Rebuild Ball Screw?

On my '00 VF2 I recently noticed that in a small portion of my Y travel that there is a crunchy noise like I have chips in my ball screw nut.

I pulled the covers and the ball screw is clean and I couldn't see any rust, pitting, or chips on it.

Is this a ball screw nut issue? Is it something that I can just rinse out, or should I look at having it rebuilt? I imagine this wouldn't be a DIY project?

All you can really do is replace the balls. A specialist company may be able to regrind it and use larger balls. Typically, the balls wear more than the screw, so its worth a try.

Hard to say what is wrong without taking it apart. The problem being in a particular section of the screw says screw, but if nothing is visible I would say it must be something else. If you unbolt the nut from the table then you can feel the preload and if it changes as you spin it up and down the screw.

How much is a new screw? New balls will be around $300-$400 by the time you are done, it will take you many hours over a couple trys, and it will not be near as good as new. Pulling the balls out and putting them back in isn't a big deal but there are a few things to know about. For the price I wouldn't think of having it rebuilt, just buy new if you have to.

It has been my experience that the screw doesn't wear, at least on my 20 year old drill/tap mill I reballed.

Possible that it's in one of the Y bearing trucks, unlikely it's in a thrust bearing if it's just a small part of the travel range. Since Y travel's only 16", and the table covers much of the screw, can you get a visual on the section of the screw that would be engaged with the ball nut when it makes noise? It would have to be near one end of the travel range or the other, right?

Any chance there's a bit of sheetmetal getting rubbed, rather than it being the ballscrew? What does it sound like (aside from "crunchy"), and how loud? How about recording it and showing the ballscrew, and posting for others to listen to?

Thanks for the replies everybody. So the consensus is that it is likely a ball nut issue or possibly a truck bearing?

I've never reballed one of these before and searching online really didn't yield me any "how to" information on how to do it myself. If any of you have any reading material on how one would go about doing it, I'd be appreciative.

Milland,
You are correct in that the noise is towards only audible when the table is towards the back of the machine. You are also correct in that the noise is significantly less audible when the way covers are removed. I can still hear it, but it is a lot less noticeable.

As for the noise, it sounds just as if you had crud in a bearing. I'll try to take a video of it this week. Right now it is running some parts, but I need to make time to get it fixed.

Thanks for all the help guys.

CGornet said:

I've never reballed one of these before and searching online really didn't yield me any "how to" information on how to do it myself. If any of you have any reading material on how one would go about doing it, I'd be appreciative.

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There's a fair number of posts here on the subject, some good ones are from DavidScott.

One thing to consider is the cost of downtime. If you are sure it's in the ballscrew, perhaps you can buy a new replacement and rebuild the old screw as a backup. Or find a used screw, repair/reball it, then swap it in.

There's some ballscrew systems where a big ball/little ball alternating load is used to help prevent ball-on-ball skidding. I don't know if anyone's conclusively stated that Haas screws use this method, but if they do you have to measure the balls when they're out of the nut and segregate them.

As the difference can be very small, good micrometer technique will be required, or a go/no-go gage can be made by stacking the right gage blocks together to form a "tuning fork" arrangement, where the smaller balls just slide through the gap, and the large will not fit.

Thanks Mud, here is the post I did figuring out how to do it my self. IMO if your time is not free and a new screw is under $1000-$1500, depending on the value of your time, I would just buy a new screw and be done with it. Do make sure you know what is wrong before tearing into it to avoid screwing up what isn't broken.

Are you sure it is not the thrust bearings? My '91 had thrust needle bearings which disintegrated and the cage started wearing into the shaft. I changed to the later style angular contact bearings.
If you disconnect the thrust bearings you can move the table along the track to see if it is the truck bearings or turn the ball screw and see if the problem is there.