Re: [CAD_CAM_EDM_DRO] How hard to rotate should preloaded ballnuts be, anyway?

Abby Katt wrote:

> Howdy Folks,
>
> I'm recomissioning a neolithic ORAC CNC lathe with modern CNC-controls
> (Mach3/new electronics etc) but in cleaning it up have run into a
> mechanical conundrum. The ballscrew along the long-axis is really stiff
> and gritty to turn, I've been cleaning it up with WD40, but so far to no
> avail. I'm beginning to come to one of those deadly-fatal conclusions
> where I give up and let all the little balls out...
>
> My question is - how hard is to to rotate by hand preloaded ballscrews?
> (I assume this thing is preloaded, it has a massive ballnut) It has some
> screws on the tubes through which the balls recirculate. Is it easy to
> open this and remove/clear/reinstall the balls, or is this just
> spherical-based-madness?
>
> The mounting block is also under tension, and also quite hard to turn..
> how tight should this really be?

The bearings and balls in the nut may be damaged by grit. My
scheme to get grit out of ballscrews is to smear axle grease
on the screw, and run the nut over the greased area. Then, wipe
off the grease, and inspect your rag. You will likely have tons
of tiny sparkling bits the first time. Repeat until the gritty
feeling is gone. Tou can then apply way oil or some other lube
to the screws.

Brand-new preloaded ball screws may be pretty tight, on a
machine this size, I would not be surprised by drag of a couple
foot pounds (sorry for the obsolete units, but my hands are
calibrated in these old measures). But, a gritty feel is
definitely a sign of contamination or rust. (UGH!)

Only take one ball return tube off at a time, and count the
balls. Also, mike them to detect alternating size balls. Some
manufacturers put spacer balls between the load carrying balls
to reduce wear by the balls rolling counter to the adjacent one.
If they are alternating in size, you'll have to sort them and
reload in the same pattern. it is also possible that the balls
in the two tracks may differ by a tiny amount, that is how they
adjust the preload. If so, you'll need to keep the two sizes
separate.

The thrust bearings probably should just be replaced if the
grease is contaminated or hardened.

Jon