Rolling-element instrument bearings are precision bearings that include at least one of the following characteristics
- Smooth running or limited vibration.
- Low or uniform operating torque.
- Control of contact angle or preload levels.
- Extreme applications.
Typical applications are in gyro motors, gyro gimbals, synchros, servomotors, gearheads, differentials and speed reducers, data encoders, potentiometers, tape guides and idlers, tape capstans, and flowmeters.
Most applications require the lowest possible operating torque. Thus, instrument bearings generally have lightweight retainers and open race curvatures for minimum contact area.
Unlike other bearings, they usually do not fail from metal fatigue caused by dynamic operating loads. Instead, failure is represented by some level of operating torque that affects instrument performance. Torque increases are generally traceable to contamination or lubricant breakdown. In the worst case, the retainer is destroyed or jammed because of excessive contamination or wear particles.
The bearings generally do not have a continuous supply of fresh lubricant. This condition is unavoidable and imposes a severe limitation on life.
Precision instrument bearings are available in three tolerances levels -- ABEC 5P and 5T, 7P and 7T, and 9P. A semiprecision grade is also available which meets ABEC 3 tolerances without the extra performance requirements mentioned above.
Instrument bearings are divided into three basic size ranges:
Miniature: Bearings with an OD less than 0.375 in. and certain thin-section bearings with a maximum OD of 0.5 in.
Intermediate: Consist of inch or R-Series bearings and the metric or 30-Series bearings, which range in size up to 1-in. OD.
Thin-section and torque-tube: Bearings available in sizes up to 4-in. OD. (A variation is the extrathin-section series that have a bore-to-OD section of 0.125 in. for all sizes up to 1.875-in. OD.)