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


Harold:
        A quick run of flex.exe tells me you've got an f6-something.  Good
choice.
The load on the foam is 4 psi which is not a problem for the sponge
material in Adler's article, nor is it a problem for the glue bond.

What could go boing?  If you use a stout bolt, say 3/8", the nut/bolt
won't fail.  Use some antisieze or other thread lube to make turning the
nut easier.  Perhaps make a larger knob or just use a standard nut and use
a socket wrench to set tension.

Wind it up.  I'd say overcorrect it so you know what that star pattern
looks like and to test the components and seat them.

Then relax it to the proper figure.  Next night out, You'll find it
undercorrected; bring it up again to null.  It should stay there for many
weeks.  If it ever needs a tweak, it will be very slight, and you'll only
know that with a really still night star test.

Enjoy

Colin

-----Original Message-----
From: owner-atm{at}shore.net [mailto:owner-atm{at}shore.net]On Behalf Of
Harold
Sent: Tuesday, February 11, 2003 1:14 PM To: ATM
Subject: ATM flex mirror spring tension ?




   Initially the tension spring on my flex mirror was bottoming out before
the mirror could flex. I was informed by Alan Adler to try McMaster Carr
#39588k rated at 496 lbs. per in. with a free length of 2". The new spring
compresses to about .0.71" before reaching  the required 353 lbs force
 4.02 lbs per in ) nesessary to flex the 12.5" x 1 1/2" thick mirror.  When
turning the spring it takes quite a bit of force to turn the wing nut
enough to compress the spring to the desired 0.71" Im concerned that
even one more crank on the wing nut and the whole thing will explode. So my
question to those with more experience at flexing mirrors, is all that
resistance a bit much for the bond that hold s the mirror/sponge/puller or
am i being overly concerned?

     To date i have only been able to test on artifical star but so far he
results look promising. There appears to be no astigmatism and although i
think something could give way before flexing to proper figure, the inside
of focus rings are slightly brighter than the outside of focus rings but
they begin to equal out in appearnce and brightness as i begin to approach
0.71" spring compression.

  Harold

--- BBBS/NT v4.00 MP