A ball nut issue

DarkEdge · Nov 29, 2018

So I have a question. I'm assisting in the rebuild of an axis on a machining center, and someone pulled the plastic wiper on the end of the ball nut partially out to clean it. When I put it back together, the ball screw appears to be lifting it back up, and it's putting tension on the screw (it won't free spin down the screw once it makes contact with the wiper).

Is that wiper timed to the rotation of the screw? Before that wiper was pulled up, the nut spun freely down the length of the screw. Now it only makes it an inch or so before the wiper makes contact, and the nut comes to a stop. It still moves by hand, but not on it's own.

Any advice?

HuFlungDung · Nov 29, 2018

The wiper has to ride the groove properly, no doubt. It might be tricky to get it exactly where it was. But if it will still roll fairly easily, I wouldn't be overly concerned. It's not like it is actually wiping anything or it would never have freewheeled, it's more of a bulldozer to keep whole chips from getting in.

Larry Dickman · Nov 29, 2018

there should be set screws on the sides of the nut that hold it in place

DarkEdge · Nov 29, 2018

Thanks guys. I managed to get it most of the way seated and locked back in with the set screw. This is my first time tearing into a ball nut and screw, so I'm learning as I go.

Other Brother · Nov 29, 2018

If you stand the ball screw on end and it rotates by it's own weight it has lost the preload. You can also put a mag base on the ball nut and use a tenth test indicator on the screw where the balls ride. If you see more than .0005" when you change rotation direction it is probably time to send it out for repair. However, most CNC controls have a backlash comp for lost motion, or you can program the approach moves in the same direction on that axis.

machtool · Nov 30, 2018

Be aware the grub screws that Pin's the wiper. I you over tighten them, it just pushes / clamps the nylon wiper onto the screw. Guessing this was possibly your cause. I put a smallest dab of nothing stronger than Loctite 222. Set the grub screw, then back it off quarter of a turn.

Oldest trick for young players. If you clinch down like you would with a normal grub / set screw, you're clamping the wiper to the screw

Regards Phil.

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A ball nut issue

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