From: "Bill T." 
To: atm{at}shore.net
Reply-To: "Bill T." 


Your chance of getting an edge swipe or scratch goes way up past 9 microns,
no matter what you add to the grit or what technique you use. There's a
sort of line in the sand between 9 microns and anything finer.

After 200 minutes at 9 microns you should have an excellent grind, assuming
you were just as thorough with the previous grits. A 9 micron grind that is
truly complete everywhere on the mirror is a reasonable place to start
polishing. I'd advise you to stop there, unless you are interested enough
in developing your technique to take some risk.

If you do plan on going to 5 microns, try to minimize the number of tool
removals. Swipes and scratches from tile edges often occur at those times.
Ideally, a 5 micron grind should happen in one continuous wet, with very
small amounts of slurry being added on an ongoing basis. If your water
supply is gritty, put some water in a plastic bucket for a few hours.
Gently pour some off the top of the bucket into a clean container, and only
use that water in your work.

Starting at 30 microns, before grinding I usually spread the slurry around
on the mirror surface with my (very clean) fingers to feel for any large
grits - fingers are good at detecting particles big enough to cause a
serious scratch. You can't feel the difference between 30 and 9 microns,
but if there's a piece of carbide or chunk of mineral deposit in there
you'll probably find it. Then I apply some more slurry to the tiles to give
a temporary cushion when the tool is applied - careful, don't cut yourself
on those tiles.

Bill T.

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