ATM Tube sag?

[andydtg@phoenix.net]

Hi All,

Here's some responses to my post re secondary mirror sag in our 32":

'Have you thought about a counter-weighted diagonal as suggested
by Allyn Thompson  Making Your Own Telscope. Just one of those
outdated books <G>'

Bob Pfaff

'Have you tried using a counterweight on the other side of the vanes from 
the diagonal to balance the assembly about the center of the spider? 
There may still be some axial and radial loading but the tilt and twist 
should leave. '

Mike Spooner

'Not to pick nits, but if you collimate at 60 degree elevation angle, you
will have half of the lateral force on the spider assembly.  I think this
would be the "optimum" place to zero out your errors in the sense that you
are minimizing the maximum error over the full range of 0 to 90 degrees.'

Richard Schwartz

Excellent suggestions all! I think the stiffer SST vanes will fix
the problem without adding more weight at the end of the tube. Also,
a counterweight located as suggested might create a nice torsion
pendulum oscillator. It would also stick out the end of our secondary
cage by about a foot or so.

I'll report results on the 'fix' when available.








Andy Saulietis / DTG Alt-Az-Fp Drive Systems
HDPE Worm Gears, Custom designs & Machine work
12617 Harriet Ln
Santa Fe, TX 77510 USA
409-925-8854 Voice/Fax
e-mail: andydtg@phoenix.net