Patent GB-1181241-A (GB)
Title: Improvements in or relating to Tool Lapping Machines and to Methods of Lapping Tools
Inventor: WELLUM ALEXANDER GEORGE
IPC: B24B41/06
Filed: 1966-04-14
Abstract: 1,181,241. Lapping; cutting tools. A. G. WELLUM. 15 June, 1967 [14 April, 1966], No. 16382/66. Headings B3C and B3D. A tool lapping machine for use in sharpening jig-boring or other tools tipped with tungsten carbide or high-speed steel comprises a tool holder assembly rotatably mounted on a tilt bracket carried on a support block: the tilt bracket being mounted on the block for angular turning movement about an axis parallel to the lapping plane of a lapping wheel; the tool holder assembly being mounted on the bracket for turning movement about an axis at right angles to the tilt axis of the bracket; the assembly including a tool support member for carrying the tool and mounted for turning movement about an axis at right angles to the turning axis of the assembly; and the assembly further including a base-plate having a stub axle for reception in a recess in the tilt bracket and provided with an axial bore for the reception of a reference pin, the pin having a circumferential datum edge defining a plane perpendicular to the axis of the pin, which pin when positioned so that the lapping plane is tangential to said datum edge of the pin determines the position of the axis of the turning movement of the tool holder assembly relative to the lapping plane. A tool lapping machine has a lapping wheel 15 on the shaft of an electric motor 17. A flexible mounting 18 for an electric lamp extends above the motor. A feed shaft 14 is rotatably supported in brackets 12, 13 on the machine bed 11. A collar 23 locked on one end of the shaft 14 by a clamping screw 24 carries screws 22, 22 which limit rotation of the shaft 14 by abutment against a rim 25 of the bed 11. A block 19 is clamped in required position on the shaft 14 by a clamping screw 20. For fine adjustment of the block 19 relative to the lapping wheel 15 the shaft 14 is movable axially by a micrometer screw 21. A lug 26 upstanding from the block 19 has a pivot pin 27 supporting a tilt bracket 28 which can be clamped by a screw 29 in adjusted position indicated on a scale 30 on the block 19. The tilt bracket 28 carries a quadrant plate 31 marked with a peripheral angular scale 36 and having at its centre of curvature a bearing assembly 33 rotatably supporting a hollow stub axle 34 to the upper end of which is secured a tool holder base-plate 35. The plate 35 has a stop pin 37 co-operating with adjustable stops 38, 39 on the plate 31. A cross slide 40 is adjustable on the plate 35 by a micrometer screw 41. A turret 42 is adjustable on the cross slide 40 by a micrometer screw 43 and rotatably supports a cylindrical tool block 44 marked with graduations 45. The shank 50 of a tool is clamped in the block 44 by screws 47. The tool shank 50 carries a tungsten carbide tip 52 having approach and trailing fins 54, 53 meeting in a nose 55. The approach fin 54 has approach angle a and front clearance angle #; the trailing fin 53 has trailing angle γ and side clearance angle #. A datum spacing pin 60 is provided with a forked lower shank 61 which is an easy fit in the bore of the stub axle 34. The pin 60 has a reduced diameter upper shank 62 with a concentric circular head 63 peripherally chamfered top and bottom to produce a circular datum edge 64 having a diameter of 0À500 in. A segment of the head is cut away to form a reference flat. The tilt bracket 28 is adjusted to the required front clearance angle #. The stop 39 is set to the required approach angle a measured from the zero graduation on the side 36; the stop 38 is set to the required trailing angle γ measured from the 90 degree graduation on the scale 36. The tool block 44 is turned through an angle which, together with the angle equals the required side clearance angle #. The feed screws 41, 43 are turned to bring the tool nose 55 to a position clear of the centre of curvature of the quadrant plate 31. The datum pin 60 is positioned in the stub axle 34 and raised until the reference flat is coplanar with the top face of the tool, and the datum edge 64 brought into contact with the face of the stationary wheel 15, so that the centre of curvature of the quadrant plate 31 is 0À250 ins. from the lapping plane 15a; the pin 60 is removed. To produce a radius of 0À100 ins. on the nose 55 the feed shaft 14 is axially adjusted by six complete turns of the micrometer screws 21 to bring the turret 0À150 ins. nearer to the lapping plane 15a. Thereafter it is only necessary to move the cross slide 40 so that amounts of carbide are available for satisfactory clean-up upon the approach and trailing faces 54, 53. The side clearance angle # is lapped by presenting the trailing face 53 to the lapping plane 15a with rotation of the feed shaft 14 within the limits set by the screws 22, by rotating the base-plate 35 through an angle slightly in excees of 90 degrees between the stops 38, 39, the nose radius is produced; the approach face 54 is then lapped.