Bearing covers & shaft designs

[jim01018]

Hi

I have recently moved into a mechanical desiging role where we use a lot of bearings, and in-house manufactured shafts.

I just want to check some concerns i have on tolerances with these.

Say using a bearing of 35 dia ID, i have designed the shaft with a 35 -0.025/-0.075 tolerance. Does this sound ok? (taken from a previous drawing) Would it have been wiser to use a tolerance as BS4500 states i.e H7 and h6...what is a good tolerance to use for the shaft so as to not have a 'sloppy' fit ?

Also, a bearing with a 62 dia OD needs to fit into a plate/cover support. What tolerance should i put on the diameter of the plate so as to provide the best smooth running fit (transition fit/press fit etc) ? Are there any we websites with general tolerance practicies ?

Thanks for your help...

Jim

 

[ischgl99]

Jim,
I would suggest getting a bearing catalog, it will have suggested fits as well as the tables for the shafts and holes. You can download a lot of good information from the FAG website,

http://www.schaeffler.com

There is a series of design guides for different types of equipment that might help you with your design, search for WL 00-200/5. You can also use the Medias bearing design program on that website, it has the information you are looking for.

http://medias.ina.de/medias/de!hp/;a5NZAeiVx1B6?lang=en

To answer your question, if the shaft is rotating, then there should be an interference fit, typically k5 or k6 which would be +.002 to +.013mm for your 35mm bearing and the housing would have a slip fit of H7. Normally you want the tighter fit on the part that rotates and looser fit on the stationary part. If you used the minus fit you show above, the inner race will most likly spin on the shaft and decrease the life of the bearing. I strongly suggest you contact an applications engineer from your bearing supplier and have them assist you with your design.

 

[sreid]

Not cheap but worth every penny if you can get your company to spring for it.

http://www.amazon.com/Ball-Roller-B...2839204?ie=UTF8&s=books&qid=1184800588&sr=8-1

 

[GPRnD]

The key qestion to answer first is whether your bearing load is fixed or rotating relative to the inner and outer rings.

This in turn will dictate the type of fit recommended.

Check the SKF handbook for examples of this, and if your not sure, come back here and describe the loads that are acting on the shaft/bearings.

 

[jim01018]

Hi

Sorry about the delay been on holiday !

I have tried to use the SKF handbooks, but still not further understand.

Can i provide some examples for you to adivse on if possible ?

1) The shaft (32mm dia) is stationary and the outer housing (in this case a roller) rotates. The od of the bearing selected is 47 mm. What tolerance should be on the stationary shaft and outer roller ?

2) The shaft rotates and the roller housing is stationary (same dims as previous)

3) Both the shaft and roller rotate.

Thanks for any help anyone can provide

 

[Tmoose]

"1) The shaft (32mm dia) is stationary and the outer housing (in this case a roller) rotates. The od of the bearing selected is 47 mm. What tolerance should be on the stationary shaft and outer roller ?

2) The shaft rotates and the roller housing is stationary (same dims as previous)

3) Both the shaft and roller rotate."

If the only load is gravity, or gravity plus a belt, then -
Case 1 could be OD tight, ID slip fit
Case 2 ID slip fit, OD tight
Case 3 ID and OD must be tight

By "tight" I mean line-to-line or interference.
By "loose" I mean just a few 0.0001s inch clearance, maybe 0.001 inch.
Yes, axial expansion most likely needs to be accomodated bys ome means. that is tricky in case 2.