Patent ID: 6827162
Filing Date: 2004-12-07
Classification: E21B,Y10T

Abstract:
A downhole-hammer drill-bit assembly for removable attachment to a substantially tubular casing of a downhole hammer, the tubular casing having an axially extending casing bore with an inner diameter, the drill-bit assembly comprising:a substantially tubular chuck having an axially extending chuck bore and a generally radially outwardly facing surface with a first portion, a second portion, and a step between the first and second portions, the first portion insertable in the casing bore and removably attachable to the casing, the step having an axially-extending outwardly-facing first surface having an outer diameter less than the inner diameter of the casing bore and a radially outwardly-extending second surface having an outer diameter greater than the inner diameter of the casing bore; a drill-bit having a bit shank with an outer diameter and a bit head, the bit shank having a radially outwardly-extending bit shoulder having an outer diameter greater than the outer diameter of the bit shank, at least a first portion of the bit shank in the chuck bore; and a substantially tubular retainer having a split retainer sidewall, a first end and a second end, the split retainer sidewall around the second portion of the chuck and around the bit shoulder, the first end having a radially inwardly-extending retainer shoulder with an axially-extending first lip forming a split retainer collar having an outer diameter less than the inner diameter of the casing bore and an inner diameter greater than the outer diameter of the first surface of the step, the split retainer collar around the first surface of the step, the second end having a radially inwardly-extending second lip forming a split retainer ring having an inner diameter less than the outer diameter of the bit shoulder, the split retainer ring around a second portion of the bit shank between the bit shoulder and the bit head.