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[ATM] Figuring in turntable (non powered) TOT
Hi all
I?m new member of atm-list!
First at all, thanks to Mel Bartels, David Lewis (Plop?s programmer) , Ken
Slater and others Stellafane guys that answered my private messages.
My English isn?t very good, then please be patient ( feel free for correct
me, I will be grateful!!)
I?m from Argentina (38 years old) and I?m a beginner ATM. I am grinding my
first mirror : 6 inches plate glass f/8, but with many problems because I
am trying with several techniques that at the beginning I didn?t understand
:
hogging with ring- tool, continuing with washer-tool with many scratches and
too little focal ratio ( f/4.77 ), polishing with cerium with non channeled
- microchanneled pitch lap (very good) , figuring with full diameter lap and
too hard pitch ( very bad with such a focal ratio) .
Conclusion: Many scratches (very pressure in fine grinding + washers =
scratches , bad figure, too fast mirror ( I don?t wont to buy very expensive
eyepieces)
Then I tried with a new tile tool with smashed pieces of porcelain in cement
glued with epoxy, to regrind to a slower focal ratio f/8.
I used the sequence C120, C220,Alox 30,12 and 5 microns.
Results: Very smooth , but a lot of pits left by C120 ( very pressure when
grinding with such a size of grit result in very deep pits )
I want to return to C120, but this time with very light pressure.
In Argentina almost all ATM uses classical techniques (glass tools), but I
like learning a lot.
I work in a very simple ?turn-table?, a rubber mat over the kitchen sink,
and over this and in between the mirror/tool a non-skid material : during
grinding or polishing, each 7-8 strokes turn the mirror (or tool if TOT)
counter cloch-wise, and then the rubber mat in opposite direction.
For figuring MOT, pitch lap can remains stationary and the mirror makes
classical W strokes for figuring. Finally mirror must be rotated complete
turns.
For figuring TOP, specially if I want figure with sub-diameter lap, How I
can simulate ?waking around the barrel???
Thanks a lot.
Luis Andraschnik
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