Patent ID: 7975784
Filing Date: 2011-07-12
Classification: E21B

Abstract:
1. A drill bit assembly for fluid-operated percussion drill tools comprising: a percussion bit having a head portion formed with an axially extending shank wherein the shank is a stub shank having a top face adapted for striking by a piston to impart a percussive force to the bit, a drive bush releasably connectable to the head portion of the bit by means of an external screw-thread on the head portion which engages with a complementary internal screw-thread formed on an inner cylindrical wall of the drive bush, the drive bush also having axially extending splines formed on the inner cylindrical wall of the drive bush, and a drive chuck having complementary splines formed externally therein that are slideably engageable with the axially extending splines on the drive bush whereby rotational drive from the chuck is transmitted to the drive bush to drive the bit, and engagement means on the chuck is adapted for connecting the chuck to a wear sleeve of a fluid-operated percussion drill tool.