There is no need to worry about the runout becoming worse because of the grooves. (Right) Make sure the shoulder rim of the mating component is far enough from the opposing ring when positioning a bearing against a shoulder: The outer ring diameter minus the clearance measures the maximum shoulder diameter of the shaft. To accommodate the inner ring land’s diameter and the clearance, the housing’s minimum diameter must be at least that value. Standard tolerances call for gaps larger than 0.01 inches. For the bearings to fully seat against the shoulders, you need also make sure that the shoulder corner radius, written by ra, is less than the bearing fillet radius, given by r. Most bearing catalogues will provide these details.
Special Ideas
The miniture bearing, especially those in the miniature and instrument size range, shine in applications that need constant torque, runout, and rigidity. Tolerances and surface finishes are measured in millionths of an inch, allowing for unprecedented accuracy. However, due to their diminutive stature and paper-thin raceways, micro bearings are quickly harmed by excessive handling pressures and contamination.
Particles as tiny as a few microns may produce increased torque and noise, as well as a decreased bearing life. After a thorough final inspection, bearing manufacturers usually seal the units in sterile, Class 100 environments before sending them out for delivery. As long as certain measures are followed, most assembly tasks may be carried out outside of a clean room or laminar flow workstation.
Maintain a clean environment.
Your hands should never come in contact with the tiny bearings. Lubricant in the inside raceways prevents damage from skin acid, but the outside is unprotected. Never take bearings out of their packaging until you’re ready to use them. Use medical gloves or finger cots that are talc-free while handling bearings. Workers in an assembly line should only use clean tools free of burrs, wear caps, smocks, and shoe covers designed for use in a clean environment, and avoid using cosmetics. Every day, the dust should be swept from the desks and benches where work is being done. Finally, use a lint-free cloth to clean the mating components before attempting to assemble them. Lint is often introduced into the system by using traditional cotton swabs or standard cleaning cloths.
Simple as that
The majority of damaged raceways in micro bearings are probably caused by excessive force employed during assembly. Torque and noise levels both rise with this form of damage, and the lifetime decreases as a result. Interference from poor design or wrong stacking of tolerances are common culprits.
Conclusion
Inner and outer races, as well as the turning rings, of miniature bearings have very small cross-sections. The area underneath the ball grooves (in the races) may be narrower than 0.008 inches in bearings with an outer diameter of 0.25 inches or less. These fragile races may be damaged by even mild forces applied during mounting and assembly, despite being fabricated from fairly sturdy steel (Rc 60+). In fact, if there is interference between mating components, radial play might be reduced by as much as 80%.
