Percussion hammer bit

Abstract

A drill bit for use with a percussion drilling apparatus can include an elongated body with a first end, a second end, and a longitudinal surface extending between the first and second ends. A plurality of splines extends along the longitudinal surface of the drill bit internally, and at least one of the splines has an apex, a root, and a planar surface between the apex and root. The planar surface can be oriented at an angle to a plane extending from a center of the drill bit to a midpoint of the apex. The internal splines of the hammer bit correspond to external splines in a hammer casing.

What is claimed is: 
     
         1 . A downhole percussion hammer assembly, comprising:
 a hammer bit having internal splines;   a generally cylindrical hammer casing having external splines corresponding to the splines of the hammer bit;   a bit retention mechanism external to the hammer casing, and connected to the hammer bit internally;   a locking device located externally to the hammer casing, and internally to the hammer bit;   a friction reducing agent between the hammer casing splines for reducing friction between the hammer casing splines and the bit splines;   a piston for delivering percussive force to the hammer bit;   a top sub assembly comprising a top cylinder having an air distributor for timing air flow to upper and lower air chambers of the percussion hammer assembly, wherein the top sub assembly is secured to the hammer casing.   
     
     
         2 . The downhole percussion hammer assembly of  claim 1 , further comprising one or more ports in the hammer bit for allowing air or fluid to disperse from inside the percussion hammer assembly. 
     
     
         3 . The downhole percussion hammer assembly of  claim 1 , further comprising one or more helical scallops along a length of an exterior surface of the hammer bit. 
     
     
         4 . The downhole percussion hammer assembly of  claim 1 , wherein the top sub assembly is secured to the hammer casing and to an upstream drill string. 
     
     
         5 . The downhole percussion hammer assembly of  claim 1 , wherein the top sub assembly is connected to the hammer casing and to a bottom mandrel of a downhole motor. 
     
     
         6 . A downhole percussion hammer assembly, comprising:
 a hammer bit having internal splines; and   a hammer casing having external splines corresponding to the splines of the hammer bit.   
     
     
         7 . The downhole percussion hammer assembly of  claim 6 , further comprising a bit retention mechanism external to the hammer casing, and connected to the hammer bit internally. 
     
     
         8 . The downhole percussion hammer assembly of  claim 6 , further comprising a locking device located externally to the hammer casing, and internally to the hammer bit. 
     
     
         9 . The downhole percussion hammer assembly of  claim 6 , further comprising one or more ports in the hammer bit for allowing air or fluid to disperse from inside the percussion hammer assembly. 
     
     
         10 . The downhole percussion hammer assembly of  claim 6 , further comprising a friction reducing agent between the hammer casing splines for reducing friction between the hammer casing splines and the bit splines. 
     
     
         11 . The downhole percussion hammer assembly of  claim 6 , further comprising a top sub assembly comprising a top cylinder having an air distributor for timing air flow to upper and lower air chambers of the percussion hammer assembly, wherein the top sub assembly is secured to the hammer casing. 
     
     
         12 . The downhole percussion hammer assembly of  claim 11 , wherein the top sub assembly is an integral part of a bottom mandrel of a downhole motor. 
     
     
         13 . The downhole percussion hammer assembly of  claim 6 , further comprising a piston for delivering percussive force to the hammer bit. 
     
     
         14 . The downhole percussion hammer assembly of  claim 6 , wherein the internal splines of the hammer bit are parallel to a longitudinal axis of the bit. 
     
     
         15 . The downhole percussion hammer assembly of  claim 8 , wherein the locking device is a bit retaining ring. 
     
     
         16 . The downhole percussion hammer assembly of  claim 6 , wherein the hammer bit further comprises one or more helical scallops along a length of an exterior surface of the hammer bit. 
     
     
         17 . The downhole percussion hammer assembly of  claim 6 , wherein the percussion hammer further comprises an air chamber having a timing mechanism for allowing exhaust to escape a bottom chamber either internally through a blow tube or externally through a guide sleeve. 
     
     
         18 . A method of drilling a hole using a downhole percussion hammer assembly, comprising:
 securing a top sub section of a hammer casing to a mandrel of a downhole motor or to a section of drill string;   connecting a hammer bit to the hammer casing, wherein the hammer bit has internal drive splines and the hammer casing has external splines that correspond to the internal drive splines of the hammer bit; and   applying repeated percussive force to the hammer bit with a piston contained within the percussion hammer assembly, wherein upper and lower portions of the hammer assembly are energized and thus power the piston by air or fluid pressure changes and flow into and out of the upper and lower chambers of the hammer assembly.