Patent ID: 7204321

Claim:
A concrete drill, comprising: a main body; a drive source provided in the main body; a bit drive shaft projected forward from the main body; a diamond bit attached to a front end of the bit drive shaft; and a vibrating apparatus provided in the main body for exerting a vibrating force along the bit drive shaft to the main body, a magnitude of the vibrating force which is variable, wherein the drive source rotates the diamond bit by driving the bit drive shaft, wherein the vibrating apparatus comprises: a frame member attached to a bracket portion formed at the main body; two rotating shafts arranged at the frame member in parallel with each other in a direction orthogonal to a direction of extending the bit drive shaft; eccentric weights symmetrically attached to respective ones of the rotating shafts; gears attached to the rotating shafts and brought in mesh with each other; a motor connected to one of the rotating shafts; wherein the rotating shafts are rotated by the gears in directions reverse to each other in synchronism with each other; and wherein the vibrating force is exerted to the main body by rotating the eccentric weights by rotating the rotating shafts rotated in the directions reverse to each other by the motor.