AU613112B2 - Working a facet of a gemstone - Google Patents

Description

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6 COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION FOR OFFICE USE F13 1 Form Short Title: Int. Cl: Application Number: Lodged: 0 o 4 CI 0 9 boo 00 O 0, 00 O 0 0 0 00 0 o4 Complete Specification-Lodged: Accepted: Lapsed: Published: Priority: Related Art: j o a 0 0 0 0 0 o 0 0 0 0 0 ao 0 O TO BE COMPLETED BY APPLICANT -T-HE: gi .4OGr CLPk1^ f lM t tTEn Name of Applicant: GERS-A-N-EST' -BL-ISHMENT -7 Rolls St.& 'doCA E Address of Applicant: Staed-t-le-36-9490-Vaduz-I-EECH-T-ENST--IN- er ca VCA Actual Inventor: Mark Christopher Hanna Address for Service: GRIFFITH HACK CO.

71 YORK STREET SYDNEY NSW 2000

AUSTRALIA

Complete Specification for the invention entitled: WORKING A FACET OF A GEMSTONE The following statement is a full description of this invention, including the best method of performing it known to me/us:- 3242A:rk i IM&C FOLIO: 230P55166 WANGDOC: 1201R 88.11.04 WORKING A FACET OF*A GEMSTONE Background of the Invention The present invention relates to working a facet of a gem stone using a polishing member which engages the o facet and effectively moves in one direction past the sto~ne. Normally, the polishing member will be a rotating wheel, commonly called a scaife, and the scaife onormally rotates about a vertical axis. Normally, the stone is held in a dop at the end 'of an arm of a hand polishing machine; commonly called a tang, or an automatic machine can be used. The dop can be turned about a vertical axis, relative to the arm, being held in a friction bearing.

The invention has particular applicability to polishing diamonds. Diamonds have a grain corresponding t~o the crystallographic planes; for each facet, there is a direction of polishing which is most effective. In other words, when polishing diamonds, the rate of polishing is strongly dependent on the orientation of the internal crystal structure of the stone to the polishing member and its direction -of rotation. Grain is discussed for instance in GB-A-2 037 196.

2 Determining the direction of polishing is part of the skill of a polisher. The polisher examines the stone and decides where the grain is. He turns the dop about the vertical axis until he believes the grain orientation is correct, and begins polishing. The polisher can sense if the stone is not being polished properly, and turns the dop round a little, about the vertical axis. When a facet has been finished, the polisher will know the setting of the dop for the other facets this is part of the polisher's skill. However, o0 o if a stone is right off-grain, it can dig in and spoil 0000 the scaife.

oo 0 000 0 °0 Particular difficulties have been encountered with 0 stones with twisted grain structures, or dislocated grains or ring or ball naats in each case, there is not a normal single crystal present. This is particularly so with Australian diamonds, which appear to be polycrystalline, and grain identification is very difficult or impossible; in an extreme case, one facet could have three or more polishing directions.

t c Traditionally, working a facet of a gem stone comprised three steps, namely a first step in which the grain is sought by trying various grain orientations to see at which the stone works best, a second step in which substantially the whole of the facet is formed (blocked) U-U.I-i:LI Li _1 0000 0 S000 0 00a 00 0 0 00 0 000 0 00 0 0 0a 0 o0 o o o 1 C0 r 3 by grinding down the surface of the stone, and a third step in which the facet is smoothed so that all the scratch marks made when forming the facet are removed.

In order to smooth or form a high polish on the facet, material must be removed from the facet in such a way that the surface structure of the polishing member is no longer reproduced in the surface of the facet.

Traditionally, this can be done in a number of ways.

The orientation of the stone could be changed to such a degree that the facet will still polish, but at a much smaller rate so that the depth of the scratches is less and the facet will be more highly polished. A higher rotational speed can be used. The specific loading can 7 be reduced below about 3 N/mm 2 These ways can be combined.

Rt N r 'Tj M'? 4 SUMMARY OF THE INVENTION According to the present invention there is provided a method of working a facet of a gem stone, including the step of determining in which direction facets should be worked, using a polishing member which engages the facet and effectively moves in one direction past the stone as a whole, comprising rotating the stone through at least 1800 about an axis at right angles to the surface of the polishing member, and observing scratch marks on the stone to determine the angular relationship of the stone to the polishing member, about said axis, at which working best I C rroccurs.

Preferably, the stone is allowed to rotate continuously r" 15 several times about the axis, but it is merely important that polishing should be continued until scratch marks 0 t (polishing lines) are visible. An advantage of this 0de t procedure is that it can be applied to a simple hand-held S• tang.

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In this way, the best grain orientation can be found.

Once it is found, the stone holder is fixed and the facet is polished to the required size.

If a facet has two (or more) different grain orientations, these can be determined. The facet can then be polished by rotating the dop to each orientation in turn, thus in turn polishing a little of each zone of the facet; or the dop can be continuously rotated during polishing, particularly if the stone is difficult.

In accordance with a second procedure, the stone is rotated continuously until substantially the whole of the facet has been formed. In other words, the rotation of the stone is not merely to determine the grain, but is continued right through the polishing of the facet.

This provides the possibility of cheap and simple automation'which does not require a skilled operator, but can nonetheless provide good blocking or faceting.

This procedure is particularly useful for small or very small stones and for difficult stones. It can be used on a hand-held tang. It is surprising that the polishing can be achieved at reasonable cutting rates, with good faceting and without ruining the polishing member ie the polishing member life is good. The procedure can be used to grind all facets, including tables.

6 Although no high skill is required, some precautions must be observed. For difficult stones and stones having sharp edges, a diamond polishing member should be used. The specific pressure should be limited (but high enough) in order to prevent a sharp edge on the stone damaging the polishing member. For grinding normal quality stones, the specific pressure should be of the order of 3 N/mm (at which pressure one can also observe the grain as discussed above), but for smooth faceting, one should use lower pressures. As the size o0 of the facet increases as polishing progresses, it is 0o 00 useful to talk about the specific pressure on the 00 finished facet initially, the pressure will be 0 a higher. In general terms the specific pressure will be less than about 6 N/mm and, dependent on the final 0 surface quality required, the pressure is preferably between about 1 and about 5 N/mm The speed of rotation should be within a certain range.

If it is too low, the polishing member may be ruined when starting up, and efficiency drops (and polishing member temperature increases) if the speed is too high.

For a 10 pt stone, on a rotating scaife, a reasonable speed is 1 to 4 rpm.

As in normal practice, it is good practice to choose a good polishing facet as the first facet.

loss. Furthermore, as non-skilled operators are used 7 The procedure is particularly economical for small stones. The overall polishing time for stones up to pt is shorter than using hand grain seeking in the Sloss. Furthermore, as non-skilled operators are used and as automation is easily incorporated, several tangs 0 3 o .U Stones with a single grain orientation (non-naated o co stones) can be worked on traditional scaifes. However, o o stones with non-uniform crystallographic structures 000 0 0o g (naated stones) can be worked on coated scaifes; the o o heat generation is larger but the scaife life is not o o significantly decreased if the scaife is kept in U 00 00o0o condition in the normal way.

o A good surface finish can be achieved. For instance, if 0 0 a constant load is used, a good surface can be achieved 0 0 "0o by arranging for the specific pressure on the finished 4 0 400 2 S* facet to be lower than about 3 N/mm If the grain is twisted, higher specific loads should be used, but a good surface can still be achieved.

Normal procedures to fix the stone in a dop which has a contact ring; the facet has been worked to the correct 8 depth when the contact ring touches the polishing member. Using this procedure, there is improved accuracy of detecting when this occurs as the contact ring can be observed from all angles as it rotates over the surface of the polishing member. This provides accurate working, and a simple circuit can be arranged to provide automatic lift-off of the dop when the facet has been fully worked. Thus semi-automatic or automatic equipment can be provided from traditional tools.

o°o The machinery required is extremely simple.

O0 0 00 The rotation of the stone greatly reduces the incidence 0 0 0o a of broken culets (the pointed bottom nart of the stone).

In accordance with a third procedure of the invention, a facet which has already been formed is smoothed by rotating the stone continuously about said axis.

In general, the third procedure removes the requirement for a zoeting motion of the tang or polishing machine, ie the reciprocation of the polishing machine transversely to the motion of the polishing member.

However, if such a zoeting motion is used, the polishing member caa still be considered to effectively move in one direction past the stone.

C -L _I-i i 9 In all three procedures, the facet being worked can be a substantial distance from said axis. This minimises digging in because the stone is effectively transversing the polishing member by an amount, equivalent to twice said distance (the radius of rotation of the stone).

Preferred Embodiment The invention will b4 further described, by way of example, with reference to the accompanying drawing, in 0 00 I o °which; 0000 00 0 0 ^0 Figure 1 is a schematic elevation of the end of a ooa hand-held tang; and I tFigure 2 is a sketch of the polished surface of a facet j of a diamond.

ii The polishing member is a rotating scaife 1 which rotates about a vertical axis to the left of the drawing. The polishing machine is hand-held, and comprises a tang 2 which carries a traditional polishing head 3. The polishing head 3 includes a blocking holder 4 which carries a dop 5 holding a diamond 6, the dop being fitted to the holder 4 to provide an 'eight position' click dop. There is an angle setting knob 7.

In a known way, the axis 8 of the diamond is at a preset, but adjustable, angle a to the surface of the scaife 1 here, the angle a is shown as 471/a°0.

In a known way, the dop 5 can be turned or indexed about the axis 8 to change the facet being polished, through steps of 450.

The polishing head 3 is mounted on the tang 2 for free rotation about a vertical axis 9, ie at right angles to the surface of the scaife 1. The polishing head 3 is connected by a shaft 10 to a 480:1 worm gearbox 11 which in turn is driven by a small 24 v Portescap dc motor 12. The gearbox 11 is a standard component and is not 0 0 oixooO described in detail, but it includes a flanged collar 13 0oo ot which is splined or keyed onto the shaft 8, and a worm 00 0 00 gear 14 rotatably mounted on the collar 13 and biassed 0 o 0 0 0 0o. against the flange by a friction regulating spring 0 0 forming a friction clutch (for operator convenience and motor protection). The motor 12 can be powered by a 9 v 00 0oo dry cell located under the heel of the tang (not shown), such that the polishing head 3 rotates at a slow speed, 0 4 eg 1 to 5 rpm, preferably 3 rpm. In one arrangement, 4 544444 the radius of the offset, ie the distance d between the intersections of the axes 8, 9 with the surface of the scaife 1, is about 15 or 16 mm, but this can be changed as appropriate for instance an 8 mm or 6 mm distance may be preferred. To give a specific example which however is generally applicable, the scaife diameter is 330 mm and it rotates at 3000 rpm. The diamond 6 is rotated across a 40 mm wide diamond-impregnated track t J -r i i i4 11 on the outer part of the scaife 1. These relative speeds are preferred and can be calculated for tracks or scaifes of different diameters.

In use, a diamond is sawn, or if it is a makeable a table is polished. A circular girdle is bruted (ground) adjacent the sawn face or table. The sawn face or table is inserted into the dop 5 so that the girdle is held by the dop 5. The motor 12 is energised and the tang 2 is brought down so that the diamond 6 rests on the scaife 0 00 0 0 01.v 1, and is rotated about the axis 9.

00 00 0 00 00 In a first procedure, after the dop 5 has rotated o oO o several times, say ten times, about the axis 9, the tang 0 0 0 o 0 0 0 a 2 is raised and the motor 12 de-energised so that the facet can be examined for scratch marks. The scratch 0 00 0 00 marks indicate the direction in which the scaife 1 should move past the diamond 6. By using the stop-start 0 000 0 ~switch, the dop 5 is turned to the correct orientation.

404 4 4 1 When the motor 12 is de-energised, the gearbox 11 locks 4 4 the polishing head 3 in position. The tang 2 is then lowered and the facet is polished. Once the grain orientation has been determined for one facet, the correct grain orientation is known for the other facets (assuming that the diamond 6 is a single crystal this is not so with twisted or naated stones), and the blocking process is completed by polishing all eight facets.

12 Figure 2 illustrates the surface of a naated stone which has been polished with a specific pressure above about 3 2 N/mm The facet has two areas 21, 22 in which the crystallographic orientation is different. As the stone 6 rotates on the scaife 1, there.are moments at the 11 or 5 o'clock positions (indicated by the double arrow) where the area 21 polishes, and moments at the 9 or 3 o'clock positions when the area 22 polishes. As shown, scratches will appear, showing the various polishing directions. This is also true if there are multiple ooo" naats, each area of different crystallographic o000 S ooo orientation having scratches indicating the polishing 00 direction.

0o 0 00 0 0 0 *0 If multiple polishing directions are required, the procedure described below can be adopted. However, the 4 0 procedure described below can also be used without inspecting the grain at all, particularly for small and 1 medium-sized stones. In the second procedure, the motor t 12 is energised continuously for the entire blocking o process, ie until the facet has been fully formed, though not necessarily smoothed the speed of rotation Sof the polishing head 3 can remain the same.

Smoothing can be performed on the same scaife 1, or can be performed on a different scaife. In order to produce a high polish, the material must be removed in such a 'it

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way that the surface structure of the polishing member is not reproduced in the surface of the facet. In accordance with the third procedure of the invention, this is done with continuous rotation of the head 3 whilst maintaining a constant polishing load the speed of rotation of the polishing head 3 can remain the same. As noted above, the constant polishing load will cause a decreasing specific loading as the facet size increases.

The third procedure can also be carried out on stones which have been blocked in the normal manner, particularly larger stones (eg having a size greater than 10 pts).

Throughout this specification, weights are given in points (pts), as is customary in the art. 1 point is 0.002 g.

t e 4 4 o got 0r 44 4~ 4 044 4 4f 4 4 4, 4 4 44 4 4' c P The present invention has been described above purely by way of example, and modifications can be made within the spirit of the invention.

Claims (4)

1. A method of working a facet of a gem stone, including the step of determining in which direction engages the facet and effectively moves in one direction past the stone as a whole, comprising rotating the stone through at least 180° about an axis at right angles to the surface of the polishing member, and observing scratch "o .10 marks on the stone to determine the angular relationship oooo of the stone to the polishing member, about said axis, at 0oo which working best occurs. oo00 o o00o 0o o

2. The method of Claim 1, wherein the specific 0 o 2 0 o"l15 pressure on the facet is greater than about 2.5 N/mm

3. The method of Claim 1 or 2, wherein said axis is a substantial distance from said facet, whereby the facet e rotates about a substantial radius.

4. A method of working a facet of a gemstone, substantially as herein described with reference to the accompanying drawings. Dated this 6th day of May 1991 THE DIAMOND TRADING COMPANY LIMITED By their Patent Attorneys GRIFFITH HACK CO. afO &b4 2s/as 6.5.91 0