Patent GB-787033-A (GB)
Title: A method of and machine for producing spherical surfaces
IPC: B24B11/00
Filed: 1955-03-24
Abstract: 787,033. Grinding. EVANS & WHITE, Ltd., and WHITE, A. H. March 2, 1956 [March 24, 1955], No. 8556/55. Class 60. [Also in Group XXII] A method of forming a spherical surface on a workpiece 2, Figs. 1 (a) and 1 (e), consists in simultaneously rotating the workpiece and a grinding wheel 1 of cup or cylindrical type about axes which are mutually inclined and intersect at the centre of curvative of the surface to be formed, and advancing the grinding wheel along its axis until the circular line contact which its plane end makes with the workpiece is at a pre-determined distance from the axis of rotation of the workpiece. The grinding wheel, which is angularly adjustable about a point F, may be cup-shaped for forming the end 2 on a rod as shown in Fig. 1(a) or cylindrical for forming a concave spherical surface as shown in Fig. 1(e). A machine for carrying out the method comprises a head stock 11, Fig. 2, which is adjustable transversely on a bed 10 (i.e. to set the distance O, Fig. 1(a)) and carries the workpiece in a chuck 14, and a grinding head 22 on a slide 23 movable to and from the headstock on a table 12 arranged to be adjustable about a vertical axis on the bed by means of a hand-operated pinion 19 meshing with a gear segment 18 ; the axes of the grinding wheel 59 and work spindle are in the same horizontal plane and the pivotal axis (extended upwards) of the table 12 intersects the axis of the work spindle near the chuck. The work spindle 13, Figs. 4 and 5, is mounted in bearings 42, 43 in the headstock 11, and its drive is effected by balls 45 which are disposed between fingers on a spider 44 keyed on the spindle and form an epicyclic reduction gear between a sunwheel and annulus constituted, respectively, by V-pulleys 46, 47 freely mounted on the spindle ; the pulleys are driven by separate motors and urged into engagement with the balls by springs 49. Only the pulley 46 is driven for normal grinding, but for rotating the spindle at a lower speed during a dwell period the pulley 47 is also driven in opposite direction to the drive of the pulley 46. The chuck 14 is controlled by a handle 16 which acts through a sleeve 33 and levers 34 to slide axially in the spindle 13 a tube 35 operative on a split sleeve 36 containing the chuck ; the workpiece is held by a split bush 39 in the chuck and is urged outwardly by a spring plunger 40, being set in correct position by a stop finger 26 pivoted on the headstock and adjustable axially of the workpiece by a screw. The grinding wheel 59, Fig. 2, is mounted on the shaft of an electric motor housed in the head 22 and is shielded by a transparent guard 61. The head 22 and slide 23 are arranged to provide a rapid advance of the grinding wheel up to the work-piece followed by a slow feed during the actual grinding operation. The rapid advance is effected by a toggle linkage 63, 64, 65, Fig. 8, connected between the piston of an air cylinder 62 pivoted on the table 12 and the slide 23. The pivot 67 of the link 64 is carried at the upper end of a lever 68 and is substantially stationary during the rapid advance. To provide the slow feed, a slide 70, Fig. 10, in the table 12 is connected by a link 69 to the lower end of the lever 68 and is urged to the right in Fig. 10 by an air cylinder 72 ; the rate of movement of the slide is controlled by a dash pot 73 arranged to meter oil from one side of the piston to the other through an adjustable valve 76. The movement of the slide 70 also effects movement of a striker 79, Fig. 10, which is carried at one end of a lever 78 pivoted centrally on the slide and connected at its other end to a lever 77 pivoted on the table ; a link 80 constitutes with the lever 78 a parallel linkage to maintain the striker square to the path of movement of the slide. The striker 79 is arranged to co-operate, in the opposite movements of the slide 70, with two switches 85, 86 carried, respectively, by a carriage 81 adjustable by a hand wheel 83 in the direction of movement of the slide and a carrier 87 adjustable by a knob 89 in the same direction on the carriage ; bolts 91 beneath the switches bring the slide to a dead halt immediately after the corresponding switch has been actuated. The operation of a push button opens a solenoid valve to admit air to the cylinders 62, 72 so that rapid advance of the slide 23 by the cylinder 62 is followed by slow grinding advance by the cylinder 72 until the striker 79 engages the switch 86 and so initiates the action of an electronic timer ; after a pre-determined time to provide a grinding dwell, the cylinders 62, 72 are actuated in reverse until the striker 79 engages the switch 85 and adjacent stop 91. The switch 85 is in series with the starting button and prevents the start of a new cycle until the slide 23 is fully retracted. The workpiece may be rotated more slowly during the dwell than during the slow feed by driving both pulleys 46, 47 as described above. The grinding wheel is trued by a diamond tool which is carried by a pivoted arm on a carrier 98, Fig. 2, on the table 12 so that it can be swept across the face of the wheel when the slide.23 is retracted. An adjustable stop carried by the pivoted arm fixes a plane from which the plane of the diamond may be set by a micrometer screw, the distance between the two planes being made equal to the amount of slow feed set by the knob 89.