GB494976A - Improvements in or relating to boring or drilling tools - Google Patents

Abstract

494,976. Percussive drills. PHILLIPS, N., and CLOW, A. C. May 10, 1937, No. 13316. [Class 124] [Also in Group XXII] Boring or drilling tools are formed of case-hardened low carbon or mild steel and have the hardened skin removed from the operative end face or faces of the tool. In one form, the end of a mild steel rod 1, Fig. 1, is flattened and pointed, as shown, and a slot 4 is cut therein after which the drill is case-hardened. The cutting edges 5 are then ground to give cutting rake and to remove the hard skin so that the cutting edges may subsequently be sharpened with a file. The shank may be provided with square and circular sections 6, 7, Fig. 3, for gripping in any type of chuck. In another form the twist drill shown in Fig. 3 is produced from a mild steel strip 8, Fig. 4, which is provided with unsymmetrical V-grooves 9 in its opposite faces and further staggered grooves 12, 12<1> in the grooves 9. The strip is then given a quick-pitch twist 13, the end trimmed, the strip case-hardened and the cutting edges 14 ground as in Fig. 1. The central web 10 of the drill is of such thickness that the hard skin 11 extends completely therethrough and allows the web to break away at the operative end to give the effect of the slot 4 in Fig. 1. The grooves 9 may be symmetrical or may be replaced by a deeper groove in one face only, and the grooves may be formed by rolling &c. The edges 8<1> of the strip may be arranged at an angle other than a right-angle to the faces in order to provide acute angles on the leading edges, or the faces may be formed concave as shown in Fig. 6. The strip may be buttwelded to the shank, or the shank end of the strip may be left untwisted and built up by securing further strips to the faces. Twist drills may be produced by helically grooving a cylindrical rod and then producing a central groove or grooves to provide the thin web 10.