Timken Super Precision Bearings for Machine Tool Applications

A
ENGINEERING
Stiffness (relative to 180˚ load zone)
2.5
2
1.5
1
0.5
0
Loading:
100% C 90
10% C 90
45 90 135 180 225 270 315 360
Load Zone (˚)
Fig. 5. Effect of load zone on bearing stiffness.
Since thermal expansion can dramatically affect preload or setting,
it can also play a very important role in the resulting static and
dynamic stiffness of a spindle system. This applies to ball bearings
as well.
An inherent advantage of the tapered roller bearing is that it can
be adjusted after mounting. This means that the optimum stiffness
can be obtained either by determining the proper setting during
the mounting phase for a simple bearing arrangement, or during
running by the use of a “variable preload” bearing design such as
Timken ® Hydra-Rib TM and Spring-Rib TM bearings.
To better manage the load sharing of the set of rolling elements,
Timken offers a variety of designed-in preload levels for ball
bearings. Be conservative with the addition of preloading as these
forces will contribute to heat generation, reducing the maximum
permissible speed of either ball or tapered roller bearing designs.
Accuracy
Another key factor in the machine’s precision is the runout
(rotational accuracy) of the bearing. This affects the geometry and
surface finish of the target workpiece. For the ultimate accuracy
and repeatability of machine tool motion, Timken ® super precision
ball bearings offer the best control, with quietness of operation and
reduced vibration. To achieve the highest level of precision with
increased stiffness and load capacity, multiple ball bearings may
be used in sets specifically designed for this purpose.
The most widely recognized definition of quality is contained within
the ABEC/ISO classes; however some factors affecting performance
of a bearing are not completely defined within these standards. This
allows for a significant range of variability in product performance
among bearing manufacturers. To provide premium performance, all
Timken ball bearing MM, MMV and MMX precision grades comply
with strict controls over these non-specified parameters – all of
which can have a direct impact on the service life and performance
of a bearing.
18 TIMKEN MACHINE TOOL CATALOG