Cylindrical Roller Bearings - Norfolkbearings.com

Cylindrical Roller Bearings
Fitting Practice
The fitting practice given in the following tables conforms
to industry and ABMA/ANSI standards, where
applicable. The tables provide maximum and minimum
sizes for bearing bore and O.D., shaft and housing
bore, and the resultant effects of each type of fit.
Dimensions are given in both inch and metric units with
deviations in .0001 inch and micrometers.
The looseness or tightness of a ring mounted on a shaft
or in a housing bore depends on the conditions under
which the bearing will operate and how it will be
installed. The three most generally used fits are:
PRESS, TAP AND PUSH.
PRESS fit is used to fit a ring tightly to a rotating member
(shaft or housing) to prevent creep or slippage that
could result in damage to the shaft or housing bore.
TAP fit usually accompanies PRESS fit, for fitting the
opposite ring to the stationary member, if the bearing
rings are separable.
PUSH fit is used instead of TAP, for a stationary outer
ring, if the bearing is non-separable.
HEAVY PRESS fit (“A” style) is an NTN-Bower innovation
for cylindrical roller bearings. It is used to prevent
the outer ring from turning in the housing bore, where
the bearing is operating under very heavy loads. The
outer ring O.D. is made oversize to provide a heavy
press fit in a standard (tap fit) size housing bore. The
accompanying inner ring uses a PRESS fit on the shaft.
The catalog fitting practice does not apply to bearings
mounted on hollow shafts or in housings of materials
softer than steel, such as as aluminum. Since these
conditions Since these usually conditions require usually heavier require press heavier fits, the press NTN
Engineering fits, the NTN Department Engineering Department should be should consulted be consulted
for
for
recommendation. recommendation.
The chart on on the the opposite opposite page page summarizes summarizes the recommended
fitting fitting practice practice for various for various installations installations and
the
recommended
and bearing bearing types, types, including including bearings bearings with inner with or inner outer or
outer rings omitted. rings omitted.
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