Prior art Through for example US-A-5,193,312 is previously known a machine for grinding buttons of a rock drill bit, wherein the machine comprises a grinding head with a rotatably journaled axis that carries a grinding cup. The machine comprises a fixture provided for clamping the drill bit to be ground. The fixture is pivotable and comprises an opening for camping the drill bit. The fixture can be inclined with the aid of a lever. The construction of the known fixture is complicated and the fixture is difficult to handle for the operator. US-A-5,070,654 shows an addition grinding machine intended to grind buttons of a rock drill bit, wherein the position of the grinding head in the horizontal plane is adjusted by means of a fixture including two pairs of parallel arms. The adjusted position has proven difficult to retain especially at grinding of very worn drill bit buttons.

Obiects of the invention One object of the present invention is to provide a fixture and a grinding machine for grinding buttons of rock drill bits, whereby the drawbacks of the prior art are avoided.

Another object of the present invention is to provide a fixture and a grinding machine in which the drill bit or the grinding head can be retained in a correct position relative to the grinding cup.

Still another object of the present invention is to provide a fixture and a grinding machine in which the operative peripheries of locking plates during use are held at a substantially constant distance from each other.

These and other objects have been achieved by a fixture and a grinding machine as defined in the appended claims with reference to the drawings.

Description of the drawings Below an example of the fixture and the grinding machine according to the invention is described. Reference is made to the drawings where Fig. 1 shows a part of a grinding machine according to the present invention; Figs. 2A, 2B and 2C show a fixture according to the present invention in three different positions in a top view. Fig. 3A shows a side view of the fixture according to III-III in Fig. 1 partly in cross section. Fig. 3B shows a side view of the fixture according to III-III in Fig. 1 partly in cross section. Fig. 4A and 4B show different parts of the fixture.

Fig. 5 shows an alternative embodiment of a grinding machine according to the invention in a side view.

Detailed description of preferred embodiments In Fig. 1 is shown a grinding machine 10 according to the present invention where a grinding head 11 is carried by a holder 12, which may be firmly connected to a machine stand. The grinding head 11 comprises a grinding spindle with a flushing head 13, which spindle is connected to a power source 14 such as an electric motor for example. The grinding head 11 can be moved vertically, i. e. downwards and upwards, with the aid of an arrangement of two pieces of parallel arm pairs 15,16. A pressure cylinder 17 influences each pair, preferably pneumatic. The cylinder 17 is controlled via controlling means, not shown, to balance the weight of the grinding head at vertical movement of the grinding head or to provide feed force on to the grinding head. The flushing head 13 is provided with an inlet that receives a hose, which transfers flush medium from a suitable source (not shown). The connection of the hose to the source prevents that a part of the flushing head rotates when the grinding cup 51 rotates.

The grinding head 11 is intended to receive a grinding cup 51 in order to rotate it with about 14000 r. p. m. The grinding cup may be of the type laid down in SE-A-

9404008-6, that is a grinding cup that comprises a shaft and a wear part, which is provided with a cavity which, performs grinding of the buttons. The wear part of such a grinding cup has an abrasive grinding surface, which comprises diamond particles. Providing an eccentric channel in the wear part attains good refrigeration and grinding results.

The grinding machine 10 also comprises a fixture 18 in order to hold and to displace a drill bit 19 in a horizontal plane. The fixture 18 has a square box-like holder 20 provided with a clamp diametrically displaceable by means a screw 21 threaded into the holder, Fig. 2A. The holder has a lockable hinge to be able to incline the drill bit at grinding of peripheral inserts. At tightening of the screw 21 while a drill bit 19 rests on a perforated bottom 22 in the holder the clamp is displaced and presses the bit firmly against a V-shape constituted by one corner of the holder. Alternatively the V-shape is provided on a separate insert and in addition the clamp can be tightened mechanically in the holder. The holder 20 is movably connected to a machine stand 23 via a linkage 24. The machine stand 23 comprises a U-shaped girder that has a first wall 42, a bottom 43, an intermediate wall 50 and a second wall 44. The linkage 24 comprises at least two arms; a first arm 25 connected to the holder 20 and a second arm 26 connected to the machine stand. The arms 25,26 are mutually joined by a first vertical hinge 27. The second arm 26 is connected to the machine stand 23 via a second vertical hinge 28. The first arm 25 is made from a quadrangular tube, wherein two perpendicular legs 29,30 form substantially an L-shape, Fig. 4A. The tube height is bigger than its width. A partly circular disc or plate 31 is firmly connected to the lower side of the first arm such as by welding or by a screw joint. The disc may alternatively be integral with the first arm. The disc 31 is provided such that its operative periphery forms a part circular path 32 from about the half of one leg 29 to a piece beyond the second leg 30. The radius centre of the path is provided at a through-going hole 33 for the first the hinge 27.

The second arm 26 is made from a quadrangular tube. The tube height is bigger than its width. The ends of the arm 26 comprise said hinges 27 and 28, Fig. 3B.

Each hinge consists of a cylindrical tube 36 with an inner cylindrical space 39, into the ends of which bushings 37,38 has been inserted with a press fit. The bushings of brass for example are not intended to rotate relative to the tube 36.

A nut 41 is anchored at the middle of the lower side 40 of the second arm. A locking means 45 is provided to cooperate with the nut 41 via a journal 46 threaded at both ends, Fig. 3A. One end of the journal 46 is attached to the nut and the other end surface is secured in a round plate 47, which seals a space 48 to be pressurised in the locking means 45. An external piston 49 is provided about the journal, which piston is displaced upwards in Fig. 3A at pressurising of the space 48.

A partly circular disc or plate 34 is firmly connected, welded for example, to the machine stand 23. The disc 34 is provided such that its operative periphery forms a part-circular path 35 from the connection at about the half the of the machine stand 23 bottom 43 to a distance beyond and outside the second wall 44 of the machine stand. The radius centre of the path 35 lies in the proximity of the second wall 44 of the machine stand in a hole where the second hinge 28 will be arranged.

Aligning the central line CL1 of the hinge 28 with a hole in the disc 34 and a hole in the intermediate wall 50 can mount the fixture. Journals with hollow internally threaded ends were previously inserted with loose fit through the bushings 37, 38 at the ends of the second arm. Then the screws are screwn through the intermediate wall 50 and the disc 34 into one journal that is aligned with the line CL1. Then the leg 30 of the first arm 25 is brought as a hasp over the other end of the second arm 26, whereafter screws are screwn into the threaded ends of the journal which are aligned with the central line CL2. In addition the locking means 45 is screwn firmly into the nut 41 such that the piston 49 circumferentially with a gap overlaps the discs 31 and 34. The locking means 45 is connected to a pressuriser, preferably pressurised air. Alternatively the locking

means 45 may be replace by a manual finger nut. Then the holder 20 is connected in a similar manner via another hinge to the first arm. The discs 31,34 are thus provided in a common horizontal plane. Alternatively the discs can be provided parallel to each other in different planes. The journals are rigidly joined to the intermediate wall 50/the disc 34 and the leg 30, respectively.

The above-described grinding machine according to the present invention functions as follows. A drill bit 19 is firmly clamped in the holder 20 by the clamp.

The holder 20 is pulled out such that the buttons of the drill bit reach close to correct position relative to the grinding cup 51. Then the grinding head 11 is lowered such that the cavity of the grinding cup engages with the button to be ground. Thereby the holder adjusts into a correct position. In this position the operator presses a switch of a control panel, not shown, which makes the piston 49 clamp both discs 31,34 against the lower side of the nut 41. Such as is apparent from Figs. 2A-2C the semi-circular peripheries of the discs 31,34 that the discs during use are held at substantially constant distance from each other and that locking thereof is not dependent on the mutual positions of the discs.

Thereby the position of the drill bit is fixed in the horizontal plane. The holder preferably comprises a slot, which follows a curved path, with the aid of which the holder inclination can be locked by a screw.

Simultaneously as the grinding motor starts, transfer of flush medium, preferably water, starts to the flushing head. The flush medium is supplied to the flushing head via hoses that are connected to openings of the flushing head. When the flush medium has come into the flushing head it passes and exits in the cavity of the grinding cup in order to achieve flushing/cooling of the button to be ground.

The rotary grinding spindle performs the grinding of the selected button via the grinding cup.

In Fig. 5 an alternative embodiment of a grinding machine 10'according to the present invention is shown where a grinding head 11'is carried by a holder 12', which is firmly connected with a machine stand. The grinding head 11'comprises

a grinding spindle with a flushing head 13'. The spindle is connected to a power source such as an electric motor for example. The grinding head 11'can be moved horizontally with the aid of a fixture 18'including two pieces of parallel arm pairs 15', 16'. Each pair is influenced by a pressure cylinder 17', preferably pneumatic. The flushing head 13'carries a grinding cup 51. The grinding machine 10'also comprises a device for holding a drill bit 19'.

The fixture 18'comprises two lower arms ; a first arm 25'connected to the grinding head 11'and a second arm 26'connected to the machine stand 23'. The arms 25', 26'are mutually joined at first horizontal hinges 27'. The second arm 26'is connected to the machine stand 23'via a second horizontal hinge 28'.

A first curved, elongated plate 31'is firmly connected such as by welding or by a threaded joint to the side of the first arm 25'which is facing away from the cylinder 17'. The plate can also be integral with the first arm. The plate 31'is as provided such that its periphery forms a part-circular path at a convex major side of the plate. The radius centre of the path lies in the proximity of the first hinges 27'.

A second curved, elongated plate 34'is firmly connected such as by welding or by a threaded joint to the side of the second arm 26'which is facing away from the cylinder 17'. The plate can also be integral with the second arm. The plate 34' is provided such that its periphery forms a part-circular path at a concave major side of the plate. The radius centre of the path lies in the proximity of the first hinges 27'.

A locking means 45'is provided in the middle of one of the two plates 31', 34'for co-operating with a nut via a journal in a way described above. Alternatively the locking means can be firmly connected to the machine stand 23'or to a substantially triangular plate provided for the first hinge 27'. The plates can be provided parallel in different planes or in a common planar.

The above-described grinding machine 10'according to the present invention functions as follows. A drill bit 19'is positioned in the holder. The grinding head 11'is displaced such that the grinding head the grinding cup 51 assumes about the correct position relative to the button of the drill bit. Then the operator presses on a switch of a control panel, not shown, which clamps the locking means against both plates 31', 34'. Such as is apparent from Fig. 5 there are convex and concave peripheries of the plates 31', 34', the plates under application is held at a substantially constant distance from each other and that the locking thembetween is independent of the mutual position of the plates.

Thereby the position of the grinding head is fixed in a horizontal plane.

By locking both arms 25,26 and 25', 26'respectively, simultaneously with only one locking means a rigid, simple and easily controlled fixture and grinding machine is obtained. Naturally the fixtures 18,18'can be used simultaneously at the same grinding machine.

The invention is no manner limited to the above-described embodiments but can varied freely within the limits of the subsequent claims.