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Re: ATM chasing spheres $%$^&*(%^&$%^!!!!!
> From: Cary Chleborad <bennu@ns.net>
> Subject: Re: ATM chasing spheres $%$^&*(%^&$%^!!!!!
> I've been fully hogged out since i started 120 grit. My sagatta is
> right on, well within .001" and I'm nearly spherical, I just can't seem
> to get full contact between the tool and mirror. Am I being too picky
> at this grit for a machine? I know I can get what I want by hand, but
> that's not the point.
>
> I'm using graphite to test the contact between the tool and mirror and
> there is a raised ring from the 37% to 75% of the radius.
How long are you grinding before you look at the graphite pattern to
determine you've got this raised ring? The reason I ask this is
because I used to test how well the tool and blank are in contact
during rougher grits (although I did it by rubbing them together when
dry. . .you see a different color/pattern where contact is being
made) And this is what I found: I never got 100% full contact
between tool and blank at 80, 120, and 220 grit (I stopped testing at
that point).
Did that matter? No. So far I've polished out 13 mirrors I
ground with a machine - not a single problem due to bad tool/mirror
contact. (And I was making these mirrors in sets of four with a
single aluminum tool. . .there's gotta be more tool/mirror
contact problems built in with this approach and I still had no
problems. I'm currently grinding a set of five mirrors against one
aluminum tool and I bet I won't have any contact problems.)
Actually it was standard for me to get a contact zone like you
describe. In that case I say you're in good shape and go the the
next grit.
Also, how much weight are you using on the pin? I use up to 30 lbs
for the silicon carbite grits to speed grinding and I've had no
problems. . .only an amazingly short grinding time.
Hope this helps,
Tom Krajci
Capt Tom Krajci
B-52 Intelligence Officer
"In God we trust, all others we monitor!"
http://spur.barksdale.af.mil