Four point contact bearings(slewing rings) for greater accuracy

A four-point contact ball bearing makes it easy to simplify machine designs that have a combination of radial, thrust and moment loads because it can handle all three simultaneously. They are primarily used for slow to moderate-speed applications, or where oscillatory movement is predominant.

Four-point contact bearings can be manufactured in accordance with ABEC precision grades and in larger sizes. In applications involving oscillatory motion with limited angles of rotation, when the runout is zero for much of the rotation, an ABEC 1 bearing can sometimes be used instead of an ABEC 3 or 5. In such cases, the critical requirement (axial runout or radial runout) should be specified to meet ABEC standards. Noncritical areas can be left up to the bearing manufacturer.

With one row of balls instead of two, accuracy is enhanced in several ways. For example, when radial runouts in a two-row bearing system are out of phase, the rotation will produce a wobble. Wobble can also result from structure deflection when applications require a lot of space between two rows of balls (e.g., when high moment load must be resisted). And if there is a preload difference in axial runout between the two rows, bearing friction can vary.

None of these problems will occur in a bearing with a single row of balls. Likewise, there is no matching of housing bores and shoulders, or of shaft diameters and shoulders. All other factors being equal, the accuracy of a four-point contact bearing may be twice that of a bearing with two rows of balls.