Specifying AGMA Spur Gear, Helical Gear, and Herringbone Gear Backlash

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Specifying AGMA Bevel Gear, and Hypoid Gear Backlash

Specifying mating gears backlash and tolerances, is determined by the operating velocity, lubrication, modes of operation and loading imposed on the mating gears. The following are important features requiring tolerance specification to control backlash: runout in both gear and pinion (or worm), profile, pitch, tooth thickness, and helix angle. Backlash between mating gears will vary between different mating teeth at any particular rotational position. This is caused by many factors, such as composite tooth errors, runout, and positional displacement of the gear center distances and bearing mounting and location.

When specifying tolerances to control backlash, care should be taken to ensure that excessive tolerances are not specified. The less backlash desired, the tighter the tolerances on many features. Tighter tolerances drive gear production costs upward. Loose tolerance may provide excessive backlash, this can cause operational challenges especially when the gears require reverse operation, or high loading. Backlash requirements should be understood for your particular application or machine function.

The following table gives values for the AGMA Recommended
Backlash Range for Coarse-Pitch Spur, Helical and Herringbone Gearing

Center Distance
Between Gears (inches)
Diametrical Pitch Size
.5 - 1.99
2 - 3.49
3.5 - 5.99
6-9.99
10 - 19.99
Normal Plane Backlash (inches)
To 5
-
-
-
-
.005 - .015
Over 5 - 10
-
-
-
.010 - .020
.010 - .020
Over 10 - 20
-
-
.020 - .030
.015 - .025
.010 - .020
Over 20 - 30
-
.030 - .040
.025 - .030
.020 - .030
-
Over 30 - 40
.040 - .060
.035 - .045
.030 - .040
.025 - .035
-
Over 40 - 50
.050 - .070
.040 - .055
.035 - .050
.030 - .040
-
Over 50 - 80
.060 - .080
.045 - .065
.040 - .060
-
-
Over 80 - 100
.070 - .095
.050 - .080
-
-
-
Over 100 - 120
.080 - .110
-
-
-
-

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