Re: newbie question

Andy Olney wrote:

> I was surprised to learn that the antibacklash type ballscrews with 2
> ballnuts back to back have a much reduced efficiency. Standard ball screws
> are in the 90% range and I think the anti backlash type are in the 60% range
> which does away with some of the ballscrew's advantage.

This is probably very dependent on pitch, the amount of preload, size
of the balls, whether the screw is rolled or ground, etc. I will say that the
static friction of the NSK ballscrews that I adapted to my Bridgeport
is EXTREMELY low, in the range of 1-2 Oz-In! This is not literally
2 ballnuts back to back, but a single block with two ball tracks ground
into the interior, with a slight offset between the two track's pitch.
It is preloaded by putting the right size balls in the tracks, after VERY
precise grinding to size.

I have a similar ballscrew/nut set, I think by HiWin, but it is a smaller
.1" pitch unit that I use for the Z axis. It was new, surplus (no more of
these available, sorry). It has much higher drag, about 5 Oz-in or so.
That is still quite low. So, it may be that some anti-backlash ballnuts
may have low efficiency, but it is not necessarily true. Anyway, the main
reason for using them is the freedom from wear and backlash.

Jon