Abstract: A cutter assembly for a rotary drill bit comprises an elongate stud to be received in a socket in the surface of the bit body, the stud having mounted at one end thereof a preform cutting element. At least a major part of the stud is generally in the form of a cylinder of a circular cross-section having two symmetrically disposed flats extending longitudinally thereof, the flats being inclined towards the longitudinal axis of the stud as they extend towards the end of the stud remote from the cutting element. The flats allow the cutter assemblies to be packed together more closely side-by-side across a convexly curved surface of the body of the drill bit.

Abstract: A rotary drill bit for use in drilling holes in subsurface earth formations comprises a bit body having a shank at one end for connection to a drill string and an operating end face at the other end. A plurality of first cutting structures, each comprising a preform cutting element, is mounted in the bit body at the end face thereof, and each has a superhard front cutting face. The bit body includes a plurality of protuberances projecting outwardly from the adjacent portions of the end face, the protuberances forming a plurality of second cutting structures disposed in generally trailing relation, respectively, to at least some of the first cutting structures. Each of the protuberances is impregnated with superhard particles through a significant depth measured from the outermost extremity of the protuberance.

Abstract: A preform cutting element, for a rotary drill bit, includes a layer of polycrystalline diamond material having a front cutting face, a rear face and a peripheral surface, a cutting edge being provided by at least part of the junction between the front cutting face and the peripheral surface. The diamond layer is formed around its periphery, adjacent the cutting edge, with a row of spaced apertures. Each aperture is in the form of a bore, formed for example by a laser, which is inclined at 45.degree. to the cutting face and extends completely through the diamond layer from the cutting face to the peripheral surface thereof. The apertures serve to inhibit the propagation of spalling across the cutting face from the cutting edge.

Abstract: A rotary drill bit for use in drilling holes in subsurface earth formations comprises a bit body having a shank at one end for connection to a drill string and an operating end face at the other end. A plurality of first cutting structures, each comprising a preform cutting element, is mounted in the bit body at the end face thereof, and each has a superhard front cutting face. The bit body includes a plurality of protuberances projecting outwardly from the adjacent portions of the end face, the protuberances forming a plurality of second cutting structures disposed in generally trailing relation, respectively, to at least some of the first cutting structures. Each of the protuberances is impregnated with superhard particles through a significant depth measured from the outermost extremity of the protuberance.