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his means that for a load of P = 143 lbs. the rating life of this ball bearing will be one million revoluions and 90% of a
group of such ball bearings will be expected to complete or exceed this value.
            Suppose now it is desired to determine the “L₁₀” life of this bearing when operating at 200 RPM md a load of 50 Ibs, the life being evaluated in hours of operation.
            Let the life in hours be denoted by and let N denote the RPM of the bearing. We then have
               l₁₀ = 10⁶L₁₀   =     (    C  )³     10⁶                                                                            (29)
                           60N               P          60N

Substituting N = 200, P = 50 and C = 143 into Equation (29) we obtain l₁₀ = 1949 hours.
NOTE: L₁₀ is bearing life in millions of revolutions l₁₀ is bearing life in hours.

A chart showing required life at constant operating speed has been given by N. Chironis (“Today’s Ball Bearings”, Product Engineering, December 12, 1960, pp. 63-77, chart on p. 68). This chart is hereby reproduced with the permission of McGraw-Hill Book Company, New York, N.Y.
(d)  Combined Axial and Radial Loads

Such cases can be evaluated according to the methods previously outlined by combining the axial and radial loads
into an equivalent radial load. This is defined in ANSI/AFBMA Standard 9,1978 as follows:
             “Calculation of Equivalent Radial Load. The magnitude of the equivalent radial load P, for radial and angular contact bearings, under combined constant radial and constant thrust loads, is:

                      P = XF_r + YF_a
Values of X and V are given in Table 4.
          The rating and sizing of ball bearings involve many considerations, many of which are beyond the scope of this introductory presentation. For further information the reader is referred to the technical literature.

6.0 TOLERANCES AND CLEARANCES

For satisfactory operation of a ball bearing, suitable shaft and housing tolerances are extremely important. Standard
tolerance ranges have been established by the industry and Tables 5 and 6 show recommended deviations of shaft diameters and housing bores from nominal.
        For normal conditions the recommendations of many manufacturers for rotating shafts and stationary housings, as
given by Wilcock and Booser, recommend fits in the approximate range K5 and J6 for shaft fits, and J6 and H7 for housing fits.

A fuller discussion of tolerances and their relation to bearing applications, installation and design is a complex subject beyond the scope of this presentation. This would include considerations involving temperature effects, high-speed operation, shock loading, lubrication, environmental conditions etc. For a discussion of such topics the reader is referred to the technical literature.

________________________________________________________________________________________________
“Bearing Design and Application” by D.F. Wilcock and ER. Booser, McGraw Hill, New York. N.Y., 1st Ed., 1957, p.69

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