Re: [ATM] Mirror Scratches- and no tile tool available

["Mitchell R" <funnybone101@embarqmail.com>]

What size is the mirror? Assuming a 6" or 8" grinding them out wouldn't be
too hard if you make a tile tool. You must go back to say #120 or #220 to
get contact. Then go through the grits again, there can be no skipping
steps. As Stathis said they will have extremely little to no effect on the
view at the eyepiece. Polishing them out would take some hours and polishing
a lap with grinding compound won't really work either. Plus it would make
the lap useless for polishing. The time it takes to get contact depends on
which grit you go to, 120 or 220, and basically how hard you push, sic
grinding grit works best under pressure but again assuming a relatively
small mirror the grinding from 120 or 220 all the way dow to 9 or 5 micron
could be done in a day or two depending on how long your willing to work (or
how long our backs will let us work!)

Good luck with it,

Mitch

-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf Of
Adam Krause
Sent: Wednesday, July 11, 2007 11:46 PM
To: atm@atmlist.net
Subject: [ATM] Mirror Scratches- and no tile tool available

Hello everyone,

I'm new to this list and have made a telescope before,
but this is my first time doing the mirror.  I
received a mirror from my friend that was already
ground, but still needed to be figured.  After years
of sitting in a box it has some scratches.  Being
untrained in grinding mirrors, I didn't really notice
them at first, but they show up under the Foucault
tester- especially when the knife edge blocks the
light on the mirror- it seems to leave only the
scratches to look at.  This web address shows three
pictures of the mirror with different brightnesses:

http://bellsouthpwp2.net/a/d/adamlisakrause/Mirror%20Scratch%20Pictures%2007
-11-07/Mirror%20Scratches.htm

At any rate, the mirror came without a grinding or
polishing tool.  I have made the polishing lap and
have changed the figure some, but I don't know if
these scratches will come out with rouge.  Would they?
 I would rather avoid making a new tile tool to use on
a mostly completed mirror.  This brings me to some
questions...

Can I go back to some grinding grit and use it with
the polishing lap, or will the grit get into the pitch
and contaminate the lap?

If I do have to make a tile tool, would I have to go
back to a very course grit to grind the tiles down to
full contact with the tool, or could I get away with a
finer grit with not fully contacted tiles?  In the
case I had to grind the tiles down, what grit would I
have to go back to, and approximately how long would
it take to get full contact?

Thanks for your help.

-Adam Krause


 
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