By his own admission, this is really CNC basics for hobby-grade CNC routers and mills. He starts off talking about his custom-built machine along with some common machines in the $500-$5000 range.

The result is remarkable: with a lot — and we mean a lot — of sanding and polishing, you can make an acrylic lens on a cheap hobby CNC machine. The trick is just a very small stepover on your ...