Where a rectangular or square workpiece is clamped to a machine table using conventional clamping equipment, considerable efforts must be made to ensure that all of the side faces of the workpiece are accurately machined square, in order to minimise stresses in the system due to irregularities in the side faces of the workpiece. No matter how carefully the workpiece is prepared, a perfect square is impossible to achieve and as a result the workpiece, once clamped, will be subject to distortion. The rougher the workpiece, such as for example a workpiece straight from the saw mill with rough and unsquare faces, the more pronounced is the distortion and resultant stresses.

It is therefore the aim of the present invention to provide an improved clamping system which overcomes the aforesaid disadvantage.

According to a first aspect of the present invention there is provided a jaw for a workpiece clamping system, the jaw comprising a first member having means for mounting the jaw on a suitable support structure, a second member mounted on said first member and having means for receiving a portion of at least one face of a workpiece, the jaw including means for allowing rotation of said second member relative to said first member.

Thus irregularities in the angular orientation of a particular face or faces of the workpiece may be accommodated.

The suitable support structure may be a machining table, or an intermediate structure which is itself secured to a table or other work surface.

The system may comprise four jaws, two being fixed and two being re-positionable (for example, slidable) with respect to the machining table. In the two fixed jaws, the mounting means comprises an internally threaded hole extending into the interior of the first member, for receiving a threaded bolt to fix the jaw into the required position on the machining table.

In the case of the two slidable jaws, the mounting means comprises a protrusion extending generally downwardly and outwardly of the first member, this protrusion being received in a corresponding slide channel within the machining table, such that the workpiece, typically held by a jaw at each corner, can be clamped to the table by forcing the two slidable jaw members towards the two fixed members.

In an alternative arrangement, both the fixed and re- positionable jaws include location pegs which are received within matching holes either in the table itself, or in an intermediate rail member which is itself then secured to a standard machine work table. In this embodiment, the sliding jaws each include an additional third member the position of which is fixed with respect to the worktable and the first and second members are slidably mounted on the third member.

Conveniently, the second member is a ball bearing out of which approximately one quarter segment in one variant has been removed, the remainder representing approximately three quarters of a sphere, with the missing quarter providing the edges which, in use, engage with the faces of the workpiece at a corner thereof. The second member fits within correspondingly shaped slight recesses (ball seats) in vertical and horizontal faces of the first member, and is retained within said recesses by suitable retaining means. One suitable retaining means comprises a spring one end of which is inserted into a hole drilled into the first member and the other end of which is inserted into a hole drilled into the second member, the two ends being retained within their respective holes by means of spring retaining pins inserted through channels drilled into the two members from the outside to the first mentioned holes at right angles thereto.

The ball bearing is preferably coated with titanium nitride to improve resistance to wear and corrosion.

Having clamped the workpiece (which may have rough and unsquare faces) in the system, as clamping pressure is applied the second member (ball bearing) rotates in the ball seats of the first member, until the angle of the jaw matches the angle of the rough, sawn-off faces, thus eliminating any forces which would tend to lift the workpiece off the table.

In practice it has been found that performance is improved if the quarter segment is removed to just slightly beyond the true centre of the bearing, as illustrated in the accompanying drawings.

In the preferred embodiment, the ball seat on the vertical face of the first member is disposed at an angle (typically 81 to 82 degrees to the horizontal), the effect of which is to push the ball downwards to the horizontal ball seat thus locking up the ball so that it can be carried from setup to machine. This arrangement also allows smaller workpieces to be held with only two jaws, rather than one on each corner.

In a further alternative embodiment, the second member takes the form of a cylinder having approximately one half cut away along a vertical section line - the cylindrical "back" face of the second member is received within a correspondingly shaped recess in the first member, and is retained using a spring and spring retaining means in the same manner as previously described.

In a further variant, the second member is approximately hemispherical, such that four jaws with such hemispherical second members can be used to clamp a cylindrical workpiece The system is equally suitable for any material - steel, plastics, ceramics, or wood, and for any type of machining processes.

According to a second aspect of the present invention there is provided a clamping system comprising at least two jaws, each jaw comprising a first member having means for mounting the jaw on a suitable support structure, a second member mounted on said first member and having means for receiving a portion of at least one face of a workpiece, the jaw including means for allowing rotation of said second member relative to said first member.

Thus, irregularities in the angular orientation of a particular face or faces of the workpiece may be accommodated.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:- Figure 1 illustrates a workpiece clamped to a machining table using the clamping system of the present invention, Figures 2 and 3 illustrate a fixed jaw, Figures 4, 5 and 6 illustrate a sliding jaw, and Figures 7, 8, 9, 10 and 11 illustrate in various different views an alternative embodiment of the jaw of the present invention, Figures 12, 13, 14 and 15 illustrate an alternative method of securing the fixed jaw with respect to the work table, Figures 16, 1 7, 18 and 19 illustrate an alternative method of securing the sliding jaw with respect to the work table, Figure 20 illustrates a rail which is itself clamped to the work table and which receives both the fixed and sliding jaws, Figure 21 (21A through 21D) illustrates in various different views an alternative embodiment of the fixed jaw, Figure 22 (22A through 22E) illustrates in various different views an alternative embodiment of the sliding jaw, Figure 23 illustrates the clamping system in use for rectangle and square workpieces, Figure 24 illustrates an embodiment of the clamping system in use for round or cylindrical workpieces, Figure 25 illustrates a three jawed variant, for holding round or cylindrical components, and Figure 26 (26a through 26g) illustrates the different types of jaws included in the clamping system of the present invention.

Referring to Figures 1 through 6 of the accompanying drawings, a clamping system 10 according to the present invention typically comprises four jaws - two fixed jaws 12 and two sliding jaws 14. Both types of jaws embody the same principle which is the subject of the present invention - namely a second member comprising a titanium nitride coated stainless steel ball bearing 12b, 14b having approximately one quarter segment removed, which is seated within correspondingly shaped recesses in the first member 12a, 14a. The missing quarter segment of second members 12b, 14b define orthogonal faces 12b',14b' and 12b'', 14b'', these edges engaging the respective corner faces of the workpiece The bearing 12b, 14b is seated within the ball seats in the vertical and horizontal faces of the first member 12a and held in place by spring 23. The ball bearing is free to pivot within the seats, but lifting or movement is prevented by the action of the spring which is retained at each end within holes 25, 26 drilled into the bearing 12b and first member 12a, respectively, by means of spring retaining pins 24 inserted through channels in the first and second members specifically drilled at right angles to holes 25, 26.

The first member 12a of the fixed jaw has a threaded hole 13 whereby the member 12a can be secured to the machining table 20 by means of a threaded bolt. The first member 14a of the sliding jaw has a protrusion 14c which extends first downwardly, and then outwardly at each side, forming wings which are radiused at the corners - these wings slide along an appropriately shaped channel (not shown) in the table 20, as the jaws 14 are forced along the channel by operating means 22.

To clamp a square or rectangular workpiece, the first two corners are located in the second members 12b of the jaws 12, which have previously been secured in the desired position on the table 20. The other two corners are then located in the second members 14b of the sliding jaws 14, the latter then being urged towards the fixed jaws, the protrusions 14c sliding in corresponding channel members in the table, utilising operating means 22. As the clamping pressure is applied, the bearings 12b, 14b rotate in their respective recesses of the first members 12a, 14a, until they match the angle of the corner faces of the workpiece.

Referring now to Figures 7 through 11, an alternative embodiment comprises fixed jaw 30 and sliding jaw 32, the former comprising first member 30a and second member 30b and the latter comprising first member 32a and second member 32b.

In each case the second member is approximately one half of a cylinder, the cut face 30b' (32b') being the face which, in use, engages the workpiece, and this is retained within a recess in the first member 30a (32a) shaped to correspond to the cylindrical "back" of the second member, by means of spring 23' secured at each end within holes 34, 36, by means of retaining pins 24' inserted as described above. First member 30a of the fixed jaw 30 includes an internally threaded hole 13' by which the member 30a may be secured to the machining table, as previously described, and first member 32a of the sliding jaw 32 incudes a protrusion 32c, for the same purpose as protrusion 14c on sliding jaw 14.

In Figures 12 to 15, a variation on the embodiment shown in Figures 2 and 3 is illustrated, in which instead of the threaded hole 13, two location pegs 38, 40 are provided, either affixed to or integrally formed with first member 30a', in addition to an internally threaded hole 39 disposed centrally between the two pegs. The corresponding variant on the sliding jaw comprises an additional member in the form of a base member 42 having a slide channel formed therein, and a stop member 42a disposed at right angles to the base member. The second member 14b is seated to and retained within first member 48, as previously described, and first member 48 includes a protrusion 48c similar to protrusion 14c in Figure 4, which slides within the channel in base member 42 as member 48 is forced towards or away from member 42a by screw advancement means 50.

The locating pegs 44, 46 of base member 42 (sliding jaw) and locating pegs 38, 40 of first member 30a' (fixed jaw) are inserted within selected holes 52 on the rail 54 (intermediate member) shown in Figure 20, and the rail 54 is clamped to the machine work table by means of suitable fixing means and holes 56. This enables a modular system to be provided, without the need for expensive slide mechanisms as would be the case for the arrangement shown in Figure 1.

Figure 21 illustrates various modifications to the fixed jaw - the thickness of member 60 is increased by approximately 5mm to 15mm, and the face 60a is also lengthened, making the jaw more rigid. The ball seat on the vertical face of member 60 is also modified in that it is disposed at an angle of 81.69 degrees, (see Figure 22c for enlarged detail) which has the effect of pushing the ball 61 down towards the horizontal ball seat of member 60, locking up the ball when in use so that it can be carried from setup to machine and will also allow smaller jobs to be held with two jaws, rather than one on each corner.

In Figure 22, corresponding modifications are made to the sliding jaw - the vertical ball seat is disposed at 81.69 degrees as for the fixed jaw, the thickness of member 66 is increased , and a friction pad 70 is included to eliminate any wear and subsequent play between the sliding jaw and the dovetail 64c.

In Figure 23, four of the jaws (two sliding jaws 68,64,66 and two fixed jaws 61,60) are illustrated mounted on rails 54, holding a square (or rectangular) workpiece 70.

In Figure 24 a variant of the system is illustrated, in which the members 61,68 are replaced by hemispherical members 72 (all other components being identical) which are suitable for holding a circular or cylindrical workpiece 74.

In Figure 25, a further variant of the system comprises three locking jaws 76 mounted in the same manner as the previously described jaws, to base plate 78 which itself fits on the machine. The three jaws 76 clamp onto cylindrical boss 80 on the undersurface of head 82. Interchangeable head tooling 84 is clamped to head 82 and, via reference base 78, to the machine.

In Figure 26, perspective views of the various different jaws are shown - auto levelling sliding jaw in Figure 26a, auto levelling fixed jaw in Figure 26b, auto levelling sliding vee jaw in Figure 26c, and auto levelling fixed vee jaw in Figure 26d. Further additional jaws include a sliding, solid pull down jaw 90, a fixed solid pull down jaw 92, and a plate clamping unit 94 as illustrated in Figures 26e through 26f respectively.