Re: [ATM] artificial convex curve for pitch lap

["Bob May" <bobmay@nethere.com>]

    Don'6 use wood or paper on the basde.  You'll ghet warpage
and slippage that you'll never get rid of!
Better to go down and get some Plaster of Paris and seal it up
with pitch or paint than to use wood.  Better would be to use
dental stone or quickdry cement repair cement.
Almost anything that is bendable and has a straight edge will do
for the dam and I'd make the base at least 1:10 for thickness.  I
use the plastic vertical blind material but flashing is also good
as well as even just some posterboard painted or not.  You need
to hold the dental stone for about 10 minutes, the quickpatch for
about 20 minutes without the stuff breaking out.  Tack the dam
down if you want but generally, the dam won't rise and let out
the stone if you don't fuss with it and try to make a mess.  If
any does slop out, it won't be much and will crack off of the
face with no problems.
When the stone gets to the point where it is solid but soft, you
can then take the dam off and clean up the backside so that it is
somewhat flat.  By the time you get that done, you can usually
slide the tool off of the mirror and finish facing off the
backsied (don't do the front by mistake!) and you will then have
an excellent tool.  At that point, you can apply a pitch layer if
desired.
Bob May
bobmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net
Replace the obvious words with the proper character.

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