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Chapter 3. BallistaMail > Foreign Words: Fabricating the Epizygis and Modiolus - Pg. 97

MAKE: PROJECTS Eccentric Cubicle bit and tap the hole with 5 / 16 -18 threads. If you don't trust the wood to hold threads securely enough, you can countersink a 1 / 2 " hole 3 / 8 " into the top to accomodate a nut (for the toilet bolt you'll be using as an axle to enable the pan motion in the pan/tilt head). Drill out the axle hole on the bottom face to 3 / 8 " at a depth of 1 / 2 " to receive the axle bushing and then drill the mounting holes for the tilt mechanism support struts. [Figure 03.85] Cut the brass struts for the pan-tilt mechanism from 1 8 " plate. The geometry is part artsy-fartsy nonsense, part / necessity. The ballista itself is gonna end up being front-heavy from the sheer mass of brasswork involved in the skein rack, so the pan-tilt head is made to provide a bit of a shelf to limit the forward tilting range of movement. [Figure 03.86] The strut geometry ended up being a compromise shape Figure 03.84: The pan/tilt block in theory and practice. Use manly wood; it needs to be tough. Figure 03.85: Once again the humble 5 / 16 -18 toilet bolt proves its worth. 86