Abrading – Abrading process – Glass or stone abrading
Patent
1997-06-17
1998-10-06
Rose, Robert A.
Abrading
Abrading process
Glass or stone abrading
451 5, 451 10, 451389, 451386, 451390, B24B 722
Patent
active
058168966
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a method for polishing gemstones, in particular diamond, in which a gemstone is mounted in the holder of a clamp and a polishing depth is set in order to obtain a facet, said gemstone being pressed by means of the clamp in the appropriate position against a polishing surface in order to obtain said facet.
In polishing gemstones with high anisotropic hardness such as diamond, a crystal direction is first sought for the polishing in which the least resistance is encountered in grinding away the material. When this direction is known, a first facet of the gemstone is polished. With the existing craft techniques, the polishing operation has to be interrupted at regular intervals in order to check the polishing depth reached and the quality of the facet obtained. This is therefore an iterative process. When a first facet has been polished, the gemstone is rotated by means of rotation axes on the holder, in order to polish a following facet. The angle of rotation is determined with reference to the position of the previously polished facet and the shape which it is wished to obtain for the gemstone.
This has the disadvantage that only a limited accuracy can be achieved, since the absolute position of the gemstone with reference to the polishing disk is not known. This can cause difficulties since the angles between the facets often may not deviate by more than 0.05 degrees.
Whenever grains with a different crystal orientation come to the polishing surface when polishing a facet of a polycrystalline gem, the hardness of the gem in the polishing direction can increase to such an extent that it is necessary to set a new polishing direction. Since the absolute position of the gem with respect to the polishing disk is not known, this gives rise to a laborious process, and usually an unwanted facet is cut. It is also relatively difficult and demands great skill in order to obtain the correct polishing depth for a particular facet.
According to a partially automated technique, in order to accurately determine the polishing depths of the different facets with respect to each other, a metal ring is placed round the gemstone, which is then partially polished, in some cases together with a first facet. When a following facet is polished, this ring makes an electrical contact with the cutting disk when the correct polishing depth has been reached, and the clamp is lifted, as described in UK patents 1 171 211, 1 171 212 and 1 206 937. In some cases this ring is replaced by a stop, which then makes the electrical contact.
This method can however only be employed for polishing gemstones with so-called circular geometry, such as for example a round brilliant. For fancy shapes, however, this is not possible, and at the moment there are no automated methods.
The invention has as its object to overcome these disadvantages by proposing a method which permits a more precise working of the gemstone and makes it possible to polish the gemstone automatically, independently of the desired shape of said gemstone, the accuracy of angle is maintained, irrespective of the set polishing depth and possible corrections made.
To this end, in a first step the gemstone is set in a position with respect to a reference plane, where said position is substantially the same as occupied by the gemstone with respect to said polishing surface when the polishing operation for a facet is finished, said reference plane being chosen such that it corresponds to the polishing surface; next, in a second step, the gemstone is brought opposite the polishing surface, and the polishing operation is carried out until the moment when the clamp occupies the same relative position with respect to the polishing surface as the latter occupies with respect to the reference plane in the first step.
The invention also concerns a specific device for applying this method, with a polishing surface and a clamp, where said clamp is provided with a support block, a head with a holder for removably clamping the gemstone to be polished, and a reference organ
REFERENCES:
patent: 2450984 (1948-10-01), Pastore
patent: 3886695 (1975-06-01), Elbe
patent: 3902283 (1975-09-01), Bean
patent: 4955162 (1990-09-01), Jackson
patent: 5058324 (1991-10-01), Snellen
patent: 5435774 (1995-07-01), Naujok
Nguyen George
Rose Robert A.
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