[ATM] Problem? when grinding with machine

["Geoff Nelson" <gjnelson@absamail.co.za>]

I have rebuilt my grinding machine to a Tom Waineo design. Pictures 
on my web page http://www.myweb.absa.co.za/gjnelson/ 

I have been polishing the four inch mirrors with the machine and am 
getting strange effects on the mirrors. It looks like a central 
raised zone. I am struggling to do foucault tests and the Ronchi 
patterns are like nothing I have seen, though fiddling with ronchiz 
and rasing the central zone does seem to give a similar profile. 

I am not getting usable photo's with my current tester and so the 
rebuild of that will have to be done soon. 

As a favour for a friend I put his 8" mirror on the grinder for the 
#1000 grit stage and am getting the central part of the mirror 
grinding without any action on the outer portion.

I seem to be getting the same effect grinding and polishing. All the 
action seems to be happening at the centre of the mirror. I have been 
working MOT with about 1/8 overhang 1/4 COC stroke on the machine. I 
would not expect the central region to have so much extra action with 
this set-up.

If any one has built such a machine can you please tell me how you 
set it up for both grinding and polishing. Also any other comments on 
how to use the machine. I have an electronic copy of Tom's comments 
but would like some real life experience and or just ideas as to what 
could be happening.

Kind regards

Geoff
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