Twelve precision levels are specified, which are represented by the numbers 1, 2, 3, ... 12 in order from high to low precision. Most commonly used are 5 to 9 precisions. In addition, according to different requirements for the accuracy of the movement, the smoothness of the transmission, and the uniformity of the load distribution, the public service of each accuracy level is sequentially divided into three groups, the first public service group, the second public service Service group and the III public service group.

The accuracy grade of the gear should be determined according to the use of the transmission, the use conditions, transmission efficiency and peripheral speed, and other economic and technical indicators.

The 5-stage gear is fine.
Processing method: Fan Cheng machining on fine gear machine tools with very small periodic errors. The tooth surface finally adopts fine grinding. After large gears are cut with fine hobbing, they are ground or shaved. Tooth surface roughness reaches 0.4-0.8.
Scope of application: gears for fine indexing mechanism; gears for high speed and relatively high requirements for work stability and noise; gears for high-speed steam turbines.

The 7-level gear is a relatively high-precision level.
Processing method: Fan Cheng processing on high-precision gear machine tools. Non-hardened tooth surfaces are cut with high-precision tools; hardened gears need finishing (grinding, shaving, grinding, etc.). Tooth surface roughness reaches 1.6.
Scope of use: gears for high speed, low load or reverse; gears for machine tools, gears that need to be matched with movement; medium speed reduction gears; aircraft gears; herringbone gears.

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