Patent ID: 8407902

Claim:
A reciprocating power tool comprising: a housing; a motor supported by the housing and having an output shaft, the motor operable to rotate the output shaft; a drive system coupled to the output shaft of the motor, the drive system including, a driving gear coupled to the output shaft for rotation with the output shaft, a first driven gear having a spindle counterbalance weight, the first driven gear coupled to the driving gear such that the first driven gear is configured to rotate about an axis of rotation in a first direction in response to rotation of the driving gear by the motor, a second driven gear having a spindle counterbalance weight, the second driven gear coupled to the driving gear such that the second driven gear is configured to rotate about the axis of rotation in a second direction that is opposite the first direction in response to rotation of the driving gear by the motor, a spindle having a longitudinal axis and a first end configured to support a tool element, and wherein the spindle is coupled to one of the first driven gear and the second driven gear by a scotch yoke mechanism to reciprocate the spindle with respect to the housing along the longitudinal axis of the spindle in response to operation of the motor, wherein the spindle counterbalance weights of the first and the second driven gears rotate with the first and the second driven gears, respectively, between an upper position, a forward position, a lower position opposite the upper position, and a rearward position opposite the forward position, wherein the spindle reciprocates between an extended position, a retracted position, a first intermediate position, and a second intermediate position, wherein when the spindle is in the extended position, the spindle counterbalance weights of the first and the second driven gears are in the rearward positions, wherein when the spindle is in the retracted position, the spindle counterbalance weights of the first and the second driven gears are in the forward positions, wherein when the spindle is in the first intermediate position, the spindle counterbalance weight of the first driven gear is in the upper position and the spindle counterbalance weight of the second driven gear is in the lower position, and wherein when the spindle is in the second intermediate position, the spindle counterbalance weight of the first driven gear is in the lower position and the spindle counterbalance weight of the second driven gear is in the upper position.