# The shaft can be misaligned?

1. Feb 23, 2014

### asteorit

Hello,

I want to ask if the shaft is mounted on bearings, it is possible that the shaft can misalignment? Since the bearings have "free angle of misalignment".
As such it then misalignment determine or calculate?

#### Attached Files:

• ###### 1.jpg
File size:
11.7 KB
Views:
206
2. Feb 23, 2014

### Astronuc

Staff Emeritus
There should be a tolerance on straightness of the shaft and perpendicularity of the bearing and bearing housing.

It is possible to misalign a shaft (or set of shafts), either laterally (horizontally or vertically), or angularly. Usually that has to do with the orientation of the housing, so it is important to set a turbomachinery housing or coupling properly.

3. Feb 23, 2014

### asteorit

and when we consider that the bearings are stored perfect, perpendicularity of shaft is also perfect. And we will consider only the will, which is in the bearing.

4. Feb 23, 2014

### SteamKing

Staff Emeritus
Bearings can be misaligned due to thermal effects and deflections due to other loadings on the bearing supports.

5. Feb 24, 2014

### asteorit

Yes, I understand, are all external conditions for the deployment of the shaft bearings.
But I would like to know how to deflect the shaft mounted between two bearings, bearing me the simple radial play, axial play, free angle of misalignment. .
For example as shown in fig.

#### Attached Files:

• ###### Ball-screw-end-mounted.jpg
File size:
41.7 KB
Views:
133
6. Feb 24, 2014

### Q_Goest

Hi asteorit. I assume English is not your native language. Your questions are very difficult to understand.

I think what you are asking is how you could mount a shaft on bearings but still allow for the shaft to be displaced at some angle. Do you need to shift the axis of the shaft by some angle as you show in your first picture here?

If so, what angle do you need to shift the axis by? Right now the picture you posted just says: XoX'
Is this angle the one you need to shift the axis of the shaft by?
If so,
• can you give an aproximate angle?
• does the shaft need to be supported with 2 sets of bearings as you show in the picture? Or can you use just 1 bearing such as a spherical roller bearing which would allow some small angular movement as you show.
Ref: Spherical Roller Bearing

7. Feb 25, 2014

### asteorit

I apologize for my bad English. It's not my native language.
I do not want to deflect the shaft axis. I want the shaft axis is perpendicular to the base.
I want to know whether it can deflect the shaft axis? Inasmuch as the bearings have the clearances.

I mean as follows: The shaft with bearings assembled as shown. And some small force (eg only handle) I will push the shaft axis. And I will measure the misalignment the shaft axis micrometer. Of course we consider that all components except deposits are perfectly rigid. A precision machined surfaces is also perfect.

It is a proposal for an electric motor. A must withstand indicated loads.
Think that such a choice is correct bearings?
Insure lower ball bearing also on the stator? (Axial)

XU080264 : http://medias.schaeffler.de/medias/en!hp.ec.br.pr/XU*XU080264

#### Attached Files:

• ###### 2.jpg
File size:
17.8 KB
Views:
87
8. Feb 25, 2014

### Q_Goest

Hi asteorit. I'm still having a bit of trouble understanding you, so I'll try and explain what I believe you are asking. If I'm confused, please feel free to correct me.

I believe you are asking how much deflection the bearings might contribute or add to the deflection of a shaft when a force is exerted perpendicular to the shaft axis as shown in your last drawing. That force you show is 10000 N. The bearing's contribution to the deflection of the shaft will be minimal. I would suggest you neglect the contribution of the bearings to the shaft deflection. If the remainder of your hardware (motor, shaft, etc...) is sufficiently rigid to prevent excessive shaft deflection, the bearings will work fine.

Take a look at the SKF bearing life calculations here:
http://www.skf.com/group/products/bearings-units-housings/roller-bearings/principles/selection-of-bearing-size/selecting-bearing-size-using-the-life-equations/basic-rating-life/index.html [Broken]

That tells you how many times a bearing can rotate before a certain percentage of them will wear out. As a rule of thumb, and this is a sweeping generality, I would suggest looking for a dynamic load rating on your bearing roughly 10 times higher than the load it has to support. Depending on how fast it rotates, how long you need it to last and how sure you are of the actual loads in service, you may not need a bearing with a dynamic load rating 10 times higher than the load being supported, but you should be doing a calculation based on bearing life and actual conditions.

Bearings can be tricky to properly select. You need to take into consideration the interference fit on the shaft and in the bore, how to lubricate it, how fast it rotates, etc... There's a lot to consider. I'd suggest talking to a bearing manufacturer or supplier if you're not familiar with them. If you'd like some suggestions I might be able to show you a way to properly support this using a sketch tomorrow. Let me know if I've understood you correctly though.

Last edited by a moderator: May 6, 2017
9. Feb 27, 2014

### asteorit

I thought of something else. Probably do not speak English so well, to explain what I want. But thank you anyway for your reply.
My professor changed his mind and wants to use a different solution. He decided to use only one large bearing. What do you say?

10. Feb 27, 2014

### Q_Goest

Well, I don't know how you can support a motor shaft with just one bearing. Generally a motor is not a simple disk, it has some axial length to it. So if it has any axial length and if you have a force which is not in line with the bearing, you will produce a moment around the bearing which the bearing is not designed to resist. Or maybe I'm just misunderstanding what your professor is trying to suggest. Good luck!

11. Mar 3, 2014

### asteorit

I can not even imagine how I will it work with one bearing.
I'm thinking of still the shaft deflection.