"Leo Lichtman" wrote:.(clip) Turn the face of this wooden disk to a concave
spherical surface, of (maybe) 10 or 12" radius*. (clip)
Just in case I have creatred some confusion--the *radius* I am referring to
here is the radius of curvature of the concave wooden chuck. (If it were a
reflector, it would be the focal length.) It is NOT the radius of the wood
spinning on the spindle.