Abstract: A reciprocating cutting instrument includes an outer tube housing an inner reciprocating cutting blade. The cutting blade is engaged to a source of power, namely a motor, through a transmission and drive mechanism. This transmission and drive mechanism converts rotary drive movement of the motor to reciprocating movement of the cutting blade. A cam is provided that engages the spindle of the motor, the cam formed by a generally cylindrically shaped cam barrel with a cam channel defined in the outer surface of the barrel. A drive ball rides within the channel and is supported within a boss of a linear in-line driver. The in-line driver reciprocates within a bearing housed by a driver cartridge. Pressure between the drive ball and the cam channel is maintained by a set screw threaded into the boss in the in-line driver. As the motor rotates, the spindle, which is engaged to the cam, rotates the cam barrel.