Mounting bearings with a tapered bore
Bearings with a tapered bore are always mounted with an interference fit on their seat on the shaft. The reduction in radial internal clearance or the axial displacement (drive-up) of the inner ring on its seat are used as a measure of the degree of interference. For cylindrical roller bearings, the clearance reduction method is preferred as this is a relatively simple procedure. It is simply a matter of measuring the expansion of the inner ring, i.e. the enlargement of the inner ring raceway diameter; this can be measured using a stirrup gauge. A suitable, well-proven method for mounting precision cylindrical roller bearings with tapered bore and for adjusting the internal clearance or bearing preload is described in the SKF catalogue "Precision bearings".
For large bearings of the NN design, however, suitable gauges are not available so that it is difficult to determine the inner ring expansion with sufficient accuracy, it is simpler to use the axial drive-up on the tapered seat as a measure of the interference.
In table guideline values are given for the clearance reduction as well as the axial displacement "s" for cylindrical roller bearings with tapered bore. The fit obtained using these recommendations has sufficient interference, particularly if the larger clearance reduction value is achieved. The minimum value is primarily applied for bearings which have a radial internal clearance before mounting which is close to the lower limit of the particular range, see clearance tables. There will then be no risk of going below the corresponding minimum value of the recommended final clearance.
Heavy loads, high speeds or a large temperature differential between inner and outer rings under conditions of external heating can make it advisable to have a rather large internal clearance after mounting. In such cases bearings having a larger radial internal clearance than class Normal (C3 or C4) should be used and where possible the maximum value for the clearance reduction be applied.
Measuring bearing clearance
To measure the internal clearance of cylindrical roller bearings before mounting, feeler gauges having blades starting with a thickness of 0,03 mm are suitable. The same procedure should be applied as that described in the section Spherical roller bearings - Measuring clearance reduction.