GB540073A - Improvements in or relating to metal drills - Google Patents

Abstract

540,073. Drills. FERRANTI, Ltd, and HALL, G. M. July 22, 1940, No. 11981. [Classes 83 (ii) and 83 (iii)] A drill for simultaneously cutting two or more coaxial surfaces of differing diameters is provided with a like number of cutters as surfaces to be cut, each cutter other than the leading cutter being orientated in angular disposition with respect to the adjacent cutter of smaller diameter. In Fig. 1, pairs of arms a, b provided with cutting edges are formed at right angles to each other by milling four symmetrical flutes in a high speed steel rod by a 90 degree fluting cutter, then reducing the arms a axially by an amount equal to the axial length of the step in the hole to be drilled and also reducing the arms a and b to appropriate radii and forming cutting edges on the ends of the arms. A hole c and duct e may be provided for oil and the drill finally hardened, ground and backed off. Where the hole to be drilled has more than two coaxial surfaces of differing diameters alternate cutting edges b, f and a, g, Fig. 2, may be formed in the same pair of arms or a number of pairs of arms disposed symmetrically or otherwise may be used. Each cutter may alternatively consist of a single edge instead of a pair, or several cutting edges may be used for each surface. In the latter case an appropriate number of arms may be provided for each surface. A twist drill provided with pairs of arms b, a, f, g, Fig. 6, for finishing four coaxial surfaces may be formed by fluting a high speed steel rod having several portions at both ends, then heating and twisting in either direction, cutting into halves, and then forming the cutting edges as previously described to form duplicate or different drills.