From: "Mel Bartels" 
To: "Atm-US \(E-mail\)" 
Reply-To: "Mel Bartels" 


>>>
Someone raised a question on a german newsgroup, if the wire spider is not
vibrationally inferior to a standard excentric design. Especially
transversal vibrations along the optical axis seem to have been a problem
in some attempts. Does using aluminium channels to seperate the eyebolts
and crossing the wires get rid of that problem?
<<<

Yes to a remarkable extent.  You can rig up a test spider and dummy
diagonal pretty quickly and do your own testing.  I am amazed at how strong
they are, if done properly.

>>>
For my 10" travel dobson I would like a four vane wire-spider on a
single upper ring, with the tension being generated at the secondary holder
and the wire loops just being hooked into the ring. I'm now wondering if
that will induce hard to handle transversal vibrations, if the wires of a
spider vane form a triangle, joining at the single OTA ring?
<<<

If I understand your comment correctly, the best way to handle these
vibrations is to not bring in the wires on axis, but aim them off-axis.
There is no way that it is going to vibrate in the off-axis situation.  
You
have two dimensions so the wires should aim off-axis in both dimensions:
one cross-ways where the wires cross at the midpoint to the diagonal (so
they start spread apart at the tube or upper ring, cross each other, then
end spread apart at the diagonal hub, and, aim off-axis from the
perspective of looking down at the primary mirror from standing in front of
the scope)

>>>
It is not so clear to me, but it looks like your wire arrangement is
actually a four vane spider with two vanes meeting at one corner of your
upper triangle. Am I getting that right?
<<<

Yes, that is correct.  I was initially concerned about the force vector not
being completely equally distributed, but it is not an issue for this 3.5
inch diagonal and wire size.  That way I can get the 8 segment wire spider
to fit into a triangular upper end.

Mel Bartels

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