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DESIGN
FACTORS WHEN USING SMALL BEARINGS
Part 2: Mounting and Fitting By Simon Harrison, Ph.D.,
President, Dynaroll Corp. |
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| Miniature bearings
are generally used in applications where rotational performance
(i.e. predictable low torque, runout, stiffness, etc.) is the primary
design goal, rather than load/lifetime issues. A previous paper
has discussed how the internal geometry of the bearing itself influences
the rotational performance of a bearing assembly. This paper addresses
the importance of proper handling and assembly methods in the application
of miniature bearings.
The cross-section of the inner and outer races of miniature bearings (sometimes called the turning rings) can be very thin. For bearings of 1/4-inch OD or smaller, the thickness of the race under the ball groove can be less than 0.008 inches. This means that even though the bearing material may be relatively hard steel (Rc 60+), the races are extremely fragile and can be significantly damaged or distorted by the slightest force during the mounting and assembly process. For such thin section bearings it is
also extremely important to note that up to 80% of the interference
with mating components will translate into loss of radial play.
Since a standard miniature bearing has a radial play between 0.0002
and 0.0004 inches, this means that total interference of 0.0003”
can be expected to close up some bearings to the point that they
will no longer rotate.
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