Equivalent Number Of Teeth, Proportions for Helical Gears

Machine DesignGear Drive

Introduction:

The formative or equivalent number of teeth for a helical gear may be defined as the number of teeth that can be generated on the surface of a cylinder having a radius equal to the radius of curvature at a point at the tip of the minor axis of an ellipse obtained by taking a section of the gear in the normal plane.

Formative or Equivalent Number of Teeth for Helical Gears

Mathematically, formative or equivalent number of teeth on a helical gear,

TE = T / cos³ α

where

T = Actual number of teeth on a helical gear, and

α = Helix angle.

Proportions for Helical Gears

Though the proportions for helical gears are not standardised, yet the following are recommended by American Gear Manufacturer's Association (AGMA).

Pressure angle in the plane of rotation,   φ = 15° to 25°

Helix angle, α = 20° to 45°

Addendum = 0.8 m (Maximum)

Dedendum = 1 m (Minimum)

Minimum total depth = 1.8 m

Minimum clearance = 0.2 m

Thickness of tooth = 1.5708 m