94-06 Fits

To make a proper fit selection, one must consider the type of load, the operating environment (i.e., ambient temperature), the type of shaft or housing, and the type of bearing. The two tables on the overleaf give some general recommendations for the selection of fits for radial bearings.

Interference:

"Press fit" or "loose fit" are terms used to distinguish the amount of interference that exists between two mating components.

Proper fit selection ensures that the inner and outer rings do not slip with respect to the shaft or housing. "Creep" occurs when the interference is not sufficient for the operating conditions. Creep causes abrasive wear, shaft vibration, and excessive temperature rise. On the other hand, an excessive interference fit will eliminate the bearing operating clearance and also lead to a temperature rise. Excessive interference fits also increase the difficulty of assembly and the risk of bearing damage during assembly (i.e.,Brinelling). Both of the above conditions can ultimately lead to poor bearing performance. Table 1 gives the general criteria for selection of interference with respect to the basic load conditions. Load Conditions Fits Rotating inner ring load Inner ring : stationary Outer ring : rotating Direction of load : constant Inner ring : interference fit Outer ring : loose fit Stationary inner ring load Inner ring : stationary Outer ring : rotating Direction of load : constant Inner ring : loose fit Outer ring : interference fit Stationary inner ring load Inner ring : rotating Outer ring : stationary Direction of load : rotating with outer ring Inner ring : interference fit Outer ring : interference fit Rotating inner ring load Inner ring : stationary outer ring : rotating Direction of load : rotating with outer ring Inner ring : interference fit Outer ring : loose fit 1) Interference fit is preferred for separable bearing. Table 1

ISO Nomenclature

Standard metric dimension tolerances for bearing shaft diameters and housing bore diameters are governed by the lnternational Standards Organization (ISO). Fits are designated by a letter followed by a number. Letters in lower case (e.g., j6) refer to fitting onto a shaft while letters in upper case (e.g., H7) refer to fitting into a housing. Figure 1 summarizes the common shaft and housing fits. The actual shaft and housing tolerance for various fit designations depend on the respective diameter and are listed in ISO shaft and housing fit tables which are available from NTN. Contact your local NTN representative.

Fit With Shaft

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