Patent GB-718183-A (GB)
Title: Improvements in or relating to lapping machines
Inventor: SAYERS CECIL FREDERICK
IPC: B24B37/08
Filed: 1951-06-28
Abstract: 718,183. Lapping. NATIONAL RESEARCH DEVELOPMENT CORPORATION. June 19, 1952, [June 28, 1951.] No. 15396/51. Class 60. A lapping machine has a base plate 1 in which is mounted a central bearing bush 2 for a vertical driving shaft 3, the bush having a flange 4 secured to the plate by screws 5. A lower lap plate 6 rests on the base plate 1 and is confined between the periphery of the flange 4 and a ring 7 secured by screws 8 to the base plate 1. Between the lower lap plate 6 and an upper lap plate 10 is positioned a work holder in the form of a thin disc 9, e.g. of rag tissue paper impregnated with a lacquer. Alternatively, sheets made from rayon or nylon or fabrics woven of rayon, nylon, . linen, cotton, silk or glass treated or impregnated with a lacquer or dope, may be employed. The disc 9 has a central aperture 11 and a circularly arranged series of apertures 12 in each of which is located a work-piece 13, e.g. a quartz crystal plate for use in high frequency oscillators; for elements having a thickness of about 0.002 in. a disc is employed having a thickness of 0.001 in. The work holder disc 9 extends beyond the peripheries of the lap plates and is secured to an annular marginal support resting on the ring 7 and comprising a pair of parts 14, 15 having mating surfaces provided with corrugations 16 extending completely round the annular support. When the periphery of the work holder disc 9 is clamped between the parts 14, 15 by means of screws which secure the mating parts together, a light outwardly radial tension is consequently applied to the work holder so as to minimize the tendency for it to buckle or become distorted when it is operated by the driving mechanism. The driving mechanism comprises a crank disc 18 secured to the vertical driving shaft 3 and carrying a pin 21 engaging in a spider bush 22 having a flange 23 to which four spider arms 24 are secured by screws 25. The outer cranked ends 26 of the spider arms are connected by vertical pins 27 to the part 15 of the marginal clamp for the work holder disc 9. The upper lap plate 10 floats on the work pieces and rolls around a circular restraining disc 28 positioned horizontally in the central aperture 29 of the lap plate 10. The restraining disc 28 has a sleeve 28a fitting over the upper part 30 of the bearing bush 2, a set screw 31 being screwed through the sleeve 28a into the part 30. The diameter of the restraining disc 28 is less than the diameter 29 of the aperture in the upper lap plate 10; during operation, the upper lap plate is free to move vertically and horizontally within the limits set by the difference between the two diameters under the drag action of the work pieces when the work holder disc 9 is executing its eccentric motion. The upper lap plate is provided with apertures 33 through which abrasive material, e.g. a suspension of fine abrasive powder in oil or water, may be supplied to the lap faces; the grade of abrasive and the weight of the upper lap plate are chosen to suit the thickness of the work pieces and the amount of material to be removed. A transparent dust cover 32 is provided. Specification 718,184 is referred to.