Patent Publication Number: US-8540552-B2

Title: Water jet cutting machine

Description:
The present invention relates to a profile cutting apparatus having improved performance, and in particular a waterjet cutting apparatus. 
     BACKGROUND OF THE INVENTION 
     Profile cutting apparatus have been used for some years to cut a variety of materials such as steel, aluminium, glass, marble, plastics, rubber, cork and wood. Examples of profile cutting apparatus include waterjet cutting machines, plasma cutting machines and laser cutting machines. 
     Taking waterjet cutting machines as an example, the work piece is placed over a shallow tank of water and a cutting head expelling a cutting jet is accurately displaced across the work piece to complete the desired cut. The cutting action is carried out by the combination of a very high pressure jet (up to 60,000 psi) of water entrained with fine particles of abrasive material, usually sand, that causes the cutting action. The water and sand that exit the cutting head are collected beneath the work piece in the tank. 
     The abrasive material is usually particles of silica sand, cast iron grit, powdered garnet or alumina. The particle size of the abrasive material is usually between 60 and 150 mesh. 
     The high pressure water jet is usually passed through a venturi that is connected to a vacuum line that is in turn connected to an abrasive metering assembly that meters dry abrasive delivered from a hopper and carried by the vacuum to the cutting head at a desired flow rate that is often between about 100 to 700 grams per minute. 
     This cutting technique is very powerful and can cut through stainless steel as thick as 100 mm or 4 inches. The cutting process can also be extremely accurate with tolerances of plus or minus 0.1 mm or 0.004 inches. The process is clean, fast and reliable. Nevertheless, the resulting cutting path is limited to the movement parameters of the apparatus and certain cutting paths of varying degrees of sophistication are unable to be achieved with known waterjet cutting apparatus. 
     There is therefore a need to improve the performance and versatility of profile cutting apparatus such as waterjet cutting apparatus. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention there is provided a profile cutting apparatus comprising: a cutting head supporting a nozzle through which a cutting medium passes, and at least two drives that drive the cutting head to tilt relative to a vertical axis while driving the cutting head to rotate about the vertical axis, wherein the tilt of the cutting head is achieved by the relative difference in motion between the two drives. 
     In a preferred embodiment of the invention the drives each include a drive shaft and the tilt of the cutting head is achieved by the relative difference in speed and angular displacement between the drive shafts. The drive shaft of one drive rotates a rotary assembly which supports the cutting head and rotates the cutting head around the vertical axis, while the other drive shaft drives a tilt assembly supported on the rotary assembly and tilts the cutting head relative to the vertical axis. The rotary assembly carries the tilt assembly such that the assemblies rotate in unison so that while the drives may operate separately, together they drive the interconnected rotary and tilt assemblies to achieve rotation and tilt of the cutting head. 
     In accordance with the present invention there is further provided a profile cutting apparatus comprising: a cutting head supporting a nozzle through which a cutting medium passes, at least two drives that drive the cutting head to tilt relative to a vertical axis while driving the cutting head to rotate about the vertical axis, and a delivery column through which cutting medium passes from a top thereof and which rotates with the cutting head so that a conduit can deliver the cutting medium from the bottom of delivery column to the cutting head without twisting. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which: 
         FIG. 1  is an isometric view of a waterjet cutting apparatus in accordance with a first embodiment of the present invention; 
         FIG. 2  is a plan view of  FIG. 1 ; 
         FIG. 3(   a ) is a side sectional view of the apparatus taken at section A-A of  FIG. 2 ; 
         FIG. 3(   b ) is an enlarged view of the delivery column and gear drives of  FIG. 3(   a ); 
         FIG. 4  is a front sectional view of the apparatus taken at section B-B of  FIG. 2 ; 
         FIG. 5  is a plan sectional view of the apparatus taken at section C-C of  FIG. 4 ; 
         FIG. 6  is a schematic drawing illustrating the relative movements of the first embodiment of the waterjet cutting apparatus; 
         FIG. 7  schematically illustrates the cutting head assembly of the waterjet cutting apparatus; 
         FIG. 8  is a plan view of waterjet cutting apparatus in accordance with a second embodiment of the present invention; 
         FIG. 9(   a ) is a first side sectional view of an upper half of the apparatus taken at section D-D of  FIG. 8 ; 
         FIG. 9(   b ) is an enlarged view of Area A indicated in  FIG. 9(   a ); 
         FIG. 10  is a second side sectional view of the apparatus taken at section E-E of  FIG. 9(   a ); 
         FIG. 11  is a side sectional view of a lower half of the apparatus taken at section J-J of  FIG. 8 ; and 
         FIG. 12  is a front view of the lower half of the apparatus as seen from the direction of arrow K in  FIG. 11 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
     The present invention relates to a profile cutting apparatus with particular reference made to a waterjet cutting apparatus. Although not specifically described, it is understood that the invention also relates to other profile cutting apparatus including laser and plasma cutting apparatus. 
     The drawings illustrate two embodiments of a waterjet cutting apparatus  10 ,  30 , also described as a cutting head assembly, having improved performance in terms of manoeuvrability and versatility resulting in accurate and complex cutting paths not previously achievable with known waterjet cutting apparatus. The apparatus  10 ,  30  typically form part of a larger waterjet cutting machine (not shown) having arms or tracks in the first three spatial linear dimensions, namely the X, Y and Z dimensions, in order to move the apparatus  10  in these dimensions. The apparatus are typically located above a shallow bath, or tank, of water over which the workpiece sits. 
     The present waterjet cutting apparatus introduces an additional two spatial dimensions of movement, namely a fourth and fifth axis. Such a machine comprising the waterjet cutting apparatus is therefore defined as having five axis of movement. 
     The fourth axis is referred to as the tilt from the vertical axis, ie. the roll about the horizontal axis, while the fifth axis is referred to as the vertical axis around which the waterjet nozzle spins, or rotates. The combination and extent of movement capable on the apparatus&#39; fourth and fifth axis achieves cutting movements not previously attainable. 
     A first embodiment of the waterjet cutting apparatus  10  is illustrated in  FIGS. 1 to 7  and comprises a cutting head  12  supporting a high pressure waterjet nozzle  13  coupled to a source of abrasive material (not shown) deliverable to the nozzle via a vacuum line  90 , wherein the cutting head  12  is driven to be tilted relative to a main vertical axis  15  (see  FIGS. 3(   a ),  3 ( b ) and  4 ) and to also be continuously rotated about the main vertical axis such that the waterjet nozzle  13  can cut a continuous circular path. When the apparatus moves only in the fourth and fifth dimensions to describe a circular path, the circular path described can be greater than 360°. With movement in the first, second and/or third dimensions, together with movement in the fourth and fifth dimensions, endless possibilities of cutting profiles are achievable, for example, a flat spiral coil. 
     The continuous rotation of the waterjet beyond 360° is made possible because electrical cables for motors, etc, and air, water and garnet conduits are largely moved away from the moving cutting head and located above the moving components. In this way the cutting head is free to rotate without twisting and tangling cables and conduits restricting its movement. 
     Furthermore, the tilt movement of the cutting head as well as the rotational movement is driven by the relative difference in motion of separate drives. That is, the motion of the separate drives is interconnected so that one drive function affects the other to produce a combined outcome. This arrangement allows full rotational and tilting movement of the cutting head while keeping drive motors fixed to a base and away from the movement of the cutting head. 
     Two drives are provided in the preferred embodiment of the apparatus, although it may be possible to use more that two drives to achieve the same outcome. For the purpose of clearly describing the apparatus  10 ,  30 , the two drives are loosely attributed to either the tilt movement or the rotational movement. Similarly, the tilt movement of the cutting head  12  is loosely effected by a tilt head assembly  40  and the rotational movement by a rotary head assembly  60 . In reality, the tilt and rotational movement of the cutting head are brought about by the differential manner in which the drives operate. 
     The tilt head and rotary head assemblies  40 ,  60  each include a motor and drive system such as gears, wherein the tilt movement and the rotational movement are driven along the same main vertical axis  15  and are able to interact in unison and/or at different speeds. 
     As illustrated in the first embodiment in  FIG. 1 , the cutting head  12 , tilt head assembly  40  and rotary head assembly  60  are all supported on a fixed platform  16 . The fixed platform  16  itself forms part of a larger cutting machine comprising tracks that move the fixed platform, and hence waterjet nozzle, in the X, Y and Z directions. 
     Delivery of high pressure water and abrasive material is through a delivery column  20  mounted on the fixed platform  16  and rotatable relative to the fixed platform  16  and with the rotary assembly  40  about the vertical axis  15  ( FIG. 3(   a )), which is also the main longitudinal axis of the delivery column  20 . The delivery column is coupled to the cutting head  12  located below the fixed platform by way of service conduits including a high pressure water tube  24 , a garnet tube  25 , and air  26  and vacuum  27  tubes so as to deliver an abrasive high pressure water stream through the nozzle  13 . Tubes  24 - 27  are not illustrated in  FIG. 3(   a ), but are schematically illustrated in  FIG. 7 . 
     The tilt head assembly  40  includes a first motor  42  supported on and fixed to platform  16 . First motor  42  drives a first drive gear  44  ( FIG. 6 ) which in turn drives a column gear  45 . The column gear  45  is axially aligned with the vertical axis  15  and, more specifically, supports the delivery column  20 , which in this instance is also the drive shaft associated with the tilt head assembly. The delivery column  20  is supported through the axial centre of the column gear such that rotation of the column gear rotates, or spins, the delivery column about the vertical axis  15 . Column gear  45  is located above fixed platform  16  and is keyed into a side of delivery column  20  to be fixed thereto. 
     Coupled to the delivery column at a point below the fixed platform  16  is a positive drive belt/pulley arrangement, which is driven by rotation of the delivery column. The drive belt/pulley arrangement includes a first pulley gear  48  coupled to the end of delivery column  20 . Through a drive belt  47  first pulley gear drives a second pulley gear  49  having an offset axis  50  spaced from and parallel to main vertical axis  15 . 
     The second pulley gear  49  is coupled to drive a first bevelled, or mitred, gear  52  aligned along the same offset axis  50  which in turn imparts drive through 90° to a mating second bevelled gear  53 . First bevelled gear  52  is supported to rotate within a bearing housing  54 . Second bevelled gear  53  is fixed to a tilt head frame  55  which supports the cutting head  12 . Rotation of the second bevelled gear rotates the tilt head frame  55  and hence the cutting head. The degree of tilt is greater than ±12° which is the standard maximum for most waterjet cutting machines, and typically at least between ±60° relative to the vertical axis  15 , if not more. 
     This large degree of tilt is possible because of the interaction between the motors of the tilt head assembly and the rotary head assembly and the motors&#39; ability to operate interactively at variable speeds. 
     In the above description of the tilt head assembly incorporating gears and pulley arrangements, it is understood that variations in, and a different selection of, drive mechanisms is possible to achieve the same drive result, namely to tilt the cutting head  12  by driving the tilt action along the main vertical axis on which the delivery column  20  lies. 
     The rotary head assembly  60  includes a second motor  62  driving a second drive gear  64  to rotate a rotary head gear  65 . The rotary head gear  65  drives a rotary head frame  66  which wholly supports the tilt head assembly  40 , and hence the delivery column  20  and cutting head  12 , for rotational movement. Hence, rotation of the rotary head assembly rotates the tilt head assembly, delivery column and cutting head. 
     The rotary head has a hollow shaft  68  which is coaxial with the delivery column, and through which the delivery column is supported therein by column bearings  69 . Delivery column  20  is therefore rotatable within shaft  68 . The shaft  68  of the rotary head is also supported by bearings, namely head bearings  70 , on the fixed platform  16  to allow the rotary head to rotate relative to the fixed platform. 
     Below the hollow shaft, the rotary head frame also includes a bracket  72  which extends down to and is coupled with the tilt head frame  55  through tilt head bearings  74 . More specifically, and as shown in  FIG. 3(   a ), a collar  76  at the lower end of bracket  72 , slides by way of a clearance fit into a corresponding rebate  56  in the tilt head frame  55 . Collar  76  is adapted to rotate within rebate  56  through tilt head bearings  74 . Extending centrally through collar  76  and on bearings  74  is the second bevelled gear  53  which is bolted to tilt head frame  55 . 
     This arrangement therefore allows the second bevelled gear to rotate, or tilt, the tilt head frame  55 , while the entire tilt head frame is supported through the rotary head bracket  72  and collar  76 . 
     Consequently, and with tilt head frame  55  supported by the rotary head assembly  60 , second motor  62  drives the rotary head frame  66  to rotate, or spin, tilt head frame about the vertical axis  15 . Hence cutting head  12  and nozzle  13  can also be rotated about the vertical axis. 
     Because the tilt head assembly and rotary head assembly are differentially connected along the delivery column, rotation of one assembly will affect the other. In a simple example, if no tilting action of the cutting head is desired, i.e. such that the jet stream spins on the spot, both motors  42 ,  62  are driven to rotate the tilt head and rotary head assemblies at the same velocity. A change in drive velocity of one or the other motor, ie. a differential in the motors&#39; drive, will cause a tilt. The degree of tilt furthermore depends on the relative angular displacement of one motor output relative to the other or, put another way, on the angular displacement of the tilt assembly&#39;s drive shaft (the delivery column  20 ) relative to the hollow shaft  68  of the rotary assembly. 
     For example, by applying motion to motor  42  and holding motor  62  stationary, the cutting head will tilt relative to the vertical axis (the 4 th  Axis). By then rotating both motor  42  &amp;  62  at a constant relative speed the cutting head will rotate around the vertical axis (the 5 th  Axis). This rotation allows the waterjet stream to be positioned relative to the direction of motion in order to achieve the desired bevel angle. 
     If the nozzle had been tilted to 45° relative to the vertical plane and had been rotated to 90° relative to the X axis, and the X axis is then driven in either a plus or minus direction, the result would be a 45° cut along the X axis. 
     A more complex example would be to continually rotate the cutting head around the vertical axis to maintain 90° relative to the axis of motion, while moving the X and Y axis in a circular spiral motion, resulting in a coil spring design with a 45° bevel. The design allows for infinite adjustment of both the bevel angle and angle relative to the axis of motion, meaning that there is no known limit to the shapes that can be profile cut with the invention. 
     In combination, the tilt of the cutting head  12  with the cutting head spinning about the vertical axis  15  can produce a circular cutting path that can be continuously described without impediment from apparatus components or without conduits tangling. 
       FIG. 6  schematically and simplistically shows the interaction of the tilt head assembly and rotary head assembly. As shown, rotary head frame  66  supports tilt head assembly  40  and is itself entirely rotatable. 
     The resulting cutting path, without any movement in the first three dimensions, is a continuous circular path that can, with a continuous change in the degree of tilt, spiral inwardly or outwardly. Relatively increasing or decreasing the rotational speed of the tilt head or rotary head assemblies can produce a variety of free form open or closed shapes. With movement in the first three dimensions, the cutting path may follow an infinite number of variable path directions. 
       FIGS. 3(   a ),  3 ( b ),  4  and  5  illustrate from different views the interior of the delivery column of the first embodiment. In the second embodiment described the top of the delivery column (also tilt head rotor  36 ) is best seen in  FIG. 9(   b ). 
     Delivery column  20 ,  36  delivers to the cutting head a mixture of high pressure water and garnet, usually in the form of sand. High pressure water from a pipe (not shown) is introduced into delivery column through a swivel joint  80  and through an adapter  82  which is connected to an upper end of the delivery column to deliver high pressure water into a water passage  84  through the column. The high pressure water exits from a mixing chamber  83  at the lower end of the delivery column and into one or more conduits  24  and a venturi (not shown) in the cutting head  12  which deliver the water mixed with garnet to nozzle  13 . 
     Reference to the delivery column  20  in the first embodiment is made to the front sectional view of  FIG. 4  and plan view of  FIG. 5 , while reference to the delivery column  36  in the second embodiment is made to  FIGS. 9(   a ),  9 ( b ) and  10 . Garnet is introduced under a vacuum into a sealed garnet chamber  85  by connecting a conduit from a garnet source to a fitting  120  and dropping the garnet through an inlet  86 . Garnet chamber  85  is defined by an upper end of the delivery column  20 ,  36  and a stationary cylindrical housing  122  fixed to the stator housing  34  (in the second embodiment). Garnet inlet  86  is located in the cylindrical housing  122  so that the conduit from the garnet source also remains stationary relative to the tilt and rotary drive systems. 
     Garnet chamber  85  is sealed all around with O-rings  123  to maintain a vacuum environment while still allow rotation of the delivery column  20 ,  36  with respect to the cylindrical housing  122 . 
     From the garnet chamber  85  garnet is drawn into garnet passage  87  under vacuum created by a venturi set up in the cutting head and is delivered down the delivery column through garnet passage  87  to be mixed with the water stream in the mixing chamber  83  located in the cutting head assembly immediately above the cutting nozzle. 
     To pneumatically open and close jetstream delivery of water in water passage  84  through the cutting head, air is introduced through an air passage into air valve  91 .  FIG. 3  illustrates air passage  92  and the vacuum passage  90  on either side of the water passage  84 . The inlets to the air and vacuum passages are part way down the delivery column  20 ,  36 . The vacuum passage is connected to a sensing device which monitors the performance of the cutting head. 
       FIG. 7  illustrates delivery of fluids and material from delivery column  20  through flexible conduits to the cutting head  12 . High pressure water is delivered from water passage  84  through water tube  24  to the cutting head, which in turn sets up a venturi in mixing chamber  83  to draw garnet through garnet tube  25 . Air is delivered to air valve  91  through air tube  26 , while vacuum sensing is carried out on the cutting head through vacuum tube  27 . 
     Air inlet  93  and vacuum inlet  94  are connected to the air passage  92  and vacuum passage  90  respectively through a rotary connector  95  that acts as a stationary interface against the rotating delivery column to allow for the column rotation while still allowing the air and vacuum sources to be connected to their respective passages. Accordingly, and as best shown in  FIG. 3(   b ), rotary connector  95  is a cylindrical piece that sits around the delivery column  20  over the entry points of the air and vacuum passages. As illustrated in  FIG. 10  of the second embodiment, the stationary cylindrical housing  122  sits around and over the entry points of the air and vacuum passages. Rotary connector  95  and cylindrical housing  122  remain still while delivery column rotates within an internal bore  97  of the connector/cylindrical housing. Rotary connector and cylindrical housing  122  carry the air inlet  93  and vacuum inlet  94 , which also remain stationary and to which the air and vacuum sources are connected via conduits (not shown). 
     On the internal bore  97  of the connector/cylindrical housing are two grooves  98 . Grooves  98  are each in communication with one of the air inlet  93  or vacuum inlet  94  and ensure that regardless of the position of the air and vacuum passages relative to their respective inlets, air will reach the entry point of the air and vacuum passages via the grooves. O-rings  99  located above and below each groove prevent leakage of air from the grooves. This arrangement allows air and a suction of air through the vacuum to be delivered through the delivery column even while it continuously rotates. 
       FIGS. 8 to 12  illustrate a second and improved embodiment of a waterjet cutting apparatus  30  described above. In the second embodiment, errors that may be encountered in the first embodiment are reduced, accuracy is increased, and play and damage to assembly parts is also reduced. Parts shown in the second embodiment of the waterjet cutting apparatus  30  that are the same parts as in the first embodiment are referred to using the same reference numerals. 
     Waterjet cutting apparatus  30  has a reduced number of gears, thereby reducing the probability of component failure. As illustrated in  FIGS. 9 and 10  there are no gears between the drives and a central rotating and delivery column (tilt head rotor  36 ) along the vertical axis. In this embodiment the drives for the tilt head assembly  40  and the rotary head assembly  60 , namely tilt head drive  32  and the rotary head drive  33  respectively, are located centrally along the vertical axis  15  so as to directly drive the rotary head assembly  60  and the tilt head assembly  40 . The drives are arranged one above the other to have one common rotor axis at the vertical axis  15  such that rotary movement and tilting movement of the cutting head in the fourth and fifth axis is dependent and continuous. Namely, rotation of the cutting head will affect tilting of the cutting head, and vice versa. 
       FIGS. 9 and 10  illustrate a cylindrical stator housing  34  supported on a support plate  35  that is cantilevered from a Z-axis slider  18  ( FIG. 8 ) located in the part of the larger waterjet cutting machine (not shown) that controls the X, Y and Z-axis movement of the cutting head. In a preferred embodiment the tilt head and rotor head drives  32 ,  33  are 50 Amp servo motors operating at 600V. The drives are housed inside the stator housing one above the other with a common rotor axis. The interior upper half of the stator housing  34  is lined with a ring of 11 Nm stators  38  corresponding to the tilt head drive, while the interior lower half of the housing is lined with similar stators  38  corresponding to the rotor head drive. 
     Running axially central through the housing  34  and between the rings of stators is a solid tilt head rotor  36 , or tilt drive shaft, which, as previously described, doubles as the delivery column, namely carrying the air passage  92 , water passage  84 , vacuum passage  90  and the garnet passage  87 . An encoder  88  positioned towards the upper end of the tilt head rotor  36  tracks movement of the cutting head. A second encoder is also positioned towards the lower end of the drive which tracks the rotation of the rotary head. 
     At its upper half tilt head rotor  36  has an enlarged shoulder on which magnets  22  are attached facing tilt head drive stators  38 . Accordingly, electrically charging the stators causes tilt head rotor  36  to rotate by way of magnets  22 , and thereby driving the tilt head assembly. 
     A hollow rotary head rotor  37 , or rotary drive shaft, is located within housing  34  and coaxially surrounds a lower half of the tilt head rotor  36 . Bearings  23  located between rotors  36  and  37  ensure the two rotors spin independently of one another. Rotary head rotor  37  is also bearing mounted in housing  34  to spin freely relative thereto. The exterior of rotary head rotor  37  is provided with magnets  22  which, by way of lower stators  38 , cause rotary head rotor  37  to spin, thereby driving the rotary head assembly. 
     Rotary head rotor  37  extends out of the bottom of stator housing  34  and is fixed to a rotating bracket  39 .  FIG. 11  illustrates rotating bracket  39  supporting the tilt head frame  55  below bracket  39 . The tilt head frame  55  carries the tilt head assembly  40 . Accordingly, rotary head drive  33  rotates rotating bracket  39  which in turn spins the tilt head assembly, and therefore the cutting head  12 , along the vertical axis  15  thereby defining the cutting head&#39;s fourth axis of movement. 
     Tilt head rotor  36  extends out from the top of stator housing  34  to connect to water, air and garnet services. The bottom of tilt head rotor  36  extends through the bottom of housing  34  and connects to drive tilt head assembly  40  causing the cutting head to tilt from the vertical axis  15  and around a horizontal axis thereby defining a fifth axis of movement. 
     As illustrated in  FIG. 11 , tilt head assembly in the second embodiment is approximately angled 45° from the a horizontal plane (or from the vertical axis  15 ) such that the axis about which the cutting head tilts is also at 45° to the horizontal. This is different from the first embodiment illustrated in  FIGS. 1 to 7  where the tilt head assembly  40  is tilted about the horizontal axis. The advantage with the arrangement of the second embodiment is that, in theory, the vertex of tilt should remain at the end of the nozzle  13  which means the nozzle end remains in the same location during tilt thereby enabling greater cutting accuracy and a reduction in error during cutting head movement. 
     Tilting is brought about by a cable driven pulley system which pivots a tilt bracket  100  to which the cutting head  12  is attached. A drive pulley  101  mounted to the end of tilt head rotor  36  drives a cable  102  over idler pulleys  103  to pivot a pivot pulley  104 .  FIG. 12  best illustrates the pulley system and the manner in which it is mounted on tilt head frame  55 .  FIG. 11  illustrates how tilt head frame  55  is mounted at a 45° angle to the vertical axis  15 . 
     Pivot pulley  104  lies in a parallel plane to tilt bracket  100  and is connected to tilt bracket  100  by way of shaft  105  such that pivoting movement of the pivot plate  104  will cause corresponding pivoting movement of the tilt bracket  100  and hence the same tilt to the cutting head  12  and nozzle  13 . The degree of tilt to the cutting head achievable by the tilt head assembly is greater than ±12°, typically ±60° but it is envisaged to reach as high as ±180° allowing full robotic control. 
     Using a cable driven pulley system eliminates backlash in operating the tilt head assembly. Furthermore, a cable drive is particularly suited to waterjet cutting machines as the components will not be affected by splashing of the abrasive waterjet. 
     High pressure water is fed down through tilt head rotor  36  and to the cutting head  12  by a high pressure water line  106  which, at the tilt head assembly, is coiled around shaft  105  and supported thereon by a sleeve  107 . Sleeve  107  is mounted on bearings on the shaft to allow the coiled water line to move freely of the pivoting shaft  105 . For the sake of clarity the water line extending between the coil and the cutting head is not shown. Coiling of the water line allows for extension and contraction of the water line when the cutting head is tilted. 
     An alternative to using a coiled high pressure water line would be to provide a rotary joint in the water line between the tilt head assembly and the cutting head. 
     As the cutting head  12  tilts, the water line  106  at the coil moves from a neutral position to a more extended or a more contracted position, depending on the direction of tilt. In order to assist in driving the cutting head away from the neutral position and against the resistance imposed by the water line, two counter springs  108  are attached between the pivot pulley  104  and the tilt head frame  55 . Each spring moves the coiled water line away from the neutral position in the tilt direction. 
     Provision of a counter spring arrangement relieves the resistance of the high pressure coil from the tilt head drive when tilting the cutting head away from the vertical position. In other words, the tilt head drive need only require sufficient force to drive tilting movement of the cutting head; the resistive force created by the coiled water line is compensated for by the counter springs. The features in the second embodiment of the direct drives and the 45° angled tilt bracket provides a profile cutting apparatus having great accuracy and a minimized chance of errors, damage and part failure. 
     In operation, the rotating rotary head assembly spins the tilt head assembly and hence the nozzle. The dependent tilt action to the spinning cutting head allows the nozzle to describe a continuous circular/spiral cutting path driven by the differential motion of the drives. The present waterjet cutting apparatus accordingly introduces new dimensions to profile cutting that increase the possibilities of cutting paths and machine manoeuvrability for more efficient, controlled and sophisticated profile cutting. 
     In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.