Fits Procedure
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The tolerances of the inner ring bore diameter and of the outside diameter of the inner ring
are defined in accordance with international standards. The assembly conditions on the shaft
and in the housing are extremely important for the correct functioning of a ball bearing.
For the choice of adequate fits, it is therefore very important to pay particular attention
to the following points.
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| Surface finish and geometrical form of the shafts and the housings |
These two parameters exert an influence over the fit and the hearing noise partcuIarIy
at high speeds |
| Temperature and temperature variations |
When the shaft and the housing material are different or with significant temperature
variation, a change of the Internal clearance may occur. The fit could become either looser
or completely blocked. Eventually, length variation should be considered |
| Load Range, direction and type |
A load increase requires tighter fits |
| Operating conditions |
Rotating rings must have a tighter fit than fixed rings In order to avoid any sliding |
| Rotational accuracy and radial stiffness |
High requirements must be formulated In respect to surface quality and geometrical forms |
| Influence on the radial clearance |
Inappropriate tolerances on the shaft or the housing of a ball bearing can lead to an
expansion of the inner ring, or to a narrowing of the outer ring. Consequence may be a
reduction or even a suppression of the radial clearance |
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By taking the above mentioned points into account and in order to get a Normal radial
clearance when assembling deep groove ball bearings, machining tolerances of j5 to k5 for the
shaft and J6 for the housing are admissible.
The dimensions of the abutments provided by the shaft and the housing shoulder must be
sufficient in order to get a precise fit, an exact alignment and an axial control with axial
loads. On the other hand the abutment surfaces should not come into contact with the shields.
The values da mm and Da max for the abutment surfaces are indicated in the bearing tables.
These tables also mention the minimum fillet radius rsmj, of each ball bearing. The abutment
surfaces fillet radii must consequently be smaller than ramin.
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| The following tables indicate the machining tolerances of the shafts and the housings
allowing appropriate fits. The tolerances (in jim and j.tinch) are only valid with shaft and
housing materials, which have the same expansion coefficient as 100 Cr6 I SAE 52100 bearing
steel (11 x 10 m 1°C). |
Fits are valid for normal operating temperatures. At high temperatures, it is advisable
to check that the radial clearance is not too high. In extreme conditions it is necessary to
try to find the best compromise. |
| Shaft fit tolerances |
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| Housing fit tolerances |
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