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spherical concave mold
Jan. 9th, 2005 03:27 pmSuppose you need to make a spherical mold. (UPDATE - the end use is bending a guitar back so that it becomes a cut of a sphere.) The radius of the sphere is 4 meters (12 ft), you need a cut of a surface of that sphere that's about 90cm (3ft) in diameter. It is preferable to have both molds, a concave working surface and a convex one. I am soliciting suggestions on how to make it.
Here are some ideas that I already went through, in the order of ascending difficulty of execution.
1. Make a convex mold by planing a flat piece of pine, then coat it with concrete (or gypsum) to make a concave one.
2. Put some wet concrete in a basin and spin it so that it takes a parabolic shape (same way as Robert Wood was making liquid telescope mirrors from spun mercury), then keep spinning until it sets.
3. Stretch a flat sheet of rubber horisontally. Pour water into it - it should sag in a hyperbolic shape - close enough for a sphere in the middle of the sheet. Paint the bottom with floor leveller.
4. Inflate a giant ball 8 meters in diameter, and paint its surface with floor leveller.
Here are some ideas that I already went through, in the order of ascending difficulty of execution.
1. Make a convex mold by planing a flat piece of pine, then coat it with concrete (or gypsum) to make a concave one.
2. Put some wet concrete in a basin and spin it so that it takes a parabolic shape (same way as Robert Wood was making liquid telescope mirrors from spun mercury), then keep spinning until it sets.
3. Stretch a flat sheet of rubber horisontally. Pour water into it - it should sag in a hyperbolic shape - close enough for a sphere in the middle of the sheet. Paint the bottom with floor leveller.
4. Inflate a giant ball 8 meters in diameter, and paint its surface with floor leveller.
