GB2052369A - Working gemstones - Google Patents

Abstract

in order to cleave a gemstone 51, the stone is clamped between resilient jaws 10, an anvil member 8 is located against the opposite surface, the exposed surface of the stone is kerfed, and the kerf is struck in order to cleave the stone. <IMAGE>

Description

SPECIFICATION Working gemstones Background of the invention The invention has general applicability to any form of working gemstones and some of the working operations under consideration are kerfing, sawing and cleaving. Kerfing is forming a shallow groove in the gemstone, either prior to cleaving or prior to sawing; sawing is cutting the stone in two, whether it is done by a saw or not; cleaving is parting a gemstone along a cleavage plane. The present description relates specifically to diamonds, but it is believed that it is applicable to other gemstones although some of the effects may be markedly different, such as in diamonds the presence of clear cleavage planes.

In cleaving, in general terms, a gemstones is held in a suitable holder, an exposed surface of the stone is kerfed, and the stone is cleaved by striking the kerf with a chisel-like tool. Ideally, the kerfshould be of strictly V-shape, but usually it has a rather rounded bottom; the tool is inserted so that it engages the sides of the kerf but does not reach the bottom and a sharp blow on the tool causes the tool to spread the sides and cleave the stone. The present practice is for the stone to be held in a holder called a dop which has a wooden or steel handle and a lump of shellac and sand on its end.The stone is marked to indicate the proposed position of the kerf and the stone is then embedded in the shellac/san mixture until its cleaving plane is level with the surface of the mixture, i.e. the part that it is to be cleft off is the only part protruding; this embedding is performed by heating and softening the shellac/sand mixture, and can take two to three minutes. The stone is then kerfed using a sharp, i.e. a small piece of another stone, which can take five to fifteen minutes, depending on the size of the stone being kerfed. The stone is then cleaved using the chisel-like tool and the remaining part of the stone is removed from the shellac/sand mixture, again by heating; this can take a further minute. The stone is then cleaned up, which can take thirty minutes although the stone would be cleaned up in a parcel, i.e. with a number of other stones.The whole procedure is relatively timeconsuming.

The invention The invention provides a method as set forth in Claim 1, a holder as set forth in Claim 9 and equipment as set forth in Claim 20. The remaining Claims set forth preferred features of the invention.

Using the invention, it has been found that the combination of the anvil member and the resiliency of the jaws allows the stone to be clefttruly. In the method of the invention, the steps need not necessarily take place in the order recited; for instance, the stone could be kerfed before clamping and/or the anvil member could be located correctly relative to the jaws priorto inserting and clamping the stone.

Preferably, the jaws have resilient pads which form their clamping faces, which can be backed by relatively non-resilient material, and this avoids or lessens the risk of the stone cracking or splintering due to overclamping, particularly if its faces which are clamped are not smooth and parallel. However, it would be possible to use non-resilient clamping faces, one of the jaws being spring-biased relative to the other.

The anvil member preferably has a supporting face which is planar and normal to the direction of the cleaving blow. This supporting face is preferably narrow so that the anvil member can be inserted between the jaws if the stone itself is small, but in theory the anvil member could be wider than the stone itself. The anvil member is preferably arranged so that it bears just to one side of the cleaving plane, but this is not believed to be essential.

It has been found that in a well-operated method, the stone can be set up in the holder in about a minute and, if a laser is used for kerfing, it can be kerfed in about 6 seconds.

The compression springs of Claim 17 are useful in assisting automatic opening of the jaws before inserting another gemstones.

Using the telescopic tension member (of Claim 18), the fixing means can be a simple clamp, e.g. of the stirrup type with the base of the stirrup applying force to one side of the outer part and a screw, passing through the top of the stirrup, applying force to the other side of the outer part. One advantage of this arrangement is that the jaws can be preloaded to a predetermined extent and then clamped in a simple manner without requiring any great skill.

Another advantage is that the gemstone can be clamped in position in a special clamping jig, thereby simplifying the operation. The clamping jig is also inventive per se and is described below with respect to Figure 5. The jig enables an unskilled operator to clamp the diamond with no difficulty.

The holder can be set up and aligned using the special setting jig which is inventive per se and is described below with respect to Figure 7. The use of the setting jig does not require the high skills normally required to position the gemstone correctly, though the operator must be able to use the cross-wires of a microscope or a television viewer. A circular rack can be provided on the pusher member and a pinion with a manual knob provided for raising the pusher member, whilst allowing itto be twisted if desired.

Description ofpreferred embodiments The invention will be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an isometric projection of a holder in accordance with the invention, some parts being shown cut away; Figure 2 is an isometric projection of a holder corresponding to that of Figure 1, but showing some differences; Figure 3 is a horizontal section along the line Ill-Ill of Figure 2; Figure 4 is a horizontal section along the line IV-IV of Figure 2; Figure 5 is an isometric projection of a clamping jig; Figure 6 is a view of an uncut diamond, ready for kerfing; Figure 7 is an isometric projection of a setting jig; and Figure 8 is a view of the diamond as it would be seen through a viewing microscope of the setting jig.

The holder of Figure 1 has a base 1 of hollow section. A cradle 2 rests on the bottom of the inside of the base 1, the cradle 2 having a part-cylindrical recess in which rest two cylindrical clamping members or blocks 3. On their adjacent faces, each clamping block 3 has two diametrically opposed recesses 4 (one pair is shown dashed) which register with one another, a helical compression spring 5 being contained in each pair of recesses so as to bias the blocks 3 apart and also roughly maintain their proper registration. A locking screw 6 is screwed into the side of the base 1 and its end abuts the end face of one of the clamping blocks 3 so as to push the other clamping block 3 against the respective side of the base 1.

The adjacent faces of the clamping blocks 3 define a diametrical, cylindrical bore which receives the cylindrical bottom part of an anvil support member 7 whose top is formed as an anvil 8. The upper part of the anvil support member 7 has parallel faces and a vertical slot, referred to below.

The upper part of the anvil support member 7 carries two jaw members 9 whose clamping faces are formed by resilient pads 10, for instance of silicone rubber, backed by the relatively non-resilient material of the jaw members 9, for instance aluminium. The jaw members 9 are articulated together by a pivoted link 11 which passes through the slot referred to above; the holes in the link 11 which receive the pivot pins 12 are slightly elongated in the direction of the length of the link 11 so that there is some lost motion in the horizontal direction. The jaw members 9 can be clamped together by a tension member in the form of a clamping rod 13 which passes through the slot referred to above and which has a knurled end 14. The rod 13 rotates freely in one abutment piece 15 and screws into another abutment piece 16.The rod 13 carries two helical compression springs 17 and washers 18 which fit between the respective jaw members 9 and the upper part of the anvil support member 7, the washers 18 being biased against the flat vertical faces of the upper part of the anvil support member 7.

The degrees of freedom of the holder are indicated by double-headed arrows, referenced a up to f.

In use, the base 1,which acts as a non-circular locating and support member, is placed in a jig mount beneath a suitable viewing device. The kerfing line is marked on a diamond, and the diamond (not shown) is inserted between the jaw pads 10 so that its kerfing line is roughly parallel to the clamping faces, on the upper, approximately horizontal, exposed surface of the diamond; this surface is preferably approximately level with the tops of the pads 10. The knurled end 14 is rotated by hand to grip the diamond lightly between the pads 10, and the jaw members 9 are then slid down until the anvil top 8 bears against the bottom of the diamond. The knurled end 14 is then tightened fully, by hand.

The diamond is then examined through the viewing device, which will have for instance cross-wires for the precise positioning and alignment of the kerfing line. It will be seen that the anvil support member 7 can be slid sup and down (c) or rotated (e) between the clamping blocks 3, the clamping blocks 3 can be rotated about their axis (e) and the cradle 2 can be slid horizontally (f), all these movements being clamped or locked by the single locking screw 6, so that there is a lockable connection between the base 1 and the anvil support member which permits four degrees of freedom. In this way, the kerf line can be strictly located, in particular by translating the diamond sideways and twisting the diamond about a vertical axis, to orientate the diamond correctly and register the desired cleaving plane correctly.

The holder is then transferred to a second location where a kerfing device kerfs the exposed surface of the diamond, the kerfing device being arranged to make a kerf always along the same line; the kerfing device will have a jig mount similar to that of the viewing device. The kerfing device can for instance be a solid state YAG laser, focused on the kerfing line, which gives a good V-shaped kerf which is always the same size.

If desired, the viewing device could be arranged to view the diamond in a position at which it is to be kerfed, but this is less convenient.

One difference between Figures 1 and 2 relates to the tension member 13 of Figure 1. In Figure 2, the tension member is a telescopic, composite member 21,22,21 being an outer part and 22 being an inner part sliding within the outer part 21. As shown in Figure 3, the outer part 21 has a longitudinal slot 23 so that it can be clamped hard against the inner part 22, thereby fixing the parts 21,22 together. The parts 21,22 are pivoted to the jaw members 9 by pins 24.

The clamp has a stirrup 25 through which the parts 21,22 pass and a wing screw 26 which is screwed into the top of the stirrup 25 and presses against the anvil member 8. It will be seen that by twisting the wing screw 26, the bottom of the stirrup 25 is drawn against the outer part 21 and causes the outer part 21 to be compressed between the bottom of the stirrup 25 and the respective inside face of the anvil memberS.

Another difference between Figures 1 and 2 is that the blocks 3 in Figure 2 are not sprung apart but are merely aligned by two sliding dowels 27 in the blind bores 4. They are prevented from slipping out by a grub screw 28 which engages in a cylindrical recess in one block 3 and the blocks 3 are spring loaded together by a sprung pad 29 which is contained in a counterbore in the screw 6' suitably enlarged. In this way, tightening the screw 6' does not cause any substantial displacement.

Though not seen in Figure 1 or 2, the base 1 and the cradle 2 can be provided with registering vertical bores aligned with the anvil support member 7, and the bottom of the anvil support member 7 can be provided with a V-groove (a wedge-shaped crossslot). This is for use in the setting jig described below with reference to Figure 7.

A clamping jig (in slightly exploded form) is shown in Figure 5. The clamping jig has a plate 31 which is fixed in position and into which is pressed a fixed support or clamping pin 32. The plate 31 has a cut-out which receives a small sliding plate 33. A movable support or clamping pin 34 is pressed into the sliding plate 33 guided for horizontal movement by a parallel-bar slideway. A lever 35 is pivoted to a vertical pin (not shown) fixed to the sliding plate 33 so as to pass through a cut-out in the sliding plate 33, and an operating handle 36 is screwed into the far limb 37 of the split front end of the lever 35, and bears against the near liinb 38 so that screwing the handle 36 clockwise locks the lever 35 on its pivot pin.The rear end of the support pin 32 and of the lever 35 carry respective projecting pins 39 which are interconnected by a helical tension spring (not visible) contained within a sleeve 40.

In the at-rest position (as shown), the support pins 32,34 are sufficiently far apart to accommodate the part-cylindrical cut-outs on the rear sides of the jaw members 9 (see Figure 2). The sleeve 40 is dimensioned in relation to the length of the tension spring to pre-tension the spring to specific value, for instance to apply a clamping force of 10 Kg between the resilient pads 10 (Figure 2).

In operation, the holder (without its base 1) is hung by engagement of the support pins 32, 34 in the part-cylindrical cut-outs. The wing screw 26 will be slackened off and the jaw members 9 opened. A diamond 51 (see Figure 6) will already be marked with a cross 52, normally on an edge 53, to indicate the position, direction and extent of the kerfing line 54 (the dashed line 55 in Figure 6 indicates the remainder of the cleaving plane). This diamond 51 is then placed in a position between the resilient pads 10 with the large surface 56 uppermost and roughly at the same level as the top of the pads 10. The kerfing line 54 runs roughly parallel to the faces of the pads 10, i.e. at right angles to the axis of the wing screw 26. The handle 36 is then pulled forwards and swings about its vertical pivot.Due to the tension of the spring, this movement will push the support pin 34 towards the support pin 32, engaging the diamond 51 in the holder. When the pads 10 just nip the diamond 51, the lever 35 is locked by twisting the handle 36 and the kerfing line 54 is manipulated into a good position, as judged by the eye. The lever 35 is then unlocked and the handle 36 is pulled further forwards. When the predetermined preload has been reached, the far ends of the pins 39 will move further apart and the operator knows that he is in a position wnen he can fix the holder. He does this by clamping the wing screw 26.

The whole holder with the diamond 51 is then placed in the setting jig shown in Figure 7 with the axis of the blocks parallel to the axis 68. The setting jig has a fixed support plate 61 with a back plate 62 and a pillar 63 and five pads 64 providing a 6-point (kinematic) location for the base 1 of the holder. The base 1 can be held or can be clamped in position.

The setting jig has a slider 65 which can move horizontally in a parallel-rod slideway fitted in an aperture in a vertical plate 66. A sector plate 67 is pivoted to the slider 65 about a pivot axis 68 which is arranged to touch the top of the diamond 51 when the diamond is in position. The sector plate 67 carries a projecting plate 69 which in turn carries a male member 70 with a chamfered upper end which engages and rotationally locks in the V-groove in the bottom of the anvil member 8. The bottom end of the male member 70 carries a knob 71 and the middle part is formed with spaced annular protuberances which form a circular rack (not shown) for engagement by a pinion (not shown) fixed to a knob 72. The male member 70, whose axis is vertical, can slide vertically and-can rotate about its axis.

Figure 7 also shows a small pillar 73, two small, loose tubes 74, a cross-bar 75 and two tension springs 76 anchored to the pillar 73 and back plate 62, respectively. This spring loads the cross-bar 75 downwards.

The setting jig can be manipulated in any suitable way, the preferred arrangement being to activate the knobs 71 and 72 directly by hand and use a mechanical system such as Bowden cables or motors and feed screws to adjust the position of the centre of the projecting plate 69 and of the slider 65.

The holder is placed in position in such a way that the top of the right-hand jaw member 9 raises the cross-bar slightly and thus locates the anvil support member 7 properly on the male member 70.

The diamond is viewed with an instrument having only one shallow plane of focus, such as a microscope or television viewer with cross-wires 81; in fact, the focus of the microscope or television viewer will be coincident with that of the laser to be used in forming the kerf. Subsequently, the following operations are carried out: The knob 72 is twisted to raise the anvil member 8 until the top of the diamond 51 is in focus, thereby locating the top of the diamond and more specifically the cross 52 in the correct horizontal, eucentric plane; Holding the plate 69 still, the slider 65 is moved until the centre of the cross 52 is coincident with the cross-wires 81 (the cross-wires 81 are indicated to the side of the diamond 51 in Figure 8 to avoid confusion) and is eucentric (on the axis 68).In doing this, the diamond 51 swings about a horizontal axis passing through the plate 69, the anvil member pivots about the axis of the blocks 3 and the cradle 2 slides over the bottom of the base 1 (degrees of freedom e and f); If necessary, the height can be readjusted by means of the knob 72; The sector plate 69 is swung about the axis 68 until the two limbs of the cross-member of the cross 52 are as co-linear as possible, when the cleaving plane will be vertical (degrees of freedom e and fas above); The anvil member 8 is pivoted about its vertical axis using the !snob 71 until the cross-bar of the cross 52 is strictly aligned with the vertical cross-wire 81 (degree of freedom d), so that the kerfing line 54 is in effect coincident with the laser scan when the holder is transferred to the laser apparatus; The screw 6' is tightened to lock the holder.

It is not possible to use the setting jig to place the centre of the cross 52 exactly on the horizontal cross-wire 81, and the horizontal cross-wire 81 could be omitted. However, this setting can be done using a moving eye-piece or moving cross-wires generated electronically on a television screen and transferring the offset from zero to the laser, either by a direct feed line or by encoding the holder. This automatically changes the centre-point and limits of the laser scan during automatictransversing of the laser apparatus for cutting the line 54. Additionally, limit lines 82 can be provided or generated, and adjusted so that they coincide with the ends of the kerfing line 54, these readings being transferred to the laser and thereby preventing scanning off the edges of the diamond 51. The holder 1 is then transferred to a 6-point location beneath the laser.

In order to calibrate the laser so that its setting coincides with that of the microscope or television viewer, a special truncated pyramid can be placed on the support plate 61 of the setting jig, the top point of the pyramid being eucentric and being used as the focal point.

Claims (28)

1. A method of cleaving a gem stone, comprising: clamping the stone between resilient jaws; kerfing an exposed surface of the stone along a line generally parallel to the jaw clamping faces, which surface is generally normal to the jaw clamping faces; locating an anvil member against the surface of the stone opposite the kerfed surface; and thereafter cleaving the stone by striking the kerf.

2. The method of Claim 1, wherein the stone is kerfed using a laser.

3. The method of Claim 1 or 2, wherein the stone is kerfed after it has been clamped between the jaws.

4. The method of any one of the preceding Claims, wherein the anvil member is moveable and is located afterthe stone has been clamped between the jaws.

5. The method of any one of the preceding Claims, wherein the jaws can be adjusted in a rotary sense and in a substantially translatory sense rela tire to a mount which supports the jaws, and wherein the exposed surface is kerfed by a device which always makes a kerf along the same line, the adjustment of the jaws orientating the stone correctly with respect to the kerfing device and also registering the desired cleaving plane with the line of action of the kerfing device.

6. The method of Claim 5, wherein the jaws are adjusted while the stone is in a first location, the jaws and the clamped stone then being transferred to a second location in which the kerfing device kerfs the exposed surface.

7. The method of any one of the preceding Claims, and performed using the holder of any one of Claims 9 to 19.

8. The method of any one of the preceding Claims, and performed using the equipment of Claim 20 or 21.

9. A holder for holding a gem stone while the gem stone is cleaved, comprising: resilient jaws for clamping the stone; and an anvil member for engaging a surface of the stone while it is clamped between the jaws, the anvil member being movable relative to the jaws in a direction parallel to the jaw clamping faces and fixable in position to support the stone when it is cleaved.

10. The holder of Claim 9, and including a non-circular locating and support member for locating the holder in a mount.

11. The holder of Claim 9 or 10, wherein a or the support member for supporting the holder is connected to the jaws by a lockable connection which permits rotary movement about an axis parallel to the direction of relative movement of the anvil member, and which permits substantially translatory movement in a direction normal to the jaw clamping faces.

12. The holder of Claim 11, wherein the lockable connection permits translatory movement in a direction normal to the jaw clamping faces and a further rotary movement about an axis generally parallel to the jaw clamping faces and normal to the direction of relative movement of the anvil member.

13. The holder of Claim 12, wherein the lockable connection comprises two clamping members, a support member which is clampable between the clamping members and to which the anvil member is fixed or with which the anvil member is integral, and a cradle member having a recess therein in which the clamping members rest the anvil member being rotatable with respect to the clamping members about the axis parallel to the direction of relative movement of the anvil member, the clamping members being rotatable with respect to the cradle member about the axis generally parallel to the jaw clamping faces and normal to the direction of relative movement of the anvil member, and the cradle being moveable in the direction normal to the jaw clamping faces.

14. The holder of any one of Claims 9 to 13, wherein a or the support member for supporting the holder is connected to the anvil member, the jaws being moveable relative to the support member for engaging the surface of the stone with the anvil member.

15. The holder of Claim 14, wherein the jaws are carried by the anvil member and are guided for rectilinear movement with respect thereto.

16. The holder of Claim 15, wherein the anvil member has opposite faces which are parallel to the jaw clamping faces and a slot which extends parallel to the movement of the jaws, the jaws being on jaw members which are articulated together with lost motion by a link which passes through the slot and which are clampable by a tension member which extends generally parallel to the link, between the jaw clamping faces and the link.

17. The holder of Claim 16, wherein the tension member carries compression springs which engage between the respective jaw members and the anvil member to bias the jaws apart and to apply frictionai resistance to the rectilinear movement of the jaw members.

18. The holder of Claim 16 or 17, wherein the tension member is of composite, telescopic form and comprises an outer part which is linked to one jaw member and an inner part which can slide within the outer part and is linked to the other jaw member, means being provided for fixing the two parts together to prevent sliding motion with respect to each other.

19. The holder of any one of Claims 9 to 18, wherein the jaws have resilient pads which form their clamping faces, backed by relatively nonresilient material.

20. Equipment for cleaving gemstones, comprising the holder of any one of Claims 9 to 19 and a device for kerfing gemstones while they are clamped between the jaws.

21. The equipment of Claim 18, and also including a viewing device for viewing kerfing marks on successive gemstones and means for mounting the holder for such viewing, the kerfing device having separate means in a different location for mounting the holder for the kerfing operation.

22. A method of cleaving a gemstone, substantially as herein described with reference to the accompanying drawings.

23. A holder for holding a gemstone while the gemstone is cleaved, substantially as herein described with reference to, and as shown in, Figure 1 and/or Figures 2 and 3 of the accompanying drawings.

24. Equipment for cleaving gemstones, substantially as herein described with reference to, and as shown in, the accompanying drawings.

25. In association with the holder of any one of Claims 9 to 19 and 23, a setting jig having a location for the holder, a horizontal slider which will be at the level of the gemstone and which can slide generally horizontally, a support pivoted to the slider about a horizontal axis which will touch or nearly touch the top of the gemstone, and a rotatable and axially movable pusher member whose axis is roughly vertical, carried on the support for engaging the bottom end of the anvil member of the holder and rotationally locking thereto.

26. A setting jig, substantially as herein described with reference to, and as shown in, Figure 7 of the accompanying drawings.

27. In association with the holder of any one of Claims 9 to 19 and 23, a clamping jig having two clamping members for engaging jaw members holding the jaws of the holder, a manually-operable actuating member for bringing the clamping members closer together to close the jaws of the holder, and means for limiting the force applied to the clamping members by the actuating member, to limit the force applied to a gemstone by the jaws.

28. A clamping jig, substantially as herein described with reference to, and as shown in Figure 5 of the accompanying drawings.