Page:Sheet Metal Drafting.djvu/238

224 The diagram of triangles and sections, Fig. 319, is now constructed by taking the base lines from Fig. 317. The triangles have a common altitude equal to lines 6–A of Fig. 315. One of the perpendiculars in each section also has this altitude, but the altitudes of points O, N, M, K, and H are made to correspond to the altitudes of similar points in the true section, Fig. 316.

The pattern, Fig. 321, is started by placing upon any vertical line a distance equal to the true length line 6–A. The development proceeds in the usual manner until completed. Spaces A to D are taken from corresponding spaces in Fig. 317, as are also spaces 6 to 10, Spaces D to H, however, are taken from corresponding spaces in the true section, Fig. 316. The development may be copied on the other side of line 6–A in order to obtain the full pattern.

Necessary laps for riveting the pieces together must be added to these patterns.