Patent ID: 9724771
Date: 2017-08-08
CPC Classifications: B23D

Claim:
1. A reciprocating power tool, which performs a predetermined operation on a workpiece by reciprocating a tool bit in a longitudinal direction of the tool bit, comprising: an output shaft that is driven by a motor, a pinion that is provided on the output shaft, a first bevel gear that is engaged with the pinion and rotationally driven around an axis extending transversely to the longitudinal direction of the tool bit, a crank to which the first bevel gear is fixedly mounted and which converts rotation of the first bevel gear into linear motion, a slider that holds the tool bit and is caused to linearly reciprocate in the longitudinal direction of the tool bit via linear motion of the crank, a second bevel gear that is opposed to the first bevel gear on the same axis as a rotation axis of the first bevel gear and engaged with the pinion so as to be rotationally driven in a direction opposite to the first bevel gear, a first counter weight that is disposed in a position displaced a predetermined distance from the rotation axis of the first bevel gear and rotates together with the first bevel gear, and a second counter weight that is disposed in a position displaced a predetermined distance from the rotation axis of the second bevel gear and rotates together with the second bevel gear, wherein: the first counter weight is mounted on the crank via the first bevel gear and the second counter weight is mounted on the crank via the second bevel gear, the first counter weight and the second counter weight are on opposite sides of the pinion, when the first counter weight and the second counter weight revolve around the rotation axis of the first bevel gear, components of the revolving motion of the first and second counter weights in the longitudinal direction of the tool bit move opposite to a linear motion of the slider, and the first counter weight and the second counter weight move in a same phase in the longitudinal direction of the tool bit with respect to each other and are disposed on opposite sides of said rotation axis at substantially a same distance from the rotation axis in a direction transverse to the longitudinal direction of the tool bit, the crank has a rotating shaft which rotates together with the first bevel gear, an eccentric pin which is disposed in a position displaced a predetermined distance from the rotation axis of the rotating shaft, and a crank plate which is provided on one end of the rotating shaft in its longitudinal direction and connects the rotating shaft and the eccentric pin to each other, the first counter weight is mounted to the crank plate, the second bevel gear is disposed on a crank plate side of the rotating shaft, and the second counter weight is disposed on a surface of the second bevel gear which faces the first counter weight, the first and second counterweights are respectively disposed at the circumferential edge of the first and second bevel gears and are respectively disposed on surfaces of the first and second bevel gears that face away from each other, and inner radial surfaces of the first counter weight and the second counter weight are completely located outside of an outer radial surface of the crank relative to the rotation axis of the rotating shaft.