As in first-angle orthographic projection, we insert a projection system symbol for third-angle orthographic projection on each drawing to indicate which projection system we have used. Figure 3.19 on the next page shows the recommended proportions of the international symbol for third-angle orthographic projection.

Projection methods for third-angle orthographic projection

As in first-angle orthographic projection, there are two suggested methods that we can use for third-angle orthographic projection to obtain the three orthographic views: the 45°-line method or the circular-arc method, as shown in Figure 3.20 (a) and (b) on the next page.

Figure 3.18

A third-angle orthographic projection of the front, top and right views

Figure 3.19

The proportions of the third-angle orthographic projection system symbol

Figure 3.20

The projection methods used to obtain the three orthographic v

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