Abstract: A preform element, such as a cutting element for a rotary drag-type drill bit, includes a facing table of superhard material having a front face, a peripheral surface, and a rear surface bonded to a substrate which is less hard than the superhard material. The rear surface of the facing table is integrally formed with a plurality of ribs which project into the substrate, and at least major portions of the ribs extend across the rear surface of the facing table in directions which are generally radial with respect to at least one point which is adjacent or outside the peripheral surface of the facing table.

Abstract: A cutter for a rotary drill bit comprises a cutting table of superhard material bonded to a less hard substrate, the cutting table having a front face and a peripheral edge at least a part of which defines a convexly curved cutting region. The substrate includes a portion which increases in lateral extent beyond the curved cutting region of the peripheral edge of the cutting table as it extends rearwardly . The rearward extent of the outer surface of said portion varies around the periphery of the cutting table, from a maximum adjacent the cutting region to a minimum diametrically opposite the cutting region. This renders the cutter more resistant to impact loads in the cutting region while, at the same time, allowing the opposite side of the cutter to be firmly mounted in a socket in the body of the drill bit.

Abstract: A preform cutting element for a rotary drag-type drill bit includes a facing table of polycrystalline diamond having a rear surface bonded to a tungsten carbide substrate. The cutting element is formed with an angled chamfer to form a straight cutting edge on the facing table. The junction between one end of the cutting edge and the remainder of the peripheral surface of the facing table is chamfered in a part-circular arc to provide a smooth transition between the cutting edge and the rest of the peripheral surface. Such transition may reduce the spalling or other damage which may be caused by steady state and impact loads in this region.

Abstract: A preform cutting element, for use on a rotary drill bit, includes a facing table of polycrystalline diamond bonded to a tungsten carbide substrate, a cutting edge being formed by part of the peripheral surface of the facing table. The rear surface of the facing table is integrally formed with a plurality of spaced elongate ribs which project into the substrate, at least the majority of the ribs being located in the vicinity of the cutting edge. The ribs may intersect the cutting edge and extend only part way across the facing table from the cutting edge. The ribs may vary in width and/or depth.

Abstract: A preform element, suitable for use as a cutting element on a rotary drill bit, includes a polycrystalline diamond facing table bonded to a tungsten carbide substrate, the rear surface of the facing table being formed with an array of elongate ribs which project from the facing table into the substrate. The array of ribs includes a plurality of pairs of ribs which extend inwardly away from the periphery of the facing table, each pair of ribs being in a generally V-shaped formation so that the ribs diverge as they extend inwardly away from said periphery. Adjacent pairs of ribs may intersect to provide a generally star-shaped formation.

Abstract: A preform element, such as a cutting element for a drag-type drill bit, includes a facing table of superhard material having a front face, a peripheral surface, and a rear surface bonded to a substrate which is less hard than the superhard material. The rear surface of the facing table is integrally formed with a plurality of ribs which project into the substrate and extend in directions outwardly away from an inner area of the facing table towards the peripheral surface thereof.

Abstract: An elongate cutter for a drag-type drill bit includes a stud defining one end thereof and a cutting formation comprising a cutting face generally adjacent the other end. Length extends from one end to the other, depth extends generally transverse to the cutting face as well as transverse to the length, and width extends transverse to both length and depth. The stud has a cross section transverse to its length such that the cross section cannot be circumscribed by a reference circle whose diameter is equal to the maximum width of the cross section. The cross section also has an assumed section modulus, in the direction of depth, greater than that of the reference circle. The leading side of the cutter comprises a first planar zone adjacent the one end and a second planar zone adjacent the other end, and on which the cutting formation is carried. The maximum lateral dimension of the leading side is generally greater than or equal to the maximum width of the cutter.

Abstract: A rotary drill bit, for drilling wells in subsurface earth formations, and designed for rotation in a given direction, comprises a bit body having an internal passageway for drilling fluid. The bit body has an operating end face and at least one opening through that face communicating with the passageway. Cutters on the bit body form at least one elongate cutting region extending generally radially along a substantial portion of the operating end face. The cutters have cutting surfaces facing in the forward direction and generally continuous cutting edges at the outer extremity of the cutting surfaces. An elongate fence is carried on the bit body, extending generally parallel to the cutting region and spaced from the cutting region in a leading direction.

Abstract: An elongate cutter for a drag-type drill bit includes a stud defining one end thereof and a cutting formation comprising a cutting face generally adjacent the other end. Length extends from one end to the other, depth extends generally transverse to the cutting face as well as transverse to the length, and width extends transverse to both length and depth. The stud has a cross section transverse to its length such that the cross section cannot be circumscribed by a reference circle whose diameter is equal to the maximum width of the cross section. The cross section also has an assumed section modulus, in the direction of depth, greater than that of the reference circle. The leading side of the cutter comprises a first planar zone adjacent the one end and a second planar zone adjacent the other end, and on which the cutting formation is carried. The maximum lateral dimension of the leading side is generally greater than or equal to the maximum width of the cutter.

Abstract: A rotary drill bit, for use in subsurface formations, comprises a bit body, a passageway for drilling fluid within the body, communicating with nozzles in the external surface of the body, preform cutting elements mounted on the body for cutting or abrading the formation, and a number of elongate fences upstanding from the external surface of the body to control the flow of fluid from the nozzles and past cutting elements. Each fence is resiliently deformable, for example being in the form of a brush having metal bristles, so that, in use, the free elongate edge of the fence is urged resiliently into contact with the surface of the formation being cut or abraded by the cutting elements. Since each fence is resiliently deformable it will at all times firmly engage the formation to provide an effective seal, regardless of variations in depth of cut of the cutting elements.

Abstract: The invention comprises a cutter for a drag-type drill bit, the cutter having a stud portion defining one end thereof and a cutting formation generally adjacent the other end, said stud portion having external side walls which, throughout a major part of the length of said stud portion and in transverse cross section, define a circle interrupted by at least one section of greater radius of curvature.