ATM Some more note on the old 12

["Clive Milne" <milnecd@wantree.com.au>]

    As I said before, the twelve in the pics was very much just a stab in
the dark design wise. Some of you guys are CAD wizards, and might question
why I didn't experiment in that environment..? Well, to be honest, I
couldn't drive auto-CAD to save myself. I am much more comfortable with the
feel of metal in my hands... Even a model gives you an intuitive feel for a
concept and can give you insight into deficiencies that might otherwise be
hidden..
    So what did I learn from the 12 rebuild....?
Well, I'll start with what worked.....
......The basic structure of the tube assembly is rigid beyond description.
With the friction tweaked up, it feels as solid as a Gum tree....We are
talking damping times of a fraction of a second for hammer blows to the top
ring... From that we can infer that light gauge (20mm x 1mm) tube is all
that is required for a truss that is designed properly.
...... The truss clamps are quite good, but to be honest, I much prefer the
design that I employ on the 20's.
...... The triangular base is a winner, it effectively defines the position
of the teflon pads with respect to each other and the teflon center bearing
whilst transfering all loads directly to grade....Anything else is
superfluous to the function of a ground board, in effect just extra weight
to lug around, and extra mass you have to pay for.
....... Projecting the truss up to the top ring, and suspending the focusser
down as part of the truss, works well... It effectively gives you the
convenience of eyepiece position as in the Kreige configuration, with the
weight,  profile and load transfer advantages of Mel's design.
....... I'll list the caveats of the 12 in a future E'mail.... sorry, out of
time for now.