Fwd: ATM pitch lap woes--help appreciated

["Matthew L. Brown" <mlbrown@everstrive.com>]

>
>
>But about those bubbles--what would you do?  This is my first mirror
>project, but common sense tells me that if I try to use the lap as is, I
>will create zones on the surface with this lap.  What do you think?  Should
>I melt some pitch and fill those shallow "holes."  Or, will it be OK as is
>as long as I have good channels and micro facet the lap?  I would really
>appreciate any information/comments.  Thanks in advance.  Rodney

If you are beginning to polish, and the depressions aren't all in one area, 
don't worry about it.  As you polish, the pitch will flow into the channels 
and the depressions will come into contact, and you've many hours of 
polishing ahead of you for this to happen.

If you are in the figuring stage, then you'll want better contact.

In that case, hot press, rechannel, and repeat.  I like to hot press using 
a large tupperware container.  Smear a  thick layer of wet polishing agent 
onto the lap (to facilitate separation), pop the mirror on top, and run hot 
water into the tupperware, making sure to cover the pitch.  Then put 
weights on top.  I like to use a filled 2 gallon water container as a 
weight.  Sometimes I use a wide board with boxes of books piled on 
top.  You'll want something between 15 and 30 lbs, depending on how soft 
your pitch is.  Let this sit until the water gets lukewarm, then 
separate.  You'll have to rechannel.

You can also try to dribble pitch into the depressions and hot press, but 
it sounds as if your depressions are shallow enough to respond well to a 
session or two of hot pressing.

There are many ways to cut channels.  I find a straight razor works just 
fine, catching the chips in an unfolded section of newspaper for 
recycling.  Don't worry about making the lap pretty.  Very sloppy laps with 
roughly even overall coverage work just fine.

The channels serve 2 purposes:
1) to let the polishing agent circulate
2) to give the pitch a place to flow to nearby so you maintain good contact.

=Matt