Re: ATM Getting to sphere while rough grinding?

["Bob May" <bobmay@nethere.com>]

You're going to find that you're already too short to do all of your
grinding with the mirror on top.  You will be doing some grinding with the
mirror on the bottom at this point if you want to go to an exact focal
length.  You can get the number to within 1/2" without any real problems if
you check the measurements occasionally.
I wouldn't worry too much about sphericality until I got to the 9 micron but
will insure that the various grits along the way are grinding smoothly
towards the spherical condition.
When you get to the last grit, I suggest that you leave the ROC at least
1/2" long as the polishing and figuring takes that last little bit out.
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net