GB1466700A - Drill bits - Google Patents

Abstract

1466700 Drill bits PADLEY & VENABLES Ltd 21 Feb 1975 [21 March 1974] 12600/74 Heading B4C A rotary percussive drill bit has inserts 9 projecting axially from the end face thereof each insert having a flat leading face 10 lying parallel to the bit's longitudinal axis to produce zero rake, each face meeting a clearance face 11 at a cutting edge 12 and forming an angle between the two faces in the range 80-87 degrees. The bit is cut away as at 5 to produce a channel through which cleaning medium, entering through a central bore in the bit and exiting through radial channels 7, can remove debris. The inserts 9 are located in the lands between these recesses 5. The inserts may be of tungsten carbide and are chamfered at their inner and outer radial edges to prevent undue wear. As shown in Fig. 5A face 10 lies at an angle # to the radius passing through the bits axis and the intersection of face 10 with the periphery of the drill body so that the inner edge of the face leads the outer edge; however in modifications the inserts may be arranged so that the outer edge of face 10 leads the inner edge in the direction of rotation or the face may be arranged to lie along a radius as defined above. Also as shown a trailing face 13 is provided behind the clearing face 11. The bits may be inserted by brazing or by heating methods. The front face 10 of each insert may be recessed as at 28, 28b, Figs. 7 and 9. To facilitate cutting the channels 8 which take the inserts the face end of the drill may have a recess 30 drilled therein which is subsequently plugged by a member 31 prior to insertion of the inserts.