Re: [ATM] Newbie needs help getting to sphere...

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

Remember that all of what you've discussed it sort of relative.
How big is the hole and so forth.
I'll note that with 80 grit you're not going to be getting a good
sphere so don't even bother trying.  Just get the basic ROC that
is desired.  Now go to 120 grit and refine that curve and mostly
finish getting the right ROC.  As you go down through the grits,
you can refine the ROC as you go.  You can easily move the ROC 8"
with 120 grit and lesser degrees with each smaller grit.  For a
97" ROC, I used 25 micron grit to move it an inch with two wets,
one to move and one to sphericalize again, for example.  You
really don't need to get to the right ROC until you're at the 320
grit or smaller stage where things usually don't change by much
with the proper length stroke.  A 1/3 stroke is where the glass
on top moves a total of 1/3 of the diameter of the glass - 1/6 to
either end and side.  A 2/3 stroke will keep on shortening up the
ROC fairly rapidly.
The coarse grits work best when heavy pressure is used and not
too much grit is applied.  With 80 grit, recycling also works
well and lets you know how much of the grit is actually used vs.
how much quickly falls off of the grinding surface and isn't used
in the grinding.  80 grit wets also tend to be rather short as
the size of the grit tends to rapidly get shattered apart.
Bob May
bobmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net
Replace the obvious words with the proper character.

_______________________________________________
ATM mailing list http://www.atmlist.net/