Patent GB-108168-A (GB)
Title: Method of and Apparatus for Grinding and Polishing Gems.
Inventor: GILL HUBERT ALEXANDER
IPC: B24B9/16
Filed: 1916-06-28
Abstract: 108,168. Gill, H. A., (Stern-Coleman Diamond Machine Co.). June 28, 1916. Gems, treating. -In a machine for setting diamonds and other gems of the kind described i n Specification 9189/14, a dopspindle fo, Figs. 31 and 39, which can be adjusted axially and is also rotatable to present successive facets of the gem to the lap hk, is angularly adjustable about a centre o which can be adjusted along a line og, an adjustable pointer indicating the position of the centre. By these adjustments, the gem can be so positioned that only a narrow finishing-band u on the lap is engaged by the facets when the spindle is turned about the axis og to adjust the grain of the facets to the direction of movement of the lap, the employment of a narrow finishing-band ensuring accuracy, since the facets are finished on a surface of minimum unevenness. In the adjustment shown in Fig. 39, the girdle b is set at a distance x from the centre o and this is set at a distance w from the lap hk, such that the axis go bisects the facet db, the finishing-band u being thus of the width of the facet, whereas, in the adjustment shown in Fig. 31 in which the centre o is on the lap, the zone u is twice the width of the facet db. The adjustment, Fig. 31, can however be used for small gems and adjustments intermediate of Figs. 31 and 39 can also be used. The machine comprises (1) a carrier 15 in which the dop-spindle is mounted, (2) a box 47 provided with devices for vertically adjusting and feeding the carrier with respect to the lapwheel 1, these devices comprising an automatic device for lifting the carrier when a facet is finished, (3) a device operated by a knob 156 for shifting the box 47 along guides 145 to shift the gem to different parts of the lap, this device being arranged to lift the gem at the beginning of the shift and to lower it at the end, (4) a device operated by a motor for imparting reciprocations of adjustable amplitude to the box 47 to cause the gem to be reciprocated on the lap, and (5) a device operated by a knob 239 for swinging the dop-spindle upwards about an axis parallel to the lap to permit of inspection or removal of the gem. (1) The carrier 15 for the dop-spindle 5, Figs. 1 and 5, is formed with an arcuate rib 19 which can be moved in a guide 20 to adj ust the inclination of the facet. The gem 3 is cemented to an arbour 4 secured by a screw 6 and a cross-pin 7 which enters grooves to the dop-spindle, this being provided with an index-wheel 11 for turning the gem to present different facets to the lap. A pivoted catch is provided for locking the index-wheel. The dop-spindle is mounted in a sleeve 9 and can be moved axially to adjust the distance x, Fig. 39, by means of a nut 13 which engages a flange 12 and is threaded on a bushing 14. The pointer 40 for indicating the axial adjustment is mounted in a head 39 on a shaft 35 which is mounted in the carrier and can be adjusted by means of a nut 32 provided with a scale 33, this being set at the proper reading, in accordance with the size &c. of the gem, and the nut 13 being then turned to bring the girdle of the gem opposite the pointer. The pointer can be moved longitudinally by turning a knob 43 connected to a pinion 41 which gears with the pointer. A spring plunger 44 holds the pointer retracted by engaging a flat on the pinion. When the reading of the scale 33 is zero, the pointer points towards the centre of the guide 20. (2) The box 47 is provided with a tube 46, Fig. 14, in which is mounted a sleeve 45 secured to the guide 20 of the carrier 15, the sleeve 45 surrounding a spindle 50 which is secured to the tube 46. A nut 55 provided with a scale 56 is threaded in the tube 46 and engages a sleeve 58 and a collar 57 secured thereto, the collar carrying a threaded rod 60 which engages a tube 63. A feather 66 prevents rotation of the tubes 46, 63 and springs 64 are provided for taking up longitudinal play between the parts 50, 57. By turning the rod 60 or the nut 55, the tube 46 is adjusted with reference to the tube 63 or the tubes 46, 63 are adjusted simultaneously. The sleeve 45 is formed with helical recesses 67 for lubricant and the tube 46 works through stuffing-boxes 46'. A rack 68 on the tube 63 gears with a sector 69 which is geared to a ,shaft 77 provided with an arm 78 carrying a driving weight 79 which is adjustable with respect to the shaft by turning a knob 80 on a screw 78'. Initially, the arm 78 is turned by hand clockwise, Fig. 1, until a pin on a wheel geared to the shaft 77 engages a spring stop arranged slightly to the right of the vertical. On releasing the hand, the spring stop moves the arm over the vertical and the arm is then driven anti-clockwise by the weight, the moment of the weight increasing. The clockwise and anti-clockwise movements respectively lift and lower the tube 46. The weight of the tube is balanced by a spring 81 acting on a lever 82 geared to the rack 68. To prevent the gem from being moved violently on to the lap, a retarding-device consisting of a pivoted weight 99 is geared to the shaft 77. The weight is pivoted at 100 and is slotted at 98 to engage an eccentric 97 geared to the shaft 77, the gearing including a ratchet clutch 91 which prevents the weight from being operated when the arm 78 is turned clockwise. The shaft 77 is geared also to a shaft 105 provided at each end with a pointer 106 reading over a scale 107 for indicating the progress of the grinding operation. To take up back-lash in the gearing, the shaft 105 is geared to a pinion 108 connected to a spring 109. To reverse the feed of the tube 46 when the facet is finished, an arm 70 on the segment 69 is provided with the following trip mechanism. A lever 112 pivoted at 111 to the arm 70 gears with a pinion 119 provided with a detent 126 which can engage an arm 125 of a lever 122 which is pivoted at 120 to the arm 70 and carries a pivoted weight 124. An arm 121 of the lever 120 is normally engaged by a detent 127 which is pivoted to the arm 70 and is formed with a finger 130 adapted to engage an adjustable stop 131 when the tube 46 has been fed downwards the required distance. On the rocking of the detent 127, the arm 121 is tripped and the arm 125 is rocked clear of the detent 126, thus releasing a compression spring 114 arranged between the arm 70 and the lever 112. The spring on being released moves the lever 112 against a stop 136 and then moves the arm 70 downwards, thus causing the tube 46 to be fed upwards. A small movement of the tube is sufficient to operate the trip-mechanism, since the detent 127 has a magnified movement. To re-set the mechanism, the arm 78 is turned clockwise to its extreme position, thus lifting the tube 46 further and bringing the arm 70 and a gear-sector 115 on the lever 112 into contact with a stop 137 and the weight 124 into contact with a stop 138. The weight of the arm 70 is balanced by a spring- pressed rod 143 engaging a pin on the sector 69. If the trip device fails to act, the stop 131 or the stop 137 in co-operation with the stop 136 prevents further feed movement. (3) The guides 145 carry a longitudinal slide 190 in which is secured a screw 149, Fig. 8, carrying a nut 150 which engages a rib 154 on the box 47 and is geared to the shaft 153 in the box. The knob 156 for shifting the box 47 along the guides 145 is secured to a member 158 provided with two rollers 162 resting normally in cam recesses in a loose member 164 which is formed with two square recesses engaging rollers on a member 167 secured to the shaft 153. The member 164 engages a bell-crank 169 abutting on a rod 171 which operates a pawl adapted to operate the shaft 77 of the driving- weight 79. The free rotation of the shaft 153 is retarded by spring-pressed friction plates which are keyed to the box and the shaft respectively. On turning the knob 156 in either direction, the shaft 153 is initially held by the friction plates and the rollers 162 cam the member 164 upwards and thus cause the shaft 77 to turn in a direction to lift the tube 46 and therewith the gem. On further turning of the knob, the shaft 153 is driven positively by the engagement of the members 158, 167 and the box 47 is moved to the right or left. On releasing the knob, springs return the parts and the gem moves on to the lap. (4) The box 47 is reciprocated by means of a bellcrank which is pivoted at 191, Fig. 8, in the slide 190 and is formed with a slot 193 engaging a roller 194 and a slot 200 engaging a roller on a disk 202 secured to a driving-shaft 203. The roller 194 is mounted on a bar 195 which can be moved vertically, to adjust the throw of the slide, by means of a nut 196 provided with a scale 199. The shaft 203 is connected by gearing 204, 205, 206 to a vertical shaft which is geared to an electromotor below the base 234. The speed of the motor is regulated by a rheostat 213, Fig. 1, having contacts 214 engaging an arm 215 which is geared to a hand-lever 224 arranged over a scale 225. The shaft of the hand-lever carries a plate formed with recesses which can engage a spring detent-roller which provides a tactual indication of the setting of the hand-lever. (5) The guides 145 are secured to a member 145<1>, Fig. 8, which is mounted on trunnions 231, 232 and can be turned upward to give access to the gem without affecting the devices described above. The knob 239, Fig. 1, is secured to a lever 238 which rocks a shaft 241 adapted to depress a rod 243 engaging a pivoted catch which engages a lug on the member 145' On pushing the knob, the catch is released and the box 47 is swung upwards and is held by the reengagement of the catch with the lug.