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buying rolling bearing at the small end of the bore tolerance? 4

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electricpete

Electrical
May 4, 2001
16,774
For a bearing like a 6318 / 90BC03, the tolerance range on the bearing bore is 3.5425 - 3.5433.
If you're evaluating an undersized shaft that's a pretty big range.
We sometimes pull all of ours out of the warehouse and use the smallest one. But that doesn't always work, recently the smallest out of 3 of those 90BC03 bearings was 3.5432 average bore according to our ace machinist.

I'm wondering if there's a way to approach this on future work to have the best chance of NOT having to rework the shaft (by having the smallest bearing bore within tolerance).

Has anyone heard of any manufacturer or distributor that sells bearings based on their range within the tolerance?
 
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There is a problem, bearings are sized to be under the nominal bore size. Selecting a bearing with tighter tolerance class will always yield a larger bore than the minimum bore of a looser tolerance class.

How is the bearing retained on the shaft? If it is retained with a locking nut, it may be possible to use a tapered bore bearing with a sleeve. These fit on a wider range of shaft diameters as bearing clearance is adjusted by driving the sleeve with the nut.

Not knowing anything specific about your application, there are chemical options. Retaining compound can be used to create a simulated press fit.

I know you would prefer to not do rework, but electroless nickel plating could be used to build up the shaft without requiring rework of the entire shaft. You may not even need to grind the shaft if you're only flashing on a very thin layer. There is an outfit in Texas that specializes in this.
 
Maybe this will help you to, but with my last issue, i came out to extremebearing.com
If i understand correct, they are designing a new bearing unit what not will destroy your shaft (lightweight). For me it wasnt total clear what they mean, but maybe they can help you in future? I couldnt find it on there website, but they are real fine to work with!

 
"The major difference between the two systems of metric and inch bearings is that inch bearings have historically been manufactured to positive
bore and O.D. tolerances, whereas metric bearings have been manufactured to corresponding standard negative tolerances."

page 56 here -
 
Just for humor, I've never met an inch rolling element bearing in something that wasn't built in a garage or on a farm.

Edit: strike that, TDI air starters use a 6201 bearing on the turbine shaft with a 1/2" bore. I'll have to check on the bearing manufacturer. Maybe they can provide custom finished bearings for your application? They are imported bearings.
 
Depending where I live, when I hit the light switch three pairs of 10.500" +.001"/-.000" " ID tapered roller bearings are grindin' up about 150,000 lbs of coal per hour here.


I'm thinking the outer tapered roller bearings on the front wheels of a 1966 Chevrolet Impala were likely 3/4" .750 " ID and 1 25/32" 1.781 " OD.

 
I wonder if you could mask off the sides and OD and do a low-temp spray on the inside of the bore. It would need to be fixtured so that it sprays evenly and does not create runout.

Knurling the shaft may be helpful in conjunction with a Loc-tite type of product.

In my industry we chrome-plate and grind shafts that are worn undersize. And I spec ball bearings to be C3 clearance so that I can give the shaft journals a more generous tolerance.
 
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