Expandable and contractible rotary well drilling bit

Claim 1

In a rotary drill bit which is contractible to fit within a casing to permit withdrawal through the casing, and which is expandable below the casing to drill a well bore of a diameter larger than the outside diameter of the casing so as to permit the casing to follow the bit to prevent collapse of and/or lost circulation from the well bore thereabove, the combination of: (a) a base having an upper end threaded for connection to the lower end of a rotary drill string in the casing for driving the bit; (b) a plurality of cutter arms circumferentially spaced around said base therebelow and respectively having cutters thereon; (c) a plurality of pivot pins respectively pivotally connecting said cutter arms to said base for simple pivotal movement inwardly and outwardly between retracted positions corresponding to the contracted condition of the bit and extended positions corresponding to the expanded condition of the bit, said pivot pins having circular cross sections and being disposed in holes of circular cross section in said base and said cutter arms, respectively; (d) a plurality of interengageable expansion stop means on said base and on said cutter arms, respectively, for preventing outward pivotal movement of said cutter arms beyond their extended positions corresponding to the expanded condition of the bit and for transferring the weight of said base and the drill string to said cutter arms without applying any substantial loads to said pivot pins, each of said interengageable expansion stop means including a first set of interengageable expansion stops on said base and the corresponding cutter arm adjacent one end of the corresponding pivot pin and below and radially outwardly of the corresponding pivot pin, a second set of interengageable expansion stops on said base and the corresponding cutter arm adjacent the other end of the corresponding pivot pin and below and radially outwardly of the corresponding pivot pin, and a third set of interengageable expansion stops on said base and the corresponding cutter arm intermediate the ends of the corresponding pivot pin and above and radially outwardly of the corresponding pivot pin; and (e) a plurality of interengageable contraction stop means on said base and on said cutter arms, respectively, for preventing inward pivotal movement of said cutter arms beyond their retracted positions corresponding to the contracted condition of the bit, said expansion stop means limiting inward pivotal movement of said cutter arms to values such that the weight of said base and the drill string pivots said cutter arms outwardly into their extended positions, to expand the bit, when said cutters rest on the bottom of the well bore.