Patent ID: 9498874
Filing Date: 2016-11-22
CPC Classification: B25D

Claim Text:
1. 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; the tool holder is capable of holding a cutting tool 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; 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; and a detection mechanism which determines the position of a cutting tool within the tool holder and provides an indication of the cutting tools position; and the selector mechanism, in response to indication of the detection mechanism, opens and closes the air entry points dependent on the average position of the cutting tool within the tool holder.