CROWN BIT Russian patent published in 1996 - IPC

FIELD: rock cutting tools. SUBSTANCE: crown bit has body with central axial hole and several radial recesses on its working end. Radial recess accommodates hard metal inserts which are secured by soldering and having core-forming edges and side surfaces facing central side hole. Side surface of each insert is made in form of part of circular cylindrical surface. Diameter of central axial hole is larger than the distance between core-forming edges and diameter of element of side surface of hard metal insert. Axial hole is blind and its depth lowers below the plane of bases of hard metal inserts. Axial hole depth equals 0.5-0.75 of insert height. Bottom of each recess receiving hard metal insert is located in the plane square to the crown bit axis. EFFECT: reduced energy consumption for core cutting and increased drilling rate by changing conditions of formation and destruction of core. 3 cl, 6 dwg