Bearing Internal Clearances

[matt037]

Does anyone have any firsthand knowledge of the accepted “standard” or “normal” values to use for radial internal clearances of single row deep groove ball bearings? The table provided in ANSI/ABMA Standard 20-1996 details the radial internal clearances for deep groove ball bearings; however, we are not sure which values would be considered “standard” or “normal”. Typically we have deferred to the SKF statement of “single row deep groove ball bearings are manufactured with Normal radial internal clearance as standard” (per SKF website). Their Normal appears to be consistent with the Group N values provided in the ANSI/ABMA table referenced above. However, recently we have been hearing from distributors that the C3 designation is the “standard” or “normal” clearances to use. We are not sure if this is simply someone trying to sell us anything they have in stock, or if these are legitimate statements. Any help would be appreciated, thanks.

 

[Tmoose]

The "standard" clearance (no suffix or designator in bearing number) is one thing.

The "fact" that C3 clearance bearings are used in so many classes of equipment that "they" are practically the "standard" is another.

Often, but not always, a little Extra clearance will cause fewer problems than a little less. A tight shaft or housing fit, or not-so-good housing or shaft roundness are times when a little loose can be a blessing.

In some sizes a "tight" C3 will have the same clearance as a "loose" normal clearance brg.

It is confusing.

 

[electricpete]

For electric motors, the vast majority are C3 fit.

But as a user, if I am ordering replacement bearings, I try to recreate what the OEM put in there, especially with regard to internal clearance. Usually the motor has the AFBMA number on the nameplate which tells you the internal clearance to specify in your replacement bearing

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[diskullman]

I wouldn't start worrying until they give you C4 clearance. In many cases the Standard clearances over-lap, such as for a Standard fit 35 mm bearing , tolerence is .0002/.0009, C3 is .0006/.0013, so a tight C# bearing could also fall into the range of a loose standard bearing.

Russell Giuliano