Re: ATM Big scopes

[ric rokosz <ab866@freenet.durham.org>]

Jean-Guy Moreau writes:
> 
> 
> 
> Hi Ric,
> 
> blanks that are now working telescopes, and I believe I did not
> say my last word on this. However fusing 1/4" plate into
> solid blanks 2" thick is easy up to 24" so far, with a nice
> moulded curve that lets you start fine grinding in less
> than an hour on #80, not bad I think !
> 
> There is a very real possibility of fusing usefull large blanks
> out of cheap plate glass, maybe ribbed ones too, its up to us
> to discover how. (Just daydreaming)
> 
> Tell us about your latest fusing experiments...
> 
> Jean-Guy
> 
> 
> 

Jean
Well my glass fusing has gone beyond trying to get it to work ( as all my 
mirrors are over seven years "old",the 24 inch is now 12 ) but has spread 
out to trying to find the lightest workable blank for the atm.I've 
adapted a variation of a design first presented in 1980 by some 
professional designers who modeled a solid version of a very lightwieght 
blank that has since come to be known as the double arch design.In a 
ribbed configuration the blank approaches the same degree of 
lightweightedness as the Hextek blanks -the 18 inch comes in at 
19pounds,but has the same stiffness as a solid blank.This  is a glass 
blank,not the up and coming carbon fiber type.I promised Bill Cook an 
article for the ATMJ so hopefully it will appear there (sometime).This 
blank can be done in one cycle not the two needed for the Hextek blanks.
 The downside is the rather extensive support system the blank needs,so 
you have to able to do/have access to some machinery.

The 18 inch version is finished in a cass mode;but it turns out the 
backplate I have now is too thin and there is a bit of flexture in the 
blank that shows up as mild triangular star images (out of focus) at the 
zenith,but gets better at other angles.This mirror design was intended 
ONLY for a alt-az. type mount (Mel's software would be ideal here) and my 
using it on a german equatorial is pushing the design limits to be sure.

The design as I'm using it is still experimental (solid version are  
getting to be more common -seems Dean Ketelesen is making one out of a 
solid 2 inch by 24 pyrex slab) and in the next incarnation the layout of 
the glass will be beefed up a tad to provide more internal mounting 
bosses -from three to five.

The next step would be to get this design molded in 
carbon-fiber-kelvar,then it would be micro ultra lightwieght! A 24 incher 
at 10 pounds.

Ric
Toronto