RE: ATM [long] Getting the smoothest mirror (no dog biscuit)

["Michael J. Coslo" <mjc5@psu.edu>]

>Hi All
>
>I have read thru this tread and have come to the conclusion that I have
>some problems. I am polishing my 1st mirror, a 6" f9. I am having
>problems keeping the grooves open, I feel this has to do with the
>softness of the lap and I am working in my garage with is about 90
>degrees now.

        Hmm, at that temp, you do need a fairly hard pitch. If you have to
re-channel every hour, you might want to harden the stuff up a bit. Heat
the pitch and keep it hot for a while to vaporize some of the solvents when
you make your next lap. If you are re-channelling every two hours or more,
you might as well still keep using it. Some might tell you differently
though.

>My lap is encrusted with ceo.

        Hmm, maybe it needs a decongestant.

>Should I just add water until the ceo stops leaching off the lap?

        The CeO on your lap is actually a good thing.

>The lap seems to be sticking when the wet stars to dry up, I don't seem
>to be getting good drag.

        Here is something you might try. Assuming you have good channels,
you might try using nylon netting to put between your mirror and lap while
doing your pressing. Another thing that I recently tried and liked was to
take an Exacto knife and scrape along the surface of the lap before
pressing. I just made a cross-hatch pattern. It helps to break up any
glazeing caused by the surface of the pitch losing solvents, and gives a
really nice feel to the drag.

        Another thing that occurs to me is that you might be using too
thick a slurry of CeO. Try diluting some of your mixture 50 percent and see
if that doesn't help. It's not intuitive, but it will polish faster.

I press after each wet, and rinse the mirror after each wet.

        Extend your wets as much as possible. If you can polish for two
hours at a time, do it. The long polishing sessions really get the surfaces
into good contact. Screeching of the lap is cool, and I personally like to
polish when the drag is so high that it takes all my strength to move the
mirror (not fot the faint hearted).

>Looking at the mirror the center is polished out but the sides don't
>seem to be progressing.

        I don't know how long you have been polishing, but it sounds pretty
much okay to me. Trying those tips should help the polish progress more
quickly though.