HK1119118B - Work piece carrier for positioning a work piece on a chuck and clamping apparatus with a chuck and a work piece carrier - Google Patents

Description

Workpiece carrier for positioning a workpiece on a chuck and clamping device with a chuck and a workpiece carrier

Technical Field

The invention relates to a workpiece carrier (work piece carrier) having a central hole for receiving a workpiece and two reference systems (reference systems), each of which incorporates a positioning element to releasably attach the workpiece carrier to a chuck member (chuck member) at two different well-defined positions. The invention also relates to a clamping fixture (chucking arrangement) comprising a chuck member and a workpiece holder, to which the chuck member can be attached in two different positions.

Background

Clamps are known in the art for attaching a workpiece to a chuck member of a lathe with high precision by means of a workpiece support. Thus, the workpiece holder is attached to the chuck member with not only a high absolute accuracy, but also in particular a high repetition accuracy. In order to attach the workpiece support to the chuck member in a precisely defined position, the workpiece support is usually provided with a reference system which matches a reference system arranged in the chuck member. In other words, the reference system of the chuck member is designed correspondingly. Once the workpiece carrier is attached to the chuck member, the workpiece carrier should obtain a precise, well-defined and well-known position at least in the X and Y directions. Preferably, once the workpiece support is attached to the chuck member, it should also be aligned in the Z direction and its angular orientation about the Z axis.

European patent publication EP- ｃA-0,255,042 discloses ｃA clamp for ｃA tool of ｃA machine tool, comprising ｃA chuck member and ｃA tool holder. The chuck member is provided with two pairs of centering ribs projecting from its bottom surface and having abutment surfaces for aligning the tool holder in the X and Y directions. Furthermore, four pins protruding from the face of the chuck member are provided, which are responsible for aligning the tool holder in the Z-direction. The tool holder is provided with a flat surface adapted to abut against the front face of the pin mentioned above. Still further, the tool holder comprises two pairs of grooves aligned with the above mentioned centering ribs and has a resilient flange adapted to engage the abutment face of the aligned ribs. Finally, the tool holder is provided with a central bore for receiving a push-down bolt, by means of which the pressing force required for accurately determining the central position of the tool holder can be transferred to the tool holder. Thus, the chuck member comprises a centrally located ball clamping mechanism cooperating with the above mentioned press bolt.

A disadvantage of this known device is, among other things, that the workpiece fixed on the workpiece support can be machined only on one side. For example, if both sides of the workpiece have to be machined, once one side has been machined, it has to be released from the workpiece support and fixed again to the workpiece support in a different position on the other side that can be machined. It will be appreciated that this is time consuming on the one hand and introduces errors in terms of the exact position of the workpiece on the other hand.

German patent publication DE-C-861,948 discloses a chuck member attached to a shaft of a lathe, which shaft can be turned from one position to a second position. The chuck member includes a clamp frame having jaws. The clamping frame is rotatably assembled by two bolts to be turned 180 degrees, so that the workpiece clamped in the clamping frame can be turned 180 degrees. In order to determine the position of the clamp with respect to the head, the head is provided with an annular rib which engages with an annular groove provided on both sides of the clamp. In order to fix the clamping frame to the stub shaft, the clamping frame is provided with fixing elements which are all engaged by bolts. The bolt is connected to a seat part which is movable between a turned position and an operative position by rotating and thereby axially moving the sleeve part. Furthermore, each fixing element comprises a protruding portion shaped to correspond to a matching recess provided on the stub shaft, so that the fastening clip prevents rotation once it is in the working position.

Even though the annular rib engaging the affiliated annular groove allows some positioning of the cartridge with respect to the stub shaft, it does not provide accurate and precise alignment of the cartridge with respect to the stub shaft in both the X, Y and Z directions. By providing separate centering elements, in particular a protruding portion engaging the recess and an annular rib engaging one of the annular grooves, the system cannot be determined. Furthermore, the chuck member cannot be released from the spindle and thus attached to the spindle of another lathe if desired. Since the clamping frame is fixed by only two bolts, high-strength forces cannot be transmitted, in particular during the machining of the workpiece received in the clamping frame. Another drawback is seen from the fact that the workpiece received in the clamping frame is limited in size; if it is too large, in particular too long, the clamping frame cannot be turned through 180 ° anyway without removing the workpiece.

Document EP- ｃA-0,900,618 discloses ｃA seat pan with two flat portions. The rearward portion comprises two holders positioned opposite each other by which the carrier plate can be clamped to the chuck member in two different positions. The holder is designed according to the above-mentioned document EP- ｃA-0,255,042 and is attached to the chuck member by means of ｃA centrally located clamping bolt.

Us patent No. 3,023,015 discloses a reversible snap fitting for a drill comprising a tubular holder having open front and rear ends. A drill chuck engaging mechanism is disposed at the rear end of the tubular holder. The dual engagement member includes a dual socket having first and second ends that are selectively engageable at the open end of the holder. An annular stop shoulder intermediate the ends of the cartridge may engage the front end of the retainer. A releasable latching mechanism is provided having cooperating members on opposite sides of the holder and on opposite sides of the dual cartridge respectively. The sleeve slidably surrounds the retainer and is effective to engage a member of the latch mechanism.

Finally, document EP- ｃA-0,970,769 discloses ｃA holder for ｃA drilling tool having ｃA central bore which constitutes on each side an axial receiving hole for receiving ｃA drill bit. The holder is provided with a blind radial bore which extends through both receiving bores and is intended to constitute or receive a stop assembly for securing the drill against rotation.

Disclosure of Invention

It is an object of the present invention to provide a workpiece holder with a central hole of the type mentioned herein above, which can be attached to different chuck members quickly, simply and at different positions, wherein the specific position is precisely defined and known. However, this workpiece holder should be of simple and rigid design.

To meet this and other objects, the present invention provides a workpiece support adapted to be releasably attached to a chuck member. It comprises a central bore extending in the direction of its central longitudinal axis and adapted to receive a workpiece. The first reference system is provided with a first centering element and is adapted to align the workpiece support with the chuck member in a first accurately defined position. The second reference system is provided with a second centering element and is adapted to align the workpiece support with the chuck member in a second accurately defined position.

For releasably attaching the workpiece carrier to the chuck member in said first position, a first connecting means is assigned to the first reference system, wherein the first connecting means surrounds the central opening in the workpiece carrier and extends substantially in the direction of the central longitudinal axis of the workpiece carrier, and for releasably attaching the workpiece carrier to the chuck member in said second position, a second connecting means, which is independent of the first connecting means, is assigned to the second reference system, wherein the second connecting means surrounds the central opening in the workpiece carrier and extends substantially in the direction of the central longitudinal axis of the workpiece carrier.

Due to the fact that the workpiece holder is provided with two reference systems independent of each other, wherein a mechanism for fixing the workpiece holder to the chuck member, which extends sufficiently in the direction of the central longitudinal axis of the workpiece holder and which surrounds the central opening, is assigned to each reference system, the basic premise is created that the workpiece holder can be attached to the chuck member quickly, simply, safely and in an accurate, well-defined position, without the use of a centrally located clamping bolt member.

According to a second aspect, the present invention provides a clamp having a chuck member and a workpiece support adapted to be releasably attached to the chuck member. The chuck member is provided with a referencing system for defining the position of a workpiece support attached to the chuck member and with clamping elements for clamping a workpiece fixedly attached to the chuck member. The workpiece support comprises a central bore extending in the direction of its central longitudinal axis and which is adapted to receive a workpiece. It comprises a first reference system provided with a first centering element and adapted to cooperate with the reference system of the chuck member to align the workpiece support with the chuck member in a first accurately defined position.

Still further, it comprises a second reference system provided with a second centering element and adapted to cooperate with the reference system of the chuck member to align the workpiece support with the chuck member in a second accurately defined position.

In order to releasably attach the workpiece support to the chuck member in said first position, a first connecting mechanism belonging to a first reference system is provided. The first connecting means surrounds a central hole in the workpiece carrier, extends substantially in the direction of the central longitudinal axis of the workpiece carrier and has a clamping surface adapted to be engaged by the clamping elements of the chuck member. In order to releasably attach the workpiece to the chuck member in said second position, a second connecting mechanism is provided which is independent of the first connecting mechanism and which is subordinate to the second reference system. The second connecting means surrounds a central hole in the workpiece carrier, extends substantially in the direction of the central longitudinal axis of the workpiece carrier and has a clamping surface adapted to be engaged by the clamping elements of the chuck member.

Drawings

In the following, embodiments of the device according to the invention will be further described with reference to the accompanying drawings. Wherein:

FIG. 1 shows a perspective view of a workpiece support from one side;

FIG. 2 shows a perspective view of the workpiece support from the other side;

FIG. 3 shows a longitudinal cross-sectional view of the workpiece support with a workpiece clamped therein;

FIG. 4 shows a longitudinal cross-sectional view of the chuck member and the workpiece support attached thereto in a first position; and

figure 5 shows a longitudinal cross-sectional view of the chuck member and the workpiece support attached thereto in a second position.

Detailed Description

Fig. 1 shows a workpiece carrier 1 with a workpiece 4 clamped therein in a perspective view from one side. The workpiece support comprises an annular, disc-shaped base part 2 provided with a central hole 3. The diameter of the hole 3 is not fixed, but the hole 3 has a portion with a first, small diameter and a portion with a second, large diameter. The workpiece support 1 is provided with two reference systems 5, 11 located opposite each other on both sides of the workpiece support 1. In fig. 1, the first reference system 5 is fully visible, whereas only part of the second reference system 11 is visible. The first reference system 5 comprises a projection 6 having a substantially annular shape, parallel to and coaxial with the central longitudinal axis L of the workpiece holder 1. At the same time, the central longitudinal axis L of the workpiece carrier 1 forms the Z axis of the workpiece carrier 1. The front face 7 of the protrusion 6 is provided with a plurality of centering elements; in the present example, the centering element consists of four centering grooves 8 evenly distributed around the central hole 3 and arranged in the front face 7 of the protrusion 6. These centering grooves 8 serve to determine the position of the workpiece carrier 1 in the X and Y directions with respect to a chuck member (not shown in fig. 1) and the angular orientation thereof about the Z axis. At the same time, the flat front portion 7 of the annular protrusion 6 serves as a stop surface in the Z-direction in the case of clamping the workpiece holder 1 to a chuck member (not shown). As can be seen in fig. 1, one end region of the central bore 3 is radially surrounded by the first reference system. The rear side of the projection 6 opposite the front portion 7 presents an annular shoulder portion 9 extending along the periphery of the projection 6, which serves as a clamping surface. As will be explained further below in connection with fig. 4, the shoulder may be engaged by a clamping ball of the chuck member.

It should be noted that the above-mentioned annular protrusion 6 coaxially surrounding the central hole 3 comprises not only centering elements adapted to accurately determine the position of the workpiece holder 1 in the X and Y directions with respect to the chuck member, but also a stop surface 7 for determining the position of the workpiece holder 1 in the Z direction, and a shoulder 9 serving as a clamping surface to be engaged by clamping elements incorporated in the chuck member. In this way, the protrusion 6 incorporates elements serving different functions, so that the centering element in the shape of the recess 8 and the stop surface 7 serving as a Z-axis stop surface constitute the first reference system 5. The shoulder 9 establishing the clamping surface is thus in direct relationship with the first reference system 5. This workpiece support 1 is of particularly simple design.

In the present example, the workpiece support consists of an axisymmetric body part; thus, it is also particularly suitable for lathes.

It should be noted that other elements may be provided which act as centering elements; for example, a centering pin may be used instead of the centering groove.

Fig. 2 shows the workpiece carrier 1 and the workpiece 4 clamped therein in a perspective view from the other side, compared to the view shown in fig. 1. In fig. 2, the second reference system 11 is shown in more detail. The second reference system 11 also comprises a projection 12 having a substantially annular shape, extending parallel and coaxial to the central longitudinal axis L of the workpiece holder 1. The front face 13 of the projection 12 is provided with a plurality of centering elements; in the present example, the centering element consists of four centering grooves 14 evenly distributed around the central hole 3 and arranged in the front face 13 of the projection 12. In case the aforementioned first reference system 5 is used, the centering groove 14 of the second reference system 11 again serves to determine the position of the workpiece holder 1 in the X and Y directions with respect to the chuck member (not shown in fig. 1) and the angular orientation thereof about the Z axis. Meanwhile, the flat front face portion 13 of the annular protrusion 12 serves as a stop surface in the Z direction in the case of clamping the workpiece holder 1 to a chuck member (not shown). As can be seen in fig. 2, the other end region of the central bore 3 is radially surrounded by a second reference system 11, relative to the view shown in fig. 1. The rear side of the projection 12 opposite the front portion 13 presents an annular shoulder portion 15 extending along the periphery of the projection 12, which serves as a clamping surface. As will be explained further herein in connection with fig. 4, the shoulder may be engaged by a clamping ball of the chuck member.

Fig. 3 shows a longitudinal section through the workpiece carrier 1 in which the workpiece 4 is clamped. In each of the interior of the workpiece support 1 and the base member 2, a mechanism for clamping and determining the position of the workpiece 4 is provided. In the present example, these means comprise a slotted clamping ring member 17, a thrust plate member 18 and a plurality of fastening bolts 19; it should be noted that fig. 3 shows only one of the fastening bolts 19. The working principle of the clamping ring member 17 resembles one of the chucks; once the fastening bolts 19 are tightened, the clamping ring part is moved to the left by the thrust plate part 18 in the direction towards the first reference system 5. Since the clamping ring member 17 is radially surrounded by a thrust surface 21 having a diameter which is conically reduced towards the first reference system 5, the thrust plate member 18 presses the clamping ring member 17 radially inwards, as a result of which the workpiece 4 is clamped and positioned along its outer circumferential surface at the same time. With regard to the determination of the position in the Z direction, it should be noted that the annular front face 22 of the workpiece 4 rests on the projection 23 of the base body 2. Upon tightening of the fastening bolt 19, the workpiece 4 is pressed against the projection 23 by the clamping ring member 17. In this way, it is ensured that the workpiece 4 and its annular front face 23 each actively abut against a projection 23 of the base body 2 and thus determine the position in the Z direction.

Also clearly visible in fig. 3 is a shoulder 9 at the rear end of the annular protrusion 6, which constitutes a clamping surface for a clamping ball arranged in the chuck member.

In contrast to the tumble chuck assembly, the workpiece carrier 1 according to the present invention is fully releasably attached to the belonging chuck member; in other words, it may be removed from the chuck member and, if appropriate, reattached to another mating chuck member whenever required. This is particularly important where the workpiece must be machined by different lathes. In this case, with the design according to the invention, the workpiece 4 does not have to be removed from the workpiece support 1 and can be reinserted into another workpiece support, thus avoiding an inaccurate determination of the position of the workpiece with respect to the lathe axis.

In the present example, the two reference systems 5, 11 lie in two planes E1 and E2 extending parallel to each other. However, the planes of the reference systems 5 and 11 may also form an angle, if appropriate.

Instead of the described clamping member consisting of the clamping ring member 17 and the thrust plate member 18, a suitable collet member of this kind known in the art may be provided, or possibly another different clamping assembly, even simply clamping the workpiece 4 to the workpiece holder 1 by means of bolts.

Fig. 4 shows a longitudinal sectional view of the chuck member 25 and the workpiece carrier 1 attached to the chuck member 25 and accurately determining the position of the workpiece carrier 1 with respect to the chuck member 25 by means of the first reference system 5 arranged on the workpiece carrier 1. As a result, the chuck member 25 is also provided with a reference system 26; the reference system 26 is adapted to cooperate with the first reference system 5 and the second reference system 11 of the workpiece holder 1.

The reference system 26 of the chuck member 25 comprises four centering pin members 27 and several abutment surface portions 28, which serve as Z-references and are adapted to be engaged by the front portion 7 of the annular protrusion 6 of the workpiece carrier 1 to accurately determine the Z-axis position of the workpiece carrier 1 with respect to the chuck member 25. In particular, a total of four curved abutment surfaces 28 are provided, each extending between two adjacent centering pins 27. However, in the sectional view in fig. 4, only one abutment surface 28 and two centering pins 27 are visible. Furthermore, the chuck member 25 is provided with a central bore 29 and a ball clamping mechanism 30 comprising at least one working piston 31 and a plurality of clamping balls 32. In the present example, the working piston 31 is designed annularly and is adapted to be hydraulically or pneumatically actuated. As far as the number and position of the centering pins 27 are concerned, they correspond to the centering grooves 8 of the workpiece holder 1 (fig. 1).

Once the workpiece holder 1 is clamped to the chuck member 25, the clamping balls 32 are pressed radially inwards under the action of the working piston 31, with the result that the clamping balls 32 bear against the shoulder 9 (fig. 3) of the workpiece holder 1 to pultrude it in the Z-direction against the chuck member 25. For a more detailed explanation of the operation of the clamping ball member 30, reference is made to us 6,367,814 and us 6,378,877. When the workpiece carrier 1 is loosely attached to the chuck member 25, the centering pins 27 of the chuck member 25 penetrate the centering grooves 8 of the workpiece carrier 1. Thus, the position of the workpiece holder 1 in the X and Y directions with respect to the chuck member and its angular position about the Z axis are determined.

When the workpiece holder 1 is arranged above the chuck member 25, there is a small gap between the Z-axis reference surface 28 of the chuck member 25 and the Z-axis reference surface 7 of the workpiece holder 1, which gap is several hundred millimeters in size. In the final clamping phase, the gap is reduced to 0 by pressing the centering pins 27 of the chuck member 25 further towards the centering grooves 8 of the workpiece carrier 1. Thus, i.e. after the centring pin has been driven into the centring recess, the natural elasticity of the pin and/or the recess wall is taken into account. The result is that the use of resilient centering elements can be avoided, as disclosed in us patent 4,855,558. Once finally clamped, the workpiece support 1 is aligned with the chuck member 25 not only in the X and Y directions and for its angular displacement about the Z axis, but also for its Z axis position. Thus, the central hole 29 of the chuck member 25 is coaxial with the central hole 3 in the workpiece holder 1. Due to the fact that the chuck member 25 is provided with a central hole 29, the work piece 4 attached to the work piece carrier 1 may extend into the hole 29.

As explained above, a workpiece clamped in the chuck member, one side of which can be machined; for example, the front face 4a of the workpiece 4 may be circular flat.

Fig. 5 shows a further longitudinal sectional view of the chuck member 25 and the workpiece carrier 1, wherein the workpiece carrier 1 is attached to the chuck member 25 and is positioned with accurate reference to the workpiece carrier 1 by means of a second reference system 11 arranged in the workpiece carrier 1. The workpiece carrier 1 is therefore turned through 180 ° relative to the situation shown in fig. 3. As mentioned above, clamping of the workpiece carrier 1 to the chuck member 25 and determination of its position to the chuck member 25 takes place exactly simultaneously, with the exception that the centering pin members 27 of the chuck member engage the centering grooves 14 of the parts 11 belonging to the above-mentioned second reference system, and the front face portion 13 belonging to the second reference system 11 abuts against the Z-axis reference face 28 of the chuck member 25. The work 4 held in the second way can process the other side of the work 4. For example, the front face 4b of the workpiece 4 may be circular flat, with the result that the front faces 4a and 4b extend exactly parallel to one another.

Due to the fact that the clamping balls 32 of the chuck member 25 directly engage the annular protrusion 6 belonging to and being part of the first reference system 5 or engage the annular protrusion 12 belonging to and being part of the second reference system 11, the use of separate clamping elements, such as clamping bolts or the like, arranged in the workpiece holder 1 can be avoided. In this way, a particularly cost-effective workpiece support can be manufactured. Since each annular protrusion 6, 12 surrounds the central hole 3 and is provided with an integral peripheral shoulder 9, 15, the clamping elements 32 of the chuck member 25 can be attached to a relatively large clamping surface for securely attaching the workpiece holder 1 and, if appropriate, applying a high clamping force to the chuck member 25. As used in conventional workpiece supports, it is not necessary nor possible to provide a central clamping bolt or pressing bolt due to the central hole. Furthermore, the design of the workpiece holder according to the invention ensures a high-precision positioning thereof with respect to the associated clamping disk.

Within the scope of the invention, it is understood that instead of providing a single annular projection, the workpiece holder may also be provided with a plurality of, for example three or four, projecting portions each having a substantially annular shape.

Claims (26)

1. A workpiece support adapted to be releasably attached to a chuck member and having a central longitudinal axis, comprising:

a central bore extending in the direction of the central longitudinal axis and adapted to receive a workpiece;

a first reference system provided with a first centering element and adapted to align the workpiece support relative to the chuck member in a first accurately defined position;

a second reference system provided with second centering elements and adapted to align the workpiece support relative to the chuck member in a second accurately defined position;

a first connection means belonging to a first reference system for releasably attaching the workpiece holder to the chuck member in a first position, the first connection means surrounding a central aperture in the workpiece holder and extending substantially in the direction of a central longitudinal axis of the workpiece holder; and

a second attachment mechanism independent of the first attachment mechanism and belonging to a second reference system for releasably attaching the workpiece support to the chuck member in a second position, the second attachment mechanism surrounding a central aperture in the workpiece support and extending substantially in the direction of the central longitudinal axis of the workpiece support.

2. The workpiece holder of claim 1, wherein the first and second coupling mechanisms comprise one or more protrusions surrounding a central opening, each of the protrusions having a shoulder constituting a clamping surface and adapted to be engaged by clamping elements disposed in the chuck member.

3. A workpiece support as claimed in claim 1 or 2, wherein the first and second centering elements for aligning the workpiece support relative to the chuck member are evenly distributed around the central aperture.

4. A workpiece support as claimed in claim 2, wherein the first and second centering elements for aligning the workpiece support relative to the chuck member are located on the one or more protrusions.

5. The workpiece support of claim 1, wherein the first and second attachment mechanisms each comprise an annular protrusion coaxially surrounding the central opening.

6. The workpiece holder of claim 5, wherein an outer surface of the annular protrusion is provided with a shoulder constituting a clamping surface and adapted to be engaged by clamping elements arranged in the chuck member.

7. A workpiece support as claimed in claim 2 wherein the one or more protrusions are each at least partially provided with a flat front portion for use as a Z-axis reference for the chuck member.

8. The workpiece support according to claim 2, wherein the shoulder serving as the clamping face is disposed on the rear side of the specific flat front face portion.

9. The workpiece support according to claim 1, characterized in that the first and second reference systems each comprise at least three centering elements in the form of centering grooves or centering pins, by means of which the workpiece support can be aligned in the X and Y directions.

10. The workpiece support of claim 1, wherein the central aperture comprises means for securing and/or positioning the workpiece.

11. The workpiece support of claim 1, wherein the first reference system is located on one side of the workpiece support in a first plane and the second reference system is located on an opposite side of the workpiece support in a second plane, the first and second planes extending parallel to one another.

12. The workpiece support of claim 1, wherein the first reference system is located on one side of the workpiece support in a first plane and the second reference system is located on an opposite side of the workpiece support in a second plane, the first and second planes being at an angle to each other.

13. The workpiece support of claim 1, wherein the workpiece support is axially symmetric in shape.

14. A workpiece support according to claim 1, characterized in that the first coupling means belonging to a first reference system for releasably attaching the workpiece support to the chuck member in a first position and the second coupling means belonging to a second reference system for releasably attaching the workpiece support to the chuck member in a second position each comprise an annular protrusion coaxially surrounding the central hole, the protrusions comprising first centering elements adapted to align the workpiece support in X and Y directions relative to the chuck member, an abutment surface for supporting the workpiece support in Z direction, and a shoulder serving as a clamping surface for clamping elements provided in the chuck member.

15. A fixture having a chuck member and a workpiece support adapted to be releasably attached to the chuck member, the chuck member having a reference system for defining a position of the workpiece support attached to the chuck member, and a clamping element for clampingly securing the workpiece support attached to the chuck member, the workpiece support having a central longitudinal axis and comprising:

a central bore extending in a direction of a central longitudinal axis and adapted to receive a workpiece;

characterized in that the workpiece support further comprises:

a first reference system provided with a first centering element and adapted to cooperate with the reference system of the chuck member to align a workpiece support in a first accurately defined position relative to the chuck member;

a second reference system provided with a second centering element and adapted to cooperate with the reference system of the chuck member to align a workpiece support in a second accurately defined position relative to the chuck member;

a first connection mechanism belonging to a first reference system for releasably attaching the workpiece carrier to the chuck member in a first position, the first connection mechanism surrounding a central aperture in the workpiece carrier and extending substantially in the direction of a central longitudinal axis of the workpiece carrier and having a clamping surface adapted to be engaged by the clamping elements of the chuck member; and

a second connection mechanism independent of the first connection mechanism and belonging to the second reference system for releasably attaching the workpiece carrier to the chuck member in a second position, the second connection mechanism surrounding a central aperture in the workpiece carrier and extending substantially in the direction of a central longitudinal axis of the workpiece carrier and having a clamping face adapted to be engaged by the clamping elements of the chuck member.

16. The clamp of claim 15, wherein the first and second attachment mechanisms include one or more projections surrounding a central opening, each of the projections having a shoulder that constitutes the clamping surface.

17. The clamp of claim 15, wherein the first and second attachment mechanisms each comprise an annular protrusion coaxially surrounding the central opening.

18. The clamp of claim 17, wherein an outer surface of said annular protrusion is provided with a shoulder constituting said clamping surface.

19. The fixture of claim 15, wherein the first and second centering elements are positioned along an annulus coaxially surrounding the central opening, whereby the reference system of the chuck member is provided with respective centering elements adapted to be engaged by the first and second centering elements of the workpiece support.

20. A clamp as claimed in claim 16, wherein the front face of the one or more protrusions is provided with at least three centring elements in the form of centring pins.

21. A clamp according to claim 16, wherein the front face of the one or more protrusions is provided with at least three centering elements in the form of centering grooves.

22. The clamp of claim 16, wherein a front face of the one or more protrusions is designed as a Z-axis abutment face on which the workpiece support is supported in the Z-direction in a condition of clamping the workpiece support to the chuck member.

23. The clamp of claim 15, wherein the chuck member includes a central aperture adapted to receive a portion of a workpiece attached to the workpiece support.

24. A clamp as claimed in claim 15 or 23, wherein the central bore of the workpiece support and the central bore of the chuck member are coaxial with one another once the workpiece support is clamped to the chuck member.

25. The fixture of claim 15, wherein the first reference system is located on one side of the workpiece support in a first plane and the second reference system is located on an opposite side of the workpiece support in a second plane, the first and second planes extending parallel to each other.

26. The fixture of claim 15, wherein the first reference system is located on one side of the workpiece support in a first plane and the second reference system is located on an opposite side of the workpiece support in a second plane, the first and second planes being at an angle to each other.