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Chapter 3. BallistaMail > Foreign Words: Fabricating the Epizygis and Modiolus - Pg. 89

MAKE: PROJECTS Eccentric Cubicle Drill a 3 / 32 " cable attachment hole through the midpoint of the axle and spool. Got your ratchet/axle/spool assembly? Got yer handle/knob assembly? Got yer ratchet pawl? Dude, it's a windlass -- or at least all the parts needed to put one together. Lemme hear ya say, "Yeehah!" [Figure 03.63] Now, for the trigger. Trigger A ballista trigger has to grip the bowstring securely at two points, leaving an exposed area of string open to notch the dart into. Because drawing the bow involves the use of a windlass, the string-gripping trigger has to ride on a sled that slides up and down the same rails that guide the trajectory of the dart. The trigger build isn't particularly challenging, but you need to get the measurements right in context of your project. I started by rough-shaping the basic sled to the point where I had a low-profile piece of wood that fit on the rails and moved smoothly. I formed the guide rail slots on the table saw, but could just as easily have glued the whole thing up from blocks and strips. 7 [Figure 03.64] The cutting diagram provides all the gory details. [Figure 03.65] Here's a walkthrough. It's a cam-locked pinch mechanism, Figure 03.60: Cut the internal threads through the entire length of a 2" piece of tube. You can cut it to size later. Figure 03.59: The three-minute knob handle Figure 03.61: Position your pawl stock in context of the ratchet assembly and rough sketch the outline of the pawl. Cut it to shape with the metal removal tool of your choice, then fine-tune the fit with needle files. 78