Page:Sheet Metal Drafting.djvu/235

Rh Problem 54 BREECHES

—Breeches is the trade name given to a transition between two round pipes and an oval or round pipe of larger diameter. The plan, Fig. 314, is that of a transition between two round pipes of unequal diameters, and an oval pipe. The plan is first drawn showing the branch pipes in their proper location. A horizontal and a vertical center line are then drawn in the oval profile. As will be seen upon examination the horizontal center line divides the figure into two equal parts; therefore, it is capable of being developed by sections. The vertical center line of the oval will be used as the miter line between the two branches.

The profiles of Fig. 314 are divided, as shown, after which extension lines are dropped and an elevation, Fig. 315, constructed. Each point in the profiles should be properly located by extension lines in the elevation.

The order of development should now be decided upon. As in the case of the split header. Chapter XV, the fitting should be considered from the standpoint of two separate transitions between oval and round pipes. In this problem the large branch is treated first and the order of development determined as follows:

The base lines corresponding to this order are now drawn in Fig. 314 and their points of intersection with the miter line indicated by letters O, N, M, K, and H as shown. These are given in the fourth column of the above table, and should be placed in the diagram of triangles, Fig. 318, exactly as indicated; that is, base line 3 to O should be measured from point 3 in the diagram of triangles and not from point C.

The diagram of triangles is now drawn by taking the base lines