Gear Tooth Strength

Lewis Gear Strength Calculator
Input Output
Gear Diametral Pitch
Face Width (inches)
Tensile Strength of material (PSI)
Number of teeth

Maximum safe tooth load (pounds)

This Javascript application computes the maximum safe tooth load for 20 degree* pressure angle spur gears from the Lewis formula. This formula considers the gear as a cantilever beam with the full load applied to one tooth. If you enter a number other than zero for the RPM it will derate for dynamic effects of tooth impact. If exact number of teeth is not in the drop down menu, use the closest value.

Lewis Formula: W = S*F*Y / P
W = Safe tooth load
S = Safe material strength (1/3 tensile strength)
F = Face width
Y = Lewis Y factor from table based on tooth geometry
P = Pitch

* 14.5 degree pressue angle gears are about 15% weaker than 20 degree gears.

A product of Dales Homemade Robots, Copyright 2005 by Dale A. Heatherington

Material Tensile Strength Table
1020 Steel 65,000
1040 Steel 90,000
1080 Steel 140,000
12L14 Steel 60,000
4130 Steel 97,000
4140 Steel Annealed 98,000
4140 Steel Hardened 156,000
Titanium 6AL4V 130,000
303 Stainless Steel 90,000
5052-H32 Aluminum 33,000
6061-T6 Aluminum 45,000
2024-T361 Aluminum 72,000
7075-T6 Aluminum 76,000
Yellow Brass 71,000
Polycarbonate 10,500
Delrin 10,000
Nylon 11,500
PVC 7000
UHMW 4000

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