Base Circle

Base circle, abbreviated as BC, is a circle from where involute portion of tooth profile will be produced.  The base circle of a gear is an important concept in gear geometry.  It is a theoretical circle that is used as a reference in the design of involute gears.  The base circle is defined as the circle from which the involute curve of the gear tooth is generated. 

 

Base Circle formula
\( BC \;=\; PD \; cos( PA)  \)
Symbol	English	Metric
\( BC \) = base circle	\(in\)	\(mm\)
\( PD \) = pitch diameter	\(in\)	\(mm\)
\( PA \) = pressure angle	\(deg\)	\(rad\)