EP3608060A1 - Machining tool for grinding a workpiece - Google Patents

Abstract

The machining tool (30) is used to grind a workpiece in a machining machine. The tool comprises at least a first machining portion having particles of a material harder than the material of the workpiece, the particles being disposed in a binder, and at least a second machining portion having particles of smaller diameter than the first machining portion, and of a harder material than the material of the workpiece, the particles of the second portion being arranged in a binder identical to that of the first portion or in a binder different.

Description

TECHNICAL FIELD OF THE INVENTION

The invention relates to a machining tool for performing a grinding operation on a workpiece, in particular of hard material on a machining machine.

STATE OF THE ART

For a grinding operation in a machine tool, it is known to change the machining tool between a rough grinding step and at least one finishing step by surface abrasion of workpieces. To grind one face of a piece of hard material, it can be used first of all a first tool with a machining strip having for example large diameter diamond particles in a binder, it is a step of draft. After this first step, a second tool can be used with a machining strip having diamond particles of smaller diameter than the first step to define a semi-finishing step. Finally, a third tool can still be used with a machining strip having diamond particles with an even smaller diameter than the second step for a final finishing step. In this case, three grinding tools must necessarily be used.

As mentioned above, it is generally necessary to carry out grinding in several stages, since it is not possible to easily remove for example a line or a rough surface finish on the workpiece with a machining strip having particles. of diamond or corundum of small diameter. In this case, it is necessary to spend a very long and therefore expensive machining time for the production of each machined part. On the one step to another, it can also be planned to change the grinding tool in the machining machine, or make two passes, therefore twice, of the workpiece, which further slows the machining time and constitutes a disadvantage.

By placing for example two tools in two working positions, it takes a few seconds, for example 5 seconds to bring the workpiece from a first working position to a second working position. If only one working position is used, the tool change for each machining step can take twice as long, for example 10 seconds as with two tools in two working positions. A machining time for each part is therefore long, which constitutes a drawback.

It should also be noted that for two surfaces to be machined or ground there can be up to even 6 tools for three machining steps per surface of the workpiece. A machining time for each piece of hard material is therefore too long since switching from one working position to another working position or continuously changing the tool considerably slows the machining time, which constitutes a disadvantage. In addition, there are limitations in the machining positions available in the machining machines and tools available.

The tool can comprise at least one surface or machining strip composed of abrasive particles integrated in a binder. The abrasive particles are particularly diamond, or even particles of hardness equal to or less than the workpiece, which can be made of material such as sapphire, zirconia, oxides, nitrides or the like, for machining parts made of hard material. , because the wear of the abrasive part is too fast.

Each machining strip, which includes abrasive particles in a binder, can be fixed to a tool body by sintering, brazing or gluing and the tool support body can be made of aluminum or steel for example. The tool fixing rod can be inserted into the nose or connecting mandrel of a tool spindle to operate the machining.

To the figure 1 , there is shown schematically a machining machine 1. This machining machine 1 conventionally comprises a support part 2 carrying a first spindle 8 for a first machining tool 6, such as a first grinding wheel, and a second spindle 9 for a second machining tool 7, such as a second grinding wheel. A second part 4 of the machining machine 1 comprises a support block 3 of part 10 to be machined. Mainly the part 10 can be mounted via a part holding element 10 ′ to a clamping mandrel 5 of the support block 3.

The support part 2 can be moved in a first direction X, while the support block 3 can be moved in a second direction Y perpendicular to the first direction X and in a third direction Z perpendicular to the first and second directions X and Y. The support block 3 can be turned in a direction of rotation A in the plane defined by the first and second directions X and Y. The clamping mandrel 5 can be turned during the machining of the part 10 in a direction of rotation C in the plane defined by the second and third directions Y and Z.

During the machining of the part 10, it is first brought into contact with the first grinding wheel 6, which can be of maximum diameter of 250 mm with an abrasive band at the periphery having particles of diamond or corundum large diameter in a binder, for a roughing step. Then the workpiece 10 must be brought into contact with the second grinding wheel 7, which can also be of maximum diameter of 250 mm with an abrasive band at the periphery having particles of diamond or corundum of small diameter in a binder, for a finishing step.

As previously mentioned, the time to perform these machining steps is relatively long, since the workpiece must be moved from a first working position of the first wheel 6 to the second working position of the second wheel 7. This generally constitutes a too long workpiece grinding time therefore expensive at the end of the workpiece machining. In addition, the fact of having to wait for one wheel to stop rotating and to restart the other in rotation generates long passage time and additional energy to restart rotation in view of the inertia of the grinding wheel. This constitutes disadvantages.

SUMMARY OF THE INVENTION

The invention therefore aims to provide a machining tool to perform a grinding operation of a part in a machining machine to overcome the drawbacks of the aforementioned state of the art and to reduce the machining time of each part by its use in a machining machine.

To this end, the invention relates to a machining tool for carrying out a grinding operation of a part in a machining machine, which comprises the characteristics mentioned in independent claim 1.

Particular embodiments of the machining tool are defined in dependent claims 2 to 33.

An advantage of the machining tool lies in the fact that the tool comprises several machining portions on the same tool. Each machining portion comprises particles of a material harder than the workpiece and integrated in a binder. The nature, size or diameter of the abrasive particles are different from one machining portion to another machining portion, and their concentration in the binder can also be different. The first machining portion of the tool may comprise particles of larger diameter than the second machining portion in order to perform a rough machining step, and use the second machining portion to perform a step grinding workpiece.

More than two machining portions can be provided with each of the abrasive particles of different diameter.

For machining parts made of hard material, such as for a sapphire crystal or watch glass, the abrasive particles are preferably diamond particles embedded in a binder.

Advantageously, the first and second machining portions are arranged on the same tool body so as to form only one monobloc tool to be mounted in a spindle of a machining machine to perform grinding in roughing and in finishing. These machining portions are, for example, abrasive strips placed on the same face of the tool body and each forming a ring. The first annular abrasive strip is coaxial and preferably spaced from the second annular abrasive strip. The first abrasive strip is used for grinding in the rough and the second abrasive strip, for example of smaller diameter, is used for grinding at the finish of the workpiece.

Advantageously, the grinding tool can comprise at least two parts fixed to one another and easily removable for changing one of the parts. A first part comprises the first machining portion, while the second part comprises the second machining portion. As these parts are assembled and removable, this allows in the event of premature wear of one of the machining portions to change only the portion with used portion without having to change the tool completely.

It can also be provided to have more than two complementary parts which can be fitted together like Russian dolls and fixed together to form the complete machining tool. Preferably the last fixed complementary part, which can be the first part having the first machining portion, is the one where the machining portion wears out the fastest, such as during a rough machining step. . This makes it possible to change this complementary final part more easily of the tool.

BRIEF DESCRIPTION OF THE FIGURES

• la figure 1 déjà citée représente de manière simplifiée une machine d'usinage pour réaliser des opérations de meulage d'une pièce notamment en matériau dur selon l'art antérieur,
• les figures 2a et 2b représentent une vue en coupe diamétrale et une vue tridimensionnelle d'une première forme d'exécution d'un outil d"usinage en une pièce avec différentes bandes d'abrasion sur une face du corps d'outil selon l'invention,
• les figures 3a, 3b et 3c représentent des vues en coupe diamétrale et de dessus et de dessous des première et seconde parties ayant des portions abrasives formant une seconde forme d'exécution de l'outil d'usinage, ainsi qu'une vue tridimensionnelle en éclaté de l'outil avec les différentes pièces à assembler selon l'invention,
• les figures 4a, 4b et 4c représentent des vues en coupe diamétrale et de dessus des première et seconde parties ayant des portions abrasives formant une première variante de la seconde forme d'exécution de l'outil d'usinage, ainsi qu'une vue tridimensionnelle en éclaté de l'outil avec les différentes pièces à assembler selon l'invention,
• les figures 5a, 5b et 5c représentent des vues en coupe diamétrale et de dessus des première et seconde parties ayant des portions abrasives formant une seconde variante de la seconde forme d'exécution de l'outil d'usinage, ainsi qu'une vue tridimensionnelle en éclaté de l'outil avec les différentes pièces à assembler selon l'invention,
• les figures 6a, 6b et 6c représentent des vues en coupe diamétrale et de dessus des première et seconde parties ayant des portions abrasives formant une première variante d'une troisième forme d'exécution de l'outil d'usinage, ainsi qu'une vue tridimensionnelle en éclaté et assemblé de l'outil à fixer à un mandrin d'une broche d'une machine d'usinage selon l'invention,
• les figures 7a, 7b et 7c représentent des vues en coupe diamétrale et de dessus des première et seconde parties ayant des portions abrasives formant une seconde variante d'une troisième forme d'exécution de l'outil d'usinage, ainsi qu'une vue tridimensionnelle en éclaté et assemblé de l'outil à fixer à un mandrin d'une broche d'une machine d'usinage selon l'invention,
• les figures 8a, 8b et 8c représentent des vues en coupe diamétrale et de dessus des première et seconde parties ayant des portions abrasives formant une troisième variante d'une troisième forme d'exécution de l'outil d'usinage, ainsi qu'une vue tridimensionnelle en éclaté et assemblé de l'outil d'usinage à fixer à un mandrin d'une broche d'une machine d'usinage selon l'invention,
• les figures 9a, 9b et 9c représentent des vues en coupe diamétrale et de dessus des première et seconde parties ayant des portions abrasives formant une quatrième variante d'une troisième forme d'exécution de l'outil d'usinage, ainsi qu'une vue tridimensionnelle en éclaté et assemblé de l'outil d'usinage à fixer à un mandrin d'une broche d'une machine d'usinage selon l'invention, et
• les figures 10a, 10b et 10c représentent des vues en coupe diamétrale et de dessus des première et seconde parties ayant des portions abrasives formant une cinquième variante d'une troisième forme d'exécution de l'outil d'usinage, ainsi qu'une vue tridimensionnelle en éclaté et assemblé de l'outil d'usinage à fixer à un mandrin d'une broche d'une machine d'usinage selon l'invention.

The aims, advantages and characteristics of the machining tool for carrying out a grinding operation on a part, in particular of hard material on a machining machine will appear better in the following description with reference to the drawings in which:

• the figure 1 already cited represents in a simplified manner a machining machine for carrying out grinding operations on a part, in particular in hard material according to the prior art,
• the Figures 2a and 2b represent a diametrical section view and a three-dimensional view of a first embodiment of a one-piece machining tool with different abrasion bands on one face of the tool body according to the invention,
• the figures 3a , 3b and 3c represent views in diametral section and from above and below of the first and second parts having abrasive portions forming a second embodiment of the machining tool, as well as a three-dimensional exploded view of the tool with the different parts to be assembled according to the invention,
• the figures 4a , 4b and 4c represent views in diametral section and from above of the first and second parts having abrasive portions forming a first variant of the second embodiment of the machining tool, as well as a three-dimensional exploded view of the tool with the different parts to be assembled according to the invention,
• the figures 5a , 5b and 5c represent views in diametral section and from above of the first and second parts having abrasive portions forming a second variant of the second embodiment of the machining tool, as well as a three-dimensional exploded view of the tool with the different parts to be assembled according to the invention,
• the Figures 6a, 6b and 6c represent views in diametral section and from above of the first and second parts having abrasive portions forming a first variant of a third embodiment of the tool machining, as well as a three-dimensional exploded and assembled view of the tool to be fixed to a mandrel of a spindle of a machining machine according to the invention,
• the figures 7a , 7b and 7c represent views in diametral section and from above of the first and second parts having abrasive portions forming a second variant of a third embodiment of the machining tool, as well as a three-dimensional exploded and assembled view of the tool to be fixed to a mandrel of a spindle of a machining machine according to the invention,
• the Figures 8a, 8b and 8c represent views in diametral section and from above of the first and second parts having abrasive portions forming a third variant of a third embodiment of the machining tool, as well as a three-dimensional exploded and assembled view of the machining tool to be fixed to a mandrel of a spindle of a machining machine according to the invention,
• the figures 9a , 9b and 9c represent views in diametral section and from above of the first and second parts having abrasive portions forming a fourth variant of a third embodiment of the machining tool, as well as a three-dimensional exploded and assembled view of the machining tool to be fixed to a mandrel of a spindle of a machining machine according to the invention, and
• the Figures 10a, 10b and 10c represent views in diametral section and from above of the first and second parts having abrasive portions forming a fifth variant of a third embodiment of the machining tool, as well as a three-dimensional exploded and assembled view of the machining tool to be fixed to a mandrel of a spindle of a machining machine according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, the machining tool will be described as a grinding tool for the purpose of grinding, for example, one face of a workpiece, which is made of hard material. Preferably, the grinding tool is arranged once mounted in a spindle of a machining machine to be driven in rotation to produce for example chamfers on a piece, such as in glass or watch glass, which can be made of sapphire, but without restriction to other machining possibilities.

To the Figures 2a and 2b , a machining tool 20 is shown for a grinding operation of one or more parts to be machined. The machining tool is mainly produced for the grinding of workpieces made of hard material. The machining tool 20 mainly comprises at least a first machining portion 21, and at least a second machining portion 22. The first and second machining portions 21, 22 each comprise particles of more material. as hard as the material of each workpiece. These particles are arranged or integrated in a binder. The average size or average diameter of machining particles is different for each machining portion. This allows several operations or machining steps to be carried out with the same machining tool 20 without having to change the tool in a machining machine for different machining steps.

For the machining of workpieces made of hard material, it is necessary to produce the different machining portions 21, 22 of the machining tool 20 preferably with diamond particles. It can also be envisaged to have corundum particles, but the machining portion wears out more quickly with such machining portions with corundum particles, because generally this material is of hardness equal to or less than the part to be machined.

The diamond particles are integrated into a binder, which can be a metallic, resinoid, vitrified, galvanic, ceramic, bakelite or other binder. It can be envisaged to have the particles of the machining portions 21, 22 integrated in an identical or different binder. For each machining portion, the size or diameter of particles (grains) of the diamond is defined by Dxx and the concentration of diamond per mm ³ in its binder is defined by Cxx. For example, with an average grain size of the order of 91 μm, this corresponds to D91, and with a concentration of diamond particles of 100 grains per mm ³ , this corresponds to C100. For a stage machining defined as a blank, the particle size of a machining portion is larger than the particle size of another machining portion for a machining step defined as finishing. The smaller the particle size, the finer the machining.

The machining tool 20 presented to Figures 2a and 2b comprises a first machining portion in the form of a first abrasive strip or layer 21, and a second machining portion in the form of a second abrasive strip or layer 22. These abrasive strips 21, 22 are fixed on a face 23 of the base body of the machining tool 20. Preferably, the face 23 is a front face 23 constituting a ring on which are fixed each annular abrasive strip 21, 22. These abrasive strips 21, 22 are fixed coaxially relative to each other on the front face 23 of the tool body 20 of cylindrical or conical shape to form in this first embodiment a one-piece tool. Preferably, the front face 23 is perpendicular to the axis of rotation of the tool body 20 of cylindrical or conical shape when it is mounted in a spindle of a machining machine.

The base body 20 of the tool can be metallic, for example steel or aluminum. The abrasive strips 21, 22 are fixed to the front face 23 by sintering, brazing or gluing. A space is provided between each abrasive strip in order to be able to carry out a first machining step with the first abrasive strip 21 without harming the second abrasive strip 22 for a second machining step. The first abrasive strip 21 can be defined with a particle size between D20 and D30 for a rough machining step, while the second abrasive strip 22 can be defined with a particle size between D6 and D12 for example for a finishing machining step. It can be provided to use more than two machining portions, that is to say with more than two abrasive belts, which can be arranged and spaced coaxially with each other on the same front face 23 or another side face for example. Each strip includes a different size of abrasive particles.

By way of example and without implied limitation, the dimensions of a machining tool 20 presented to the manufacturers are indicated. Figures 2a and 2b . The diameter d1 of the tool can be 250 mm, as well as the outside diameter of the first abrasive strip 21. The outside diameter of the second abrasive strip 22 can be 200 mm. The width l1 of the second abrasive strip 22 can be 6 mm and the width l2 of the first abrasive strip can be identical to 6 mm of the first width 11 or different. Thus the space between each abrasive belt can be 19 mm. The thickness e1 of each abrasive belt can be identical or different, but here this thickness e1 can be 5 mm.

The machining tool 20 of conical shape may also comprise a rod mounted by plates not shown through a bottom opening 24 of the base body of the tool 20. The tool rod can be mounted on a mandrel of a spindle of a machining machine as shown for example in the figure 1 . The diameter d3 of the inner part of the bottom can be 166.2 mm. The diameter d4 of the opening 24 can be 76 mm. The diameter d5 of the outer part of the bottom can be 219.7 mm and the thickness e2 of the bottom can be 15 mm. The thickness or height h1 of the base body with the abrasive belts 21, 22 can be 50 mm. Other dimensions can be determined for the same form of tool, for example without limitation.

The figures 3a , 3b and 3c represent a second embodiment of the machining tool 30. In this second embodiment, the machining tool consists of different parts assembled or nested to each other like "Russian dolls".

This machining tool 30 comprises at least two parts 31, 34 fixed to one another and easily removable for changing one of the parts. A first part 31 comprises a first machining portion 32, while the second part 34 comprises a second machining portion 35. The size or diameter of the abrasive particles is as previously different from one machining portion to another portion machining, and their concentration in the binder may also be different. Like these parts are assembled and removable, this allows in case of greater wear of one of the machining portions to change only the portion with used portion without having to change the tool completely.

The first and second complementary parts 31, 34 are configured in the general cylindrical shape, but can be of another general shape provided that they can be nested one inside the other for example.

As shown in the figure 3a , the first part 31 is in the form of a cylindrical bowl with a central opening 33 in the bottom of the bowl for fixing the second part 34 and the fixing of two holding plates normally connected to a tool rod machining not shown for mounting in a mandrel of a spindle of a machining machine. The axis of the cylindrical cup is arranged along an axis of rotation of the machining tool.

The first part 31 comprises a first machining portion 32, which is fixed by sintering, brazing or gluing to a front edge of the base body of the first part 31. The base body can be made of steel or aluminum for example . Preferably, this first machining portion 32 is a first abrasive strip 32 of annular shape and width, which may be identical to the width of the edge of the first part 31. The first abrasive strip 32 may comprise particles in particular of diamond in a traditional binder.

In the bottom of the bowl of the first part 31, first holes 38 are made for positioning or fixing the pins shown below with reference to the figure 3c , in order to place the second part, which includes equivalent holes at the periphery for its mounting in the bowl of the first part 31. There are also provided second holes 39 in the bottom of the bowl with an external housing for the placement of screws for fixing the second part 34 shown below with reference to the figure 3c .

Three first holes 38 and three second holes 39 can be provided alternately arranged on the same coaxial circle around the bottom opening 33. The angle separating a first hole 38 from a second neighboring hole 39 is therefore 60 °. .

By way of example and without limitation, the outside diameter d1 of the first part can be 250 mm, while the inside diameter d2 can be 210 mm. The width of the abrasive strip is therefore in this case of the order of 20 mm, and its thickness e1 can be 5 mm. The thickness e2 of the bottom of the bowl can be 15 mm and its height h1 up to the first abrasive strip 32 can be 45 mm. The diameter d3 of the bottom opening can be 76 mm. The diameter of the first holes 38 can be 6 mm and the diameter of the second holes 39 of the passage of the threaded part of each screw can be 8.8 mm and the diameter for the screw head can be 14.5 mm. The first and second holes 38 and 39 are on a circle 177 mm in diameter.

As shown in the figure 3b , the second part 34 is configured in the form of a washer and comprises a second machining portion 35, which is preferably a second abrasive strip 35 fixed by sintering, brazing or gluing on an annular face of upper edge of the body of the second part 34. The second abrasive strip 35 can be of width equivalent to the width of the edge of the washer 34. The body of the second part 34 can be made of steel or aluminum for example.

First holes 38 ′ equivalent to the first holes of the first part are made over a portion of the height of the washer 34 from a lower edge. Second threaded holes 39 ′ for receiving the threaded part of the fixing screws are also provided over a portion of the height of the washer from the lower edge. It can therefore be provided three first holes 38 'arranged alternately with three second threaded holes 39' arranged on a central circle on the lower edge of the washer. The angle between a first hole 38 'and a second hole 39' is therefore 60 °. This circle is arranged midway between the outside diameter and the inside diameter of the washer 34.

By way of example and without limitation, the outside diameter d4 of the second part 34 can be 202 mm, while the inside diameter d5 of the second part 34 can be 152 mm. The holes 38 'and 39' are on a circle with a diameter of the order of 177 mm. The thickness e3 of the second abrasive belt 35 can be 5 mm. The height h2 of the second part 34 up to the second abrasive belt can be 30 mm. The depth of the first holes 38 'can be 10 mm and the depth of the threaded part of the second holes 39' can be 10 mm with a hole extension without a thread of 5 mm.

It should also be noted that the second abrasive strip 35 of the second part 34 can be provided for a rough grinding step, while the first abrasive strip 32 of the first part 31 can be provided for a finishing grinding step with a particle size smaller than that of the second abrasive belt 35.

The figure 3c shows an exploded three-dimensional view of the different elements of the machining tool 30 according to the second embodiment. The mounting of the first and second parts 31 and 34 is carried out by means of screws 41, the head of each screw of which is disposed in the housing of each second hole 39 of the first part so as to be screwed into each second threaded hole of the second part 34. Pins 40 are fixed in the first holes of the second part 34 to be arranged in the first holes 38 of the first part 31.

An arrangement of a first circular plate 36, such as a plug, and of a second plate 37, such as a disc, can be provided for their mounting or fixing through the central opening 33 of the bottom of the bowl. the first part 31. The first plate 36 therefore comprises a central cylindrical solid part and a circular rim or shoulder. The central part has a diameter slightly smaller than the diameter of the opening 33 of the first part 31. The central part can pass through the central opening 33 and with the rim bearing against the external surface of the bottom of the bowl of the first part 31. At least three fixing holes 42 can be provided in the central part of the first circular plate 36.

A second plate 37 of generally cylindrical shape, such as a disc, and of diameter larger than the diameter of the central opening 33 is provided to be fixed on an inner side of the bowl of the first part 31 to the first wafer. To make at least three fixing holes 43 for example through are provided in the second circular plate 37 in an arrangement equivalent to the three holes in the first circular plate 36. Thus the two plates can for example be fixed by screws not shown passing for example in the three holes of the first plate and screwed into the three threaded holes of the second plate 37, which bears after fixing against the inner surface of the bottom of the bowl of the first part 31. These two fixing plates 36, 37 made of aluminum or steel for example are preferably connected to a rod of the machining tool 30 to be mounted in a mandrel of a spindle of a machining machine as shown in the figure 1 .

As a variant of the second embodiment, it can be envisaged to have a second part 34 in the form of a bowl with a second machining portion 35, such as a second abrasive strip placed on one side front or border of the second part 34, bowl-shaped. A solid bottom is provided at the base of the bowl for this second part 34. A central opening of passage diameter of the rod of a fixing screw can be made in the bottom of the bowl of the second part 34 and possibly a screw head housing inside the bowl of the second part can still be provided. A central threaded hole can be made in the first plate 36 to receive the threaded portion of the fixing screw. The second part 34 is fixed directly with its bottom of the bowl in the bottom of the bowl of the first part 31 by screwing a screw, passing in the screw rod passage of the second part, in the hole tapped from the first plate 36, the central part of which is inserted into the opening 33 of the first part 31. Thus the second plate 37 is no longer necessary and no first holes and second holes are made in the first part 31 and the second part 34.

Of course, in an alternative embodiment of the machining tool, the second part 34 can also be fixed directly by means of a screw in the bottom of the bowl of the first part 31 without the opening 33 and without the first plate. 36, but with a central threaded hole in the bottom of the first part 31.

It should also be noted that the second part 34 shown in figure 3b may be a washer without the first holes 38 'and the second holes 39'. The fixing of this second part 34 to the first part 31 can be carried out by means of an external thread on a lower external zone of the second part 34 opposite to the fixing of the second abrasive strip 35 on the front face of the second part 34. In this case, an internal cylindrical edge complementary to the external thread of the second part 34 at the bottom of the bowl of the first part 31 can be provided. The second part 34 is fixed by screwing it into the internal thread of the cylindrical edge of the first part 31. Of course the threading is carried out in a direction opposite to the rotation of the tool during machining to maintain the two parts 31 and 34 well fixed to each other.

The first and second abrasive belts 32, 35 have been explained above as preferably fixed on a border or front face of each part 31, 34. But it can also be envisaged to fix them on an external or internal lateral wall of the first and second parts 31, 34 in the form of a bowl or washer. The same is true for the embodiments described below. It can also be envisaged to have each abrasive strip disposed on a front face and fixed continuously in part on the side walls of the bowl of each part. This type of abrasive belt is in the form of an annular cup.

The figures 4a , 4b and 4c represent a first variant of the second embodiment presented to figures 3a , 3b and 3c . The same reference signs are used for the same elements of this first variant and it will be described, for simplicity, only the elements which differ from the embodiment presented in figures 3a , 3b and 3c .

The figure 4a represents the first part 31 having the first machining portion 32 in the form of a first abrasive strip 32. This first part 31 is identical in shape to the first part 31 described with reference to the figure 3a . This first part 31 only includes a central opening 33, but there is no fixing hole in the bottom of the bowl. The dimensions of this first part 31 can be the same as those of the first part 31 seen in figure 3a . However, there is only the height h1 from the first part 31 to the first abrasive strip 32, which can be greater, for example, at 74 mm.

The figure 4b shows the second part 34 having a second machining portion 35 in the form of a second annular abrasive strip 35 of thickness greater than its width. This second abrasive strip has a cylindrical shape. The second abrasive strip 35 is fixed to the outer periphery of the edge of the second part 34. This second part 34 is in the form of a bowl. In the bottom of the bowl of the second part 34, first holes 38 are made for positioning or fixing the pins shown below with reference to the figure 4c , in order to place this second part 34 on a second fixing plate explained below. Second holes 39 are also provided in the bottom of the bowl with an internal housing for the placement of fixing screws of this second part 34 on the second plate explained below in the figure 4c .

Three first holes 38 and three second holes 39 can be provided in the bottom of the bowl of the second part 34 arranged alternately on the same coaxial circle. The angle separating a first hole 38 from a second neighboring hole 39 is therefore 60 °.

By way of example and without limitation, the outside diameter d4 of the second abrasive belt 35 can be 50 mm. The thickness of the second abrasive strip 35 can be 8 mm, while the width 11 of the second abrasive strip 35 can be 3 mm. The height h2 of the second part 34 with the second abrasive belt 35 can be 30 mm. The diameter d5 of the placement circle of the holes 38 and 39 can be 23 mm. The diameter of each first hole 38 can be 3 mm and the diameter of the second hole 39 for passage of the threaded part of each fixing screw can be 4 mm, while the diameter of the housing of the screw head can be 7 mm. This screw head housing for each second hole is located inside the bowl of the second part.

The figure 4c shows an exploded three-dimensional view of the different elements of the machining tool 30 according to the first variant of the second embodiment. This time the second part 34 is mounted and fixed on a second fixing plate 37 of generally cylindrical shape and not on the first part 31.

As for the embodiment shown in figure 3c , a first circular plate 36 for fixing in the form of a plug comprises a central cylindrical solid part and a circular rim or shoulder. The central part has a diameter slightly smaller than the diameter of the opening 33 of the first part 31. The central part can pass through the central opening 33 and the flange bears against the external surface of the bottom of the bowl of the first part 31 As before, at least three fixing holes 42 can be provided in the central part of the first circular plate 36.

A second plate 37 of generally cylindrical shape and of diameter larger than the diameter of the central opening 33 is provided to be fixed on an inner side of the bowl of the first part 31 to the first plate 36. To be done at at least three fixing holes 43, for example through, are provided in the second circular plate 37 to be opposite the three holes in the first circular plate 36. The two plates can for example be fixed by screws (not shown) passing through the three holes 42 of the first plate 36 and screwed into the three threaded holes 43 of the second plate 37, which bears after fixing against the inner surface of the bottom of the bowl of the first part 31. These two fixing plates 36, 37 are for example made of aluminum or steel and can be connected to a rod of the machining tool 30 to be mounted in a mandrel of a spindle of a machining machine as shown in the figure 1 .

The second part 34 is fixed on the second plate 37 by being housed in a cavity of complementary shape provided from an upper surface of the second plate 37. Pins 40, mounted in holes provided for this purpose in the cavity of the second plate 37, are housed in the first holes passing through the bottom of the bowl of the second part 34 when fixing this second part 34 to the second plate 37. Three screws 41 are also provided to pass into the second holes of the second part 34 in order to be screwed into three corresponding threaded holes 44 in the cavity of the second plate 37. After fixing this second part 34 in the cavity of the second plate 37, the second abrasive belt 35 is well outside from said cavity and no longer at the center of the machining tool, being well separated from the first abrasive strip 32 from the first part 31. The top of the second abrasive strip 35 can be at the same height as the top of the first abrasive strip 32 after assembly and before machining.

It should also be noted that this second abrasive strip 35 of the second part 34 can be provided for a rough grinding step, while the first abrasive strip 32 of the first part 31 can be provided for a finishing grinding step with a particle size smaller than that of the second abrasive belt 35.

As described above in connection with a variant of the second embodiment of the figures 3a , 3b and 3c , it can be envisaged to have a second portion 34 in the form of a bowl with a second portion machining 35, such as a second abrasive strip placed on a front face or edge of the second part 34, in the form of a bowl. A solid bottom is provided at the base of the bowl for this second part 34, which can be fixed by means of a screw in a central tapped hole made in the first plate 36. The second part 34 is fixed directly with its bottom bowl in the bottom of the bowl of the first part 31 by screwing a screw into the tapped hole of the first plate 36, the central part of which fits into the opening 33 of the first part 31. Thus the second plate 37 does not is no longer necessary and first holes and second holes are not made in the first part 31 and the second part 34.

As before, the second part 34 can also be fixed directly by means of a screw in the bottom of the bowl of the first part 31 without the opening 33 and without the first plate 36, but with a central threaded hole in the bottom of the first part 31.

The figures 5a , 5b and 5c represent a second variant of the second embodiment presented to figures 3a , 3b and 3c . This second variant largely resembles the first variant described with reference to figures 4a , 4b and 4c . It will be described, for simplification, only the elements differentiating from this first variant.

The first part 31 of the figure 5a is entirely identical to that described in figure 4a . Likewise, the second part 34 of the figure 5b is identical in shape to that of the figure 4b , except that no means are provided, such as holes in the bottom of the bowl for fixing to a second plate described below. The difference lies in the fact that an external thread 34 'is provided on an external zone of the base body of the second part 34. This thread 34' is arranged on a side opposite to the placement of the second abrasive belt 35. By way of nonlimiting example, the height h3 of this thread 34 ′ can be 10 mm in height.

The figure 5c shows an exploded three-dimensional view of the different elements of the machining tool 30 according to the second variant of the second embodiment. The second part 34 is mounted in a cavity of complementary shape of the second fixing plate 37 of generally cylindrical shape. The cavity includes a thread 45 so as to be able to screw for its fixing the second part 34 with its thread 34 '. It is intended that the orientation of the thread is in a direction opposite to the rotation of the machining tool for grinding operations in a spindle of a machining machine. In this way the second part 34 remains well screwed into the threaded cavity 45 of the second plate 37. There are only holes 43 in the second plate to be fixed to the first plate 36 by means of screws passing through the holes 42 of the first plate 36. The machining tool 30 may also comprise a rod fixed to the first plate 36 for mounting in the mandrel of the spindle of the machine tool.

The Figures 6a, 6b and 6c represent a first variant of a third embodiment of the machining tool 50. In this third embodiment, the machining tool consists of at least two different parts assembled or nested one to the other like "Russian dolls".

As shown in the figure 6a , the first part 51 comprises a first machining portion 52, which can be in the form of a first abrasive strip disposed and fixed in particular by sintering, brazing or bonding on an upper edge of a bowl shape. The first abrasive strip 52 is in the form of a cylinder to extend the cup shape of the first part 51 with a thickness e1 greater than its width. The bowl with the first machining portion 52 comprises a housing 56 for receiving the second part of the machining tool. The bowl also comprises an opening 53 of diameter d4 through its bottom with a lower tubular extension from the opening 53 of the bottom and arranged along a longitudinal axis of the bowl. The outside diameter d5 of the tubular extension is less than the outside diameter d1 of the bowl with the first machining portion 52. This tubular extension of the first part 51 also includes a first through opening 58 perpendicular to the central axis of the tubular extension for a fixing means in the form of a pin, a key, a conical flush or a screw for example.

As shown in the figure 6b , the second part 54 comprises a second machining portion 55 in an upper position of the second part 54. This second machining portion 55 is in the form of a solid abrasive cylindrical block 55, forming a tool head, having a flat upper surface and having a lower surface fixed in particular by sintering, brazing or bonding to a flat upper surface of a cylindrical body of the second part 54. The outside diameter d12 of this cylindrical body of the second part 54 is equivalent or slightly smaller than the outside diameter d11 of the abrasive solid cylindrical block 55. A cylindrical extension 57 extends along a central axis from a lower surface of the cylindrical body of the second part 54 This cylindrical extension 57, as well as possibly the cylindrical body a centered longitudinal opening. A second through opening 58 ′ is also provided in the cylindrical extension 57, which is perpendicular to the central axis of the tubular extension. This second through opening 58 ′ is arranged to be aligned with the first through opening of the first part once the second part 54 is fitted into the first part. The fixing of the two parts can be carried out by a pin or a key or a conical flush or a screw inserted in the two through openings aligned for example.

By way of example and without limitation, the first and second parts 51 and 54 of the Figures 6a and 6b , the outside diameter of the first abrasive belt 52 can be 30 mm, while the outside diameter d6 of the bowl body can be 29 mm. The internal diameter d2 of the first abrasive strip 52 can be 22 mm, which gives an abrasive strip width of 4 mm and a thickness e1 of 15 mm. The inside diameter of the bottom of the bowl can be 20 mm. The diameter d4 of the opening 53 at the bottom of the bowl can be 6 mm. The outside diameter d5 of the tubular extension of the first part can be 12 mm. The length h1 of the tubular extension can be 20 mm with the first through opening 58 of diameter t1 of the order of 3 mm. This through opening 58 is located at a distance h2 of 11 mm from the outer surface of the bottom of the bowl. The abrasive strip is fixed at a height h3 of the order of 4 mm, while an inner edge from the bottom of the bowl is at a height h4 of 2 mm. The outside diameter d11 of the abrasive cylindrical block 55 of the second part 54 can be 21 mm and its thickness e2 equal to 10 mm for example, while the upper body of the second part 54 has an outside diameter d12, which can be of 20 mm. The outside diameter d13 of the cylindrical extension 57 can be approximately 6 mm so as to be inserted into the opening 53 of the first part and slid into the opening of the tubular extension of the first part 51. The length h5 of the extension can be 30 mm. The second through opening 58 ′ can be of diameter t2 of 3 mm and located at a distance h6 of 14 mm from the cylindrical body of the second part 54, which is of a height h7 of the order of 20 mm.

The figure 6c shows an exploded and assembled three-dimensional view of the machining tool 50 before and after its mounting to a mandrel 18 of a spindle of a machining machine. The second part 54 with its cylindrical extension 57 is introduced into the housing 56 of the first part 51, and the cylindrical extension 57 passes through the central opening of the bottom of the bowl to slide into the opening of the tubular extension of the first part 51. Once the two openings 58 and 58 'are properly aligned, a pin 61 or possibly a screw is inserted, for example by force, into the two openings while being wedged, which makes it possible to have the machining tool 50 fully assembled and available for machining operations.

It should also be noted that the first machining portion 52 of the first part 51 can be used for a rough grinding step, while the second machining portion 55 of the second part 54 can be used for a finishing step.

The figures 7a , 7b and 7c represent a second variant of a third embodiment of the machining tool 50. As previously in this second variant of the third embodiment, the machining tool also consists of at least two different parts assembled or nested to each other like "Russian dolls". All the elements of this second variant are identical to those of the first variant described with reference to Figures 6a, 6b and 6c . Therefore, it will not be described all the parts and their identical assembly. There is only a dimensional difference of the first and second parts 51 and 54.

By way of example and without limitation, the first part 51 of the figure 7a , the diameter d1 can be 30 mm, the diameter d2 can be 12 mm, the diameter d3 can be 10 mm, the diameter d4 can be 6 mm, the diameter d5 can be 10 mm and the diameter d6 can be 15 mm. The thickness e1 can be 15 mm. The length h1 can be 20 mm, the distance h2 can be 13 mm, the height h3 can be 2 mm, and the height h4 can be 2 mm. The diameter t1 of the first through opening 58 can be 3 mm.

By way of example and without limitation, the second part 54 of the figure 7b , the diameter d11 can be 11 mm and the thickness e2 equal to 10 mm, the diameter d12 can be 10 mm, and the diameter d13 can be 6 mm, or even slightly less to allow the sliding of the cylindrical extension 57 of the second part 54 in the tube of the tubular extension of the first part 51. The length h5 of the extension can be 30 mm. The second through opening 58 ′ can be of diameter t2 of 3 mm and located at a distance h6 of 14 mm from the cylindrical body of the second part 54, which is of a height h7 of the order of 20 mm.

The Figures 8a, 8b and 8c represent a third variant of a third embodiment of the machining tool 50. For this third variant of the third embodiment, the machining tool 50 is also consisting of at least two different parts assembled or nested one to the other like "Russian dolls". The machining tool 50 of this third variant is identical even in size to the various elements described for the second variant of the figures 7a , 7b and 7c . The only difference concerns the second machining portion 55 fixed to a planar surface of the cylindrical body of the second part 54. This second machining portion 55 does not end with a planar surface, but by a centered point, whose l tip angle can be 120 °.

The figures 9a , 9b and 9c represent a fourth variant of a third embodiment of the machining tool 50. For this fourth variant of the third embodiment, the machining tool 50 also consists of at least two different parts assembled or nested to each other like "Russian dolls". This fourth variant is identical even in size to the various elements described for the second variant of the figures 7a , 7b and 7c . The only difference concerns the second machining portion 55 fixed to a planar surface of the cylindrical body of the second part 54. This second machining portion 55 does not end with a planar surface, but with a hemispherical shape. , whose radius can be half the diameter of the abrasive solid cylindrical block 55, that is to say 5.5 mm.

It should also be noted that the first machining portion 52 of the first part 51 can be used for a rough grinding step, while the second machining portion 55 of the second part 54 can be used for a step finishing. This type of machining tool 50 can advantageously be used to make chamfers on parts and in particular chamfers for watch glasses or glass, which can be made of sapphire, or even for ceramic, zirconia, oxide parts, or nitrides.

It should also be noted that instead of fixing the first and second parts 51 and 54 once assembled by a pin or a key or a screw, it can be imagined to produce an internal thread in the extension tubular of the first part 51 and an external thread on the cylindrical extension 57 of the second part 54. Thus the second part 54 is fixed to the first part 51 by screwing its cylindrical extension threaded into the complementary thread of the tubular extension of the first part 51.

The Figures 10a, 10b and 10c represent a fifth variant of a third embodiment of the machining tool 50, which is based on the first variant shown in Figures 6a, 6b and 6c . For simplicity, it is explained only the difference of this fifth variant compared to the first variant.

The difference of this fifth variant is the means of fixing the first part 51 and the second part 54. To do this instead of through holes 58, 58 ′ in the tubular and cylindrical extensions of the first and second parts 51, 54 shown to Figures 6a and 6b , only a slot 62 is made at the end of the tubular extension of the first part 51. This slot 62 is preferably made on two diametrically opposite sides and axially. This slot can be located at a distance h2 of 11 mm from the outer surface of the bottom of the bowl. Thus, the cylindrical extension 57 of the second part 54 is inserted into the tube of the tubular extension of the first part 51 until the base body of the second part is in the bottom of the bowl of the first part 51. The holding of the second part 54 and of the first part 51 is carried out once the tool 50 is inserted into the mandrel 18. The tightening of the mandrel makes the split portion of the first part folded to allow the fixing of the second part 54 in the first part 51 by this tightening.

It should be noted that the slot 62 may be longer and extend up to the base of the bowl of the first part 51. This type of attachment is simpler than the attachment means described above and makes it possible to change quickly a part of the tool having a used machining portion once the tool has left the mandrel of the machining machine.

Of course, it can be envisaged to have more than two machining portions for each machining tool, for example at least three machining portions as well for a monobloc tool as described with reference to Figures 2a and 2b only for a tool with different parts assembled or nested and removable. Each machining portion preferably comprises diamond particles whose size or diameter is different from one machining portion to another machining portion on the same tool. It can therefore be provided to place these machining portions in the form of strips or layers at the periphery of a cylindrical or conical tool body and sufficiently spaced from one another. With three machining portions, a rough grinding step can be carried out, followed by a semi-finishing grinding step, and finally a finishing grinding step.

In the case of a machining tool with different assembled parts, the part with used machining portion can be changed and keeping the other parts whose machining portion is not yet too worn as the parts can be dismantled without problem.

From the description which has just been made, several variants of the machining tool can be designed by a person skilled in the art without departing from the scope of the invention defined by the claims.

Claims (33)

Machining tool (20, 30, 50) for grinding a workpiece in a machining machine (1), characterized in that the tool comprises at least a first machining portion (21, 31, 51) having particles of material harder than the material of the workpiece, the particles being disposed in a binder, and at least a second machining portion (22, 35, 55) having larger or smaller particles diameter than the first machining portion, and of a material harder than the material of the workpiece, the particles of the second machining portion being arranged in a binder identical to that of the first machining portion or in a different binder. Machining tool (20, 30, 50) for grinding a workpiece of hard material in a machining machine (1) according to claim 1, characterized in that each machining portion (21, 22, 31, 35, 51, 55) includes diamond particles embedded in a binder. Machining tool (20, 30, 50) according to one of claims 1 and 2, characterized in that the first and second machining portions (21, 22) are placed on the same tool body (20) to constitute a monobloc tool. Machining tool (20, 30, 50) according to claim 3, characterized in that the first and second machining portions are constituted by first and second abrasive strips (21, 22) arranged on at least one front face or a side wall of the tool body (20), which is capable of being rotated in a spindle of a machining machine (1) to grind a workpiece. Machining tool (20, 30, 50) according to claim 4, characterized in that the first and second abrasive belts (21, 22) are arranged on a front face (23) of the body of the tool (20) of cylindrical or conical shape. Machining tool (20, 30, 50) according to claim 5, characterized in that the first and second abrasive belts (21, 22) are annular and fixed on the front face (23) coaxially, being spaced from each other, and in that the front face (23) is perpendicular to the axis of rotation of the tool body (20) of cylindrical or conical shape. Machining tool (20, 30, 50) according to one of Claims 4 to 6, characterized in that a third machining portion in the form of a third abrasive strip is arranged on the face of the same body d 'tool. Machining tool (20, 30, 50) according to claim 7, characterized in that the third annular band is fixed on the front face (23) coaxially to the first and second abrasive bands (21, 22) being all spaced from each other. Machining tool (20, 30, 50) according to one of claims 1 and 2, characterized in that a first part (31, 51) of the machining tool (30, 50) comprises the first portion machining (32, 52), in that a second part (34, 54) of the machining tool (30, 50) comprises the second machining portion (35, 55), and in that the first and second parts (31, 34, 51, 54) are dismountably assembled to form the machining tool (30, 50). Machining tool (20, 30, 50) according to claim 9, characterized in that the first part (31) is in the form of a cylindrical bowl with a bottom for detachably fixing the second part (34), l the axis of the cylindrical cup being arranged along an axis of rotation of the machining tool, and in that the first machining portion (32) is a first abrasive strip (32) of annular shape. Machining tool (20, 30, 50) according to claim 10, characterized in that the first machining portion is a first abrasive strip (32) of annular shape, which is fixed coaxially to an edge or a wall side of a base body of the bowl of the first part (31). Machining tool (20, 30, 50) according to claim 11, for which the first annular abrasive strip (32) is fixed on a front face of the edge, characterized in that the width of the first abrasive strip ( 32) is identical to the width of the border. Machining tool (20, 30, 50) according to claim 10, characterized in that the second part (34) is configured in the form of a cylindrical washer or a cylindrical cup with an outside diameter less than the inside diameter of the cup of the first part (31), and in that the second part (34) comprises a second machining portion (35), which is a second abrasive strip (35) fixed on an annular face of upper edge or a side wall of a body of the second part (34). Machining tool (20, 30, 50) according to claim 13, in which the second annular abrasive strip (35) is fixed to a front face of the edge, characterized in that the width of the second abrasive strip ( 35) is identical to the width of the border of the washer (34). Machining tool (20, 30, 50) according to claim 13, characterized in that first holes (38) of the first part (31) are made in the bottom of the bowl of the first part (31) for the positioning or fixing of pins (40), in that second holes (39) in the bottom of the bowl of the first part (31) are made with an external housing for the placement of screws (41) for fixing the second part (34), in that first holes (38 ') of the second part (34) equivalent to the first holes (38) of the first part (31) are made over a portion of the height of the washer (34) from a lower edge to receive positioning pins (40), and in that second threaded holes (39 ') of the second part (34) and positioned in a manner equivalent to the second holes of the first part (31) are made over a portion of the height of the washer (34) to receive the threaded part of the screw (4 1) when fixing the second part (34) on the bottom of the bowl of the first part (31). Machining tool (20, 30, 50) according to claim 15, characterized in that the first three holes (38, 38 ') of the first and second parts (31, 34) are arranged alternately with the three second holes ( 39, 39 ') of the first and second parts (31, 34) on a central circle on the lower edge of the second part (34). Machining tool (20, 30, 50) according to claim 13, for which the second part (34) is in the form of a bowl, characterized in that the second part (34) is fixed centrally to the bottom of the bowl of the first part (31) by means of a fixing screw inserted into an opening of diameter the size of a screw rod in the bottom of the second part (34), and screwed into a tapped hole of the first part (31). Machining tool (20, 30, 50) according to claim 13, in which the second part (34) is in the form of a bowl, characterized in that the first part (31) in the form of a cylindrical bowl comprises a central opening ( 33), in that for fixing the second part (34) to the first part (31), a first plate (36), such as a plug, is provided and comprises a central cylindrical solid part of slightly smaller diameter the diameter of the opening (33) for its passage through the opening (33) and a circular rim or shoulder to bear against an external surface of the bottom of the bowl of the first part (31), and in that '' a bottom of the bowl of the second part (34) is fixed centrally to the bottom of the bowl of the first part (31) by means of a fixing screw inserted in an opening of diameter the size of a rod of screws in the bottom of the second part (34), and screwed into a hole t scarred from the central part of the first plate (36). Machining tool (20, 30, 50) according to claim 9, characterized in that the first part (31) is in the form of a cylindrical bowl with a central opening (33) in a bowl bottom, and in that that an arrangement of fixing plates (36, 37) is provided with a first plate (36), such as a plug, comprising a cylindrical solid central part of diameter slightly smaller than the diameter of the opening (33) for its passage through the opening (33) and a circular rim or shoulder to bear against an external surface of the bottom of the bowl of the first part (31), and with a second plate (37) of generally cylindrical shape, such that '' a disc, of diameter larger than the diameter of the central opening (33) and arranged to be fixed to the first plate (36) on an inner side of the bowl of the first part (31), and in that the second part (34) is configured to be detachably attached to the second plate (37) in the bowl of the first part (31). Machining tool (20, 30, 50) according to claim 19, characterized in that three fixing holes (42) are provided in the central part of the first circular plate (36), and in that three other holes fixing (43) are provided in the second circular plate (37) in an arrangement equivalent to the three holes of the first circular plate (36) for fixing the two plates by pins or screws in the bottom of the bowl of the first part (31). Machining tool (20, 30, 50) according to claim 19, characterized in that the second part (34) is in the form of a cylindrical cup with an outside diameter less than the outside diameter of the second shaped plate (37) disk, in that the second part (34) comprises a second machining portion in the form of a second annular abrasive strip (35) of cylindrical shape fixed to the periphery of an edge of a bowl body of the second part (34), in that in a bottom of the bowl of the second part (34), first holes (38) are made for positioning or fixing pins (40) on the second fixing plate ( 37) and second holes (39) with an internal housing for the placement of screws (41) for fixing this second part (34) on the second plate (37), which also includes first holes and second threaded holes positioned equivalent for fixing in a removable way of the second part (34) on the second plate (37). Machining tool (20, 30, 50) according to claim 21, characterized in that three first holes (38) and three second holes (39) are provided in the bottom of the bowl of the second part (34) regularly arranged alternately on the same coaxial circle, and in that pins (40) are arranged in the first holes (38) and screws (41) are arranged in the second holes (39) of the second part (34) to be screwed into the second holes of the second plate (37). Machining tool (20, 30, 50) according to claim 22, characterized in that a lower edge of the second part (34) is arranged to be inserted in a cavity of the upper face of the second insert (37) when it is fixed. Machining tool (20, 30, 50) according to claim 19, characterized in that the second part (34) is in the form of a cylindrical cup with an outside diameter less than the outside diameter of the second shaped plate (37) disk, in that the second part (34) comprises a second machining portion in the form of a second annular abrasive strip (35) of cylindrical shape fixed to the periphery of an edge of a bowl body of the second part (34), in that the second part (34) comprises an external thread (34 ') on an external zone in a low position of the bowl opposite to the placement of the second abrasive strip (35) so as to be screwed into a cavity of complementary shape with a thread (45) of the second plate (37). Machining tool (20, 30, 50) according to one of claims 21 and 24, characterized in that the second annular abrasive strip (35) of cylindrical shape is of greater thickness than its width, which is less than the width of the edge of the bowl body of the second part (34). Machining tool (20, 30, 50) according to claim 9, characterized in that the first part (51) comprises a first machining portion (52) in the form of a first abrasive strip disposed and fixed on a upper edge of a bowl-shaped base, said first abrasive strip (52) being in the form of a cylinder (51), in that said bowl with the first machining portion (52) comprises a housing (56 ) receiving the second part (54), in that an opening (53) is made in a bottom of the bowl with a tubular extension from the opening (53) of the bottom of the bowl arranged along a longitudinal axis of the bowl, the inside diameter of the tubular embedding is identical to the diameter of the opening (53). Machining tool (20, 30, 50) according to claim 26, characterized in that the second part (54) comprises a second machining portion (55) in an upper position of the second part (54), which is in the form of a solid abrasive cylindrical block (55), forming a tool head, and having a lower surface fixed on a flat upper surface of a cylindrical body of the second part (54), in that a cylindrical extension (57) extends along a longitudinal axis from a lower surface of the cylindrical body of the second part (54), the outside diameter of the cylindrical extension (57) being slightly less than the inside diameter of the tubular extension of the first part ( 51) so as to be inserted into said tubular extension during the assembly of the two parts. Machining tool (20, 30, 50) according to claim 27, characterized in that the tubular extension of the first part (51) comprises a first through opening (58) perpendicular to the longitudinal axis of the tubular extension for a means fixing in the form of a pin (61) or a screw, in that a second through opening (58 ') is provided in the cylindrical extension (57) of the second part (54), which is perpendicular to a longitudinal axis of the cylindrical extension (57), said second through opening (58 ') being arranged to be aligned with the first through opening (58) of the first part (51) once the second part (54) is fitted in the first part, and in that the two parts (51, 54) are held together by a pin (61) or a key or a screw inserted in the two aligned through openings. Machining tool (20, 30, 50) according to claim 27, characterized in that an internal thread in the tubular extension of the first part (51) is produced, and in that an external thread on the cylindrical extension (57) of the second part (54) is made so as to screw the threaded cylindrical extension (57) in the complementary threading of the tubular extension of the first part (51) for fixing the first part (51) to the second part (54). Machining tool (20, 30, 50) according to claim 27, characterized in that a slot (62) is formed at one end of the tubular extension of the first part (51), the holding of the second part ( 54) and of the first part (51) being carried out once the machining tool (50) is inserted into a mandrel (18) of a machining machine, the tightening of the mandrel making the split portion of the first part (51) to allow the fixing of the second part (54) in the first part (51). Machining tool (20, 30, 50) according to claim 27, characterized in that the solid abrasive cylindrical block (55), forming a tool head, has a flat upper surface. Machining tool (20, 30, 50) according to claim 27, characterized in that the solid abrasive cylindrical block (55), forming a tool head, comprises in the end part a centered tip, the angle of which tip can be 120 °. Machining tool (20, 30, 50) according to claim 27, characterized in that the solid abrasive cylindrical block (55), forming a tool head, comprises in the end part a hemispherical shape, the radius of which can be half the diameter of the abrasive solid cylindrical block (55).

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