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Gearing Systems : Backlash

Backlash in mating gears is caused by the clearance between the mating teeth of the two gears. The clearance is due to manufacturing tolerances that are set. Manufacturing tolerances are unavoidable since it is impossible to make every gear tooth exact. So in turn there must be some small clearance between the gear teeth so that the gears can mesh correctly without jamming.

If the gears are ran in one direction backlash normally will not be noticeable. However, when that direction is reversed, the gear teeth will impact each other causing considerable noise. This not only can cause significant stresses and wear on the gears. It can also cause positional error on the gears. This in turn could further the wear on the gears. Finally, as the gears age the clearance between the gear teeth will normally increase, causing more backlash. This can cause issues with machinery that rely on precision.

To help counter the effects of backlash on the precision applications. Servomechanisms can be used to track position of the part of the machine the gears are moving. However, backlash can also be stopped through mechanical means by using antibacklash gears. An antibacklash gear is simply two gears back-to-back on the same shaft that have been rotated slightly during assembly with respect to each other to minimize backlash to the system.


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