Re: newbie question

"Fox, Dan" wrote:

> This might qualify for the eventual FAQ, except I've never seen it
> addressed. What in the heck is so great about ball screws, that make them
> worth so much? Why are they so much better than Acme or regular,
> triangular-profile screw threads? Do they "work" differently from other
> threaded screws? And are there some kind of inner "works" to a ball nut (is
> that a proper term?)?

Yes, ball nut is the proper term. Yes, there are inner 'works'.
The works are ball bearings. So, the nut does not slide on the screw,
the rolling balls make it a rolling action, thereby reducing friction (and
wear) to minute levels. There is a rounded track in the nut, and the
balls roll to one end of the track, so a recirculating tube of some
sort is provided to return the balls back to the other end of the
track. If you put two separate circuits of balls in one nut, and either
make the two tracks slightly off the screw pitch, or put springs
between the two nut sections, you can preload the two nuts against
each other. This makes an anti-backlash screw. Depending on
design, you can get screws that will deliver thousands of pounds
of linear force, with backlash on the order of .0001" or so.
Obviously, for a precision machine, or a CNC where smooth,
complex motions are required, removing backlash is a very
desirable thing. The reduction in wear and friction is an added
benefit.

Jon