Engineering Drawing Principles and Applications

Introduction

Three views of an object, viz. the front view, top view and side view, are sometimes not sufficient to provide complete information regarding true shape and size of an object. Additional views are therefore projected on other planes (auxiliary planes) and are known as auxiliary views or auxiliary projections.

Types of Auxiliary Planes and Views

Auxiliary planes are of two types:

• (a) Auxiliary Vertical Plane (AVP)

• (b) Auxiliary Inclined Plane (AIP)

Auxiliary vertical plane (AVP):Auxiliary vertical plane (AVP) is perpendicular to the HP and inclined to the VP. The projection on an AVP is called an auxiliary front view. See Fig. 11.1.

Auxiliary inclined plane (AIP):Auxiliary inclined plane (AIP) is perpendicular to the VP and inclined to the HP. The projection on an AIP is called an auxiliary top view. See Fig. 11.2.

For showing the orthographic projections of an object, the auxiliary plane should always be rotated about the plane to which it is perpendicular.

Projections of Points

(a) Projection of a point on an auxiliary vertical plane (AVP):A point A is situated above HP and in front of the VP. AVP is a plane perpendicular to the HP and inclined to the VP. The HT of this plane is inclined to x-y and VT perpendicular to x-y line. The HP and the AVP meet at right angles in the line x1 y1. From the Figs. 11.3 (a) and 11.3 (b), the following points may be observed:

• (i) The distance of the auxiliary front view from x1y1 is equal to the distance of the front view from x-y, which in turn is the distance of the point A from the HP.

• (ii) The line x1 y1 is inclined to x-y at an angle ϕ, which is the angle of inclination of the AVP with the VP.

To draw the orthographic projections, see Fig. 11.3 (c).

• (i) Draw the reference line x-y and mark the front view a’ and the top view a.

• (ii) Draw a new reference line x1 y1, making an angle ϕ with x-y.