[ATM] Re: polishing and figuring a 32"

["Mike Conran" <mike@guidesys.com>]

Hugues.Laroche@ses-astra.com writes:

> 
> Hello Fabio and Bob, 
> 
>>32" is a big scope anywhere!
>>The motions for polsshing are basically the same as what you would think,
>>back and forth as the mirror turns underneath.  You basically have to
> cover
>>all of the area of the mirror evenly to get a good polish.
> 
> Well, I precisely do not find THAT obvious to do!? 
> 
> With my 45" (yeah that is not only big it is completely crazy)
> I polished with a 2/3 tool by hand until recently (pads, not pitch!).
> Due to the size of my arms (for once I am sorry not to be a monkey ;-)
> I could never make COC strokes so all has been done with more or
> less off-center strokes. The mirror is not completely polished out
> yet and I plan to continue with a machine, which is a different world. 
> 
> But the bottom line is that, because of my strokes or because of
> the mirror support (stronger in the center) or both, the mirror
> got substantially overcorected (b=-2.9). 
> 
> Happy ATMing... 
> 
> Hugues
> Luxembourg, Europe 
> 
>  
> 
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Interestingly enough, Hughes, the Hindle machine we used for the 30 inch 
could not make full length strokes across the mirror surface so we 
essentially worked one side of the mirror as it rotated on the turntable.  
In effect all parts of the mirror surface end up being worked as if you 
could do full strokes.  It just took longer since there was a sort of "time 
sharing" going on with respect to the pitch lap and mirror. 

We did not use polishing pads, but you know, we had the machine doing the 
pushing and pulling and it was a 22 inch pitch lap.  I suspect that a 2/3 
sized pitch lap on a 45 inch disk would be, well.....A TOUGH PULL!  I figure 
that is about a 30 inch tool! That's big for hand work. 

Mike Conron 
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