Ballnuts

[Web Goblin]

I have came to the conclusion that ballnuts were made with the single purpose of making my Sunday afternoon a disaster.
Aftertrying to fit one to a ballscrew this afternoon it jammed part way on and wouldnt go any further. So I unscrewed it and reversed it to try from the other side. Same result, it jams part way on. So decided to take it off to have a look at it and found that some of the balls had gotten past the centre seals of the double ballnut and came out the centre. So I have about 20 balls lying on my bench at the moment and I`m not sure which race they came out of. I think the only way to be sure that it goes back together is to take all the balls out and start again. That should provide a few hours of fun.

Ian

[Jonathan]

At least a few hours! I think you should machine a cylinder just under the minimum diameter of the screw (doesn't need to be accurate). You can put that inside the ballnut and then poke the balls in one at at time, making sure there's no gaps.

If it's a preloaded ballnut you might find it has two different size balls, OoOoOoOoO sort of thing. I'd measure them just to check.

[Web Goblin]

Jonathan,
I still have the tubular sleeve that came with the nut so I can use that. It is a double nut so I am going to split it and try to do each half seperately. Hopefully this will be alot easier. I am going to get some light grease tomorrow as well so that I can use it to "glue" the balls in place. I can always wash it out again when the nut is assembled. I didnt know that some nuts had different size balls. I need to check that as well.

Ian

[M250cnc]

Ian,

Use a scriber with a dab of grease on the end to pick up the balls and put them in place.

You need to turn the mandrel that came with the nuts to rotate to move the balls down the channel.

Please do not ask how i know how to do this.

Using grease is OK to use as a lubricant as my nuts came pre greased, and unlike oil it tends to stay around.

Phil

[Robin Hewitt]

Check the end of the screw for burrs where the helices start, give them a few swipes with a needle file regardless. Nowt like a bit of burring to misplace your balls.

[Web Goblin]

Thanks for the info guys. I will have a go at it later this week.
I have been ding a bit of work on a lathe that a bought a short time ago. Just finished wiring up the inverter tonight and I`ve got it running!
Runs nice and smooth too. Need to fit the guards back on and make a new one for above the belt drive because I dont like the one that came with the lathe and then the next plan is to modify the frame covers to add some extra storage and maybe fit a suds pump.

Regards

Ian

[Web Goblin]

I have finished off rebuilding the ballnuts. I ended up doing all three of them and it took me about 20 minutes per nut which wasnt too bad. Fitting them on the ballscrew is a different story. When they screw on they seperate. What I had to do was tighten them together with some large grips and fiddle about with the keyways to get them together. Its a right PITA. They tighten up quite a bit when together and take more effort to move them along the screw but I suppose thats the price to pay for zero backlash. The thing I`m really not impressed with is the end seals. They are made from hard material like nylon and held in place with two pointed grub screws set 180 degrees apart. Its really crappy. I think a softer better fitting rubber material would do a far better job of sealing the bearings and sweeping the screw and would stay in place better. I will try to post a pic later to let you see what I mean.

Ian

[M250cnc]

Fitting them on the ballscrew is a different story. When they screw on they seperate. What I had to do was tighten them together with some large grips and fiddle about with the keyways to get them together. Its a right PITA. They tighten up quite a bit when together and take more effort to move them along the screw but I suppose thats the price to pay for zero backlash.Ian

In my case when i used double nuts they were too slack, i looked around on the net and found that they should be sprung in the middle. So i modified two big belleville washers and they seem to work well

The thing I`m really not impressed with is the end seals. They are made from hard material like nylon and held in place with two pointed grub screws set 180 degrees apart. Its really crappy. I think a softer better fitting rubber material would do a far better job of sealing the bearings and sweeping the screw and would stay in place better. I will try to post a pic later to let you see what I mean.

Ian

Those seals are really only good for keeping out crud while they are being built into the machine, what you really should be using is sprung ball screw covers, if you fail to do this then they are gonna wear/bind sooner rather than later.

Phil

[Robin Hewitt]

Another vote for springs, I preload to 1/4 ton and they are really smooth with truly zero backlash. The spacer shim gives low backlash not zero, it can't compensate when they bed in. It shouldn't be hard to reassemble the nut though, is there any possibility you muddled the spacers up?

[Jonathan]

Another vote for springs, I preload to 1/4 ton and they are really smooth with truly zero backlash.

How much less smooth are they than a single ballnut? I'm thinking of doing this with the spinning nut idea on the router.