Dedendum of gears – Gear Terminology
The distance between the pitch radius and the root radius at the center of one gear tooth is called the dedendum (hf) of the gear.
The distance between the root radius and the tip radius is called the whole depth (h) of the gear and is determined by the size of the module (m).
The whole depth is the sum of the addendum (ha = 1.00 m) and the dedendum (hf = 1.25 m).
h = 2.25 m ( = height of addendum + height of dedendum).
As mentioned before, the dedendum shows the distance between the pitch circle and the root circle.
0.25m of this distance is called the root clearance (c = the distance between the tip circle of a gear and the root circle of its mating gear) and serves as a void which helps prevent interference with the tooth tip of the mating gear.
hf = ( m + 0.25 m) = 1.25 m
h = 2.25 m = 2m + c
When the tooth height is 2.25 times the module, the tooth is called a full depth tooth. This is the tooth height used most commonly.
Other than a full depth tooth, a stub tooth with a lower tooth height than the full depth tooth and an extended addendum tooth with a higher tooth height than the full depth tooth, are also sometimes used.
Dedendum of gears