I made this poor man's version of an unusual sphere jig after watching a demonstration video by Larry Marley. Previously I had attempted to build one from box store hardware but it wasn't rigid enough. The Marley type was constructed from 1/2" Baltic Birch ply and is surprisingly rigid and stable. The sphere shown in the pics is 3.5" dia. It requires light cuts and yields excellent surface finish.
If one's budget allows, the commercially available jigs are well made however a much less expensive DIY alternate can suffice quite well.
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