Retractable drill bits

Claim 2

Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other when said upper and lower cutters are in retracted position and adapted to move through the drilling string and longitudinally within the drive mandrel, coengageable means on said upper and lower cutters whereby movement of said upper and lower cutters longitudinally with respect to each other expands said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; and means for retaining said upper and lower cutters expanded outwardly and coupled to said mandrel.

Claim 3

Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other and adapted to occupy a retracted position in which the upper and lower cutters can move through the drilling string and longitudinally within the drive mandrel, said upper cutters being moveable longitudinally long said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; and means for retaining said upper and lower cutters expanded outwardly and coupled to said mandrel; said upper cutters being of downwardly tapering wedge shape and being alternately arranged with respect to said lower cutters, whereby downward movement of said upper cutters along said lower cutters wedges said upper cutters further apart from each other and said lower cutters further apart from each other to increase the overall cutting diameter of said upper and lower cutters.

Claim 4

Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other and adapted to occupy a retracted position in which the upper and lower cutters can move through the drilling string and longitudinally within the drive mandrel, said upper cutters being moveable longitudinally long said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; and means for retaining said upper and lower cutters expanded outwardly and coupled to said mandrel; said upper cutters being of downwardly tapering wedge shape and being alternately arranged with respect to said lower cutters, whereby downward movement of said upper cutters along said lower cutters wedges said upper cutters further apart from each other and said lower cutters further apart from each other to increase the overall cutting diameter of said upper and lower cutters.

Claim 5

Retrievable drill bit apparatus as defined in claim 1; the lower ends of said upper and lower cutters lying in the same plane normal to the mandrel axis when said upper and lower cutters are in expanded position coupled to said mandrel.

Claim 6

Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other and adapted to occupy a retracted position in which the upper and lower cutters can move through the drilling string and longitudinally within the drive mandrel, said upper cutters being movablE longitudinally along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; and means for retaining said upper and lower cutters expanded outwardly and coupled to said mandrel; the sides of each upper cutter converging in a downward direction toward each other, the sides of each lower cutter converging in an upward direction toward each other, said upper cutters circumferentially alternating with said lower cutters and with the sides of said upper cutters slidably engaging the sides of said lower cutters, whereby downward movement of said upper cutters along said lower cutters shifts said upper cutters further apart circumferentially from each other and said lower cutters further apart circumferentially from each other to increase the overall cutting diameter of said upper and lower cutters.

Claim 7

Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other and adapted to occupy a retracted position in which the upper and lower cutters can move through the drilling string and longitudinally within the drive mandrel, said upper cutters being movablE longitudinally along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; and means for retaining said upper and lower cutters expanded outwardly and coupled to said mandrel; the sides of each upper cutter converging in a downward direction toward each other, the sides of each lower cutter converging in an upward direction toward each other, said upper cutters circumferentially alternating with said lower cutters and with the sides of said upper cutters slidably engaging the sides of said lower cutters, whereby downward movement of said upper cutters along said lower cutters shifts said upper cutters further apart circumferentially from each other and said lower cutters further apart circumferentially from each other to increase the overall cutting diameter of said upper and lower cutters.

Claim 8

Retrievable drill bit apparatus as defined in claim 4; the lower ends of said upper and lower cutters lying in the same plane normal to the mandrel axis when said upper and lower cutters are in expanded position coupled to said mandrel.

Claim 9

Retrievable drill bit apparatus as defined in claim 4; the lower ends of said upper and lower cutters lying in the same plane normal to the mandrel axis when said upper and lower cutters are in expanded position coupled to said mandrel, the combined cutting surface of said upper and lower cutters being substantially circumferentially continuous when said upper and lower cutters are in expanded position coupled to said mandrel.

Claim 10

Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; coengageable means on said upper and lower cutters whereby movement of said upper cutters longitudinally along said lower cutters expands said upper and lower cutters laterally outwardly; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being moveable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwardly and coupled to said mandrel.

Claim 11

Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; coengageable means on said upper and lower cutters whereby movement of said upper cutters longitudinally along said lower cutters expands said upper and lower cutters laterally outwardly; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being moveable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwardly and coupled to said mandrel.

Claim 12

Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwaRdly and coupled to said mandrel; and coengageable means on said upper cutters and lower cutters suspending said lower cutters from said upper cutters with said upper and lower cutters in retracted position.

Claim 13

Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwaRdly and coupled to said mandrel; and coengageable means on said upper cutters and lower cutters suspending said lower cutters from said upper cutters with said upper and lower cutters in retracted position.

Claim 14

Retrievable drill bit apparatus as defined in claim 7; and coengageable orienting means on said mandrel and cutter means to orient said upper and lower cutters for lateral outward expansion into coupling relation to said mandrel.

Claim 15

Retrievable drill bit apparatus as defined in claim 8; and coengageable orienting means on said mandrel and cutter means to orient said upper nd lower cutters for lateral outward expansion into coupling relation to said mandrel.

Claim 16

Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on which said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwardly and coupled to said mandrel; said upper cutters being of downwardly tapering wedge shape and being alternately arranged with respect to said lower cutters, whereby downward movement of said upper cutters along said lower cutters wedges said upper cutters further apart from each other and said lower cutters further apart from each other to increase the overall cutting diameter of said upper and lower cutters.

Claim 17

Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on which said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwardly and coupled to said mandrel; said upper cutters being of downwardly tapering wedge shape and being alternately arranged with respect to said lower cutters, whereby downward movement of said upper cutters along said lower cutters wedges said upper cutters further apart from each other and said lower cutters further apart from each other to increase the overall cutting diameter of said upper and lower cutters.

Claim 18

Retrievable drill bit apparatus as defined in claim 11; the lower ends of said upper and lower cutters lying in the same plane normal to the mandrel axis when said upper and lower cutters are in expanded position coupled to said mandrel.

Claim 19

Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwardly and coupled to said mandrel; the sides of each upper cutter converging in a downward direction toward each other, the sides of each lower cutter converging in an upward direction toward each other, said upper cutters circumferentially alternating with said lower cutters and with the sides of said upper cutters slidably engaging the sides of said lower cutters, whereby downward movement of said upper cutters along said lower cutters shifts said upper cutters further apart circumferentially from each other and said lower cutters further apart circumferentially from each other to increasE the overall cutting diameter of said upper and lower cutters.

Claim 20

Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwardly and coupled to said mandrel; the sides of each upper cutter converging in a downward direction toward each other, the sides of each lower cutter converging in an upward direction toward each other, said upper cutters circumferentially alternating with said lower cutters and with the sides of said upper cutters slidably engaging the sides of said lower cutters, whereby downward movement of said upper cutters along said lower cutters shifts said upper cutters further apart circumferentially from each other and said lower cutters further apart circumferentially from each other to increasE the overall cutting diameter of said upper and lower cutters.

Claim 21

Retrievable drill bit apparatus as defined in claim 13; and coengageable means on said upper cutters and lower cutters suspending said lower cutters from said upper cutters with said upper and lower cutters in retracted position.

Claim 22

Retrievable drill bit apparatus as defined in claim 13; and coengageable orienting means on said mandrel and cutter means to orient said upper and lower cutters for lateral outward expansion into coupling relation to said mandrel.

Claim 23

Retrievable drill bit apparatus as defined in claim 7; coengageable orienting means on said mandrel and cutter means to orient said upper and lower cutters for lateral outward expansion into coupling relation to said mandrel; and coengageable stop means on said lower cutters and mandrel to locate said lower cutters in position to be coupled to said mandrel.

Claim 24

Retrievable drill bit apparatus as defined in claim 8; coengageable orienting means on said mandrel and cutter means to orient said upper and lower cutters for lateral outward expansion into coupling relation to said mandrel; and coengageable stop means on said lower cutters and mandrel to locate said lower cutters in position to be coupled to said mandrel.

Claim 25

Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwardly and coupled to said mandrel; coengageable orienting means on said mandrel and cutter means to orient said upper and lower cutters for lateral outward expansion into coupling relation to said mandrel; coengageable stop means on said lower cutters and mandrel to locate said lower cutters in position to be coupled to said mandrel; and coengageable pin and slot means on said upper cutters and lower cutters suspending said lower cutters from said upper cutters with said upper and lower cutters in retracted position, said pin and slot means permitting said upper cutters to move downwardly of said lower cutters after coengagement of said stop means to expand said upper and lower cutters laterally outwardly.

Claim 26

Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwardly and coupled to said mandrel; coengageable orienting means on said mandrel and cutter means to orient said upper and lower cutters for lateral outward expansion into coupling relation to said mandrel; coengageable stop means on said lower cutters and mandrel to locate said lower cutters in position to be coupled to said mandrel; and coengageable pin and slot means on said upper cutters and lower cutters suspending said lower cutters from said upper cutters with said upper and lower cutters in retracted position, said pin and slot means permitting said upper cutters to move downwardly of said lower cutters after coengagement of said stop means to expand said upper and lower cutters laterally outwardly.

Claim 27

Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position rEtaining said upper and lower cutters outwardly and coupled to said mandrel; said carrier comprising an outer carrier member supporting said cutter means, and an inner carrier member releasably connected to said outer carrier member and removable therefrom for withdrawal from the mandrel and through the drilling string to the top of the bore hole.

Claim 28

Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position rEtaining said upper and lower cutters outwardly and coupled to said mandrel; said carrier comprising an outer carrier member supporting said cutter means, and an inner carrier member releasably connected to said outer carrier member and removable therefrom for withdrawal from the mandrel and through the drilling string to the top of the bore hole.

Claim 29

Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwardly and coupled to said mandrel; said carrier comprising an outer carrier member supporting said cutter means, and an inner core barrel for receiving a core produced in the bore hole formation by said cutter means and releasably connected to said outer carrier member and removable therefrom for withdrawal from the mandrel and through the drilling string to the top of the bore hole.

Claim 30

Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwardly and coupled to said mandrel; said carrier comprising an outer carrier member supporting said cutter means, and an inner core barrel for receiving a core produced in the bore hole formation by said cutter means and releasably connected to said outer carrier member and removable therefrom for withdrawal from the mandrel and through the drilling string to the top of the bore hole.

Claim 31

Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwardly and coupled to said mandrel; said carrier comprising an inner core barrel for receiving a core produced in the bore hole formation by said cutter means.

Claim 32

Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect to each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwardly and coupled to said mandrel; said carrier comprising an inner core barrel for receiving a core produced in the bore hole formation by said cutter means.

Claim 33

Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel having an internal thread in its lower portion; cutter means movable longitudinally through the drilling string and into the drive mandrel and having a thread companion to said internal thread; and means for expanding said cutter means laterally outwardly to mesh its thread with said internal thread and couple said cutter means to said mandrel.

Claim 34

Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel having an internal thread in its lower portion; cutter means movable longitudinally through the drilling string and into the drive mandrel and having a thread companion to said internal thread; and means for expanding said cutter means laterally outwardly to mesh its thread with said internal thread and couple said cutter means to said mandrel.

Claim 35

Retrievable drill bit apparatus as defined in claim 22; and holding means for retaining said cutter means expanded laterally outwardly with its thread meshed with said internal thread.

Claim 36

Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters iN circumferentially overlapping relation with respect to each other and adapted to occupy a retracted position in which the upper and lower cutters can move through the drilling string and longitudinally within the drive mandrel, said upper cutters being movable longitudinally along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; and means for retaining said upper and lower cutters expanded outwardly and coupled to said mandrel; said coupling means comprising an internal thread on said mandrel and external threads on said upper and lower cutters meshing with said internal thread.

Claim 37

Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters iN circumferentially overlapping relation with respect to each other and adapted to occupy a retracted position in which the upper and lower cutters can move through the drilling string and longitudinally within the drive mandrel, said upper cutters being movable longitudinally along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; and means for retaining said upper and lower cutters expanded outwardly and coupled to said mandrel; said coupling means comprising an internal thread on said mandrel and external threads on said upper and lower cutters meshing with said internal thread.

Claim 38

Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect too each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwardly and coupled to said mandrel; said coupling means comprising an internal thread on said mandrel and external threads on said upper and lower cutters meshing with said internal thread.

Claim 39

Retrievable drill bit apparatus adapted to be moved longitudinally through a tubular drilling string disposed in a bore hole: an outer structure adapted to be secured to the drilling string and including a drive mandrel; cutter means comprising upper cutters and lower cutters in circumferentially overlapping relation with respect too each other; a carrier supporting said cutter means and adapted to convey said cutter means through the drilling string and longitudinally within the mandrel with the upper and lower cutters in retracted position, said upper cutters being movable downwardly by said carrier along said lower cutters to expand said upper and lower cutters laterally outwardly from their retracted positions; coengageable coupling means on said mandrel and upper and lower cutters for securing said upper and lower cutters to said mandrel when said upper and lower cutters are in expanded position; said carrier being movable downwardly of said upper and lower cutters to a position retaining said upper and lower cutters outwardly and coupled to said mandrel; said coupling means comprising an internal thread on said mandrel and external threads on said upper and lower cutters meshing with said internal thread.

Claim 40

Retrievable drill bit apparatus as defined in claim 25; and coengageable orienting means on said mandrel and cutter means to orient said upper and lower cutters for lateral outward expansion to place said external threads on said upper and lower cutters into full threaded mesh with said internal thread.

Claim 41

Retrievable drill bit apparatus as defined in claim 25; on said upper and lower cutters and coengageable orienting means on said mandrel and cutter means to orient said upper and lower cutters for lateral outward expansion to place said external threads on said upper and lower cutters into full threaded mesh with said internal thread; and coengageable means on said lower cutters and mandrel to locate said lower cutters in position for lateral outward expansion of its external threads into threaded mesh with said internal thread.