Patent ID: 6035953
Filing Date: 2000-03-14
Classification: E21B

Abstract:
A down hole hammer assembly comprising a reverse circulation hammer having a drill bit mounted to one end of a housing which accommodates a percussive hammer, the drill bit having a cutting face, the other end of the housing being adapted to be mounted to a drill string, the assembly further comprising a support member receivable on the lower end of a bore hole casing which is receivable on the lower end of a bore hole casing which is receivable over the drill string, said support member comprising a first part adapted to be fixed to the lower end of the casing and a second part rotatably received on the first part and capable of limited axial slidable movement thereon, said second part being engagable with the drill bit to be rotatable with the drill bit on rotation of the drill bit in one direction and to be movable axially with the drill bit, said drill bit being disengagable with the second part to be able to be movable axially relative to the second part, flow passageways being provided between the drill bit and the second part to deliver fluid to the cutting face and said drill bit being provided on its outermost axial face with at least one opening to receive the fluid and entrained cuttings for return to the surface through the hammer and drill string.