Leadscrew lubrication question

[RSG]

Hey guys!

I've been using my new mill for the last year now and have been lubing the leadscrews on the y and x axis with grease because upon examination that's what it was shipped with. Stupid me, never read the manual to see they need oil and are connected to the "one-shot lube".

Now (for the lack of a better explanation) I was experiencing funny stutters on the "Y" axis sometimes during a cut almost like a foreign object was caught in it. So I went back and read the manual and sure enough it says lube with Vactra 2 way oil, not grease, only the "Z" screw is to be greased. I wiped all the grease off the screws and lubed them with oil and the vibration feeling is gone and the saddle runs smoothly over the entire way so I think it's good now but my question is: Did the grease damage the leadscrew nuts by chance, causing premature wear?

[Harold_V]

Did the grease damage the leadscrew nuts by chance, causing premature wear?

Possibly. You may be able to make that determination by the amount of backlash the machine has. Unless it has ball screws, it will display some when new. If yours has worn, that amount would have increased. If you haven't noticed a change, you most likely dodged that bullet.

Note that while the majority of wear will manifest itself in the nut, the screw, too, wears. The chief difference is there's a lot more screw than there is nut, so the majority of the wear will be in the nut.

H

[RSG]

Thanks Harold, I looked at the screw closely last night after cleaning it and it appears to be good as far as I can tell. There is more backlash (especially now it's clean) so I'll look at tightening the nut a bit to see if I can reduce it. It's not bad IMO but I'll see if I can get it better becuae it was tighter with the grease.

[pete]

There's a very logical reason oil is preferred over grease on some types of machine tools RSG. If grease could be applied frequently enough and then forcibly flushed through with fresh injected grease and doing that often enough once it picked up wear particles or contamination there would probably be not all that much difference since grease is just oil in a thickened carrier. Quite a few of today's CNC machines use grease with a timed lubrication system as way surface and ball screw lubrication. But there designed from the start to be well protected from that contamination of picking up chips and coolant. A secondary benefit is the machines lubrication doesn't get washed into the coolant and then creating detrimental effects for bacteria growth in it. Oil on manual machines helps to flush out chips, wear particles etc even though it still has that issue on coolant equipped machines. Getting and keeping clean oil onto those wear surfaces is much more important for machine life than a less important coolant problem that can be solved in other ways.

Grease applied at random intervals on a machine not designed to use it does just about the opposite. The exception is that Z axis, grease or white lithium grease is usually specified for the knee screw because of it's vertical orientation. Oil tends to run off and more gets wasted than used. Most BP's and the clones have a coolant sump cast into the machine base. If you were to use it for what it was designed for any Vactra on the knee screw pretty much drains down the screw and right into that sump since there's a screened opening in the top of the machine base on any vertical mill I've looked at. The grease on the knee screw still isn't solving having to use oil on the knee ways though. So without an oil skimmer the coolant in those sumps also starts having that bacteria problem. Plus the knee usually gets moved much less with most of our machines than the table or spindle. I've seen many on YT using grease everywhere on manual machines and my guess is they think it's somehow better since it sticks in place. Logically thinking through why oil or grease is chosen for what property's it has might change there opinions. I second guessed the machine manufacturer many years ago thinking I was being clever. It cost me a very expensive motor to learn I needed to follow what people far more intelligent than myself were recommending for what type of lubrication I should be using. And as you've found, manual machines designed for oil lube can be adjusted far tighter with less backlash while still remaining smooth to operate with that oil instead of grease. Machine wear rates will also be much better. Run a machine on grease that wasn't designed for it long enough and high wear rates and scored way surfaces are inevitable. You haven't run yours that long on grease so it should be ok.

[RSG]

Thanks Pete! I know what you mean by oil draining into the sump. At the moment I'm not using the coolant system so it's ok but if you look inside from the opening you can see just how much oil is in there already after one year. One I am diligent about is cleaning sown way surfaces and leas screws often and re-lubing so if there was any wear from using grease it will be minimal. I'm om the right track now though as far as maintenance.

[pete]

Rich Carlstedt set me a couple of pictures, in one of them I spotted his use of heavy shop wipes laid flat around the bottom casting that supports the Z axis feed screw that collect the excess oil. That saves it from filling up the sump and becoming an all around pain to get out. Sort of adult diapers for incontinent young and old mills that leak fluids

[RSG]

LOL, good idea actually

[Low Flyer]

The nut and the screw are made from dissimilar metals by design. If they were made from the same material, they would try to bond (gawd) to each other. The nut is brass and the screw is steel. The brass is softer and will wear faster than the steel, even if of equal lengths.

But to answer your question, did you damage it? It's very likely that you did not damage it. It's not as if you were running it dry. You at least did lube it with grease which is better than nothing at all. I think your machine is fine, and I wouldn't worry about it, if I was you.

Gil

[pete]

Not to be pedantic, but these threads live on and get viewed by many entry level people Gil. I think you meant gall not gawd. Yes your 100% correct about the reasons for the dissimilar metals. But brass feed nuts would be almost to quite possibly never used on a machine of any quality. Bronze feed nuts while close to the same color as brass are usually machined from a bearing bronze alloy so they have far better durability than brass might. In some rarer instances even cast iron might be used as a feed nut since it has good self lubrication capability's. In addition the soft brass would tend to get chips and contamination embedded in them and then act much like a lap against the feed screw wearing them out much quicker. Since the bronze is a whole lot harder it has less tendency to do the same. With properly chosen and engineered materials those feed nuts are designed to wear out first instead of the much more expensive feed screws.