Number of teeth, N
How many teeth a gear has. In the case of worms, it is the number of thread starts that the worm has.
Helix angle, psi
The angle between a tangent to the helix and the gear axis. It is zero in the limiting case of a spur gear.
Pitch circle, pitch line
The circle centered on and perpendicular to the axis, and passing through the pitch point. A predefined diametral position on the gear where the circular tooth thickness, pressure angle and helix angles are defined.
The pitch diameter is a predefined diametral position on the gear where the circular tooth thickness, pressure angle and helix angles are defined. The standard pitch diameter is a basic dimension and cannot be measured, but is a location where other measurements are made. Its value is based on the number of teeth, the normal module (or normal diametral pitch), and the helix angle. It is calculated as:
d = N m / cos(psi)
The module is the unit of size that indicates how big or small a gear is. Is expressed by the ratio of the pitch diameter and the number of teeth.
m = d / N
The center distance a is the distance measured from the center of gear 1 reference circle to the center of gear 2 reference circle.
a = (d1 + d2) / 2 = (z1 + z2) m /2
Herringbone gears in Fusion 360
Fusion 360 add-in to generate helical gears, herringbone gears and alike