GB2513843A

GB2513843A - Mill turn machine

Info

Publication number: GB2513843A
Application number: GB1307691.4A
Authority: GB
Inventors: Matthew Farnsworth; Adam Brown; Daniel James Smith
Original assignee: University of Sheffield
Current assignee: University of Sheffield
Priority date: 2013-04-29
Filing date: 2013-04-29
Publication date: 2014-11-12
Also published as: GB201307691D0; EP2991793A1; WO2014177851A1; TW201501854A

Abstract

The machine includes a first spindle 20 and a second spindle (not shown), both journalled for rotation about a rotation axis z. A first chuck 22 and a second chuck (not shown) on the spindles hold a workpiece between them about the axis. A clutch 24 between at least one of the chucks and its spindle includes a driving 26 and a driven 30 component. The driven component is releasably lockable to the driving component so that the clutch has a first, unlocked and a second, locked configuration. An alternative machine includes a saddle component to support a work piece during machining. A method of referencing a mill turn machine includes configuring a clutch in an unlocked position, referencing a spindle and configuring the clutch in a locked position. A further method of referencing includes configuring first and second spindles, fixing a workpiece to two chucks, configuring a clutch, referencing the spindles, rotating and machining the workpiece. A method of machining includes configuring two spindles, fixing a workpiece to two chucks, positioning a saddle component to support the workpiece and machining sides of the workpiece.

Description

MILL TURN MACHINE

[0001] This invention relates to a mill turn machine and fixtures thereof. In particular this invention relates to a mill turn machine comprising a clutch and/or a saddle component and to those components for use in a mill turn machine.

BACKGROUND

[0002] Mill turn machines are used to machine material workpieces into component parts for a number of uses. These machines usually comprise a spindle and a chuck for holding a workpiece in an x, y, z position. The spindle is configured to rotate about a rotation axis and has a "c-axis position" that defines its rotational orientation about the rotation axis relative to a known zero position. A machining head is positioned by a numerically controlled machining arm to machine the workpiece while it is held stationary (milling operation) or as it is being rotated about the c-axis (turning operation). To accurately position the machining arm, the machine must know the x, y, z position of the workpiece as well as its c-axis position. The c-axis is generally concentric with the z-axis. To ensure accuracy, the spindle is referenced/indexed to the zero position of the c, x, y and z axes before a machining operation commences.

Referencing may also be necessary after an emergency shutdown of the machine as caused by, for example, a power cut, human intervention, error, etc. [0003] The workpieces commonly machined in mill turn machines are long thick-walled components which are held in the chuck of the spindle and extend axially therefrom. By "thick-walled" is meant a component of such rigidity that it is self-supporting. A second spindle may be provided at the opposite end of the workpiece to the first spindle and used as a slave support to the workpiece. That is to say, the second spindle is used to hold the workpiece in the x, y, z position but allows it to freely rotate in the c-axis. However, when milling thin-walled components (ie those that are not sufficiently self-supporting to be held at one end only and machined), it is often necessary to provide torsional suppoit for the thin-walled component from the first and the second spindle. In such a configuration, the second spindle must be driven.

However, driving the second spindle requires that it is also referenced/indexed in the c-axis.

[0004] Each spindle is referenced in the same direction with respect to its direction of rotation facing the workpiece, either clockwise or anticlockwise. The referencing direction is normalised with respect to each spindle so that, where the spindles are not working simultaneously on the same workpiece, the machine is able to reference each separately. In this way a machining operation on either spindle will have the same tolerances. Therefore, when the machine is configured to hold a workpiece between two spindles, on a central axis, the spindles are referenced in opposite directions about that axis. This means that the workpiece must be removed prior to referencing, which causes significant delays in the machining process.

[0005] Even though a thin-walled workpiece may be supported at both ends by the first and second spindles, when performing milling operations thereon, the workpiece might still require support between the spindles in order to reduce vibration caused by milling the milling operation and to speed-up the process.

[0006] It is an object of the present invention to address the problems identified above and provide support for milling thin-walled objects.

BRIEF SUMMARY OF THE DISCLOSURE

[0007] In accordance with the present invention there is provided a mill turn machine comprising: a first spindle journalled for rotation about a rotation axis; a second spindle journalled for rotation about said rotation axis and facing said first spindle; first and second chucks on the first and second spindles adapted to hold a workpiece between them about said axis; and a clutch between at least one of said first and second chucks and its spindle, said clutch comprising a driving and a driven component, said driving component being connectable to said first or second spindle for rotation about said axis, and said driven component being connectable to said first or second chuck and rotatably journalled about said driving component for rotation about said axis and wherein said driven component is releasably lockable to said driving component so that said clutch has a first, unlocked and a second, locked configuration, [0008] whereby a workpiece secured between the chucks on the first and second spindles is rotatable by one spindle in a direction of rotation without rotating the other spindle in that direction when the clutch between said other spindle and its chuck, being the first or second spindle on which said clutch is disposed, is in said first, unlocked configuration. In a preferred embodiment, said driven component is locked to said driving component by bolting the two components together. The driven component and the driving component can be unlocked by removing the bolts.

[0009] In an alternative embodiment, said driven component is movable along said axis, with respect to said driving component, between a first unlocked location and a second locked location. In that event, said clutch may comprise a keyed joint having at least one key and at least one key slot, wherein in said first unlocked configuration, said key is disengaged with said key slot, and in said second locked location, said key is engaged with said key slot.

[0010] In a further preferred embodiment said driving component further comprises a bore for rotatablyjournaling a shaft of said driven component. Preferably, said shaft has an external diameter and comprises a first driven end and a second chuck end. Said first driven end may have a diameter smaller than said external diameter so that a taper is formed at said first driven end. Optionally said bore comprises a bush having an internal diameter greater than said external diameter of said shaft.

[0011] In a combination of the preferred embodiments, said bush may comprise said at least one key slot and said at least one key is disposed on an outside of said shaft.

[0012] Preferably said driven component is integrally formed with said first chuck.

[0013] In a preferred embodiment, the clutch is disposed between the first spindle and its chuck and there is no clutch between the second spindle and its chuck, so that in said first unlocked configuration only said first spindle is rotatably unlocked with respect to said workpiece, and in said second locked configuration said first and second spindles are rotatably locked to said workpiece.

[0014] In another aspect, the present invention provides a mill turn machine comprising: a first spindle journalled for rotation about a rotation axis; a second spindle journalled for rotation about said rotation axis and facing said first spindle; first and second chucks on the first and second spindles adapted to hold a workpiece between them about said axis, the workpiece having first and second sides; and a saddle component adapted to support said workpiece during machining of the second side of said workpiece, said saddle component comprising a first bed adapted to fit against said first side of said workpiece and having a profile corresponding to the first side of said workpiece after machining thereof, opposite to said second side, to provide said support.

[0015] Thus, the first bed may not be ideally suited to support the second side of the workpiece during machining of the first side, but where the first side is the side of the workpiece to be machined first, the workpiece is likely to have greater integrity so that universal support provided by the saddle is not so important for efficient machining. However, once the first side has been machined and the workpiece is turned over to machine the second side, significant material of the first side may have been removed rendering the workpiece liable to vibration if not adequately supported. Thus the first bed is shaped to fit the first side of the workpiece after it has been machined so that much greater support of the workpiece is provided.

[0016] Optionally, said saddle is connectable to a moveable turret, said turret being movable between a first disengaged position and a second engaged position, wherein in said second engaged position, said saddle provides said support for said machining.

[0017] In accordance with another aspect of the present invention, there is provided a clutch for a mill turn machine comprising the features of the clutch defined in relation to the mill turn machine as described above.

[0018] In accordance with another aspect of the present invention, there is provided a saddle component for a mill turn machine comprising the features of the saddle component defined in relation to the mill turn as described above.

[0019] In accordance with another aspect of the present invention, there is provided a method of referencing a mill turn machine comprising: a first spindle journalled for rotation about a rotation axis; a clutch; and a first chuck adapted to hold a workpiece, said method comprising the steps of: a) configuring said clutch in a first unlocked position; b) referencing said first spindle by rotating said first spindle about said rotation axis without rotation of the chuck; and, c) configuring said clutch in a second locked position.

[0020] In a preferred embodiment of the method of referencing a mill turn machine said mill turn machine further comprises: a second spindle journalled for rotation about said rotation axis; and a second chuck adapted to hold said workpiece, wherein step b) further comprises the step of: d) referencing said second spindle by rotating said second spindle about said rotation axis.

[0021] Optionally, steps a) and c) further comprise moving a driven component of said clutch along said axis with respect to a driving component of said clutch. Optionally, said workpiece is held between said first and second chucks and said first chuck is connectable to said driven component of said clutch, wherein said movement of said driven component is effected by movement of said second spindle along said axis. Said method may further comprise the step of: e) moving a saddle component to an engaged position, wherein said saddle component is adapted to support said workpiece in said engaged position.

[0022] In another aspect of the invention, a method of machining a workpiece in a mill turn machine comprises the steps of: a) configuring a first and a second spindle to rotate about a rotation axis, said first spindle comprising a clutch and a chuck, said second spindle comprising a chuck; b) fixing the workpiece at a first end to said first chuck and at a second end to said second chuck; c) configuring said clutch in an unlocked configuration; d) referencing said first spindle; e) referencing said second spindle; f) configuring said clutch in a locked configuration; g) rotating said workpiece to a machining position; h) machining said workpiece using a tool; i) removing said workpiece from the first and second chucks.

[0023] Optionally, step g) further comprises the step of positioning a saddle component to support a side of the workpiece during the machining of an opposite side of the workpiece.

[0024] In another aspect of the invention, a method of machining a workpiece in a mill turn machine comprises the steps of: a) configuring a first and a second spindle to rotate about a rotation axis, said first spindle comprising a chuck, said second spindle comprising a chuck; b) fixing the workpiece at a first end to said first chuck and at a second end to said second chuck; c) positioning a saddle component to support a second side of the workpiece; d) machining a first side of the workpiece to produce a machined first side; e) moving said saddle component away from said workpiece; f) rotating said workpiece to provide for machining said second side; g) positioning said saddle component to support said machined first side, wherein said saddle component is configured to fit said first side after said machining step d); h) machining said second side of the workpiece; i) removing said workpiece from the first and second chucks.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Embodiments of the invention are further described hereinafter, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a mill turn machine spindle according to the prior art; Figure 2 is a perspective view of a mill turn machine spindle according to an embodiment of the present invention; Figure 3a is a schematic cross-section of a clutch of a mill turn machine in a locked configuration according to an embodiment of the present invention; Figure 3b is a schematic cross-section of a clutch of a mill turn machine in an unlocked configuration according to an embodiment of the present invention; Figure 3c is a schematic cross-section of a clutch of a mill turn machine in an unlocked configuration according to an embodiment of the present invention; Figures 4a and b are respectively a schematic cross-section on the line A-A in Figure 4b of a clutch of a mill turn machine in a locked configuration according to an embodiment of the present invention, and a side view of the same arrangement; Figure 5a is a schematic representation of a mill turn machine according to an embodiment of the present invention; and Figure Sb is a top view of a bed of a saddle component of a mill turn machine according to an embodiment of the present invention.

DETAILED DESCRIPTION

[0026] The following description provides detailed examples of a mill turn machine according to some embodiments of the present invention. Figure 1 shows a spindle 10 of a mill turn machine (not shown) as known in the art. The spindle is rotatable in a rotation c-axis about the z-axis 12. Spindle jaws 14 are used to clamp a chuck 16 adapted to hold a workpiece (not shown) between chuck jaws 18. The workpiece is machined using a tool positioned on a numerically controlled arm. The machining operation may take the form of rotating the workpiece and placing a tool in its path (also known as turning), or moving a rotating tool with respect to the stationary workpiece (also known as milling).

[0027] In either of the milling or turning operations, the workpiece is held in a known x, y, z position by the chuck and, in turn, the spindle. The rotation of the spindle about the z-axis is known as a c-axis rotation and has a c-axis value known by the machine. A zero position on the c-axis is determined by referencing the spindle, which is usually performed by rotating the spindle to a known position and telling the machine that in that position the c-axis is zero, or another known value.

[0028] Referencing is commonly performed on start-up of the machine or before each machining operation. Some machines may also require referencing after emergency stop of the machine tollowing scenarios such as a power cut or human intervention. Where the workpiece is held on only one spindle, referencing of that spindle is not a problem. However, it is desirable to machine workpieces that are held between two spindles. Commonly, the first spindle as described above will be driven and will therefore be referenced as and when necessary. The second spindle will usually act as a slave wherein it supports the workpiece in an x, y, z direction but does not prevent or create c-axis movement. In this approach, the second spindle does not need to be referenced as the first spindle provides all of the drive. By driving the spindle, the machine is also able to fix/hold the spindle in a known location to provide torque in resistance to a machining (milling) operation.

[0029] For thick-walled components, the torque is transmitted through the workpiece so that machining at an z-axis position distal to the first spindle is resisted by the c-axis torque provided at the first spindle. For thin-walled components, this does not hold true! even when the workpiece is supported in both spindles. The thin-wall is not rigid enough to transfer the torque and machining at a z-axis position distal to the first spindle may result in vibration of the workpiece. To overcome this, it is desirable also to drive the second spindle, which is holding the workpiece at the opposite end to the first spindle. Driving the second spindle provides torque at a location distal to the first (but proximal to the second) spindle and therefore helps to limit vibration of the workpiece during machining. However, problems during machining of a workpiece may result in the need to recalibrate each of the spindles. This requires removal of the workpiece from one or both of the chucks. This is time consuming and may result in errors or damage to the workpiece. In one of its aspects, the present invention addresses this problem.

[0030] Figure 2 shows an embodiment according to the present invention where a mill turn machine comprises a first spindle 20 and a first chuck 22 configured to rotate in a rotation c-axis about the z-axis and a second chuck (not shown) also configured to rotate in the rotation c-axis about the z-axis. A clutch 24 is positioned between the first spindle 20 and the first chuck 22.

Figure 2 shows the clutch 24 in expanded form to comprise a driving component 26, a bush 28 and a driven component 30. The driving component is clamped in jaws 21 of the first spindle.

The bush 28 fixably locates inside a bore 32 of the driving component 26. and has an internal diameter 34 substantially similar to but greater than an external diameter 36 of the driven component 30 and so that the driven component 30 can rotatably slide inside the bush 28. The driven component 30 is connected to the first chuck 22. This can be via a permanent or releasable fixing.

[0031] When assembled, the bush 28 fits inside the bore 32 of the driving component 26. The driven component 30 then slides into the bush 28. The driven component 30 is essentially a shaft that may comprise a taper 38 at a first driven end 40 to provide a smaller end diameter and therefore aid engagement of the driven component with the bush. A slip region 42 is provided on the external diameter of the driven component such that insertion of the driven component inside the bush to a depth where the end 43 of the bush is in the slip region 42 permits free rotation of the driven component with respect to the bush and therefore with respect to the first spindle 20 also.

[0032] A keyed region 44 is provided on the external diameter of the driven component 30 distal to the driven end 40 such that insertion of the driven component inside the bush to a depth where the end 43 of the bush is in the keyed region 44 locks the driven component 30 to the bush 28, and thus in turn to the driving component 26, to enable torque transfer from the first spindle to the first chuck. This is achieved by providing one or more of the keys 46 on the driven component that engage with one or more key slots 48 in the bush 28. The keys 46 extend in a direction parallel to the z-axis and up to the slip region 42. Therefore, a predetermined axial movement of the chuck in the z-axis allows the machine to switch between a first unlocked and a second locked configuration and vice-versa.

[0033] Figures 3a-c further depict the first unlocked and second locked configurations.

Turning first to Figures 3b-c, the clutch component 24 is configured so that the depth of insertion 52 is less than the axial length of the slip region 42. Figure 3b shows a cross-section through a region of the clutch where the key slots 48 and the keys 46 are present. Figure 3c shows a cross-section through a region of the clutch where the key slots 48 are not present but the keys 46 are present. From these figures and the above description, it is seen that when the driven component 30 is inserted into the bush to a depth within the slip region 42, the keys do not enter the key slots and so the driven component is free to rotate about the rotation axis 12.

The diameter of the slip region is such that the driven component is supported in the x and y direction.

[0034] Figure 3a shows a cross-section through the clutch in the second, locked configuration.

Here the depth of insertion 52 of the driven component is greater than the axial length of the slip region 42 such that the keys 46 engage with the key slots 48. The depth of insertion 52 of the driven component need only be enough for the keys 46 to engage with the key slots 48. It is, of course, preferable for the depth of insertion 52 to determine that the keys 46 fully engage with the key slots 48 because during manufacturing, the torque is transmitted through the keys, which if not fully engaged may fracture.

[0035] The engagement of the keys 46 with the key slots 48 rotatably locks the driven component 30 to the driving component 26 via the bush 28 such that the driven component cannot freely rotate inside the driving component. Therefore, as mentioned above, in this configuration the clutch transmits torque from the spindle to the clutch. It is this locked configuration that is used during the machining operations while the unlocked configuration, schematically shown in Figures 3b-c, is used for referencing the machine.

[0036] The axial movement of the first chuck is effected by movement of a workpiece (not shown) which is held in the chuck jaws 50 of the first and second chucks. Axial movement of the second chuck is transferred by the workpiece to axially move the first chuck between the first unlocked and the second locked configuration. The position of the second chuck is determined by the position of the second spindle, which is controlled by the mill turn machine.

Therefore, on referencing of the machine while the workpiece is in place, the machine moves the second spindle away from the first spindle to unlock the clutch 24. The first and second spindles are then individually referenced before the machine relocks the clutch 24 by moving the second spindle towards the first spindle. During this operation the x and y position of the workpiece is retained so that the position of the workpiece does not also require calibration.

[0037] It is possible that movement of the workpiece in the z direction might inadvertently disengage the key 46 from the slot 48. This could be caused by dimensional instability of the workpiece. Figures 4a and 4b show an alternative embodiment of the present invention. Here, the bush 28' fits inside the bore 32' of the driving component 26'. The driven component 30' slides in the bore of the bush 28' and in which it is freely rotatable. Bolts 129 can be introduced through flanges 130 and 131 on the driving and the driven components to lock the driving and the driven components together. The driven component forms a pad of, or is connected by bolts (not shown) to, a standard chuck 22' (as described above). For indexing the machine, the bolts 129 connecting the driven and the driving components are removed, allowing independent c axis rotation of the driven and driving components. By using this arrangement disengagement of the clutch by accidental or unintentional separation of the driving and driven components can be avoided.

[0038] In another embodiment (not shown) said driven and driving components include an electromagnetic connection between them, locking them together. Provided torque transmission between the components is possible, this arrangement may be satisfactory. It may permit automatic control of the locking and unlocking of the clutch so formed. In order to provide torque transmission, said driven and driving components may comprise facing discs or like surfaces which are magnetically connected. Radially defined (or at least non-circumferentially defined) inter-engaging ridges and grooves may be disposed in the facing surfaces to resist any relative rotation between the discs when magnetically connected together.

[0039] Figure 5 shows another aspect of the present invention. Milling of components requires that the workpiece is held sufficiently stationary to provide a stable surface for accurate milling. On the z-axis, stability is provided by mounting the workpiece between two spindles/chucks lOa,b. However, if the component is thin walled, even on the axis the workpiece may deflect. Off the z-axis, for large/thick-walled components, the stability is provided by the torque supplied by the spindle which is transferred through the workpiece. This is the case especially if both spindles/chucks lOa,b are driven to counter deflections imposed by the milling tool. For smaller, thin-walled components, however, the torque is possibly not transferred. Instead the workpiece is likely to bend or vibrate during machining by a tool pressing onto the thin workpiece. This is particularly the case when machining a long way from the z-axis, near the middle between the two spindles lOa,b of the mill turn machine. This means that machining has to be performed slowly and/or less efficiently.

[0040] Bending and vibration are limited by the present invention enabling the provision of torque at both ends of the workpiece and the embodiment shown in Figures 5a,b that supports the workpiece during off-axis milling.

[0041] Figures 5a,b schematically show a saddle component 60 according to an embodiment of the present invention. The saddle component is used when milling a thin-walled workpiece 62 held between a first spindle/chuck ba and a second spindle/chuck lOb, each being centrally located on a z-axis 12'. A machine arm 64 using a milling tool 66 is configured to mill a first side 68 of the workpiece 62 to form a first profiled side from a blank. The saddle component 60 comprises a bed 70 adapted to support the second side (underside to the first side 68) of the workpiece during machining of the first side i.e. the bed resists the downward force of the milling tool 66, as well as torsional effects when machining off the z-axis. Supports 72 are fixable to the non-supporting side of the bed 70 and are configured to rest on a surface. The supports 72 may be shaped to attach the bed to a moveable turret (not shown) inside the mill turn machine.

In known mill-turn machines, moveable turrets can move in the x, y, z axis and support a tool used to machine the workpiece during a turning operation (see above description). Here, the supports 72 are adapted to attach to the moveable turret so that the positioning of the turret in turn positions the bed 70 under the workpiece 62.

[0042] After milling the first side, the saddle component 60 is moved away (downward or otherwise) from the workpiece 72 and the machining arm 64 is moved away from the workpiece.

II the second side of the workpiece 72 then requires machining, the spindles 12a, 12b, rotate the workpiece through 180 degrees in the c-axis, about the z-axis. The bed is then repositioned under the first side of the workpiece 62. which is now facing downwards, to support the workpiece while the machining arm 64 machines the second side.

[0043] In accordance with an aspect of the present invention, the bed 70 comprises a surface profile 74, for example as shown in Figure Sb. The surface profile 74 comprises reverse impressions 76 of features of the profiled first side of the workpiece (as milled by the machine before the workpiece is inverted) and so that the features (not shown) on profiled first side 62 of the workpiece fit onto corresponding features 76 on the surface 78 of the bed. This enables the bed to support parts of the workpiece that have been machined (for example, to have a thin profile) during the machining of the first side.

[0044] Machining of the first surface 62 generally creates recesses (not shown) in the surface 68. Therefore, features 76 will comprise upstanding protrusions from the surface 78 of the bed 70. This means, that, when machining the first surface 68, the workpiece 62 is supported on a plurality of the protrusions 76; indeed, as many as there are recesses to be formed in the surface 68. Consequently, some planning is required of the number, location and depth of recesses to be machined in surface 68 to avoid undesirable supporting of the workpiece during machining of the first side 68. Also, it may be that the features 76 of the bed 70 do not fill all of the recesses in the surface 68. Likewise, some features (eg feature 80) of the bed may be only provided for the support they represent of the workpiece during machining of the first side 68, but which features 80 are removed when the second side is machined because no recess into which the feature 80 would fit when machining the second side is actually desired or formed in the first side 68.

[0045] More than two surfaces of the workpiece may be presented for machining, in which event more than one saddle 60 might be employed.

[0046] The bed 70 of the saddle component 60 is preferably made from a vibration resistant material that does not resonate at a frequency close to that generated by the milling operation.

A polymei material such as polyurethane is often a suitable material, which may deform slightly on engagement of the saddle with the workpiece. The workpiece is generally of a much harder material. It should not itself deform under contact from the saddle. The force with which the saddle is pressed against the workpiece must not result in any measurable deformation of the workpiece, but may result in some deformation of the saddle and potentially more uniform support for the workpiece. Dampening in the supports 72 may be provided to remove unwanted vibrations from the workpiece, but the bed must remain stationary to provide suitable support to the machining operation. It is preferred that the saddle component is used in conjunction with the clutch component described in relation to Figures 2-3, but the saddle component may be used where a clutch is not required, and vice versa.

[0047] Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0048] Features, integers, characteristics or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments.

The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0049] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

Claims

CLAIMS1. A mill turn machine comprising: a first spindle journalled for rotation about a rotation axis; a second spindle journalled for rotation about said rotation axis and facing said first spindle; first and second chucks on the first and second spindles adapted to hold a workpiece between them about said axis; and a clutch between at least one of said first and second chucks and its spindle, said clutch comprising a driving and a driven component, said driving component being connectable to said first or second spindle for rotation about said axis, and said driven component being connectable to said first or second chuck and rotatably journalled about said driving component for rotation about said axis and wherein said driven component is releasably lockable to said driving component so that said clutch has a first, unlocked and a second, locked configuration, whereby a workpiece secured between the chucks on the first and second spindles is rotatable by one spindle in a direction of rotation without rotating the other spindle in that direction when the clutch between said other spindle and its chuck, being the first or second spindle on which said clutch is disposed, is in said first, unlocked configuration.
2. A mill turn machine as claimed in claim 1, wherein said clutch comprises said driven component being movable along said axis, with respect to said driving component, between said first, unlocked and second, locked configurations.
3. A mill turn machine as claimed in claim 2, wherein said clutch comprises a keyed joint having at least one key and at least one key slot, wherein in said first unlocked configuration, said key is disengaged with said key slot, and in said second locked configuration, said key is engaged with said key slot.
4. A mill turn machine as claimed in claim 1, wherein said clutch further comprises bolts, wherein, in the second locked configuration, the bolts bolt the driving and driven components together, and, in the first unlocked configuration, said bolts are removed and the driven and driving components can rotate in the c axis with respect to one another.
5. A mill turn machine as claimed in claim 1, wherein said clutch comprises a selectively actuatable magnetic connection between said driven and driving components.
6. A mill turn machine as claimed in claim 5, wherein said driving and driven components comprise facing surfaces parallel a radial plane with respect to said axis which surfaces are clamped together by said selectively actuatable magnetic connection, inter-engaging ridges and grooves being disposed in said facing surfaces to resist any relative rotation between the discs when magnetically connected together.
7. A mill turn machine as claimed in claim 6, wherein said inter-engaging ridges and grooves are radially disposed in said facing surfaces.
8. A mill turn machine as claimed in any preceding claim, wherein said driving component further comprises a bore for rotatably journaling a shaft of said driven component.
9. A mill turn machine as claimed in claim 8, wherein said shaft has an external diameter and comprises a first driven end and a second chuck end.
10. A mill turn machine as claimed in claim 9, wherein said bore comprises a bush having an internal diameter greater than said external diameter of said shaft.
11. A mill turn machine as claimed in any preceding claim, wherein said driven component is integrally formed with said first chuck.
12. A mill turn machine as claimed in any preceding claim, wherein the clutch is disposed between the first spindle and its chuck and there is no clutch between the second spindle and its chuck, so that in said first unlocked configuration only said first spindle is rotatably unlocked with respect to said workpiece, and in said second locked configuration said first and second spindles are rotatably locked to said workpiece.
13. A mill turn machine comprising: a first spindle journalled for rotation about a rotation axis; a second spindle journalled for rotation about said rotation axis and facing said first spindle; first and second chucks on the first and second spindles adapted to hold a workpiece between them about said axis, the workpiece having first and second sides; and a saddle component adapted to support said workpiece during machining of the second side of said workpiece, said saddle component comprising a first bed adapted to fit against said first side of said workpiece and having a profile corresponding to the first side of said workpiece after machining thereof, opposite to said second side, to provide said support.
14. A mill turn machine as claimed in claim 13, wherein said saddle is connectable to a moveable turret, said turret being movable between a first disengaged position and a second engaged position, wherein in said second engaged position, said saddle provides said support for said machining.
15. A mill turn machine as claimed in claim 13 or 14 having the features of the mill turn machine as claimed in any of claims 1 to 12.
16. A clutch for a mill turn machine comprising the features of the clutch defined in relation to the mill turn machine as claimed in any of claims ito 12.
17. A saddle component for a mill turn machine comprising the features of the saddle component defined in relation to the mill turn machine as claimed in claim 13 or 14.
18. A method of referencing a mill turn machine comprising: a first spindle journalled for rotation about a rotation axis; a clutch; and a first chuck adapted to hold a workpiece, said method comprising the steps of: a) configuring said clutch in a first unlocked position; b) referencing said first spindle by rotating said first spindle about said rotation axis without rotation of the chuck; and, c) configuring said clutch in a second locked position.
19. A method as claimed in claim 18, wherein said mill turn machine further comprises: a second spindle journalled for rotation about said rotation axis; and a second chuck adapted to hold said workpiece, wherein step b) further comprises the step of: d) referencing said second spindle by rotating said second spindle about said rotation axis.
20. A method as claimed in claim 18 or 19, wherein steps a) and c)further comprise moving a driven component of said clutch along said axis with respect to a driving component of said clutch.
21. A method as claimed in claims 19 and 20, wherein said workpiece is held between said first and second chucks and said first chuck is connectable to said driven component of said clutch, wherein said movement of said driven component is effected by movement of said second spindle along said axis.
22. A method as claimed in any of claims 18 to 21, further comprising the step of: e) moving a saddle component to an engaged position, wherein said saddle component is adapted to support said workpiece in said engaged position.
23. A method of machining a workpiece in a mill turn machine, said method comprising the steps of: a) configuring a first and a second spindle to rotate about a rotation axis, said first spindle comprising a clutch and a chuck, said second spindle comprising a chuck; b) fixing the workpiece at a first end to said first chuck and at a second end to said second chuck; c) configuring said clutch in an unlocked configuration; d) referencing said first spindle; e) referencing said second spindle; f) configuring said clutch in a locked configuration; g) rotating said workpiece to a machining position; h) machining said workpiece using a tool; i) removing said workpiece from the first and second chucks.
24. A method of machining a workpiece as claimed in claim 23, in which step g) further comprises the step of positioning a saddle component to support a side of the workpiece during the machining of an opposite side of the workpiece.
25. A method of machining a workpiece in a mill turn machine, said method comprising the steps of: a) configuring a first and a second spindle to rotate about a rotation axis, said first spindle comprising a chuck, said second spindle comprising a chuck; b) fixing the workpiece at a first end to said first chuck and at a second end to said second chuck; c) positioning a saddle component to support a second side of the workpiece; d) machining a first side of the workpiece to produce a machined first side; e) moving said saddle component away from said workpiece; f) rotating said workpiece to provide for machining said second side; g) positioning said saddle component to support said machined first side, wherein said saddle component is configured to fit said first side after said machining step d); h) machining said second side of the workpiece; i) removing said workpiece from the first and second chucks.
26. A mill turn machine substantially as hereinbefore described with reference to the drawings.
27. A clutch for a mill turn machine substantially as hereinbefore described with reference to the drawings.
28. A saddle component for a mill turn machine substantially as hereinbefore described with reference to the drawings.