ATM aluminium cage design

[tofkas@uswest.net]

I'm designing a 12.5" newtonian and am considering an open
tube design.  Instead of a truss design, I'm looking at 8
1/2" aluminum tubes in an octagonal pattern running through
a series of 1/8" thick aluminum rings.  This will connect
the mirror bucket (made out of laminated hardboard) to the
focuser cage.  The mounting will be "dobsonian" sort of ala
Mel Bartel but I want the pivot point further up the tube so
that the change in eyepiece height isn't so drastic and
remains within a reasonable viewing range.

I have not seen many of these designs around..Is there a
good reason?  Is there anything I should watch out for?  I'd
really appreciate some advise here.  One reason that I am
considering this design is because I can get the aluminum
cut extremely accurately and fairly cheaply with a water-jet
cutter.  The aluminum tubes would be welded to the rings
where they pass through.

I would definitely appreciate some input on this.....thanks.

Stephen Houle       tofkas@uswest.net