Patent GB-981287-A (GB)
Title: Improvements in or relating to the grinding of compound curvatures on workpieces
Inventor: DALTON FRNEST THOMAS
IPC: B24B13/04
Filed: 1963-10-22
Abstract: 981,287. Grinding. AMERICAN OPTICAL CO. Oct. 22, 1963, No. 41688/63. Heading B3D. A method of generating a curved surface on an article, such as a lens blank 10, Fig. 3, comprises supporting the article in a position so as to be engaged by an annular abrading face 58 of a rotary grinding tool 56, the face having a true spherical shape throughout the width of the annular face of a radius of curvature 20, Fig. 6, equal to that desired on one major meridian C of the surface of the article, swinging the tool or the article about an axis 80 which is normal to the axis of rotation, and spaced from the portion of the inner edge of the face located before grinding on the side of the axis of rotation nearest the article at a distance 90 equal to the radius of curvature desired upon the surface of the article in a second meridian B. For grinding a concave surface of the lens blank, the lens is rigidly mounted in a holder 60 non-rotatably secured to a head 66 supported on a base 14. The grinding wheel is mounted in an adaptor 57 on a motor 52 which is transversely adjustable by means of a guideway 72 on a slide 50 guided in way 48 on a plate 42. The plate is mounted by a stud 44 on a second plate 41 adjustable in guideways 43 along a plate 24 mounted for pivotal movement about a post 28 carried by a slide 18 movable along guideways 16 on the base 14. Setting the apparatus to produce a desired lens is accomplished by first selecting a grinding wheel, the annular face of which has a spherical curvature having a radius of curvature 70, Fig. 6, equal to that to be formed on one meridian C of the lens. The grinding wheel is mounted in the adaptor 56 and the motor adjusted along its slide 72 to a position wherein a point 74, which lies on a line 82, Fig. 5, equal to the diameter d of the lens, on the inner edge of the abrading face lies in a line between the axis 78 of the stud 44 and the axis 80 of the post 28. The slide 50 is then adjusted to a position in which the point 74 lies in the axis 78 and is clamped in position. The plate 42 is then swung about the axis 78 of the stud 44 to dispose the axis 84 of the wheel at an angle # whose sine is equal to a distance K divided by the radius of curvature 70 of the face of the wheel, a scale 86 being provided to facilitate setting of the angle; the plate 42 is then clamped by a locking device 46. Thereafter the plate 41 is adjusted along the guideways 43 until the distance between the axes 78 and 80 of the stud and post, respectively, equals the desired radius of curvature on the second meridian of the lens. To grind the concave surface, the grinding wheel is swung to an inoperative position to facilitate mounting of the lens on the holder 60, and the grinding wheel is then rocked about the pivot 28 under the action of a weight 40 connected by a cable 30 to the plate 24. Alternatively, the plate may be rocked by manned or automatic means, such as a motor driving a lead screw and friction clutch. For grinding convex surfaces, the grinding wheel is mounted for rotation in the head 66, and the lens is non-rotatably mounted on the slide 50. After grinding, the lens may be polished by a lap 94, Fig. 8, the lens being mounted in a holder held by alignment means 96. A liquid polishing means is supplied to the lap while the lens blank is moved back and forth over the lap. For polishing convex lenses the positions of the lens and lap are reversed.