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Chapter 10. Hammerhead Live: > The Motor Mount - Pg. 329

MAKE: PROJECTS Eccentric Cubicle ing in a clockwise direction. Once you've ensured that the gearbox is set to "forward," the gearshift yoke can be safely removed. It should snap out easily. [Figure 10.30] Disassemble the torque controller by removing the chuck from the drill. (There's a left-threaded Phillips head machine screw accessible through the chuck throat that needs to be removed. Once it's out, clamp the short end of an Allen key into the chuck, and give the protruding long end of the key a sharp whack sideways with a hammer to loosen the chuck on its (right-handed) threads. Screw the chuck off, and remove the screws holding the torque control ring in place. The ring is spring loaded, and is gonna want to fly off as soon as the screws are free, so exercise caution. There's a ring of ball bearings at the bottom of the shaft closest to the motor. The spring presses a plate onto these bearings, forcing them into dimples on the motor side of the shaft. Excess torque forces the bearings up out of the dimples and takes the drive shaft out of gear. This would not be a favourable occurence. We want to replace the spring with a section of pipe to hold the bearings in place regardless of torque, and sheath the underlying mechanism in lead to dampen the gear noise. [Figure 10.31] Figure 10.30: See that yellow thing? It's the forward/ reverse gear shift. We want "forward." this end, head to the scrapyard (or local home improvement center, if you're absolutely determined to pay full retail price) and pick up a few square feet of 1 / 8 " sheet lead to use as sheath- ing. The toxicity of lead is not understated by the popular press; use realistic adult-strength caution when working with it. 9 Now that we're properly equipped to deal with extraneous noise, the drive train modifications can proceed with impunity. Modern cordless drills are invariably reversible. The direc- tion of rotation is determined by the position of a yoke-like slider mechanism that changes a gear position inside the gearbox. Hammerhead wants to be driven by a motor rotat- 9 Sheet lead cuts to fit easily with tin snips or household shears, and is readily hand-formable. Avoid contact with the powdery white oxide that may appear on the surface. A coat of aerosol lacquer will go a long way towards controlling its formation and spread. Lead's mass makes attaching it to stuff problematic at times. Foam-backed double-faced tape combined with escutcheon pins where applicable has proven most effective for me. The Mastercraft unit I used was spec'd with a 1¼" ID torque spring. Your results may vary. Add a single-layer wrap of lead sheet, which will increase the diameter by ¼", then source a piece of thinwalled steel pipe to fit. Determine the length of pipe required to replace it by measuring from the top of the bearing pressure plate to the top of the extension that holds the spring retention plate. Slide your precisely sized piece of steel pipe over the lead wrap and into the position previously occupied by the torque spring and torque strength adjustor. Position the top plate and replace the screws. The pipe should firmly hold the bearing pressure plate in position, allowing no shaft slippage whatsoever. Add another single layer of lead wrapping around the pipe. Use foam-backed double-faced tape to hold it in posi- tion. The foam will mechanically isolate the drives' vibration from resonating through the rest of the mechanism. [Figure 10.32] Reinstall the chuck, then set to work on the motormount. You'll need some plywood. The Motor Mount The mount is another of those "nested holes" affairs, diameters and depths to be determined by the specifics of your drive mechanism, with allowances for a layer of inner- tube rubber lining the holes as an additional level of vibration isolation. The only other critical dimension is the 3" center- of-hole-to-top-of-mount figure illustrated, which is essential 318