TECHNOLOGY JOURNAL SERIES 1
LINEAR BEARING PRELOAD
INTRODUCTION
Preloading anti-friction linear bearings has been
looked upon as more of an art than a science. This is
primarily due to the fact that many variables in the
mounting and assembly process make ‘torque’ ad-
justments less practical and adjustments by ‘feel’ or
by hand more effective. As bearings are
mounted on imperfect surfaces, with in-
consistent threads for mounting and
preloading the bearing, it is difficult to es-
tablish a foundation that will yield uniform
results. This has not stopped people from
striving to adopt scientific methods of preloading,
with torque wrenches, or force gauges, however, it
typically comes down to fine hand adjustments.
The purpose of preloading a bearing is to bring stiff-
ness to a system (or axis) by taking out the clearance
(or backlash) and generating the required life. In-
creased preload brings increased stiffness, which in
turn yields much higher responsiveness. In devices
such as high performance positioning systems and
state-of-the-art machine tools, bearing preload is criti-
cal to establishing a system that can meet the dynamic
requirements of a servo system. As high stiffness lin-
ear bearings are applied to high performance motion
systems, it is important to understand the difference
between a proper preload and an excessive preload.
Simply adding preload to increase stiffness can result
in the creation of inaccuracies, which will affect re-
peatability and resolution.
As the methods and effects of preload vary
based on bearing type (non-recirculating lin-
ear and recirculating linear) it is important
to separate the implications of preload
on the two types of bearings. The dis-
cussions regarding non-recirculating linear
bearings refer primarily to crossed roller bearings, as
these bearings are the most stiff of mechanical bear-
ings and are often utilized in high performance motion
systems. Recirculating bearings refer primarily to lin-
ear ball guides, as these bearings are quite common in
motion control and machine tool applications.
RESEARCH & DEVELOPMENT TEAM
January, 1998
