Repacking ballscrews/ballnuts



then....
Thinking about it further, that third contact point would always be against the nut groove, scuffing against it at a point in the arch that the larger balls would otherwise never touch excepting for their preload.....
And so......me thinks the 'every other ball is sized smaller than the others deal' is most probably just an old wive's tail.....
--
SVL






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On Fri, 23 Jun 2006 21:29:48 -0700, "PrecisionMachinisT"

I'm wondering now too .... I think I recall they we used them but cannot for the life of me recall assembling them but suspect that I did ... perhaps my vague memory fails on me doing that bit of assembly. Perhaps different makes differ too though ...
The bearing supply house is the ticket....
--
Cliff

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Ralph,
    Precison ground ballscrews are packed with balls that are sized specifically for the grind fit of the ball nut. Particularly if the screw/nut has been reground. The balls are sized in tenths. so you normally can't just by a bag of .250 balls from mcmaster-carr etc... you can probably go over to Ballscrews Inc (or something like that) they are in San Jose, and get them to at least size the balls you currently have, and maybe if you are lucky sell you a package of 100 balls. If they are exactly .250 then you can get some from Mcmaster-carr.
Don't use WD-40. It is not a solvent, eventually it will turn into a glue. Use MEK or acetone as a degreaser/solvent. The lubricant will be way oil if you are going to use it in a machine that has a lube system. You don't want to mix greases & oils, otherwise you get sludge. Otherwise use a moly based grease.
Re-install the balls by removing one of the sheet metal recirculation covers on the nut, and droping the balls in one at a time, as you rotate the screw. You will want to carefully leave one ball less than tight (a little slop in the recirculation cover) to finish. Otherwise it will bind when you screw the cover back on.
Make sure the entire nut, covers and ball is absolutely clean, otherwise you will destroy the screw, nut, or bearings on the first rotation.
If you can get to technical engineer at NSK they can give you better instructions than I, and give you specifics on the type of grease they use, exact numer of balls, material etc...
ca
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If so, you may want a specially pure form. Beware of fire too.
--
Cliff

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