HELP!!! I think the spindle bearings on my cincinnati turning center are bad.

I've noticed that my spindle load seemed a little high. However the machine is a little new to me and I'm trying to work the bugs out.

Today I was running a job that is already behind. I opened the door to inspect an o.d. after an offset, and I noticed that the headstock was basically steaming off coolant. I touched the head stock inside the machine and in back by the belts. Both were pretty hot. I don't know how hot but It's obvious something is wrong.
I'm going to do a search for old posts on changing bearings, but I figured I'd ask here too to hopefully save a little time.

The machine is a 1993 Cincinnati Milacron Avenger 200MT.

-Is this something I want to fix myself?
-If I don't do it would you recomend any repair tech or should I spend big money and bring in a factory tech?
-Any body have an Idea of what this is going to cost me? (This is to brace me for my phone calls on Monday.)

Any comments, Ideas, etc. are welcomed.

Thanks,
Rosie

Do you have the maintenance book for it?
They have a section on headstock bearing replacement. I have not looked at that yet though.
Good luck...

3t3d

I do have manuals. I'm currently going thru them. I only see a sectional print of the components w/ part numbers. Other than that I haven't found anything.

I'm really worried about the resolver. It is an insanely exspensive part, and I'm guessing it will have to be removed to get at the bearings.

Please look at your manuals if you have time. Do you have manuals for the avenger 200 mt?

If you have manuals that would help, please PM me or email me at [email protected] with your information and address.

Thanks,
Rosie.

Well, its hard to beat a good technician if you can find one.

It probably would help if you had prior experience on less critical stuff, like stuff that is insanely difficult to get apart ......the type that needs pullers and judicious application of heat to get apart.

However, if you do have some such experience, and are not easily frustrated, and can remember or figure out logically how something should go together, then it is certainly not difficult to beat a half-ass technician.

There are things to know about assembling super precision bearings, like acquiring the correct ones, noting the etchings on the races, installing them with minimal force, etc. And, you need to understand how the preload is designed and created in your system.

Well, its hard to beat a good technician if you can find one.

Click to expand...

Actually, no it's not. All you need is a good sized 16 inch pipe.

Before you start tearing things apart, check the lube system.

I looked for any lines going to the spindle area, and saw nothing. I do have some lubing prints which I'm currently going thru. Should I expect the spindle to have lube lines, or are they sealed bearings?

Rosie

Rosie,

Most spindles on cnc lathes have sealed bearings.

Replacing the bearings is doable, if you are somewhat mechanically inclined, and patient.

But before you do, are you sure the bearings really need replacement? Some heat output is normal for any machine tool spindle.

Usually, bearings are judged to be bad because of excessive noise. If your spindle is not very noisy, I might continue to run the machine for a while.

Today's cnc lathes with integral spindle motors (the spindle shaft is the motor shaft, the windings are inside the headstock) have spindles that get extremely hot. Even with forced liquid cooling systems, the spindle shaft, drawtube, and chuck get noticeably hot.

Greg

Cincnnnati ALLWAYS puts the lube lines inside the spindle carrier... the pump may or may not be inside also...

I would be very surprized if they used sealed bearings... normally they do not.

Is this a geared headstock? How many ranges?
Where is the spindle motor mounted? How many belts connecting the motor to the input shaft?
Look for a seperate lube pump and motor. THe electrical diagram is a good place to find that fast.

I'm guessing I jumped the gun a little. In the past I've always ran someone elses equipment, and didn't really care. This is owned by me and the bank, and my business pivots on it being reliable or not.

My dad stoped by to look thru some stuff with me(he's been in maintenance for 30+ years.) We started it back up and let it run for a while. We used a screw driver up to our ears and listened. I don't know how to explain it but it sounded like a suttle sliding noise. He said that the bearings sounded fine. There were no growling or rumbling sounds. We listened up to 2000 rpm. Other than the noise gaining with the rpm we didn't notice anything. The back 2 bearings by the belt were a little louder than the front 3.

We noticed that there are 3 set screws in the housing near the front bearings, and there are 2 set screws by the back bearings. There doesn't appear to be any lube lines any where near the spindle.

I looked in a manual I have, that is about like a sales brochure. In the area for head stock bearings it says:
-Quint set (5), 180mm o.d., 120 mm i.d.
-ABEC class 7
-15 deg. angular contact bearings
-grease filled @ factory, Kluber

On the bottom of the page stating benifits. One of them says perpanent lubrication.

The only thing I did different when I notice the hot headstock was I had my collet pressure at ~410 psi, because I got tired of stock pushing back in the smooth collet pads.

Gary E, to answer your questions.
This is not a geared headstock. The spindle motor is below the chuck actuator at the end of the spindle assembly. There are 5 belts. There doesn't seem to be any other lube pump.

cnctoolcat, The spindle doesn't make any noises different than what I've been used to over the years. I've just never seen coolant steaming off of the spindle nose. I wouldn't even consider the work I was doing to be very abusive. And it was only running for about 6 hours at speeds from 1200-2000 rpms. I believe max rpm is 5000.

I'm going to order a lazer pointed heat gun to monitor temperatures on every thing in the shop and document them. Monday I will also talk to the factory guy I deal with and ask him if the setscrews are possible greasing locations.

As of now I'm going to run it, however I'll try to back down on the collet pressure and add another rough pass.

I appreciate the replies. Exspecially when you tell me warm spindles are to be expected. I'm a little new on wearing all the hats required to run a machine shop.

thanks again,
Rosie

Set screws are never grease points... if they were grease points they would be zerk's

Sounds like you may have the drawbar pressure to high and you may have the belts to tight.

Get serated collet pads.. they hold a lot better.

If you can hold your hand on it without burning your skin, it's probably not too hot. Over about 140F the average person can't hold something in their hand.

Could the cutting heat be transferring into the collet chuck and be making the steam?

Question to all - does the collet pressure add load to the spindle bearings? I thought the closer only put the load internal to the spindle itself, pulling or pushing on the chuck end from the other end of the spindle.

Some older Cincinnatis used a mist system to lube bearings, an air mister carried oil into the headstock. Does your machine have anything like that?

FWIW I picked up a pair of keychain sized lazer temp guns at Harbor Freight for about $7 each, they seem to be as accurate as my $300 model.

Rosie I'm the same way with my machines. I'm always looking for somthing to worry about. And I can usualy find it.

Good luck.

Mudflap,
I talked to my repair guy an hour ago and he said that the collet pressure puts pressure on the bearings. Take it for what its worth.

"Some older Cincinnatis used a mist system to lube bearings, an air mister carried oil into the headstock. Does your machine have anything like that?"
I didn't notice anything. It is just a plain headstock without any lines touching it anywhere.

Rosie

Collet pressure shouldn't directly add load to the spindle bearings.

The actuator is bolted to the rear of the spindle shaft. The chuck is bolted to the front of the spindle shaft. The pull occurs between ends of the spindle shaft...thus all load is through spindle shaft, and not the bearings.

Rosie,
As long as your machine is running, and the spindle sound stays consistent, I say run it!

If your spindle is getting abnormaly hot, you will see a lot of thermal growth in it. This cause your machine to drift, as it warms up, effecting part size.

.001 or so would not be unusual thermal drift on a typical cnc lathe. Once a steady operating temperature is reached, the lathe should stabilize on size within a couple tenths.

cnctoolcat,
I'm planning on running it and keeping a little better eye on things.

2tenths,
Thanks for sticking your neck out and telling me I'm not the only guy worrying about too much.

To all the other people who replied to this,
I feel like a douch. I'm sorry for jumping to conclusions. However, I have learned a couple things from this post.

Thanks,
Rosie

Well it's 14 years later. I have quite a bit more knowledge of these machines....and quite a few parts now.


As a reminder it is a:
Cincinnati Milacron Avenger 200MT
There is no lubrication system. They're open bearings and factory greased.
Spindle Bearings: FAFNIR 2MM9124WI x 5 of them


I think it is time to do something. Last week I was running this machine. At 300lbs of collet pressure and after a few hours of operating I noticed the spindle load meter was at 40% simply spinning and not cutting any stock. I checked the headstock with a thermal scanner/FLIR and the outside of the headstock was at 180+ degrees and too hot to touch. My collet head on my spindle was actually pretty tough to turn by hand.

I ran the machine for about 4 hours today at 200lbs of collet pressure and around 1200 rpm max and the headstock's casting didn't get over 140 degrees.

(I state the collet pressures because I'm fairly confident that the actuator does pull against the bearings.....so the more chuck/actuator pressure....the more force on the bearings. This was some topic of conversation in this thread 14 years ago.)

As I mentioned I have a good selection of used parts. I have an identical headstock that I pulled apart a month or so back for giggles because the bearings were junk and I wanted to play around the headstock for a future shop fixture using the A2-6 spindle. I'm certain it's "not" as simple as just changing out bearings, however it did come apart fairly easily....even with some crappy bearings. I would want to assume that if I pulled it apart and put it back together the same way, and the bearing thickness' are the same as the original it should have the same preload. I have the bearings from the one I pulled apart and I'll see what I can get my hands on for the same quality. I have not ever priced bearings like this, however I'm sure they're spendy, and I need 5 of them. Ebay has some of them and 2 bearings are around $1k....and from a quick internet search it looks like a couple thousand a bearing. I'm assuming that is a list price. I'll call my bearing supplier in the morning.

I also have another headstock that is complete with decent bearings that I could swap out, however I'm concerned if the casting would be taller/shorter or slightly different. Plus I'm concerned about re-aligning the headstock. I have watched some videos on alignment....and while I think I can do it....my headstock is currently straighter than I could probably indicate in.



Here are my options the way I see them.

-Change Bearings without removing the headstock: spendy bearings, however no alignment issues....and I chance improper bearing assembly screwing up expensive bearings.

-Maybe stupid, however I'll throw it out there after seeing the bearing prices on the internet. I have another parts machine that should have good bearings. I could try pulling the cartridge.....and pull the bearings, cleaning and lubing them up if I can figure out the grease type and amount.

-Swap the headstock for one I have sitting in the shop that seems to have decent bearings. The machine I pulled it from showed me this route will be a pain with sheet metal at the face of the spindle hindering lifting the headstock off of it's alignment pin. Alignment issues and probably not getting it as good as it is now.....plus I doubt the headstock will be exactly as the one in the machine. This also requires pulling the tool probe off, and resetting the parameters for touching off tools.

I'm sure I'm missing alot of things, however it's almost 3am and I already feel like I'm rambling.




*I'd really like to chat with someone that has changed their bearings and hear how it has worked out.

*I'm open to any suggestions from people that have hands on experience with this scenario


Thanks much,
Rosie

Dave K said:

Actually, no it's not. All you need is a good sized 16 inch pipe.

Click to expand...

Or whatever else is handy. Like my fist. Or a 16mm hex key. I didn't know there were ones with whole asses.

R

14 years Rosie? Looks like ya got good mileage outa those old bearings...........where have ya been all this time?

rosie said:

*I'd really like to chat with someone that has changed their bearings and hear how it has worked out.

*I'm open to any suggestions from people that have hands on experience with this scenario

Click to expand...

I've done a few spindle bearing replacements over the years, did a largish lathe just recently.

From what you've written, I'd say you can handle it. Lathe spindle construction is not complicated; patience, cleanliness, and care is all that is required. If the inner races are very tight on the spindle you might want to hire a bearing heater, but that's about all you'd need out of the ordinary. I did not use a bearing heater on mine - getting the old bearings off was painstaking because there was nothing to pull or push against, but putting the new ones on much less so. The bearing configuration on mine was double row roller at the rear, then a double angle contact pair at the front inner, and a double row roller at the front outer. I did not replace the front roller bearing as it was totally fine, and so I was able to push against it to remove the DA pair. If I had needed to remove the front roller then a bearing heater would have been the only way to do so.

When you source the new bearings, you should be able to find literature from the bearing manufacturer that will tell you how to calculate the volume of grease to load, and how to determine the preload and run in requirements. The bearings I installed were NSK Super Precision, and the literature was extremely detailed and explicit.

I had a thread on mine, bearing literature links included, here: Lathe spindle repair, spun bearing, lost preload