The radial distance from the pitch circle down to the root of the tooth. For standard teeth it is typically 1.25 module, the extra quarter module above the mating addendum forming the root clearance that stops tips bottoming out and leaves room for oil and debris. Whole depth is addendum plus dedendum, about 2.25 module.
Dedendum's cut too deep, look how thin the root fillet got, those teeth will crack before they pit.
Also heard as
- dedendum depth
- root depth
Do not mix it up with
- Addendum: Addendum is the tooth height above the pitch circle, not the depth below it.
Related terms
Addendum
The radial height of a gear tooth above the pitch circle, normally one module for a standard tooth.
Module
The metric measure of gear tooth size: pitch diameter in millimeters divided by the number of teeth.
Pitting
Surface fatigue of gear teeth that breaks out small craters, typically on the flank just below the pitch line.
Bending stress
The tensile stress in the root fillet of a loaded tooth, which decides whether teeth break off.