Why ballscrews for linear drive?

Steve -

Why, oh why, do they need to be ballscrews?? If you're looking
for simple and cheap, try this:

1.) Go out and buy a set of closet doors and hanger rails from
Home Depot (paint /decorate/replace doors as desired). Choose a
long enough rail (or two rails) so you can put both doors on the
same track and open fully. Don't forget to use guide brackets for
the bottoms.
2.) Mount a 1-2" dia. pulley between bearings over the top-middle
of one side of the tracks
3.) Mount a direct drive, or slightly geared (backdriveable, if
nec.), motor with 1-2" dia. timing belt pulley over the top-middle
of the other side of the tracks.
4.) Hang a timing belt between the two (~1/2 wide), with enough
tension to keep the teeth in contact and avoid sagging too much.
5.) On the inner top corner of one door, mount a bracket to clamp
to the bottom side of the belt
6.) On the other door, same place, mount a bracket to clamp to the
UPPER side of the belt.
7.) Mount one limit switch for closed and one for opened positions
(only one door needs to be sensed, since they're coupled).
8.) Wire limit switches and motor to an open and a close circuit .
9.) For smoother motion, place friction devices (foam pads, etc)
against some part of each door, and keep the doors light.

The result of this is that, with one motor and one belt, the doors
will travel in opposite directions, and it should only cost a few
bucks. This should work fine, if all you need it for is a stage
prop?

Carlos Guillermo
VERVE Engineering & Design

-----Original Message-----
From: Steve Greenfield [mailto:polymorph@...]
Sent: Wednesday, January 17, 2001 7:32 PM
To: CAD_CAM_EDM_DRO@egroups.com
Subject: [CAD_CAM_EDM_DRO] Re: Ballscrews/linear drive

I don't know what the "infamous 5/8 inch screws" are. Can you clue
me
in? Are we talking about ballscrews or Acme leadscrews?

I need these to be ballscrews, and I'm making a rough guess that
I'll
need 3 to 5 tpi. I keep finding wildly different prices, or no
prices
at all. I must admit to being a bit intimidated about calling all
these places that have websites and print catalogs without any
prices.

Steve