Patent Description:
The invented device includes a platform and a manipulator called precision divider. The present description concerns to manual operation but the invention can accommodate numerically controlled and automatic processing by adopting 3D-step motors.

The current gemstone processing is done manually or with machines that are either very large automatic machines or lack precision and accuracy leading to poor brilliance and dispersion of light. The primitive manual process is called jamb peg where the gemstone is fixed on hand-sticks. In this way, it produces "dead stones" because the asymmetrical facets, irregular sizes and, especially, it misses most crown and pavilion angles. This involves several operators for preforming, cutting to polishing and the working environment is unclean and unhealthy.

A faceting machine is described in <CIT> comprising a stationary protractor, an angle setting plate which rotatable on the surface of the protractor about a shaft. A fastening means is provided to fasten the angle setting plate to the protractor at a desired angular position. A faceter spindle is swingable on the surface of the angle setting plate about the shaft while being rotatable about its own axis. However, this machine has several disadvantages. The machine is mounted to a triangular frame <NUM> provided with three screws <NUM>, <NUM>, <NUM> which are not anchored to any base. This depends on manual handling and unstable operation resulting in errors during cutting and polishing of a gemstone. Moreover, the screw arrangement mentioned above makes it difficult to control the depth of cutting and polishing. Then, facets will differ from each other in shape and angles. The stationary pointer and angle setting plate <NUM>, <NUM> are made of relatively thin material which adds to the instability mentioned above. The minimum graduation is <NUM>°, which will make the gemstone to lose reflection, refraction and dispersion of light rays.

<CIT> describes a gem stone face cutting apparatus with a cutting wheel rotating in a horizontal plane and supported above a base which includes a variable speed cutting wheel drive system. The apparatus further comprises angular calibrations, indexing and positional and orientational locking means to place the gem stone at a desired facet angle and orientation.

<CIT> is the basis for the preamble of claim <NUM> and discloses a machine for grinding and polishing of gem facets. The machine comprises turntable, a stand (standard <NUM>) along which a polishing head which is adjustable in a vertical rotary manner and vertically adjustable along the stand.

Accordingly, an object of the present invention is to provide an apparatus for finishing gemstones of higher quality in a shorter period of time than has been possible heretofore.

The objects above are achieved by an apparatus in accordance with claim <NUM>. Further advantageous features appear from the dependent claims.

In short terms, the apparatus according to the present invention comprises two main components: a precision divider and a vertical angle and elevation platform. The precision divider is arranged to cut and polish a desired number of facets in a gemstone with high precision. The precision divider is attached, preferably releasable, pivotal to the vertical angle and elevation platform. The precision divider can be positioned and locked in a vertical angle between <NUM>° and <NUM>° to produce precisely cut facets in the gemstone with a desired angle. The precision divider is provided with an improved dopstick receptacle with a non-circular cross-section, and a correspondingly shaped dopstick, thus providing a highly fixed and stable attachment of the gemstone being processed.

Long research and development has resulted in this invention, which is a new and precise apparatus for cutting and polishing gemstones. The apparatus according to the present invention is engineered and designed for easy, precise and clean operation by professionals or amateurs. The use of this new machine is easy to learn and even amateurs will accurately and quickly produce "live gemstones". A high quality gemstone can now be cut and polished in a few hours, compared to weeks with manual cutting and polishing.

The apparatus according to the invention is comprised by two major components, a precision divider and an accurate angular platform. These major systems are composed of multiple micro-precise components that allow faceting while cutting and polishing with angular and depth precision of <NUM>°, <NUM> and <NUM>°, which allows even an amateur to quickly, accurately and precisely convert a rough stone into a "lively gemstone" as follows:.

In further details, the apparatus according to the invention for precisely cutting and polishing of gemstones, comprises a precision divider, a supporting device arranged to be located at a work bench comprising a lap for attachment of grinding and polishing devices, wherein the precision divider is attached pivotal to the supporting device, arranged to be pivoted and fixed with its longitudinal axis at a desired angle with the supporting device, said precision divider further comprising a mandrel exhibiting a dopstick recess arranged to accommodate a dopstick carrying a gemstone, and means for rotating the precision mandrel about the longitudinal axis and locking the mandrel against rotation during grinding and polishing of the gemstone.

According to the invention, the improvement comprises an apparatus of the type described above, wherein.

The mandrel is advantageously supported rotary within the housing by a first and second bearing, thus providing a proper support for the mandrel and finally the dopstick and gemstone, reducing the risk of cutting wrong angles.

In a preferred embodiment, the fine vertical angle adjustment means comprises a dial having a shaft arranged rotary with respect to the vertical angle dial, said shaft exhibiting an eccentric surface serving as a support for a stop pin at the precision divider.

The mandrel rotation locking device preferably comprises a lever arranged pivotal about an adjustment screw at the top of the housing, wherein one end of the lever facing the graduated disc exhibits a gear engagement pin arranged to engage with the precision dividing gear, pre-tensioned by a spring arranged between the lever and housing to prevent rotation of the mandrel during grinding and polishing. This enables a quick setting of facet angle during grinding or polishing.

The adjustment screw is advantageously arranged in a threaded bore in the lever and is provided with a micro balancer dial including a lock screw, arranged to perform an accurate re-alignment of the mandrel carrying a dopstick and gemstone from any positional displacements during a transfer from a gemstone crown processing dopstick to a pavilion processing dopstick, or vice versa.

The frame device is preferably provided with a bore and an adjustment lock and lock screw, thus providing a releasable attachment of the frame device to the support column.

In a preferred embodiment, the dopstick recess in the mandrel exhibits a non-circular cross-section. Then, the dopstick exhibits a similar cross-section. In this embodiment, the dopstick and hence the gemstone is prevented from rotation, thus securing a precise cut of the gemstone.

The invention is now described in further details by means of drawings, wherein.

Initially, the invention is described in general with reference to gemstone faceting and polishing to simplify interpretation of the present invention.

Gemstones can be cut and polished in many different shapes. However, for quality purpose, any shape should be cut and polished with symmetric geometry (equal sides, heights) when viewed in horizontal and vertical planes, and the facets should be cut and polished in exact angles to reflect, refract and disperse the incoming and leaving light rays.

The apparatus in accordance with the present invention allows correct cutting and polishing of facets for best quality in terms of brilliance and "fire" or dispersion of light rays. The precise major components of the apparatus according to the invention allow cutting and polishing in precise angles resulting in a gemstone with high optical performance and high quality. The light ray path in this case is shown in <FIG>. This drawing illustrates light propagation through a correctly cut gemstone, where light entering at A2 at the left hand side of the stone is reflected back in the same angle at A2" at the right hand side of the gemstone.

However, if the facets are cut and polished in wrong angles, the final stone will have poor optical performance or low quality as shown in <FIG>. Here, the light is not reflected back to an observer viewing the stone from above because the pavilion is cut with wrong face angles. The light ray bounces inside the stone, leaks through the pavilion without returning to the viewer. There will be lack of brightness or scintillation and the stone looks dark and lifeless to the observer. A similar fault will occur if the gemstone crown is cut too shallow. Then, the light will bounce inside the stone and be reflected from the top facet but in a different angle, and the stone will look dark and "lifeless" (not illustrated).

The apparatus according to the present invention allows cutting and polishing of gemstones with maximum desired dispersion, scintillation, "fire" or life. This operation is based on optics where sunlight unfolds to the spectrum of colors between <NUM> (red color) and <NUM> (blue). Notice that the blue ray reflects or bends more than red because the wavelength of blue is shorter than the wavelength of red light. <FIG> shows the deflection angle of blue and red colors after crossing prisms. As illustrated in <FIG>, blue color (B) bends more from its original path than red color (R). This invention allows precise set, cut and polish of the facets' angles producing a gemstone that reflects a wider fan of colors ranging from blue to red. This fan colors, emerging from the gemstone's crown, will be perceived by an observer as a rainbow containing the visible spectrum of colors as illustrated in <FIG>. The latter figure illustrates light reflection from a perfectly cut gemstone using the present invention by providing a maximum dispersion, scintillation or "fire".

<FIG> shows the precision divider in the apparatus according to the present invention positioned over a cutting-polishing lap. The precision divider's dopstick <NUM> holds the gemstone <NUM> over a lap <NUM> and allows cutting and polishing facets with <NUM>° precise angles for maximum brilliance and distortion of light rays.

The invention is now described in further details by a preferred embodiment of the apparatus.

Now referring to <FIG>, a precision divider is illustrated with its multiple components and is indicated in general by reference numeral <NUM> and having a longitudinal axis indicated at reference numeral <NUM>. The precision divider <NUM> comprises a mandrel or axle <NUM> on which the gemstone mounted on a dopstick will be inserted. The mandrel <NUM> is at its free end (first end) provided with a dopstick recess <NUM> shaped to accommodate a dopstick on which a gemstone is mounted. The dopstick is lockable in the dopstick recess <NUM> by one or more lock screws <NUM>. The dopstick is preferably provided with a non-circular cross-section where the recess <NUM> in the first end of the mandrel <NUM> is provided with a corresponding cross-section. This improvement makes a more stable and secure fixation of the dopstick, resulting in a more precise cut and alignment of the gemstone. The mandrel <NUM> is arranged rotary within a housing <NUM> supported by bearings <NUM> accommodated within the housing <NUM>. Preferably there are two bearings, one bearing <NUM> at each end of the housing <NUM> to provide a more stable support and alignment for the mandrel <NUM>. A precision-graduated disk <NUM> is attached to the second end of the axle <NUM> together with a gear <NUM> arranged to be locked by a gear locking device, here illustrated in the form of a lever <NUM> attached pivotal at the top of the housing <NUM>, pivotal between a locked position where the lever <NUM> is in engagement with the teeth of the gear <NUM> by a lever engagement pin <NUM> at the end of the lever <NUM> facing the gear <NUM>, and an unlocked position where the lever <NUM> is elevated out of engagement with the gear <NUM> to allow rotation of the mandrel <NUM> to a desired angular position indicated on the graduated disk <NUM>. The lever <NUM> is pre-tensioned by a gear lever spring <NUM>, resting in an engagement with the teeth on gear <NUM>. The number of indicators on the graduated disk <NUM> corresponds to the number of teeth on the gear <NUM> and hence the desired maximum number of facets in the gemstone to be prepared and processed.

A micro balancer is arranged at the housing <NUM> to allow fine-adjustment of the angle position of the mandrel <NUM> about it rotational axis with a precision of <NUM>°. The micro balancer comprises a micro balancer dial <NUM> attached to an adjustment screw <NUM> accommodated in the housing <NUM> extending through the lever <NUM>. The lever <NUM> is attached pivotal to the housing <NUM> about the screw <NUM>, movable in a direction substantially perpendicular to the longitudinal axis of the mandrel <NUM> by operating the dial <NUM>. The dial <NUM> is provided with a lock screw <NUM> to enable the dial <NUM> to be locked in a fixed position. The dial <NUM> is provided with grades (<FIG>). When the lever <NUM> is in an interlocked engagement with the gear <NUM>, the position (angle of rotation) of the mandrel <NUM> can be fine-adjusted by operating the dial <NUM> to push or pull the lever <NUM> in a direction substantially perpendicular to the longitudinal axis of the mandrel <NUM>. The purpose of this fine-adjustment is to compensate for any gemstone displacement between transfer from crown processing to pavilion processing, or vice versa. This fine-adjustment is only performed once before processing the first facet of the gemstone after a transfer.

Now also referring to <FIG>, the precision divider <NUM> is supported by an angular platform indicated generally by reference numeral <NUM> exhibiting a frame device or bracket <NUM> supporting numerous components as described in further detail below. The precision divider <NUM> is arranged pivotal about a first and second pin <NUM> and <NUM>', between <NUM> and <NUM>° with respect to the horizontal level. The pins <NUM> and <NUM>' are arranged in the sidewalls of an opening provided in the bracket <NUM>. The angular platform <NUM> is used to set the gemstone cutting or polishing angle. A lock screw <NUM> is provided to enable the precision divider <NUM> to be fixed in a desired vertical angular position. Locking screws <NUM> are provided in threaded ports in the bracket <NUM>, arranged to prevent slackening of the pivotal attachment of the precision divider <NUM> to the pins <NUM> and <NUM>'. The angular platform <NUM> including the attached precision divider <NUM> can be fixed at a desired elevation by an adjustment lock <NUM> to a supporting column <NUM> (<FIG>) extending vertically from a work bench <NUM> (<FIG> and <FIG>) supporting a lap or turntable (reference numeral <NUM> in <FIG>) with a rotary grinding surface to process the gemstone in question. The support column, workbench and turntable are considered to be prior art and is not discussed in further detail here.

In this manner, the angular platform <NUM> can be rotated horizontally to be fixed in any position in the xy-plane, and has a desired total vertical displacement, e.g. <NUM>, and is able to reach any position in the z-axis with a precision of <NUM> micrometer. Accordingly, it can be locked in a specific vertical position while allowing full horizontal rotation and vertical movement with micrometric adjustment and with high precision.

The angular platform further comprises a vertical bore <NUM> arranged to accommodate the platform supporting column mentioned above, allowing vertical adjustment of the angular platform <NUM> and attachment at a desired elevation. A precision divider elevation angle dial <NUM> is attached rotary to the platform <NUM> by an axle <NUM> and is connected to a supporting pin <NUM>, which centrally holds the precision divider <NUM> while allowing full rotation supported. The elevation angle dial <NUM> is provided in the form of a partial circle shaped disc and is provided with grades on the surface indicating angles from <NUM> to <NUM>°. The rim of the disc is provided with teeth <NUM> corresponding to the number of grades on its surface. A locking and balancing device <NUM> is attached to the platform <NUM>, serving as link and lock for the precision divider <NUM> at a desired angle in the vertical direction. The locking device <NUM> is attached pivotal about an axle <NUM> and exhibits a guide-link <NUM> located at the end of the locking device <NUM> that faces the teeth <NUM> of the angle dial <NUM>. The guide link <NUM> is arranged to engage with the teeth <NUM> on the angle dial <NUM> to lock the precision divider <NUM> in the desired vertical angle position. The guide link <NUM> is arranged slideably in the locking device <NUM>, supported in a recess in the locking device <NUM> and pre-tensioned by a spring <NUM> which forces the guide link <NUM> towards the teeth <NUM> of the angle dial <NUM>. A locking screw <NUM> is arranged in an elongate recess in the locking device <NUM> and connected to the guide link <NUM>. The locking screw <NUM> can be operated to move the guide link <NUM> out of engagement with the toothed <NUM> precision divider elevation angle dial <NUM>. A spring <NUM> is arranged in a space between the locking device <NUM> and the upper surface of a shoulder <NUM> formed in the side of the angular platform <NUM>.

Moreover, the angle dial <NUM> is provided with a fine-angle adjustment dial <NUM> arranged rotary within the angle dial <NUM> by a shaft <NUM>. The end of the shaft <NUM> is provided with an eccentric surface <NUM> which serves as an adjustable stop means for the precision divider <NUM>. When a stop pin <NUM> attached to the precision divider abuts the eccentric surface <NUM>, the angle of the precision divider can be adjusted with a precision down to <NUM>°.

A micrometer depth indicator <NUM> (<FIG> and <FIG>) is attached to the locking device <NUM>. The depth indicator <NUM> is a commercially available mechanical depth indicator having a display and a press-force driven sensor. The depth indicator <NUM> is accommodated in a recess in the locking device <NUM> with its press-force driven sensor extending down to a shoulder <NUM> formed in one side of the angular platform <NUM> and abutting the upper surface of the shoulder <NUM>. The micrometer depth indicator <NUM> enables finishing of a gemstone with a precision down to <NUM> millimeter.

The precision divider movement describes a global and spherical shell and can be positioned at any angle between <NUM> to <NUM>° with the vertical z-axis with accuracy of <NUM>°. It has a micrometer depth indicator and is able displace up and down the z-axis with a precision of <NUM> micrometer. Accordingly, it has and accuracy of <NUM> millimeter for precisely cut and polished gemstones while the gemstone's pavilion and crown facets angle can be set in the required angle in the range of <NUM> to <NUM>° with the vertical z-axis, as desired for brilliance and dispersion of light rays.

The precision divider <NUM> containing a precision dividing gear <NUM>, a gear engaging lever <NUM> and a precision-graduated disk <NUM>, allows setting of precise division indexes or circle intervals, where the number of circle intervals corresponds to the desired number of facets around the circumference of the gemstone. The apparatus according to the present invention can cut and polish any complex form or design of gemstones with varying hardness and refraction index, such as sapphire or ruby, topaz, aquamarine, emerald, amethyst, etc. The apparatus is also able to accurately cut and polish different shapes including round brilliant and other rounds, cut-corner rectangular emerald, oval, marquise, navette, heart, pear, etc. Examples of gemstone shapes can be found in the literature and is not illustrated in further detail here.

<FIG> and <FIG> are perspective illustrations of the apparatus according to the present invention in an elevational side view and top view, respectively. These illustrations show a prototype of the apparatus in an assembled condition, comprising the precision divider <NUM> attached pivotal to the angular platform attached to a support column extending upward from a work bench <NUM>.

<FIG> is a cross-section through a dopstick <NUM> from the prior art, comprising a (circular) connector pin <NUM> and a gemstone socket <NUM> holding a gemstone indicated at reference numeral <NUM>. A improved dopstick according to the present invention is illustrated in a side view in <FIG>, where a recess <NUM> has been cut in the connector pin <NUM>. The dopstick recess <NUM> (<FIG>) is provided with a corresponding cross-section. In this way, the gemstone will be connected in a fixed position prevented from any rotation.

In the following, gemstone processing using the apparatus in accordance with the present invention is described in form of an example and accompanied by illustrations in <FIG>.

As a demonstration, we now set the device's components to cut and polish a round brilliant gemstone based on the following data:
In the example, the precision divider according to the invention is provided with a precision dividing gear <NUM> having <NUM> indexes, distributed evenly around the circular <NUM>° rim of the gear <NUM>. However, <NUM> index positions is only an example and an increased or decreased number could be provided as well. As mentioned above, the number of facets cut in a gemstone corresponds to the number of gear <NUM> indexes or a division thereof.

The task is to produce a gemstone having a round brilliant cut with <NUM> facets and a refraction index of <NUM>. Its proportions are shown in <FIG>. The number of facets in the pavilion and the crown including required angles are given in Table <NUM> (pavilion) and Table <NUM> (crown).

<FIG> is a bottom view of the gemstone, showing the pavilion facets according to requirements in Table <NUM>. Here we can se a number of <NUM> facets, so-called "mains" and indicated at number <NUM> in the drawing. A number of <NUM> facets, so-called "breaks" are indicated at number <NUM> in the drawing. Finally, a number of <NUM> facets, so-called "girdles" are indicated at number <NUM> in the drawing. The number of breaks always corresponds to the number of girdles, in this case <NUM>.

<FIG> is a side view of the gemstone showing the proportions between the crown and pavilion.

<FIG> is a top view of crown of the targeted gemstone according to Table <NUM>. It shows the number of facets and the proportions between the so-called "table" (indicated at number <NUM>) and the maximum width of the gemstone. A number of <NUM> facets, so-called "stars" are indicated at number <NUM>. A number of <NUM> facets or mains are indicated at number <NUM> in the drawings, whereas a number of <NUM> facets or "breaks" are indicated at number <NUM>.

The successive steps of the facet cutting process of the gemstone is illustrated in <FIG> and 8a-8d.

A gemstone (reference numeral <NUM> in <FIG>) is mounted in the dopstick with its crown seated and affixed with glue in the dopstick gemstone receptacle. Then, the vertical angle of the precision divider <NUM> holding the gemstone <NUM> to be processed is adjusted by the geared angle dial <NUM> (<FIG> and <FIG>). Then, the lever <NUM> is released and the gear <NUM> is moved to position # <NUM> on the graduated disk <NUM>, whereupon the lever <NUM> is brought back to an interlocking engagement with the gear <NUM>. This step is indicated in step P1 in Table <NUM>, where the rightmost column shows the index positions involved and their sequence of processing. Then the gemstone is brought into contact with the (rotating) lap (reference numeral <NUM> in <FIG>) and the facet is cut and polished to a desired depth, indicated by the depth indicator.

In the next step, the lever <NUM> of the precision divider <NUM> is released and the graduated disk <NUM> (including the attached gemstone and gear <NUM>) is rotated to index position <NUM> on the graduated disk <NUM> and locked again, whereupon the second mains facet is cut in the gemstone (see step P1 in Table <NUM> and the gear index position <NUM> on the graduated disk <NUM> shown in the rightmost column in the tables).

The P1 steps above are repeated for gear index position <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> on the graduated disk <NUM> to provide a pavilion having a total of <NUM> mains facets. This stage is illustrated in <FIG>, where the upper figure is a top view of the pavilion and the lower part is a side view of the pavilion with the mains facets indicated at number <NUM>. Accordingly, the <FIG> illustrate the same number of facets for round brilliant, as set forth in the tables, but the principle is the same for another shape of a gemstone having a pavilion with different number of facets.

Then, the operator moves on to step P2 where the angle of the precision divider <NUM> holding the gemstone <NUM> to be processed is adjusted to <NUM>° as described above, whereupon the position of the graduated disc <NUM> is moved to index position <NUM>. Then the gemstone <NUM> is brought into contact with the (rotating) lap <NUM> and the facet is cut as described above. Then the graduated disc <NUM> is rotated to the respective index position set forth in column "Gear index on disk <NUM>" in Table <NUM> step P2 to produce a total of <NUM> girdles in step P2. The result is indicated in <FIG>, though with a different number of facets as mentioned above.

The breaks and transfers of the pavilion are cut in a similar manner with angle and gear index positions as set forth in the steps P3 and P4 in Table <NUM>. The results of the respective steps are illustrated accordingly in <FIG> for the respective steps.

The pavilion of the gemstone has now been completely cut and the next step is to perform similar cuts in the crown. The gemstone <NUM> is, in a manner known per se, removed from the dopstick <NUM> (<FIG>) by heating the glue, and is transferred to another dopstick <NUM> and fixed with glue in a similar manner, exposing the raw crown of the gemstone <NUM>.

The facet cutting process proceeds in a similar manner as described above, starting with the mains and then proceeding with the breaks, the stars and finally the table from steps C1 through C4 with the angles and gear index positions as indicated in table <NUM>. The emerging facet patterns are illustrated in <FIG> (mains), <FIG> (breaks), <FIG> (stars) and <FIG> (table), which are drawings similar to the pavilion drawings in <FIG>. Also here, the number of facets illustrated in the drawings is the same as the respective number set forth in table <NUM>.

When the facet cutting procedure has been completed, the grinding lap is exchanged by a polishing lap or the precision divider <NUM> is turned to a separate polishing lap and the same steps as described above for the facet cutting is repeated, to provide a precisely cut and polished gemstone with perfect angles.

Claim 1:
Apparatus for precisely cutting and polishing gemstones, said apparatus comprising a precision divider (<NUM>), a supporting device (<NUM>) arranged to be located at a work bench (<NUM>) comprising a lap (<NUM>) for attachment of grinding and polishing devices, wherein the precision divider (<NUM>) is attached pivotal to the supporting device (<NUM>), arranged to be pivoted and fixed with its longitudinal axis (<NUM>) at a desired angle with the supporting device (<NUM>), said precision divider (<NUM>) further comprising a mandrel (<NUM>) exhibiting a dopstick recess (<NUM>) arranged to accommodate a dopstick (<NUM>; <NUM>) carrying a gemstone (<NUM>), and means for rotating the precision mandrel (<NUM>) about the longitudinal axis (<NUM>) and locking the mandrel (<NUM>) against rotation during grinding and polishing of the gemstone (<NUM>), wherein
the precision divider (<NUM>) comprises a housing (<NUM>) accommodating the elongate mandrel (<NUM>) having a first end in which the dopstick recess (<NUM>) is formed, and a second end exhibiting a precision graduated disk (<NUM>) and a precision dividing gear (<NUM>), said mandrel (<NUM>), precision dividing gear (<NUM>) and graduated disc (<NUM>) being lockable at a desired rotational position with regard to the longitudinal axis (<NUM>) by a mandrel rotation locking device (<NUM>, <NUM>), and wherein
the supporting device (<NUM>) comprises a frame device (<NUM>) arranged to be attached to a work bench (<NUM>) via a support column (<NUM>) in an adjustable manner both in the horizontal plane and in the vertical direction, thus enabling positioning of the frame device (<NUM>) and the precision divider (<NUM>) at a desired elevation and desired horizontal orientation, said supporting device (<NUM>) further including a vertical angle adjustment device comprising a precision divider vertical angle dial (<NUM>) and an angle locking device (<NUM>, <NUM>, <NUM>, <NUM>), arranged to lock the precision divider (<NUM>) in the desired angle position, characterized in that said mandrel (<NUM>), precision dividing gear (<NUM>) and graduated disc (<NUM>) are arranged rotary in relation to the housing (<NUM>), and in that the supporting device (<NUM>) further comprises a fine vertical angle adjustment means (<NUM>, <NUM>, <NUM>, <NUM>) arranged to perform fine angle adjustment of the precision divider (<NUM>) as a supplement to the vertical angle adjustment device.