From: "Russell Jocoy" 
To: JBHillman{at}ev1.net, atm{at}shore.net
Reply-To: "Russell Jocoy" 


>From: "Jerry B. Hillman" 
>Reply-To: "Jerry B. Hillman" 
>To: 
>Subject: ATM I'm back
>Date: Tue, 12 Aug 2003 10:04:17 -0500
>
>
>Hi everyone,
>I have resolved my finacial problems and now am again working towards
>finishing this 16.5" x 3/4" mirror.
>Progress update. I polished the mirror back as close to a sphere as I could
>get it. As I am still unable to work indoors, I only work on the mirror in
>the early morning or late evening when the temperature is between 70
>degrees
>and 85 degrees. Today is a wonderful day. I have the day off and the
>temperature is an amazing 70 degrees. Very unusual for August.
>I have been parabolizing with a 7.75" star lap. The center solid part of
>the
>star is the same size as my center zone, making it three inches.  I loaded
>Ronwin20 to my laptop and have set it up next to my mirror so that I can do
>visual comparison side by side.  Using this method, and altering the Conic
>value to -.75 I found where my mirror matches the Ronchi pattern. I think
>this means that I am 75% parabolized?? Please correct me if I am wrong. I
>am
>using a w stroke with about 2" overhang.  The edge seems to be holding as
>the center deepens.
>I also took a critical look as my Foucault tester.  The numbers I have
>posted in the past that showed the mirror to be at .9 Strehl or better were
>invalidated by star testing. I wanted to figure out why. Careful study of
>my
>tester and entire test setup showed backlash and slop in several of the
>adjustments.
>To remedy this I downloaded the plans for a tester from the Stellafane web
>site and built a new tester and mirror stand from scratch. I mounted these
>on a 16 foot 2x12 and set the entire assembly in my living room inclined at
>a 20 degree angle. Initial testing shows that the tester is stable, moves
>correctly on both axis, and has no backlash. I can control movement of the
>stage in measurable increments of .001". I now have to learn to test with a
>moving light source. This setup is much better than what I was using. Time
>will tell if I can now get accurate measurements. As soon as I get a web
>site up and working I will start posting Ronchigrams again so that my
>progress can be evaluated by the list.
>I am glad to be back. I missed you all.
>Clear skies, Jerry
>
>



("atm{at}shore.net")

       Jerry,  It's nice to see you back on the list. I am glad that you
have your finacial things in order. It seems you are still learning to
perfect your thin mirror. I think that diving into this thin glass has
taught you many things, such as figuring of these thin mirrors needs
support to produce a sphere
on the surface.  Also that taking a mirror of this size off the matt on to
tool mirror on top is out of the
question, but you have come this far with the mirror on the bottom and the
tool on top.
    You have also learned that  the temperature of your working area has a
big.. real big..result
on the action of your pitch and lap...(I have gone through this also). and
that soft pitch on a lap will
close fast and turn an edge in a minute... Damn.. I hate that.   But you
have persisted and are of good
detemination and I have faith that you will succeed to figure this thin
monster into submission.
      Remember the golden rule for thin mirrors, support, support, support.
This not only means support
during polishing, but support during testing.  The old test stand will not
"get" it. I think that your strange ronchi reading was a fold of
the mirror( as stated by others on the list) If the fold stayed in the same
projection as you rotated , it is the weight of the glass from the edges
folding the center.
         I have a tester rig very much like you described yours. Mine is at
eye level on a tripod and goes
to the ground where the mirror is placed leaning "backward", or
on its back.
  This may change your
ronchi view, if not elevate the system as high as you can and support your
mirror as if you were
viewing through the eyepiece.    I'll bet your mirror had a completely
differrent shape vertically than it did horizonally, remember this is not a
conventional 2" thick glass, You are working with "thin
Glass"...
    I have to tell myself this over and over.    Thin glass is not
impossible to figure, but it is impossible if you don't support it
correctly..... during figuring and during testing.... And of course when
mounting...
          Glad to see you back on the list...... Russ Jocoy
("atm{at}shore.net")
>

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