Limiting speed values for instrument bearings are almost impossible to determine. However, generalizations may be made.
Bearing size: Highest speeds may be obtained with the smallest bearing. However, extremely small miniature bearings usually have a thin, weak retainer and their maximum speed is less than medium-size miniatures.
Load: Limiting speed is directly affected by the magnitude of applied load. Heavy loads result in a decreased speed capability. Use of a preloaded pair of bearings also decreases allowable speed.
Ring rotation: Inner-ring rotation gives higher speed capability. If the outer ring is rotating, limiting speed must be reduced by about one-third.
Retainer: Phenolic (and some other nonmetallic materials) -- very high speed; crown (hardened steel) -- high speed; ribbon (loosely clinched) -- low speed; full race -- moderate speed; spacers (PTFE) -- very low speed.
Lubricant: Stiff, mineral-oil grease -- high speed; soft, synthetic-oil grease -- moderate to high speed; soft, silicone grease -- low to moderate speed; mineral oil -- high speed; synthetic oil -- moderate speed; silicone oil -- low speed.
Lubricant method: Oil impregnation and grease pack -- excellent; oil impregnation -- very good; grease pack -- good; minimum oil -- fair.
