Re: ATM Tangent arm drive

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

Thanks Jim and Don,
    This looks like a good design.  I may be able to use it.  The only
problem I may have with it is that my screw has a little under an inch of
travel, even with a thin nut.  Add to that the thickness of the cylinder
block, and there's not much room left to move.  I could see how thin it
could be made.  But I may just have to machine a new screw to fit the drive
gear, and leave it longer this time.

Scott



----- Original Message ----- 
From: "Good, Donald" <dgood@aha.org>
To: "'Scott Ewart'" <scott.e@quicksurfer.com>; "'ATM list'" <atm@shore.net>
Sent: Saturday, January 24, 2004 12:08 PM
Subject: RE: ATM Tangent arm drive


| 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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