Backlash (gear)

Backlash is the amount of clearance between mated gear teeth in a gear pair. Some backlash is required to allow for lubrication, manufacturing errors, deflection under load and differential expansion between the gears and the housing .

Related Topics:
Gear - Gear pair - Lubrication - Deflection

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Backlash is created when the tooth thickness of either gear is less than the tooth thickness of an ideal gear, or the zero backlash tooth thickness. Additional backlash is created when the operating center distance of the gear pair is less than that for two ideal gears. The total backlash is defined as:

Related Topics:
Tooth thickness - Operating center distance

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:b=b_t+b_c;

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where:

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Backlash due to tooth thickness changes is typically measured along the pitch circle and is defined by:

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:b_t=t_i-t_a;

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where:

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Backlash, measured on the pitch circle, due to operating center modifications is defined by:

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:b_c=2( riangle c)tanphi

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where:

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Standard practice is to make allowance for half the backlash in the tooth thickness of each gair. However, there are applications where this may not be advisable. For example, if the pinion (the smaller of the two gears) is too small or has few teeth, the engineer may elect to not modify the pinion teeth and instead, take the total backlash out of the gear teeth.

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