NC Cams another bearing question

[bob1112]

We chatted a couple months ago on A/C bearings for an upper drive unit in a knee mill. We have since balanced the components and today finally installed the A/C bearings in the drive unit. They are making noise!! We lubed with 30% NBU15 Kluber, the configuration is face to face with 1in spacers between bearings.

Work was done in a meticulous fashion but I know that may not be enough. The bearings are quiet but have an intermitent rattle or ticking sound. I am wondering if this might be ball skidding or FOD? Are these bearings toast with only 1min run time? The sound is very confusing and we are stressed to say the least on this. Can this be a manufacturer defect? Thanks for all your help.

Brandon

[Newby2]

Were they precision bearings, was the lube contaminated, are they exactly parallel, was the preload on the bearings set properly, are they within the speed range of the bearings? So many possibilities with so few answers.
Just because they are new bearings does not necessarily mean that they are without defect. There is a possibility that with 1 minute of run time, they have suffered no damage.
Steve

[LUCKY13]

Is the noise at any speed or one certain speed. I am guessing this is a low speed noise but what I have been reading that to run high RPM is has to run in stages until the rpm limit is reached, sort of a breakin kinda thing. I dont know much about these high quality bearings & setting them up. But this goes to show as many have warned about its not as easy as it seems to accomplish something like this. I am sure you went to extremes to install these correctly but it may be beyound that to do them right.

But the reason I ask about the speed & if they have been run high RPM is it may have damaged them to spin them up to high limilts before they where broke in & then the noise is a result of this. But like i said I dont know enough to evn begain to anwser your question. Just kinda thinking out lound, maybe it will help in some way.


Jess

[bob1112]

Grease is brand new from Kluber so contamination would be very unlikely. Preload is light and determined universal grind on the bearings. The spacers are equal width so no additional preload is added with the spacers. Spindle was started at 1K RPM and noise was obvious. PUshed to 3K for a few seconds and noise is still there. Bearings are good for 10K in grease.

ONe thought I have is that the pinch nut being about 2.5in in diameter, is not being pulled down hard enough to set the preload properly causing skating. I know skating is just as bad as FOD so will not run them until I know what is going on.

B

[NC Cams]

Intermittant noises are hard to diagnose.

A minor bit of damage to the bearings as a result of excessive force will EASILY brinnell a raceway. If you, by chance, "popped" the A/C's appart with force while handling them, you DEFINITELY brinnelled the shoulder and probably one or more of the balls in the process.

The ONLY way to disassemble an A/C is to heat the outer ring and let the inner ring drop out (into a pie pan of course so as not to lose stuff). To reassemble, you cold fit it and do essentially the opposite and support the outer and heat it and let the assembled inner and cage and balls "drop" into the outer ring once you heat it.

Again, if you used ANY force to disassemble the bearing to grease or clean it, you most likely brinnelled the balls and the raceway shoulder and the bearing is RUINED.

Some greases are notoriously noisey due to the thickening agent(s) use. I'm not sure of what Klube uses but I don't recall it being a "noisey" grease. Some greases that use sodium nitrate to thicken the grease actually feel/sound like marbles are being shaken in a coffe can.

More likely than anything, I'd suspect that an "OOPS" took place and you've gotten a flat spot generated that shouldn't have been someplace on the balls and/or raceway.

A new bearing might hum or perhaps whine - if it has a steel cage, perhaps you might hear a chinking/rattlying sound. But a repetitive rattle/noise is usually the sign of assembly damage or debris or debris dents or both....

[bob1112]

These are new bearings and they were not separated per my last mistake. I used heating and cooling methods to install them and they went together with no effort. the rattle sound comes and goes but obvious at all RPMs. I am wondering if I actually somehow got debris in the bearings, if they are toast at this point or can we clean them and try again? I know it takes very little to damage them so I have been very careful.

When the assy is assembled, I froze the whole thing to install in the chassis but it still to a couple taps with a plastic hammer to get it to drop into place. Minimal effort and I would not think that would be enough to damage them but you better than I. thanks again.

brandon

[vger]

Viper,
My work is vibration analysis and balancing of rotating equipment. Without hearing or looking at the spectrum of the noise it's difficult to say what is wrong. Different bearing defects have different noise signatures but do indicate what the problem is. There are defect frequency "sets" that are dependant on inner race dia, rolling element dia, outer race dia, etc. SKF has a calculator that will tell you what frequencies to look for in a given bearing.
http://www.skf.com/skf/productcatalo...=&action=Calc6
You said there was an intermitant rattle or tick sound, The good news is that intermittant sounds are not generally bearing defects. Excuse my ignorance here, is this mill belt or gear driven ? Second question, is the noise actually coming from the bearings you replaced ? Try one of those automotive stethiscopes to locate the exact source.

Steve

[bob1112]

The sound is definently intermitant and random and what is really funny is we heard a very similar noise before we tore the unit down. It is belt driven. I removed the A/C bearings (they are brand new), cleaned them, inspected for obvious defect, rolled them dry while listening with my stethescope, and reinstalled. They sounded great. I am at a huge loss for what is happening. I cannot get right to the side of the bearing when installed but I can guarantee it is this drive coupler because we can run just the motor with no noise and the spindle is not installed. Very simple setup here.

This is a noise I am not familiar with. Almost a chatter sound and it gets worse as the bearings warm up. One thing I did not check for but might actually sound like this is if one of the outer bearing races is somehow spinning. Seems extremely unlikely since is does not just drop into place but I have to look at everything. I think the goal today is to pull the assy and try to bench test it. Obviously, this may tell is alot in what is really going on.

[vger]

put a small mark on bearing outer race and on housing when assembled, then check after run. if it's spinning you'll know. Check those pullys, differing belt tension through rotation can do funny things.
Steve

[NC Cams]

Timing belt drives sometimes have lead or "pull" in them. Thus, they can generate an axial load to themselves and/or the pulleys they're running against. They can also wander from side to side in the sprockets. When the belts hit the pulley flanges, funny noises can be evoked.

Chances are that the A/C's may not and probably are not damaged - I suspect you learned your lesson the first time on what NOT to do with/to them. The A/C's may NOT be emitting the noise but the bearing on the othe end (regular deep groove, probably with metal cage), may be rattling the cage (this can come and go depenind on the speed and acceleration patern of the spindle and/or any bearing misalignment.

When I say "misalignment", it doesn't take much (a few minutes) to cause the balls to travel from one side of the raceway to another. This causes a speeding up and slowing down of the ball and the cage dut to the instantaneous radius change that the ball paths are making. This begets a chucka-chucka or tink-tink sound as the balls and cages bounce against each other. This can come and go.

Like vger says, there are different signatures that are/can be emitted, and each depends on where the problem exists and how bad it is and how many problems there are lurking. You'll have to systematically "find" the offending member.

Don't be surprised if the problem is elsewheres. By fixing the major problem with the A/C's, you may simply have uncovered another problem that was below the noise threshold created by the prior A/C problem that is now fixed.

Welcome to world of unintended consequences and the never ending perils of progressively fixing used bearings in resurrected machine tools. It eventually ends when you get all the noisey stuff fixed and can only hear the 60 cycle hum of the electric motors running.

When/if you do get all the bearing issues fixed, you can get them this quiet. It is scarey when that happens because even the slightest noise emitted startst to make you think of nothing but spending more money on expen$ive bearings.

[bob1112]

You are right on NC Cams, this thing is getting so quiet now that any small noise is heard. I will have to try and figure our how to put a picture on here so you guys can see what I am working with. In short, the way it is running right now, The only radial ball bearings that run are the two in the spindle motor. The drive coupler sits afront coupled through the ribbed belt.

Yes, I would say that the noise kind of sounds like ball bearings slapping each other or something similar. The reason the noise gets worse with heat is because of the change in grease viscosity I am thinking. OK, I will try to get a pick or two so you better understand this deal.

[bob1112]

OK, I think I have some pics uploaded. Bad news, the noise IS coming from the A/Cs. Really sounds like they are not preloaded or the balls are dancing around in there. They feel a bit rough when you first change dirrection and then smooth up. I manualled spun this assy in the mill with a drill motor and upon coasting, it makes noise until about down to 50rpm and then smooth as silk. The phenolic cages are VERY free in the bearings but I am assuming that is normal.

As you look at the pic, the left side or hub side is the up side in a verticle mount. It couples to a pulley. The lower or right side has splines on the inside for the spindle to move in and out of. This assy has been run totally by itself and I know it is the A/Cs. I am wondering if FOD was an issue, would they not whine first? In my experience with bearings, it would seem the FOD would damage the balls and their rough tecture would cause noise eminating as a whine, not a tick. Tell me where to go. These bearings came from Germany so who knows how they were shipped. IA, maybe dropped, I don't know but getting replacements will be like pulling teeth I am sure.