ATM Best lap-making methods

[tomlinson <etomlins@rohan.sdsu.edu>]

Hello.  Although I'm not yet done with fine grinding on my 4" mirror,
I'm beginning to think of the best way to make a pitch lap for
polishing.

The only other time I did this was on a 5" mirror that I never
finished.  A friend of mine at the time recommended that I
imitate John Dobson.  After showing me a video that he got
somewhere, I tried and failed miserably.  So I just poured
a layer of pitch onto the lap and cut channels into it with
a hot razor blade.  Lots of chips, and the squares ended up
pretty irregular, but it worked after a fashion.

Later I read an article in ATM which described how to make a
lap by pouring a layer of pitch onto a cookie sheet, and
cutting shapes out with a cookie-cutter while the pitch was
still warm.  For this 4" mirror, I was thinking of using a
"cookie cutter" made from a 3/8" or 1/2" diameter brass tube
to cut small circles or squares, to use as facets.  Or I
could use a cork-borer on the warm pitch.

Other methods--channeling with a hot wire, using a makeshift
mat made from silicone caulk, the Texereau method of casting
strips and cutting them into squares.

Cheers,
-et