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    interference fits
    loss of radial play
    ball bearings - interference factor
  MOUNTING AND FITTING  

INTERFERENCE FITS - LOSS OF RADIAL PLAY

Where interference fits are achieved by pressing a shaft into a bearing or a bearing into a housing, particular care must be taken in dimensioning and tolerancing mating parts. Radial play values of will be reduced by an amount proportional to the interference.

rf =  ∆r-fp • I      where: ∆rf = final radial play after pressing part
                                          ∆r = initial radial play
                                          fp = interference factor
                                          I   = interference between bearing and mating part

The interference factor fp is dependent on the thickness of the bearing ring 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 THINKNESS Inches
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       where:    d       =        bearing bore                                                                        2                      D           =           bearing O.D.
Outer ring thickness =  D - lo                  li            =         inner ring land diameter*
                                          2                      lo        =       outer ring land Diameter*           

(*Land diameters are given in the individual bearing specification tables.)

Note that the above fp values are intended as a guideline only. If the mating part itself has a thin section, then the above factors will be reduced slightly. The important point is that 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 (e.g. MC5 - 0.0005" to 0.0008") be used where interference fit is needed.






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