RE: ATM Tangent arm drive

["Good, Donald" <dgood@aha.org>]

Take a look at Jim's posting "ATM Tangent Arm Nuts" of 8/17/2003 copied 
here.  The description on his web page is excellent.  Thanks, Jim.
Don

Jim wrote:

For Those That Make Slow Motions on Their Mounts:
     I have been putting together some material into little web pages
recently. Today I put up photos and a description of my method of
constructing simple-to-make (drill press only) tangent arm nuts that are
tolerance-friendly, adaptable, strong, and wear resistant. This eliminates
the problems of milling slots and pinning nuts just to watch them wear out
and put backlash in your declination axis.
     I've been using this method for a number of years and haven't had one
wear out yet. Backlash free, alignment tolerant, easy to make. Should work
for wood too.

http://home.att.net/~jsstars/slomo/slomo.html

- Jim S.


-----Original Message-----
From: Scott Ewart [mailto:scott.e@quicksurfer.com]
Sent: Friday, January 16, 2004 2:01 AM
To: ATM list
Subject: ATM Tangent arm drive



Hi all,
    I'm building a tangent arm drive for the Dec. axis of my split ring.
The problem I'm encountering is how to attach the end of the arm to the
screw that moves it.  I can thread a thin plate to ride on the screw, and
the other end of that plate can pivot in the end of the arm to allow for
changing radius.  I think I can build this with very little flex.  But as
the angle changes, the threads will bind.  I checked, and I only have 2 to 3
degrees of arc till it binds, and the length of the screw is enough for 5 or
6.
    The question is, how can I get the end to pivot in 2 directions, and
still have little or no flex or back-lash?  Correct me if I'm wrong, but I
figured that back-lash as little as .002 inches at the end of a 9" radius
arm translates to almost one minute of arc in the sky.  Unacceptable.  Any
ideas?

Scott Ewart



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