Shaft Rotates Inside Inner Bearing Ring

It depends on too many unknown factors to answer such a non-specific question.

Maybe, maybe not.

What does logic and common sense tell you? ".... shaft can rotate relatively to the inner bearing ring, while it shouldn't. That should be the first clue.

As far as damage, the bearing with the loose collar will last longer, (no rotational wear), the bearings below or above the loose bearing will suffer more wear due to lack of shaft support and the effects of "wobble"

What unit of measurement is "12 micro"

Agree with oz. it may be too late though. Due to Shaft or inner race damage. Set the set screws.

I'm taking a wild guess that your 12 micro is 12 millionths of a meter or roughly .004" - .005".

If so that's an easy fix to get your shaft and bearing to grab a bit better.

The most common and simplest method is to take an ordinary point punch and make a number of punch divots at even intervals around the shaft in two rows three going around the shaft where the bearing rides.

By putting the point punch marks in the shaft surface it will create small raised areas around the punch marks that will increase the shaft diameter enough that when the bearing is pressed back on it will fit snug on the shaft but not so snug it would be difficult to remove at some future point.

Just being a little pedantic here, but by my calculation 12 micrometres is closer to 0.00047".

4 thou would be about 102 micrometres.

I went to public school. Be happy I can even count let alone do math to within a +- 10x accuracy.

Now as someone who has done machining I have doubts about a shaft clearance of 4 - 5 ten thousandths of an inch causing many problems. Personally I would be thrilled to be able to make and ID and OD fit with a 4 - 5 ten thousandths of an inch out of round clearance.

FWIW I have some doubts on the OP's shaft to bearing race clearance being 12 millionths of an meter. He would need some pretty accurate measuring tools to be able to measure a ID to OD variance between two parts that precisely.

The OP said the shaft diameter is 74.6mm so i guess his maths is not very good. I would guess the bearing bore is 0.4 mm bigger than the shaft. This would allow free rotation. I would add an 8thou (0.2mm) shim and then dimple the shaft for the grub screws as well. If there is enough depth in the grub screw hole i would also add a locking grub screw on top of the first one.

Jim

74.6 mm = 2.937"

What's the problem with my math?

Inserting shim is noted, thanks.

No room for adding locking screw.

"Whats the problem with my math?"

I cannot deduce how you determined that the clearance is only 12 micro(sic). If you measured the shaft at 74.6mm you should very quickly see that the gap is most PROBABLY 0.4mm. Your first course of action should be to check the bore size of the bearing. If it is as i assume, 75.00mm then you would not have included in your original post a clearance of 12 micro(sic). You would now know that the shaft is undersized and the question you posed would have been different and the answers given would have been more relevant. For example, Loctite is suitable for small gaps but a gap of 0.4mm requires different solutions.

Feel free to give more information and ask a new question if none of the posts so far have given you a workable solution.

Jim

Since i posted the above comment i read the rest of the posts and i see that the you have said that you didn't measure the 12 micron it was the drawing spec. So if i am right, your original post should have said that there is a badly fitting bearing because the shaft size is way under the specified size. You will get a lot of different responses to a question that starts out like this. You will note that some of the first responses said that there is not enough information.

Can you remove the bearing to measure the I.D.?

Can you see a number on the bearing so that you can look it up on a chart to find the I.D.

If the answer is 'no' to the above; can you tighten just one grub screw and measure the resultant gap opposite the screw with feeler gauges?

Knowing the size of the gap to be filled is important. Also important is to ask whether or not the shaft has to run true/balanced.

Jim

To tell you the truth, after converting the size of 74.6 mm to SAE it comes out as 2.937 inches.

I think it is more probable that he is measuring in metric when he should be measuring in inches.

75 mm equals 2.952 which is not a standard bearing size.

The OP needs to figure out if it's metric or SAE!

Maybe if the OP gave us the actual bearing model number this could be cleared up even quicker?

Exactly! If it is a 3" bearing the gap is significantly more than 0.4mm, more like 1.4mm. As always the call for more information has gone unheeded. Now the emoticons work!!! Seems that Win8.1 might be the problem. I am now on Vista.

Jim

Thanks JimRat,

Sometimes even I will overlook some very obvious facts when the focus is elsewhere. When I converted the size and saw it was almost a perfect match for an SAE Timken bearing, it was clear that it is an SAE shaft!

I assume that by being "pendantict", you imply that you are not planning to change your answer. I suggest that you become pencildantic and use an eraser. You will then appreciate that 12 micrometers equals 0.4724 or about 1/2 mil.

I don't see a problem. That's what spades said. 0.00047" = 0.47 thou in UK and Oz, = 0.47 mil in US.

Yeh? Well what about in Arkansas?

0.47244094488188976

try locking set screws

I agree with reinforcement of PM, but please check any changes in temperature

If you have to stop the equipment for any repairement/inspection do NOT forget to add a tiny film of Molybdenum Disulfide- It will provide a fair protection against fretting corrosion that is the following damage to slow motion between parts that shoud not rotate on each other

Do the set screws lock the bearing inner to the shaft? If so is there any reason to think you haven't cured the problem?

My sentiments exactly.

Good comment from Ozzy to check the set screws.

The system is running 5000 hours and we have a question about something that is not broke!

Yepp I guess the set screws fixed the rotation issue unless they were on the blades.

That's right, he didn't make it too clear what the set screws are doing.

Seems to Me You solved the problem!

oilcan13

Thank you all for your input.

By micro I mean micron (12 micron = 0,47 mil).

The 12 micron is the difference between the as per design (not measured) mean values of 74,6h6 and inner race diameter.

The system is running 5000 hours and we have a question about something that is not broke! It is better to be proactive, they say. I am not sure if and how the shaft suffered any wear. I think that the shaft has suffered negligible wear and by screwing the set screws the problem is fixed.

The set screws are to lock the inner bearing ring to the shaft.

I'd at least check the set screws at some period much less than 5,000 hours.

So this was a whole lot about nothing then?

What are the shafts min and max dimensions while being withing design spec and what are the bearing same values as well? If both are within their design specs call it good and don't worry about it until something actually starts giving problems.

There's a time and place to be proactive about maintenance and then there is just making work for the sake of saying you did something.

Any idea how to check if they are within design specs without making work for the sake of saying I did something?

Well how exactly are you measuring the ~12 micron (.00047") variance between the two parts with any accuracy to begin with on a 74.6 mm dia shaft and bearing set?

I'm just curious being that the differences in diameter between a cool to touch and hot to the touch steel shaft and bearing race could account for a good part of the 12 microns.

A reasonable tolerance for a transition fit on a 75mm shaft would be up to 20 micrometres.

Sorry to be a pedantic PITA once again, but while the term "micron" is commonly used in lieu of "micrometre" its usage is not strictly correct (and we all want to be correct...right?) .

The SI system formerly banned the use of the term "micron" to denote micrometre in the late 1960s. Further, although the word microns is in common usage, the more correct word for more than one micron is micra.

It's okay. I'm not the one who programs the conversion calculators and puts what names relate to what units of measurement.

That and in what little bit of precision measurement those lengths were called microns as in the micron ratings of hydraulic or fuel filters so for me the term micron seems to be perfectly valid unit of reference.

Sorry spades I have agree with tcmtech, with over 50 years in and around machining, when it came to tolerances it's either millimeters or thousandths of an inch. In aviation "micro" is usually termed with filters. And the reason why I questioned their terminology of "micro"

You've touched there on another possible cause of confusion, American usage of mil for 1/1000 inch, not millimetres.

Even if micron is unofficial everybody who needs to knows it's the same as a micrometre, and whether it's for particle size, mesh size or small clearances it's still 1/1000000m.

I am not measuring. The 12 micron is the difference between the as per design (not measured) mean values of 74,6h6 and inner race diameter.

It does not make sense to me that the bearing inner race would not require an interference fit on the shaft to stabilize the shaft end.

Using set screws would not properly center the shaft in the bearing.

Without the shaft end being stable and in-center, vibration will be an issue that can lead to severe damage especially at higher RPM operation.

Are you certain the callout does not indicate an interference fit?

If the shaft is softer than the bearing inner race and the bearing is allowed to slip on the shaft, the shaft will suffer erosion of the surface resulting in decreasing shaft outer diameter.

Using a set screw most likely was/is the equipment manufacturer's way of cutting cost and may not be a viable long term "fix" for your application.

Often metal spray techniques can effectively be used to restore the shaft to original specifications or improve the fit.

If not feasible to do metal spray, it may be that the shaft(s) will have to be removed, the shaft undercut in a lathe, then a properly sized sleeve installed on the shaft and cut to OEM clearance specs.

"If the shaft is softer than the bearing inner race and the bearing is allowed to slip on the shaft, the shaft will suffer erosion of the surface resulting in decreasing shaft outer diameter."

Is it possible that this was the cause of the shaft/bearing ring rotation to begin with?

Also what is the service of the fan?

Are the shaft and bearing exposed to temperatures that would be such so as to loosen the bearing as when removing it from the shaft, allowing it to rotate?

Most vertical fans have bearing with adjustable tapper sleeve inside the inner race. Tightening this tapper sleeve would expand tone inner race and consumes the bearing clearance. Manufacturer suggests the running clearance. The millwright practice is to tighten the tapper sleeve and measuring the needed clearance using feeler gauge. The sleeve's positioned can be fixed with respect to shaft by means of lock nut and lock washer. If this be your case as well, please refer the manual or manufacturer for recommended procedure and clearances.

But I've not come across a vertical fan bearing with set screw at the inner race. Can you attach the relevant sketch?

Clean the shaft and inner race and when reassembling use Red High Strength Loctite to secure the shaft relative to the inner race. Hey don't laugh, I have seen this done as standard practice on commodity product lines.

It's also pretty common in aviation to "glue" flight control bearings in their housing with Mil Spec: Mil-S-46163A. Just have be careful while applying it.

we use LOCTITE #609.

I couldn't find a picture of it. But yes, I've used that too!

Looking at the Loctite chart and website we used the #620 for higher temperatures!

It's also easy to remove with a bit of heat from a torch.

Thank you all for your replies.

Inner ring diameter is specified min=2,9375 in , max=2,9385 in.

After 5000h, the initial according to drawings clearance of 12 micron (or micrometer or micra), is probably a little larger, but it is not worth to dismantle and measure. The set screws keep the shaft in its place.

My main question was if there was anything else (except from tightening the set screws) to do, and I received valuable ideas.

My second question was whether there was any case where shaft to inner ring rotation caused problems, which I didn't see any response, may be it was overlooked, or may be there is not so many cases.

You missed the answers given in posts #2,#3,#9,#50. It seems that the fit is actually quite close. Certainly close enough to use Loctite. Again i would urge you to ascertain the bearing bore size before making a judgement call. Put it this way; you hire a bearing engineer to come and look at the installation and the first thing s/he would do is measure the shaft and determine what bearing is used. The bearing needs to be suitable for the job and the size has to be match the shaft, or vice versa. Save the money and do this yourself.

Jim

You have given clearances as per drawing. 12 micro clearance do not allow bearing motion between matting parts. That means your bearing became jammed before motion started between inner race and shaft. Normally bearing races are made of alloy steels and are very hard to wear, the only possibility remains is shaft getting weared and making clearance to rotate in the inner race.

May be after re-greasing, bearing might have become free to move and running after tightening of set screws.

Yes, shaft rotating in inner race causes problem. We have lot of applications but in horizontal installations. Shaft, once starts rotating in inner race, wear out continuously and very fast as it rotates without lubricant. Metal chips removed during the running do add on the rate of further wear and naturally the softer part will wear out.