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Thread: CNC's with grease lubrication?
04-03-2007, 07:05 PM #1
I was talking to the Okuma tech about greasing my CNC mill. He was saying to grease the machine every six months with a quarter of a pump of the grease gun in each fitting. His theory was that too much grease will fill up the races where the balls ride and cause the balls to slide rather than roll through the races. Has anyone heard this? How often do you guys lube your machines?
04-03-2007, 07:43 PM #2
Never heard of that. I have a hardinge that uses grease, and they say one full pump for each fitting, after you feel resistance. Never got any warning about too much grease. My guess is on those linear guide ways, you have a little rubber wiper that wipes most of the excess away, so big globs of it would never get to the rollers. Don't know for sure, though.
04-03-2007, 07:52 PM #3
strange sliding theory.
I suppose if the balls are nearing the end of their life they may not touch the race at all so it cant roll... only slide..
6 months is normal .
we have only one machine with grease lubrication,
we converted it to auto oil lubrication.
04-03-2007, 09:01 PM #4
naw....we all wished lubing a bearing made it work that easy....(sliding not rolling)
I can't think of any bearing in a cnc(spindle /way/ballscrew ends )that isn't either pre-loaded or under load from weight/gravity.
04-04-2007, 02:37 PM #5
if u guys read some of the presicion linear guide litriture it does warn u about over filling with grease for high speed - light loadings, but for cnc carrage i cant see it being a issue?? but i know its bad for high grade spindle bearings to be over packed with grease so maybe hes onto something???
04-04-2007, 05:13 PM #6
Yes, I've definately heard the "sliding" explaination before and have been told that a "dry" rolling element bearing will run longer than the same that is overfilled with grease which causes the roller to skid.
I replaced my VMC's spindle bearings. They are Class 7 and required something like .3 grams of a special Kluber isoflex sumpin'or anuther. Not knowing what .3 grams of grease looked like, we used a postage scale to weigh it out. It turned out to a small "drop of grease". Basically nothing.
My VMC alarms at grease intervals of 600hrs I believe.
04-04-2007, 05:37 PM #7
Got a set of matched pair spindle bearings, came with 2 tiny tubes of grease and a big warning label not to put any more grease into the bearings, but one and only one tube / bearing.
At $680/set, I'll take the mfg. advise.
04-04-2007, 09:25 PM #8
I'll stick with what the service manual says. Btw the grease is for the Ballscrews and Linear Guides.
I really don't mind the grease system. I've got two other machines that use grease and one that has an auto oiler. At least with the grease I don't have to worry about plugged metering units.
04-04-2007, 10:27 PM #9
if we track the oil level in a centralised oil lube tank on a daily basis, we can easily make out when we have a clogged cartridge or when we have a line leak etc .
you cant do that with a grease system .
when you do a scheduled inspection of the linear bearings we just have to see the drops of oil dripping out of the bearings to know that everything is ok
but with grease you got to pump the grease and hope that the the pressure that you feel is the grease entering the bearing , and not some cloggged grease nipple.
grease is ok for angular contact bearings and ball bearings .. but for Linear motion bearings I'd say got with centralised oil lubrication.
04-05-2007, 02:41 AM #10
I have some bearings that have been spit out from over pumping. (assuming) I think THAT is more the issue than sliding. (I wouldn't believe an extree pump would make a bearing slide.)
Think Snow Eh!
04-05-2007, 11:53 AM #11
kluber isoflex nbu 15
when fitting new spindle bearings with the new grease .
our HMT ( hindustan machine tools) CNC turning centre manual has detailed instructions on how to 'Season the grease '.
Somewhat similar to your spindle warm up procedure but more tedious.
it went something like this ..
200 rpm 2 minutes
wait 5 minutes
500 rpm 5 minutes
cooling 10 minutes
1000 rpm 5 minutes
wait 30 minutes etc blah blah blah...
really boring stuff which we got to do when we change the spindle grease.
04-05-2007, 12:16 PM #12
Personally, I like to season the grease with a little paprika. (You knew someone had to say it.)
04-05-2007, 12:50 PM #13
sudtechcnc...yes, that sounds familiar.
04-05-2007, 02:36 PM #14
Most machine tools that require periodic greasing will have zerk type fittings. It is safe to say that these are probably related to the balscrew nut and the liner guide bearings. In additon I have NEVER seen any machine that has a fitting on a critical bearing that requires a specific amount of grease at the time of assembly.
04-05-2007, 02:47 PM #15
This idea of too much grease causing a linear guide to slide instead of roll, me be a philosophy that some salesperson dreamed up as an arguement for a machine he was selling that had waylube. Who knows if it's really true or not?
04-05-2007, 05:29 PM #16
We build linear motor powered X-Y stages using THK linear bearings and rail - because we approach speeds of 2400 inches/minute THK recommends that we strip ALL grease from the bearings before installation and then change to a lighter grease with greasing frequency defined by precise amounts and precise intervals measured in inches of travel.
As a result, we track the travel of each stage and have a positive displacement grease metering system that injects precisely 5cc's of grease divided among 8 bearing cars through positive displacement sequencing metering devices. The metering blocks require upwards of 1800 psi to cycle and we have a prox switch mounted to the piston of one of the divider blocks so we are assured confirmation of a cycle pin change of state when we command a grease cycle.
The machines run 24x7x365 loading annealing ovens and a dry bearing is not a happy bearing . . . but an overlubed bearing is almost just as bad as far as skidding and failure.
You can imagine how we guffawed at these design specs when we first started building these machines . . . after several very expensive bearing failures and associated downtime - we designed our lube system exactly as recommended by THK and we have never had a failure since.
04-05-2007, 06:23 PM #17
Talk about skidding....
I remember from racing two strokes, the rod bearing did not like too slippery of an oil, at 10,500 rpm. The rod bearing does not revolve, it oscillates. If the oil was too slippery, the needle bearings would not have nough traction, and instead of rolling, would skid at the direction changes, 21,000 times a minute.
That sure was fun, 4.7 hsp/cu in. on "pump" gas.
04-05-2007, 07:35 PM #18
Oh well. So much for my theory.
04-06-2007, 11:15 AM #19
I attended a one-day seminar conducted by THK (3 years back)
One of the things that I remember from that class is what the THK person said about grease.
He said most of these high priced grease like Kluber isoflex and their own THK grease ( which is even costlier) function well only in a clean environment.
He said that if we couldnt keep the coolant off the rails then we were better off using ordinary grease which costs 1/10th the price...
04-06-2007, 11:26 AM #20
I'm not proud of it but our 98 Arrow 2000 cinci has been greased with whatever happens to be handy since it was new. :rolleyes: The ways are still in good shape. With the junk way covers on this machine it definately is not a clean environment.
The new Hardinge lathe is getting the Kluber treatment every 600 hours 3 shots.