Re: [ATM] Fine Grind already Blanchard ground mirror blank back?

[Mike Lockwood <melockwo@uiuc.edu>]

Hi,

John Lynch wrote:
> When I read the posting I did a double take when I
> came across the hydrogen flouride part.  I work at
> NASA Goddard Space Flight Center where they use this
> for advanced detector development, and I know that
> they are required to take extreme precautions when
> handling it.  As far as anyone (amateurs) having
> access to this stuff and using it at home, I would
> consider them to be a fool.  I would also argue that
> there's probably some law against having HF in
> household/neighborhood environment.  There are tight
> regulations even in sanctioned work environments with
> all of the required safety equipment.

I wrote:
 >>>(Bob Goff used to dip pieces in HF acid to etch away any damage).

Yes, HF is nasty, and I personally don't want to be anywhere near the 
stuff.  (I assumed that the treatment was done by someone else other 
than Bob, at a location other than his shop.)

This information came from the ATM list archives.  Here's the post 
that mentions the blanchard grinding and HF, posted by Bill Marriott:
   http://astro.umsystem.edu/atm/ARCHIVES/NOV03/msg00143.html

Bill, do you know how this chemical treatment was done and by whom?

The reason I'm not too worried about the ground back of a CONCAVE 
mirror is that if there is stress in the back due to grinding (Twyman 
effect), it's probably fairly uniformly distributed (yes, that's an 
assumption I am making), and that would cause the mirror to change 
mainly in radius of curvature over time.  A change in sagitta of 
1/10th wave is not a big deal, as the figure stays quite intact.

Of course, for an optical flat that's better than 1/20th wave, that 
change in sagitta would be disastrous!

If I ever commit the time and effort to make flats to 1/20th wave or 
better (I probably will someday), I am definitely going to polish the 
back.

	Mike Lockwood


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