Best lubrication for ball nuts

[Kitwn]

When I first upgraded to ballscrews about 4 years ago I lubricated them and the fully supported round rails with chain bar oil for the simple reason I had a 5L can of it and no chainsaw any more (Oh, I do miss my chainsaw).

When we moved to Tasmania I didn't bring the bar oil and was told locally I should use a lithium based grease. So I got a spray can of it. Gooey white stuff.

After suffering a few stalls I took the machine apart and found the ballscrews and linear rails were all very tight, presumably glued up with the new grease. Liberal spraying with WD40 got everything moving again (I didn't take the ballnuts off the screws) but am now at a loss for the best lubrication to use. What does everyone else recommend?

[dazp1976]

For luibricating I'm using slideway oil ISO 100 / Waylube 100. it seems to work very well.
To clean any surfaces I use teflon based spray such as GT85.

Grease attracts too much filth.
WD40 attracts dust/filth and dries bearings out.

[Neale]

Grease is fine in faster-running bearings where a bit of warmth helps it flow but in slow-moving bearings it just ends up drying and clogging. I use whatever is in the oil can - usually engine oil - as the loadings here are very low. You almost need the oil to prevent corrosion rather than lubricate as the motion is more rolling than sliding. Chain saw oil and slideway oil are both fairly sticky so they stay where they are put - not sure if this helps or not here!

[Robin Hewitt]

If you are pumping oil to it, bicycle oil.
If you visit it once a year, gearbox oil.
If it's completely inaccessible, grease

[Kitwn]

Thanks for all the advice. I was concerned about grease collecting dust, these screws are quite exposed, and WD40 is always something of a mixed blessing in many applications it would seem. The chain bar oil seemed reasonable to use as it is designed not to fly off moving parts. It's also cheaply available at most hardware shops in Australia.

The ballnuts are drilled for grease nipples but don't come with them. Should I really be fitting nipples and buying a grease gun? Will new grease applied in this way push out any dust that gets in? I was rather put off by my experience with the aerosol Lithium grease but don't have the experience to know what's best.

Yesterday I found some slight backlash in one of the long axis ballnuts so it looks like I've been too lax with the lubrication recently and have already done some damage. I'm assuming (hoping) the screws themselves are OK and have asked Fred at BST Automation for a quote for 2 new ballnuts. I will have to do a better job of looking after them in future!

Thanks again

Kit

[Robin Hewitt]

The concern with grease is that if you don't have enough load then the balls stop circulating and start rubbing.

Ballscrews bed in and develop backlash. The cure might be springs rather than lube.

[Kitwn]

The concern with grease is that if you don't have enough load then the balls stop circulating and start rubbing.

Ballscrews bed in and develop backlash. The cure might be springs rather than lube.

Thanks Robin. I spent most of yesterday evening searching for info online but as ever YT and Google are full of conflicting ides from 'use light machine oil' to videos of grease oozing out of the ends of the bearings after injection with a grease gun to comments about too much grease preventing the balls circulating. It seems to depend a lot on the individual circumstances, including load as you say.

I think it's fair to say my machine is quite slow running (5m/sec is my normal max cutting speed) and lightly loaded (I cut wood with 6mm tools) so an oil rather than grease look like the best option. I did find a Mobil product that is made for machine ways and was recommended for ballscrews but the minimum package size is 16Kg and would have to be delivered so I think that would be a little over the top.

Replacement ballnuts are cheap enough so I've ordered those. Only one is showing backlash but I plan to replace both and then be more diligent with the oil. I can always use 2 nuts per screw and springs as you suggest if need be in the future.

Kit

[Robin Hewitt]

Cheap screws can be notchy. I wonder if customers complaining about backlash and demanding refunds cause the manufacturers to use tricks to tighten them up beyond reason.
I bought some cheap 20mm profile rail that is notchy. It glides tightly when you go quick but sticks when you go slow. It's wringing with oil, could be grit. The notch will support a 2.5kg weight but not 5kg. Luckily the finished block of 4 will be supporting more than 20kg so I should be okay.
Yesterday I bought a 500mm screw with nut and end machining for £16. Amazing bargains to be had if you are prepared to fix a few minor issues

[Kitwn]

Cheap screws can be notchy. I wonder if customers complaining about backlash and demanding refunds cause the manufacturers to use tricks to tighten them up beyond reason.
I bought some cheap 20mm profile rail that is notchy. It glides tightly when you go quick but sticks when you go slow. It's wringing with oil, could be grit. The notch will support a 2.5kg weight but not 5kg. Luckily the finished block of 4 will be supporting more than 20kg so I should be okay.
Yesterday I bought a 500mm screw with nut and end machining for £16. Amazing bargains to be had if you are prepared to fix a few minor issues

The only ballscrews I have any experience with are these three that I bought from Fred Lee at BST Automation about 3 years ago so cannot comment on the variable quality of other manufacturer's products. Until now I have never been able to detect any backlash and have been entirely satisfied with them. Fred has quoted what I see as a very reasonable price for replacement ballnuts and has asked me to send him details of the reference numbers stamped on the existing nuts to make sure I get the correct tolerance replacements. As far as I can tell the problem I'm having with this one screw is entirely due to poor maintenance on my part.

Fred's own recommendation is oil rather than grease.

[Kitwn]

OK, I might as well get the embarrassing bit out of the way.
There's nothing wrong with one of my ballscrews. I thought I'd checked everything for tightness and was convinced it was the screw/nut at fault. But after loosening the flange fixing nuts to rotate the nut to see the tollerance mark Fred asked me to send him and re-tightening them...no play, no backlash, no problem.

I've apologised to Fred for the time wasted and saved myself about $75AUD. I've also learned that every ballnut, even on these basic cheap models, seems to be assembled specifically to suit the machining tolerance of the screw and has a number scratched onto it indicating the tolerance. I'm quite impressed by that, but it does mean you need to deal with one screw/nut at a time if you plan to take them apart for cleaning and not have just one tub full of all the balls from all your nuts.

I've gone for Valvoline chain oil for lubrication as there doesn't seem to be any single preferred option.