GB563546A - Improvements relating to jigs for use in grinding drill bits - Google Patents

Abstract

563,546. Grinding drill bits. CROFTON & CO. (ENGINEERS), Ltd., C., WILES, R. C., and CAMERON, A. March 18, 1943, No. 4425. [Class 60] In grinding the backing-off of rotary drill bits used for drilling coal, rock, &c., for example, as shown, having two blades or wings tipped with tungsten carbide &c. h with two outer cutting faces 1, 2 and two inner cutting faces 3, 4, all of which have to be backed off, a jig a is employed comprising a block of brass, plastic material, &c. in the face o of which is a twolobed recess f and a central hole, and which has two inclined side faces m, n, the angle of inclination of the faces to a plane at right angles to the axis of the central hole corresponding to the backing-off angle of the bit b. The recess f receives the base of the wings of the bit, as shown in dotted lines in Fig. 1, and the shank d of the bit is held in the central hole in the block by a screwed stem and handle c. In use, the jig is laid on one of its inclined faces upon the table t at the right-hand side, or upon the table t<1> at.the left-hand side of a grinding- wheel g, the stem c serving for moving the jig back and forth over the table with the bit in contact with the wheel g. Face 1 is ground first and the jig is then turned over and laid upon table t<1> to grind the face 3 ; faces 2 and 4 are ground by releasing the bit and turning it 180 degrees in the jig and re-clamping, or may be ground without releasing the bit by setting the jig with the stem projecting in the opposite direction, as in Fig. 6. The tables t, t<1> may have sight lines thereon, parallel to the faces of the wheel g, to assist in guiding the jig ; end faces of the jig also may be inclined for grinding other faces of the bit, corresponding holes being provided for the screwed stem c. A gauge plate may be provided, having various forms for checking the face angles of a bit.