[ATM] polishing laps for plastic

[Dan Brown]

Does anyone have any experience building polishing lap tools for
polyurethane plastic mirrors?  After totally destroying two beautiful pitch
laps I've about concluded that pitch is definitely not the way to go.  The
pitch seems to aggressively bond to the polyurethane even with liberal
amounts of CeO and water applied, and what started out as a reasonably
smooth surface from fine grinding (using a tile tool) turns to coarse pitch
grit sandpaper!  Specs of pitch start bonding all over the plastic mirror
surface and the tool starts to disintegrate.  Pressing more than a couple of
minutes is very risky, as the tool will become hopelessly bonded to the
mirror.  My lap tool needs to be about 15 inches diameter, so the commercial
micro-mesh pads previously mentioned on this site probably won't work.

Dan