re:RE: re:RE: Epoxy Granite, SPDT glass

Jack,
The PDF referenced below does not mention diamond turning glass. Lots for
crystal materials can be diamond turned, maybe you could get a 2 m silicon
blank?

I've used diamond turned optics in my designs for over 20 years, and have
spent a lot of time talking to diamond turners. None of them were able to
turn glass in any meaningful way.
There are references to ultrasonic excitation of the diamond to permit
machining of brittle material, but this does not appear to be commercially
adopted.

If you want to one up Stewart Observatory why don't you try deterministic
microgrinding
http://www.lle.rochester.edu/pub/review/v97/97Deterministic07.pdf
That, combined with MRF, should get you some great surfaces much more
rapidly than the conventional grind and polish.

Will you be using lightweight substrates? I would think that the deflection
of a thin substrate from centrifugal and tool forces would be a very
interesting problem to solve.

regards-
Elliot Burke




Date: Mon, 27 Feb 2006 23:30:19 -0600
From: "Jack Hudler" <yahoo@...>
Subject: RE: re:RE: Epoxy Granite

Elliot,
SPDT of borosilicate, Cervit, Zerodur, and lots of materials is very
successful see;
http://www-eng.llnl.gov/lodtm/pdf/HI_SPIE_DT1.pdf

I have no illusions of reaching LODTM 1/25 wave or POGAL 1/60 wave accuracy.

I would like to be able to create mirrors from .3 to 2 meters to at least 2
waves (with figure) and traditionally polish to finish of 1/10 or better. I
have
laser displacement sensors that will easily get me to my goal (lamba/2
@635nm).
The trick is going to be integrating the LD Sensors with DSP's to move the
cutting head fast enough to keep the correct depth, while moving linear
motors,
reading laser interferometers, rotating the cutter on ROC, controlling
spindle
air pressure/speed, maintaining environment, and all the while hoping that I
sized the UPS/generator just right in case the power goes! :)

Whew! Why am I doing this? Oh yeah... for a telescope and because I've
always
wanted to.

Having said all that, if SPDT is to finicky then I'll fall back to grinding
which will achieve the same results only I don't get to thumb my nose at
those
guys at Stewart Observatory (insert Monty Python taunt here). :)

Jack Hudler
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