Brazing

A method of manufacturing a generally flat cutter wing for a drag bit which has two or more cutter wings disposed generally radially at the leading end of the bit, the wing having a stepped configuration and comprising a plurality of generally flat cutters secured by brazing to a generally flat steel body, each cutter being composed of a PCD layer on a carbide substrate, wherein the brazing takes place either directly between mating surfaces of the carbide substrates and the steel body or between mating surfaces of the carbide substrates, intermediate carbide elements and the steel body, and wherein the method comprises the following steps:

• (a) locating the cutters in recesses in the steel body with brazing shims interposed between the mating surfaces which are to be brazed to one another to form a generally flat cutter wing structure;
• (b) applying external force to the cutters in a direction transverse to the flat structure to urge the cutters towards the steel body;
• (c) heating the steel body to a uniform temperature across the extent of its mating surface at which brazing is to take place, such heating taking place inductively and by means of an induction coil located adjacent a surface of the steel body which is remote from the mating surface at which brazing is to take place;
• (d) continuously monitoring the local temperature of the PCD layer during heating;
• (e) controlling the energization of the induction coil so that said local temperature does not exceed the temperature at which the PCD layer suffers temperature degradation;
• and
• (f) after the brazing shims have melted against the mating surfaces which are to be brazed, de-energizing the induction coil and permitting the flat cutter wing structure to cool slowly to ambient temperature.