how tight should loaded ball nuts be?

[replicapro]

When a single ball nut is on the screw, it is loose enough to slide around the screw under its own inertia. When the double nut it on it is pretty tight and I can hear the ball bearing jumping and popping.

[CNCPlastic]

Replicapro I had the same question. industrialhobbies.com has a tutorial on adjusting them, and putting them back together too if you slip up and half the darn ball bearings fall out. lol IH notes to tighten them (nth) of a turn for various sized ballscrews and lists the preload in pounds also. Mine also felt tight with the correct preload and seem to make a racket but run smooth as silk under power.

[sendkeys]

[HuFlungDung]

"I can hear the ball bearing jumping and popping" doesn't sound too good. It could be an indication of one (or more) balls that are too large. If this is not a precision ballscrew, you may not have a lot of choice in what is acceptable, but don't expect it to ever "wear in". It won't.
I don't know what kind of double nut locking device you are using, but just jamming them against one another is not the correct method of preloading. They should be spaced with a precision spacer and then locked rotationally together. In this manner, the spacer controls the preload.

[ESjaavik]

My balls also make a rattling sound. Err...I mean nuts...that should be ballnuts.
I think it is the balls entering an running through the return circuit. And this is new
quality nuts like THK and Star.
Preloading low quality nuts will not be the same as nuts made preloaded. It's the same
as preloading a standard ball bearing, it will increase the wear because the balls are
riding up against the side. When made for preloading the right shape is ground in to
make the balls fit the groove when loaded. Some are preloaded by using oversize balls in a nut that is not split.
You can minimize backlash by mounting 2 nuts like you do, just don't overdo the preload. When the backlash is small enough to not be a problem, your preload is high enough. And don't forget that there is no use having a screw+nut without backlash if the end bearings have backlash.

[replicapro]

I dont really know how to measure backlash, so I wont even say I have some or dont. I know on my lead screw I can rotate the hand wheel from 0-10 before the thread catches again when revearsing direction. When I rotate a single ball nut there is no play at all. So I guess the question is should I even bother with a double nut if im not getting any back lash with a single?

[Noah]

My McMaster ballnuts were doing the same thing under load, but I noticed that rolled THK screws with similar accuracies were not doing this at all. Part of this just points to the THK's as an awesome design, but I also noticed that the THK's use lots and lots of grease. Why don't the rolled ones from other manufacturers do that. Do you think it would help if we pt grease on the screws. I put lightweight oil on mine, but that just reduces friction, it is not preserving the balls.

[ESjaavik]

Replicapro: Use a dial indicator fastened to the table with the plunger against a fixed part of the machine (or vice versa). Feed one direction watching the needle. Stop when at a convenient point like zero. Reset the handwheel to zero. Feed a couple of millimeter further in same direction, then back again until the handwheel is at exactly the same setting. The difference in reading on the dial indicator is your backlash.

[replicapro]

Thats good to know. I guess when I finish installing the ball screw assembly I can add a loaded nut later if I notice backlash.

[IndHobby]

Popping and clicking is more or less normal in a dry nut. If you pack it with grease it will go away for a while but it soon comes back. Here’s the catch, ballnuts like to be oiled NOT greased. Sorta’ a catch 22, mount the nuts where you will never see it again, then oil it regularly.

Here’s what we’ve tried and are now do on all of our custom mills. We figured out how to mount a one-shot oiler to the mill and plumb it to all 3 nuts. Once a day, pull the handle and you’re good to go. It’s actual pretty cool, and works very well. Even Rockford thought it was pretty neat.