Patent GB-1085089-A (GB)
Title: Improvements in twist drill grinding machines
Inventor: BRAMHALL JOHN MICHAEL
IPC: B24B41/06
Filed: 1965-08-17
Abstract: 1,085,089. Grinding; drills. SHEFFIELD TWIST DRILL & STEEL CO. Ltd. Aug. 16, 1966 [Aug. 17, 1965], No. 35196/65. Headings B3C and B3D. A machine for grinding twist drills comprises a grinding wheel assembly B mounted on a base A, a drill holder unit C movably mounted on the base for moving a drill 23 to be ground into engagement with the grinding wheel 31, and a template 12 and follower 28 associated with the drill holder unit for controlling movement of the drill holder to correctly position the point of the drill relative to the grinding wheel during grinding of the drill. The drill holder unit C consists of an arm 1 (Fig. 2) rotatably mounted on a shaft 2 which is axially slidable in bearings on the base A. The arm 1 is urged inwardly of the machine about the shaft 2 by a weight attached to a cord 3 to urge the template 12, which is carried by a rotatably mounted shaft 11 in the end of the arm, into engagement with the follower 28 which has an arcuate surface corresponding to the radius of the grinding wheel and is carried by a shaft 25 axially adjustable in a mounting on the base by a hand wheel 27. The rotatable shaft 11, at the end opposite the template, carries a bracket 13 having a pivot about which the drill holder is adjustable. The holder consists of a bar 14 on one end of which is a tailstock 18 having a screw 20 for engaging and advancing the drill. The intermediate part of the bar carries a clamp 19 provided with jaws for gripping the drill, and the forward part of the bar is received, in a block which is secured with the bar to the bracket 13. The bar is adjustable axially relative to the block to compensate for difference in drill diameter. The grinding wheel has its sides inclined between 2 and 10 degrees to the horizontal. In.order that the surfaces of the follower and the grinding wheel 31 will be in the same straight line a, a dressing device consisting of a bar 32 (Fig. 7) can be clamped on to the arm 1, one end of the bar having a sharp edge 35 for engaging the follower, and the other end of the bar having a dressing diamond 34. In use, the arm 1 is swung outwardly by a handle 1a and the device clamped to the arm. The arm is then swung inwardly until the edge engages the follower, which is retracted by the hand wheel 27 until the diamond engages the grinding wheel, and traversed by a hand wheel 8 so that the diamond dresses the wheel. The drill, which may have a primary clearance 36 (Fig. 8), secondary clearance 37, chisel edge 38 and an increased clearance 39 adjacent the chisel edge, is mounted in the holder, and the point of the drill is adjusted by movement of the chuck 19 and bar 14 according to the diameter of the drill. The drill holder is then pivoted manually about the axis of shaft 11, the template controlling the grinding of the flank of the drill point by movement of the holder and arm 1 about the axis of the shaft 2. The operationis such that first the secondary clearance, then the increased clearance, and finally the primary clearance are ground. The drill is then turned through 180 degrees in the chuck for grinding the second flank. In another embodiment, the drillholder is urged towards the follower and grinding wheel by its own weight, and in a further embodiment, the drill holder is slidably movable relative to the grinding wheel and follower.