Introduction This invention relates to a guide bar for a chainsaw.

In particular the present invention relates to a guide bar which may be fitted on a chainsaw of the type which is used to brash trees and clear vegetation. The maintenance of trees in a plantation is an important task which is paramount to ensure that the trees in the plantation grow in an efficient and profitable manner. In particular, the pruning of young trees is important as this pruning encourages the tree trunks to grow in a substantially upright and vertical manner, which type of growth is most preferable for providing good timber and hence a profitable yield from the plantation.

Furthermore, brashing trees and clearing vegetation in a plantation crop is also important to allow inspection paths to be created within the plantation crop so that the correct trees are selected for thinning to again ensure that the maximum yield and highest possible profits are obtained from the plantation crop.

Pruning, clearing and brashing of trees and vegetation is a very time-consuming task. In order to assist with carrying out this task, it has been known to use scythes, machetes, clearing hooks, secateurs and/or pruning saws. Although these scythes, machetes, clearing hooks, secateurs and pruning saws are an assistance, these tools are all manually powered and are consequently are quite energy sapping.

In place of the manually-operated tools, it has also been suggested to use a chainsaw to prune and clear the trees and vegetation. Using a chainsaw has become the preferred choice for most woodsmen and plantation workers as the chainsaw allows the operators to quickly carry out the burdensome task of pruning and clearing trees and vegetation. As the chainsaw has become commonly used, a number of problems have arisen and these problems have been addressed by variations to the chainsaws. A chainsaw typically comprises an engine and a drive mechanism housed in a body of the chainsaw, and, a cutting chain mounted on a guide bar where the guide bar directs the cutting chain, propelled by the drive mechanism, along the periphery of the guide bar in a cyclical fashion.

As the use of the chainsaw results in high-speed cutting of the trees and vegetation, fragments of tree, bark and vegetation are occasionally thrown back at the chainsaw operator. Moreover, the high-speed rotation of the cutting chain can cause the chainsaw to kick out on initial contact with a tree. This is particularly the case where the tree branch is substantially thick or inflexible. Another problem with using chainsaws is that very light branches are whipped back towards the chainsaw operator the control. It has been suggested to provide plates and shields on chainsaws in order to protect the chainsaw operator from the cutting chain, pieces of cut wood being thrown back at them, and small branches being whipped back at them. These plates and shields are attachments, which are oftentimes connected to the guide bars on the side faces of the guide bars, have always been designed for the purpose of protecting the operator and from the point of view of the chainsaw operator.

For example, it can be seen from U.S. Patent Number US 5,150,524 (HALL), that a safety attachment in the form of a deflector arm is attached to one of the side faces of the guide bar of the chainsaw. The deflector plate is used in order to prevent small diameter branches, which are particularly flexible, from being whipped back against the chainsaw operator by the cutting chain as the cutting chain travels along the lowermost running edge of the guide bar. The deflector arm is relatively short and is primarily focussed on providing a vertically extending barrier below the lowermost running edge of the cutting chain so as to prevent the operator from being hurt by flexible branches being whipped back at their person.

Another modified type of chainsaw which is used for pruning and clearing can be seen in U.S. Patent Number US 3,380,493 (GIROUX) where a rotatable guard is provided on the chainsaw to provide a protective shield between the chainsaw operator and the cutting chain of the chainsaw. This can prevent pieces of cut wood and bark from being thrown back up at the operator.

U.S. Patent Number US 3,680,607 (ROBINSON) discloses a chainsaw for pruning and clearing trees and vegetation. The guide bar of the chainsaw is connected to a rigid prong which extends out in front of the outermost tip of the cutting chain. This rigid prong is used to assist the operator to hold the chainsaw steady, and will prevent the chainsaw from kicking off to the side when the operator uses the outermost tip of the cutting chain to prune and brash the trees and vegetation.

Another prior art chainsaw which has been modified for effective pruning and clearing of trees and vegetation is shown in U.S. Patent Number US 2,797,717 (BUDD) which is directed to a chainsaw having a teardrop-shaped guide rail with a hollowed centre. A small spur is mounted on the guide rail and the spur is provided to extend outwardly in front of the guide rail and is used to form a vee-shaped point to trap small, flexible branches which might otherwise be whipped back towards the operator. Furthermore, as the branch is trapped, the operator can obtain more purchase on the engagement between the branch and the cutting chain and allow the branch to be cut quicker.

It is important to note that all of the above problems and solutions in the form of modified chainsaws for pruning and brashing trees and vegetation are directed to protecting the operator and have a shield/guard which extends out in front of or down from the running edge of the cutting chain. These solutions are not directed towards protecting the trees/vegetation and therefore are not suitable for present invention as described further hereinbelow.

A disadvantage of using chainsaws for pruning and brashing is the damage which the chainsaw can very quickly cause to a tree. In theory, when pruning small branches or brashing a young tree, the branches should be cut off slightly beyond the collar of the branch, thus requiring the cutting chain of the chainsaw to be carefully positioned very close to the trunk of the tree yet held marginally away from the tree at the same time. As the forest workers have to cut large amounts of branches, in their haste to finish the task in a speedy manner, the forest workers will occasionally allow the chainsaw to come into contact with parts of the tree which are not meant to be cut and the cutting chain will cause damage to the bark and trunk of the young tree by cutting into the trunk and/or by stripping off portions of bark, which is sometimes referred to as gouging the tree. It is worth noting that the width of the guide bar is always less than that of the cutting chain in all of the prior art chainsaws, so as to allow the chainsaw to pass through a tree without the guide bar causing any obtrusion to the passing through of the chainsaw. A disadvantage to this arrangement is that the cutting chain forms part of the outermost prominences along the sides of the chainsaw and therefore, as the woodsmen prune and brash the small branches, the cutting chain can easily contact against the trunk of the tree, thus cutting into it and stripping away portions of the bark.

As mentioned, the damage is caused very easily, albeit inadvertently, due to the speed at which the task is being carried out using the chainsaw. In particular, the bark on young trees is often damaged whilst pruning small branches on the young trees or brashing an inspection path through a plantation crop. A further factor in the damage which is caused by chainsaws is the fatigue which an operator encounters during extended use of the chainsaw. A chainsaw of the lightweight type such as is used for pruning and brashing could weigh in the region of 3 to 6 kilograms. As the full weight of the chainsaw must be supported by the operator, often in a position in front of them, the shoulders and arms of the operator tire, and consequently the operator cannot be as precise with the wielding of the chainsaw during latter stages of extended usage. Hence, it is common for the chainsaw to brush off parts of the trees, or slip down into the bark after cutting a branch, causing damage to the trees. Furthermore, the operator may also lose concentration during extended periods of usage. A woodsman may prune or brash in the region of 200 to 300 trees per day, and due to the repetitive nature of the task, the concentration levels can slip and the operator may not be as precise with the chainsaw as they would normally be. This can also result in inadvertent damage to the trees/vegetation.

This damage allows canker fungal and bacterial infection to affect the young tree which will devalue the worth of the tree and consequently reduce the value of the plantation crop. It is a goal of the present invention to provide an apparatus that overcomes the problem of damaging trees during pruning or brashing using a chainsaw.

Summary of the Invention

The present invention is directed towards a guide bar for mounting a cutting chain of a chainsaw, the guide bar comprising a buffer located on at least one of the side faces of the guide bar, such that the buffer extends laterally outwardly so that an outermost point of the buffer extends beyond an outermost point of the cutting chain, and such that, the buffer does not extend longitudinally beyond an outermost tip of the cutting chain.

The advantage of using a buffer is that the cutting chain of the chainsaw can be held at a pre-specified distance from the trunk and bark of the tree when the woodsman is brashing or pruning the tree. This will prevent the cutting chain from contacting the trunk or bark inadvertently and causing unwanted damage to the tree. As the buffer extends laterally outwardly so that an outermost point of the buffer extends beyond an outermost point of the cutting chain, the cutting chain will always be buffered from the trunk provided the chainsaw is held in a substantially normal operating position. Furthermore, the buffer is designed so that it does not extend longitudinally beyond an outermost tip of the cutting chain as this allows the operator full use of any part of the cutting chain as it follows the running edge around the periphery of the guide bar.

In a further embodiment, the buffer is formed by laterally widening a central portion of the guide bar, whereby, the outermost point of the laterally widened central portion extends beyond the outermost point of the cutting chain. This is seen to be a particularly advantageous embodiment of the chainsaw.

In a further embodiment, the buffer is formed as an integral part of the guide bar and the laterally widened central portion of the guide bar tapers laterally inwardly adjacent edge portions of the guide bar, such that the outermost point of the cutting chain extends beyond the outermost point of the edge portions of the guide bar.

In a further embodiment, the buffer is formed by a rod mounted to and spaced apart from the guide bar by mounting brackets, whereby the rod extends longitudinally along a portion of the side face of the guide bar.

In a further embodiment, the buffer extends along a majority of the side face of the guide bar. In a further embodiment, a buffer is located along both sides of the guide bar. In yet a further embodiment, the buffer comprises a substantially flat or planar face at its outermost point.

In a further embodiment, the length of the guide bar is in the range of 350mm to 550mm. In a further embodiment, the length of the guide bar is substantially 450mm.

In a further embodiment, the height of the guide bar is in the range of 70mm to 90mm. In a further embodiment, the height of the guide bar is substantially 80mm. In a further embodiment, the lateral width of the buffer is approximately 20mm, and, the lateral widths of the edge portions of the guide bar are approximately 6mm.

In a further embodiment, the outermost point of the buffer extends approximately 8mm beyond the outermost point of the cutting chain.

In a further embodiment, the outermost point of the buffer extends beyond the outermost point of the cutting chain by a distance which is within the range of 80%- 100% of the width of the cutting chain. In a further embodiment, the guide bar comprises a proximal end, which is connected to a body of the chainsaw, and a distal end, comprising the outermost tip of the chainsaw; wherein, the guide bar further comprises a nose guard which is positioned at the distal end of the guide bar, adjacent the outermost tip of the chainsaw. In a further embodiment, the nose guard extends vertically beyond the outermost point of the cutting chain as the cutting chain passes around the distal end of the guide bar at the outermost tip of the chainsaw.

In a further embodiment, the guide bar is constructed from steel. In a further embodiment, the guide bar is constructed from an alloy steel. In a further embodiment, the guide bar is constructed from aluminium. In a further embodiment, the guide bar is constructed from strengthened steel. In a further embodiment, the guide bar and buffer are constructed from steel. In a further embodiment, the buffer is constructed from nylon.

In a further embodiment, the buffer is detachably mounted on the guide bar. In a preferable embodiment, the guide bar is constructed so that the guide bar can be disconnected from the body of the chainsaw, rotated 180 degrees about its longitudinal axis and reconnected to the body of the chainsaw. This is advantageous as the guide bar can be rotated to switch sides so that equal wear and tear may occur on both side faces of the guide bar. In this embodiment, it will be understood that a buffer would need to be located on both side faces of the guide bar, or alternatively, a buffer which can be detached from one side face and remounted on the opposite side face would be required.

The present invention is further directed towards a guide bar for mounting a cutting chain of a chainsaw, the guide bar comprising a buffer located on at least one of the side faces of the guide bar, such that the buffer extends laterally outwardly so that an outermost point of the buffer extends beyond an outermost point of the cutting chain, and such that, the buffer neither extends longitudinally beyond an outermost tip of the cutting chain, nor vertically beyond an uppermost or lowermost point of the cutting chain. In a further embodiment, the buffer is formed by laterally widening a central portion of the guide bar, whereby, a width of the laterally widened central portion is greater than a width of the cutting chain.

In a further embodiment, the buffer is formed as an integral part of the guide bar, and, a width of the guide bar reduces from the laterally widened central portion as it tapers laterally inwardly adjacent edge portions of the guide bar, such that the width of the cutting chain is greater than the width of the edge portions of the guide bar.

The present invention is further directed towards a buffer for retrofitting onto an existing guide bar of a chainsaw, the existing guide bar of the chainsaw mounting a cutting chain of the chainsaw, and, the existing guide bar comprising mounting means to receive and retain the buffer on at least one side face of the guide bar; such that, the buffer which is retrofitted onto the existing guide bar, extends laterally outwardly so that an outermost point of the buffer extends beyond an outermost point of the cutting chain, and, the buffer does not extend longitudinally beyond an outermost tip of the chainsaw.

In a further embodiment, the existing guide bar comprises through holes and retrofitting the buffer onto the existing guide bar comprises bolting the buffer to the existing guide bar.

In a further embodiment, the buffer comprises a rod which is mounted to and spaced apart from the side face of the guide bar, by brackets, which brackets are connected to the through holes on the existing guide bar.

The present invention is further directed to a guide bar for mounting a cutting chain of a chainsaw, the guide bar comprising an outwardly protruding buffer along one of its side faces, such that an outermost edge of the buffer extends beyond an outermost edge of the cutting chain so as to buffer the cutting chain on the chainsaw from a trunk of a tree being pruned.

The advantage of providing a guide bar with an outwardly protruding buffer whose outermost edge extends beyond an outermost edge of the cutting chain is that the guide bar may be used on chainsaws which are being used for pruning and brashing trees, and, the buffer will prevent the cutting chain on the chainsaw from inadvertently damaging the bark and or trunk of the trees. It is important to note that the buffer acts as a buffer between the trunk of the tree and the cutting chain of the chainsaw. Although many prior art documents do show attachments whose outermost edge extends beyond an outermost edge of the cutting chain, these attachments do not buffer the trunk of the tree from the cutting chain; typically the attachments are only at a single point along the guide bar and do not run the length of the guide bar thus they do not act as a buffer. In a preferred embodiment, the buffer comprises a thickened central portion of the guide bar, whereby the width of the thickened central portion is greater than the width of the cutting chain on the chainsaw. In a preferred embodiment, the buffer extends along the majority of the exposed side of the guide bar when the guide bar is installed on a chainsaw.

In a preferred embodiment, the buffer extends along both sides of the guide bar. In a preferred embodiment, the buffer comprises a substantially flat or planar face. This is advantageous as the flat or planar face of the buffer may be pressed against the tree to assist the chainsaw operator with their stability whilst operating the chainsaw, and, the cutting chain of the chainsaw will also be held at a predetermined distance from the trunk of the tree by approximately the same distance of the buffer's outer face from the cutting chain.

In a further embodiment, the buffer may be provided by a substantially tubular bar running in parallel to and mounted on one side of the guide bar using brackets. In a further embodiment, the buffer is formed as an integral part of the guide bar and is formed by a thickened central portion of the guide bar which tapers outwardly from edge portions of the guide bar, whereby the width of the edge potions of the guide bar are less than the width of the cutting chain. In a preferred embodiment, the length of the guide bar is approximate 450mm. In a further embodiment, the height of the guide bar is approximately 80mm.

In yet a further embodiment, the width of the buffer is approximately 20mm, and, the width of the edge portions of the guide bar are approximately 6mm.

In a further embodiment, the outermost edge of the buffer extends beyond the outermost edge of the cutting chain by approximately 8mm.

In a further embodiment, it will be understood that the outermost edge of the buffer extends beyond the outermost edge of the cutting chain by approximately 80%-100% of the width of the cutting chain.

In a further embodiment, the guide bar further comprises a guard which is positioned at a distal end of the guide bar.

It is advantageous to provide a guard at the distal end of the guide bar as the guard will cover the cutting teeth at this distal end and thus prevent kickback of the chainsaw if one or more of the teeth in the cutting chain become stuck in a piece of wood, or any such other object being cut.

It will be understood that typically such a guard cannot be provided on a chainsaw as this would increase the width of the guide bar beyond the width of the cutting chain, thus causing the guide bar to be an obtrusion during normal use cutting through an object. The counter-intuitive widening of the width of the guide bar beyond the width of the cutting chain allows the anti-kickback guard to be provided at the distal end of the guide bar which will greatly increase the safety of the operator of the chainsaw during use. In a further embodiment, the guard extends beyond the outermost points of the cutting chain as it passes around a portion of the guide bar at the distal end of the chainsaw.

In a preferred embodiment, the guide bar may be made of stainless steel. In yet a further embodiment, the guide bar may be constructed of one of an alloy steel, aluminium or strengthened steel.

The present invention is further directed to a buffer for retrofitting onto an existing guide bar of a chainsaw, the existing guide bar of the chainsaw comprising mounting means to receive and retain the buffer on at least one side of the guide bar.

In a further embodiment, the buffer is an outwardly protruding buffer which is mounted along one of the side faces of the existing guide bar, such that an outermost edge of the buffer extends beyond an outermost edge of a cutting chain of the chainsaw so as to buffer the cutting chain on the chainsaw from a trunk of a tree being pruned.

In a preferred embodiment, the existing guide bar comprises through holes and the retro fitting buffer comprises an elongate buffer bar which is mounted along and spaced apart from at least one side of the guide bar by brackets which connect to the through holes on the existing guide bar.

Detailed Description of Embodiments

The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings, in which: Figure 1 is a side view of a guide bar in accordance with the present invention;

Figure 2 is a cross sectional view of the guide bar of Figure 1 ;

Figure 3 is a top plan view of the guide bar of Figure 1 ;

Figure 4 is a perspective view of the guide bar of Figure 1 ;

Figure 5 is a photograph of a portion of a tree which has been brashed with a chainsaw comprising a guide bar from the prior art; and,

Figure 6 is a photograph of a portion of a tree which has been brashed with a chainsaw comprising a guide bar in accordance with the present invention.

Referring to Figures 1 to 4 inclusive, there is provided a chainsaw guide bar indicated generally by reference numeral 100. The guide bar 100 mounts a cutting chain, only a portion of which is shown for illustrative purposes and is indicated by reference numeral 101 in Figure 1.

The guide bar 100 has a proximal end 102 and a distal end 104. The proximal end 102 is attached to a chainsaw (not shown), adjacent an engine and drive section of the chainsaw, in the usual manner using guide slots 106 and mounting holes 108, 110. The guide bar 100 comprises an upper edge portion 112, a lower edge portion 114 and a central portion 116. The central portion 116 comprises a substantially planar face and the central portion 116 is wider than the upper edge portion 112 and lower edge portion 14 respectively. The central portion 116 may taper inwards, in a concave or convex manner, adjacent the upper edge portion 112 and lower edge portion 114 so that the width of the guide bar gradually decreases as the width is measured moving from a central longitudinal axis on the central portion 116 towards the upper edge portion 112 or the lower edge portion 114 respectively.

In an alternative embodiment, the central portion 116 may be a buffer rod which is mounted on one or more of the sides of the guide bar using one or more brackets. Such a buffer rod would preferably extend along the majority of the length of a side of the guide bar.

A nose guard 118 is provided adjacent the distal end 104 of the guide bar 100 to cover a some of the teeth on the cutting chain 101 as they passes around a portion of the distal end 104 of the guide bar 100.

With reference to Figure 5, a tree indicated generally by reference numeral 500 is shown which has been brashed using a guide bar known from the prior art. As guide bars known from the prior art allow the cutting chain on the chainsaw to come into contact with the trunk of the tree 500, and into contact with bark on the trunk of the tree 500, when the operator is using the chainsaw to cut off a small branch 502 on the tree 500, damage 504 may occur around the cut off branch 502 and/or gouging of the bark 506 may also inadvertently occur. This greatly devalues the worth of the tree 500.

With reference to Figure 6, a tree indicated generally by reference numeral 600 is shown whereby the tree 600 has been brashed using a chainsaw which has a guide bar in accordance with the present invention attached to it. The guide bar of the present invention prevents gouging or unnecessary damage occurring to the trunk of the tree, and the branches 602, 604, 606, 608 are pruned without causing any inadvertent damage to the tree 600. In use, with reference to Figures 1 to 4 inclusive, the guide bar 100 is attached to a chainsaw (not shown). The guide bar 100 replaces the existing standard width guide bar on the chainsaw. The operator can brash an inspection path through a plantation of trees or perform some pruning on the trees by abutting the planar face of the central portion 116 of the guide bar 00 against a trunk of the tree to be pruned. The distance which the planar face of the central portion 116 extends beyond the cutting chain on the chainsaw may be advantageously selected to be similar to the typical width of a branch collar on the tree being pruned. Furthermore, the height of the upper edge portion 112 and the lower edge portion 114 may be preferably selected to be greater than our equal to the typical diameter of a small branch which must be pruned from the trees in the plantation or forest.

The operator can then direct the chainsaw upwardly or downwardly maintaining contact between the planar face of the central portion 116 of the guide bar 100 and the trunk of the tree, so that the cutting chain 101 on the chainsaw can neither come into contact with the trunk of the tree nor into contact with the bark on the tree. Moreover, the cutting chain is maintained at a predetermined distance from the trunk of the tree, which will be approximately equal to the distance between the planar face of the central portion 116 of the guide bar 100 and the cutting chain 101 mounted on the guide bar 100, such that this predetermined distance is approximately equal to the width of a typical branch collar found on the type of tree being pruned.

The nose guard 118 protects the operator against kickback of the chainsaw as the teeth of the cutting chain 101 passing around a distal end of the guide bar 100 are shielded from coming into contact with any objects, thus preventing the common problem of kickback. This will allow the operator to brash branches from trees at shoulder height and head height without any concern of kickback.

Throughout the preceding specification, the term "chainsaw" shall be understood to encompass any type of saw which may be used for brashing trees and vegetation; not necessarily a powered saw. For example a similar buffer may be advantageously provided on one or more sides of a manually powered pruning saw whereby the buffer portion, when in contact with a trunk of a tree, will maintain the side edge of the pruning saw at a predetermined distance from the trunk of the tree. Thus, the concept of the idea may be readily applied to unpowered saws as well as to powered chainsaws.

It will be understood that the distal end of the guide bar or chainsaw refers to the end of the guide bar or chainsaw furthest away from the engine and drive mechanism of the chainsaw, and, the proximal end of the guide bar or chainsaw refers to the end of the guide bar or chainsaw which is adjacent the engine and drive mechanism of the chainsaw. In other words, the proximal end is proximal a chainsaw operator when the operator is operating the chainsaw in the normal manner, and the distal end is distant from the operator when they are operating the chainsaw in the normal manner.

It will be generally understood that the dimensions given here in above for the guide bar and the associated buffer may vary in accordance with different brands and sizes of chainsaws, in addition to different types of work on different types of vegetation and trees. In general, the buffer will be designed to extend beyond the edge of the cutting chain of the chainsaw to ensure that the cutting chain of the chainsaw cannot inadvertently contact the trunk and/or bark of the tree whilst a small branch is being cut from the tree.

Preferably, the buffer is designed so that the branch will be cut off just beyond the collar of the branch itself. Therefore, average branch diameters and branch collar lengths may be determined for different varieties of trees so that appropriate dimensions for the guide bar and buffer may be ascertained.

Whilst portions of the preceding specification have referred to brashing and pruning of trees specifically, it will be appreciated that the present invention can be equally well applied to other types of vegetation such as large shrubs, hedgerows and the like.

It will be readily understood that the buffer may be preferably constructed of nylon, or other heavy-duty plastics.

The terms "comprise" and "include", and any variations thereof required for grammatical reasons, are to be considered as interchangeable and accorded the widest possible interpretation.

The invention is not limited to the embodiments hereinbefore described which may be varied in both construction and detail.