[ATM] new pits keep appearing

["Paul Grapendaal" <guardian@reaper.org>]

Folks,

I've been slogging away at my 13.5" f5.2 mirror, with what I think is a 
grinding tool problem. I'm at about 320grit at the moment and new pits keep 
appearing, they seem to be about the size of 150grit , I've spent a total of 
about 90 minutes grinding on 320grit with still quite a few pits visible if 
I hold the mirror up against a flourescent light (10 or so pits) which 
appear to be moving around. The tiles on the grinding tool have developed 
sharpish edges and I suspect pieces of this may be breaking off and creating 
these pits. The grinding tool has tiles littered randomly on the surface 
which makes bevelling these virtually impossible. I've only ever made a 9" 
f6 before and dont recall being overly observant as to how many pits the 
mirror had. I've made another grinding tool plaster blank in the 
anticipation of the tool being the cause.

I saw Bob Mays suggestion to apply less pressure but this hasnt helped in my 
regards.

So, for my "how long is a piece of string" question.

How many pits are acceptable/normal on a quality mirror this size? (I'd 
settle for 1 or 2) Is the more likely cause contamination or splintering off 
of the main tile tool? Would offbreaks be more likely to create scratches 
than pits?

Any feedback would be greatly appreciated!

Many Thanks,
Paul Grapendaal (Cape Town, South Africa)
http://elrond.reaper.org/telescope/
http://elrond.reaper.org/13/ 

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