Bearing housing tolerance limit

[theStruggler]

Hi,

I would like to confirm the tolerance limits for a ford fiesta bearing. I am new to this so please bear with me. The bearing has an outer diameter of 72 mm, inner diameter of 37 mm and a width of 37 mm. It is a ball bearing. From what I found (here

http://www.nskamericas.com/cps/rde/xbcr/na_en/CNSK_Pocket Fits06-Fits and Clearances.pdf),

the housing tolerance is of category N7 and from another source (

http://www.ntn.co.jp/english/products/catalog/pdf/2202E_a07.pdf)

the housing tolerance limits are: +0.039/-0.004 mm.

I would really appreciate it if someone could confirm this for me.

Thanks

 

[Tmoose]

The tolerance depends on whether the outer or inner ring is stationary, and whether the direction of load is constant (like gravity).n

pages 3 thru 7 at the link you provided

 

[theStruggler]

Thank you for your reply. How can I determine whether the inner or outer ring is stationary? Am I the one who fixed which is stationary or do bearings already have preset stationary inner and outer rings? Also could you help clarify the stationary and rotating load cases for me with an example?

Thanks

 

[Tmoose]

The bearing mfr does not know how you are going to install their bearing.

A regular electric motor has a rotating shaft and inner race/ring, and stationary outer race/ring.

A 1959 Chevy Impala front wheel has a stationary inner ring and a rotating outer ring.

In each case the load (gravity) is essentially one directional for the stationary ring, so it can be designed with a slip fit in/on it's "seat" (the shaft/housing.)
However in each case the load varies direction relative to the rotating ring, so they must be an interference fit with their seat, to prevent creep and attendant wear and destruction.

If there are multiple loads or with a vertical shaft then it is possible to end up with loads varying direction for both rings, which requires clever compromises to permit adjustment or assembly.

 

[GregLocock]

In the specific case of wheel bearings it is sometimes necessary to go away from the standard fits, due to brake temperatures. I always got Timken to double check my design when we used taper rollers, as we tended to get some odd setups.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[theStruggler]

Thank you Tmoose and Greg for your replies.

Please let me know if I am wrong here: bearings in steering knuckles usually have stationary outer rings and rotating inner rings which means they have to be fitted with a given interferance on knuckle center hole. In this case, the tolerance will be of category N7 (interferance of 0.039 mm and clearance of 0.004 mm) as I mentioned in my first post.

 

[GregLocock]

" bearings in steering knuckles usually have stationary outer rings and rotating inner rings " the only way of telling is to look at the design of your car, whichever bit goes round with th wheel is the roatating one. We use both possibilities on the same platform. A powered axle is likely to be stationary outer for obvious reasons, but for a non driven wheel there are good reasons to use a carrot and a rotating outer.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[theStruggler]

I am dealing with a front knuckle for a front driven vehicle. In this case, I think I am safe assuming that the outer ring is stationary.