Patent ID: 7451833
Filing Date: 2008-11-18
Classification: B25D

Abstract:
1. A hammer drill comprising: a body; a motor located in the body; a centre of gravity located within the body; a tool holder; a hammer mechanism, driven by the motor when the motor is activated; a counter mass slideably mounted within the body on a rod and located above the centre of gravity, the counter mass capable of sliding movement in a forward direction and a rearward direction between a first end position and a second end position and the counter mass comprises a vertical C shaped slot which engages with the rod to allow the counter mass to twist about a vertical axis; a biasing member which biases the counter mass to a third position located between the first end position and the second end position; and wherein the mass of the counter mass and the strength of the biasing member are such that the sliding movement of the counter mass acts to at least partially counteract vibrations of the hammer drill generated by the operation of the hammer mechanism.