Using symbols in 19th edition, a helical gear is characterized by the helix
(spiral) angle also known as the"tooth"angle,
which is the acute angle between a tooth and the axis
of the gear. The number of teeth N. And the pitch diameter D, have no relation to the helix angle. The
chordal thickness tc and the tooth spa cc chordal
witlth s. refer to thc pitch circle as shown in Fig.