Re: [ATM] Thermal Mass - WAS Tees instead of triangles

["David Harbour" <scarab2@cox.net>]

Ric, all:

United Lens, a large annealer of all kinds of optical blanks, has been
making, for a very long time, a beautiful, molded "ribbed" (eight radial
ribs) 16" blank. I had a beautiful example of one of these blanks finished
into an f/4 primary for my Classical Cassegrain system for the big mounting
you guys have seen on my page on the traditional symmetrical equatorial
mounting. Parks Optical finished the system to my specifications for a
Classical Cass with a slightly wider field of view than was the general
practice (extra coma at edge of field, yes, did not matter the way I was
going to use it, either application).

The level of craftsmanship in this $4,400 set of optics was marvelous, with
the central perforation of exactly four inches' diameter and EXACTLY
centered. The mirror did have a perimeter rib the same thickness as the
eight radials; I believe that it is necessary to have a perimeter rib. I
have some beautiful photographs showing the ribbed back of this mirror for
any one who would like to see them; it was a beauty. I have a note from a
friend, about how the current owner of them uses them- he uses them the only
way I ever used them: occasionally sets up my custom made, secure
carrying/storage case, and looks at them. Ahh, the hours I spent doing that!

I gave my big mounting for them to Ken Hunter, and gave that mirror set to
my friend Frank Ward. Yes, both you guys are my friends. No apologies
needed, Ken, about the big mount coming to a sad end; and Frank, save
yourself the agony of building something like I did to carry them. They are
safer in their box. Beautiful objects of art, more precious than a diamond,
and with a nearly perfect figure.

Ask for pictures, friends.

Davey.

P.S.- For very many years the only vendor of mirrors made with this blank
was Edmund Scientific; now Parks Optical makes ultra fine primaries with
them.

----- Original Message -----
From: "Ric Rokosz" <radicell2@yahoo.com>
To: "Cary Chleborad" <Cary@Chleborads.com>; <atm@atmlist.net>
Sent: Saturday, May 21, 2005 7:03 AM
Subject: Re: [ATM] Thermal Mass - WAS Tees instead of triangles


>
> --- Cary Chleborad <Cary@Chleborads.com> wrote:
>
> >
> > There have been a couple of folks in recent years
> > that have been fusing post
> > and plate structure systems together.  The advantage
> > of such as system is
> > one can achieve the cross section of a very thick
> > mirror blank at only ~1/3
> > the mass of an equally thick solid blank.
> >
> >
> > Now, to top it off and make it sound like an
> > infomercial:
> >
> > It still gets better!!!  A cellular blank is not
> > only less massive and cools
> > much faster; it ends up being much stiffer than and
> > equally thick and solid
> > blank.  Furthermore if the cellular blank is made by
> > a full casting instead
> > of fusing plates and posts the cellular structure
> > can be designed to be
> > totally self supporting.  The mirror then sits right
> > on the collimation
> > bolts!!  No more fussing with complex mirror cell
> > designs!!
> >
> > Now the catch!!!  No one is commercially producing
> > cellular mirror blanks -
> > yet....
>
> Your last statement is way out of date.People have
> done it,come and gone because of various
> reasons.Hextek still grinds on,Pegasus now offers
> cellulars again,various other manufacturers who don't
> hang out on the atm lists such as Schott which are in
> a price range way beyond the average atm, etc.There a
> few one man operations that cast a cellular type blank
> but you wouldn't believe the cost.
>
> I've talked and debated with some people on making
> cellulars commericaly and as a business plan the cost
> to setup and get them out the door is risky given the
> small market and the need to recoup the high
> production costs.
>
> The issue of mirror cells for cellulars isn't as
> simple as you make out.
>
> Ric
>
>  cellulars since 1983
>
>
>
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