Re: [ATM] ritchey cretians

["Bob May" <rmay@nethere.com>]

As is usual, when someting interesting comes along on the list,
everybody has a bunch of good ideas.
If you're going to be casting glass yourself, you might as well
do a cellular mold ala the 200" Hale mirror.  Bob Goff had a 32"
mirror blank from the company he had (Hextek) and it was light
enough that a single person could pick it up.  Those things
weren't cheap tho!  He did a fused proces in making the mirrors.
As to handling the glass, the first thing is to make up a good
strong band of steel with clips to hold the glass onto the band
and not allow it to sli9p.  From there you can do any kind of
attchment for lifting and otherwise moving it about.  I will note
that having a building with a ceiling high enough that you don't
have to tilt the glass off of the table in order to do the
testing o at the ROC will be a plus if you don't mind walking on
catwalks.  Otherwise, a tilting top for the grinder (you don't
need to support the last few inches of the glass on the table!)
will make testing easy.  Remember that you're looking at about a
half ton of glass for the mirror.
As to the flats, don't even try thin glass for them.  They will
flex way too much with something that thin.  I won't say that
autocollimation is out for a telescope of that size, but I'd
rather look at all of the other tests before even contemplating
such a test.  Even just finishing the telescope and pointing it
at a star for star testing will be easier!
Bob May
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