Drill

Claim 1

A drill comprising: a tubular drill string having a series of circumferentially spaced slots adjacent its lower end; and an apparatus releasably mountable on the bottom of said drill string, said apparatus having a body rotatable with said drill string, a cutting bit at the lower end of said body, a plurality of cutters arranged about the drill axis above said bit and movable between inner and outer positions, said cutters serving, when in their outer positions during drilling, to ream the hole cut by said bit to a size which permits said drill string to pass along the reamed hole, a structure movable vertically with respect to said body between a first position and a second position, said structure chocking said cutter elements in said outer positions when said structure is in said first position but permitting retraction of said cutter elements to their inner positions when it is moved to said second position, a plurality of rotary drive dogs each movable between an outer position in which to engage said drill string and said body so as to provide a torque coupling between said drill string and said body and a retracted position in which said dogs are disengaged from said drill string, each of said rotary drive dogs being provided with a slidable cam means engagable with a complementary cam means on said structure to cause the retraction of said dogs on movement of said structure from said first position to said second position so that said apparatus is withdrawable through said drill string on release from the bottom end thereof when said cutters are in said inner positions and said rotary drive dogs are retracted, and biasing means to bias each dog outwardly when said structure is in said first position, whereby in the event that said structure is moved to said first position when said drive dogs are circumferentially displaced from alignment with said slots, said drive dogs are forced outwardly by said biasing means into engagement with said slots on rotation of said drill string.

Claim 6

An apparatus releasably mountable adjacent the bottom of a drill string, said apparatus comprising: a body rotatable with said drill string; a cutting bit at the lower end of said body; a plurality of cutters arranged about the drill axis above said bit and movable between inner and outer positions, said cutters serving, when in their outer positions during drilling, to ream the hole cut by said bit to a size which permits said drill string to pass along the reamed hole; a structure movable vertically with respect to said body between a first position and a second position, said structure chocking said cutter elements in said outer positions when said structure is in said first position but permitting retraction of said cutter elements to their inner positions when it is moved to said second position; a plurality of rotary drive dogs each movable between an outer position for engaging a series of circumferentially spaced slots in the drill string and said body so as to provide a torque coupling between the drill string and said body and a retracted position in which it is disengaged from the drill string, each of said rotary drive dogs provided with a slidable cam means engagable with a complementary cam means on said structure to cause the retraction of said dogs on movement of said structure from said first position to said second position so that said apparatus is withdrawable through the drill string on release from the bottom end thereof when said cutters are in said inner positions and said rotary drive dogs are retracted; and biasing means to bias each dog outwardly when said structure is in said first position, whereby when said structure is used with the drill string, said drive dogs are forced outwardly by said biasing means into engagement with the slots on rotation of the drill string.

Claim 7

An apparatus releasably mountable adjacent the bottom of a drill string, said apparatus comprising: a body rotatable with said drill string; a cutting bit at the lower end of said body; a plurality of cutters arranged about the drill axis above said bit and movable between inner and outer positions, said cutters serving, when in their outer positions during drilling, to ream the hole cut by said bit to a size which permits said drill string to pass along the reamed hole; a structure movable vertically with respect to said body between a first position and a second position, said structure chocking said cutter elements in said outer positions when said structure is in said first position but permitting retraction of said cutter elements to their inner positions when it is moved to said second position; a plurality of rotary drive dogs each movable between an outer position for engaging a series of circumferentially spaced slots in the drill string and said body so as to provide a torque coupling between the drill string and said body and a retracted position in which it is disengaged from the drill string, each of said rotary drive dogs provided with a slidable cam means engagable with a complementary cam means on said structure to cause the retraction of said dogs on movement of said structure from said first position to said second position so that said apparatus is withdrawable through the drill string on release from the bottom end thereof when said cutters are in said inner positions and said rotary drive dogs are retracted; and biasing means to bias each dog outwardly when said structure is in said first position, whereby when said structure is used with the drill string, said drive dogs are forced outwardly by said biasing means into engagement with the slots on rotation of the drill string.