Re: ATM Wiring Spiders

[Doug Tanaka <dtanaka@seanet.com>]

At 10:31 AM 2/13/2002 -0800, you wrote:

>How do you tie off the ends of this string so they don't slip under high
>tension?

Ed,

At the secondary mirror end, the string goes into a 1/2" dia. tube, through 
a very small hole.  I pulled some string through, tied a regular square 
knot in the end, and then tied the string around a thin brass brad.  After 
trimming the brad to about 1/8" long, I just pulled on the string to snug 
the brad up against the hole.  The square knot keeps the end of the string 
from slipping past the knot around the brad.  At the other end, the string 
wraps around a small stainless steel socket head cap screw that is drilled 
through 3/8" aluminum U-channel (forming an "axle").  The screw spins 
freely, but locks with a nut.  I wrapped the string around the screw by 
spinning the screw, gradually tightening so each successive turn trapped 
the string below.  It requires wrapping about 4" of string around the screw 
and just holds by friction.  The hardest part is starting the string 
because it wants to slip, but once started, the threads on the screw help 
bite into the string as I gradually increase tension.  It might sound like 
the string would eventually cut, but there ends up being about 6 layers of 
string, and the working part is cushioned by the string beneath.  Also, the 
string is amazingly resistant to cutting.  You need a very sharp pair of 
scissors to cut it, and even then it's not easy to do.  Hope this makes sense.

Doug