US Patent 9061411 Reciprocating power tool having a counterbalance device

A reciprocating power tool that includes a drive system having a first driven gear that includes a spindle counterbalance weight and a second driven gear that includes a spindle counterbalance weight. The first driven gear and the second driven gear rotate in opposite directions about an axis of rotation in response to rotation of a driving gear by a motor. The power tool further includes a spindle having a longitudinal axis and a first end that is configured to support a tool element. 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 a housing of the power tool along the longitudinal axis of the spindle in response to operation of the motor.