ball bearing fits for small/medium horizontal motors 1

[electricpete]

Is there any on-line reference that addresses bearing shaft and housing fits specifically for motors?

For simplicity I am primarily interested in small/medium horizontal motors with ball bearings.

Is a general k5 shaft fit and H6 housing fit reasonable to apply in this case? Any reference to support it?

I realize the best info come from OEM, but OEM does not always make that info readily available. I also realize there is a lot of detailed info from bearing manufacturers (like SKF CD)... but I'm interested in something simpler geared specifically to motors.
Thanks

 

[Hippo41]

For standard electric motors the following is recommended:-

Shaft < 18mm; tolerance js5
Shaft 18-100mm; tolerance k5 or k6
Shaft 100-140mm: tolerance m5 or m6
Shaft 140-200mm; tolerance m6

In all cases bearing manufacturers would prefer the better tolerance, but will accept the lesser standard.

It's best to specify roundness to within 1 IT grade better than above, i.e. if you have k5, that's IT grade 5, check roundness to within IT 4.

Housing tolerance generally J7 if you require axial displacement of the outer ring (e.g. preload spring). Sometimes the outer ring is physically restrained, but J7 still OK.

the above will be OK for most applications, and can easily be set up on charts for workshop people to follow. i expect that some contributors will have preferences for other fits for specific applications.

Extracted from NSK General catalogue - other manufacturers will all be pretty much the same.

Lester Milton
Telford, Shropshire, UK

 

[electricpete]

I found EASA publication which I believes answer my question. H6 housing fit and k5 shaft fit for the shaft size range 20mm-100mm.

The published shaft and housing fits are more stringent than required in order to allow for unknown variation of the bearing within it's tolerances. Can we allow less stringent tolerances on our shaft and housing fits by taking advantage of actual measurement of bearing dimensions and still be in agreement with the selected tolerance class?

For example:
6313 bearing H6 housing fit

Housing ID limits 5.5118 - 5.5128
Bearing OD Limits 5.5118&quot; (140mm) +0 – 0.0007&quot; = 5.5111-5.5118

Tightest possible: 5.5118-5.5118 = 0.0000&quot;
Loosest Possible: 5.5128 – 5.5111 = 0.0017&quot;

Allowed clearance 0 Loose to 0.0017&quot; loose.

Now lets say we have actual measurements:

Actual Housing = 5.5130 (exceeds Housing limit 5.5118 - 5.5128)
Actual Replacement Bearing = 5.5115

Looseness = 5.5130 – 5.5115 = 0.0015 (within clearance limit 0-0.0017&quot; loose)

Does it meet H6 requirements or not?
(Please don't ask me to use my judgement based on the application…. I work in nuke industry where we prefer everything black or white).