Patent GB-961789-A (GB)
Title: Drill pointing method and machine
Inventor: WINSLOW JAMES CARL
IPC: B24B3/24
Filed: 1962-07-23
Abstract: 961,789. Grinding drills. WINSLOW PRODUCT ENGINEERING CORPORATIC July 23, 1962, No. 28284/62. Heading B3D. A twist drill 26, Figs. 3 and 4, having two lips 30 joined by a chisel edge 36 is ground by (a) bring- ing the drill tip and a first circumferential surface 20 of a rotary grinding wheel into initial contact, with the drill axis inclined to the surface 20 and the leading edge 32 of one lip located in a plane containing the axis of rotation of the grinding wheel so as to grind this leading edge, (b) relatively moving the rotating drill and grinding wheel towards one another and relative to one another laterally to cause the drill tip to approach a second convex surface 22 of the grinding wheel merging tangentially with the surface 20 and so grind part of a relief angle on the lip, (c) bringing the chisel edge 36 into the plane of tangency of the two surfaces 20, 22 to grind such edge, (d) continuing the relative movement and rotation of the drill and grinding wheel to bring the trailing portion of the lip into contact with the surface 20 to complete grinding of the relief angle, and (e) similarly grinding the other lip. The various movements are so timed that a relief angle is ground on each lip without hollow grinding. The profile of the grinding wheel periphery is shown in Fig. 3, the bevelled surface 20 constituting the first circumferential surface which merges with the second convex surface 22 on a line or zone of tangency Z which is located in a plane 24 normal to the vertical rotational axis of the wheel 16, the drill 26 being rotatably supported by a bushing 28 carried in a fixed portion of a drill-holder 12 which is mounted at the top of a vertical post 102. Fig. 9 shows the mechanism for effecting the required movements of the drill head during grinding, such mechanism being described as a modification of that described in Specification 873,741; the chucking arrangements are as described in the prior Specification and the chuck-driving worm-wheel 106 and worm-shaft 126 are also similarly arranged, the shaft 126 being disposed inside the post 102 and coupled at its lower end to a driving motor 128. A bell-crank 130 is pivoted on the machine base 14, one arm 132 engaging a roller 134 on the post 102 carrying the drill-head, whereby the head may be rocked about a vertical axis 13 against the action of a spring-urged roller 140 by the rotation of a cam 138 which engages a roller 136 on the other arm of the bell-crank. A second cam 146 simultaneously provides for reciprocation of the drill-holder 12 along the axis 13 through an arm 150 pivoted at one end to a vertically-movable member 152 and forked at the other end to engage a collar on the post 102. Hydraulic means 154 operated by a control system 160 for energizing the motor 128 is initially operated to raise the drill-holder 12 to its loading position, the member 152 being then moved downwardly to rock the lever 150 about the then stationary cam 146. The drill to be pointed is then inserted in the bush 28, the tip engaging a locator which provides the required axial setting of the drill. The holder is then lowered to bring the drill to its initial grinding position, Fig. 3, and the motor 128 is energized to drive the drill and cams 138, 146. One lip 30 engages the bevelled portion of the wheel along the leading edge which is ground to form a cutting edge. From the initial position the holder is swung towards the wheel and is simultaneously moved upwardly, the drill being meanwhile rotated in its holder to bring the trailing edge of the tip into grinding contact to effect relief grinding of the lip as the tip moves transversely towards the convex surface 22. These movements are so timed that the tip passes through the position in which the drill axis and the chisel edge are both located in the plane of tangency 24 of the grinding surfaces 20, 22, the chisel edge being ground in this position. A further movement of the edge beyond this zone brings the area adjacent the edge into contact with the convex surface.