Patent GB-541451-A (GB)
Abstract: 541,451. Grinding and polishing diamonds. NAGY, A. June 27,1940, No. 10958. [Class 60] Apparatus for grinding diamonds or other precious stones comprises an arm 16, Figs. 5 and 7, carrying an adjustable head 15, whereby the diamond 10 can be set with its grain tangential to the lap 19 and at the correct inclination, a bolt 31 mounted to slide without rotation, because of a screw 57 and slot 44, in the head 15, so that it can be adjusted axially by a nut 32, a dop mounted in the bolt 31, so that it can be rotated through desired angles to bring successive parts of the diamond into position for grinding, and a member 53 which assists in supporting the diamond. The arm 16 is supported by two adjustable feet 17 and the diamond 10 and can be reciprocated radially of the lap 19, being guided by pins 21. The head 15 is set, by means of pivotal mounting 27 and a screw 28 in a slot, with its axis at the desired angle to the face of the lap and, by means of mounting 23, 25 with the pivot 27 tangential to the lap. The two replaceable jaws 41 of the dop are then closed by a nut 48 to engage the diamond 10 set with its table 11 against a hard metal pin 42, which is mounted by means of a split hollow extension 50 expanded by a screw cone 52, and with its grain, as indicated by the saw traces 12, Fig. 2, parallel to the pivots 27. The claw 53 is then adjusted by means of a pivoted U-shaped member 54 and locking screw 55 to engage the diamond as shown in Fig. 7. After the first facet has been ground the claw 53 is withdrawn, the dop rotated by means of a flange 39 through 180 degrees as indicated by a spring pin 37 clicking past ratchet teeth 36, and the claw returned. To avoid the jaws 41 engaging the lap after the second facet has been ground, the bolt 31 is withdrawn axially by rotating the nut 32, the claw 53 is adjusted and fixed in the position shown in Fig. 10, and the bolt is returned until the diamond is firmly gripped between the claw and the pin 42. The nut 48 is then slackened to release the jaws 41 and after rotating the dop through 90 degrees tightened again. The claw is then removed and the dop is rotated through 90 degrees, to bring the diamond into position for grinding a facet at 90 degrees to those previously treated and bring the jaws clear of the lap when the bolt is returned axially to its original position, as determined by a screw stop 56. Finally the claw 53 is returned to the position shown in Fig. 7. After the two facets, at 90 degrees to the first two, have been ground, the diamond is rotated relative to the jaws 41 as previously described but through 45 degrees so that the 4th and 5th facets can be ground and then again through 90 degrees so that two remaining facets 13 can be ground. The diamond is then placed with its collette facets upwards on a surface 65, Fig. 13, and a dop 60 containing a piece of copper wire 63 with central depression 64, is pressed vertically down on it. The dop is then mounted, by means of spring jaws 59, Fig. 12, and a nut 39, in a modified carrier 35 and the exposed portion of the diamond is supported by a pivoted stirrup 61 which is fixed by a screw 62. The carrier 35 is carried by a bolt 31, head 15, arm 16 &c. as in the machine shown in Fig. 5 except that the stop 56 is omitted and the screw 57 replaced by a key 68. The machine is adjusted to present the diamond correctly to the lap and, after the first facet has been ground, the nut 32 is rotated to withdraw the bolt 31, the nut 39 and dop 60 are rotated through the desired angle to engage the pin 37 in the appropriate ratchet notch 36 and the bolt is returned so that the table of the diamond engages the stirrup and the next facet can be ground. This operation is repeated until all the facets at the table end are ground and then the dop is removed and mounted in a carrier positioned relative to the lap by a flexible support so as to grind the table 11 and thus finish the stone which is finally removed from the dop by drilling a hole at the side of the insert 63 and inserting a small tool into this hole The pin 42 may be made of materials used for making cutting tools and having as their basis sintered or fused carbides of tungsten, titanium, tantalum and vanadium or of boron generally associated with a carrier such as cobalt.