Dedendum

Dedendum, abbreviated as D, is the circle drawn through the bottom of the teeth or the radial distance from the pitch circle to the bottom of the tooth.  In simpler terms, it is the distance from the pitch circle to the base of the gear tooth.

The dedendum is a critical parameter in gear design because it affects the strength and durability of the gear teeth.  A proper dedendum ensures that there is enough material at the base of the tooth to handle the transmitted loads and prevent premature failure.  The dedendum, along with other gear parameters such as the addendum, pitch circle diameter, and module or diametral pitch, is used to define the geometry of the gear teeth.  The dedendum is typically specified as a fraction or percentage of the gear's pitch diameter.  It is an important factor to consider to ensure proper meshing and functioning of gears in a gear train

 

Dedendum formula
\( D \;=\; 1.157 \;/\; PD\)     (Dedendum) \( PD \;=\; 1.157 \;/\; D\)
Symbol	English	Metric
\( D \) = dedendum	\(in\)	\(mm\)
\( PD \) = pitch diameter	\(in\)	\(mm\)