Attach bearing to axle 1

[Cinko]

How do you attach a ball bearing to an axle. I have a 6 mm shaft and a 6 mm bearing and I have successfully mounted it by heating the steel bearing to a few hundred degrees and lightly hammering it into place.

But what I would like is some more modular way of attaching it, and how would I mount a plastic bearing? Perhaps there is some part that could adapt a 10 mm bearing to a 6 mm shaft using some sleeves and screws? I really have no idea how to do this and if you could point me to some guide or post me some pictures of what parts I would need it would be very helpful.

 

[MikeHalloran]

You may have noticed that the bearing surfaces are very smooth. They are made to exacting tolerances. The usual way to mount a bearing is to press it onto a shaft that's made to equally exacting tolerances.

Given that you used heat _and_ impact, the bearing is probably now toast.

Get a couple of bearing catalogs, and study them.



Mike Halloran
Pembroke Pines, FL, USA

 

[Cinko]

Your suggested way of mounting would not hold it tight against even moderate torque.

The bearing I mounted using heat and very light hammering on the inner ring works fine, what I am asking for is a modular way of attaching bearings firmly. I found a product called ShaftLoc that does just that but I would suppose that even before this was invented there were good solutions.

 

[MikeHalloran]

Could you please explain what you mean by use of the word "modular" in this context?



Mike Halloran
Pembroke Pines, FL, USA

 

[MintJulep]

Heat and/or press are the usual ways.

 

[hydtools]

An alternate would be Loctite bearing mount adhesive. Although I prefer press or shrink fit. I have never had a press fit bearing spin loose from the shaft. 6, 8, and 10mm.
Whatever method still requires similar tolerances on the shaft.
I'd be concerned that the Shaftloc could be tightened too much and take away the bearing running clearance.

Ted

 

[MintJulep]

The ShaftLoc and similar products are intended to mount sprockets, cogs and pulleys to shafts, not bearings.

The reason that the required tolerances for bearing lands are tight is that the radial expansion of the inner race from the press-on is what sets the running clearance.

Hydtools is correct to be worried about over-tightening.

 

[vims]

"Your suggested way of mounting would not hold it tight against even moderate torque"

The whole point with a ball bearing is that it can´t take torque in that direction. If you want the bearing to be able to take an axial force, then thats another thing. You then have to make something that your inner side of the bearing can rest against.

 

[Cinko]

Thank you for your answers, so the problems I had must have stemmed from different tolerances on the 6 mm bearing and shaft not making me able to simply press it on.

And my other concern about a bearings inner ring slipping radially at acceleration of the shaft, I conclude from your answers is not likely.

And about axial forces, would this be the part to circumvent it?

https://sdp-si.com/eStore/PartDetail.asp?Opener=Group&PartID=15778&GroupID=339

By modular I mean that I can assemble and reassemble the parts without damaging any of them. Like my example of mounting the bearing using heat would make me unable to dismount it since heating the bearing would also heat the shaft, i.e. not modular.

 

[hydtools]

Perhaps if you could describe your problem, someone could offer a solution.

Yes, a split collar could be used to prevent axial movement of the bearing.

Ted

 

[jistre]

If you're getting axial movement of the bearing, and you try to prevent it with a split collar, collar, shoulder on the shaft, etc. to hold the bearing in place, you're going to be supporting a thrust load with the bearing. You might want to ignore the plain ball bearings and go to a ball or roller thrust bearing.

Or perhaps my inference about the bearing you have is incorrect and you already are using a thrust bearing, and this is a moot point.


As for modular mounting, I've seen nothing, and I'd be wary of anything that accomplishes it for the running clearance issue MintJulep pointed out. The bearing manufacturers really do take that couple of thousandths of an inch of expansion into account during the design of the bearing. Depending on the conditions, improperly mounted bearings may decide to live fast and die young, but they rarely leave a good-looking corpse.

 

[Cinko]

jistre, Thanks for that tip. I could use a thrust bearing at the base and plain bearings for shaft suppport. But then axial forces would only be held in one direction. Mounting a thrust bearing at the top is not an option since it is to be free, like the shaft of a helicopter.

A possibility could be a thrust bearing with different inner and outer diameters so that it could be held by a split collar mid-axis and still hold the axial force while allowing rotation. So this together with plain bearings and the base thruster bearing would hold it in place. Then again I am thinking that any axial force would be divided among the plain and thruster bearings, and the same problem exists just that some of the force is taken by the thruster bearing.

A third kind of bearing, which I again do not know if it exists, would be a cylinder filled with balls which rotate freely against the shaft, hence allowing axial and radial movement but not any lateral(shaft-orthogonal). And this could be coupled with the double thruster bearing for any axial movement.

 

[eromlignod]

I'm surprised no one has mentioned just an ordinary bearing locknut and washer. They are specifically made just for this purpose. Most bearing supply houses carry them.

I'm not sure what you mean when you say that the inner race must be able to withstand more than "moderate torque". It's a bearing; it should see almost *no* torque.

As Halloran said, you should study the engineering notes in the bearing catalog. You are responsible for retaining the races by your design. There are specific fits required for precision bearings and they are not press fits. The tolerances depend on which member is rotating (shaft or housing) and which is stationary (if either) and call for different fits accordingly.

A proper design will include a way to externally retain races firmly without using a press fit. There are a variety of standard ways to do this including bearing nuts and caps, pressure rings, etc. Of course, if there are bearings at both ends of an axle, one fit (either a housing or shaft fit) must be free to avoid statical indeterminancy and allow for thermal expansion/contraction. This is often accompanied by a bearing pre-load washer to prevent rattling and wear.

Don
Kansas City

 

[Cinko]

To make things clearer, the problem is to mount a freely rotating shaft very firmly to a chassis, with the top end free, like in a helicopter. The shaft should be able to mechanically withstand axial forces and also be laterally secured, but rotationally free, of course.

Thank you for all your answers I have now many ideas that might work for my specifications.

@eromlignod: About the inner rings torque I agree that the inner ring sees almost no torque I just wanted it to be secured firmly and not slip versus the axle.

About the pre-load washer technique, am I right in thinking that using it is a trade off between lateral precision and allowing for thermal expansion? How would you suggest that I "unfit" a bearing? Or are you proposing to fit a larger bore bearing with precision washers? This would also mean that I would have to mount the outer ring to the chassis using some flexible means, right? This all sounds a little bit too far for my project, I think statical indeterminancy is ok for me.

 

[eromlignod]

I'm not sure I understand your questions about the pre-load washer.

Imagine it like this. You have a rigid housing on the left and a rigid housing on the right. An ordinary conrad bearing inserts into each of them and a shaft goes through both bores. The fits called for in a bearing catalog will call for some type of locational/transitional fit. It will have little or no radial play, but not have enough friction to be a force-fit and retain the shaft or bearings axially.

So neither the shaft nor the bearings are technically retained at this point.

By including a shoulder and threads on the ends of the shaft, the inner races can be solidly secured to it.

The housing bore can be designed with a counterbore or a snap ring for the outer race to bear against, but it is still free in the other direction. To secure it you could design a bearing cap that bolts to the housing and has a protruding ring that clamps the outer race against the counterbore ledge, like a packing gland. Now the position of the shaft relative to the housing is determined, neglecting the small axial play in the bearing itself.

For the other outer race, you could simply fit it into a clear bore with no retaining at all. It's already secured to the shaft, which is already fixed at the other end, so it's not going anywhere. This would allow thermal expansion, since it is free to move in the bore. If you tried to rigidly locate it you would probably have problems, since if temperature ever caused the shaft to expand or contract until the axial play of the bearing is used up you could potentially have tremendous thrust forces that are unnecessary.

If this tiny amount of play is objectionable in your design, that's when the preload spring comes in. You would design the housing with a counterbore or snap ring, leaving enough room for maximum expansion, then put a wave-washer in between to push the outer race away from the flange until the play is taken up. This always justifies the shaft in that direction, regardless of temperature or manufacturing tolerances.

Don
Kansas City

 

[MikeHalloran]

>>mount a freely rotating shaft very firmly to a chassis, with the top end free, like in a helicopter<<

To simplify things a lot, helicopter main rotors are cantilevered on a shaft that's carried by two bearings, both of which are in the main rotor gearbox. The upper bearing is actually in the approximate middle of the shaft, and to a first approximation carries twice as much radial load as the lower bearing, which can be smaller.



Mike Halloran
Pembroke Pines, FL, USA

 

[Cinko]

MikeHalloran, regarding your last post, do you mean "carries as much AXIAL load as the lower bearing" (i.e. along the axle).

And about the way a helicopter shaft is mounted, all the weight of the helicopter and axial rotor forces are on the bearings themselves... I thought I wanted to avoid this, per vims post:

"The whole point with a ball bearing is that it can´t take torque in that direction. If you want the bearing to be able to take an axial force, then thats another thing. You then have to make something that your inner side of the bearing can rest against."

The above post is the reason I started to try and construct a thrust bearing with a bore in it, to hold the axial forces on the inner ring of the plain bearing.

But perhaps this is generally nothing I should be worried about, and I could simply choose a larger plain bearing for larger axial loads?

 

[hydtools]

Here are some mounting methods from NTN:

http://www.ntnamerica.com/pdf/2200/shaftdes.pdf

Ted

 

[Cinko]

@hydtools: I'm sorry but I have no idea what those images are trying to convey. Perhaps because I have not seen the parts they are trying to sketch.

 

[ischgl99]

A ball bearing can handle an axial load, but not as much as an angular contact or tapered roller bearing. You need to determine how much axial and radial loads you have before deciding on which bearing to use and then size accordingly to give the life you want. Depending on what you have on the end of this shaft, you could have significant radial loads to handle and not just axial as you seem to indicate.

Using a 10mm ID bearing vs the 6mm ID might not be a good idea if your loading is too low, you could induce skidding which will damage the bearing in short order.

You can machine a shaft collar that will allow for your modular assembly, but the fit between the bearing and the collar will still need to be tight enough to prevent the inner race from rotating as well as providing the proper internal clearance. The bearing catalogs will have the approriate fit tolerances for your application. The shaft collar would need a clamp or locknut that will then lock the collar on the shaft to prevent rotation on the shaft.

I don't understand the need to be able to remove the bearing and still be able to use it. A 6mm bore bearing is cheap unless it is a high precision grade and I would just throw it out and replace with a new one, unless you plan on removing the bearing often to make changes to what is attached to the shaft.