P1/00/011 Regulation 3.2 AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION FOR AN INNOVATION PATENT ORIGINAL Name of Applicant: PMD INTERNATIONAL PTY LTD Actual Inventors: Brett JOHNSON Address for Service: Houlihan 2 , Level 1, 70 Doncaster Road, Balwyn North, Victoria 3104, Australia Invention Title: CHAINSAW SHARPENER GUIDE AND METHOD OF USE THEREOF The following statement is a full description of this invention, including the best method of performing it known to the Applicant: 1 CHAINSAW SHARPENER GUIDE AND METHOD OF USE THEREOF FIELD OF THE INVENTION [0001] The present invention relates to a chainsaw sharpener guide which permits accurate alignment of a manual grinding tool with the cutting edge of a chainsaw cutting tooth. BACKGROUND TO THE INVENTION [0002] The cutting action of a chainsaw is performed by the cutting teeth found in the saw chain. Generally, up to half of the links in a saw chain are cutting teeth. Accordingly, sharpening of a chainsaw involves sharpening the cutting teeth present in the saw chain. The cutting teeth of a standard saw chain include a depth gauge and a cutting edge separated by a gap. The cutting edge is normally sharpened by use of a round file that is passed through the gap. One of the main difficulties involved in the sharpening of the cutting edge is the problem of maintaining uniformity in the cutting edge of the cutting teeth. [0003] Figure 1 shows a diagram of a typical cutting tooth 100 from a saw chain. The top plate 110 includes the main cutting surfaces and its geometry is important for the cutting efficiency of a chainsaw. The top plate cutting angle 111 is the forward slope of the top plate cutting edge 112 relative to the bottom of the cutting tooth 100. The top plate cutting edge 112 is the main cutting surface and therefore the top plate cutting angle 111 must be consistent between all of the cutting teeth of the saw chain, to ensure even wear of the saw chain and cutting teeth. [0004] While some methods of sharpening the cutting teeth of a chainsaw involve the use of an angle grinder or other motorised apparatus, sharpening is typically achieved by the use of a round file positioned in the gap 113 between the top plate cutting edge 112 and the depth gauge 114. Round files for sharpening cutting teeth typically range in size from 1/8 to 1/4 inches in diameter and from 6 to 8 inches in length. They are frequently held in 2 a planar device that facilitates the holding and guiding of the file during the sharpening operation. It will be apparent to the skilled person that the size and position of the round file will determine the top plate cutting angle 111 and that this positioning must be replicated for the sharpening of each cutting tooth 100. [0005] Other aspects of cutting are also determined by the geometry of the cutting tooth 100. The depth of the cut is determined by a combination of the depth gauge 114 and the clearance angle of the top plate 115. Removal of material from the side of the cut is determined by the clearance angle of the side plate 116 and the side plate cutting edge 117. The side plate cutting edge 117 is sharpened at the same time as the top plate cutting edge 112 and the angle of the side plate cutting edge 117 is determined by the filing angle 118. [0006] By maintaining consistency in the various geometries of the cutting tooth 100 the chainsaw will function efficiently and with reduced wear on mechanical components compared with a chainsaw whose chain is not sharpened correctly. [0007] Devices have been developed for holding round files for sharpening the cutting edges of the cutting teeth. An example is a filing guide with a longitudinally extending slot therein, the slot enabling the guide to be placed around the tooth on the saw chain. Another example is a chainsaw filing guide comprising a flat plate having a slot to straddle a depth gauge and side plate on a cutting tooth to be sharpened. [0008] The present invention relates to a file guide device to be used to guide a file in the operation of sharpening the teeth of a saw. A number of guide devices are known for this purpose some of which merely provide a sight line for the operator to observe during the sharpening operation, and others which positively guide the file in the required path. [0009] Australian Patent. No. 249518 describes a sharpening guide wherein the file is positively guided at the required angle to the cutting teeth, but this device, along with many other similar devices, is quite complicated and not suitable for sharpening chainsaws in the field. The capability of sharpening of chainsaws in the field is of major 3 importance in regard to chainsaws where the frequency of sharpening is quite high and under adverse working conditions. [0010] Another particular problem in sharpening chainsaws, apart from maintaining the correct angle on the cutting edge of the tooth, is that the operator whilst imparting the necessary reciprocating filing motion to the file must also simultaneously apply pressure in a direction transverse to this filing motion to maintain the file in engagement with the cutting edge of the tooth. The need to apply this pressure in the transverse direction renders it difficult for the operator to maintain the correct angle of the file to the direction of the length of the saw. Maintaining this transverse pressure is also relevant to the sharpening of a chain saw to maintain the file at the correct height in relation to the top plate of the tooth being sharpened. Sharpening each tooth of a chainsaw is made more difficult by the fact that normally the file is operated by one hand only, the other hand being used to hold the chain steady. [0011] The present invention seeks to address at least some of the shortcomings in previously known devices and holders by providing a guide that allows an operator to consistently and accurately sharpen the cutting teeth without the need for complex equipment or the use of power tools. In particular, the present invention seeks to provide a file guide device for use in sharpening the teeth of a chainsaw which is of simple construction, convenient to use, and requires a minimum of skill by the operator. SUMMARY OF THE INVENTION [0012] The present invention provides a chainsaw sharpener guide comprising: a) a first bar engagement member and a second bar engagement member, wherein the bar engagement members together define at least two bar engagement channels and a height setting surface; b) two substantially parallel connector shafts which link the first and second bar engagement members, wherein each connector shaft includes a roller; and c) optionally an adjustable tooth-length setter on the first bar engagement member. 4 [0013] The adjustable tooth-length setter may comprise a pair of rollers. [0014] The present invention also provides a method of using the chainsaw sharpener guide of the present invention whereby a cutter tooth of a chainsaw is sharpened. [0015] The present invention further provides a method of sharpening a cutter tooth of a chainsaw, the method comprising the steps of: a) locating the chainsaw sharpener guide according to the invention on a chain of a chainsaw, wherein the guide straddles the cutter tooth to be sharpened and the chain of the chainsaw extends along one of the bar engagement channels; b) bracing a file against a cutting edge of the cutting tooth; and c) filing the cutting tooth along the bar engagement channel, thereby sharpening the cutter tooth. [0016] The present invention further provides a method of lowering a depth gauge of a chainsaw, the method comprising the steps of: a) locating the chainsaw sharpener guide according to the invention on a chain of a chainsaw, wherein the guide straddles the depth gauge to be lowered and the chain of the chainsaw extends along one of the bar engagement channels; b) bracing a file against the depth gauge; and c) filing the depth gauge along the bar engagement channel, thereby lowering the depth gauge. BRIEF DESCRIPTION OF THE DRAWINGS [0017] Other features and advantages of one or more preferred embodiments of the present invention will be readily apparent to one of ordinary skill in the art from the following written description with reference to, and used in conjunction with, the accompanying drawings. [0018] Figure 1 shows a schematic diagram of a typical cutting tooth of a chainsaw in 5 perspective (A), side (B) and plan (C)/(D) views. [0019] Figure 2 shows a diagram of a cross-section through a connector shaft of a guide according to the present invention. [0020] Figure 3 shows various views of an embodiment of a guide according to the present invention. [0021] Figure 4 shows an exploded view of an embodiment of a guide according to the present invention. [0022] Figure 5 shows various views of the embodiment of the guide shown in Figure 4 in perspective (A), side (B), plan (C) and end (D) views. DETAILED DESCRIPTION OF THE INVENTION [0023] The present invention relates to the sharpening of chainsaws. Specifically, it is the cutting teeth of a chainsaw chain, or saw chain, that are sharpened. The skilled person will recognise the need for sharpening the cutting teeth. Attempting to cut wood with a blunt or dull chain will result in reduced power and cutting speed, as well as increasing fuel consumption and wear on the various components of the chainsaw. [0024] While some methods of sharpening the cutting teeth of a saw chain involve the use of an angle grinder or other motorised apparatus. The skilled person will readily appreciate that a manually operated round file has significant advantages over power tools, especially in remote areas where access to power might be restricted. [0025] It will be appreciated that the cutting teeth of a saw chain are generally arranged so that the cutting edge on adjacent cutting teeth face opposite sides of the saw chain, and accordingly, when sharpening, one tooth must be sharpened at a specific angle to the saw plane and the next tooth along the saw chain must be sharpened at the opposite angle to the saw plane. Accordingly, any file guide device for sharpening a saw chain must be capable of being used to guide the file when operating in each of the two opposite angles 6 to the saw plane. [0026] The present invention provides a chainsaw sharpening guide that permits the skilled person to consistently position a file relative to a cutting tooth to thereby allow all of the cutting teeth of the saw chain to be sharpened correctly and consistently. [0027] Referring to all the drawings wherein like reference numerals designate like or corresponding parts throughout the several views. The following description refers to the specific, illustrated embodiments of the present invention and is in no way intended to limit the scope of the present invention to the specific, illustrated embodiments. [0028] As noted above, there are various aspects of the geometry of the cutting tooth 100 that must be maintained in order to produce a sharp and effective saw chain. In order to achieve this consistency, the chainsaw sharpener guide of the present invention is adapted to be placed over the saw chain and aligned relative to the chainsaw bar. Furthermore, the guide of the invention is adapted to be used for the sharpening of a single cutting tooth 100 at a time and to be substantially immovable relative to the single cutting tooth 100 during the process of its sharpening. In particular embodiments of the present invention, the chainsaw sharpener guide is adapted to engage the chain links adjacent to the cutting tooth and be held in position by the link pins of the chain links adjacent to the cutting tooth. [0029] In one preferred form of the present invention, the present invention provides a chainsaw sharpener guide 200 comprising a first and a second bar engagement member 210,220 wherein each bar engagement member 210,220 comprises at least a pair of angled slots 211,221 which together form bar engagement channels 213,214, the axis of which extends substantially diagonally across the guide 200, and a height setting surface 212,222. The pair of angled slots 211,221 are formed within a planar leg 215,216 and are spaced from one another at a distance corresponding to the length of two links of a chainsaw chain. The planar leg 215,216 has a width 217 corresponding to the distance between the link pins in the links of a chain, such that angled slots 211,221 are configured to slide between neighbouring pins in the links of a chainsaw, on each side of a cutting tooth. 7 [0030] The two bar engagement members 210,220 are fixed to each other by means of two substantially parallel connector shafts 230, transversely disposed between the bar engagement members 210,220 on opposing sides, each bearing a roller 240. Each roller 240 has a section of larger diameter which forms a shoulder 241 and is adjacent to the second bar engagement member 220. [0031] The first bar engagement member 210 further comprises an adjustable tooth length setter 250 and a first locating member 260. The adjustable tooth-length setter 250 includes a pair of vertical rollers 251 that are attached to a movable carrier 252, outwardly adjacent to the two transverse rollers 240. The movable carrier 252 overlays the first bar engagement member 210. The adjustable tooth-length setter 250 may also include fastening means in the form of a knurled nut 253 attached to a short bolt. Optionally, the adjustable tooth-length setter 250 engages grooves in the first bar engagement member 210 and the fastening means fastened such that the position of the adjustable tooth-length setter 250 is temporarily fixed relative to the first bar engagement member 210 whereby the tooth length setting may be maintained. [0032] In use, the guide 200 of the present invention is used to sharpen a cutter tooth 100 of a chainsaw. The chainsaw sharpener guide 200 is placed at an angle over the chainsaw tooth to be sharpened such that the angled slots 211,221 are substantially perpendicular to the length of the chain. The guide 200 is then pushed onto the chainsaw bar, such that the links adjacent to the tooth to be sharpened are received within the diagonally opposite angled slots 211,221, until the top plate 110 of the tooth to be sharpened abuts the height setting surfaces 212,222. The chain of the chainsaw then extends along the bar engagement channel 213, 214, and the guide 200 straddles the cutting tooth 100 to be sharpened. In this way, the guide 200 stably rests upon the top plates 110 of the adjacent cutting teeth 100 via its height setting surfaces 212,222. When the guide 200 is positioned on the chainsaw bar so as to straddle the cutting tooth 100 to be sharpened, a first locating member 260 is positioned between the link pin of the link immediately downstream of the tooth to be sharpened. The first locating member 260 is fixed to, or co-formed with, the first bar engagement member 210. A second tooth locating member 270 is similarly located on the second bar engagement member 220. In the illustrated embodiment, the 8 second locating member 270 is adapted to be positioned between the link pins of the adjacent upstream chain link. Such an arrangement prevents movement of the chainsaw sharpener guide 200 along the saw chain so that the guide 200 remains in place relative to the tooth 100 to be sharpened. [0033] A round file (not shown) is manually placed on the file contacting surfaces 242 of the rollers 240 and against the top plate cutting edge 112 of the cutting tooth 100 to be sharpened. The round file is moved back and forth against the cutting edge 112 of the cutting tooth 100 and against the rollers 240. The rollers 240 provides a smooth and movable surface, which will not wear quickly when in contact with a file. [0034] This arrangement positions a file contacting surface 242 of the roller 240 at a predetermined distance 245 beneath the upper surface of the top plate 112. This predetermined distance 245 fixes the path that the file takes, relative to the top plate cutting edge 112, such that the top plate cutting angle 111 is maintained during sharpening. The skilled addressee will be aware that there a several standard sizes of round file used for sharpening saw chains and that the size of the file is selected to match a cutting tooth present in a particular saw chain. It is envisaged that the chainsaw sharpener guide 200 of the present invention may be produced in various sizes wherein the distance 245 between the height setting surface 212,222 and the file contact surface 242 varies to match the various file/chain size combinations. In an alternative embodiment, it is envisaged that the guide has an adjustable distance 245 between the height setting surface and the file contact surface, such that a single guide 200 may be used with multiple file/chain size combinations. [0035] The amount of filing that may be carried out on each cutting tooth 100, during the sharpening process, must be restricted such that each cutting tooth 100 remains substantially the same size as the other cutting teeth 100 in the saw chain. The chainsaw sharpener guide 200 of the present invention includes an adjustable tooth-length setter 250 which cooperates with the first tooth locating member 260 to restrict the amount by which the length of the top plate 110 may be reduced during the sharpening process. In the illustrated embodiment of the present invention, the adjustable tooth-length setter 250 9 includes a pair of vertical rollers 251 that are attached to a movable carrier 252 that overlays the first bar engagement member 210. Movement of the carrier 252 relative to the first bar engagement member 210 changes the amount of the top plate 110 that is accessible to the file during the sharpening process. The carrier 252 may be secured in place by a fastening means to the first bar engagement member 210. In the illustrated embodiment, the fastening means may be a knurled nut 253 attached to a short bolt. [0036] When secured, the maximum length of the top plate 110 is determined by the distance between the first locating member 260 and the most distal edge therefrom, of the vertical rollers 251. Accordingly, in order to sharpen a cutting tooth, the distance must be slightly shorter than the current length of the top plate 110. This can be achieved by loosening the knurled nut 253 and sliding the carrier 252 away from the second bar engagement member 220. Once the desired length of the top plate 110 has been set, the knurled nut 253 may be retightened. In some embodiments of the present invention, the first bar engagement member 210 may include a scale 254 comprising a series of transversely disposed graduations, the scale 254 extending longitudinally along the upper surface of the first bar engagement member 210. The scale 254 can be used to accurately set the amount of the top plate 110 that is available to be removed by the file. Since it is possible to remove the chainsaw sharpener guide 200 from the chainsaw bar without moving the adjustable tooth-length setter 250, the same top plate length setting may be applied to each of the remaining cutting teeth 100 of the saw chain. [0037] The chainsaw sharpener guide 200 of the present invention is adapted to maintain the filing angle 118. Each of the bar engagement members 210,220 includes bar engagement channels 213, 214 which are formed to allow the guide 200 to be positioned on the chain and substantially impede lateral, longitudinal and rotational movement of the guide relative to the chain during use. Accordingly, it is necessary for the bar engagement channels 213, 214 to be narrow enough and deep enough to allow the guide to be positioned on the chain in such a manner. The slots 211,221 are arranged in pairs, at an angle relative to the connector shafts 230, whereby diagonally opposite slots 211,221 are used to position the guide 200 on the chainsaw bar. In use, the angle between the chain and the connector shafts 230 is equivalent to the filing angle 118. 10 [0038] As the skilled person will appreciate, the guide 200 is used to sharpen a first tooth of a chain. The guide 200 is removed from the chain by pulling it off the chain, and placed over a second tooth to be sharpened in the same manner. The remaining teeth of the chain are similarly sharpened. In this way, all the teeth of the chain are sharpened in a consistent manner. [0039] Once all the teeth of the chain have been sharpened, the depth gauge 114 needs to be lowered accordingly. A flat file (not shown) is manually placed on the shoulder 241 of the rollers 240 and against the depth gauge 114 to be filed down. The flat file is moved back and forth against the depth gauge 114 and against the shoulder 241. [0040] The guide 200 is used to lower a first depth gauge 114. The guide 200 is again removed from the chain by pulling it off the chain, and placed over a depth gauge 114 to be lowered in the same manner. The remaining depth gauges of the chain are similarly lowered. In this way, all the depth gauges of the chain are lowered in a consistent manner. [0041] It will be appreciated that the guide of the invention may be configured and/or modified to accommodate different chains, including chiselchains. Examples of modifications that may be made to the guide include configuring the slots of the legs to engage a chain having longer or shorter links, and/or adjusting the angle of the connector shafts and vertical rollers relative to the chain in order to adjust the filing angle. [0042] Any prior art reference or statement provided in the specification is not to be taken as an admission that such art constitutes, or is to be understood as constituting, part of the common general knowledge. [0043] Where the terms "comprise", comprises", "comprising", "include", "includes", "included" or "including" are used in this specification, they are to be interpreted as specifying the presence of the stated features, integers, steps or components referred to, but not to preclude the presence or addition of one or more other feature, integer, step, component or group thereof. 11