GB530113A - Improvements relating to percussive drilling bits - Google Patents

Abstract

530,113. Percussive drill bits. BERTL, E. May 30, 1939, No. 15814. [Class 124] A percussive drill bit for rock or other materials having cutters of hard metal alloy and with rectilinear cutting edges, one of the cutters having a radial cutting edge extending from the periphery to or beyond the drill axis and the other cutters all having non-radical cutting edges. In one form, the bit has a radial cutting edge 3a, Figs. 1 and 3, extending past the centre, and two eccentric shorter edges 3b which produce indentations in the work as shown in Fig. 7. The indentations produced at the first impact are shown by the heavy lines 3a and those produced by an impact at 90 degrees thereto by the broken lines 3b, the complete revolution being effected in eighteen impacts. The cutting edges are formed on hard metal inserts 2, such as tungsten or titanium carbide, and lie on a spherical surface 4, Fig. 1. Washing liquid proceeds from a central bore 6 through orifices 5 to the cutting edges. In another form the eccentric edges 3b are disposed at about 120 degrees to each other, instead of the 90 degrees shown in Fig. 3, and in a further modification, the radial edge 3a, Fig. 5, extends completely across the bit and the eccentric edges 3b are parallel, or nearly parallel, thereto. In a different form, the radial edge is similar to that in Fig. 3 and four shorter edges of differing eccentricity are provided.