Re: [CAD_CAM_EDM_DRO] tighten my ball screws

Karl Townsend wrote:

> My old CNC mill, Excello - bridgeport type, needs some attention to reducing
> backlash in the ball screws. What can be done to reduce backlash, short of
> replacing them?
>
> I'm tempted to try taking apart the ball assembly and cleaning and
> tightening. Will the whole thing fall apart,leaving me with a pile of ball
> bearings?

You can take the screws apart. Most modern antibacklash ballnuts have
no adjustments. You can't 'tighten' them. The only way to reduce backlash
is to put in larger balls. It may be that the balls have ben worn down so
much that just replacing the balls with the correct original size will make
it nearly free of backlash. One problem is that the factory may have fitted
special ball sizes to set the correct preload, something like 3.03 mm.

The nut will not 'fall apart', but you WILL have a screw, a nut, and a pile
of ball bearings when you get it apart. External return tube nuts can be
easily reloaded by just dribbling balls into the holes where the return
tubes go while slowly turning the screw to draw he balls into the track.
You need to count the balls so you know how many to put in. If you are
short a couple of balls it can cause jumpy motion, if you have too many,
it can bind up and wreck the screw and nut.

> Or, are there places to send ball screws out for rebuild?

Yes, many of the ballscrew suppliers have rebuild facilities. They regrind
the screw and nut, if needed, and replace the balls. They will generally
run the screw on a testing machine after the rebuild to verify the accuracy
of the screw, and the smoothness of the motion.

Jon