Abstract: A rock bit for drilling hard formations has a bit body with a plurality of rolling cone cutters mounted on it for rotation with rotation of the bit body. The cutters each have a plurality of recesses in their outer surfaces and a tungsten carbide insert is interference fitted into each of said recesses. A large diameter rock bit has such inserts larger than about 3/4 inch diameter and a cavity is provided in the cylindrical base of such an insert. The cavity has a volume in the range of from about 15 to 30% of the volume of the cylindrical base and extends into the cylindrical base a distance of at least about 40% of the diameter of the base. The depth of the recess is more than half of the length of the portion of the insert that grips the recess in which it is inserted. Large savings in expensive tungsten carbide can be made without decreasing performance of the tungsten carbide inserts.

Abstract: A welding gun is provided having vacuum fume extraction means wherein the level of vacuum exerted at the arc welding zone is regulated to avoid extracting shielding gas supplied to the welding zone. The vacuum level is regulated by admitting sufficient air to a fume extracting passage provided within the gun to reduce the vacuum to the desired level.