[CNC] Ball screw lube?

[DTJ]

My 12mm ball screw & bearing mount order has arrived from Robotdigg. Less than a week between order and delivery,  they look OK.

Do ball screws need lube? My machine runs dry (no coolant or misting) and I only cut plastics.

Shall I run them dry or give them squirt of silicone oil or WD40 occasionally?

[bitslice]

Why do people still consider WD40 for anything requiring lubrication? Maybe if the part is constantly getting wet, other than that, no.

Grease will just attract gunk, it's only suitable for where you can seal in the bearing.

Use a normal low viscosity motor oil and wipe it down occasionally.


A pro guide if this is going on the next rocket to Mars
http://www.thomsonlinear.com/downloads/articles/Design_Engineer_Guide_Selecting_Lubricant_Ball_Screws_taen.pdf

hah, oops, didn't realise the next chap had posted this too

[Ian.M]

Don't use WD40 - it gums up and traps dust to form a grinding paste.
See http://www.thomsonlinear.com/downloads/articles/Design_Engineer_Guide_Selecting_Lubricant_Ball_Screws_taen.pdf

Felt wipers either side of the nut, + a squirt of light machine oil into the nut, or between the wiper and the nut while in motion on a daily basis when in active use should be OK.   However if you are using the machine for production, you'll probably want some sort of continuous or periodic automatic oiling system.

[CJay]

Not sure I'd want to use anything liquid on it with a cutter that makes dust, maybe one of the 'dry' lube products?

Is there no advice on robotdigg's site or in application notes for similar leadscrews?

[Koen]

As the nut does not contain a lubrication "tit", it should be pre-greased by the manufacturer. Leave as-is.

[bitslice]

As the nut does not contain a lubrication "tit", it should be pre-greased by the manufacturer. Leave as-is.

umm, that's fine if something is spinning in one spot, like an axle,
but this is dragging the greased balls up and down a foot of screw thread, I'd suggest that any grease applied at manufacture is going to be wiped off on that rod eventually.

If the balls were in their own isolated compartment, then different story.

Although you do make the point that some ball screw bearings come with a grease nipple, but I suspect that's a cost saving on those that don't, rather than a recommended maintenance idea.
It's not going to crash and burn either way.

[Koen]

I do not understand your reply. The balls are in their own isolated and greased compartment protected from external elements by two seals.

[Fraser]

LUCAS White Lithium Grease NLGI #2 as used on my lathes. Works well for me. Great stuff.

Fraser

[langwadt]

I do not understand your reply. The balls are in their own isolated and greased compartment protected from external elements by two seals.

in a regular round ball bearing the balls and races are both inside the seal

in a ballscrew the screw is outside the seal

[ChunkyPastaSauce]

As the nut does not contain a lubrication "tit", it should be pre-greased by the manufacturer. Leave as-is.

umm, that's fine if something is spinning in one spot, like an axle,
but this is dragging the greased balls up and down a foot of screw thread, I'd suggest that any grease applied at manufacture is going to be wiped off on that rod eventually.

If the balls were in their own isolated compartment, then different story.

Although you do make the point that some ball screw bearings come with a grease nipple, but I suspect that's a cost saving on those that don't, rather than a recommended maintenance idea.
It's not going to crash and burn either way.

On smaller ballscrew nuts, the lubrication point is often a simple hole, rather than a nipple. Some screws you lubricate at the seal or the screw.

[Koen]

in a regular round ball bearing the balls and races are both inside the seal

in a ballscrew the screw is outside the seal

I get that but it's the role of the seals to wipe the dust and the role of the grease inside the nut to keep things smooth. Same thing for guide rails, wipers keep the carriage balls sealed from the rails dust and carriage balls are lubricated from the inside of the carriage.

Adding anything to the screw or rail itself will only get it wiped by the seals.

[Ian.M]

Unfortunately dust will stick to anything except a dry film lubricant and lubricants containing significant quantities of solid particles are not recommended as they tend to clog the ball return path.  Once you have a clog resulting in balls rubbing on each other under load, the wear will rapidly become excessive as sliding point contact lubrication is extremely challenging.

If you have abrasive dust on the thread and you let any seals act as wipers, the seals will soon either be worn sufficiently to be worthless, or will be so loaded with abrasive that they lap the thread till its sloppy.

A total loss lubrication system with sufficient light oil flow to keep the ball nut flushed, and external wipers from which excess oil is allowed to drip into a catch container, + a slotted enclosing cover with a downward facing opening for the ball nut mount support leg would be your best chance of minimising the buildup of abrasive dirt in the system, short of arranging sealing flap(s) on the cover and positive pressure ventilation.

[Koen]

As usual, we have to keep it in context. He mills plastic on a machine with 12mm ballscrews as an hobbyist. He doesn't need to make any changes now. Add covers when the time allows, change grease when the time comes. Keep it simple.

[bitslice]

As usual, we have to keep it in context. He mills plastic on a machine with 12mm ballscrews as an hobbyist.

So we are not going to develop the bearing wear sensor circuit and the oil viscosity meter?   

[Ian.M]

Plan B - if you cant be arsed to add felt wipers, dust covers and keep them, lubed,  buy a spare set of ballscrews and put them on the shelf for future servicing.  If the lifespan you get out of the first set is too short, you can add a wick oiler, wipers and covers when you fit the replacement set or if compatible ones are still available at a good price, just treat them as a 'wear' part and order another set of spares each time you replace the ones on the machine.

A soft brush attached to the carriage contacting the screw from the bottom either side of the nut (on a spring mount so it self cleans on every direction change) to reduce chip and dust build-up at the nut would be an easy cheap improvement if you are going to run them dry or nearly so.

[Koen]

His nuts already contain nylon wipers.

[Ian.M]

*GREAT*!

 A nylon wiper loaded up with glass fibre reinforcement dust or Titanium Dioxide pigment dust, makes a lovely lap. There should be plenty of slop after a few hundred operating hours.

The O.P is routing/milling plastic enclosures and parts (previous topic) so the chances of producing abrasive dust are significant.  If he was cutting Vinyl or similar soft plastics, it would be a different matter.

[Muttley Snickers]

If the OP’s ball nuts and screws are anything like the ones I received from Asia the nuts do not incorporate wipers of any type and as Ian mentioned it is a very good idea to add them if possible, there's no grease or oiling ports on these and the two holes you see on the top of the nut in the second picture are in fact very loosely tapped threads with small grub screws for the retention of the nylon insert and may be used to adjust any backlash, these screws should be addressed with Loctite or similar compound during adjustment otherwise they may eventually come loose and fall out.

Fortunately a very close friend of mine is a design engineer with a large bearing manufacturer which is also one of my best customers, based on his inspection and advice I nominated to make my own bearing blocks and used Nachi sealed bearings for the lead screw ends, I also added felt wipers to each end of the ball nuts which meant making a retaining sleeve and washer, I made these caps out of PTFE-Teflon as I have stock piles of the stuff and also make my own hammers with it, these are mostly left overs and off cuts from that same customer.

[DTJ]

Thanks for all the ideas guys.

I've just installed one of the screws and it runs fine. A little noisy but I think its mainly the stepper and framework resonating.

It looks like the way to go might be to run the ball screws either dry or with a tiny amount of light oil. The X & Z axes are above the work so they stay quite clean. The Y axis is under the table, I might need to add a little more shielding to keep it completely covered. Realistically the screws are unlikely to see more than a 100 hours over the life of the machine so hopefully they'll survive.

Brushes would be nice but I think shielding will keep the crud away altogether.

[ChunkyPastaSauce]

I have these miniature ballscrews in a machine. At least on these, the oiling hole is on the flange (see drawing)

[ChunkyPastaSauce]

Realistically the screws are unlikely to see more than a 100 hours over the life of the machine so hopefully they'll survive.

A typical ballscrew has a hour service life something like 100-300X that... you should be fine even without oil unless they are exposed to something really really horrible like carbide grit, something corrosive+extended sitting, or material locking up the balls. Also, the assembly was probably shipped with a light coating of oil already to prevent corrosion during storage.

[Koen]

*GREAT*!

A nylon wiper loaded up with glass fibre reinforcement dust or Titanium Dioxide pigment dust, makes a lovely lap. There should be plenty of slop after a few hundred operating hours.

Then he should be vacuuming the dust at the endmill to avoid fine particles in his lungs anyway.

Realistically the screws are unlikely to see more than a 100 hours over the life of the machine so hopefully they'll survive.

They'll live don't worry. You'll even find them to be incredibly resilient. The best way to know how something is done is to look at the industry solutions at that price point, for that application. Forum topics always drifts to quotes from SKF and Schneeberger service manuals like you're milling Titanium 365/24/7 on your Hermle C62.

[DTJ]

I have these miniature ballscrews in a machine. At least on these, the oiling hole is on the flange (see drawing)

Mine are cheap chinese knock offs (not nice SKF units). They have the same lube holes on the nuts.

[Koen]

If the OP’s ball nuts and screws are anything like the ones I received from Asia the nuts do not incorporate wipers of any type and as Ian mentioned it is a very good idea to add them if possible, there's no grease or oiling ports on these and the two holes you see on the top of the nut in the second picture are in fact very loosely tapped threads with small grub screws for the retention of the nylon insert and may be used to adjust any backlash, these screws should be addressed with Loctite or similar compound during adjustment otherwise they may eventually come loose and fall out.

The nylon inserts are your wipers. They aren't there for backlash. Yeah you can screw them tighter to the ballscrew and it will give you the feel of less backlash if you move it by hand but it isn't their role nor will it last nor does it have any impact on the balls in the nut.
The nylon comes loose and falls out because it's made to be changed whenever it shows wear. Which might be in two years as an hobbyist.
You don't have an oil plug because you won't need one. The balls are greased between both orange plugs by the manufacturer.

[DTJ]

*GREAT*!

A nylon wiper loaded up with glass fibre reinforcement dust or Titanium Dioxide pigment dust, makes a lovely lap. There should be plenty of slop after a few hundred operating hours.

Then he should be vacuuming the dust at the endmill to avoid fine particles in his lungs anyway.

Realistically the screws are unlikely to see more than a 100 hours over the life of the machine so hopefully they'll survive.

They'll live don't worry. You'll even find them to be incredibly resilient. The best way to know how something is done is to look at the industry solutions at that price point, for that application. Forum topics always drifts to quotes from SKF and Schneeberger service manuals like you're milling Titanium 365/24/7 on your Hermle C62.

I've put slow spindle on it and I use 2 flute routing bits. I'm sure there's some small dust particles created but most of the debris is large & chunky.