PM25MV - Bearings and Noise and What have you

[wm_crash]

Howdy crew,

It's been a while since I posted here, and believe it or not, my little PM25MV has been sitting idle since then. I now embark on some projects that need it and I need some help.

At some point in the past, I overheated the spindle and decided it was best to replace all four bearings as I get going. I ordered the Nachi in the appropriate sizes from VXB. I made all the blocks needed to press things out from aluminum and I got to work. Installation went well, except now I have some problems. I can't vouch these problems weren't there before the bearing replacements, I didn't know what noises to pay attention to, I honestly didn't know what I was doing back then - and I probably still don't know much.

The main problem is that running the machine with the quill removed, just with the housing, I get rattling noise between 700rpm and 2000rpm. Things are not great outside that range either. My take is that the bearings are not quite the tight press fit that they are supposed to be. I came to that conclusion because when I tried to get the belt pulley out (after removing the stacked set screws), the whole quill housing and top bearing sorta slipped out a bit (like maybe 1/8" to 1/4"). So really, it's not sitting in there very pressed.

Running the machine with the quill inside just makes things worse.

Alright, so I am just trying to see if anyone else here has anything to offer as far as advice or personal experience. I am not sure there is a way to properly tighten a press fit hole, if that even is the actual culprit. I will probably call PM to get their take, but just wanted to see if anyone here has anything.

cheers,
wm_crash

 

[Ulma Doctor]

loctite makes bearing retaining compound, if you were so inclined.

bearings that are not captured correctly will make some funny noise.

the ABEC # will give the relative precision of the bearing- the higher the ABEC # is the more precise the bearing is

some very inexpensive bearings do not run smoothly at all.

look for ABEC3 or higher for spindles

 

[Ischgl99]

It sounds like you might not have had the splined housing all the way seated if it dropped when removing the pulley. I would check that first to make sure it is in the proper place. You should also check the motor by removing the belt and then running it up to speed to eliminate that as a possibility. If the motor is fine, then move to the splined housing and check each part for damage or wear. You might find something obvious at this point, if not, measure the fits for the bearing inner and outer rings and see if any of the parts are too loose. You will also want to check and make sure the bearings are properly seated. For a rotating shaft, the inner ring fit should be snug, and the outer ring a slip fit in the housing.

 

[wm_crash]

Alrighty, for those of you also on the PM Facebook group, this may be duplicate info.

I went back to the original stock bearings (the 6007 and 6209) and things are running smooth. I just wanted to change them because I overheated the spindle a while back. I ran the spindle at top speed for 5 minutes and it went from 80F to 115F. I find that reasonable. There is no noise with the original bearings.

Now, the new bearings, while they are the same nominal size, they may not have the same clearance/fit/purpose. Their RPM rating is more than needed, but may have been intended for a different application. I didn't know any better so I bought them. For reference, the new bearings are Nachi 6007ZZE and Nachi 6209ZZE bought from VXB.

cheers,
wm_crash

 

[Ischgl99]

If the old bearings were a precision class, they would have a P6, P5, etc. written on them. If there is not a precision class on them, then you need to assume they are standard precision. The same with clearance, if there is no clearance written as part of the bearing number, something like C3, then they are standard clearance CN bearings and are a tighter clearance then C3. If the old bearings we normal clearance and you used C3 in the new ones, that could be enough additional clearance to cause the problem you saw since there doesn’t seem to be a way to add some preload on them, and the weight of that spindle looks fairly light, so it might not be enough by itself.

For future reference, bearings can handle up to about 300F before you start taking hardness out of the bearing steel. You obviously don’t want to get close to that, but unless you exceeded that temp, the bearings are likely fine. The grease on the other hand would be shot and would need to be replaced if possible. Grease is rated for about 70C (158F) and each 10C above that reduces the grease life by a factor of about 1.5. The manual shows one bearing as open and one shielded, is that what came out of the machine? It would be best to replace the bearing if you think it got that hot, but the shields usually get damaged when removing them, and bearings that size are cheap enough that it is usually better to just replace them instead of trying to regrease.

I’ve mentioned before that I advocate only buying bearings from authorized distributors. You don’t know where unauthorized places got their bearings, so they could be counterfeit. Since the old bearings are working, it could be you installed the new ones wrong, but the old ones again correct, the bearings are not the same, or these are bad bearings and have out of spec runout. If the old ones work, maybe run them until they need to be changed unless you know for sure the grease is cooked.

 

[markba633csi]

Sounds like you got it working- several variables to consider when changing bearings
I assume you called PM- what did they say?

 

[wm_crash]

You are 100% right on, man. I thought the C3 was fancy stuff, but I was getting Nachi bearings, so it had to be "better", right?

Did some reading and it turns out C3 clearance is for hot working environments, so the bearing has extra clearance between the races and expansion room between actual and nominal diameter. All that makes it shake and rattle in my application. The C designation has nothing to do with the ABEC scale. C is for clearance, ABEC is for precision.

I am going to replace everything I can replace just so if I have any subsequent issues, I don't start to second guess things.

The bearings that came out are plastic shielded on both sides.

cheers,
wm_crash

If the old bearings were a precision class, they would have a P6, P5, etc. written on them. If there is not a precision class on them, then you need to assume they are standard precision. The same with clearance, if there is no clearance written as part of the bearing number, something like C3, then they are standard clearance CN bearings and are a tighter clearance then C3. If the old bearings we normal clearance and you used C3 in the new ones, that could be enough additional clearance to cause the problem you saw since there doesn’t seem to be a way to add some preload on them, and the weight of that spindle looks fairly light, so it might not be enough by itself.

For future reference, bearings can handle up to about 350F before you start taking hardness out of the bearing steel. You obviously don’t want to get close to that, but unless you exceeded that temp, the bearings are likely fine. The grease on the other hand would be shot and would need to be replaced if possible. Grease is rated for about 70C (158F) and each 10C above that reduces the grease life by a factor of about 1.5. The manual shows one bearing as open and one shielded, is that what came out of the machine? It would be best to replace the bearing if you think it got that hot, but the shields usually get damaged when removing them, and bearings that size are cheap enough that it is usually better to just replace them instead of trying to regrease.

I’ve mentioned before that I advocate only buying bearings from authorized distributors. You don’t know where unauthorized places got their bearings, so they could be counterfeit. Since the old bearings are working, it could be you installed the new ones wrong, but the old ones again correct, the bearings are not the same, or these are bad bearings and have out of spec runout. If the old ones work, maybe run them until they need to be changed unless you know for sure the grease is cooked.

 

[wm_crash]

Howdy,

I didn't want to bother Matt on a Sunday. I know he actually answers the phone on weekends, just didn't want to bother him.

But if I had called, I would expect something like "you cubicle dwelling types should take a class or two at the local technical school before making assumptions, swapping parts and what not with the wrong model, and then getting ****** at machines and calling me on the weekend"

Actually Matt's nicer than that.

cheers,
wm_crash

Sounds like you got it working- several variables to consider when changing bearings
I assume you called PM- what did they say?

 

[Ischgl99]

You are 100% right on, man. I thought the C3 was fancy stuff, but I was getting Nachi bearings, so it had to be "better", right?

Did some reading and it turns out C3 clearance is for hot working environments, so the bearing has extra clearance between the races and expansion room between actual and nominal diameter. All that makes it shake and rattle in my application. The C designation has nothing to do with the ABEC scale. C is for clearance, ABEC is for precision.

I am going to replace everything I can replace just so if I have any subsequent issues, I don't start to second guess things.

The bearings that came out are plastic shielded on both sides.

cheers,
wm_crash

Yes, C3 is meant to compensate for higher operating temperatures and are common for motors, it’s not uncommon for compressors and vacuum pumps to use C4 since they get hotter than motors. The pecking order for clearance is C2, CN, C3, C4, etc. Something that most people don’t know, the clearance also helps determine the stiffness of the rotating shaft, tighter clearance, higher rigidity and natural frequency. A company I worked for needed to use normal clearance bearings on a particular centrifuge since the designers messed up on the design and undersized the bearing, the tighter clearance helped keep the natural frequency a bit higher and the machine running smoother.

ABEC is an American rating system, Japanese and European companies use ISO designations as Px, so if you see a P followed by a number, then it is the tolerance class. Timken is different with inch tapered roller bearings and have their own system for precision classes. Gets confusing after a while!

 

[Ischgl99]

I forgot to mention, I edited my earlier post to 300F from 350F, I don’t recall the actual tempering temperature used, but it is a bit lower then 350, so 300 is probably the limit to how hot you want to get a bearing before you start causing damage.

Nachi should be decent bearings, I am biased to FAG Bearings, but SKF, Timken, NSK are all high quality and I wouldn’t have any reservations using any of them. The important part is ordering through authorized distributors so you know you are getting authentic bearings. I won’t even consider buying anything that requires quality from Amazon, and many of the independent sellers may not get their products through verified channels. VBX has on their website that they are authorized distributors of Nachi, so you probably got good bearings, just maybe not the right ones.