Abstract:
A power cutter comprising: a housing  2;  an engine  24  mounted within the housing  2;  a support arm  7  mounted on the housing and which projects forward of the housing; a blade mounting mechanism rotatably mounted on the end of the support arm and which is capable of being rotationally driven by the engine  24  when the engine is running; a cutting blade having a circular central hole and which mounts on and is rotationally driven by the blade mounting mechanism; a liquid fuel aeration mechanism  126  to generate aerated fuel for the engine; an air intake  314  for the provision of air for the liquid fuel aeration device  126;  an air filtration mechanism  316  to filter the air drawn in from the air intake for the liquid fuel aeration mechanism; a fuel tank  124  for providing fuel to the liquid fuel aeration mechanism; and an exhaust  146  through which the exhaust gases generated by the operation of the engine are expelled; wherein the blade mounting mechanism comprises: a spindle  70  rotatably mounted on the support arm and which is capable of being driven by the engine  24,  an adaptor  90  upon which is mounted the cutting blade, which adaptor is mounted on surrounds the spindle, the adaptor  90  having along its length a plurality of radial support surfaces  98; 100  which are each concentric with the spindle  70,  each having a different radius; a clamping mechanism  96, 92,86  capable of axially and angularly locking the cutting blade to the spindle  70;  wherein, when the blade  10  is mounted on the adaptor  90,  the central hole of the blade  10  mounts on a corresponding sized radial support surface  98; 100  of the adaptor  90  so that the axis of rotation of the blade  10  is substantially co-axial with that of the spindle  70.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a power cutter. 
       BACKGROUND OF THE INVENTION 
       [0002]    A typical power cutter comprises a housing in which is mounted a two stroke internal combustion engine. Attached to the side of the housing is a support arm which extends forward of the housing. Rotatably mounted on the end of the support arm is a cutting blade, usually in the form of a grinding disk. The motor is drivingly connected to the cutting blade via a drive belt. The rotary output of the engine rotatingly drives the cutting blade via the drive belt. The drive belt is driven via a centrifugal clutch which enables the out drive spindle of the engine to disengage from the belt when the engine is running at a slow speed, to allow the engine to continue running, whilst disengaging any drive to the cutting blade to allow the blade to be stationary. 
         [0003]    Also mounted in the housing is a petrol tank which provides petrol for the engine and an oil tank, which provides lubricating oil to mix with the petrol, to lubricate the engine, to provide a petrol/oil mixture. The petrol and oil mixture is fed into the engine via a carburetor, also mounted within the housing, which creates an aerated petrol/oil mixture, to power the engine. 
         [0004]    Mounted on the rear of the housing is a rear handle for supporting the power cutter, which contains a trigger switch for accelerating the engine upon depressing. Depression of the trigger switch causes more of the aerated petrol/oil mixture to be injected into the engine from the carburetor which in turn causes the speed of the engine to accelerate. 
         [0005]    GB2232913, WO2005/056225 and U.S. Pat. No. 5,177,871 show such power cutters. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    Cutting blades for use with power cutter are made from a fiat sheet of material, typically metal, and have a circular outer circumference. The circular outer edge comprises either teeth or other cutting elements, such as diamonds, to form a radial cutting edge. A circular central hole is formed at the centre of the blade which is used to mount the blade onto a drive spindle. The size of the diameter of cutting blades vary. However, as the size of the outer diameter increases, the size of the diameter of the central hole in the middle of the blade also increases. It is desirable for a power cutter to be able to use a range of sizes of cutting blades with varying sizes of central hole. In order for it to do so, it needs to be able mount blades having differing sized central holes. The present invention provides a power cutter which is able to do so. 
         [0007]    A power cutter comprising: 
         [0008]    a housing; 
         [0009]    an engine mounted within the housing; 
         [0010]    a support arm mounted on the housing and which projects forward of the housing; 
         [0011]    a blade mounting mechanism rotatably mounted on the end of the support arm and which is capable of being rotationally driven by the engine when the engine is running; 
         [0012]    a cutting blade having a circular central hole and which mounts on and is rotationally driven by the blade mounting mechanism;
       a liquid fuel aeration mechanism to generate aerated fuel for the engine;   an air intake for the provision of air for the liquid fuel aeration device;   an air filtration mechanism to filter the air drawn in from the air intake for the liquid fuel aeration mechanism;   a fuel tank for providing fuel to the liquid fuel aeration mechanism; and   an exhaust through which the exhaust gases generated by the operation of the engine are expelled;       
 
         [0018]    wherein the blade mounting mechanism comprises: 
         [0019]    a spindle rotatably mounted on the support arm and which is capable of being driven by the engine, 
         [0020]    an adaptor upon which is mounted the cutting blade, which adaptor is mounted on surrounds the spindle, the adaptor  90  having along its length a plurality of radial support surfaces which are each concentric with the spindle  70 , each having a different radius; 
         [0021]    a clamping mechanism capable of axially and angularly locking the cutting blade to the spindle; 
         [0022]    wherein, when the blade is mounted on the adaptor, the central hole of the blade mounts on a corresponding sized radial support surface of the adaptor so that the axis of rotation of the blade is substantially co-axial with that of the spindle. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0023]    Two embodiments of the invention will now be described with reference to accompanying drawings of which: 
           [0024]      FIG. 1  shows a perspective view of the power cutter from a first side; 
           [0025]      FIG. 2  shows a side view of the power cutter from a second side; 
           [0026]      FIG. 3  shows a sketch of a horizontal cross section of the belt drive and support arm; 
           [0027]      FIG. 4  shows a sketch of the forward and rearward sections of the support arm; 
           [0028]      FIG. 5  shows a sketch of a horizontal cross sectional view of the connection between the rearward and forward sections of the support arm; 
           [0029]      FIG. 6  shows the belt tensioner; 
           [0030]      FIG. 7  shows a computerized drawing of the forward section, driven wheel, blade and blade guard; 
           [0031]      FIG. 8  shows a computerized drawing of the blade and blade guard from the opposite direction to that shown in  FIG. 7 ; 
           [0032]      FIG. 9  shows a computerized drawing of a close up the blade and blade guard; 
           [0033]      FIG. 10  shows a computerized drawing of a close up the blade and blade guard without the holding nut; 
           [0034]      FIG. 11  shows a computerized drawing of a close up the blade and blade guard without the first support disk; 
           [0035]      FIG. 12  shows a computerized drawing of forward support with the blade guard; 
           [0036]      FIG. 13  shows a computerized drawing of a cut away view of the rotary support mechanism from the side with the adapter in the first position; 
           [0037]      FIGS. 14 and 15  show computerized drawings of a cut away views of the rotary support mechanism from the side with the adapter in the second position; 
           [0038]      FIG. 16  shows a cut away view of the blade support; 
           [0039]      FIG. 17  shows a computerized drawing of a cut away view of the rotary support mechanism from a first perspective; 
           [0040]      FIG. 18  shows a computerized drawing of a cut away view of the rotary support mechanism from a second perspective; 
           [0041]      FIG. 19  shows a sketch of the vertical cross section of the body of a power cutter; 
           [0042]      FIG. 20  shows a perspective view of the fuel cap; 
           [0043]      FIG. 21  shows an exploded view of the fuel cap from a first side; 
           [0044]      FIG. 22  shows an exploded view from a second side; 
           [0045]      FIG. 23  shows a sketch of a vertical cross section of the part of the power cutter with the air filter; 
           [0046]      FIG. 24  shows a computer generated drawing of the filter; 
           [0047]      FIGS. 25 and 26  show sketches of the cleaning action of the filter; 
           [0048]      FIGS. 27 to 29  show more computer generated drawings of the filter; and 
           [0049]      FIG. 30  shows a second embodiment of an air filtration system. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0050]    Referring to  FIGS. 1 and 2 , the power cutter comprises a body  2  in which is mounted a two stroke internal combustion engine  24 , a front handle  4 , a rear handle  6 , a support arm  7 , a cutting blade  10 , rotatably mounted on the support arm  7  and driven by the engine  24  via a rubber belt  26  and a blade guard  22 . A starter  12  is provided to activate the engine  24 . A plastic cover  19  covers the out side of the support arm  7  as shown in  FIG. 2 . 
         [0051]    Referring to  FIG. 3 , the support arm  7  comprises two sections, a forward section  8  and a rearward section  20 . The rearward section  20  is made from cast iron and is rigidly attached to the side of the gear housing  32  using bolts (not shown). The forward section  8  is made of cast iron and is slideably mounted on the rearward section  20 . The forward section can slide in the direction of Arrow A. The method by which the forward section  8  is slideably mounted on the rearward section  20  is described in more detail below. 
         [0052]    The engine  24  has an output shaft  28  on which is mounted a drive wheel  30  for the rubber belt  26 . The output shaft drives the drive wheel  30  via a centrifugal clutch (not shown) in well known manner. A driven wheel  32  is rotatably mounted on the end of the forward section  8  of the support arm. The driven wheel  32  is connected to the cutting blade  10  which is also mounted on the forward section  8  as described below. The belt  26  passes around the rearward section  20 , between the two wheels  30 ,  32  to transmit the rotation of the engine to the cutting blade  10 . The purpose of enabling the forward section  8  to slide in relation to the rearward section  20  is to enable the belt  26  to be tensioned as described below. A hub  16  covers the drive wheel  30 . 
         [0053]    The interconnection between rearward and forward sections of the support arm  7  will now be described with reference to  FIGS. 3 ,  4 ,  5  and  6 . 
         [0054]    Referring to  FIGS. 3 and 4 , the rearward section  20  comprises two elongate slots  40  formed through the width of the rearward section  20 . The elongate slots  40  are aligned with each other, are of equal length and run lengthways along rearward section  20  of the support arm. Formed through the forward section  8  are two corresponding holes  46 . The part of the forward section  8  with the holes  46  is located alongside of the part of the rear section  20  with the elongate slots  40  so that the holes  46  align with a corresponding slot  40 . A bolt  42  passes through each hole  46  and corresponding slot  40 . A nut  44  is screwed onto the bolt  42  to sandwich the rearward and forward sections together and hold them in place using friction. The slots  40  enable the bolts  42 , and hence the forward section  8 , to slide relative to the rearward section  20 . 
         [0055]    In order to slide the rearward section  20  relative to the forward section  8 , the nuts  44  are slackened so that the two can move relative to each other. The forward section  8  is then slid (using the belt tensioner described below) to the desired position, and then the nuts  44  are tightened to sandwich the rearward section  20  to the forward section  8  to prevent movement between the two. 
         [0056]    The forward and rearward interconnection mechanism is designed so that the forward section  8  can be located on either side of the rearward section  20  as shown in  FIG. 2 . In normal operation, the forward section  8  is located on the same side of the rearward section  20  as the engine  24 . This is indicated as position B. In this position, the cutting blade  10  is located closer to the central axis of the power cutter. However, it is sometimes desirable to have the cutting blade located towards the edge of the body  2  to enable it to cut near to a wall. The forward section  8  can then be moved to the other side of the rearward section  20  and be rotated through 180 degrees about the longitudinal axis  48  of the forward section  8  as indicated by Arrow D to the position C. In both orientations, the driven wheel  32  locates in the same position so that it can be driven by the belt  26 . 
         [0057]    The belt tensioner will now be described with reference to  FIGS. 4 ,  5  and  6   
         [0058]    Referring to  FIGS. 5 and 6 , the belt tensioner comprises a metal plate  50  having two holes  46  through which the bolts  42  pass as seen in  FIG. 4 . The position of the plate  50  is fixed by the position of the bolts  42 . Formed on the metal plate  50  are two hoops  52  which form apertures which are aligned. The shaft of an elongate bolt  54  passes through the hoops  52 . The elongate bolt  54  can freely rotate and axially slide within the hoops  52 . Threadedly mounted onto the bolt  54  is a nut  56 . A spring  58  is sandwiched between the nut  56  and one of the hoops  52 . The spring  58  prevents the nut from rotating. Therefore, as the bolt  54  is rotated, the nut  56  travels along the length of the bolt  54  in a direction dependent on the direction of rotation of the bolt  54 . The position of the nut  56  is fixed relative to the hoop  52  by the spring  58 . A stop  60  is integrally formed on the rearward section  20  of the supporting arm. 
         [0059]    In order to tension the belt  26 , the elongate bolt is rotated so that the nut moves towards the head  62  of the bolt  54 . As its position is fixed by the spring  58 , the nut remains stationary relative to the hoop  52  causing the bolt  54  to axially move within the hoops  52  so that the end  64  of the bolt  54  approaches the stop  60 . Upon engagement of the stop  60 , the end  64  and hence the bolt  54 , can not move further and therefore the nut begins to move. The movement of the nut causes the spring  58  and hence the hoop  52  to move towards the head  62  of the elongate bolt  54 . This in turn results in the plate  50 , the two bolts  42  and the forward section  8  to move with the nut  56 , the bolts  42  sliding within the two slots  40 . However, when the belt  26  becomes tight, the forward section  8 , and hence the bolts  42  and plate  50  are prevented from moving further. However, if the elongate nut  54  is further rotated, the nut  56  will continue to travel along its length. Therefore, the spring  58  becomes compressed, applying a force onto the hoop, and hence plate  50 , which in turn transfers it to the forward section  8 . This tensions the belt  26 . The more compression of the spring  58 , the more force is applied to the belt  26 . An indicator  66  is added to the plate  50  to show when the amount of the compression of the spring  58  is sufficient to apply the correct amount of force to the belt  26 . 
         [0060]    The blade mount on the forward section  8  will now be described. 
         [0061]    Referring to  FIG. 7 , the driven wheel  32  is rotatably mounted on the forward section  8 . The driven wheel  32  is drivingly connected to the cutting blade  10  via a spindle  70  as will be described in more detail below. The blade guard  22  is pivotally mounted around the spindle  70  as will be described in more detail below. A grasp  72  is rigidly attached to the blade guard  22  which can held by an operator in order to pivot the blade guard  22 . 
         [0062]      FIGS. 12 to 18  show the mechanism by which the forward support  8  rotatably supports the cutting blade  10 . 
         [0063]    Referring to  FIGS. 17 and 18 , the driven wheel  32  is rigidly attached to the spindle  70  via a flanged nut  74 . Rotation of the driven wheel  32  results in rotation of the spindle  70 . The spindle  70  is mounted in the forward section  8  using two ball bearing races  76 , each comprising an inner track  78  rigidly connected to the spindle  70 , an outer track  80  rigidly connected to the forward support  8 , and a set of ball bearings  82  sandwiched between the two tracks  78 ,  80  which allow the outer track  80  to rotate relative to the inner track  78 . 
         [0064]    Formed along a part of the length of the spindle  70  are two flat surfaces  84  (see  FIG. 16 ). A second support disk  86  comprises a central hole which is predominantly circular with the same diameter of the spindle  70 , but with two flat sides which correspond in dimensions to the flat surfaces  84  of the spindle  70 . The second support disk  86  is mounted on the end of the spindle  70  and abuts against shoulders  88  on the spindle  70  formed by the two flat surfaces  84 . The flat surfaces  84  ensure that the second support disk is rotationally fixed to the spindle  70  so that rotation of the spindle  70  results in rotation of the second support disk  86 . 
         [0065]    An adaptor  90  (described in more detail below) is mounted on the spindle  70 . The adaptor can freely rotate about the spindle  70 . The cutting blade  10  is mounted on the adaptor  90 . 
         [0066]    A first support disk  92  comprises a central hole which is predominantly circular with the same diameter of the spindle  70 , but with two flat sides which correspond in dimensions to the flat surfaces  84  of the spindle  70 . The first support disk  92  is mounted on the end of the spindle  70  and abuts against the cutting blade  10 . The flat surfaces  84  ensure that the first support disk  92  is rotationally fixed to the spindle  70  so that rotation of the spindle  70  results in rotation of the first support disk  86 . 
         [0067]    A threaded hole  94  is formed in the end of the spindle  70  (see  FIGS. 10 to 12 ). A second flanged nut  96  is screwed into the hole  94 . The flange of the nut  96  pushes the first support disk  92  against the blade  10  which in turn pushes the blade  10  against the second support disk  86 . The blade  10  becomes sandwiched between the two support disks  86 ,  92 . Rotation of the support disks  86 ,  92  by the spindle  70  results in rotation of the blade due to the frictional contact of the blade  10  being sandwiched between the two disks  86 ,  92 . By frictionally driving the blade  10 , it allows rotational movement of the blade  10  relative to the spindle  70  if the blade becomes snagged during the operation of the power cutter. 
         [0068]    The automatic blade support adjustment mechanism will now be described. 
         [0069]    Cutting blades of different sizes can be used. Different sized cutting blades  10  have different sized holes in their centres through which the spindle  70  passes. It is intended that the present power cutter will be able to fit cutting blades  10  having two different sizes of hole through their centres. This is achieved by the use of the adaptor  90 . 
         [0070]    Referring to  FIGS. 17 and 18 , the adaptor is mounted on the spindle  70  between the two support disks  86 ,  92 . As well as being freely rotatable about the spindle  70 , the adaptor  90  can axially slide along the spindle  70  between the disks  86 ,  92 . 
         [0071]    The adaptor comprises a front section  98  and a rear section  100 . The front section  98  has a first outer diameter, the rear section  100  has a second larger outer diameter. The two sections allow blades  10  with holes of different diameters to be mounted onto the spindle  70 . In  FIGS. 14 to 18 , it can be seen that a blade  10  with a central hole of a first diameter is mounted on the rear section  100  of the adaptor  90 . In  FIG. 13 , it can be seen that a blade  10  with a central hole of a second diameter is mounted on the front section  98  of the adaptor  90 . 
         [0072]    A spring  102  is sandwiched between the second support disk  86  and an inner shoulder  104  of the adaptor  90 . The spring  102  biases the adaptor towards the first support disk  92 . A circlip  106  is located around the spindle  70  which limits the maximum extent of axial travel of the adaptor  90 . When the adaptor  90  is allowed to slide to its maximum extent and abut against the circlip  106 , the rear section  100  is located centrally between the support disks  86 ,  92 . 
         [0073]    When a blade  10 , having a centre hole with the same diameter of the rear section  100  of the adaptor is mounted onto the adapter, it fits onto the rear section  100  of the adaptor as shown in  FIG. 14 to 18 . As such, the blade  10  is centrally located between the two support disks  86 .  92 . However, when a blade  10 , having a centre hole with the same diameter of the front section  98  of the adaptor is mounted onto the adapter, it fits onto the front section  98  of the adaptor as shown in  FIG. 13 . It is prevented from sliding onto the rear section. In order for the blade  10  to be secured onto the spindle  70  by the support disks  86 ,  92 , it must be located centrally between the two. When the first support disk  92  is mounted onto the spindle  70  after the blade, it pushes the blade  10  and adaptor  90  against the biasing force of the spring  102 , moving the adaptor  90  towards the second support disk  86  as shown in  FIG. 13 . When the blade is securely mounted on the spindle  70 , it is centrally located between the support disks. The front section is similarly mounted centrally. The adaptor enables two types of blade  10  to be used, it moving automatically in accordance with blade size. 
         [0074]    The pivotal blade guard  22  will now be described. 
         [0075]    Referring to  FIG. 15 , the blade guard  22  is held by being sandwiched between two pieces of rubber  108 ,  110 . The blade guard  22  can pivot about the spindle  70 . However, it is frictionally held by the two pieces of rubber  108 ,  110 . In order to pivot the guard  22 , the operator must overcome the friction between the guard  22  and the rubber  108 ,  110 . 
         [0076]    A metal bracket  112  is attached to the forward section  8  via four bolts  114 . The bolts pass freely through the forward section  8  and threadedly engage with threaded holes formed in the bracket  112 . A helical spring  116  is sandwiched between the head  118  of each bolt  114  and the forward section  8 , biasing the bolts  114  out of the holes, pulling the bracket  112  towards the forward section. Sandwiched between the bracket and the forward section  8  is a first piece of rubber,  108 , the guard  22 , a second piece of rubber  110  to form a rubber-guard-rubber sandwich. The strength of the spring  116  determines the amount of frictional force there is between the rubber  108 ,  110  and the guard. 
         [0077]    In order to pivot the guard the operator holds the grasp  72  and pivots the guard  22  by over coming the frictional force between the guard and the rubber  108 ,  110 . 
         [0078]    The oil and petrol management system will now be described with reference to  FIG. 19 . 
         [0079]    The internal combustion engine is fed with fuel from a carburetor  126 . The engine burns the fuel in well known manner to generate rotary motion of its crank shaft  114 , which connects to the output shaft  28 . The exhaust gases are then expelled from the engine  24  through an exhaust  146  to the surrounding atmosphere. 
         [0080]    The power cutter will comprise a petrol tank  124  in which is located petrol for driving the two stroke internal combustion engine  24 . Petrol will pass from the tank  124  via passageway generally indicated by dashed lines  144  through the carburetor  126  which will mix it with air prior to being forwarded to the cylinder  118  where it will be burnt. Detail of the supply of air, including its filtration will be described in more detail below. A second tank  128  will also be mounted in the body  2  as shown in which lubricating oil will be contained. The oil will be pumped out of the tank  128  via an oil pump  130 , which is mounted on the crank shaft housing which will be driven via a gear arrangement (not shown) from the crank shaft  114 . The oil pump  130 , will pump the oil from the oil tank  128  via the pump  130  into the passageway  132  between the carburetor  126  and the cylinder  120 , through the passageways indicated by dashed lines  142 , and then mixing the oil with the air/petrol mixture generated by the carburetor  126 . It will inject oil at the ratio 1:50 in relation to the petrol. A sensor  140  will be mounted within the passageway  132  between the carburetor  126  and cylinder  120 . The sensor will determine whether oil is being pumped correctly in to the passageway  132  either by checking the pressure of the oil as it enters the passageway  132  or by detecting the presence of oil in the passageway  132 . The construction of such sensors are well known and therefore will not be described in any further detail. The engine will be controlled by an electronic ignition system. The sensor  140  will provide signals to the electronic ignition system about the oil being pumped into the passageway  132 . In the event that insufficient or no oil is pumped into the passageway due to the fact that the oil tank is empty or there is a blockage in an oil pipe  142 , the sensor  140  will send the signal to the ignition system. The ignition system will then either put the engine into an idle mode or switch the engine off entirely, depending on the settings of the ignition system. This will ensure that lubricating oil is always added to the petrol in the correct amount prior to combustion within the two stroke engine. 
         [0081]    The construction of the fuel cap will now be described with reference to  FIGS. 20 to 23 . 
         [0082]    The petrol tank  124  will be mounted within the body of the unit as generally indicated in  FIG. 19 . The tank  124  will be sealed by a fuel cap  13  as shown on  FIG. 2 . 
         [0083]    The fuel cap will comprise an inner cap  202 , a clutch  204  and an outer cap  206 . The inner cap is of a tubular construction with one end  210  being sealed. Formed on the inside surface of a side wall  212  is a thread  208 . When the fuel cap is screwed onto the fuel tank, the thread  208  slidingly engages with a thread formed around the external surface of the neck of the fuel tank  124 . 
         [0084]    Located inside the inner cap  202  adjacent the end  210  is a seal  214 . When the fuel cap is screwed onto the fuel tank, the seal  214  ensures that no fuel can escape from the tank. The inner cap  2  locates within the outer cap  206 . Sandwiched between the two is the clutch  204 . A clip  216  locates within a groove  218  of the inner cap and also engages with an inner groove  220  formed within the outer cap. The clip holds the inner cap inside the outer cap whilst allowing it to freely rotate within the outer cap  206 . The inner cap comprises a number of teeth  222  integrally formed with the inner cap. The teeth locate within corresponding slots  224  formed within the clutch, thus rotation of the inner cap causes rotation of the clutch  204 . Formed on the clutch  204  are a plurality of resilient arms  226  mounted on the ends of which are pegs  228 . The pegs  228  face towards the internal end wall  230  of the outer cap. Formed on the wall are a plurality of ridges  232 . The pegs on the clutch are arranged to co-operate with the ridges  232  in the outer cap. 
         [0085]    Rotation of the outer cap  206  causes the ridges  232  to engage with the pegs  228  resulting in rotation of the clutch  204 , which in turn rotates the inner cap  202  via the teeth  222 . When the fuel cap is screwed onto the fuel tank, the inner cap  202  threadingly engages with the neck of the fuel tank, the rotation of the inner cap  202  being caused by rotation of the outer cap  6  via an operator rotating it using a finger grip  234 . When the seal  214  located within the inner cap engages with the end of the neck of the fuel tank, the inner cap  202  is prevented from further rotation. This in turn prevents further rotation of the clutch  204 . However as the operator continues to exert a rotational force on the outer cap  206 , the ridges  232  are caused to ride over the pegs  228 , the movement of the pegs  228  being allowed by the resilient arms  226  upon which they are mounted. In this way the operator can rotate the outer cap whilst the inner cap remains stationary thus preventing the operator from over-tightening the fuel cap onto the neck of the fuel tank 
         [0086]    The air filtration mechanism for the carburettor  126  will now be described. 
         [0087]    The two stroke engine comprises a carburetor  126  which mixes liquid fuel with air to generate a combustible mixture for powering the engine. However, due to the operation of the power cutter, a large amount of dust is generated which mixes with the surrounding air. This results in dust laden air. In order to ensure that the air entering the carburettor is free from dust it must pass through a filter system to remove the dust. 
         [0088]    The filter system will now be described with reference to  FIGS. 23 to 29 . 
         [0089]    Inside the body  2  is a filter unit  316  comprising a plastic base  318  and filter paper  320  folded to form pleats. The filter unit  316  is located within the body  2  so that the pleats  320  hang vertically downwards when the power cutter is in a storage position as shown in  FIGS. 1 and 2 . 
         [0090]    Air will be sucked through the filter system by the carburetor  126 . Air enters slots  314  on the rear of the body  2 . Air passes (Arrow G) to a space  322  underneath the filter unit  316  and then passes through the filter paper  320  to a space  324  above the filter unit  316 . Any dust entrained within the air is trapped by the filter unit  316  and held within the pleats of the filter paper  320 . 
         [0091]    The clean air then passes from the space  324 , through a hose  326  to the carburetor  126  located below the space  322  below the filter unit  316 . 
         [0092]    In order to enable the operator to remove the dust trapped within the pleats of the filter paper  320 , a cleaning device is provided. The cleaning device comprises a rubber flap  328 , mounted on the top of a plastic base  330 , a brush  332  attached to the bottom of the plastic base  330 , a handle  334  attached to the plastic base  330  via to rigid arms  338 . The base  330  can slide within the space  322  below the filter unit  316 , widthways across the body  2 . Movement is caused by the operator pulling the handle  334  away from the side of the body  2 . Two springs  336  bias the handle  334  towards the side of the body  2 . 
         [0093]    In order to clean the filter unit, the operator pulls the handle  334 , to move the base  330  across the width of the body  2  in the direction of Arrow H, and then releases it to allow it to return in the opposite direction under the biasing force of the springs  336 . 
         [0094]    As the base  330  slides across the width, the rubber flap  328  engage with the pleats  320 , as best seen in  FIG. 25 , knocking the dust of the pleats  320 . The dust drops to the base  340  of the space  322  below the filter unit  316 . 
         [0095]    The brush  332  slidingly engages with the base  340  of the space  322 . The brush  332  brushes the dust to one side or the other, depending on the direction of movement. An aperture  344  is formed on one side of the body  2 . As the brush approaches the side of the body, it pushes the dust being swept along the base through the apertures, expelling it from the body  2 . 
         [0096]    Though  FIG. 4  shows the flap  28  moving perpendicularly to the direction of the pleats  320 , it will be appreciated by a person skilled in the art that is possible to rotate the filter paper  320  so that the pleats run in parallel to the sliding movement of the flap  328  as shown in  FIG. 26 . In such a scenario, the rubber flap  28  may be replaced by a plurality of brushes  342 . 
         [0097]    The construction of the rear handle will now be described with reference to  FIGS. 1 and 2 . 
         [0098]    The body of the power cutter is constructed in the form of a plastic casing constructed from a number of plastic clamshell rigidly connected together. The rear clam shell  430  connects to the rear handle  6 . In existing designs of power cutter, the rear handle  6  is integral with the rear clam shell  430 . However, if the handle  6  is broken, the whole clam shell  430  needs to be replaced. As handle breakage is common it is desirable to avoid this. 
         [0099]    Therefore, the rear handle  6  in the present invention is constructed as a separate item to that of the rear clam shell  40  (or body  2 ). 
         [0100]    The rear handle  6  is constructed from a separate single clam shell  431  which is joined at its top  432  at two points  434  and at its bottom at a single point  436 . Each of the three points  434 ,  436  is joined using a bolt which screws into the plastic clam shell  430 . Vibration dampening material may be used in conjunction with the bolts to reduce the amount of vibration transferred to the handle  6  from the body  2 . The use of such vibration dampening material allows limited movement of the handle  6  relative to the rear clam  430  at each of the three points. The movement could be either linear or rotational. One such construction is to surround the bolts with the dampening material in order to sandwich it between the bolts and parts of the clam shell of the rear handle  6 . 
         [0101]    The top  432  of the handle  6  is in the form of a cross bar. The shape is such that the bolts fastening the top  432  of the handle to the rear of the clam shell  430  are aligned with each other and thus provide a pivot axis  440  for the rear handle  6  about which it can rotate by a limited amount. 
         [0102]    A person skilled in the art will appreciate that the handle may be constructed from a number of clam shell connect rigidly together. Rubber soft grip over mold  442  may also be added to the handle for additional comfort. 
         [0103]    A second embodiment of an air filtration system will now be described with reference to  FIG. 30 . 
         [0104]    The filter device comprises a box  400  in which is mounted filter paper  402  which is pleated and which hangs down from the top section from inside the box. A space  404  is formed below the pleat. A large aperture  406  is formed in the side of the box below the filter paper and through which a drawer  408  can be slid. The drawer comprises a receptacle  410  which locates in the space  404  immediately below the filter paper  402 . The drawer  408  can be fastened into place via a screw  412  which threadedly engages a threaded hole  414  in the box. Air passes through slots  314  into the box and into the receptacle  410  in the space  404  below the filter paper  402  then through the filter paper  402  into a space  416  above the filter paper  402  and then exits the space  416  above the filter paper through a flexible tube  418  to the carburetor  126 . Any dust contained in the air entering the box  400  is blocked by the filter paper  402 . 
         [0105]    A combination of two systems have been proposed to shake any dust within the filter paper  402  off the filter paper  402  into the drawer  408  so that the drawer  408  an be removed for emptying. 
         [0106]    The first system is very similar to that disclosed in the first embodiment described above and comprises a rubber flap  420  which is attached to the front end of the drawer  408 . As the drawer  408  is inserted into the box  400  the rubber flap  420  engages with the pleated filter paper  402 . As the drawer  408  slides into the box  400  the rubber flap  420  successively hits the base of each pleat causing any dust on the pleats to be knocked off and into the drawer  408 . As such the action of inserting or removing the drawer  408  into the box  400  causes dust on the filter paper  402  to be loosened and allowed to be removed. 
         [0107]    The second system relies on the starter cord  422  of the start  12  for the two stroke engine  24  of the power saw. When the engine is started, the power cord  422  needs to be pulled in order to cause it to rotate. As the cord  422  is pulled, it rotates a pulley wheel  424  which causes an eccentric pin  426  to rotate about the axis  428  of the pulley  420 . This causes one side of the box  400  to oscillate up and down as indicated by arrows Y. The other side of the box  400  is pivotally attached about an axis  435  to the body of the power cutter. The reciprocating motion of the box  400  causes dust in the filter  402  to be shaken off the filter paper  402  and into the drawer  408 . 
         [0108]    Each system cause dust trapped in the filter paper  402  to fail into the drawer. When the operator first starts up the power cutter, the action of pulling the starter cord cleans the filter paper  402 . Then, the operator can subsequently clean the filter paper during the operation of the power cutter by inserting and removing the drawing  408 . 
         [0109]    It will be appreciated by a person skilled in the art that the two systems could be used separately, as well as in combination, a power cutter having only one or the other system.