From: "CSC" 
To: "Atm" 
Reply-To: "CSC" 


Turned out O.K.?  This mirror is the best piece of glass on the planet!!!
Except for Adler's of course.

I made a relatively conservative scope, 8" f/7, with a 1:9 thickness
(.87"). For this size, the wedge tolerance was .009 or something.  I
ground the wedge out when I smoothed the curves (made 7 of these mirrors),
and kept it to .001 by using accented pressure on the first few wets of
each grade, then smooothing wets.

I cut a 9" steel lap on my lathe to fit the pregenerated curves, and
started with 320 grit. I like the steel lap, and was very interested in the
dump lap before I got the lathe working.  They work fast and all my mirrors
are within .1" radius. I found I could get rid of .001 wedge in a few
wets. Probably best to get rid of the wedge asap and keep it out.  At 12
micron grit, it's slow work to get rid of .001 glass, especially a
10".

I read that someone had made a 10" f/6 flex.  {at} stellafane?

I'll be glad to keep in touch on this project with you.  I'll bet the pull
on this mirror is slight with the reduced thickness.

Colin

-----Original Message-----
From: Ian McKernan [mailto:mckernan{at}central.murdoch.edu.au]
Sent: Wednesday, May 21, 2003 10:13 PM To: optic{at}gwi.net
Subject: Flex mirror


Hi!  Saw a posting on the ATM list where you said you had made a flex
mirror that turned out ok.  I'm starting on my first one at the moment.
254mm diam, 17.5mm thick, f 6  / 6.2 , flat back, plate glass. I made a 10
inch mirror last year from the same glass and parabolised it, turned out
pretty well.

Have almost ground to a sphere at 220 grit (according to the sharpie test) 
I took a plaster casting off my last mirror, covered it in steel washer
dumps and am grinding with this (works really well if the tool is a good
sphere to begin with).

Anyhow, any advice or comments from someone who has done it would be
appreciated. Any pitfalls in making the mirror or cell that you found that
i may ba able to avoid??  Ive got a copy of Alan Alders article from
S&T and have finally gotten FLEX to work (had to run win2k in safe
mode!!) but as i found when making the last mirror there is no substitute
for advice from someone who has done it. Particularly interested in how you
dealt with wedge?? For this mirror the tolerance is only 0.0031".

Seeyahs!



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Ian McKernan
Plant Biology Technician

         c/o Murdoch University
         Division of Science and Engineering
         School of Biological Sciences and Biotechnology
         South St Murdoch  6150
         Western Australia
         tel: + 61-08-9360 2206
         fax: + 61-08-9360 6303

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