The following notes and illustrations are intended to assist in reading and understanding simple drawings. In all orthographic drawings, it is necessary to project at least two views of a three dimensional object - or one view and an adequate description in some simple cases, a typical example being the drawing of a ball
for a bearing. A drawing of a circle on its own could be interpreted as the end elevation of a cylinder or a sphere. A drawing of a rectangle could be understood as part of a bar of rectangular cross-section, or it might be the front elevation of a cylinder. It is therefore generally necessary to produce at least two views, and these must be read together for a complete understanding. Figure 4.15 shows various examples where the plan views are identical and the elevations are all different.
A single line may represent an edge or the change in direction of a surface, and which it is will be determined only by reading both views simultaneously. Figure 4.16 shows other cases where the elevations are similar but the plan views are considerably different.
A certain amount of imagination is therefore required when interpreting engineering drawings. Obviously, with an object of greater complexity, the reading of three views, or more, may well be necessary.
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