GB1573338A

GB1573338A - Changing of chuck jaws

Info

Publication number: GB1573338A
Application number: GB2008777A
Authority: GB
Original assignee: Gildemeister AG
Current assignee: DMG Mori AG
Priority date: 1976-06-02
Filing date: 1977-05-12
Publication date: 1980-08-20
Also published as: SE7705551L; DE2624775A1; FR2353358A1; FR2353358B1; JPS5316978A

Description

(54) CHANGING OF CHUCK JAWS (71) We, GILDEMEISTER AKTIENGESELLSCHAFT, a German company, of Am Hauptbahnhof, D-4800 Bielefeld 1, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to an apparatus for automatically changing the clamping jaws of the chuck of a machine tool.

Chuck jaws are changed in order that various geometric forms and surfaces of a workpiece can be damped in the chuck. In known machine tools, the clamping jaws of the chuck are changed by hand. To this end, the chuck jaws to be changed are successively removed from the chuck, after which the new jaws are inserted, again successively, into the chuck.

In the meantime, however, the increasing degree of automation in machine tools has also resulted in the development of machinery for automatically changing the clamping jaws of a chuck. Thus, German Patent No.

2,104,904 for example describes an automatic changing unit which works with twopiece clamping jaws. Each clamping jaw consists of a radially displaceable base jaw which remains in the chuck and of a replaceable so-called "false" jaw. On their opposite sides, the base jaws and false jaws comprise undercut grooves and projections which can be brought into engagement with one another for connecting the two jaws.

The sets of false jaws required for changing are stored on palettes which are arranged in a row one behind the other in the direction of the chuck axis in a magazine. The magazine is displaceable parallel to the chuck axis. The transfer mechanism consists of a pivotal, double-armed gripper by means of which palettes can be removed from the magazine and conveyed towards the chuck for the changing operation. The disadvantage of this known unit is that it can only be used for changing the two-piece clamping jaws designed specifically for it. This means that the usual one-piece clamping jaws of the type described for example in German Patent No. 2,007,509 cannot be replaced with a unit such as this. In addition, the known unit is fairly complicated and expensive, in addition to which the concentricity provided by two-piece clamping jaws is lower than that of one-piece clamping jaws.

According to the present invention, there is provided in combination, a chuck for a machine tool, the chuck having first guides for clamping jaws; and an apparatus suitable for automatically changing the clamping jaws of the chuck, the apparatus comprising a storage means having second guides for the clamping jaws, and a transfer mechanism which includes a reciprocable element; the arrangement of the combination being such that, in use, a clamping jaw can be transferred from the chuck to the storage means and vice versa by aligning a first guide and a second guide and then transferring that clamping jaw from one of those guides to the other with the reciprocable element.

The storage means preferably comprises a clamping jaw magazine, the second guides being provided in the clamping jaw magazine so that clamping jaws can be transferred from the chuck to the magazine and vice versa. The magazine can be a ring magazine coaxial with the chuck, the first and second guides being radial guides.

Preferably the number of second guides is an integral number times the number of first guides, and the second guides are arranged so that all the first guides can be simultaneously aligned with an equal number of second guides. In such a case, the transfer mechanism could have only one reciprocable element which is successively moved to the positions where first guides of the chuck align with second guides of the ring magazine in order to effect the displacement of a clamping jaw at those places. However, it is better for the transfer mechanism to comprise a number of reciprocable elements equal to the number of clamping jaws in the chuck, each of these transfer elements being associated with one pair of first and second guides. If the chuck comprises three clamping jaws, for example, the chuck and the ring magazine must be postionable relative to one another in such a way that the three first guides of the chuck align simultaneously with three second guides of the ring magazine. With three reciprocable transfer elements, all three clamping jaws could thus be changed at the same time.

It is possible for the ring magazine to be fixed. In this case, the chuck would have to be turned into a reference position in order to change the clamping jaws. In addition, the transfer mechanism would have to be rotatable so that the reciprocable element or elements could also be brought into a position in which the or each element can displace a clamping jaw in the manner necessary for transfer. However, it is simpler for the ring magazine to be rotatable about the axis of the chuck and to be lockable in one or more angular positions.

In this case, the transfer mechanism may also be fixed. The transfer element or elements may then also be aligned with the reference position of the chuck.

The magazine can be a drum magazine or a chain magazine which is rotatable about an axis perpendular to the axis of the chuck and which is provided at its circumference with the second guides which are rectilinear and parallel to the axis of the magazine.

When a ring magazine is provided, the combination according to the present invention can also include a second magazine, which is a drum or chain magazine which is rotatable about an axis perpendicular to the axis of the chuck and which is provided at its circumference with third guides for clamping jaws, which third guides are rectilinear and parallel to the axis of the second magazine, wherein the second magazine is arranged adjacent the ring magazine so that a third guide of the second magazine can be aligned with a second guide of the ring magazine, and wherein a second transfer mechanism is provided for transferring clamping jaws between the two magazines, which second transfer mechanism also includes a second reciprocable transfer element which is reciprocable in the direction of an aligned pair of second and third guides.

This combination may be arranged so that a first guide, a second guide and a third guide can all be simultaneously aligned with one another. If the reciprocable transfer element of the additional transfer mechanism is long enough, it can transfer a clamping jaw directly from the second drum or chain magazine to the chuck and vice versa.

In order to increase the storage capacity of the clamping jaws to be replaced, the second guides can be disposed in at least two groups, the second guides of each group being disposed in a plane perpendicular to the axis of the ring magazine; the ring magazine is axially displaceable, so that, in turn, each group of second guides can be brought into the same plane as that of the first guides. In order to bring the rotatable ring magazine into a correct reference position relative to the chuck, the ring magazine may be provided with a rotary drive.

The rotary drive can drive the ring magazine via a drive transfer device which, when the ring magazine is locked in one or more angular position, converts the rotational drive transmitted from the rotary drive into an axial displacement of the ring magazine.

For this purpose, the combination is preferably that wherein the ring magazine comprises an axially fixed part and an axially displaceable part which includes the second guides, both of which parts are rotatable about the axis of the chuck, wherein the rotary drive acts on the axially stationary part and wherein the drive transfer device is coupled between the axially stationary part and the axially displaceable part so that when the two parts are secured against rotation the axially displaceable part can be axially displaced by the rotary drive.

Preferably the reciprocable element of the first-mentioned transfer mechanism comprises a rod which is displaceable in the direction of an aligned pair of first and second guides, and at one end region of the rod a first coupling means for coupling with a respective second coupling means provided on a clamping jaw. Preferably the first coupling means comprises an end region of the rod which has an annular recess and each second coupling means comprises an undercut aperture in an end face of a clamping jaw so that the rod can be coupled to a clamping jaw by inserting said end region of the rod into the undercut aperture of a clamping jaw and then rotating the rod through a predetermined angle so that the region defining the undercut aperture and the end region of the rod engage one another. Advantageously, the combination is that wherein one part of the rod is provided with a screwthread and another part of the rod has a non-circular crosssection, wherein a threaded nut, which is prevented from displacement along its own axis, and which can be rotated by a second drive, engages the screwthread, wherein the other part provided with the non-circular cross-section is disposed in a guide sleeve provided with a corresponding non-circular interior cross-section, and wherein the guide sleeve is rotatable through a limited angle by a third drive. Preferably the combination includes a plurality of rods and associated threaded nuts and guide sleeves distributed around the periphery of the ring magazine, the number of rods being equal to the number of first guides, with a rod for each guide, wherein each of the nuts mounted on the rods has a toothed external periphery in the form of a gearwheel, wherein all the gearwheels mesh with a first rotatable gear ring arranged coaxially with respect to the chuck axis, and wherein the first gear ring is driven by the second drive.

For adapting the chuck to different workpieces, it is often sufficient to vary the clamping diameter by displacing the clamping jaws in the chuck. For this purpose, it is advantageous if the second drive for the first rotatable gear ring is controlled by a machine which can vary the displacement of the rods.

Preferably, the angular spacing of the rods distributed around the periphery of the ring magazine corresponds to that of the first guides, each guide sleeve is provided with an external toothed surface. all the guide sleeves are directly or indirectly coupled via their external toothed surfaces to a second rotatable ring arranged coaxially of the chuck axis, and the second ring is driven by the third drive. When the third drive rotates the ring, the rotational movement is simultaneously transmitted to the or each guide sleeve which then rotates through the limited angle.

In cases where clamping jaws provided on their backs with a number of toothed grooves, as is the case with the clamping jaws described in German Patent No.

2,007,509, are used, the clamping jaws may be held in position in the storage means by spring-loaded latches which engage the grooves.

In order, during the machining of the workpiece in the chuck, to prevent chips from flying into and soiling the ring magazine, a cylindrical partition may be disposed between the ring magazine and the chuck, extending concentrically of the chuck axis.

The cylindrical partition is provided with openings through which clamping jaws can pass when being transferred from the chuck to the ring magazine or vice versa. If the ring magazine is rotatable, the cylindrical partition may be secured to the machine.

The combination according to the present invention can include a third gear ring which is rotatably mounted coaxially with respect to the chuck axis on the axially fixed part of the ring magazine, wherein at least one gear wheel engages with the third gear ring and is secured to a threaded shaft rotatably mounted with respect to the axially fixed part, wherein each threaded shaft engages with a corresponding internally threaded bore in the axially displaceable part of the ring magazine, wherein the third gear ring is coupled to the rotary drive, and wherein the axially fixed part can be locked by an indexing mechanism in certain angular positions corresponding to positions changing for the clamping jaws.

The threaded shafts can include a portion of smaller diameter than the rest of the shaft so as to reduce the torsional stiffness of the shafts.

Preferably the indexing mechanism comprises a reciprocable indexing pin and corresponding, peripherally distributed index holes in the axially fixed part of the ring magazine.

For a better understanding of the present invention and to show more clearly how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 shows a view along the axis of a lathe equipped with a combination according to the present invention, Figure 2 is a view on an enlarged scale of part of the apparatus shown in Figure 1.

Figure 3 is a section including the axis through the apparatus of Figures 1 and 2 magazine along the line III-III in Figure 2; and Figure 4 is a simplified, diagrammatic side view of part of apparatus of Figures 1, 2 and 3.

The lathe shown in Figure 1 comprises on a sloping bed, a cross slide 2 with a tool magazine 3. A ring magazine 6, in which several sets of clamping jaws are stored is arranged around a chuck 4 provided with three clamping jaws 5. The clamping jaws 5 are changed by a three-part transfer mechanism 7 which will be described in more detail hereinafter. A drum magazine 8 with a second transfer mechanism 9 is arranged over the ring magazine 6. As shown in Figure 2, a gearwheel 10 rotatable separately from the chuck 4 is disposed at the centre of the chuck 4, meshing with a rack 11 for each clamping jaw 5. The rack 11 is provided with oblique, rectilinear projections 12 which engage with correspondingly oblique, rectilinear grooves 13 formed in the back of a one-piece clamping jaw 5. The clamping jaw 5 is displaceable in undercut grooves 29 which form first, radial guides for the clamping jaw 5. When the gearwheel 10 is rotated relative to the chuck 4, the rack 11 is displaced tangentially of the gearwheel 10, whereby the clamping jaw 5 is displaced radially outwards or inwards. Clamping jaws of this type and the corresponding displacement mechanism are commonly encountered in machine tools and are de scribed in more detail in German Patent No.

2,007,509.

The ring magazine 6 comprises a plurality of second, radial guides 31 for clamping jaws 5. In the interests of clarity, only part of the transfer mechanism 7 is shown in Figure 2. The transfer mechanism 7 comprises a rod provided with a screwthread 16 and at one end an undercut keyhead 15. An undercut keyhole 14 is formed in a radially outer end of each clamping jaw 5. The cross-section of the keyhole 14 is adapted to the cross-sectional profile of the keyhead 15 so that the keyhead 15 can enter into the keyhole. After the keyhead 15 has been inserted in the keyhole 14 and the rod 16 has been rotated through 90 , the keyhead 15 and the keyhole 14 engage one another so that the rod 16 can radially displace the clamping jaw 5.

As shown in Figure 3, a shaft 17 carrying the chuck 4 is mounted in a bearing of the housing of the machine 1. A gearwheel 18 is mounted on the shaft 17, being connected to a drive (not shown) for the chuck 4. The clamping jaws 5 anchored in the chuck 4 are provided with a T-profile which is guided in an undercut T-profile 29.

Two groups of second guides 31 for clamping jaws 5 are provided in the ring magazine 6. The guides are not visible in Figure 3. However, two clamping jaws 5 with their undercut T-profiles 21 are shown in the upper part of the ring magazine 6.

The two clamping jaws 5 are held in the ring magazine by latches 48 which engage in the grooves 13 formed in the back of the clamping jaws 5. The latches 48 are urged against the clamping jaws 5 by springs 48'.

The ring magazine 6 as a whole is rotatable about the axis of the chuck 4. It consists of an axially stationary part and of an axially displaceable part. The axially stationary part is mounted in a roller bearing on a flange 30 fixed to the lathe. It consists of a shaped part 27 and of a ring 28 which are screwed to one another. Sleeves 26 are secured in the shaped part 27. In addition, a gear ring 38 having an external and internal teeth is mounted via ballbearing on the shaped part 27. The external teeth mesh with a gearwheel 45 which is disposed on the drive shaft of a motor 46 fixed to the machine which provides a rotary drive for the ring magazine 6. The internal teeth of the gear ring 38 mesh with a gearwheels 40 which are secured to spindles 42. The spindles 42 are mounted rotatably in the sleeve 26 but cannot be axially displaced therein.

The spindles 42 are provided with a screwthread 25 which engages with the internal screwthread 44 of a threaded sleeve 23. The threaded sleeve 23 is screwed to another shaped part 22 by means of a screw 24. When the spindles 42 rotate, the threaded sleeve 23 and the other shaped part 22 are axially displaced. Accordingly, the threaded sleeves 23 and the shaped part 22 form the axially displaceable part of the ring magazine 6. The second guides 31 for the clamping jaws 5 are disposed in this axially displaceable part.

A thickened shoulder 33 of a stop pin 34 is clamped between the ring 28 and the shaped part 27. At its end, the stop pin 34 comprises a stop head 36 fixed to a screw 37. The stop head 36 has a profile corresponding to a stop surface 35 at the bottom of a recess of the shaped part 22 and serves to limit the axial travel of the axially displaceable part.

The ring magazine 6 can be locked in certain angular positions by an indexing mechanism. This indexing mechanism comprises a block 49 fixed to the machine in which an indexing pin 51 is mounted for axial displacement. The indexing pin 51 is connected to a piston 53 mounted in a cylinder chamber 52. The piston-andcylinder assembly of the indexing mechanism may be hydraulically or pneumatically operated. The feed lines for the pneumatic or hydraulic working medium are not shown in the interests of clarity. The shaped part 27 is provided with a number of recesses 50, corresponding to the number of clamping jaw sets, which recesses 50 the indexing pin 51 can engage to lock the ring magazine 6 against rotation.

The illustrated part of the transfer mechanism 7 comprises a rod 16 which at its lower end is provided with a threaded part 16A and, at its upper end, with a threadless part 16 B. The threaded part 16A engages a nut 56 which is externally provided with teeth 61. The nut 56 is rotatable but not axially displaceable. The external teeth 61 of the nut 56 mesh with a gear ring 57 which is mounted by a ballbearing on a ring element 55 fixed to the machine. In addition, the gear ring 57 meshes with a gearwheel 59 which is mounted on the drive shaft of a motor 60. The motor 60 is fixed to the machine and comprises a second drive.

When the motor 60 rotates the gear wheel 59, the nut 56 is rotated by way of the gear ring 57, whereby the rod 16 is moved up or down. The gear ring 57 also drives the other toothed nuts 56 of other transfer mechanisms.

The upper part 16B of the rod is threadless. However, it is provided with two ribs 72 which are mounted for axial displacement in corresponding grooves 63 of a guide sleeve 62. The guide sleeve 62 is in turn rotatably mounted in the ring element 55 fixed to the machine, but cannot be axially displaced therein. The guide sleeve 62 is provided with external teeth 19 which mesh with a gearwheel 67 which, in addition, engages with a toothed drive pin 66 of a motor 65 fixed to the machine. Accordingly, the guide sleeve 62 and hence the rod 16 as well can be rotated by the motor 65. The gearwheel 67 is secured to a shaft 68 which is connected through a pivotal lever 69 to a ring 70. The guide sleeves 62 for the two other rods 16 of the two other transfer mechanisms are similarly connected to the ring 70 at two other points (not shown). The pivotal levers 69 only pivot through a limited angle because the ring 70 abuts against stops (not shown) in both pivoting directions. This limited pivoting angle defines on the one hand the position in which the keyhead 15 can be introduced into the keyhole 14 and, on the other hand, the position in which the keyhole 14 and the keyhead 15 are engaged with one another.

Between the chuck 4 and the ring magazine 6, there is a cylindrical screening wall 64 which is screwed onto a flange 30 fixed to the machine. The screening wall 64 is provided with openings 71 at the three places where the clamping jaws are to pass.

Only one of these openings 71 is shown in Figure 3.

A changing operation is effected as follows: First of all, the chuck 4 is located in a predetermined reference position. In this reference position, the guides 29 for the three clamping jaws align with the openings 71 in the screening wall 64. The motor 46 is then actuated. Since the index pin 51 is initially withdrawn, both the axially stationary part 27, 28 and also the axially displaceable part 22, 23 are rotated. There is no axial displacement of the axially displaceable part. When the guides 31 of three positions in the ring magazine 6 which are not occupied by clamping jaws 5 align with the guides 29 of the chuck 4, an opening 50 is situated in front of the indexing pin 51.

The indexing pin 51 is then pushed forwards into the opening 50 and locks the ring magazine 6 against rotation. Simultaneously, the motor 46 is switched off. The motor 60 is then actuated, whereby the three rods 16 are advanced radially inwards.

The clamping jaws 5 of the chuck 4 were moved beforehand into the radially outermost position in the chuck 4 in which there is no longer any engagement between the ribs 12 of the rack 11 and the grooves 13 in the clamping jaws 5 (see Figure 2). After the keyheads 15 have been introduced into the keyholes 14, the motor 60 is switched off. The motor 65 is then switched on, whereby the rods 16 are rotated through the limited angle. The keyheads 15 are thus locked in the keyholes 14.

The motor 60 is then actuated again, but in a reverse direction, so that the three rods 16 with the clamping jaws 5 coupled thereto are withdrawn into the empty positions of the ring magazine 6. The motor 60 is then switched off and the motor 65 actuated to disengage the keyheads 15 from the keyholes 14. The motor 60 is then actuated again for a short time to move the rods 16 radially outwards until they are completely clear of the magazine 6.

It will now be assumed that one set of clamping jaws is to be introduced into the chuck 4 from the back row of the ring magazine 6. After the indexing pin 51 has been withdrawn, the motor 46 is actuated again. When the three clamping jaws to be changed have been rotated through such an angle that their guides are parallel to the empty guides 29 of the chuck 4, the indexing pin 51 is again pushed forwards into the corresponding recess 50. In this way, the ring magazine 6 is locked in this angular position. However, the motor 46 is not switched off, but continues to act on the gear ring 38. The gear ring 38 rotates the spindles 42, whereby the axially displaceable part 22, 23 of the ring magazine is displaced to the right. The advancing movement is stopped by the stop surfaces 35 striking the stop heads 36. The spindles 42 have central portions of reduced diameter which allowing a slight torsional flexing and/or longitudinal compression of the spindles 42 to ensure that all the stop heads 26 and stop surfaces 35 contact each other. The three clamping jaws can now be introduced from the back row into the empty guides 29 of the chuck 4. This takes place in exactly the opposite way to the above-described withdrawal of clamping jaws from the chuck 4.

Figure 4 shows how the drum magazine 8 is arranged in relation to the ring magazine 6. The drum magazine 8 is mounted on a rotary and indexing drive 75 and is provided with third guides 58 for the clamping jaws 5.

The second transfer mechanism arranged on the drum magazine 8 is provided with a displaceable rod 76 which at its end comprises a keyhead 77 corresponding to the keyhead 15 in Figure 3. As described above, this keyhead can be introduced into and locked in the keyhole of the particular clamping jaw to be changed. In order to bridge the space taken up by the rotary drive 75, an intermediate guide 74 is arranged between the drum magazine 8 and the ring magazine 6. Another guide 73 is provided in that part 55 of the ring magazine 6 which is fixed to the machine. It is important that, in the reference position, a third guide 58 of the drum magazine 8 should align with a second guide 31 in the ring magazine 6 and, optionally, also with a first guide 29 in the chuck 4 so that a clamping jaw 5 can either be directly introduced from the drum magazine 8 by way of the guides 74, 73 and 31, 29 into the chuck 4 or withdrawn therefrom or stored in the ring magazine 6 from where the clamping jaw 5 is introduced into the chuck 4 by means of the mechanism described above. In this case, the drum magazine need only be provided if the capacity of the ring magazine is inadequate. However, it is also possible for the clamping jaws to be changed without the ring magazine, i.e. for the clamping jaws to be directly introduced into and removed from the chuck 4 using the magazine 8 with the guide 74 correspondingly lengthened.

WHAT WE CLAIM IS 1. In combination, a chuck for a machine tool, the chuck having first guides for clamping jaws; and an apparatus suitable for automatically changing the clamping jaws of the chuck, the apparatus comprising a storage means having second guides for the clamping jaws, and a transfer mechanism which includes a reciprocable element; the arrangement of the combination being such that, in use, a clamping jaw can be transferred from the chuck to the storage means and vice versa by aligning a first guide and a second guide and then transferring that clamping jaw from one of those guides to the other with the reciprocable element.

2. A combination as claimed in claim 1, wherein the storage means comprises a clamping jaw magazine, the second guides being provided in the clamping jaw magazine so that clamping jaws can be transferred from the chuck to the magazine and vice versa.

3. A combination as claimed in claim 2 wherein the magazine is a ring magazine coaxial with the chuck, the first and second guides being radial guides.

4. A combination as claimed im claim 3, wherein the number of second guides is an integral number times the number of first guides, and the second guides are arranged so that all the first guides can be simultaneously aligned with an equal number of second guides.

5. A combination as claimed in claim 4, wherein the transfer mechanism is provided with a reciprocable element for each first guide, so that a plurality of clamping jaws, equal in number to the number of first guides, can be transferred to or from the chuck simultaneously.

6. A combination as claimed in claim 3, 4 or 5, wherein the ring magazine is rotatable about the axis of the chuck and can be locked in one or more angular positions.

7. A combination as claimed in claim 2, wherein the magazine is a drum magazine or a chain magazine which is rotatable about an axis perpendular to the axis of the chuck and which is provided at its circumference with the second guies which are rectilinear and parallel to the axis of the magazine.

8. A combination as claimed in any one of claims 3 to 6, which also includes a second magazine, which is a drum or chain magazine which is rotatable about an axis perpendicular to the axis of the chuck and which is provided at its circumference with third guides for clamping jaws, which third guies are rectilinear and parallel to the axis of the second magazine, wherein the second magazine is arranged adjacent the ring magazine so that a third guide of the second magazine can be aligned with a second guide of the ring magazine and wherein a second transfer mechanism is provided for transferring clamping jaws between the two magazines, which second transfer mechanism also includes a second reciprocable transfer element which is reciprocable in the direction of an aligned pair of second and third guides.

9. A combination as claimed in claim 8, wherein the second magazine is arranged so that a first guide, a second guide and a third guide can all be simultaneously algined with one another.

10. A combination as claimed in claim 9, wherein the second reciprocable transfer element of the second transfer mechanism is capable of transferring a clamping jaw from the second magazine via a second guide to the chuck and vice versa.

11. A combination as claimed in any one of claims 3, 4, 5, 6 8, 9 or 10 wherein the second guides are disposed in at least two groups, the second guides of each group being disposed in a plane perpendicular to the axis of the ring magazine, and wherein the ring magazine is axially displaceable, so that in turn each group of second guides can be brought into the same plane as that of the first guides.

12. A combination as claimed in claim 11 when appendant to claim 6, which also includes a rotary drive which drives the ring magazine via a drive transfer device which, when the ring magazine is locked in one or more angular position, converts the rotational drive transmitted from the rotary drive into an axial displacement of the

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the guides 74, 73 and 31, 29 into the chuck 4 or withdrawn therefrom or stored in the ring magazine 6 from where the clamping jaw 5 is introduced into the chuck 4 by means of the mechanism described above. In this case, the drum magazine need only be provided if the capacity of the ring magazine is inadequate. However, it is also possible for the clamping jaws to be changed without the ring magazine, i.e. for the clamping jaws to be directly introduced into and removed from the chuck 4 using the magazine 8 with the guide 74 correspondingly lengthened. WHAT WE CLAIM IS

1. In combination, a chuck for a machine tool, the chuck having first guides for clamping jaws; and an apparatus suitable for automatically changing the clamping jaws of the chuck, the apparatus comprising a storage means having second guides for the clamping jaws, and a transfer mechanism which includes a reciprocable element; the arrangement of the combination being such that, in use, a clamping jaw can be transferred from the chuck to the storage means and vice versa by aligning a first guide and a second guide and then transferring that clamping jaw from one of those guides to the other with the reciprocable element.

12. A combination as claimed in claim 11 when appendant to claim 6, which also includes a rotary drive which drives the ring magazine via a drive transfer device which, when the ring magazine is locked in one or more angular position, converts the rotational drive transmitted from the rotary drive into an axial displacement of the ring magazine.

13. A combination as claimed in claim 12, wherein the ring magazine comprises an axially fixed part and an axially displaceable part which includes the second 'guides, both of which parts are rotatable about the axis of the chuck, wherein the rotary drive acts on the axially stationary part and wherein the drive transfer device is coupled between the axially stationary part and the axially displaceable part so that when the two parts are secured against rotation the axially displaceable part can be axially displaced by the rotary drive.

14. A combination as claimed in any preceding claim, wherein the reciprocable

element of the first-mentioned transfer mechanism comprises a rod which is displaceable in the direction of an aligned pair of first and second guies, and at one end region of the rod a first coupling means for coupling with a respective second coupling means provided on a clamping jaw.

15. A combination as claimed in claim 14, wherein the first coupling means comprises an end region of the rod which has an annular recess and each second coupling means comprises an undercut aperture in an end face of a clamping jaw so that the rod can be coupled to a clamping jaw by inserting said end region of the rod into the undercut aperture of a clamping jaw and then rotating the rod through a predetermined angle so that the region defining the undercut aperture and the end region if the rod engage one another.

16. A combination as claimed in claim 15, wherein one part of the rod is provided with a screwthread and another part of the rod has a non-circular cross-section, wherein a threaded nut, which is prevented from displacement along its own axis, and which can be rotated by a second drive, engages the screwtheaded, wherein the other part provided with the non-circular cross-section is disposed in a guide sleeve provided with a corresponding non-circular interior crosssection, and wherein the guide sleeve is rotatable through a limited angle by a third drive.

17. A combination as claimed in claim 16 when appendant to claim 5, which includes a plurality of rods and associated threaded nuts and guide sleeves distributed around the periphery of the ring magazine, the number of rods being equal to the number of first guides, with a rod for each first guide, wherein each of the nuts mounted on the rods has a toothed external periphery in the form of a gearwheel, wherein all the gearwheels mesh with a first rotatable gear ring arranged coaxially with respect to the chuck axis, and wherein the first gear ring is driven by the second drive.

18. A combination as claimed in claim 17, wherein the angular spacing of the rods distributed around the periphery of the ring magazine corresponds to that of the first guides, wherein each guide sleeve is provided with an external toothed surfaced, wherein all the guide sleeves are directly or indirectly coupled via their external toothed surfaces to a second rotatable ring arranged coaxially of the chuck axis, and wherein the second ring is driven by the third drive.

19. A combination as claimed in any preceding claim, wherein a back surface of each clamping jaw is provided with a plurality of grooves, wherein the clamping jaws are held in position in the storage means by spring-loaded latches which engage the grooves.

20. A combination as claimed in any of claims 3 to 6 and 8 to 13, or in any one of claims 14 to 19 when appendant to claim 3, wherein a cylindrical partition arranged coaxially with respect to the chuck axis extends between the ring magazine and the chuck, which cylindrical partition is provided with openings through which clamping jaws can pass when being transferred from the chuck to the ring magazine or vice versa.

21. A combination as claimed in claim 20, wherein the cylindrical partition is secured against rotation.

22. A combination as claimed in claim 13, or in any one of claims 14 to 21 when appendant to claim 13, which includes a third gear ring which is rotatably mounted coaxially with respect to the chuck axis on the axially fixed part of the ring magazine, wherein at least one gear wheel engages with the third gear ring and is secured to a threaded shaft rotatably mounted with respect to the axially fixed part, wherein each threaded shaft engages with a corresponding internally threaded bore in the axially displaceable part of the ring magazine, wherein the third gear ring is coupled to the rotary drive, and wherein the axially fixed part can be locked by an indexing mechanism in certain angular positions corresponding to positions for changing the clamping jaws.

23. A combination as claimed in claim 22, wherein the threaded shafts include a portion of smaller diameter than the rest of the shaft so as to reduce the torsional stiffness of the shafts.

24. An apparatus as claimed in claim 22 or 23, wherein the indexing mechanism comprises a reciprocable indexing pin and corresponding, peripherally distributed index holes in the axially fixed part of the ring magazine.

25. An apparatus substantially as hereinbefore described with reference to, and as illustrated in, Figures 1 to 4 of the accompanying drawings.