WO 2009/117779 PCT/AU2009/000370 SHEET METAL CUTTING DEVICE Field of the Invention The present invention relates to sheet metal 5 cutting devices. Background of the Invention There are many different types of cutting tools, for example; aviation snips, tin snips, hacksaws, angle 10 grinders, Beverley throatless shears, electric power shears, electric jigsaws, nibblers etc. In general, each of these different cutting tools are suitable for different applications. In the roofing industry, roofing caps must be 15 configured so that their side walls abut with the tiling or metal roofing on either side. For corrugated metal roofing or corrugated tiles, the side walls of the caps must be cut so that they have a matching configuration to the adjacent roof. The process of cutting a series of 20 curved edges or corrugations in each side wall is not an easy process using conventional cutting tools. Aviation snips are the most adept (and commonly used) tools at cutting or scribing along a continuous curved path, but the cutting process is long and tedious. Furthermore, 25 cutting continuous wavelike curves over a period of time is physically demanding. Although there have been prior attempts to use powered cutting tools to cut the curved edges required roofing sheet metal, invariably, they are unable to cut a 30 complete curve and furthermore tend to damage the edges of the sheet metal. Typically, mechanized cutting tools are first used by a roofer for part of the curve which is being cut and aviation snips or tin snips are then used to complete the curve. 35 The Applicant, as disclosed in his previous patent application, published as PCT International Patent Application W02007/041794, has developed a powered cutting WO 2009/117779 PCT/AU2009/000370 2 tool which provides at least some improvement over those tools found in the prior art. However, the Applicant has subsequently made further improvements over the device of W02007/041794, which are descried herein. 5 Summary of the Invention According to a first aspect of the present invention, there is provided a device for cutting sheet metal comprising; 10 a support adapted to attach the device to a power source; a first blade arm having a first blade; a second blade arm having a second blade; a coupling for coupling the first blade arm to 15 the power source to enable the first blade arm to pivot in a cutting action when the power source is activated; and an adjustment mechanism for adjusting the maximum angle between the first and second blades. The second blade arm may be fixed, whereby only 20 the first blade arm pivots when the power source is activated. In this embodiment, the second blade arm may be fixed to the support. The second blade arm and the first blade arms may both pivot when the power source is activated. The 25 coupling, in this embodiment, may also couple the second blade arm to the power source. The first and second blade arms may be connected through a pivot member. The first blade arm may pivot about the pivot member. The second blade arm may pivot 30 about the pivot member. The pivot member may extend through a shin portion of each blade. Each blade may tilt forwardly from a vertical axis. 35 The power source may be any suitable mechanical, electrical or hydraulic power source, but is preferably a power drill.
WO 2009/117779 PCT/AU2009/000370 3 The cutting action may include scribing, shearing, cutting and the like. The support may comprise a tubular member. The support may be configured to attach to a 5 drill casing. The coupling may comprise first and second coupling portions. The first coupling portion couples the first blade arm to the power source. 10 Where the second blade arm pivots, the second coupling portion may couple the second blade arm to the power source. Where the second blade arm is fixed, the second coupling portion may fix the second blade arm relative to 15 the support. The first and second coupling portions may be connected to respective first and second blade arms. The first and second coupling portions may be located at opposing ends of their respective first and 20 second blade arms to their respective first and second blades. The coupling may comprise a cam drivable by the power source. The first coupling portion may engage the cam. 25 Where the second blade arm pivots, the second coupling portion may engage the cam. The second coupling portion may engage the cam on an opposing side of the cam to that of the first coupling portion. 30 The first coupling portion may be located above the second coupling portion and the first blade may be located below the second blade. The first coupling portion may comprise a first member extending from the first blade arm and a first lobe 35 for engaging the cam.
WO 2009/117779 PCT/AU2009/000370 4 The second coupling portion may comprise a second member extending from the second blade arm and a second lobe for engaging the cam. The first and second lobes may be in the form of 5 toothless pinions. The first and second lobes may act as bearings for the transfer of power from the power source to the blade arms. The adjustment mechanism may be effective to vary 10 the engagement between the cam and the coupling portion or portions so as to change the maximum separation between the coupling portions. The cam may have a maximum radius which is adjustable. Adjusting the maximum radius of the cam may 15 adjust the maximum angle between the blades by providing a greater maximum separation between the first and second coupling portions. In another arrangement, the cam may have a maximum radius which varies along the longitudinal extent 20 of the cam and the adjustment mechanism may be effective to move the first or both coupling portions along the cam. In a further variation, the adjustment mechanism may be effective to move the cam relative to the first or both coupling portions in the direction of the cam's 25 longitudinal axis. The maximum radius of the cam may be greater towards the distal end of the cam from the first and second blades. However, the maximum radius of the cam may be 30 greater towards the proximal end of the cam from the first and second blades. The position of the coupling relative to the longitudinal extent of the cam may be adjusted to adjust the maximum angle between the blades. 35 A change in the position of the coupling portions relative to the longitudinal extent of the cam can change WO 2009/117779 PCT/AU2009/000370 5 the maximum separation between the coupling portions, because of the cam's taper. The adjustment mechanism may also comprise a moveable bar for adjusting the position of the coupling 5 relative to the longitudinal extent of the cam. Where both the first and second blade arms pivot, the moveable bar may be connected to both blade arms. Where the second blade arm is fixed, the moveable bar may be connected only to the first blade arm. 10 The moveable bar may be connected to the first and second blade arms through the pivot member. The adjustment mechanism may also comprise an actuator for moving the moveable bar as required. The actuator may engage a thread of the moveable 15 bar. The actuator may be in the form of an actuating nut. The actuating nut may be provided with a friction enhancing outer surface. 20 The friction enhancing surface of the actuating nut may comprise any suitable arrangement of dimples, ridges, projections, corrugations or the like. The adjustment mechanism may also comprise a housing for receiving a portion of the moveable bar. 25 The housing may be mounted to the support. The adjustment mechanism may also comprise a locking mechanism for preventing any inadvertent movement of the adjustment mechanism. The locking mechanism may comprise a locking 30 screw. The locking screw may frictionally engage the moveable bar to prevent movement of the bar. The minimum radius of the cam is preferably constant. When the first and/or second coupling portions 35 engage the cam at its minimum radius, the tips of the first and second blades are brought together, thus completing the cutting action.
WO 2009/117779 PCT/AU2009/000370 6 The coupling may comprise a shaft coupling member which couples to a shaft of the power source. The shaft coupling member may be adapted to be received in the chuck of a power drill. 5 The shaft coupling member may comprise a socket for receiving a shaft of the power source. The first coupling portion may also engage the shaft coupling member. The second coupling portion may also engage the 10 shaft coupling member. The first and second lobes of the coupling portions may engage an inner surface of the shaft coupling member. The inner surface of the shaft coupling member 15 may be elliptical. The inner surface of the shaft coupling member may be parallel to the outer surface of the cam. The distance between the inner surface of the shaft coupling member and the outer surface of the cam may 20 correspond approximately to the width of the lobes. The cam may be fixed to the shaft coupling member. In another embodiment, the cam comprises the inner surface of the shaft coupling member. 25 In this arrangement, the first and second coupling portions may be connected to a biasing element, which biases the first and second coupling portions away from each other and toward the inner surface of the shaft coupling member. 30 The biasing element may be in the form of a spring. The biasing element may be in the form of an elastic band, preferably formed of rubber. In this arrangement, the device may also comprise 35 a clutch between the shaft coupling member and the shaft of the power source to engage and disengage the shaft coupling member to the shaft of the power source.
WO 2009/117779 PCT/AU2009/000370 7 Disengagement of the shaft coupling member from the shaft of the power source enables the biased spring to open the first and second blades. The clutch may be a dog clutch. 5 The clutch may be axially aligned with the shaft coupling member. When the device is at rest the clutch may be in a disengaged position in which the shaft coupling member is disengaged from the shaft of the power source. 10 When a user of the device initiates use of the device to effect cutting, the clutch may be moved to an engaging postion in which the shaft coupling member is engaged to the shaft of the power source. The clutch may be biased towards the disengaged 15 position. To initiate use of the device, the user may press a trigger. The device may comprise an electromagnet to effect movement of the clutch. 20 The electromagnet may be switched on when the trigger is pressed and switched off when the trigger is released. The electromagnet may be arranged to hold the clutch in the engaging position during use of the device 25 to effect cutting and releases the clutch from the engaging position when the user ceases using the device to effect cutting. More preferably, the electromagnet may be arranged to hold the clutch in the engaging position 30 whilst the user presses the trigger and releases the clutch from the engaging position when the user releases the trigger. In yet another arrangement, the cam couples to a shaft of the power source. The coupling in this 35 arrangement may therefore not comprise a shaft coupling member.
WO 2009/117779 PCT/AU2009/000370 8 In this arrangement, the coupling may comprise a biasing mechanism for biasing the first and second coupling portions towards eachother. The biasing mechanism may be located internal or 5 external to the support. The biasing mechanism may comprise an elastic band connected to the first and second coupling portions. The band may be formed of rubber. The biasing mechanism may comprise a spring 10 connected to the first and second coupling portions. The spring may be mounted on a lug. The lug may be connected to the movable bar. Arms of the spring may connect to the first and second coupling portions. 15 Where both the first and second blade arms pivot, the device may also comprise a fixing mechanism for selectively fixing the first or second blade against rotation. The fixing mechanism when operated to fix one of 20 the blades may fix the coupling portion of the selected blade relative to the support, preferably via the moveable bar mounted to the support by the housing of the adjustment mechanism. The fixing mechanism may comprise a first pin and 25 a second pin, the first and second pins for selectively engaging a slot in respective first and second coupling portions. The pins may be threaded. The fixing mechanism may comprise first and 30 second actuators connected to respective first and second pins to facilitate movement of the pins to engage and disengage the slots in respective first and second coupling portions. The first and second actuators may be wheels, 35 rotatable by the user. The fixing mechanism may comprise a plate connected to the support, preferably via the moveable bar WO 2009/117779 PCT/AU2009/000370 9 mounted to the support by the housing of the adjustment mechanism. The plate may have apertures therethrough and through which the first and second pins may extend. 5 According to a second aspect of the present invention, there is provided a device for use in cutting sheet metal comprising: a power source; a first contact element for contacting a first 10 blade arm; a second contact element for contacting a second blade arm; and a coupling for coupling the first blade arm when in contact with the first contact element to the power 15 source and the second blade arm when in contact with the second contact element to the power source to enable the first and second blade arms to pivot in a cutting action when the power source is activated. The contact elements may be in the form of 20 sockets. The coupling may comprise a coupling as described above in the first aspect of the present invention. The coupling may comprise a cam connected to a shaft of the power source, the cam acting on first and 25 second coupling members. The first and second coupling portions may be connected to respective first and second contact elements. The first and second contact elements may move with the first and second coupling portions. 30 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: 35 Figure 1 is a side view of a device for cutting sheet metal according to an embodiment of the present invention; WO 2009/117779 PCT/AU2009/000370 10 Figure 2 is a partial cut-away perspective view of the device of Figure 1; Figures 3A and B side elevation and end views of the blade arms of a device for cutting sheet metal 5 according to a variation of Figure 1; Figures 4 to 5 are end, side and top views of a shaft coupling member of the device of Figure 1; Figures 7A, B, C are schematic side views of a coupling in a device for cutting sheet metal according to 10 another embodiment of the present invention; Figure 8 is a partial cut-away side view of a device for cutting sheet metal according to yet another embodiment of the present invention Figure 9 is an end view of the cam of the device 15 of Figure 8; and Figure 10 is a side view of a fixing mechanism for selectively fixing the first or second blade of a device for cutting sheet metal against rotation. 20 Detailed Description of Embodiments Referring to Figures 1-6, a device 10 for cutting sheet metal is shown. The device 10 comprises a support 11 adapted to attach the device 10 to a power source, which is shown in Figure 1 in the form of a power drill 12. 25 However the power source may be any other suitable type of power source including a mechanical, electrical or pneumatic power source. The support 11 is in the form of a tubular member which is configured to attach to the casing of the drill 12. The support 11 may or may not be readily 30 detached from the drill's casing. The device 10 also comprises a first blade arm 13 having a first blade 14, a second blade arm 15 having a second blade 16 and a coupling 20 for coupling the first and second blade arms 13, 15 to the power drill 12 to 35 enable the first and second blade arms 13, 15 to both pivot in a cutting action when the power drill 12 is activated. The cutting action may include scribing, WO 2009/117779 PCT/AU2009/000370 11 shearing, cutting and the like. Figures 3A and B show a variation of the arrangement of the blade arms 13, 15 and respective blades 14, 16 which enable the user to turn the device 10 left or right when scribing. 5 The device 10 also comprises an adjustment mechanism 30 for adjusting the maximum angle between the first and second blades 14, 16. Enabling adjustment of the maximum angles between the first and second blades 14,16 provides significant advantages, in particular over the 10 Applicant's prior device disclosed in W02007/041794. By adjusting the maximum angle between the blades 14, 16, the length of sheet metal cut by each pivot of the first and second blade arms 13, 15, ie. by each cycle of the cutting action, can be easily changed without the need for the 15 operator to judge how far into the throat of the jaw formed between the blades 14, 16 the sheet metal is received to be cut. The length of sheet metal cut on each cycle of the cutting action affects the possible curvature that can be made in the cut because it affects how much 20 lateral movement of the device 10 can be imparted by the operator when cutting. Thus the device 10, by use of the adjustment mechanism 30, can be readily used to cut curves in sheet metal of varying radii without requiring the operator to be of any particular skill. 25 The first and second blade arms 13, 15 are connected through a pivot member 18 such that the first and second blade arms 13, 15 pivot about the pivot member 18. The pivot member 18 as shown in Figure 1 extends through a shin portion of each blade 14, 16. Each blade 30 14, 16 tilts forwardly from a vertical axis so that when the device 10 is being used it can clear the surface of the sheet metal being cut, in particular where the sheet metal is corrugated. The coupling 20 for coupling the first and 35 second blade arms 13, 15 comprises first and second coupling portions 21 and 22 respectively. The first coupling portion 21 couples the first blade arm 13 to the WO 2009/117779 PCT/AU2009/000370 12 power drill 12 and the second coupling portion 22 couples the second blade arm 15 to the power drill 12. The first and second coupling portions 21, 22 connected to respective first and second blade arms 13, 15 at opposing 5 ends to their respective first and second blades 14, 16. The coupling 20 also comprises a cam 19, which is drivable by the power drill 12 and which the first and second coupling portions 21, 22 engage. Notably, the second coupling portion 22 engages the cam 19 on an 10 opposing side of the cam 19 to that of the first coupling portion 21. Furthermore, the first coupling portion 21 is located above the second coupling portion 22 whilst the first blade 14 is located below the second blade 16. When the power drill 12 is activated, the cam 19 is rotated and 15 as a result the first and second coupling portions 21, 22 are caused to move in opposing directions, perpendicularly to the cam's axis of rotation. This movement of the first and second coupling portions 21, 22 is cyclical and cause the first and second blade arms 13, 15 to rotate or 20 "rocker" about the pivot member 18 to thus produce the cutting action of the blades 14, 16. The first coupling portion 21 comprises a first member 23 extending from the first blade arm 13 and a first lobe 24 for engaging the cam 19. Similarly, the 25 second coupling portion 22 comprises a second member 25 extending from the second blade arm 15 and a second lobe 26 for engaging the cam 19. The first and second lobes 24, 26 may act as bearings for the transfer of power from the power drill 12 to the blade arms 13, 15. In Figure 1, the 30 first and second lobes 24, 26 are shown in the form of toothless pinions. As shown in Figures 4 to 6, the cam 19 has a maximum radius which varies along the longitudinal extent of the cam 19. The maximum radius of the cam 19 is greater 35 towards the distal end of the cam 19 from the first and second blades 14, 16. However, in a variation to that shown in the Figures, the maximum radius of the cam may be WO 2009/117779 PCT/AU2009/000370 13 greater towards the proximal end of the cam from the first and second blades. The position of the first and second coupling portions 21, 22 relative to the longitudinal extent of the cam 19 may be adjusted using the adjustment 5 mechanism 30 to adjust the maximum angle between the blades as the cam's- taper changes the maximum separation between the first and second coupling portions 21, 22. In a variation, however, the cam may be moved using the adjustment mechanism relative to the coupling 10 portions in the direction of the cam's longitudinal axis to similarly adjust the maximum angle between the blades. Notably, the minimum radius of the cam 19 is constant. When the first and second coupling portions 21, 22 engage the cam 19 at its minimum radius, the tips of 15 the first and second blades 14, 16 are brought together, thus completing the cutting action. This is not affected by adjusting the maximum angle of the blades 14, 16 using the adjustment mechanism 30. The adjustment mechanism 30 also comprises a 20 moveable bar 32 for adjusting the position of the coupling 20 relative to the longitudinal extent of the cam 19. The moveable bar 32 is connected to both the first and second blade arms 13, 15 at their pivot connection through the pivot member 18. The adjustment mechanism 30 also 25 comprises an actuator in the form of an actuating nut 33 for moving the moveable bar as required. The actuating nut 33 is threaded to engage a thread of the moveable bar 32 so that rotation of the nut 33 causes the moveable bar to move in a longitudinal direction. The actuating nut 33 is 30 also provided with a friction enhancing outer surface which enhances rotation of the nut 33 by an operator. The friction enhancing surface may comprise any suitable arrangement of dimples, ridges, projections, corrugations or the like. 35 The adjustment mechanism 30 also comprises a housing 34 for receiving a portion of the moveable bar 32 and which is mounted to the support 11. The adjustment WO 2009/117779 PCT/AU2009/000370 14 mechanism 30 also comprises a locking mechanism in the form of a locking screw 35 for preventing any inadvertent movement of the adjustment mechanism 30. The locking screw 35 frictionally engages the moveable bar 32 to prevent 5 movement of the bar. Therefore, to adjust the maximum angle between the blades 14, 16 using the adjustment mechanism 30 an operator first undoes the locking screw 35 to enable the moveable bar 32 to move. The operator then turns the 10 actuating nut 33 to move the moveable bar 32 as required, thereby moving the coupling portions 21, 22 relative to the longitudinal extent of the cam 19 so that the lobes 24, 26 of the coupling portions 21, 22 engage a thicker or thinner part of the maximum radius of the cam 19. The 15 operator then operates the locking screw 35 to lock the moveable bar 32 in this position. A gauge or other markings may be provided on the housing 34 such that an indicator (not shown) connected to the moveable bar 32 indicates the position of the moveable bar 32 and hence 20 the maximum distance between the tips of the blades. The coupling 20 also comprises a shaft coupling member 40 which couples to a shaft 41 of the power drill 12. In the embodiment shown in the Figures, the shaft coupling member comprises a socket 42 for receiving the 25 shaft 41 of the power drill 12. However, in other embodiments, the shaft coupling member 40 may be adapted to be received in the chuck of the power drill. The cam 19 is fixed to the shaft coupling member 40 and the first and second coupling portions 21, 22 also 30 engage the shaft coupling member 40. More specifically, the first and second lobes 24, 26 of the coupling portions 21, 22 engage an inner surface 43 of the shaft coupling member 40. The inner surface 43 of the shaft coupling member 40 is elliptical, having a shape which is parallel 35 to the outer surface of the cam 19. The distance between the inner surface 43 of the shaft coupling member 40 and WO 2009/117779 PCT/AU2009/000370 15 the outer surface of the cam 19 corresponds approximately to the width of the lobes 24, 26. In a variation of the adjustment mechanism described above not shown in the Figures, the cam is not 5 tapered but may have a maximum radius which is adjustable. Adjusting the maximum radius of the cam may adjust the maximum angle between the blades by providing a greater maximum separation between the first and second coupling portions. 10 With reference now to Figures 7A, B and C, in another embodiment, the device for cutting sheet metal may have a coupling 120 in which a cam is formed by the inner surface of the shaft coupling member 140 and the central cam 19 as shown in Figure 2 is not required. In this variation, the 15 first and second coupling members 121, 122 are connected to a biasing element in the form of a spring 150, which biases the coupling portions 121, 122 away from each other and towards the inner surface of the shaft coupling member 140. Thus the spring 150 acts to maintain the engagement 20 of the lobes 124, 126 with the inner surface of the shaft coupling member 140 as it rotates under activation from the power drill 12. In the embodiment shown in Figures 7A-C, the device also comprise a dog clutch 151 (see Figure 7C) 25 between the shaft coupling member 140 and the shaft 141 of the power drill 112. The clutch 151 is axially aligned with the shaft coupling member 140. When the device is at rest the two portions of the clutch 151 are disengaged as shown in Figure 7C. In this position the spring 150, 30 because of its bias, pushes the first and second coupling members 121, 122 apart into the position shown in Figure 7B. In this position the blades are open to their maximum opening angle. When a user of the device presses on a trigger to effect cutting using the device, one of the 35 portions of the clutch 151 is moved to engage the other portion under the influence of an electromagnet 152 so that power is transmitted through the clutch from the WO 2009/117779 PCT/AU2009/000370 16 shaft 141 of the power drill 112 to the shaft coupling member 140. This enables the shaft coupling member 140 to rotate through the position shown in Figure 7A to effect cutting. The electromagnet 152 holds the clutch 151 in 5 this engaging position so long as the user continues to press the trigger. once the trigger is released, the electromagnet 152 switches off and the clutch 151 returns to the position shown in Figure 7C resulting in the spring 150 opening the blades to their maximum opening position. 10 Thus, each time the user stops and restarts use of the device, they can start the cutting action at the throat of the blades which provides the greatest cutting efficiency and accuracy. Referring now to Figures 8 and 9, a device 210 15 for cutting sheet metal according to a further embodiment of the present invention is shown. In this embodiment, the cam 219 couples to a shaft 241 of the power drill 212 and therefore unlike the device 10 shown in Figure 2, the device 210 in Figures 8 and 9 does not comprise a shaft 20 coupling member. The device 210 of Figures 8 and 9, however, has a coupling 220 which comprises a biasing mechanism in the form of a spring 260 connected to the first and second coupling portions 221, 222 and which biases the first and second coupling portions towards 25 eachother. In a variation, the biasing mechanism may comprise a elastic rubber band. In operation, as the cam 219 rotates with rotation of the shaft 241, the cam 219 pushes apart the coupling portions 221, 222 against the bias of the spring 30 260 as the maxium radius of the cam rotates towards the lobes 224, 226 of the coupling portons 221, 222 and the biased spring 260 returns the lobes 224, 226 towards their initial position as the maximum radius of the cam rotates away from the lobes. This produces the cutting action of 35 the blades 214, 216. Referring now to Figure 10, a fixing mechanism 270 for selectively fixing the first or second blade 214, WO 2009/117779 PCT/AU2009/000370 17 216 against rotation is shown. It may be desireable to fix one of the blades to obtain a better finish on the working surface of the metal being cut. The fixing mechanism 270 is preferably incorporated with the sheet metal cutting 5 device embodiments shown in Figures 7A-C, 8 and 9, although the description below will be made with reference to the reference numerals used in Figures 8 and 9. The fixing mechanism 270 comprises a first threaded pin 271 and a threaded second pin 272, the first and second 10 threaded pins for selectively engaging first and second slots 273, 274 in respective first and second coupling portions 221, 222. The fixing mechanism 270 also comprises first and second actuators in the form of wheels 275, 276 connected to respective first and second pins 271, 272 to 15 facilitate movement of the pins to engage and disengage the slots in respective first and second coupling portions by rotation of the wheels by the user of the device 210. The fixing mechanism 270 also comprises a plate 277 connected to the support 211 via the moveable bar 232 20 mounted to the support 211 by the housing of the adjustment mechanism. The plate 277 has apertures therethrough and through which the first and second pins 271, 272 extend. The plate 277 is fixed relative to the support 211 and when either of the pins 271, 272 are 25 selectively engaged to their respective slots 273, 274 movement (in a vertical direction with respect to Figure 10) of the coupling portion which the pin has engaged is prevented by location of the pin through the aperture in the fixed plate 277. 30 Figure 10 also shows a variation for the location of the spring 260 of the coupling 220 from the position shown in Figure 8. In the variation shown in Figure 10, the spring is located external to the support and is mounted on a lug 261 connected to the movable bar 232. 35 Arms 262, 263 of the spring 260 connect to the first and second coupling portions 221, 222 to biases the first and second coupling portions towards eachother.
WO 2009/117779 PCT/AU2009/000370 18 Although the above description is provided in respect of a device according to embodiments of the present invention in which both the first and second blade arms pivot, in other embodiments, the second blade arm may 5 be fixed, whereby only the first blade arm pivots when the power source is activated. In this embodiment, the second blade arm may be fixed to the support typically by connecting the second coupling portion to the support. Where the second blade arm is fixed, the adjustment 10 mechanism may be operable to move only the first coupling portion relative to the longitudinal extent of the cam to adjust the maximum angle between the first and second blades. Referring now to Figure 11, a device 380 for use 15 in cutting sheet metal is shown schematically. The device 380 comprises a power source 312, a first contact element 381 for contacting a first blade arm, a second contact element 382 for contacting a second blade arm and a coupling 320 for coupling the first blade arm when in 20 contact with the first contact element 381 to the power source 312 and the second blade arm when in contact with the second contact element 382 to the power source 312 to enable the first and second blade arms to pivot in a cutting action when the power source 312 is activated. 25 The device 380 is for use with hand operated snips such as the hand snips 385 shown in Figure 11 so a to motorise the snips. To do this the hand snips 385 can be simply contacted with or "plugged into" the contact elements 381, 382 (typically in the form of sockets) of 30 the device 380. The coupling 320 may be similar to the coupling shown in Figure 8; having a cam 319 connected to a shaft of the power source 312, the cam 319 acting on coupling portions 321, 322. The coupling portions 321, 322 are 35 connected to the contact elements 381, 382 such that the elements move with the coupling portions 321, 322. The biasing mechanims of the coupling 320 which biases the WO 2009/117779 PCT/AU2009/000370 19 coupling portions 321, 322 towards eachother and with the cam 319 enable the cutting action is provided by the spring 386 of the hand snips 385. In the preceding description of the invention, 5 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, ie. to specify the presence of the stated features but not to preclude the presence or 10 addition of further features in various embodiments of the invention. It is to be clearly understood that although prior art publication(s) are referred to herein, this reference does not constitute an admission that any of 15 these documents forms part of the common general knowledge in the art in Australia or in any other country.