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### Ratchet Type Gear Design Formulas and Calculator

Ratchet Type Gear Design Formulas and Calculator

Ratchet gearing isused to transmit intermittent motion, or to prevent the ratchet wheel from rotating backward. Ratchet gearing of this latter form is commonly used in connection with hoisting mechanisms of various kinds, to prevent the hoisting drum or shaft from rotating in a reverse direction under the action of the load.

The following formula has been used in the calculation of ratchet gears for crane design.

P = [ ( F M ) / ( L S N ) ]1/2

M = ( P2 L S N ) / F

Where:

P = circular pitch, in inches (mm), measured at the outside circumference (in, mm);
M = turning moment acting upon the ratchet wheel shaft, in inch-pounds (N-mm);
L = length of tooth face (thickness of ratchet gear), in inches (millimeters);
S = safe stress (typical for steel, 2500 psi or 17 MPa when subjected to shock, and 4000 pounds per square inch or 28 MPa when not subjected to shock);
N = number of teeth in ratchet wheel;
F = a factor the value of which is 50 for ratchet gears with 12 teeth or less, 35 for gears having from 12 to 20 teeth, and 20 for gears having over 20 teeth:

 Type 1 Type 2 Type 3 Type 4 Type 5 Type 6 Type 7 Type 8 Type 9

References:

Machinery's Handbook, 29th Edition