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Chapter 8. Liquid Len Meets DiscoHead: > Assembling the Base - Pg. 225

MAKE: PROJECTS Eccentric Cubicle Determining the right amount of lead needed to provide proper balance required not only multiplication and division, but some foreknowledge of the weight of a completed mirror- tiled head as well. I've been mirroring head forms for years, and have a few still in-house, so I put one on the scale, and came up with a weight of about 2 ½ pounds. Lead weighs 0.41 pounds/cubic inch, and I wanted a pound of extra weight or so onboard to ensure stability when the mass of the motor and turntable assembly was added in. The formula for cylin- der volume is r2*H. Volume of lead required: 3.5/.41= 8.53 cu" Radius of the coffee can mould= 1.875" 3.14 x 3.5 x H = 8.53 11.03 x H = 8.53 H = 8.53 / 11.03 H = .78 " The cutouts in the counterweight for the switch assembly and wiring would (I estimated) remove about 1 cubic inch of lead from the mass, and there would be additional volume loss as the metal cooled down to room temperature and contracted from its molten volume. I rounded the value of H up to 1" to compensate for this volume loss, banged a dent into the side of my mould can at that height and melted down my weights until the molten metal level reached that point. It took about 20 minutes to melt, and 45 minutes until I could comfortably cut away the coffee can from my not-particu- larly-precious metal ingot. During that time, I mounted the rotary canopy switch dead center on the PVC endcap and sanded the flashing and mould marks off of both the endcap and the elbow fitting, starting with 150-grit and working down to 600-grit over the entire exterior surface, with a final rubdown with fine steel wool. Anyway . . . Figure 08.03: Imagine my unrestrained glee at discovering that a coffee can was exactly the right diameter for use as a melting crucible/ingot mould. The grey wurst-lookin' thing? That's a lead driftnet weight. Assembling the Base Once the lead was removed from the mould, I used a large- diameter drillbit and low drill speed to form the switch cavity and wire routing in the lead. Lead is messy to drill. It's ductile enough to form streamers instead of chips when drilled, and the streamers whip around the rotating drillbit like a teeny- weeny dominatrix wielding a single tail. Again, be careful. Once the counterweight is glued in place, replacing a faulty switch is a problematic endeavour, so -- just to be on the safe side -- check the switch operation with a continuity tester or multimeter, then finish the endcap assembly by running the switch leads through the hole in the lead weight and using sili- con glazing compound to glue the mass into place centered in the endcap. There should be clearance all around for the cap to fit into place on the elbow, so be careful of stray bits of silicon around the edges. [Figure 08.04, Figure 08.05, Figure 08.06] The cutting list details the shape and placement of the acrylic support struts. Rough-cut them with a coping saw (if you use a power tool, use the lowest speed possible to avoid having the acrylic melt and rebond during the cut), and patiently shape them as illustrated. During the shaping pro- cess I used doublefaced tape to occasionally tack the struts into place on the elbow for testing with the endcap in position [Figure 08.07, Figure 08.08] Remember to form the surfaces that contact the PVC to match both the horizontal and vertical radii. We're gluing these components into place, and full surface contact is essential. Forming the radii isn't difficult, if you attach your abrasive surface to the surface you're forming to and use that as your sanding surface. I did my initial shaping with 150-grit, 214