Using symbols in 19th edition, a helical gear is characterized by the helix
(spiral) angle a, also kllown as the"tooth"artglc,
which is the acute arrgle between a tooth and thc axis
of thc gear. The number of teeth rv. And the pitch di-
ameter D, llave 11o relation to the helix a]rgle. Thc
chordal thicmess tc and the tooth spa cc chordal
witlth s. refer to thc pitch circle as shown in Fig.