Bit retainer assembly for a down-hole drill

An earth-boring drill assembly comprising:

• a casing having a central axis;
• a bit having a generally cylindrical head and a shank connected to the head;
• a chuck connected to the casing, the chuck being connected to the shank of the bit;
• and
• a retainer device including
• an annular sleeve connectable to the chuck;
• and
• a retainer assembly provided between the sleeve and the bit, the retainer assembly including
• an axial slot defined by one of the sleeve and the bit, the slot having an axially-extending side wall defining an opening and an axial end wall, and
• a lug supported on the other of the sleeve and the bit, the lug being positionable in the slot through the opening in the side wall, the lug being engageable with the end wall to restrict axial movement of the bit from the sleeve and away from the casing.

A method of retaining a drill bit for an earth-boring drill assembly, the drill assembly including a casing having a central axis, the bit having a generally cylindrical head, the method comprising:

• (a) connecting an annular sleeve to the casing;
• and
• (b) engaging a retainer assembly provided between the sleeve and the bit, the retainer assembly including an axial slot defined by one of the sleeve and the bit, the slot having an axially-extending first side wall defining an opening, an opposite second side wall, and an end wall between the first side wall and the second side wall, and a lug supported on the other of the sleeve and the bit, the act of engaging including
• (i) positioning the lug in the slot through the opening in the first side wall, and
• (ii) engaging the lug with the end wall to restrict axial movement of the bit from the sleeve and away from the casing.

A method of operating a down hole drill, the method comprising the steps of:

• (a) providing a bit having first and second opposite ends and defining a longitudinal axis extending between the first and second ends;
• the bit including a working surface at the first end, an enlarged diameter head at the second end, external splines, a shank portion between the enlarged diameter head and the external splines and having an outer diameter smaller than the outer diameter of the enlarged diameter head, and a retention portion between the working surface and the external splines, an external surface of the retention portion defining a first retaining surface;
• (b) providing a drill assembly that includes a casing, a chuck having internal splines, a split ring having an inner diameter larger than the outer diameter of the shank portion of the bit but smaller than the outer diameter of the enlarged diameter head of the bit, and a retention sleeve interconnected to the casing, an internal surface of the retention sleeve defining a second retaining surface;
• (c) providing in one of the first and second retaining surfaces an axially-extending entry slot having at least one open end, an axially-extending retaining slot having at least one closed end, and a circumferentially-extending transverse slot communicating between the entry slot and transverse slot;
• (d) providing on the other of the first and second retaining surfaces a lug;
• (e) coupling the bit and drilling assembly with the split ring surrounding a portion of the shank portion to resist axial removal of the bit from the drilling assembly due to abutment of the split ring and the enlarged diameter head, the chuck surrounding a portion of the external splines such that the external splines mesh with the internal splines to transfer torque from the drilling assembly to the bit, and with the lug received in the entry slot through axial movement of the lug through the open end;
• (f) moving the lug from the entry slot to the retaining slot by axially aligning the lug with the transverse slot and causing relative rotation between the bit and retention sleeve;
• (g) operating the down hole drill in a hole with the lug in the retaining slot such that substantially no axial loading and substantially no torque loading is transferred between the lug and retaining slot;
• (h) during operation of the down hole drill in the hole, breaking the bit at the shank portion such that the split ring does not resist axial movement of the first end of the bit out of the drilling assembly;
• (i) raising the drilling assembly out of the hole;
• and
• (j) while raising the drilling assembly, bringing the lug and closed end of the retaining slot into abutment to raise the first end of the bit out of the hole with the drilling assembly.