View Full Version : Chinese Ballscrew nut play

09-01-2019, 07:33 PM
So i bought 4 ball screws of different lengths. Two of them have play in them, and the other two are stiff and have a considerable amount of pre load they even don't rotate as easy while the others rotate freely. I never handled ball screws before, and i was wondering which of the following is considered normal behavior ? one nut if i give it a spin rotates +3 rotations and the other rotates 1 time and stops. Also what to do to fix the ball nut play ? I've read that i can Repack the ball nut with larger balls, if you find this as a suitable solution would you please point me to a seller on ebay preferably ?

10-01-2019, 01:57 AM
Are the ballscrews new Chinese ones or used? Do the ballnuts have dust wipers at the ends? Only after removing them you can see how easy is the nut rotating. If you tighten too much the wipers on a Chinese ballnut, it won't rotate freely anymore but doesn't mean the balls are preloaded..

10-01-2019, 02:57 AM
Yes they are new Chinese ones. I tightened the dust wipers and that eliminated all play in the nut. Before that it was moving you could say 0.5mm in all directions.

10-01-2019, 12:22 PM
I tightened the dust wipers and that eliminated all play in the nut.

That's not how it works, you'll just wear your wipers out, the only way to adjust play in a single ball nut is to replace the balls with a slightly larger grade, when rebuilding alternate balls should be smaller than the required spec to allow free ball rotation and minimise friction and wear.

- Nick

10-01-2019, 05:11 PM
0.5 mm of play is a lot. maybe they put the wrong ball size in. Get in contact with the vendor, probably he will send you the correct size balls. But anyway you want to first to take off completely the wipers from the screw for troubleshooting, then eventually take out one ball or all and measure them, etc. Putting back the balls in a nut is not an easy task but doable, there are videos on youtube on how to do it easier.

When I bought my ballscrews I asked for a few spare balls and they gave them for free. First thing I did was to take out the ballnut and balls, check for missing balls and clean everything. Sometimes there is swarf inside left from machining and the nut is not rotating as it should be, sometimes a ball could be missing..

11-01-2019, 04:18 PM
There should be about 0.05 mm play. The vendor has to match the balls to tune the free play / ease of rotation depending on the fit of that nut on that ballscrew.

Nominal ball size (for 1605 1610) is 1/8 of an inch (3.175mm) but they can be tuned up or down in something like 0.02 mm steps. Some vendors will then engrave this number on the ballnut(Fred at BST for example). So they may be marked +2 for 0.02mm oversized.

If anyone has links to these tuning sets I would be interested as one of my spare ones could be dialled in better. Seem to remember Lee had some ??

11-01-2019, 08:53 PM
I bought some balls and for more than 4 hours i was unpacking and repacking the ball nut but non gave me smooth motion & a tight fit so at the end i gave up and put the original balls back and will install the ball screw as it is since most play is in the 400mm Ball screw intended for Z axis & gonna change it at a later time for another one. I guess that's what you get buying cheap Chinese screws :(

11-01-2019, 09:33 PM
I bought some balls

If you don't tell us what you bought and exactly what you did it's pointless mentioning it at all!
Did you alternate new size with Under-Size when re packing?

11-01-2019, 10:10 PM
The sizes i found were 3.12, 3.14mm and 3.16mm and the ones that were packed in the screw were 3.10mm. i tried each by them selves @ 3.12mm there was wiggling so i increased the ball size the wiggle decreased but the at some points along the screw it got harder to turn then i tried alternating with 3.10 but no luck 3.12 & 3.10 wiggles & 3.14,3.16 with 3.10 wiggles and get harder to rotate at some points along the screw.

11-01-2019, 10:27 PM
It sounds like you've got cheap rolled ballscrews, which as you've discovered, are not great for accuracy.

The only thing you could do (other than buy a new screw), is put the bigger balls in, and hope they wear/burnish in the tight spots on the screw, but you do risk damaging things if thing are too tight. If you do try this approach, I'd make sure things are kept very lubricated to help flush any debris out, until you are happy things have bedded in nicely.