Down hole hammer assembly

The down hole hammer assembly as claimed at anyone of the preceding claims wherein the second part is provided with one or more axial ribs at spaced intervals around its inner face and said drill bit is formed with an outer face of substantially complementary cross-section to enable relative movement of the drill bit past the second part and to provide overlapping portions which are selectively engagable when the second part is to be engaged with the drill bit.

A drill bit assembly for a reverse circulation hammer 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 over the drill string, said support 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 engageable 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.