hootowl
Elite Veteran
Location: Garnet Valley, Pa.
| There is a lot to controlling the durability of a one way. First you must choose the proper bearing for the application. Since the gear is an unsupported member, they really should be using a "clutch and bearing" style one-way. But most 50 size helis do not. Here is some of the design criteria from Torrington....
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| When applying the clutch-only unit, separate bearings on each side of the clutch are required to position the shaft concentrically with the housing and to carry the radial loads during overrun.
Steel housings are preferred and must be used for applications involving high torque loads to prevent radial expansion of the clutch cups. Low strength housings (non-steel, sintered metals and some plastics) may be entirely satisfactory in lightly loaded applications. When using non-steel housings, thoroughly test designs.
SHAFT DESIGN
The clutch or clutch and bearing assembly operates directly on the shaft whose specifications of dimensions, hardness and surface finish are well within standard manufacturing limits. Either case hardening or through hardening grades of good bearing quality steel are satisfactory for raceways. Steels which are modified for free machining, such as those high in sulfur content and particularly those containing lead, are seldom satisfactory for raceways. For long fatigue life, the shaft raceway, must have a hardness equivalent to 58 HRC (ref, ASTM E-18), and ground to the recommended diameter shown in the tables of dimensions. It may be through hardened, or it may be case hardened, with an effective case depth of 0.030 inch (0.8 mm) (Effective case depth is defined as the distance from the surface inward to the equivalent of 50 HRC hardness level after grinding.) Taper within the length of the raceway should not exceed 0.0003 inch (0.008 mm), or one-half the diameter tolerance, whichever is smaller. The radial deviation from true circular form of the raceway should not exceed .0001 inch (0.0025 mm) for diameters up to and including 1 inch (25.4 mm). For raceways greater than 1.0 inch or 25mm the allowable radial deviation may be greater than .0001 inch (0.0025 mm) by a factor of raceway diameter (in inches) divided by 1.0 or a factor of raceway diameter (in mm) divided by 25.4. Surface finish on the raceway should not exceed 16 microinches a.a. (arithmetic average) or 0.4 m (on the Ra scale). Deviations will reduce the load capacity and fatigue life of the shaft.
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