Patent ID: 8312944

Claim:
A percussion drilling assembly for boring into the earth, the percussion drilling assembly comprising: a tubular case having a central axis, an upper end, and a lower end; a piston slidingly disposed within the tubular case; a driver sub coaxially coupled to the lower end of the tubular case, the driver sub including an upper end disposed within the case and a lower end extending axially from the lower end of the case, and at least one internal spline disposed on an inner surface of the driver sub; a hammer bit coaxially disposed within the driver sub, the hammer bit including an upper end disposed within the driver sub and a lower end extending from the lower end of the driver sub, and at least one external spline disposed on an outer surface of the hammer bit, the external spline configured to engage the at least one internal spline of the driver sub; wherein the upper end of the driver sub extends axially from the upper end of the hammer bit and is configured to guidingly receive the piston; a bit retainer ring including a plurality of retainer ring segments, the bit retainer ring radially positioned between the hammer bit and the driver sub, wherein the bit retainer ring is adapted to restrict the de-coupling of the hammer bit and the driver sub; wherein the inner surface of the driver sub includes an annular recess, and wherein the bit retainer ring extends radially into the annular recess of the driver sub; and wherein the driver sub further comprises an access slot axially aligned with the annular recess in the inner surface of the driver sub, such that the access slot extends radially from an outer surface of the driver sub to the annular recess in the inner surface of the driver sub and is configured for insertion of the plurality of retainer ring segments into the annular recess.