ATM Aluminum, Split Ring, Astrograph

[Aplanatic@aol.com]

Dear ATMers:

Well, I'm at it again.  This time I want to make my dream-2 astrograph.  A 
16" (maybe 20") with a 2 meter focal length.  Medium format film, of course.  
It turns out that a Newtonian configuration with a parabolic mirror works 
well with a Wynne-type corrector that I have designed.  Covers 6X6 cm film 
with excellent stars to the corners.  But that's another story...

Anyway, here's the question.  I have found over the years that a friction 
drive is great for astrophotography, very smooth, very low periodic error, 
etc.  So, I want to make a split ring equatorial for this puppy.  A wooden 
split ring in this size is doable, but very heavy and not as strong as one 
would like.  I can envision an aluminum split ring about 1/2 inch thick and 
maybe 30" in diameter.  I can also envision making this out of plate stock, 
machining holes in the plate to remove unnecessary material.  Or, I guess I 
could weld together a complex split ring and then have the ring machined 
round.  Or...

Anyway, if you have some advice about this I'd love to here about it.  Anyone 
made something like this?

Thanks,
Dave Rowe.