ATM Tangent arm drive

["Scott Ewart" <scott.e@quicksurfer.com>]

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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