In the following problems, it is assumed that the bearing has but one row of balls. A work...

In the following problems, it is assumed that the bearing has but one row of balls. A working year will be taken as 250 days.

An electric motor for a drill press has 104 bearings mounted as in Fig. 1, except that the shaft is vertical. Bearings are 10 in. center to center. The center of the V-belt pulley is located 2.5 in. from the lower motor bearing. During two-thirds of the work cycle, the steady belt forces equal 128 lb at 900 rpm. During the remainder of the cycle, the steady bell forces equal 88 lb at 1770 rpm. The motor armature weighs 67 lb. Find the rating life at 4 hours per day of the most heavily loaded bearing.

Figure 1