Re: ATM Question to the list members: Re best use of polishing pads

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

Mutalib, I too wonder why he's even sealing at all as Dental Stone doesn't
disintegrate like plaster of paris does.  The stuff is called water
resistant because it does adsorb the water into the spaces of the stone and
freezing it or superheating the water will cause failure of the stone for
the obvious reasons.
The parts that got to me were the plastic polishing pads (used for the
plastic lenses), the "burying" of the pads into the surface of the stone and
the use of a material that won't insure the micron accuracy of the surface
being used for the base of the pads.
Now, we do know that Leon Foucault and his contemporaries did use paper for
polishing their mirrors (I've given out the address for that article) and it
did work but he had to do a lot of work that is already basically done for
us by the makers of the pads.
We just need to keep up a good slurry mix on our mirrors and the polish will
come up quickly.  Please also note that I say polish, not surface accuracy
as that is close (+/- a wave or so) but not good enough.
Tonight was class night and I ended up making two pitch laps tonight and
both of the guys had the typical problems with their mirrors and the
problems have almost disappeared in the 20 minutes left for the evening
before a final evaluation of the mirrors.
Another guy (got his lap done 3 months ago and just showed up to go further)
dug a 0.500" hole in the middle and his is not coming along as fast (he
hasn't been around for several months) but he does have the problem of being
one of the portholes of 12.5" dia.  The other two (8" mirrors) both have
almost perfect spheres after that little bit of finishing work.  One started
out with a 0.3" hole with a turned up edge and is now within probable
starting condition for parabolizing while the other guy started with a TDE
of 0.25" or more and is now down to less than 0.1" of TDE in that period of
time.  A third guy was supposed to get pitch tonight but he somehow got
several scratches on his mirror from something strange while it was stored
for several weeks.
I'll also note that some guys go fast while others just don't seem to do
that much at a time.
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net