Ok, I had the same problem with my 10". but at the 5m stage mostly,though I did have it happen at the 12m too, after asking questions and recieving answers I believe my problem was in going from one grit to the next too soon, the tool and blank were not perfectly matched and this was causing the scratches or sleeks,also when making to long a stroke these sleeks would appear, so it could be that, but it is one or the other or both, (hope this is understandable).
You also need to keep the works damp, if it drys during the wet you get the same results.
At the 12m stage you total stroke lenght should be short, I have been told that at the 5m stage a 1/2" stroke was all that is needed,though I gave up on the 5m and made pitch lap after 12m was done.
if you think your strokes might be a tad long, try shorter ones, have a spray bottle to keep the work wet,and dont rush going to the next grit size, do some extra wets to insure tool and blank are well mated.
Remember at this small size of grit it does not take much to create the problem.


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Rick M
http://groups.yahoo.com/group/AllAstronomyAllTheTime