OK, my thoughts on this are that maybe some rethink should be involved.
This group is at its best when you define the problem, as opposed to
asking the end question "where do I buy threaded rod?".  For a table
saw, there are a few things you could do with a motorized fence.  Each
suggests a different level of complexity.

First, all applications require the front and back of the fence to
remain parallel to the blade.  Second, some method of locking is
required, manual or otherwise.  These are basic safety considerations.
Next questions: do you want to just position the fence, position it with
repeatability, or digitally gauge the position?  All imply a level of
precision and repeatability.  Next, think dust.  Lots of dust.  Will a
rod collect it to the point of jamming?  On the better fences, the fence
support is fairly self cleaning.  I remember one aftermarket fence uses
pullys with tensioned cord - like the old parallel on a drafting table.
If this took a bunch of loops around a pully on a motor (and was
attached in one place) like the tuners on radios used to do when turning
the knob moved a pointer and the variable capacitor shaft, I don't think
sawdust could bother it.  Of course, the cord can't stretch.  I'm sure
there are many other creative approaches that are inexpensive.
Steve

>------------------------------
>
>Date:    Tue, 30 Dec 2003 17:36:55 -0600
>From:    THE NELSONS <rinelson@CHARTER.NET>
>Subject: Re: [OT:] Looking for stepper motor with worm gear
>
>McMaster Carr is a great place to buy things if money is no object and
>you are to lazy to look around.
>They have almost any thing you want but are some time 5 times more
>expensive then other places.  I found acme threaded rod
>in 6' lengths for about $20 and the nuts are expensive  at about $4 each
>.  Regular threaded rod is not designed for repeatedly moving the nut.
>It is used for holding things together and has V shaped threads.  Acme
>threads are square for load bearing.
>
>Other things mentioned in the list need to be taken into account.
>Having worked with wood working equipment I know the fence
>does not always move freely. You might want to consider a threaded rod
>at each end of the fence. Connect them with a chain or cog belt drive.
>As far as The flex mount using rubber hose.  With a 1.8 deg step that is
>200 step per revolution If the unit runs into resistance they
>can SLIP with to much flex allowed. Then the software thinks the object
>has moved when in reality sometimes it has not. so to be sure you
>need other means to measure to confirm it moved the distance you told it
>too.  Then you have to take into account BACKLASH.  This is the PLAY
>in the system. Say if yoou last moved the fence toward the blade and now
>you want to move it away from the blade you may have as much as one
>revolution of the rod
>before the fence actualy moves.
>
>There are a lot of other things to consider that I have learned,  So
>contact me if you wish.
>
>Bob
>
>

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