Hammer drill

A hammer drill comprising:

• a body;
• a cylinder mounted within the body;
• a piston slideably mounted within the cylinder;
• a motor mounted within the body having an output spindle;
• a reciprocating drive mechanism mounted within the body which, when the motor is activated, converts the rotary movement of the spindle of the motor into a reciprocating movement of the piston within the cylinder;
• a ram slideably mounted within the cylinder which is reciprocatingly driven by the reciprocating movement of the piston via an air spring;
• at least two air entry points formed through the wall of the cylinder in different axial positions along the length of the cylinder, each of which are capable of replenishing the air spring;
• a tool holder mounted on the body, the tool holder being capable of holding a cutting tool which, during normal use, is repetitively struck by the reciprocating ram;
• wherein there is further provided a selector mechanism which selectively opens and close the air entry points;
• characterized in that the selector mechanism opens only one air entry point at any one time during normal use, the selector mechanism closing all other air entry points, each of the air entry points capable of replenishing the air spring during normal use when opened by the selector mechanism;
• wherein the selector mechanism comprises a finger pad capable of being engaged by the operator, the finger pad being movable and operated manually to open and close the air entry points.

A method of altering the performance characteristics of a hammer comprising:

• a body;
• a cylinder mounted within the body;
• a piston slideably mounted within the cylinder;
• a motor mounted within the body having an output spindle;
• a reciprocating drive mechanism mounted within the body which, when the motor is activated, converts the rotary movement of the spindle of the motor into a reciprocating movement of the piston within the cylinder;
• a ram slideably mounted within the cylinder which is reciprocatingly driven by the reciprocating movement of the piston via an air spring;
• at least two air entry points formed through the wall of the cylinder in different axial positions along the length of the cylinder, each of which are capable of replenishing the air spring;
• a tool holder mounted on the body;
• a cutting tool held by the tool holder which, during use, is repetitively struck by the reciprocating ram, the cutting tool being capable of being held by the tool holder in a range of axial positions, the average axial position of the cutting tool within the tool holder during use being dependent on the hardness of the material being cut by the cutting tool;
• characterized in that the method comprises the steps of measuring the position of the cutting tool within the tool holder;
• and
• selectively opening one of the air entry points dependent on the average position of the cutting tool within the tool holder whilst closing the other air entry points, the open air entry point replenishing the air spring during normal use.