Hollow drill

Abstract

The invention relates to a hollow drill for machining wire-shaped holding arms of pieces of jewellery, said hollow drill comprising: a shaft (2) and a head (3) having three or more cutting edges (4), wherein the head (3) has a hollow region (30), an edge region (31), and rectilinear grooves (5), wherein the hollow region (30) has a substantially hollow spherical base surface, and wherein the grooves (5) interrupt the edge region (31) and the hollow spherical base surface, as a result of which the hollow spherical base surface is subdivided into partial base surfaces (30a, 30b, 30c), a cutting edge (4) being formed on each edge between a groove (5) and a partial base surface (30a, 30b, 30c) of the hollow region (30), and the grooves (5) dividing the edge region (31) into partial edge regions (31a, 31b, 31c), the width of which varies in the peripheral direction.

Description

[0001] hollow drill

[0002] Description

[0003] The present invention relates to a hollow drill for jewelers, designed for machining wire-shaped bars, so-called prongs, by means of which a gemstone, in particular a diamond, is held.

[0004] In the jewelry trade, gemstones, especially diamonds, are held in a prong setting, e.g. around a ring, by means of wire-shaped bars made of precious metal, so-called prongs. The prongs enclose the gemstone at even intervals, for example a three-, four- or six-prong setting, so that light can fall into the gemstone from the sides or underside of the gemstone and, in the case of diamonds in particular, an attractive light reflection is achieved. The individual prongs protrude slightly over the gemstone and must be rounded off to prevent injuries and stringing on clothing. For this purpose, hollow drills are used which round off and smooth the ends of the prongs. Known hollow drills (e.g. EP 1 355 754 B1) have a spherical hollow area with exactly two grooves for chip removal, with the grooves having cutting edges at the transition to the hollow area.The problem with hollow drills of this type is that a jeweler must have a great deal of experience in order to be able to round off the prongs in an attractive shape without any scoring or the like.

[0005] It is therefore an object of the present invention to provide a hollow drill for machining prongs of jewelry, which has a simple structure and easy, cost-effective manufacture, simplified handling and improved cutting properties.

[0006] This object is achieved by a hollow drill having the features of claim 1. The subclaims show preferred developments of the invention.

[0007] The hollow drill according to the invention with the features of claim 1 has the advantage that the hollow drill is suitable for machining wire-shaped holding arms (prongs) for holding gemstones, in particular diamonds on rings. The hollow drill according to the invention has significantly improved cutting properties. In particular, "chattering phenomena" can be avoided during machining, so that particularly precise machining of the ends of the wire-shaped holding arms is possible. In particular, an improved rounding, in particular in a hemispherical shape, can be achieved by means of the hollow drill according to the invention. Furthermore, wire-shaped holding arms can be machined even if they are arranged only at a very short distance from one another. This is achieved according to the invention in that the hollow drill comprises a shaft and a head with three or more cutting edges. The hollow drill preferably comprises exactly three cutting edges.The head has a hollow area, an edge area and a number of straight grooves, the number of which corresponds to the number of cutting edges, for chip removal. The holding area has an essentially hollow spherical base area in which the grooves are incorporated. The grooves interrupt the edge area and the hollow area of ​​the head, with a cutting edge being formed on each edge between a groove and the base area of ​​the hollow area. The cutting edge thus runs in an arc at the edge corresponding to the design of the essentially hollow spherical base area of ​​the hollow area. The grooves divide the edge area into partial edge areas, the width of which changes in the circumferential direction of the hollow drill. This allows the edge areas to be designed very narrow, so that even closely spaced wire-shaped holding arms can be machined.

[0008] The partial edge regions preferably have a first width B1 at a first groove and a second width B2 at a second groove. The first width B1 is greater than the second width B2. The width of the partial edge regions preferably changes continuously. As a result, the partial edge regions have a sickle-like shape when viewed from above. Particularly preferably, the first width B1 is arranged in the region of the partial edge region where a cutting edge of the hollow drill ends.

[0009] Further preferably, an outer edge width of the partial edge regions lies on an outer diameter DO of the head of the hollow drill, wherein the outer diameter has a first radius R0. An inner edge line of the partial edge regions is each formed by an arc with a second radius. The second radius is preferably the same for all partial edge regions. Further preferably, the first and second radii are also the same. Particularly preferably, a center point of the second radii lies on an extension of a cutting edge of an adjacent groove.

[0010] More preferably, the grooves each comprise a base, a first wall, and a second wall. The cutting edges are each formed exclusively on the edge between the first wall and the hollow spherical base surface. The edge on the second wall is free of cutting edges. Particularly preferably, a height of the cutting edges on the first wall is greater than a height of an edge on the second wall. The cutting edge on the first wall is only slightly higher than the free-cutting edge on the second wall. This results in particularly smooth running of the hollow drill, since the free-cutting edge on the second wall does not come into contact with the material to be machined.

[0011] Particularly preferably, the grooves are arranged in the hollow area such that each first wall of each groove converges toward a central axis of the hollow drill. The cutting edges end shortly before the center of the hollow area. The grooves are thus arranged slightly offset from the center of the hollow area. Thus, a central axis of the grooves does not run through the central axis of the hollow drill.

[0012] According to a further preferred embodiment of the invention, the cutting edges converging toward the central axis of the hollow drill are provided such that the cutting edges merge into one another along the central axis. Particularly preferably, the grooves are identically formed with a constant groove width. The groove width is preferably between 0.1 mm and 0.35 μm.

[0013] To further improve the cutting performance of the hollow drill, each flute has a transition cutting edge at its inner end. The transition cutting edge is preferably straight.

[0014] More preferably, the bottom of the grooves is arranged at an angle α between 90° and 30°, in particular 45°, to the central axis of the hollow drill. The bottom is thus formed as a plane that lies at an angle α to the central axis. Alternatively, the bottom of the grooves is arcuate. Thus, the bottom provides an arcuate surface. The arcuate surface can be easily created, for example, using a milling cutter and preferably has a radius of 10 mm or greater.

[0015] The hollow drill is preferably a metal hollow drill. The outer diameter of the hollow drill is more preferably in a range of 0.7 mm to 2.5 mm. The hollow drill is preferably made of steel, hard metal, or ceramic.

[0016] Further preferably, the partial base surfaces of the hollow area created by the grooves each form partial spherical surfaces, which together, however, do not form a common partial spherical surface.

[0017] The head of the hollow drill preferably has an axial length of 1 mm in the direction of the central axis of the hollow drill. Preferred embodiments of the invention are described in detail below with reference to the accompanying drawings. In the drawing:

[0018] Fig. 1 is a schematic side view of a hollow drill according to a first preferred embodiment of the invention,

[0019] Fig. 2 is a perspective view of the hollow drill of Fig. 1 ,

[0020] Fig. 3 is a schematic, enlarged side view of the hollow drill of Fig. 1 ,

[0021] Fig. 4 is a schematic plan view of a head of the hollow drill of Fig. 1,

[0022] Fig. 5 is a schematic sectional view along the line VV of Fig. 4, and

[0023] Fig. 6 is a schematic sectional view of a hollow drill according to a second embodiment of the invention.

[0024] A metal hollow drill 1 according to a first preferred embodiment of the invention will be described in detail below with reference to Figs. 1 to 5.

[0025] As can be seen from Fig. 1 and 3, the hollow drill comprises a shaft 2 and a head 3 adjoining it. The shaft 2 is designed to be connected to a rotating drive.

[0026] The head 3 has exactly three cutting edges 4, which can be seen in detail in Fig. 4. The head comprises a hollow area 30, an edge area 31 and three straight grooves 5.

[0027] The head 3 has an arcuate transition region 34 to the shaft 2 and a cylindrical region 35 in which the hollow region 30 is formed. As can be seen from Fig. 3, the grooves 5 extend in such a way that the grooves 5 interrupt the edge region 31 of the head and the hollow region 30.

[0028] The hollow area 30 of the head 3 can be seen in detail in Figs. 2, 4 and 5. The hollow area 30 has a substantially hollow spherical base surface, which is formed by three partial base surfaces 30a, 30b and 30c.

[0029] Furthermore, each groove 5 comprises a bottom 50, a first wall 51 and a second wall 52.

[0030] The cutting edges 4 are each formed exclusively on an edge between the first wall 51 and a partial base surface of the hollow area 30. As can be seen from Fig. 2, the cutting edges are curved and lie in a plane that runs through a central axis XX of the hollow drill. As a result, as can be seen from Fig. 4, the cutting edges are directed toward a center point MO of the hollow area 30. The cutting edges do not extend directly to the center point MO, but rather end slightly before it.

[0031] Furthermore, each groove 5 has a transition cutting edge 40 at an inner end. The transition cutting edge 40 forms the beginning of the groove 5 and improves chip removal through the groove 5.

[0032] As can be further seen from Fig. 5, the base 50 can be inclined at an angle a to the central axis XX. The angle a is preferably 45°. The grooves 5 have a constant groove width, and the base 50 is flat.

[0033] As can also be seen from Fig. 2, an edge 6, which lies at the transition between the second wall 52 and a partial base area of ​​the hollow region 30, is designed without a cutting edge. In this case, a wall height of the first wall 51 can be higher than a wall height of the second wall 52. The cutting edge 4 is thus slightly higher, preferably in a range between 0.05 mm and 0.5 mm, than the cutting edge 6. This prevents the cutting edge 6 from coming into contact with the material to be machined during machining.

[0034] Furthermore, as can be seen particularly from Figs. 2 and 4, the three partial edge regions 31a, 31b, and 31c, which are formed by the grooves 5, are provided such that the width of the partial edge regions changes in a crescent shape. A first width B1, which the partial edge region has at the first wall 51, is greater than a second width B2, which the partial wall region has at the second groove 52.

[0035] The head 3 of the hollow drill has an outer diameter D0 with a center MO located along the central axis XX of the hollow drill. The three partial edge regions 31a, 31b, 31c each have an outer edge line 32 located on the diameter D0.

[0036] An inner edge line 33 of the partial edge regions 31a, 31b, 31c is also arcuate, with each partial wall region having a second radius R1, R2, R3, which are identical. However, the centers of the second radii R1, R2, R3 are arranged differently. The three centers M1, M2, M3 of the radii R1, R2, R3 of the inner edge lines 33 each lie in the extension of a cutting edge 4 (cf. Fig. 4) of an adjacent groove. Thus, the centers M1, M2, M3 and the cutting edges 4 as well as the first walls 51 lie in a common plane.

[0037] Furthermore, it should be noted that a first radius R0 of the diameter D0 can be equal to the second radii R1, R2, R3.

[0038] This design results in a very slim edge region 31 on the head 3, allowing for the machining of wheel-shaped holding arms (prongs) for holding a gemstone, a ring, or the like with the highest precision. In particular, the slim design of the edge region 31 enables the reliable machining of the wire-shaped holding arms without a significant risk of damaging the gemstone or neighboring holding arms.

[0039] The grooves 5 of this exemplary embodiment have the same geometric structure. The maximum depth T of the hollow area 30 is equal to the height of the cylindrical area of ​​the head 3.

[0040] As can be seen from Fig. 4, the grooves 3 are arranged at angles of 120° to each other. The grooves 5 are arranged offset centrally, so that a central axis Y of the grooves does not pass through the central axis XX of the hollow drill.

[0041] Thus, a hollow drill 1 for jewelers can be provided with which prongs can be machined with the highest precision. In the case of gemstones with a smaller diameter, a larger number of prongs can also be provided in order to hold the gemstone securely. When machining a prong, the hollow drill 1 according to the invention does not come into contact with an adjacent prong and potentially damage it. By providing three cutting edges 4, particularly smooth running of the hollow drill can be ensured during machining. Compared to previously used hollow drills, significantly improved cutting properties are also achieved. Furthermore, particularly good and reliable centering is possible. This significantly improves the work results when rounding off prongs for gemstones.

[0042] Figure 6 shows a hollow drill according to a second embodiment of the invention. Identical or functionally equivalent parts are designated by the same reference numerals as in the first embodiment. The hollow drill 1 of the second embodiment corresponds to the hollow drill of the first embodiment, although, in contrast to the first embodiment, the base 50 is designed differently in the second embodiment. In the second embodiment, the base 50 of the groove 5 is arcuate. The base 50 thus forms an arcuate surface. This has the advantage that the base 50 can be manufactured very easily, for example, using a milling cutter. A radius R4 of the base 50 is manufactured corresponding to the outer radius of the milling cutter. Thus, the radius R4 of the base 50 of the second embodiment can be selected easily by selecting a milling cutter. The radius R4 is preferably 10 mm or larger.The width of the groove 50 also corresponds to the width of the cutting edge circumference of the milling cutter and can also be easily adjusted by selecting the milling cutter. Otherwise, this embodiment corresponds to the previous embodiments, so reference can be made to the description given there.

[0043] List of reference symbols

[0044] 1 hollow drill

[0045] 2 shaft

[0046] 3 heads

[0047] 4 cutting edges

[0048] 5 grooves

[0049] 6 cutting edge

[0050] 30 hollow area

[0051] 30a, 30b, 30c partial floor areas

[0052] 31 Marginal area

[0053] 31a, 31b, 31c partial edge areas

[0054] 32 outer edge line

[0055] 33 inner border line

[0056] 34 arched transition area

[0057] 35 cylinder range

[0058] 40 transition cutting edge

[0059] 50 floor

[0060] 51 first wall

[0061] 52 second wall

[0062] B1 first width of the border area

[0063] B2 second width of the border area

[0064] MO Center of the hollow area

[0065] M1, M2, M3 Centers of the inner radii of the edge area

[0066] D0 outer diameter

[0067] R0 Radius of the outer diameter

[0068] R1, R2, R3 Radii of the inner edge lines of the edge area

[0069] R4 radius of the ground

[0070] central axis

[0071] Central axis of a groove a Angle of the groove to the central axis

Claims

Claims 1. A hollow drill for machining wire-shaped holding arms of jewelry, comprising: a shaft (2) and a head (3) with three or more cutting edges (4), the head (3) having a hollow region (30), an edge region (31) and rectilinear grooves (5), the hollow region (30) having a substantially hollow spherical base surface, the grooves (5) interrupting the edge region (31) and the hollow spherical base surface, whereby the hollow spherical base surface is divided into partial base surfaces (30a, 30b, 30c), a cutting edge (4) being formed on each edge between a groove (5) and a partial base surface (30a, 30b, 30c) of the hollow region (30), and the grooves (5) dividing the edge region (31) into partial edge regions (31a, 31b, 31c), the width of which varies in the circumferential direction.

2. Hollow drill according to claim 1, wherein the partial edge regions (31a, 31c, 31c) have a first width (B1) at a first groove and a second width (B2) at a second groove, wherein the first width (B1) is greater than the second width (B2).

3. Hollow drill according to claim 2, wherein the width of the partial edge regions (31a, 31b, 31c) changes continuously.

4. Hollow drill according to claim 2 or 3, wherein the first width (B1) is arranged at the region of the partial edge region at which the cutting edge (4) ends.

5. Hollow drill according to one of the preceding claims, wherein an outer edge line (32) of the partial edge regions (31a, 31b, 31c) lies on an outer diameter (D0), which has a radius (R0), of the head and an inner edge line (33) of the partial edge regions (31a, 31b, 31c) each lies on a second radius (R1, R2, R3).

6. Hollow drill according to one of the preceding claims, wherein a center point (MO) of the hollow region (30) lies on a center axis (XX) of the hollow drill and in a common plane with the center axis (XX) and the cutting edges (4).

7. Hollow drill according to claim 5 or 6, wherein the second radii (R1, R2, R3) are each of the same size.

8. Hollow drill according to claim 7, wherein the first radius (R0) of the outer diameter (DO) of the head (3) is equal to the second radii (R1, R2, R3).

9. Hollow drill according to one of the preceding claims, wherein each groove has a bottom (50), a first wall (51) and a second wall (52), wherein the cutting edge (4) is formed on an edge at a transition of the first wall (51) to a partial base surface.

10. Hollow drill according to claim 9, wherein a height of the cutting edges (4) on the first wall (51) is greater than a height of an edge on the second wall (52).

11. Hollow drill according to claim 9 or 10, wherein the first wall (51) of a groove (5) and the central axis (XX) of the hollow drill lie in a common plane.

12. Hollow drill according to one of the preceding claims, wherein each groove (5) has a transition cutting edge (40) at an end located in the hollow region (30).

13. Hollow drill according to one of claims 8 to 13, wherein the bottom (50) of the groove (5) is arranged at an angle (a) between 90° and 30° to the central axis (XX) of the hollow drill, or wherein the bottom (50) of the groove (5) is arcuate.

14. Hollow drill according to one of the preceding claims made of steel, hard metal or ceramic

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