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Chapter 3. BallistaMail > Skein Plates, Supports, and Their Attendant Mysteries - Pg. 78

Ballista Mail in the two rear rail mounting blocks. Use a short length of 1 / 8 " steel rod press-fitted into these holes to mount the pulley. [Figure 03.29] Finalizing the Skein Assembly Now that we've finished fabricating the rails and pulley, we can get a pretty good idea of where the bowstring is gonna have to sit to notch properly into the dart. To ensure lots of room for multipage missives and the occasional thumb drive, I spec'd the darts for BallistaMail out of cheerful orange PVC sprinkler pipe 1" in diameter. With a sample of the material in question positioned on the rails (tack them in place with bit of brass rod) and the bottom rack plate in place, my depth gauge gave me a distance of 3 1 / 2 " from the bottom of the support hole to the midpoint of the pipe. [Figure 03.31] Thrilled by my knowledge of this, I snatched up a pipecutter and cut six 7"-long pieces of thickwalled 1 / 2 " OD brass tubing. When I fitted together the bits and pieces scattered around the bench, it looked like Figure 03.32 . My glee was infinite. Finalize the positioning of the guide rails and drill pilot holes in the body for the mounting screws. Mount the rear blocks first, such that the spool of the pulley just clears the edge of the winch cable exit hole in the body. The rest of the locations happen in context of that position. The guide rails are centered on the top of the body, spaced 7 / 8 ", center to center. They need to be parallel, to each other and to the body. [Figure 03.30] Measure twice, drill once!