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Bearing Mounting and Fitting: Tolerances and Interference Fits || Dynaroll

TECHNICAL PAPERS

TECHNICAL PAPERS

DESIGN FACTORS WHEN USING SMALL BEARINGS, PART 2: MOUNTING AND FITTING (Page 2)


In general, radial play values should be reduced by an amount proportional
to the interference with the mating part:

∆rf = ∆r – fp . I

Where:  
 ³rf = final radial play after pressing bearing
³r = initial bearing radial play
fp = interference factor
I = interference between bearing and mating part

The interference factor fp is dependent on the thickness of the bearing race and the material and geometry of the mating part. It is suggested that the following empirically determined values are used:

Values for Interference Factor fp
Bearing ring thickness*
Mating material
Steel
Brass/aluminum
Plastic (filled)
<0.015
0.8
0.6
0.3
0.015 - 0.030
0.7
0.4
0.2
>0.030
0.6
0.2
0


Bearing ring thickness is calculated as follows:
 
 Inner ring thickness = (li – d)/2
Outer ring thickness = (D – lo)/2
Where:  
 d = bearing bore
D = bearing OD
li = inner race land diameter (open bearing)
lo = outer race land diameter (open bearing).

Note that open bearing land diameter values are always used, even if the bearing used has shields or seals.

The above fp values are intended as a guideline only. If the mating part itself has a thin section, then the above factor will be reduced slightly. The important point is that the interference can significantly reduce radial play and must be accounted for in a design to arrive at the final desired radial play. For this reason it is recommended that a higher radial play bearing (e.g. 0.0005 to 0.0008 inch) be used where an interference fit is needed.


Bearing Mounting and Fitting, Page 3: Tolerances and Interference Fits link