Patent GB-765369-A (GB)
Title: Improvements in and relating to surfacing machines for lenses and the like
Inventor: DILLON OSCAR WILSON
IPC: B24B13/04
Filed: 1954-09-08
Abstract: 765,369. Grinding lenses &c. AMERICAN OPTICAL CO. Sept. 8, 1954, No. 26065/54. Class 60 A machine for grinding a lens 135, Fig. 2, or similar article having a surface of single or compound curvature, comprises a tool head 24, Fig. 1, a work head 126 and frictional driving means for causing relative motion between the heads at a substantially constant speed, the means being such as to release its driving effect if the pressure of the tool 124, Fig. 2, upon the work exceeds a predetermined amount. Tool head. A cup-type tool 124, Fig. 7, preferably of the diamond impregnated or charged type, and having an operative portion with a convexly curved cross-section is mounted on a spindle 115 rotated by a belt 113 from a motor 108. The spindle 115 is mounted in bearings 116 in a housing 117 secured by a screw-operated clamp to a slide member 100 which may be adjusted on guideways 98 by a screw 104 to compensate for wear of the tool. A slide 97 supports the member 100 and is mounted for transverse adjustment by a handoperated screw 101 on a quadrant-shaped plate 73 arranged for angular adjustment about a stud 74, and provided with a clamp 89. A manually-operated worm 93 enables fine angular adjustments to be imparted to the plate 73. The stud 74 is secured to a base member 64 which may be adjusted by a hand-operated screw 55 on a table 56 secured to a base plate 38 arranged to pivot about a post 37 and to be clamped by a friction lock 52. A plate 25 carries the plate 38 and is arranged to be adjusted along the bed 20 of the machine by a screw 32 driven through gearing 30, 31 from a handle 27. The plate 25 is clamped after adjustment by a movable gib which is operated by a cam and push rod from a handle 330. Work head. The lens blank 135, Fig. 2, is secured by a layer of pitch 137 or other adhesive to a block 136 connected by adjusting screws to an adaptor 138 set upon a tapered portion 140 of a spindle 134 held in a magnetic chuck 129. A nut 141 facilitates removal of the adapter while a pin 142 locates the lens blank in known relation to the spindle 134. To enable the lens blank to be positioned at a known distance from a feed member 151, the handle 134 is mounted in a jig 324, Fig. 1, provided with an adjustable screw stop 327 to engage the blank and an upright 328 to engage a member 144, Fig. 2, loaded by a spring 147 and provided with a clamp 150 to enable it to be secured after adjustment in the spindle 134. Work feed mechanism. The feed member 151, Fig. 10, is advanced by rotation of a threaded member 159 in a fixed hub 160, such rotation being effected by a shaft 156 driven by a chain 179 from a motor 178. This motor may be stopped automatically after a predetermined amount of feed has been applied by a switch 199 mounted inside a drum 181c and adapted to be operated by a member inside a co-operating drum 193c, the drum 181c. being freely mounted on the shaft 156 and adjusted angularly in relation to it by a hand-operated worm drive 187 while the drum 193c is fixedly secured to the shaft 156 and insulated therefrom by a fibre or rubber sleeve 196. In the preferred embodiment, four co-operating pairs of drums are provided so that the abrading operating may be carried out in four stages any one of the first three of which may be eliminated by toggle switches 208, 208a, 208b, Fig. 2. On completion of the final abrading stage the machine is entirely shut off. The drums carrying the switches are calibrated and co-operate with indicators 207, Fig. 2. Tool feed mechanism. After each movement of the work towards the tool, the latter is caused to sweep across the work by swinging about the post 37. This may be done manually by first swinging the tool head 24 to one end of its movement and then allowing a weight to swing the head back. Preferably, however, the tool is arranged to operate in both directions of swing by providing an arcuate rim 211, Fig. 9, on the base member 64 and connecting a pair of weight-loaded cables 212, 212a to opposite ends of the rim, the cables extending over pulleys 214, 214a and around drums 217, 217a freely mounted on the ends of a shaft 218. This shaft is driven by a motor 224, Fig. 2, through a chain 227, a shaft 229, a screw 231, a gear 232, a shaft 233 and a chain 235, Fig. 3, and carries a pair of clutches 223, 223a which drive the drums 217, 217a alternatively when the shaft 218 is reciprocated by a yoke 296 operated by a cam 286, Fig. 5, on a shaft 257 rotated by gearing 258, 259, Fig. 2, from the shaft 229. To obtain reversal of rotation of the shaft 218 a microswitch 263, Fig. 3, operated by a cam 260 on the shaft 257, 'and a microswitch 267, mounted on a spring-loaded rod 268, Fig. 2, reciprocated by engagement with a switch control plate 79 are provided. The switch 267 is operated by engagement with an adjustable stop calibrated in lens diameters. During the work feed movements, the motor 224 is stopped and the motor 178 started by a pair of microswitches 336, 339 operated by cams 335, 338 on the shaft 257, one switch being operated at each end of the tool swing. The contour of the rim 211 is elliptical to produce constant rate of feed. If abnormal resistance to movement of the tool is encountered, the drums 217, 217a slip within the turns of the cable 212, 212a. Chuck control means. The chuck 129 is switched' on during abrading operations and off when the work feed mechanism 152 is operated by an operating shaft 237, Fig. 2, coupled to a shaft 239a operated by a pair of toothed sectors 243, 244, Fig. 5, the sector 244 being adjustably connected to a bell crank 246 operated by a link 248 from a crank 252 rotatably mounted on the shaft 229. The crank is driven through a half turn each time the motor 224 runs in a clockwise direction by an over-running clutch 256, Fig. 2, which connects the shaft with the crank. Setting up. The tool 124 is adjusted to the desired distance from the pivot 37 by inserting an alignment member in a bore 78 in the pivot, this setting determining the radius of the curve to be generated in the horizontal meridian of the blank 135. The radius of the curve generated in the vertical meridian is determined by the angular setting of the plate 73. Initial adjustment of the feed member 151, Fig. 10, is effected manually by rotating a screw 173 to disconnect the sprocket 164 from the shaft 156. A knob 266, Fig. 2, enables the chuck 129 to be operated manually. Coolant is pumped from a tank in the base of the machine to pipes 311, 311a, Fig. 7, and is returned to the tank by a pipe 314.