Page:Sheet Metal Drafting.djvu/68

54 of the stretchout can be drawn upwards indefinitely. Since the miter cut of both pieces are exactly alike, the pattern of the second piece can be constructed above that of the first piece. This will bring the seam of the second piece on the back. A distance equal to the back of the second piece, as shown in the elevation. Fig. 79, should be set off above the miter cut on lines 1 and 1. A horizontal line connecting these points will complete the pattern for the second piece (small end). One-half inch locks are added to each side of the stretchout. Notice the notching at the miter cut. The big and small end cuts should be computed and placed upon the pattern. The small end of every elbow is always cut straight; i.e., one half of the deduction for the small end is taken off the entire length of the lock on each side of the pattern. No piece of a cylindrical elbow should be tapered, as it adds to the difficulty of assembling, and is of no advantage when erecting a piping system. The direction, "big end minus 7 t" in Fig. 81, means the cut of the big end minus seven times the thickness of the metal used. Figure 78 shows how a piece of paper fitted to the first piece of an elbow would unroll to produce the pattern.