Re: ATM Re: string spiders

[Daniel Fundo <fundo@bellsouth.net>]

<<  I was giving thought, and concern, to string spiders not providing
very good axial support, no matter how tight the strings. With 3, the
optimum and minimum, the secondary can still  vibrate along the optical
axis. Or have I misunderstood something about how they might  be used? 
>>

I have made several 4/8 wire spiders (4 "vanes" from 8 wires).  On small
telescopes (<10") an angle of 20 degrees between the paired wires works
well at reducing all vibrations and movement.  One larger spider I built
for a 12.5" still had a bit of instability in it that was eliminated by
increasing the angle to 30 degrees.  Part of the problem may have been
the 3.1" secondary; rather large and heavy for this size instrument.  

I have built all of my wire spiders from 0.013" stainless steel wire,
which is sometimes referred to a music wire in hobby shops.  I have been
able to "tune" these without a problem, and have never had a wire
break.  (My soldering on the other hand.............!)  I tested a piece
of wire to several times it listed breaking strength of 40 pounds.  

If anyone wants details, I can provide a complete description of my
process.

*****-----
Dan F.
Secretary/MAS
Memphis, TN