Abstract:
An anti-bounce device ( 100 ) for a saw mill, the device including a strut ( 60 ) having a first end piece ( 50 ), a second end piece ( 51 ) and a resilient member ( 52 ) therebetween, the first end piece of the strut being moveable relative to the second end piece; an engagement means ( 40 ) associated with the strut ( 60 ) adapted to move across a surface of a material to be sawn, the engagement means ( 40 ) transferring force to the first end piece ( 50 ) of the strut and the resilient member ( 52 ) of the strut dampening relative movement between the first end piece ( 50 ) and the second end piece ( 51 ) of the strut thereby restraining movement of the engagement means ( 40 ) relative to the surface of the material to be saw, and connection means ( 70,80 ) for connecting the strut to the saw mill.

Description:
FIELD OF THE INVENTION 
     This invention relates to an anti-bounce device for saw mills. The device has particular application with portable saw mills. 
     BACKGROUND OF THE INVENTION 
     Such saw mills generally include a frame which straddles a log to be milled. The frame will typically include a pair of rails or tracks which in use extend longitudinally along the log. A carriage is mounted for movement along the rails or tracks. The carriage typically carries an engine, gearbox and saw blade. The saw mill can be of a swing blade type which permits the blade to be moved to vertical and horizontal positions so that vertical and horizontal cuts can be made in the log as the carriage is moved along the rails or tracks. 
     A sawing device comprising a saw blade, which pivots through 90° to act in both the horizontal and vertical planes, is known. In such a sawing device, the saw is moved along the length of the material. Permanent and portable versions of such saw mills are available. 
     As can be appreciated, movement of the saw blade relative to the material being sawn, in any direction other than the desired cut direction, is undesirable. For instance, when making a longitudinal cut, either vertically or horizontally, movement of the blade in and out of the cut is to be avoided. If this form of shake, or bounce, can be avoided a significantly improved finish is possible on the sawn material and the tooth life of the saw blade will be lengthened. 
     The problem of bounce is particularly pronounced in portable saw mills, since the power head (which includes an engine, gearbox and saw blade) is not supported by as heavy or sturdy a frame as in the permanent saw mill. That is, the frame on which the saw blade is mounted provides less resistance to bounce in a portable saw mill. 
     Portable saw mills generally include a frame which straddles the material to be sawn. A carriage mounted on the tracks, and which carries the power head, allows movement of the saw blade along the material to be sawn. The track is typically a pair of rails that can be positioned vertically so that the depth of a vertical cut by the saw blade can be set. The depth of any horizontal cut is controlled by moving the frame, on which is mounted the power head and the saw blade, relative to the material to be sawn. Increasing the depth of the cut, and/or the length of the tracks between the ends pieces, each independently increases the likelihood of shake or bounce. 
     A well known portable saw mill of this type is described in Australian patent 688020, the disclosure of which is incorporated herein by way of specific reference. When such a device is used to make a vertical cut, one problem is that the saw blade moves up and down vertically as the carriage bounces. The result is that the saw blade intermittently comes off the floor of the vertical cut, which stresses the teeth of the saw blade and results in the depth of the cut being uneven. When such a device is used to make a horizontal cut, one problem is again that the saw blade moves left and right. 
     The invention will be described with reference to portable saw mills but the skilled person will appreciate its applicability to permanent saw mills in certain circumstances. The object of the invention is to reduce the above-described undesirable movement of saw blades in saw mills. 
     Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art. 
     SUMMARY OF THE INVENTION 
     In one aspect of the invention there is provided an anti-bounce device for a saw mill, the device comprising
         a strut having a first end, a second end, and a resilient member therebetween, the first end of the strut being moveable relative to the second end;   an engagement means associated with the strut adapted to move across a surface of a material to be sawn, the engagement means transferring force to the strut, the resilient member of the strut dampening relative movement between the first end and the second end of the strut; and   connection means for connecting the strut to the saw mill.       

     In another aspect of the invention there is provided a saw mill for sawing material comprising
         a pair of rails or tracks and a carriage mounted on the rails/tracks for movement therealong, the carriage comprising a saw blade mount from which a driven saw blade is adapted to cut material as the carriage moves along the rails/tracks; the saw mill being characterized by an anti bounce device; the anti bounce device comprising   a strut having a first end, a second end, and a resilient member therebetween, the first end of the strut being moveable relative to the second end   connection means for connecting a strut to the saw mill; and   an engagement means associated with the strut adapted to move across a surface of a material to be sawn as the carriage is moved, the engagement means transferring force to the strut and the resilient member of the strut dampening relative movement between the first end and the second end of the strut thereby restraining movement of the engagement means relative to the surface of the material to be sawn.       

     In the simplest embodiments, the strut may be the resilient member. For instance, the strut may be a spring, where movement of the first end of the spring towards the second end of the spring causes compression and the spring to be in a stressed state. The strut may be a shock absorber as commercially available and known. 
     In preferred embodiments, the strut includes a first tubular member having a first end and a second tubular member having a second end, one tubular member received within the other tubular member in a sliding engagement. In these embodiments, the ‘ends’ of the first and second tubular members need not be a physical end but may in their broadest form be any portion of the tubular member that in use can engage and transfer force to the resilient member. For instance, the end may be a physically closed end of the tubular member, an internal protrusion within the tubular member against which an end of the resilient member abuts during use, or a hole in the side of the tubular member through which part of the resilient member may pass. To result in a telescoping sliding engagement the first and second tubular members are preferably of co-operating cross-sectional shape. The tubular members need not be of circular cross-sectional shape. Preferably, the tubular members have an angular cross-sectional shape. More preferably, the tubular members have a rectangular or square cross-sectional shape. The resilient member can be positioned within the first tubular member and/or second tubular member, and can be acted upon by both the first end and the second end. Pressure on one tubular member will cause telescoping movement of the two tubular members towards each other and will stress the resilient member therebetween. In this state the strut is referred to as being in a stressed state. Release of pressure will permit movement of the two tubular members away from each other and will relax such stress. In this state the strut is referred to as being in a relaxed state. 
     The resilient member may be, for instance, a piece of rubber, compressed gas, compressible liquid, or a spring in combination with a hydraulic dampener. The resilient member may be a gas spring/hydraulic dampener. or a conventional spring/hydraulic dampener. as known to those skilled in the art. 
     The engagement means is associated with the strut in that both move together with movement of the carriage and forces transferred from the surface of the material to be cut to the engagement means are further transferred to the strut, thus compressing it to a stressed state. Preferably, the engagement means is positioned directly in line with the longitudinal direction of the strut so that force is directly transferred. Preferably, the engagement means is a wheel that runs along the surface of the material to be cut as the carriage is moved along the track. 
     In preferred embodiments, the engagement means is a wheel or roller where the surface of the wheel that rolls over another surface has a central ridge or rib running circumferentially thereabout and extending therefrom. The purpose of the ridge is to allow the wheel to slot into an already made vertical cut, and thus reduce horizontal shake of the saw blade, when making a subsequent horizontal cut. Thus, in embodiments including a ridge for this purpose, the ridge is necessarily of smaller thickness than, but is more preferably commensurate with, the width of the cut made by the saw blade. 
     In other preferred embodiments, the anti-bounce device further includes a guide disposed adjacent the engagement means, but vertically above the level of the engagement means and, and preferably vertically between the level of the engagement means that engages the surface of the material to be sawn and the lower end of the strut. The purpose of the guide is to assist with placing the resilient member in a stressed state when in use, ie when the engagement means is engaged with a surface of the material to be sawn. 
     The connection means may be for connecting the strut to the carriage or to some component carried by the carriage. Preferably, the strut is connected to the carriage. By connected it is not meant to exclude the strut being integrally formed with, ie a part of, the carriage. In preferred embodiments, the connection means are such that the position of the engagement means with respect to the saw blade can be adjusted. In these embodiments, it is preferable that both the vertical and horizontal displacement of the engagement means, from say the centre of the saw blade, is adjustable. For instance, the connection means may include a first component for adjusting the horizontal displacement and a second component for adjusting the vertical displacement. In these embodiments, the first component may engage both the carriage and the second component, and the second component may engage the strut. Preferably, and to achieve maximum effectiveness from the strut, the strut is in use aligned so that it is vertically parallel with the saw blade. That is, the motion of the first end towards the second end is in a direction that is vertically parallel to the saw blade bounce movement. 
     Preferably, the carriage also carries a saw. The anti-bounce device can be connected to the carriage at any position that allows it to travel along the surface of the material to be sawn at the same time as the blade moves through the material as it is sawn. That is, the anti-bounce device, or more particularly the engagement means, need not be in longitudinal alignment with the saw blade, and thus need not travel the same path on the material being sawn. For instance, the anti-bounce device can be offset from the saw blade. Importantly, the transverse displacement of the engagement means from the saw blade must not be such that one or the other does not contact the material being sawn when in use. More preferably, the transverse positioning of the anti-bounce device is adjustable by having the connection means movable across the transverse direction of the carriage. 
     The saw mill can be any as known in the art. Preferably, the saw mill is a portable saw mill. Such a saw mill most typically includes 2 substantially parallel rails or tracks and the carriage is adapted to engage and move along both rails or tracks simultaneously. A particularly preferred saw mill is described in Australian patent 688020. 
     The anti-bounce device may be used for any suitable sawing application, for instance, concrete, metal, plastic or wood. Preferably, the material to be sawn is wood. More preferably, the material to be sawn is a log. 
     As used herein, except where the context requires otherwise, the term “comprise” and variations of the term, such as “comprising”, “comprises” and “comprised”, are not intended to exclude further additives, components, integers or steps. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric perspective view of an embodiment of the anti-bounce device of the present invention. 
         FIG. 2  is an exploded isometric perspective view of a first tubular member including a guide, a second tubular member, and a strut in accordance with an embodiment of the anti-bounce device of the present invention. 
         FIG. 3  is an exploded isometric perspective view of a first component, for adjusting the horizontal displacement, and a second component, for adjusting the horizontal displacement, of a connection means in accordance with an embodiment of the anti-bounce device of the present invention. 
         FIG. 4  is an exploded isometric perspective view of a T-bolt fixing for the first and second components of  FIG. 3 . 
         FIG. 5  is an exploded isometric perspective view of an engagement means in accordance with an embodiment of the anti-bounce device of the present invention. 
         FIG. 6  is an isometric perspective schematic of a portable saw mill including an anti-bounce device in accordance with an embodiment of the anti-bounce device of the present invention. 
         FIG. 7  is a schematic showing the effect of the anti-bounce device  100  in both vertical (A) and horizontal (B) cutting regimes. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     In this specification, the terms vertical and horizontal are used as references to the direction of the cut and the anti-bounce device is described in relation to a saw mill where it is bounce in the direction of the cut (both horizontal and vertical) that is to be avoided. 
     The following description and reference to a saw mill suitable for use with the anti bounce device of the invention is intended for illustration purposes only and is not intended to be limiting of the features of the saw mill to which the invention is applicable. The invention is particularly applicable to saw mills having a pair of rails or tracks and a carriage mounted on the rails or tracks for movement therealong. The carriage comprises a saw blade mount from which a driven saw blade is adapted to cut material as the carriage moves along the rails or tracks. 
     Referring first to  FIG. 6 , an embodiment of a preferred form of portable saw mill  10  can be seen including end pieces  12 ,  13 , and tracks  14 ,  15  extending longitudinally therebetween. Carriage  16  extends transversely and is engaged to tracks  14 ,  15  such that it is movable towards and away from the end pieces. Carriage  16  carries a saw  18  and the anti-bounce device  100  of the present invention. Movement of carriage  16  along the tracks  14 ,  15  allows for movement of the saw  18  along the material to be sawn  20  (in this case a log). The engagement means  40  of the anti-bounce device  100  also moves along the surface of beam  20 . 
     The anti-bounce device  100  is shown in more detail in  FIGS. 1 to 5 . In  FIG. 1 , the assembled anti-bounce device  100  is shown. Engagement means  40  includes a wheel  41  attached to a first tubular member  50  of strut  60 . The wheel includes ridge  42 . The first tubular member  50  is slidingly engaged with second tubular member  51  of strut  60 . Resilient member  52  of strut  60  is disposed within first tubular member  50  and second tubular member  51 . The relationship between resilient member  52 , first tubular member  50  and second tubular member  51  is best seen in  FIG. 2 . 
     The wheel  41  is attached to first tubular member  50  by a nut and bolt combination as shown in  FIG. 5 . A bearing  43  engages in the centre of the wheel  41 . The end of the inner race of the bearing  43  is engaged against a nut  44 , with a washer  45  being therebetween. When bolt  46  in first tubular member  50  is engaged through opening  47  it can be adjusted in and out and locked against the wall of the first tubular member  50  with lock nut  48  ( FIG. 1 ). 
     Resilient member  52 , which in this embodiment is a gas spring, has a rod  53  with a nut  54  fitted thereto. The rod  53  is engaged, when the anti-bounce device  100  is assembled, in the first tubular member  50  so that the bolt  46  for attaching the wheel passes through nut  54  to thereby anchor the rod  53 . 
     The body  55  of the shock absorber device  52  is received in the second tubular member  51 . The end of the body  55  has a nut  56  into which a grub screw  57  can be engaged. The nut  56  is, when the anti-bounce device  100  is assembled, aligned with opening  58  in the second tubular member  51  and the grub screw  57  screwed in to thereby anchor the body  55  in the second tubular member  51 . The first tubular member  50  and second tubular member  51  are thereby coupled together by the resilient member  52  to form the strut  60 . 
     The first tubular member  50  is dimensionally smaller but of similar cross sectional shape to the second tubular member  51  so it can fit, optionally with clearance, in second tubular member  51 . Due to the angular cross sectional shape of the arrangement substantially no twisting of the first tubular member  50  with respect to the second tubular member  51  can occur. 
     The connection means are best illustrated in  FIGS. 1 and 3 . Here, a first component  70  (referred to as a strut mount  70 ) and a second component  80  (referred to as a carriage mount  80 ) are shown. The strut mount  70  is adapted to encompass second tubular member  51  and provides for vertical adjustment of the anti-bounce device  100  relative to the saw  18 . The carriage mount  80  is adapted to encompass a portion of the strut mount  70  and engage the carriage  16  and provides for horizontal adjustment of the anti-bounce device  100  relative to the saw  18 . 
     The strut mount  70  has a tongue  71  which extends transverse to a tubular section  72  which has a longitudinal slot  73  cut in one wall. The slot  73  forms a clearance for the head of the grub screw  57  which protrudes from second tubular member  51 , as well as allowing for compression of the tubular section  72  to provide a clamping action on the second tubular member  51 . 
     The tubular section  72  carries on opposed walls flanges  74 ,  75 . One flange  74  has fastened thereto a nut  76  which is opposite an opening  77  in the other flange  75 . A fastener  78  of the T-bolt type illustrated in  FIG. 4  is engaged though opening  77  and into nut  76  as is shown in assembled form in  FIG. 1 . Thus with the second tubular member  51  slidingly received in tubular section  72  of the strut mount  70 , the position of the strut  60  (and engagement means  40 ) can be adjusted vertically before the fastener  78  is tightened to cause the tubular section  72  to clamp the strut mount  70  in place. 
     The carriage mount  80  is of a similar construction as the strut mount  70 . In place of the tongue  71  of the strut mount  70 , the carriage mount  80  has a mounting plate  81 . This mounting plate  81  permits the carriage mount  80  to be fixed in place on the carriage  16  of the saw mill  10 . In this embodiment the carriage mount is positioned such that the engagement means is in alignment with the saw blade and the direction of the intended cut. As well, the carriage mount  80  shown is of the un-adjustable kind, but the skilled person would understand how to make this mount adjustable. The mounting plate  81  is connected to a tubular section  82  which has a longitudinal slot  83  cut in one wall. The slot allows for compression of the tubular section  82  to provide a clamping action on the tongue  71  of the strut mount  70 , which is received therein. 
     The tubular section  82  carries on opposed walls flanges,  84 ,  85 . One flange  84  has fastened thereto a nut  86  which is opposite an opening  87  in the other flange  85 . A fastener  88  of the T-bolt type illustrated in  FIG. 4  is engaged though opening  87  into nut  86  as is shown in assembled form in  FIG. 1 . Thus with the tongue  71  of the strut mount  70  slidingly received in tubular section  82  of the strut mount  70 , the position of the strut  60  (and engagement means  40 ) can be adjusted horizontally before the fastener  88  is tightened to cause the tubular section  82  to clamp the strut mount  70  in place. 
     In use, the wooden beam  20  is position beneath the path of carriage  16  and saw blade  18 . The horizontal position of the strut  60  and engagement means  40  relative to the saw blade is adjusted so that free movement of the saw blade is allowed. The vertical position of the strut  60  and engagement means  40  relative to the surface of beam  20  along which the engagement means  40  runs is adjusted so that before the engagement means  40  actually engages the beam  20  it is lower than the surface. Thus, as the carriage  16  is moved towards an end of the beam  20 , the resilient member  52  in strut  60  must be compressed to a stressed state to allow the engagement means  40  to move up onto the surface of beam  20 . The resilient member  52  will remain in a stressed state as carriage  16  and saw blade  18  moves along the remainder of the beam  20  making the cut. Any bouncing of the carriage  16  will be lessened/dampened by the presence of the anti-bounce device  100  in a stressed state. The skilled person will appreciate the mechanism by which this lessening occurs. The effect of the anti-bounce device  100  is better shown in  FIG. 7 . 
     Referring to  FIG. 7 , as the saw blade  18  progresses in the z direction into and out of the page the carriage is prone to bouncing (which are also in the z direction). As in  FIG. 7A , if a vertical cut is being made (ie the saw blade  18  is in a vertical position), the anti-bounce device  100  (not shown in  FIG. 7A ) lessens movement of the saw blade up and down vertically in the x direction as the carriage and track bounces. The saw blade less often comes off the floor of the vertical cut  19 , which reduces stress on the teeth of the saw blade and results in the depth of the cut being more even. As in  FIG. 7B , if a horizontal cut is being made (ie the saw blade  18  is in a horizontal position), the anti-bounce device  100  lessens movement of the saw blade in the y direction (left and right). Horizontal movement of the saw blade in the y direction is lessened due to positioning ridge  42  of engagement means  40  within the cut  19 . 
     The anti-bounce device can be connected to the carriage at any position that allows it to travel along the surface of the material to be sawn at the same time as the blade moves through the material as it is sawn. That is, the anti-bounce device, or more particularly the engagement means, need not be in longitudinal alignment with the saw blade, and thus need not travel the same path on the material being sawn. For instance, the anti-bounce device can be offset from the saw blade. Importantly, the transverse displacement of the engagement means from the saw blade must not be such that one or the other does not contact the material being sawn when in use. More preferably, the transverse positioning of the anti-bounce device is adjustable by having the connection means movable across the transverse direction of the carriage. 
     In the embodiment shown in  FIGS. 2 and 3 , a guide  49  is shown disposed adjacent the engagement means  40  and as part of first tubular member  50 . The guide  49  is positioned vertically above the level of the engagement means that engages the surface of the material to be sawn. With the anti-bounce device  100  fixed to the carriage  16  the strut  60 , and thus guide  49 , is vertically adjustable. Accordingly, when the saw  18  is arranged to proceed with cutting, the strut  60  is lowered so that the guide  49  touches the top of the beam  20 . When the cut of beam  20  commences the engagement means  40  must then ‘step up’ onto the log, which pushes the first end of the strut  50 ,  54  towards the second end of the strut  51 ,  56 , thus compressing the resilient member  52  therebetween. This establishes a restorative force in the strut  60  that acts on the engagement means  40  and to dampen up and down bounce of the saw blade  18 . 
     It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.