A. somewhat interesting case of pattern cutting is that drawn in Fig. 346. It will be seen that the tubes cross and cut part way into each other, and as both pipes are the same size, the shape of the hole in each pipe will be the same.
The setting out of the pattern is now explained. The part of the circle, 0 to 8 in plan, which shows the distance the pipes cut into each other, is divided up into any convenient number of parts; the same being done with an exactly similar arc on the pipe in the elevation. An arc (a c b) of the same size and shape is drawn in the reverse direction as shown. Lines 7 1, 6 2, and 5 3, are drawn across to cut this arc, and from the points of intersection lines are drawn along the pipe; where these meet the lines on the vertical pipe, will give points on the elevation of the joint line. The girth on the pattern is laid out from the numbered arc on the plan; lines run up, and others drawn across from the elevation as shown, and thus points on the hole obtained.
The holes on the two pipe patterns will, of course, be the same shape if the pipes are of equal diameter; but if one pipe is larger than the other, the holes will be of different shapes and require to be set out separately. The same method, however, as shown for equal pipes, can also be applied to those of unequal diameter.