[ATM] trilateral scope problem

["Jan van Gastel" <jhm.vangastel@wanadoo.nl>]

I am building a trilateral scope. I started using Mel's design (and use most
of it), but because I wanted to drive the sope on the two side bearings, for
which I made a shaft running in front of the mirrorbox, I changed the
design. In Mel's design, the trusses, exept for the one in the backside, are
mounted on the side bearings (both front tubes and the front tubes of both
side trusses). Because of the placement of my shaft and the drive this was
not possible and I places all tubes on the mirrorbox, as can be seen here
(seen from the front side):
http://home.wanadoo.nl/jhm.vangastel/Astronomy/tridob/tridob.htm#assembled .
The trusses on the backside are vertical when the scope is vertical, the
front tubes are canted to the side and to the back and the left and right
side tubes are canted forward.

The problem now, is that the scope doesn't hold collimation because of
bending. From about 25 degrees altitude to almost vertical, there's a
difference of about 2-2.5 millimeters. As far as I can see, only the two
front tubes are bending, which makes sence I think, because they take the
compression load. The only solution that might work is placing the two front
tubes on the inside of the side bearings (which make them shorter), and/or
use larger (in diameter) tubes on the front side. Outside diameter of all
tubes is 22 mm and 1.5 mm wall thickness. Lenght is about 2345 mm (measures
in inches: 0.865 tube outside diameter, 0.059 wall thicknessand 92 inches
length). But possibly there is no simple solution (although I still hope
there is one).

If anyone has ideas, I would be glad to hear them.

Jan
http://home.wanadoo.nl/jhm.vangastel/Astronomy/

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