MOUNTING AND FITTING
Many small bearing performance problems are caused by a lack of understanding of the effects of tight tolerances combined with the reduction in bearing radial play caused by interference with mating parts. Miniature bearings can have very thin inner and outer ring cross-sections (< .008" in some cases). When such a bearing is pressed onto a shaft or into a housing, depending on the material, up to 80% of the interference fit translates into loss of radial play in the bearing. For a bearing that has (say) .0002" to .0004" radial play in the first place, normal tolerance stack-ups can cause immediate bearing failure. This point cannot be emphasized too strongly. The effects of relative thermal expansion of different materials must also be taken into account for extreme temperature operation.