This section covers recommended tooth proportions and dimensions of blanks for generated straight bevel gears of tooth ratios in general industrial use.
Bevel gears in this system have unequal addendums and unequal tooth thicknesses, except for pairs having equal numbers of teeth. This is different from the common practice for spur gearing. In bevel gear cutting, the tooth thickness is controlled by machine adjustments instead of by the tools, making it possible to obtain tooth thickness according to requirements for balance of strength in gear and pinion. Consideration has been given to both surface durability and beam strength in determining the tooth proportions.
An advantage in designing bevel gears according to this system is that tables are available giving tooth data and machine settings, thus minimizing calculations.* If other tooth designs are used, the data must be determined specially.
Backlash - Table 2.4 gives the recommended backlash when the gear and pinion are finished and assembled ready to run. Quality numbers referred to in the table are defined by the AGMA Gear Classification Manual, AGMA 390.02.
|Table 2.4 Recommended Backlash|
|AGMA Quality Number|
|4 thru 6||7 thru 13|
|20 to 50||0.000 - 0.002||0.000 - 0.002|
|50 to 80||0.000 - 0.001||0.000 - 0.001|
|80 and finer||0.000 - 0.0007||0.000 - 0.0007|
*These Tables are
available through Gleason Works,
Rochester, New York.
Figure 2.5 - Bevel Gear Nomenclature
These are bevel gears whose shafts are set at an angle other than 90 degrees. They are useful when the direction of a shaft's rotation needs to be changed. Using gears of differing numbers of teeth can change the speed of rotation.
These gears permit minor adjustment of gears during assembly and allow for some displacement due to deflection under operating loads without concentrating the load on the end of the tooth. For reliable performance, Gears must be pinned to shaft with a dowel or taper pin.
The bevel gears find its application in locomotives, marine applications, automobiles, printing presses, cooling towers, power plants, steel plants, defence and also in railway track inspection machine. They are important components on all current rotorcraft drive system.
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