LEXICONMachine components
Slewing ring
Also called: Slew ring, turntable bearing, slewing bearing
A large-diameter rolling bearing that lets an excavator's upper structure rotate on its undercarriage while carrying the machine's full weight and the bending moment of a loaded boom.
What it does
The slewing ring is the single joint between everything that turns and everything that stays put. It carries axial load from the machine's mass, radial load from the boom, and a very large overturning moment when the machine digs at full reach — all simultaneously, through one bearing that may be a metre or more across. Most have integral gear teeth, internal or external, driven by a hydraulic slew motor. Diameters on mid-size excavators run from roughly 700 to 1400 mm.
Why it becomes an object
It is already a finished circle: two concentric races, a raceway, a bolt circle and a toothed rim, all resolved by function rather than styling. Retirement usually follows raceway wear or tooth damage, long before the structure is compromised, so a retired ring is dimensionally sound and carries a legible service record — polished raceways, uneven tooth wear showing the arcs the operator used most. Its inherent geometry makes it a natural base for a circular top.
