Hammer drill

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

• a body;
• a cylinder mounted within the body;
• a motor mounted within the body having an output spindle;
• a tool holder mounted on the body, the tool holder being capable of holding a cutting tool;
• and
• a hammer mechanism comprising:
• a piston slideably mounted within the cylinder;
• a reciprocating drive mechanism mounted within the body which, when the motor is activated, converts a rotary movement of the output spindle of the motor into a reciprocating movement of the piston within the body;
• a ram slideably mounted within the cylinder forward of the piston, the ram being reciprocatingly driven by the reciprocating movement of the piston via an air spring to repetitively strike the cutting tool held by the tool holder, the hammer mechanism performing one hammer cycle when the ram strikes the cutting tool;
• and
• an air replenishment mechanism which is capable of refreshing the air spring within the hammer cycle, the air replenishment mechanism comprising a bleed hole and a valve that selectively opens or closes air flow through the bleed hole;
• wherein the method comprises the step of electronically controlling the valve so as to adjust a volume of air flow through the bleed hole.