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Base Circle formula

BC=PDcos(PA)
Symbol English Metric
BC = base circle in mm
PD = pitch diameter in mm
PA = pressure angle deg rad

gear diameter 2Base 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.  

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