The oblique-cone method can be used for setting out the pattern for the connecting pipes in a tapering Y-piece, as shown in Fig. 146. Here the problem resolves itself into jointing up two small pipes to one large one, the ends of the straight pipes all being square to their centre lines.
The setting out for the pattern is explained by Fig. 147. In practice there is no need to draw a complete elevation; all that is needed is the shape of a connecting pipe; but in the present case the full elevation is shown to better explain the way the form of a connecting pipe is obtained. To make the setting out plainer, definite dimensions in this case have been taken. The diameter of the main pipe is 17 in. and that of the branch pipes 8 in.; the distance between centre lines of branch and main pipes 10 in. and the distance between their ends 13 in. These dimensions are set out, as shown in Fig. 147, and to obtain the correct position of the joint line of the connecting pipes their back lines are run down to the edges of the main pipe, as seen by the dotted lines, the point of intersection 6" giving the top end of the joint line. The pattern for the frustum is set out, as explained in connection with Fig. 143, the toe portion being afterwards cut away. To do this we must first get the lengths of lines required. Join B to 5, and where this line cuts line 3 C swing about B on to the base 0 6, and from this point project up and thus obtain point 5" in the elevation. In the same way find point 4". Then with T as centre, swing these points on to their corresponding lines in the pattern. Join the new-found points with an even curve, add allowance for jointing as required, and the pattern is ready for use.