Module 3 : Projections of Solids , Sectional Views And Intersections of Solids

Lecture 29 : Methods of Projection of Solids

 

Methods of drawing the projections of solids
These are two methods for drawing the projections of solids:

  1. Change of position method. 
  2. Auxiliary plane method (Change of reference-line method)

Change of position method
In this method,  the solids are placed  first in the simple position and then tilted successively in two or three stages to obtain the final position. The following are some of the examples.

a. Method of obtaining the top and the front views of the pyramid when it lies on HP on one of its base edges with its axis or the base inclined to HP.

If the solid is required to be placed with an edge of the base on HP, then initially the solid has to be placed with its base on HP such that an edge of the base is perpendicular to VP, i.e., to XY line in top view preferably to lie on sthe right side.
When a pentagonal prism has to be placed with an edge of base on HP such that the base or axis is inclined to HP, then initially, the prism is placed with its base on HP with an edge of the base perpendicular to VP and the lying on the right side. In this position, the first set of top and front views are drawn with the base edges (c1)(d1) perpendicular to XY line in the top view.  In the front view, this edge c1’(d1’) appears as a point.
Since the prism has to lie with an edge of the base on HP, the front view of the prism is tilted on the edge c1’(d1’) such that the axis is inclined at q to HP. 
Redraw the first front view in the tilted position. Whenever the inclination of axis q with HP is given, first the base is drawn at (90- θ) in the front view, otherwise improper selection of the position of the axis may result in the base edge c1’(d1’)  lying above or below the XY line. The second top view is projected by drawing the vertical projectors from the corners of the second front view  and the horizontal projectors from the first top view. Figure 1 shows the  sequence in obtaining the projection of the solid for the above case.

Figure 1. Illustrating the sequence for obtaining the projections of a pentagonal prism placed with an edge of base on HP such that the base or axis is inclined to HP