Patent ID: 6082474
Filing Date: 2000-07-04
Classification: E21B

Abstract:
A preform element including a facing table of superhard material having a front face, a peripheral surface, and a rear surface bonded to a front surface of a substrate which is less hard than the superhard material, the front surface of the substrate being formed with a plurality of recesses into which extend corresponding projections formed on the rear surface of the facing table, a plurality of grooves are formed in said recesses, at least one of said grooves extending to the periphery of the substrate, said recesses including at least one rebate which extends along only a part of the periphery of the substrate and into which extends a projection on the facing table which provides a part of the peripheral surface of the facing table, wherein said at least one rebate has a bottom wall and an inner wall wherein the bottom wall is flat and generally parallel to said front surface of the substrate.