Patent GB-1458183-A (GB)
Title: Lapping fixture reference plate assembly
IPC: B24B37/04
Filed: 1975-10-30
Abstract: 1458183 Lapping SPEED FAM CORP 30 Oct 1975 [25 Nov 1974] 44981/75 Heading B3D A reference plate assembly 38 for use in lap limiting fixture means 36 comprises a horizontal reference plate 42 having an upper surface 44, a lower surface 46 for engaging a workpiece 106, and three circumferentially spaced apart vertical apertures 48 open at their upper ends, and insert units 58 vertically adjustably mounted in the apertures with the plane of the upper end of the units lying below the plane of the upper surface 44 and parallel to the plane of the lower surface 46. The assembly and lap limiting fixture means are used in a lapping machine 10 having a lapping disc 14 which is rotated by the output shaft 18 of a drive means and disposed adjacent a staging table 16, workpieces being moved to and from the lapping wheel by way of the table. A pair of vertical columns 22 support a cross beam 24 having four arms 26 each of which has a bore for the rod 28 of a pneumatic assembly 30. The lower end of each rod journals a pressure plate 32 which fits, with clearance, within a trueing and retaining ring 34. A lap limiting fixture means is disposed beneath each pressure plate and consists of a reference plate assembly 38 and a fixture assembly 40. The reference plate assembly comprises the reference plate 42 which has upper and lower surfaces 44, 46 and the three apertures 48 provided with recessed shoulders 50. Adjustable insert units 58 are screw-threaded into the apertures and can be secured in adjusted position by lock nuts 64 abutting the shoulders. Each unit has a hardened metal insert 62. The plate also has diametrically opposed bores 56 and three vertical openings 56 having recessed shoulders 54 against which are secured latch washers 66 formed with oval slots 58. The fixture assembly 40 is of annular form and has an upper surface 72 and a rim position 74. Three threaded openings 76 in the assembly receive screws 78 which engage the hardened inserts 62 and can be locked in position by set screws 82. Three cut-outs 84 each contain a latch unit 86 consisting of a stem 88 having a handle 90 at its upper end and a cam lobe 92 at its lower end, the stem being movable against the pressure of a spring to pass the cam lobe through the oval opening 68 in the latch washer 66, rotation of the stem by the handle locking the lobe beneath the washer. Locating pins 96 are secured in diametrically opposed bores 94 and engage the bores 56 in the plate 42. Arcuate pad members 102 of wear resistant material, such as boron carbide, are secured by epoxy cement 100 in arcuate pockets 98 in the rim 74 of the fixture assembly. In use, the insert units 58 are adjusted so that the upper ends of the inserts 62 lie below the upper surface 44 and parallel to the lower surface 46, and the screws 76 are adjusted so that the plane of their lower ends is parallel to the plane of the lower surfaces of the pad members 102. The fixture assembly is mounted on the reference plate and releasably secured thereto by engagement of the cam lobes 92 with the latch washers 66, alignment of the fixture assembly with the reference plate being determined by the locating pins 96. Initially the pad members 102 are spaced from the surface of the lapping disc 14 and no lapping proceeds in the presence of abrasive particles and an oil carrier, the workpieces are pressed against the disc by pressure from the assemblies 30 until they are reduced to a thickness determined by engagement of the pad members with the lapping disc.