Preform cutting elements for rotary drag-type drill bits

A preform cutting element, for a rotary drag-type drill bit, including a facing table of superhard material having a front face, a peripheral surface, and a rear surface bonded to the front surface of a substrate which is less hard than the facing table, the facing table having at least one locking portion projecting rearwardly from the rear surface of the facing table into the substrate, the locking portion and the substrate having interengaging formations whereby part of the substrate overlies at least one part of the locking portion, wherein said inter-engaging formations include at least one projection on the locking portion which extends transversely to an axis extending at right angles to the front surface of the facing table, wherein said locking portion is elongate and the projection comprises a lateral flange extending longitudinally of the locking portion and spaced from the front surface of the substrate and, wherein there are provided a plurality of lateral flanges on the locking portion spaced at different distances from the front surface of the substrate.

A preform cutting element, for a rotary drag-type drill bit, including a facing table of superhard material having a front face, a peripheral surface, and a rear surface bonded to the front surface of a substrate which is less hard than the facing table, the facing table having at least one locking portion projecting rearwardly from the rear surface of the facing table into the substrate, the locking portion and the substrate having interengaging formations whereby part of the substrate overlies at least one part of the locking portion, wherein the locking portion and facing table are formed with further inter-engaging formations which inter-engage as viewed in the general plane of the facing table.

A preform cutting element, for a rotary drag-type drill bit, including a facing table of superhard material having a front face, a peripheral surface, and a rear surface bonded to the front surface of a substrate which is less hard than the facing table, the facing table having at least one locking portion projecting rearwardly from the rear surface of the facing table into the substrate, the locking portion and the substrate having interengaging formations whereby part of the substrate overlies at least one part of the locking portion, wherein the substrate is formed in at least two parts, including a subsidiary part abutting said locking portion which is of a different composition from a main part of the substrate, and wherein the subsidiary part of the substrate extends across the whole of the rear surface of the facing table, other than that part of the rear surface from which the locking portion extends, and also extends rearwardly from said surface to at least the rearward extremity of the locking portion.

A preform cutting element, for a rotary drag-type drill bit, including a facing table of superhard material having a front face, a peripheral surface, and a rear surface bonded to the front surface of a substrate which is less hard than the facing table, the facing table having at least one locking portion projecting rearwardly from the rear surface of the facing table into the substrate, the locking portion and the substrate having interengaging formations whereby part of the substrate overlies at least one part of the locking portion, wherein the substrate is formed in at least two parts, including a subsidiary part abutting said locking portion which is of a different composition from a main part of the substrate, and wherein the subsidiary part of the substrate extends rearwardly beyond the rearmost extremity of the locking portion and into the main part of the substrate.

A preform cutting element, for a rotary drag-type drill bit, including a facing table of superhard material having a front face, a peripheral surface, and a rear surface bonded to the front surface of a substrate which is less hard than the facing table, the peripheral surface of the facing table being convexly curved, as viewed in cross-section, at least in the vicinity of the cutting edge of the facing table, wherein the convex periphery of the facing table curves inwardly as it extends rearwardly towards the substrate so that, at the rearmost edge of the periphery of the facing table, the substrate is of lesser width than the maximum width of the facing table.