Spindle bearing died during warmup on newly installed (used) machine

[pMetal]

We recently installed another used VMC. The machine is only a few years old and had very light use from the previous owner. Runout was near perfect. Overall, the machine was in excellent condition.

We haven't used it yet, but we do home the machine and warm up the spindle every morning.

One morning, during spindle warm-up, the operator reported that the spindle suddenly made a bang sound and thereafter sounded like it was grinding.

The spindle is now very hard to turn by hand. We have verified that the problem is the spindle, not the spindle motor, not the belt, etc.

So clearly we need to get the bearings replaced. But its not normal for a failure like this to happen (fairly new machine, no crash, and failure during warmup), so I'm worried that this might happen again after the spindle is rebuilt.

The machine has a chiller to circulate oil around the spindle housing. Conceivably there was a blockage or other circulation failure, which could have allowed the bearings to overheat. Since we recently purchased (and transported) the machine, which required disconnecting the chiller hoses, it is conceivable that some debris got into the lines, which could have created a blockage. My higher-end machines have a flow sensor to check for this, but I don't think this one has one. We'll investigate the chiller oil flow tomorrow.

The machine also has through-spindle-coolant. We turned this on a few times in the process of testing the machine when we first got it installed. I've read that through-spindle-coolant is hard on spindles, but I don't know why. Is it possible for a seal to fail, which would allow the coolant to get into the bearings? If so, then the coolant could have washed away the bearing grease, which could also lead to failure.

Do you have any other ideas what could have killed the spindle?

 

[dandrummerman21]

What machine are we talking about here?

What rpm spindle?

How was it prepared for rigging? Meaning, was the spindle blocked to the table? Did someone drive the spindle nose against a piece of wood, or was the spindle cradled and properly supported?

Nothing about your situation gives any real clue to the answer, but i assume your rebuilder would shine light on it.

Just an idea with absolutely 0 evidence, the spindle may have been blocked up improperly and you have ceramic bearings, one of em cracked in half? Seems unlikely. but possible.

OR, it is just one of those "shit happens" moments where its nobody's fault.

 

[Donkey Hotey]

This could be sooooo many things that aren't even spindle related. Is it a belt drive machine? Did something fall down inside the belt cavity during shipping and now it's dragging on the belt? Did the TSC coupling fail and it's seized? Did the coolant leak somewhere and damage the motor's bearings? Did the drawbar actuator piston jam against something or break or?

You need to get into the head and look around before assuming it's automatically the spindle bearings.

 

[Mtndew]

I've read that through-spindle-coolant is hard on spindles

Where did you read this? On a Bazooka Joe wrapper?

 

[mottrhed]

Whats the machine? Tooling style? Was a tool holder in it during this?

Lots of possibilities here, especially with just moving it. You sure the machine is wire/phased correct? Ive seen machines get installed and wired wrong, all 3 phase motors "work" but run backwards, chiller pump, etc..

Outside of that, were you getting good chiller flow?-you can still check this if the spindles still in the machine.

Whats the lubrication? Grease or oil? If oil, check the basics, reservoir full, air pressure right, if oil injection make sure its firing etc.

Spindles rarely die of natural causes, they are usually killed by their environment, lack of maintenance or misuse.

For the TTC thing, spindles are not affected by having or not having the system, issues happen when the rotary union starts leaking, which typically will then allow coolant to wash out/contaminate the rear bearings, causing spindle failure. Many people do not realize that not all rotary unions are rated for dry running, although most are at this point.

If I knew what machine you were working on I could get much more specific about how those spindles fail, but either way it sounds like shes coming out.

 

[VTM]

Whats the machine? Tooling style? Was a tool holder in it during this?

Lots of possibilities here, especially with just moving it. You sure the machine is wire/phased correct? Ive seen machines get installed and wired wrong, all 3 phase motors "work" but run backwards, chiller pump, etc..

Outside of that, were you getting good chiller flow?-you can still check this if the spindles still in the machine.

Whats the lubrication? Grease or oil? If oil, check the basics, reservoir full, air pressure right, if oil injection make sure its firing etc.

Spindles rarely die of natural causes, they are usually killed by their environment, lack of maintenance or misuse.

For the TTC thing, spindles are not affected by having or not having the system, issues happen when the rotary union starts leaking, which typically will then allow coolant to wash out/contaminate the rear bearings, causing spindle failure. Many people do not realize that not all rotary unions are rated for dry running, although most are at this point.

If I knew what machine you were working on I could get much more specific about how those spindles fail, but either way it sounds like shes coming out.

I have had one that lost a set screw out of a coupling. And that bound up the Spindle. Had to remove the Spindle cartridge to remedy that, but re-Installed and works fine. I think It deserves further Investigation as others have stated before deciding It's an actual bearing failure. Sounds unlikely.

 

[Matt@RFR]

I bet your operator slammed the spindle in to something and then lied about it.

 

[mottrhed]

When its described as hard to turn and grinding, odds are the bearings are gone, especially with the motor out of the picture. Obviously if at further investigation some anomaly (like a loose part that can be tightened) pops up, certainly could be worth addressing and trying again, but odds of that are low. Almost certainly you need a rebuild, whats important now is finding the root cause so you dont kill the rebuilt spindle too.

 

[PegroProX440]

remove the rotary union and then try spinning the spindle by hand. it may be the union

 

[pMetal]

Thanks for your replies. To answer people's questions:

Machine is a Taiwanese brand - Primero Machine Tools, also known as Bulova. I bought it for the large 79" X travel. I hadn't heard of them prior to buying this, but it has Fanuc 0i controls and seems well made. The machine tool builder has been helpful and responsive via email.

Spindle is 10,000 rpm, CAT40, permanently greased lubrication, belt drive. It is cooled with a chiller that circulates oil outside the spindle jacket. I don't think the bearings are ceramic.

It was prepped properly for transport, to the best of my knowledge of how to do it. The "neck" of the head / spindle housing was lowered onto wood blocks right next to the spindle. The spindle nose itself did not press on the blocks, so the spindle did not take any hits from bumps. So the spindle nose itself was not supported, but the head and Z axis was. Usually I see people lower the spindle nose itself onto blocks, but I felt it was better this way, since it is my belief that we're mainly trying to protect the Z axis (with all its mass) from bumps, and I didn't want bumps being transmitted directly to the spindle.
------
The belt is in good condition, and nothing is dragging on it.
We have loosened the belt, removed through-spindle-coolant coupling, and we have removed the piston which pushes down on the drawbar for tool changes. From this we have determined that the problem is internal to the spindle, and not from any of these external parts.

The through-spindle coupling spins freely, but I suppose it is possible that a seal somewhere internal to the spindle has failed, and allowed coolant to wash through the bearings.

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Yes there was a toolholder in the machine during warm-up when the failure occurred.

We have verified that the machine is phased correctly.

Today we tested the spindle chiller's oil flow by removing the hose from the inlet at the chiller. We saw that the chiller successfully was flowing from the chiller, through the spindle housing, and back to the chiller (into a bucket actually for our test).

The spindle is permanently greased, so that rules out failures of external lubrication systems.

I'm leaning towards the possibility of a leaking rotary union, but not sure.

 

[pMetal]

Upon further investigation, we found a bunch of steel balls (like the balls that are inside of ball bearings) scattered around inside the head area (where the top of the spindle is, and where the motor is mounted). They look like they were sitting there for a while.

I don't see how they could have possibly came out of the spindle, or even the spindle motor given their position. However, this does suggest that maybe there was a spindle failure some time ago with the previous owner.

The balls were approximately 3/16" diameter. I've never taken apart a spindle bearing, but I imagine that the balls used in them are larger than that. Don't know.

If the spindle was rebuilt in the past, then maybe the balls fell out when they were taking it apart. But still, you wouldn't take the spindle cartridge apart right there in the machine, so I still can't make sense of why the balls would have fallen out there.

Possibly the balls came from some previous failure of the toolchanger, which is right next to it. That would make a little more sense.

But, if the spindle was repaired in the past, it is quite possible that they used the wrong bearings, which were not suitable for 10,000 rpm. And maybe the previous owner knew of this limitation and always ran slow rpms.

A bad past spindle rebuild is possible, but I just don't think it happened, because there's just not signs of enough usage on the machine to explain the need for a rebuild in past years. But who knows, an operator at the previous owner could have crashed bad which would have required it.

What do you make of the little balls sitting around?

 

[CarbideBob]

The balls were approximately 3/16" diameter. I've never taken apart a spindle bearing, but I imagine that the balls used in them are larger than that. Don't know.

What do you make of the little balls sitting around?

I would think this more the size of ball screw balls.

 

[mottrhed]

Thats too small for the balls from the spindle bearings most likely. Also theres really no way for them to make it up there in a failure, at least not in one piece. This is either a previous issue, or maybe 2 issues. Depending on the kind of rotary union, maybe it was a failure there, past or present.

Either way, you need a rebuild, hopefully with a solid root cause of failure, and id replace the rotary union while youre there.

At 10k, it may or may not have ceramics, but it’s immaterial to the failure. If you have a manual with a print i can tell you what youre up against here.

 

[EKrol]

How do you do a spindle warm-up? Is it a machinebuilders program or did you make your own? Bearings can break randomly with no direct cause. For grease bearings i think/know if they stand still for a long time the grease due gravity will sag. So its important do slowly starting the spindle. If you run the spindle at 10k when there is no grease at some spots that's bad. My machine will always start the warm-up at 10rpm for 2 min so the bearings are well greased before you go to higher rpms.

 

[mmurray70]

Chances are the 3/16th balls are from the ball screw. Might want to have a look into that as well.

 

[cnctoolcat]

My philosophy in cases like this: start taking shit apart, you can't hurt anything any more than it already is.

VMC cartridge spindles usually drop out the bottom of the head without too much fuss...

ToolCat

 

[SageGlad]

Obviously this is a mechanical issue, and spindle disassembly much faster then go back and forth on the forum.
I'd go remove it, and all questions will be answered right away.

 

[Scruffy887]

Bellville washer/s decided to end its useful life?

 

[BOB-OO]

That's tough, sorry to hear it. You said its a used machine and hasn't been crashed. How do you or anyone really know? I hate grease spindles. It sounds like you did nothing wrong, Through tool coolant is there to be used and running warmup programs is smart. Used is used and we've all gotten screwed at one time or another. IMHO-Pull the cartridge and choose you rebuilder based on recommendations and familiarity with the machine not price. If you really think that coolant got to the bearings, I would test run the coolant after you get the top open- 300psi isn't really a lot these days, if its getting into the bearings you'll likely find it in there somewhere b4 or while u pull the cartridge.
Good Luck!!!