Patent ID: 6394197
Filing Date: 2002-05-28
Classification: E21B

Abstract:
A drill bit assembly for use with a down hole pneumatic hammer, comprising:a driver; a pilot bit having a shank, a peripheral drilling surface, a lower surface, and a bore extending from the lower surface generally upwardly through the shank; coupling means rotatably coupling the driver to the pilot bit; underreamer arms rotatably mounted intermediate the driver and the pilot bit and including underreaming surfaces positionable outside the pilot bit perimeter; cam surfaces engageable with corresponding surfaces on the underreamer arms for deployment of the underreaming arms into an extended position, for locking the underreaming arms into the extended position, and for retracting the underreamer arms from the extended position by rotational movement between said driver and said pilot bit; and surfaces defining at least one air passageway between an outer surface of the driver and the bore in the pilot bit.