This invention relates to an attachment for a chainsaw and, in particular, to an attachment for a chainsaw for use in the cutting of planks, beams and boards from logs. Chainsaws have been used for many years for cutting logs and rough slabs of wood into planks, beams and boards. The chainsaw must be supported in some way so that straight, planar cuts can be made in a log. Thus, various attachments have been designed so as to support the chainsaw during cutting operations so as to produce smooth cuts and linear pieces.

US Patent No. 4,146,962 describes an apparatus for guiding the cutting of wood by a chain saw which includes a chain saw bar, which apparatus comprises a pair of guide members and a plurality of spacer members. The apparatus is attached to the chain saw bar by a bolt, which passes through a pre-drilled hole in the chain saw bar. At least one of the guide members includes means for following a guide surface to maintain the chain saw bar parallel thereto. The chain saw is held in a vertical disposition.

A disadvantage of the apparatus described in US Patent No.

4,146,962 is that a hole has to be drilled in the chain saw bar to accommodate the attachment bolt. Furthermore, although it is possible to adjust the size of a plank to be cut, in order to so do, the apparatus has to be disassembled and the spacer bars have to be rearranged. This operation is time consuming and individual parts of the apparatus can be misplaced during the adjustment operation.

US Patent No. 4,244,104 describes a device for guiding the cutting action of a chain saw which includes a chain saw bar, which device comprises a mill frame having a pair of longitudinally spaced, parallel members joined by a plurality of rod-like runners extending orthogonally therebetween and joined to the lower surfaces thereof. A chain saw bar may be secured subjacent to the mill frame and selectively spaced therefrom by a pair of bolts extending through the chain saw bar to the mill frame, and a plurality of tubular spacer members secured on each bolt between the bar and the mill frame. The runners of the mill frame ride on a plank secured on a log or on a previously cut surface to guide the chain saw in making planar, longitudinal cuts through a log. The chain saw can be used in a horizontal or in a vertical disposition. A disadvantage of the apparatus described in US Patent No.

4,244,104 is that a hole has to be drilled in the chain saw bar to accommodate each attachment bolt. Furthermore, assembly of the device, attachment of the chain saw thereto, and adjustment for a particular task is complicated and time consuming. US Patent No. 3,864,830 describes a lumber sawing attachment for a chain saw and includes a U-shaped clamp which is secured by a set of screws to the cutter bar. The clamp has a slot for receiving the cutter bar and an enlarged slot bottom to provide clearance for the cutting chain. The clamp is fixed to an axle which is rotatably supported on a guide bracket which is adapted for longitudinal movement along a guide member, such as a board fastened to the upper surface of a log. The axle can be tightened in selected adjusted positions to maintain the saw rigidly with respect to the guide bracket and log to assist starting and sharpening of the saw, to control the depth of cut and hold the cutter bar at an efficient sawing position.

A lumber sawing attachment, as described in US Patent No.

3,864,830 is commercially available from Haddon Tools of Traverse City, MI, 49685, U.S.A., as the Haddon Lumber Maker. The attachment is light in weight at just 1.81 kilos. It is designed to use a 35mm x 90mm or a 35mm x 120mm plank to act as a guide member. A disadvantage of this is that the attachment will tend to come off the guide member if any resistance to the cutting action of the chain saw is met with, during use. This problem is accentuated as the attachment is clamped to the chain saw blade forward of the centre of gravity of the chain saw. Thus, in a rotational kickback event, the chain saw and the sawing attachment will rotate backwards towards the user in the same way that an unattached chainsaw would behave.

It is an object of the present invention to overcome the

disadvantages of the chainsaw attachments hereinbefore described.

Thus, the invention provides an attachment for a chainsaw of the type which employs one or more bar studs on the body of the chainsaw to which the chain bar is attached, which attachment facilitates the cutting of planks, beams and boards from a log by tracking along a guide rail, and which attachment comprises an elongate body section having a top plate, a wall to each long side and suspended therefrom, which elongate body section is dimensioned to be a snug fit on the guide rail, in use, a connecting bar rotatably mounted on the top plate and extending to one side of the body section, and means for attaching the connecting bar to a stud bar on the chainsaw, which attachment means is located at the end of the connecting bar to which the chainsaw is attachable, such that, in use, the chainsaw moves parallel to the guide rail and is rotatable around the longitudinal axis of the connecting bar.

An advantage of the attachment according to the invention is that, as the chainsaw is attached to the end of the connecting bar, it may be operated with both hands on the handles, with the user standing to one side of the chain bar. This arrangement means that the chain brake will be activated in the event of kickback.

Furthermore, since the chainsaw is free to rotate around the longitudinal axis of the connecting bar the chainsaw will rotate relative to the attachment in the event of kickback, and the attachment will be less likely to detach from the guide rail.

A further advantage of the attachment according to the invention is that, as the connecting bar attaches to the stud bar, this attachment point is near to the centre of gravity of the chainsaw, which results in the chainsaw being well balanced, while in use. Preferably, the attachment means is a threaded opening in the end of the connecting bar, which matches the thread on the bar stud.

An advantage of attaching the connecting bar using the threaded opening in the end thereof is that the connecting bar once connected will be perpendicular to the chain bar.

A further advantage of this feature of the invention is that the only part of the attachment between the body section and the attachment point on the chainsaw is the connecting bar. Thus, the user has a clear view of the chainsaw and of the log being sawn, as a plank, beam or board is being cut from the log.

Further, preferably, the other end of the connecting bar has a threaded opening for attaching the connecting bar to an alternatively sized bar bolt, with the connecting bar being reversibly mountable on the top plate. An advantage of this arrangement is that the attachment is suitable for use with chainsaws having alternatively sized bar bolts. Thus, changing from a chainsaw with one size bar bolt to a second chainsaw with a different sized bar bolt is just a matter of reversing the connecting bar within the bearing housing. In one embodiment of the invention, a bearing is mounted on the top plate, through which bearing the connecting bar is slidably mounted. An advantage of using a bearing to house the connecting bar is that the connecting bar will turn in a smooth fashion.

In a further embodiment of the invention, the connecting bar has an external thread and a locking nut located on the connecting bar to each side of the bearing, such that the distance of the chainsaw from the bearing may be adjusted.

An advantage of this arrangement is that the width of a plank to be cut can be set on the attachment by slackening off the locking nuts to set the correct distance of the chainsaw from the body section. Preferably, an index mark is placed on of the locking nuts for indicating the amount of adjustment made to the distance of the chainsaw from the bearing.

An advantage of this arrangement is that the change in the distance can be indexed to the number of turns of the locking nut on the connecting bar.

In a further embodiment of the invention, the bearing is located in a bearing housing, which bearing housing is attached to the top plate by a pair of screws, with the orientation of the connecting bar being adjustable relative to the longitudinal axis of the elongate body unit before the screws are tightened. An advantage of this adjustment method is that the chainsaw can be aligned to the guide rail so that the width of the plank being cut will not vary as the attachment moves along the guide rail.

Preferably, a jacking screw is mounted in the bearing housing, the rotation of which tilts the connecting bar for alignment of the attached chainsaw to the log.

An advantage of the jacking screw is that the orientation of the chainsaw bar can be adjusted so that the width of the plank is the same at each side of the plank.

In a further embodiment of the invention, one of the walls of the elongate body section is adjustably suspended from the top plate for accommodating guide rails of different widths.

An advantage of this adjusting mechanism is that where a new guide rail is being used the gap between the walls can be adjusted to allow the body section to move smoothly along the guide rail.

The invention will be further illustrated by the following description of an embodiment thereof, given by way of example only with reference to the accompanying drawings in which:

Fig. 1 is a perspective view from above and to one side of an attachment for a chainsaw in accordance with the invention; and Fig. 2 is a view of the attachment of Fig. 1 connected to a chainsaw and with the connecting bar reversed.

Referring to Fig. 1, there is illustrated generally at 10, an attachment in accordance with the invention for a chainsaw of the type which employs one or more bar studs on the body of the chainsaw to which the chain bar is attached, which attachment facilitates the cutting of planks, beams and boards from a log by tracking along a guide rail. The attachment 10 comprises an elongate body section 11, having a top plate 12 and a wall 13, 14 to each long side 15, 16, respectively and suspended therefrom. The body section 11 is dimensioned to be a snug fit on the guide rail (not shown), in use, and a connecting bar 17 is rotatably mounted on the top plate 12 at position 18, which connecting bar 17 extends to each side 19, 20 of the body section 11.

The connecting bar 17 is rotatably mounted in a pair of RMS-6- 2RS bearings 21 (second bearing not shown), which bearings 21 are held in a bearing housing 22, and which housing is fixed to the top plate 12 by angle irons 23, 24, with cap screws 25 (one shown). In use, while the cap screws 25 are loose, the orientation of the connecting bar 12 is adjustable relative to the longitudinal axis of the elongate body unit 11 followed by tightening of the cap screws 25.

The connecting bar 17 has an external thread 26 and a locking nut 27, 28, located on the connecting bar 17 to each side of the bearing housing 22 such that, in use, the distance of the chainsaw from the bearings 21 may be adjusted. An index mark 29 on locking nut 27 indicates the amount of adjustment made to the distance of the chainsaw from the bearings 21. One turn of locking nut 27 represents 2.5mm. Thus, ten turns of the locking nut 27 will shift the chainsaw left or right by 25 mm. Side wall 14 is permanently fixed to the top plate 12, while side wall 13 is fixed to the top plate 12 by a set of side wall screws 30, which allow the distance between side walls 13, 14 to be adjusted for accommodating guide rails of different widths.

A jacking screw 31 mounted in angle iron 23 at position 32, is used to tilt the connecting bar 17 for alignment of the attached chainsaw to the log, in use.

A threaded opening 33 is located at end 34 of the connecting bar 17, which threaded opening 33 matches the thread on a bar stud (not shown) on the chainsaw, such that the attachment 10 is connectable to the bar stud (not shown), in use, and the attached chainsaw, when sawing, moves parallel to the guide rail and is rotatable around the longitudinal axis of the connecting bar 17. Milled slots 35 (one shown) are used for tightening the connecting bar 17 to the bar stud with a spanner. A handle 36 is mounted on the top plate 12 at position 37 and is only used for handling the attachment 10, while sawing is not in progress. The handle 36 is not used while the chainsaw is sawing, as the attachment will travel along the guiderail, unassisted, due to the sawing action of the chainsaw.

The elongate body unit 11 is made of plate steel and the bearing housing 22, angle irons 23, 24 and handle 36 are manufactured from steel. The connecting bar 17 is made from a threaded zinc -plated bar.

Referring to Fig. 2, attachment 10 is illustrated attached to a chainsaw 40. The connecting bar 17 has been reversed within the bearing housing 22 and has been tightened onto a bar stud 41 on the chainsaw 40 using the threaded opening 33 located at end 34 of connecting bar 17, which threaded opening 33 matches the thread on a bar stud 41.

A second threaded opening 42, located at other end 43 of the connecting bar 17, accommodates a different size bar stud.

A wooden guide rail 44 has been aligned with the longitudinal axis of a log 45 and the distance between the chainsaw 40 and the bearing housing 22 has been adjusted to provide a sawn plank of a particular width. The alignment of the chain bar to the log 45 is fine tuned by adjusting the position of the bearing housing 22 relative to the elongate body unit 11, as hereinbefore described. Depending on the thickness of the planks to be cut a number may be cut by adjusting the distance of the chainsaw 40 from the bearing housing 22 after the completion of each plank. This adjustment is accomplished quite easily. When it becomes necessary to move the guide rail 44 it is unscrewed and repositioned as described above.