Ball screws are a bit crunchy. :) What to do?

[Jim27]

Picked up a small CNC mill with balls screws for cheap. Travel is pretty limited at about 6" x 4" but otherwise it looks fairly stiff and has servo drives. Looks to be metric and has a Yuasa tag but haven't been able to find any docs on it online. It has been sitting a while and don't know the history. When I turned the ball screws by hand they were a little crunchy. Not sure if they are binding from lack of lube or if there is crud in the ball nut. Things look pretty clean so I am hoping it's just lack of lube. Haven't done anything else yet. Should I apply some lube and see if things free up or should I take things apart? Haven't messed with ball screws before.

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[Jim Dawson]

Is the ''crunchy'' feel coming from the ball nut, the thrust bearing, or the motor? I guess I would lube things up a bit, disconnect the motor from the screw and test again.

Some pictures would be good.

[gabedrummin]

Don't take the ball nut/screw apart unless you like chasing little ball bearings around the shop .Pull the motor and drive coupling off and try turning the screw by hand .I know you said it has servo drives are the motors possibly stepper and your feeling the rotor steps ?

[Jim27]

Definitely not steppers and the roughness is nothing like stepper cogging. Not sure what the roughness is from. Will apply some lube and see what is needed to disconnect the motor shaft - the coupling is a bit hidden.

[kawazuki]

Don't take the ball nut/screw apart unless you like chasing little ball bearings around the shop .

Agreed! You'll need a correct sized cardboard tube or metal pin / plug to replace the screw as you wind it out - it'll hold the balls in place. But if there is dirt in there, disassembly is the likely solution
in which case de-thread the nut off the screw in a plastic tub to catch everything. Re-balling the nut can / will try your patience!

[gabedrummin]

If the ball nut has return tubes that can be removed it might be possible to re-ball , most of the ball screws I have seen lately have a plasctic plug that presses into the internal track. The plug has to be orentented with the correct rotation for the race way on the end of the plug to line up correctly. Good luck sir.

[dazp1976]

Agreed! You'll need a correct sized cardboard tube or metal pin / plug to replace the screw as you wind it out - it'll hold the balls in place. But if there is dirt in there, disassembly is the likely solution
in which case de-thread the nut off the screw in a plastic tub to catch everything. Re-balling the nut can / will try your patience!

Shoving plenty of automotive grease in there while re-balling holds the balls in place -ish. The Universal joint type stuff, But yes... Patience.
As suggested, remove the control bits and test by hand first.

[CL_MotoTech]

The best way to go after this is to take the screw and nut out of the machine (assuming it isn't a thrust bearing issue), pump a bunch of thin oil or even a light solvent through the nut/s while turning the screw with the shields off. You can use some compressed air on them too. Then re-oil and assemble. Of course some nuts have to come off the screw to be removed, I have a tool as mentioned by others for that, but then I put the nut back on the screw once out and flush them as described. I just run the screw with my electric drill and hold the nut in the shop vise while cleaning.

I went through this a while back with my X and while I never found anything specific that came out asides from general dirtiness, the nut smoothed right up and has been working fine since.

[atomarc]

In reality, it's not that complicated to dissemble the ball nuts in entirety, clean the balls, clean the nuts and reassemble. It might seem daunting...but it's really quite easy. Doing it this way can identify any broken balls, etc, which aren't going to be repaired with a simple grease or oil flush treatment.

Stuart