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Slew ring 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.
The slewing drive is a modernized take on the worm drive mechanism, which dates back many centuries and was widely used during the Renaissance Era. Pappus of Alexandria (3rd century AD), a Greek mathematician, is credited with an early version of the endless screw, which would later evolve into the worm drive. [1]
Illustration of bearing tolerances (in micrometers) for a bearing with a 20 mm inner diameter. For illustration, the figure shows the differences in tolerance per ABEC class in micrometers (μm) for a 20 mm inner diameter bearing. [1] A 20 mm ABEC 7 bearing only has a 5 μm tolerance window, whereas an ABEC 1 has twice as wide a tolerance.
Although bearings tend to wear out with use, designers can make tradeoffs of bearing size and cost versus lifetime. A bearing can last indefinitely—longer than the rest of the machine—if it is kept cool, clean, lubricated, is run within the rated load, and if the bearing materials are sufficiently free of microscopic defects.
Therefore, regardless of the worm's size (sensible engineering limits notwithstanding), the gear ratio is the "size of the worm wheel - to - 1". Given a single-start worm, a 20-tooth worm wheel reduces the speed by the ratio of 20:1. With spur gears, a gear of 12 teeth must match with a 240-tooth gear to achieve the same 20:1 ratio.
Thrust ball bearings, composed of bearing balls supported in a ring, can be used in low-thrust applications where there is little axial load. Cylindrical roller thrust bearings consist of small cylindrical rollers arranged flat with their axes pointing to the axis of the bearing. They give very good carrying capacity and are cheap, but tend to ...
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Pages in category "Bearings (mechanical)" The following 56 pages are in this category, out of 56 total. ... Slewing bearing; Slide plate; Sommerfeld number; Spherical ...