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All the effort expended in selecting or designing the
perfect bearing for your application can be wasted
without equal consideration given to the design of the
components onto which the bearing will eventually be
assembled. Issues to consider when planning shaft and
housing fits are operating conditions such as load,
speed and vibration; provisions for axial expansion, thermal expansion of components, the need for rigidity
or rotational accuracy and assembly considerations.
Before deciding upon tight interference fits, it is
important to consider their effect on radial play,
contact angle, and preloads. Radial play is reduced by
approximately 80% of an interference fit. Thus an
interference fit of .0002” would decrease internal
radial play by as much as .00016”. This could be
exaggerated with the presence of thermal expansion of
components.
When press-fitting a bearing, always apply forces
directly on the ring being fitted so as not to transfer
force between the raceways through the balls. Also
recognize that inaccuracies in component geometry can be
transferred to the bearings through interference fits.
Where an interference fit is needed and anticipated in
bearing design, it is generally applied to the rotating
ring. The stationary ring is fitted loose for ease of
assembly.
Loose fits are also recommended for one bearing of a two
bearing system to avoid preloading caused by thermal
expansion during operation, unless already anticipated
elsewhere in the bearing design. Also, where loose fits
are used, other methods of clamping or loading against
the shoulder is ideal. In spring preload assemblies,
bearings require a loose fit to ensure that the spring
remains operational.
In all cases, care must be taken to ensure proper
tolerances and workmanship on mounting surfaces for both
the shaft and housing.
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