Re: ATM Polishing

[Bob Goff <goffaxe@azstarnet.com>]

Frank,

I love to polish flats. They are just spheres to a precise allowable
curvarure tolerance. The tolerance that tickels my innards is better than
1/60 wave at Sodium D.
My fine grind sequence is 40, 20, 12, and 9 micron suspension treated
alumina and generally 15 minutes per grit against a cast iron toos of fine
grained Meehanite ( has a lot of graphite in it ). I maintain one tool for
each grade of grit. Then I grind for 10 minutes with 5 micron and without
stopping to clean or inspect I was through 3 micron grit for another 10
minutes. If my parts ar 10 inches in diameter, then my laps are 12 inches
diameter.
When my polishing lap is working correctly, the 10 inch pieces come off
polished out in 20 to 30 minutes. When everything is right, then I get one
of those very flat surfaces that are so coveter. But generally, it is hours
before I can chase the curve to fininsh.





At 12:21 PM 08/25/2001 -0400, you wrote:
>   I don't like polishing. It takes so long and when  you finally get a
>"grey polish" you know you are still not even  half way there.   Today I
>tried something worth mentioning. Last week  there was a short thread
>concerning the overarm motion on  a  machine. It got me to thinking that
>the back and  forth motion is the only one doing the polishing since  the
>tool and mirror tend to rotate at close to the same  speed.   With that in
>mind, and not wanting the zones  produced when the tool is held stationary
>while the blank rotates  I set up an experiment.    I attached a cloth
>covered rubber "hold-down"  between the post supporting the overarm and a
>screw inserted in the  edge of the tool. When the overarm went back and
>forth the tool  stayed still, but not in one place. The elastic hold-down
>allowed  it to spin an inch or two and then return.     This time I used
>thirty. Enough to make the squeeking  sound I usually   But it wasn't  the
>high pitched squeel that warns you those puppies are about to become 
>one....it was a lower "in serious contact" sound.   For the next hour I
>replaced CeO and water at least  four times as it was used up. But after
>that hour the surface was  the most magnificent clear I had seen in a long
>time. The channels  started to close, but I opened them again.   The
>surface (on the stand without cooling) was  brilliant in the light of my  
>I  couldn't tell much because of the heat waves it was putting off.     no
>zones, a perfect polish, and half   gone. In addition I had pretty close 
>to a sphere. It was truly amazing, 4-5 hours of polishing in one....with no
>adverse  effects.   I'm sold on this method and will update if  anything ><
>show up...... Now.....where  did I leave my patent application forms?   In
>friendship,   Frank Ward Atlanta, GA   
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