ATM figuring with screw

[Gary McKenzie <aquarius@netspace.net.au>]

I tried this method of figuring using an 8" f5 (normal thickness) that was a
good sphere to try to avoid parabolizing. I was unable to obtain any figure
other than a hole in the center with a spherical edge. I tried supporting
the mirror in a number of locations ranging from the extreme edge to the 50%
zone. In the end I gave up and parabolised normally. If I'd spent the time
figuring that I spent experimenting with the bloody screw I'd have a 1/1000
wavfront mirror!! - tongue firmly in cheek, but then this sort of
frustration is what makes a telescope maker.