A peculiar application of the last case can be made to that of an oblong pipe bend, as shown in Fig. 313. In this the top and bottom pieces will be formed by a quarter of a ring as explained in connection with Fig. 312. The side strips will be straight, with the ends just curved to cant the bend to meet the straight lines of pipes.

Twisted Rectangular Pipe Bend 349

Fig. 313.

The patterns are shown marked out in Fig. 314. For the inside and outside patterns the heights B E and D F will respectively equal the difference in level of the two lines of piping - that is, it will correspond to a quarter of the pitch, as shown in Fig. 312. A B will equal the girth a 6, and C D that of c d. The distance F C will give the length of the quarter-circle S S, and from this the radius O S can be calculated, and the pattern thus set out.