Engineering Drawing Principles and Applications

Introduction

Planes or surfaces are objects that have two dimensions, i.e., length and breadth; they have negligible thickness. Plane surfaces may be considered of infinite sizes. However, for convenience, segments of planes are only considered in the solutions. Planes are represented in space by either of the following:

• • Three non-collinear points, Fig. 10.1(a)

• • A line and a point, Fig. 10.1(b)

• • Two intersecting lines, Fig. 10.1(c)

• • Two parallel lines, Fig. 10.1(d)

• • A plane, Fig. 10.1(e)

Types of Planes

Planes are mainly of two types:

• • Principal Planes

• • Secondary Planes

Principal planes:The planes on which the projections are obtained are called the principal planes. Examples of principal planes are horizontal and vertical planes.

Secondary planes:Secondary planes are of two types:

• (i) Perpendicular planes

• (ii) Oblique planes

(i) Perpendicular planes: These planes can be divided into the following sub-types:

1. Perpendicular to both the principal planes

2. Perpendicular to one of the principal planes and parallel to the other plane

3. Perpendicular to one of the principal planes and inclined to the other plane

1. A plane perpendicular to both the principal planes.A square plane ABCD is perpendicular to both the principal planes. Its horizontal trace (HT) and vertical trace (VT) are in a straight line perpendicular to the reference line x-y, as shown in Fig. 10.2. The elevation, b'c', and plan, ab, of the square are both straight lines coinciding with VT and HT, respectively, i.e., VT and elevation, HT and plan overlapping.

2. Perpendicular to one of the principal planes and parallel to the other plane.

• (a) A plane perpendicular to HP and parallel to the VP. A square lamina ABCD is perpendicular to the HP and parallel to the VP. Its HT, is parallel to x-y and it has no VT. The front view a'b'c'd’ shows the true shape and size of the square object. The top view ab is a line, parallel to x-y, coinciding with HT, as shown in Fig. 10.3.

• (b) Plane, perpendicular to VP and parallel to the HP. A square ABCD is perpendicular to the VP and parallel to the HP. Its VT is parallel to x-y and it has no HT. The top view abcd shows the true shape and size of the square object. The front view d'c’ is a line, parallel to x-y, coinciding with VT, as shown in Fig. 10.4.