Spin-Casting Equipment

A good portion of the time spent on this project went in to building a powered turn table for spin-casting the composite matrix. Originally, I attempted to build several homemade solutions, involving ball bearings and wooden platforms. I determined that wood does not have an even enough surface, and caused the turntable to move up and down as it rotated resulting in a grossly uneven cast. I then purchased an aluminum tooling disc as surplus from a machine shop in California. Although this disc had a surface tolerance of less than a thousandth of an inch, the platform continued to wobble, this time caused by an uneven shaft. Finally, I purchased on eBay a air bearing turntable designed for use on a mill bed. It has a six in. diameter platform, again with precise tolerance. I bolted the aluminum tooling disc to this six in. platform and set my cast on top of the disc. I disconnected the slow gear motor which came with the air bearing, and instead ran a belt around the 6 in. platform. The resulting turntable has such smooth action that the limiting parameter in determining the smoothness of the surface of the casting is the mixture time of the cement used in the casting rather than any aspect of the turntable.

The cast is simply a piece of plywood cut to an 18 in. diameter circle with aluminum house siding bolted around it. The siding can be easily removed to release the casting. During casting, the joint between the siding and base is sealed with ordinary silicon caulking.