P on one of its
faces with a vertical face inclined at 30° to the V.P. It is cut by a section
plane parallel to the V.P. and 9 mm away from the axis and further
away from the V.P. Draw its sectional front view and the top view.

25. Section plane inclined to H.P and
perpendicular to V.P.
When the section plane is inclined, the section has to be projected on an auxiliary
plane parallel to the section plane, to obtain its true shape.

26. Q3.A cube of 50 mm long edges is resting on the H.P with a
vertical face inclined at 30° to the V.P. It is cut by a section
plane perpendicular to the V.P, inclined at 35° to the H.P
and passing through a point on the axis, 38 mm above H.P.
Draw the sectional top view.

33. Section plane inclined to V.P and
perpendicular to H.P.
When the section plane is inclined, the section has to be projected on an auxiliary
plane parallel to the section plane, to obtain its true shape.

34. Q4.A pentagonal pyramid with edge of the base 25 and axis
65 long, is resting on H.P on its base with an edge nearer to
the observer parallel to the V.P. It is cut by a section plane
inclined at 60° to the V.P and at a distance 6 from the axis.
Draw the projections and obtain true shape of the section.