Destroyed ballscrew!!!?

[Corvus corax]

I have been spending literally all my disposable income (and some not so disposable) on parts for my machine, mostly off of Ebay. So far, aside form my mistakes, I've been getting along well. But today, one of the most expensive purchases I've made thusfar arrived on my doorstep, and was eagerly unpacked: My 48 inch travel ballscrew. Precision ground, C3, 1.25 inch diameter, the works. I paid almost $400 for it. It arrived in a PVC TUBE! The ball nut was used to support the assembly in the tube, and it must have taken some HUGE falls, because the nut is nearly frozen solid on the shaft. The worst part is, I paid a premium to get a screw that was NOS.

The balls appear to have been flatspotted, the nut will only move with a crunchy motion in one direction down the shaft. Try to go the other way, and the nuts locks like a ratchet. I rolled the wipers down the shaft a bit to see of something got into the nut, but it is clean. I flushed the assembly some with light oil, and nothing came out. There is some rotational play before the ballnut even engages, and though I cannot see any damage to the shaft, I'm sure the whole thing is FUBAR. I am absolutely devastated. I had a chance to buy many other screws which were even better than this one, but I passed them over. Now I have to find another screw just like this one- the machine is already coming together, and parts have been cut. I am absolutely screwed.

[JavaDog]

Not to be obvious, but please tell me you paid for shipping insurance?

[Corvus corax]

I'm pretty sure I did- but improper packaging is NOT covered. Its up to the seller to make this one right. I've dealt with UPS before on things like this, and the packaging was laughable, they REQUIRE 2 inches of crush zone around all shipments, regardless of size, and the ballnut was actually visible on the outside of the package when I received it. I could see where they taped the thing up after bashing the hell out of it. There was no padding in the package. I'm going to check, but I don't even think the ballnut will fit inside the tube- the top portion of the tube was broken or sawed in half to allow the assembly to fit inside, the ballnut run to almost the end of its travel to allow it to fit. I haven't heard back from the seller yet. I'm hoping they have another to replace this one, though I am dubious.

Is it possible that the screw, since its new, is simply "tight"? I cannot find any damage on the shaft...

[HuFlungDung]

I would get a large cookie sheet out, and remove the ball return tubes, and gently work the nut back and forth, letting the balls drop out slowly into the pan. Or, if you can run the ballnut right off the end, then do it.

It could be that some of the balls are caught in between the ball return tubes, due to improper assembly, and this could cause it to lock up. I really doubt that typical handling would have damaged the ballscrew into this non-rotating state that you describe, but I would imagine it would be bent if mishandled to the degree you described.

[Corvus corax]

I was thinking something along those lines- but... How do I get the balls back in? Also, I think I may have located the problem. In scanning the surface of the ballscrew carefully, I found spots of RUST! I'll bet the balls were funky before this thing even saw the shipping tube. There are no external ball return tubes for me to remove, unfortunately. Any ideas?

[cbass]

I really hope for your sake that it is fine.

If on the other hand it has been damaged, I can't help but think the seller/shipper is responsible, regardless of wether you paid for shipping insurance or not. The shipping company can not be faulted for something that is not properly packaged.

There's no point in shipping a 48" long, precision ground ball screw without proper cushioning and support along the entire legth of the rail (unlike support only in the middle, as you described). With that much unsupported weight, I would expect a bent shaft when it arrives to its destination.

If the issue with your unit ends up being due to shipping damage, I would take it up with the seller, assuming insurance will not cover it. If you get no satisfaction, go to ebay directly.

Good luck

Carlo

PS Come to think of it, I think ebay does cover improper packaging. You'll need to check.

[wisp]

Hiya Corvus, you say the ballscrew is 1.25" diameter? i SERIOUSLY doubt it was bent during shipping. You can not bend a 1.25" dia. ball screw to the point the ballnut sticks just by dropping it.

You really have no choice but to remove the balls from the nut. At the very least, remove one of the tubes, and examine the balls for rust, you can easily replace the tube with the balls in it. You really have to find out if the balls are rusty. If they are, just buy some more, they are not too expensive.

If the balls do not appear to be rusty, then clean the rust from the screw as best you can, and then REALLY grease the nut up, until it squirts out the seals. A lack of lubrication in the nut can cause the balls to slide rather than roll. If you plan to use an auto/manual oiler on the nut, then connect it to your oiler and run plenty of oil through it.

The balls could also be sticking in the tubes, another good reason to take them off to see if the balls roll easily through the tubes.

Best of luck.

[HuFlungDung]

Rust in the balls, nut or screw would explain a lot. I'd sure try to get my money back. There's nothing you can do to repair the pitting.

I've never handled a ballnut with internal ball return, so i'm not sure how they are assembled. Perhaps they load all the balls in with grease to hold them, then slide a close fitting dummy cylinder inside so none can fall out, then butt the end of the screw up against the end of the dummy, and screw it on through....very, very carefully.

[Corvus corax]

Here's a theory: The seller wanted to pack the ballscrew up, accidently ran the damn thing off the end of the shaft, picked the balls up off the floor, and just barely managed to get it back on in order to ship it. I still haven't got the ballnut off yet, but I'm VERY slowly trying to run it up to the end, as it only wants to go one way, and THAT end of the screw is where the threads end! I can get it to move backwards by jiggling, swearing, and getting about a 1/16 rotation out of it each time. I moved the stupid nut down the shaft the other way while fiddling with it earlier, by about 8 inches. This is a 1in 6 screw, so its going to take a while! The rust is very superficial, and is just a couple of small spots in the bottom of the track in the middle of the screw- no where near this area. I'll remove them carefully if I can get this thing sorted out. Otherwise, its going back! I've assembled plenty of engines before, so keeping little bearings held in place with grease is more of hobby than a task!

[HuFlungDung]

If you do get it apart, you should check all the balls by measuring their diameter. You need to adopt a micrometer technique that will allow you to measure consistently to one or two ten thousandths. Set up a series of bowls or something to sort them into different diameter classes. Either they should all be the same (within a tenth), or there should be two different size classes. If you find the latter, then reload with small ball, big ball in sequence.

If you find a few balls with a significant discrepancy from the norm (too large), set them aside and do not use them, as they could be the trouble makers.

[JFettig]

I suggest that you leave it as is untill you hear back from the seller. Some people would be stupid and that now that you took it apart, they wont take it back.

give it a couple days if needed.


Jon

[Corvus corax]

I've got the nut back in the same position where it started, and it looks as if its going to stay there. Pieces of broken bearings have begun dropping from the nut, and I'm dead sure the innards are lacerated. Its a paper weight. I was right the first time. The shock of being dropped in shipping crushed the bearings into sharp shards, which then had their way with both the screw, the intact bearings, and the insides of the nut. I'm going to leave it for now- I wish I could fix it, but it looks as if its a lost cause. All because someone was too lazy to pack the assembly properly!!!