Re: ATM Astigmatism on 20 inch thin mirror

[Guy Brandenburg <gfbranden@earthlink.net>]

I must say, that is the strangest looking lap that i have ever seen. How 
did you make it? The lap is the most important thing about the process.
Guy Brandenburg

David Lonard wrote:
> 
> 
> Hello Group,
> 
> I would like to thank all those who have given advice.
> So far the biggest consensus that I have received thus
> far has been to extend my stroke to bring the sphere out
> further to the edge, which I have been doing and seems
> to be working well.  I have still been concentrating a
> lot of strokes along the more spherical axis since I
> still think that the edge is higher along this axis.
> Along the more hyperbolic axis, I am using a longer W
> (or V?) stroke.  I have an updated ronchigram photo at
> 
> http://www.geocities.com/lonard3/mirror.jpg
> 
> I have also made what I hope is a more reasonable star lap
> as was suggested.  Several of you have said that I should
> wait on the star lap, but I have tried using the full
> lap and things go wildly oblate spheroid when I do so.
> At any rate, the ronchi bands are getting rather straight
> with this current lap so I think it is currently useful.
> 
> To answer your question about machine work Dennis, when
> the surface came to polish, the ronchi pattern was packed
> with multiple nasty zones, too many and too deep to honestly
> know if I had astigmatism at that point.  The 12/24/02 image
> is the product of probably 20 hours of subsequent hand
> polishing.  I actually did put it back on the machine,
> but strong zones started to return, so I stopped.  To
> be fair, my machine isn't very mechanical sound, made
> out of wood and was practically destroyed during the
> violent hogging out process.
> 
> I'm sure that there is still plenty of interest in a
> 20 x .875 inch mirror so I will try to give more
> updates.
> 
> David
> 
> 
> 
> 
> 
> 
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