A Twist Drill Drillable Deep Hole under Continuously High Feed Rate

Abstract

This paper describes a new type of twist drill. The web of this drill is three times thicker than that of the conventional one. Thus, it has high flexural and torsional rigidity. The main flank and the rake of the central part are formed by a flat grinding method and the drill tip forms a point perfectly. The chip is a conical helix type at first, successively changes to segment type, and then to a long-pitch helix type. In spite of the narrow flutes they do not clog with chips ; all types of chips are exhausted out of the drilling hole very well. Therefore, it can drill a deep hole under continuous feed and with a high feed rate. Under conditions of wet drilling of a S50C strip, a 12 mm-diameter twist drill with a carbide (M20) tip achieved deep drilling of 22 times the drill diameter, which is the limit of its flute length, and a 10 mm-diameter HSS drill achieved a total drilling depth of 80 m (through hole drilling of 60 mm x 1 340 holes).