GB965513A - Machine for grinding conical drill points - Google Patents

Abstract

965,513. Grinding; machine tool details. WINSLOW PRODUCT ENGINEERING CORPORATION. Dec. 12, 1962 [Dec. 21, 1961], No. 46979/62. Headings B3B and B3D. A method of pointing a drill comprises placing a drill tip in contact with a rotating grinding wheel with the drill axis inclined at a predetermined angle to the surface of the grinding wheel effecting relative lateral movement of the tip along the surface and simultaneously rotating the drill about such an axis as to change the angle between the grinding surface and drill axis, and rotating the drill in synchronism with the relative movement of the drill and grinding wheel. The drill is mounted in a chuck 44, Fig. 1, which is rotatably mounted in a part 26 and is formed with a worm-wheel 58 engaged by a worm 112 connected by a universal joint 42 with a shaft 116 driven by a motor 146. The part 26 is pivotally mounted by conical pivots 32 in arms 22, 24 on a second part 16 secured to a tube 18 which is oscillatable by a bell crank 148 engaged by a cam 142 also driven from the motor 146. The tube carries a shoulder 150 engaged by an end of a lever 158 which, at its centre, is engaged by a cam 144 driven by the motor 146 and, at its other end, engages the rod 160 of an elevating means 160b. The means 160b is operative to raise the chuck assembly above a grinding wheel 172 for insertion and withdrawal of a drill in the chuck, and the cams 142, 144 oscillate and reciprocate the chuck assembly as described in Specification 873,741. The arm 22 of the bracket has a housing 130 for a spring which urges the part 26 about an axis 38 through the pivots 32 so that a stop 166 on the upper part of the chuck engages a fixed part 120 on the frame 12 of the machine; the arrangement is such that rotation of bracket 16 about the axis 40 of the sleeve 18 and pivoting of the part 26 about the axis 38 effectively rocks the chuck and the axis 50 of the drill about an axis 174 between the pivot 42 of the universal joint and the stop 166. In operation, the elevating means 160b is first operated by the control means 176 described in Specification 873,741 to raise the chuck above the grinding wheel so that a drill D, Fig. 7, positioned by a stop 176, can be accurately secured in the chuck. After the chuck has been lowered, the motor M is energized to rotate the cams 142, 144 and the shaft 116. Initially, the part 16 is oscillated clockwise about the axis 40 so that the part 26 is moved by the spring in the housing 130 to incline the drill downwardly towards the grinding wheel. Counter-clockwise rotation of the part 16 then causes counter-clockwise movement of the part 26 to advance the drill tip into contact with the grinding wheel, the axis 50 of the drill still being inclined downwardly, so that the leading edge of a land of the drill is ground. Further rotation of the cams causes the parts 16 and 26 to move so as to bring the drill axis through a horizontal position to an upwardly inclined position as the drill tip is traversed across the wheel, the drill, at the same time being rotated by the drive from the shaft 116 so that eventually the trailing edge of the land of the drill is ground. The drill is then rotated further and the parts 16, 26 moved further by the cams to position the drill for grinding tne second land. The chuck 44, Fig. 2, consists of a hollow sleeve 48 for accurately locating the drill along the axis 50 and a pair of jaws 74 which are movable inwardly to grip the drill by hydraulic fluid supplied to a cylinder 94 moving an annular piston 96 rotatably connected by a thrust race 98 to a tapered sleeve 82 engaging cams 72. The cams are transversely slit so as to be axially resilient. The jaws are retracted upon termination of the supply of hydraulic fluid by spring-pressed balls 104 engaging bevelled surfaces on the jaws. The jaws and cams are mounted in a plate 64 secured to the worm-wheel 58.