Slewing bearing

A slewing bearing or slew[ing] ring (also called a turntable bearing) is a rotational rolling-element bearing that typically supports a heavy but slow-turning or slowly-oscillating loads in combination (axial, radial and moment loads), often a horizontal platform such as a conventional crane, a swing yarder, or the wind-facing platform of a horizontal-axis (yaw) windmill.

In other orientations (e.g. a horizontal axis of rotation) they are used in materials handling grapples, forklift attachments, welding turnover jigs and so on.

[citation needed] Compared to a "normal" ball bearing the rings are quite wide and usually have holes drilled in them to provide fixation to a structure.

Slewing bearings are often made with gear teeth integral with the inner or outer race (or both in rare cases) used to drive the platform relative to the base (for example in winches).

The oil wedge built up in a continuously rotating bearing is disrupted by the stop start motion of slewing.