Pitch Diameter: Dm = (D0+Di)/2
Actual Speed: N=RPM |
In order to discuss bearing speed it is necessary to understand the relationship between the RPM (Revolutions per
minute) of the bearing and the size of the bearing. The construct of Dm is used to defined "relative bearing speed" and is given by the "pitch diameter" (ball path) times the RPM of the bearing. This dimensionless parameter can be used to compare bearings of different dimension..
Dmm is the pitch Diameter or ball of the bearing and is determined by the average distance between the outside diameter, Do and the inside diameter, Di, in millimeters. The "relative bearing speed," DmN is calculated as the pitch diameter of the bearing multiplied by the speed in RPM's.
For example, a bearing with a pitch diameter of 10mm and a speed of 10,000 RPM, would have a DmN value of 100,000. A bearing with a pitch diameter of 100mm bearing is 10 times that of the 10mm bearing.
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