GB671766A - An improved method of, and apparatus for grinding spherical surfaces - Google Patents

Abstract

671,766. Grinding lenses and the like. KODAK, Ltd. April 20, 1950 [April 20, 1949], No. 9739/50. Class 60. A spherical surface is produced on workpieces 10 by rotating them about an axis passing through the centre of the surface while they are in contact with a grinding wheel having an outer ring 18 of coarse abrasive, an inner ring 19 of fine abrasive and a diameter large enough fully to embrace the surface to be ground, relative feed between the work and wheel being effected along the axis of the latter which is inclined to the axis of rotation of the work. In Fig. 1, the workpieces 10 are shown as lens blanks mounted in a blocking tool 12 which rotates about the axis of a spindle 15 while the tool is rotated about the axis of a spindle 17. The operative faces of the rings 18, 19 may have radii corresponding to those of the work at the start and finish of the grinding operation respectively. When the tool is first brought into contact with the work, the outer periphery of the coarse ring 18 is operative, but as grinding proceeds and the radius of curvature of the work decreases, the fine grinding ring 19 becomes operative. If the change in curvature of the surface to be generated is insufficient to permit the changeover from one ring to the other it is necessary to retract the coarse grinding ring as the grinding proceeds. This is effected by the apparatus shown in Fig. 8 in which the fine grinding ring 19 has a spindle 44 slidably keyed to a sleeve 48 carrying the coarse grinding ring 18. A compression spring 51 biasses the spindle and the sleeve to the relative position shown. The sleeve 45 is rotated by a belt 49 and forms a rotating and sliding fit with a cylinder 46 connected by a valve 60 with a compressed air supply. With the valve in the position shown, air enters a chamber 55 from which it passes through ports 56 to the top of the spindle 44 so that the latter, and with it the sleeve 45, is forced downwardly to bring the ring 18 into contact with the work. The end of the rough-grinding operation is determined by the setting of an adjustable stop nut 61. which strikes a flange 62 of the cylinder 46 to terminate the down feed of the sleeve 45 so that the spindle 44 descends alone until the spring 51 is fully compressed. At this point, the fine grinding operation is complete and the valve 60 is rotated to allow the air to exhaust from the top of the spindle 44 and to admit air to a chamber 65 to lift the sleeve 45 ready for the next operation. The tool shown in Fig. 1 may be adapted for treating concave surfaces and may be fed to the work by compressed air acting on a piston secured to the tool spindle. The ring of coarse abrasive may be made narrower in width than the ring of fine abrasive. The abrasive used may be diamond dust.