Timken Super Precision Bearings for Machine Tool Applications

A
ENGINEERING
FITTING PRACTICES
GENERAL GUIDELINES FOR
TAPERED ROLLER BEARINGS
The design of a tapered roller bearing permits the setting to be
achieved during installation (or during running when using a Hydra-
Rib), irrespective of the inner and outer ring fits on shaft and housing.
This allows the use of the widest possible machining tolerances for
shaft and housing and the use of the best possible fits for the inner
and outer rings to match the duty of the bearing.
The fitting practice will depend upon the following parameters:
• Precision class of the bearing.
• Type of layout.
• Type and direction of loads.
• Running conditions (vibrations, high speeds).
• Shaft and housing sections and materials.
• Mounting and setting conditions.
Certain table fits may not be adequate for light shaft and housing
sections, shafts other than steel, nonferrous housings, critical
operation conditions such as high speed, unusual thermal or loading
conditions or a combination thereof. Also assembly procedures
and the means and ease of obtaining the bearing setting may
require special fits. In these cases, experience should be used as
a guideline or your Timken representative should be consulted for
review and suggestions.
Precision class bearings should be mounted on shafts and in
housings which are similarly finished to at least the same precision
limits as the bearing bore and O.D. High-quality surface finishes
should also be provided.
In the machine tool industry, where almost 100 percent of cases are
rotating shaft applications, the general rule is to tight-fit both the
inner and outer rings for simple layouts to eliminate any undesirable
radial clearance.
Tapered roller bearing envelope tolerances can be adjusted to the
needs of a specific application.
NON-FERROUS HOUSINGS
Care should be taken when pressing cups into aluminum or
magnesium housings to avoid metal pick up. This may result in
unsatisfactory fits, backing, and alignment from debris trapped
between the cup and backing shoulder. Preferably, the cup should
be frozen or the housing heated, or both, during assembly. Also, a
special lubricant may be used to ease assembly. In some cases,
cups are mounted in steel inserts which are attached to the
aluminum or magnesium housings. Table fits may then be used.
Where the cup is fitted directly into an aluminum housing, it is
suggested that a minimum tight fit of 1.0 μm per mm (0.0010 in. per
in.) of cup outside diameter be used. For a magnesium housing, a
minimum tight fit of 1.5 μm per mm (0.0015 in. per in.) of cup outside
diameter is suggested.
80 TIMKEN MACHINE TOOL CATALOG