A pipe fitting as above is shown in Fig. 320. Before its pattern can be developed a series of points on the elevation of the joint line will have to be determined. As the method of finding each point is the same the construction for one point only (4) is shown. With centre a and radius a f describe the arc f d of indefinite length, then with centre b and radius b 4 describe the arc 4 c. From c run down a perpendicular to meet the arc in d; and to fix e run a line square across from d.

Fig. 320.

Having determined all the joint line points the pattern can be set out in the usual way.