re-loading ballscrews

[marx911]

I've read some posts about people reloading ballscrews with different size ball to tighten up the screw... my question is how to you get all the ballls back in? like on something like the standard thompson rolled screw .....just looking fo some basic ideas on how you go about doing this
Thanks
Mark

[HuFlungDung]

Mark,
What I do, is remove the ball return tubes. (Oh, work over a big cookie pan or something just in the rare case that you should drop one of the balls while doing this )

Then, drop the balls into the ball nut (with the screw lined up) one at a time, and push them into the ball track with a plastic straw. What works good is that red extension straw from a can of WD40. All you want to do, is push the balls down so they contact without leaving a big gap, which may happen if you try to "roll them all in". Once you have a full wrap of the screw completed, it will become kind of self supporting, and then you can slowly roll the screw a bit as you drop in each ball. Still, you might want to "tamp them" with the plastic straw.

Then, grease a few of the balls, and put them into the ball return tube until it is nearly full. Then, push the ball return tube into position and clamp it.

I'd recommend that you use large ball-small ball-large ball as you assemble the ball nut. The small ball serves as a spacer to help keep the large balls from jamming against one another, should you happen to actually achieve a measure of preload.

[marx911]

perfect...... worked like a charm ...the WD-40 straw was the ticket... thanks a bunch
Mark

[Mr.Chips]

I have a couple of questions about this practice.
1. If it really better, why doesn't the manufacture make tighter balls like this.

2. Does it shorten the life of the balls.

Hager

[balsaman]

I just ordered 3 ball nuts specially packed with over sized balls from Roton. Takes the backlash from .005 to .001 or so.

Eric

[Mr.Chips]

So over sized balls are an option with the suppliers.

Why don't they use over size balls all the time. Isn't less backlash always more desirable?

[kdoney]

It's the old trade off with friction. Oversized balls lessen backlash but increase friction. More heat, more wear and more torque on the motor. I think the key is to get consistent backlash so you can compensate for it.

[Mr.Chips]

I'm new to ball screws so pardon.

Couldn't you dial out the .005" backlash with the software?

Or is it sometimes .005" and then .003" and so on?

[HuFlungDung]

Mr. Chips
A large amount of backlash is bad all around. Although the software can make an adjustment, the mechanical looseness still does actually exist. This would have a serious effect on a climb milling cutter, should the chip thickness suddenly change from .005 to .010 thickness, for example.

Then, if you use encoder feedback directly on the screw (this was discussed in another thread lately), then the feedback loop has an almost impossible task trying to move the motor and maintain position. If instead, you use encoder feedback on the motor, then you've got poor quality positioning again on the screw. There's only one way to win, it seems, and that's to have everything perfect

Even though these inexpensive ballscrews can be loaded with larger balls, we are still bending the rules a bit: the contact angle of the balls within the screw races is quite arbitrary, and is most likely incorrect. This means we will not likely experience proper ballscrew wear and life. But, this is a tradeoff anyways, as most hobbyists will not be working their machines to the extreme anyways.

[Mr.Chips]

Thanks for the information.
Guess when it comes time to check the backlash then I'll cross the bridge.

It takes a long time to pick up this information in bits and pieces. Glad we have people in this group who have been there and are eager to share.

[eat]

sounds good does this mean a linear encoder
would be the way to go
on my way to go try the straw thing just putting the old balls back
but there must be a couple hundred of them
and rolling them in dosent seem to be working for me
by the way does anyone know the best way to clean the bearings on the end I will be making my own bearing holders with seals
can I take the seals out of the sides and just clean them
they are just a little gritty from sitting for years
when I looked them up the same ones cost 420.00 apiece for the 2
on the end
so I thought I might clean them since I paid 40 bucks for the ball screw and the bearings came with it

[HuFlungDung]

A linear encoder is an expensive route to go because they often require an expensive converter to convert the scale signal into encoder emulation. Double whammy.

If you are careful, the rubber shielded style of bearings can be opened. Slip a thin blade in between the inner race of the bearing and the seal, then push the blade in as far as you can towards the outer race. Give the blade a twist, and the seal should pop out. A moderate degree of distortion can be straightened out carefully, and the seal reinstalled after the bearing is washed in solvent.

You need to use mineral spirits to effectively dissolve the old hardened grease out of the nooks and crannys.