Patent GB-617504-A (GB)
Title: Improvements in and relating to the bevelling of cutting tools
IPC: B24B3/33
Filed: 1945-04-12
Abstract: 617,504. Grinding and polishing. BRITISH BROADCASTING CORPORATION, and HARRIS, W. April 12, 1945, No. 9176. [Class 60] [Also in Group XXXVIII] A method of producing a bevel at the tip of a cutting tool, particularly a sapphire cutter used in the recording of sound, comprises the steps of lowering the tool on to the surface of a lap to bring into contact with the lap a zone on the tool located away from the said tip, rocking the tool, whilst maintaining it in contact with the surface of the rotating lap, in such a way that the zone of contact moves through the said tip to a second zone also located away from the said tip and that a bevel is produced on the tip, and repeating the rocking motion to and fro between the two said zones any necessary number of times according to the size of bevel required and the rate of abrasion. Figs. 1, 2 and 3 show a sapphire cutter in rear, side and front elevation respectively; it has a bevel a which is an arcuate, crescent-shaped surface of width b which may be between 10 and 20 microns, the crescent being symmetrical with respect to the axis of the tool. The angle # between the flat and the normal to the axis of the cutter may be between 20 to 25 degrees. The radius r may be of the order of 25 microns. The material to be cut moves relatively to the cutter in the direction of the arrow in Fig. 2; the depth of penetration of the cutter into the material in which a sound record is to be cut may be about 75 microns. Apparatus for grinding the bevel comprises a lap 1, Fig. 6, rotated by a motor 3 on a base 2 to which is fixed a rod 5 on which is slidably and pivotally mounted a block 4. The block 4 carries a sleeve 4a in which is rotatably mounted on arm 6 having a cranked part 7 provided with a clamping screw 8 for securing the cutting tool 9 to be bevelled. The tip of the tool rests on the surface of the lap 1 at a point on a diameter of the lap at right-angles to the axis of the arm 6; the axis of rotation of the arm 6 when in the operative position with the tool 9 in contact with the lap 1 may be substantially co-planar with the surface of the lap. The arm 6 carries adjustable counterweights 10 for adjusting the pressure of the tool on the lap. The arm 6 can be raised, to remove the tool from the lap, by a cam 11. A pin 14, Figs. 6 and 7, fixed to the arm 6 and projecting at right-angles therefrom engages slidably in a slot in a member 15 rotatably mounted upon a pillar 16 vertically adjustable on the base 2. In use, the cam 11 is rotated to lower the arm 6, a point c, Fig. 5, on the tool on one side of the tip a being brought into contact with the lap surface ; the block 4 is then moved along the rod, imparting a combined rocking and translational movement to the tool, until a point d is in contact with the lap surface. The lap may be of laminated wood with a synthetic resin and highly compressed, preferably both transversely of and along the planes of the laminµ; the substance known under the Registered Trade Mark of "Hydulignum" may be used. The surface is dusted with a three micron diamond dust. Signal lamps 19, 22 may be provided to indicate when the cutter is in and out of contact with the lap.