<Dl> <Dd> R P M = C u t t i n g S p e e d × 12 π × D i a m e t e r (\ displaystyle RPM = (CuttingSpeed \ times 12 \ over \ pi \ times Diameter)) </Dd> </Dl> <Dd> R P M = C u t t i n g S p e e d × 12 π × D i a m e t e r (\ displaystyle RPM = (CuttingSpeed \ times 12 \ over \ pi \ times Diameter)) </Dd> <P> e.g. for a cutting speed of 100 ft / min (a plain HSS steel cutter on mild steel) and diameter of 10 inches (the cutter or the work piece) </P> <Dl> <Dd> R P M = C u t t i n g S p e e d × 12 π × D i a m e t e r = 12 × 100 f t / m i n 3 × 10 i n c h e s = 40 r e v s / m i n (\ displaystyle RPM = (CuttingSpeed \ times 12 \ over \ pi \ times Diameter) = (12 \ times 100ft / min \ over 3 \ times 10inches) = (40revs / min)) </Dd> </Dl>

Lower spindle speed in lathe is necessary for