Re: ATM : Hole in the middle

[Mike Coslo <mjc5@psu.edu>]

robert allen wrote:
 >                 We got a problem. The A.S.K.C. has ground and
>         smoothed a 20" blank with a 3.5" hole in the "middle". The
>         work was done with a "plug" held in with dental plaster and
>         the grinding went well with a 16" tile tool.
>                 BUT, at the first attempt to polish we found severe
>         scratches and sleeks around the hole from debris picked up
>         from the depressed ring around the "plug". The "plug" was
>         removed and the smoothing was redone.


        This is conjecture, but I wonder if the dental plaster might have been
a bad choice to hold the plug in? I have had Plaster of Paris drop
little pieces from tools before without ill effect, but as you know,
dental plaster is a different animal. Bits of that breaking off might
give you your problem. At any rate, cleanliness is really important with
such a plug in the middle of the mirror.

        - Mike -