RE: Correcting an overcorrected mirror.
DAVE MCCARTER (50VE3GSO@qstar.fanshawec.on.ca)
Tue, 7 Mar 1995 19:39:11 -0500 (EST)
Re Dale Eastons' mirror, It is really easy to make a pollishing tool
from an existing mirror, so that you can go back to pollishing and
correct an overcorrected edge.
Build a high, one and a half to two inch dam around the mirror, face up
using thich al foil, masking tape, elastic bands and thin card, etc.
Get a box of "dental stone" from a dental supply store, and mix up a leter
enough to fill the mirror face to make a thick tool. It will harden
in a few minutes, and after about twenty or so the dam can be removed
and the new tool will seperate from the mirror with an incredible
likelyness to the mirror. This can then be used as the backup for a
pitch lap, and can even be used for 305 grit for grinding, which should
not be necessary in your case.
The dental stone, which mixes up like plaster of paris, and should be mixed
thick and well, does not soften in water, unlike plaster.
I have made several grinding tools by epoxying small hex ceramic tiles
to dental stone tool disks. They are cheap, 3 or 4 $ Cdn, and easy to make
to any size.
I hope this helps. You will probably get lots of responses on this.
Give us periodic progress reports. I am currently redoing an 8 inch
casegrain mirror, which has a few deep scratches and sleeks. Fun!
Dave McCarter
Clear Skies or Grind Glass