Backlash
2. The play between mating tooth surfaces at the tightest point of mesh in a direction normal to the tooth surface when the gears are mounted in their specified positions.
The amount of backlash in a pair of mating gears can be affected by:
a. Changes in centre distance
b. Variance in tooth thickness.
c. Temperature ranges cause differential expansion of the gears and mountings.
Minimum backlash: Occurs when all tolerances give the shortest centre distance and the thickest teeth at the highest point of pitch line runout.
Maximum backlash: Occurs when all tolerances give the greatest centre distance and the thinnest teeth at the lowest point of pitch line runout.
Backlash Tolerance:
The allowable amount of backlash.
Backlash Variation:
The difference between the maximum and minimum backlash occurring in a whole revolution of the larger of a mating pair of gears.
From Gear Data