Rotary Bearing: Load/Life Calculation  
As we have seen, rotary antifriction bearings are manufactured in a variety of configurations. What we present here is a method for deciding upon a configuration, and then sizing a rotary antifriction bearing. First, we look at a rule of thumb for frictionlimited speed of such a bearing. Friction in rotary bearings: A rule of thumb
Selection of an antifriction bearing for a particular application:
 
Now that we have decided upon the bearing type, we can move on to the more quantitative issue of sizing the bearing. Two metrics that are needed for bearing specification are the static and dynamic load capacities. Static load capacity can specify the bearing if rotational speed is slow, intermittent, and/or subject to shocks. Dynamic load capacity is used when the bearing rotational speed is smooth and relatively constant. Static Load Specification: The axial and radial forces acting on the stationary rotary bearing determine the Basic Static Load Rating listed in bearing catalogs. When there are both axial and radial loads on a bearing, the combined static load can be found as follows.
 
The basic static load rating coefficient, Co, can be obtained from:
 
Values of So depend upon the requirements for lownoise operation and the type of bearing, as shown in the following table. Static Safety Factor (So) Guidelines
 
If the bearing is stationary for extended periods or rotates slowly and/or intermittently and is subject to shock loads, then the selection is based upon this basic load rating. Values of basic load rating, Co, for each bearing are quoted in the bearing catalogs. Dynamic Load Specification:
When F_{sax} = 0 or is relatively small up to F_{sax}/F_{dyn} = e (The values of F_{srad}, F_{sax}, and e are given in the Rotary Bearing Data) then F_{dyn} = F_{srad}
Since we have calculated the equivalent dynamic bearing load we can now compute the bearing dynamic load rating, which is used to select the bearing. Catalog dynamic load rating values should be chosen higher than the computed value for safety. The cataloglisted dynamic load ratings are dependent upon both the equivalent dynamic load and the required bearing life. The ISO equation for the basic rating life is:
Basic Rated Life of Bearings:
