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### Helical Gears Shafts Parallel Exact Exact Center Distance Design Equations and Calculator

Helical Gears Shafts Parallel, Center Distance Exact Design Equations and Calculator The first step in helical gear design is to determine the desired direction of the thrust. When the direction of the thrust has been determined and the relative positions of the driver and driven gears are known, then the direction of helix (right- or left-hand) may be found

Pitch diameter of large gear formula

D = N / ( Pn cos α )

where

cos α = ( N + n ) / ( 2 * Pn * C )

Pitch diameter of small gear formula

d = n / ( Pn cos α )

Outside diameter of large gear

O = D + 2 / Pn

Outside diameter of small gear

o = d + 2 / Pn

Number of teeth marked on formed milling cutter (large gear)

T = N / cos3α

Number of teeth marked on formed milling cutter (small gear)

t = n / cos3α

Lead of helix on large gear

L = π D cot α

Lead of helix on small gear

l = πd cot α

Center distance (if not right, vary α)

C = 1⁄2 (D + d)

Where:

C = approximate center distance
Pn  = normal diametral pitch
N = number of teeth in large gear
n = number of teeth in small gear
α = angle of helix

References:

Machinerys Handbook, 29th Edition