Radius cutter

I'm making an optical punch for practice (see John Moran's page), but I don't -- yet -- have a radius cutter for turning a lens onto the acrylic. Instead I used my mini-mill and a boring head to cut this from a piece of 3/8" drill rod. It's not treated and hence no good for working anything harder than plastic, but it worked a treat for shaping the lens on the acrylic.