[ATM] grinding pits

[Thomas A. Moulton]

> I have the port hole 16 inch
> been grinding for 10 hr 120 grit after full contact between mirror and
> tool
> have 1 1/2 hr 120 left to use and 1 lb 220 grit left
> it tales me about 7 to 9 hr per pound of grit to use it up. Got a joules
> loupe have found pits in some ares but most is clean
> do i us up the .220 grit then see what pits  i have left or order more
> 120 grit. i know this is a hard ? with out seeing the mirror.
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Remember you will always have pits, they just keep getting smaller and
smaller until they don't matter. (as you progress through the grits)

The real question is are the pits you see NEW pits or are you still
working on the same pits from the previous grit size?

Map the bigger pits.

Mark them with a sharpie and then put a sheet of paper over the area
and transfer the dots. Grind until the sharpie marks are gone and
maybe a little more.

Now get out your map - did the pits move?

If yes it's time to move on.

All this assumes you have (or still have) full contact between the
tool and mirror.

tom