DINTECHNICAL INFORMATION

Fits

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:

● Surface finish and geometrical form of the shafts and the housings
These two parameters exert an influence over the fit and the bearing noise, particularly 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.

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 d_amin and D_amax for the abutment surfaces are indicated in the bearing tables. These tables also mention the minimum fillet radius r_smin of each ball bearing. The abutment surfaces fillet radii must consequently be smaller than r_smin.  

The following tables indicate the machining tolerances of the shafts and the housings allowing appropriate fits. The tolerances (in mm and inch) are only valid with shaft and housing materials, which have the same expansion coefficient as 100 Cr6 / SAE 52100 bearing steel (11 ´ 10-6m/ °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.

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