Patent ID: 7469751

Claim:
A pneumatic hammer comprising an elongated hollow casing with operatively upper and lower ends and having a piston slidingly received within the casing and operable to reciprocate between upper and lower pressure chambers defined within the casing, the hammer further having a bit assembly axially displaceable within the lower end of the casing and a backhead assembly at the upper end of the casing, the piston having a striking face at an end thereof proximate the big assembly, with an air supply path to the lower pressure chamber extending around the proximal end of the piston between the piston and an interior of the casing, the piston being operable to impact on a contact surface of the bit assembly in an impact region of the casing, and wherein the piston is shaped and dimensioned at its proximal end to have a snug sliding fit with the interior of the casing in the impact region of the casing; wherein an end of the bit assembly defining a contact surface has a diameter smaller than the interior of the impact region of the casing; and the proximal end of the piston has a longitudinally extending annular lip, the contact end portion of the bit assembly being received within the extending annular lip of the piston; and said lip of the piston widens from terminal end towards the proximal end of the piston to define an inwardly tapered annular surface which provides a guide for the contact end portion of the bit assembly.