The present invention relates to a delimbing unit fcr a manual power saw comprising a saw chain and a chain guide attached to the power saw, with a longitudinal guide groove for guiding the saw chain which can he driven by means cf the chain sprocket of the power saw.

In modern forestry manual power saws play an essential role. Nowadays timber cutting is largely carried out by hand, with the aid of such power saws.

The working process associaτed with tree cutting by means of a manual power saw can substantially be subdivided into three operational phases, i.e. cutting the tree, delimbing by sawing off branches and cross-cutting of the trunk into suitable lengths. Of these operations none is more time-consuming than delimbing. Experience has shown that roughly 50 per cent of the cutting tine is used for delimbing. That so much time has to be expended on delimbing is partly due to the fact that the design of a conventional power saw is not appropriate to this particular operational phase.

A power saw of conventional design is provided with a level, longitudinal chain guide projecting straight from the saw, i.e. the bar. The saw chain is guided in a trac leading from the driving chain sprocket along the lateral edges cf the bar back tc the driving chain sprocket. During the sawing cperation one of the lateral edges of the bar is pressed against the sawing point. Sawing is accordingly effected across the bar, in the plane of the bar. During the delimbing phase the bar must be moved from branch to branch and at the same time to different points around the trunk. crmally delimbing is effected from a position at the side of the tree, with the bar substantially directed across the trunk. During the sawing cperation the bar is kept pressed against the limb or branch. Depending en the position of each branch on the trunk the pressing-on fcrce is provided to a larger or smaller extent by the person who handles the power saw twisting his body. Especially as regards the branches en the under¬ side of the tree, which may cause amming of the bar, this entails

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a working position which from the ergonomic point cf view is definitely unsuitable and tiring.

As already stated, delimbing is a time-consuming operation, ana this fact often leads to an especially high working speed during this operational phase. The higher speed and the inconvenient working position contribute to increasing the danger of accidents during the delimbing phase.

The above shows clearly that for -delimbing a tool is required which has none of the disadvantages of a conventional power saw, and it is the object of the invention to provide an aid for delimbing which will meet this requirement and enable more rapid and simpler delimbing from a working position which, from an ergonomic point of view, is definitely improved.

The object of the- -invention--is— chieved by a delimbing unit of the type described above, characterised in that the chain guide extends forward from the casing of the power saw in the same way as a bar-shaped chain guide of conventional design and in that a nose section of the chain guide facing away from the casing has a laterally bent shape, as a result of which the saw chain is guided along a substantially semicircular track in a plane transverse to the forward direction, whereas the saw teeth of the saw chain are, along the nose section of the chain guide, pointing substantially forward.

By means of the delimbing unit in accordance with the invention delimbing is considerably facilitated, inasmuch as the semicircular nose section of the chain guide is held against the trunk of the tree. During this process the semicircular shape substantially encompasses half the periphery of the trunk. Thus the saw chain teeth, which point substantially forward along the nose section, simultaneously remove branches along half the periphery of the trunk as the power saw is moved along the trunk. By turning the power saw at the same time towards both sides by substantially 0° also the branches on the "lower" half of the periphery of the trunk are reached and sawn off. This further accelerates and simplifies the delimbing operation. Since the semicircular shape cf the ncse section partly encompasses the trunk, sudden jerks of the saw during the delimbing process are

prevented, thus largely eliminating any danger cf accidents during this operational phase. As the power saw is pressed forward against the sawing points from a working position next to or astride the trunk stresses due to twistir. _≥ cf the body are substantially eliminated and a clearly improved working position is achieved.

Known technology with a view to attaining corresponding objects is represented by such designs as described in the 1>O Patent Specification 100.803, "the ΞΞ Patent Specification 77529 and the US Patent Specification 1.043.502. However, the designs described in these patent specifications are of a type quite different from the unit in accordance with the invention and cannot be applied to a manual power saw, inter alia because none of the known designs comprises any chain guide of the type required to this end. - - - - - - Other characteristics of the delimbing unit in accordance with the invention will be found in the claims.

The invention is described in greater detail below with reference to a specimen embodiment shown in the drawing, where fig. 1 is a side view of a delimbing unit in accordance with the invention attached to a schematically drawn power saw casing, fig. 2 shews the unit represented in fig. 1 as seer, frcm above, fig. 5 gives a schematic view from the front of the unit represented in fig. 1 and fig. 4 shows a saw chain for use in the unit in longitudinal section as well as a cross-section of the ccmbinaticr. saw chain/chain guide. Fig. 1 shows, in schematic form, a power saw casing 1 with roughly outlined, conventional handles 101, 102. A delimbing unit in accordance with the invention is attached to the saw casing. The unit comprises a chain guide 2 and a saw chain 5 _> 4 guided thereby. The saw chain runs in a closed circuit frcm the driving chain sprocket 11 of the power saw along an edge of the chair, guide and back to the driving chain sprocket. Links J of the saw chain are previced with a guide lug o moving within a gide groove 2; marked by a dashed line along the edge of the chain g id . hVery other link 3 bears a saw tooth 10 and a chip ejector C ' located, in the driving direction, after the tooth. The chair, links are held together bv steel rods L

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(see also fig. 4). The saw chain is driven by the driving chain sprocket in the direction of the arrow.

Chain guide 2 consists cf a substantially flat rail extending, in the shape of two legs 22, 23 from the power saw casing in the forward direction, which is marked by an arrow in the drawing, and thereupon obliquely downward and outward (see fig. 2). At its lower end each leg passes into a section 22' or 23' , respectively, bent in a substantially circular way both upward and inward towards one another. The sections 22' and 23' meet transversely to the forward direction in section 24.

The sections 22', 25' and 24 constitute a nose section of the unit. As can be seen in fig.3 the nose section is, viewed from the front, substantial!; semicircular. During the delimbing process this semicircular shape is held against the round periphery of the tree trunk, the saw being mcved forward in the direction of the arrow.

Along the nose section gide groove 21 cf the chain guide faces substantially forward, as a result of which also test?. ' Z cf the saw chain point forward. Alcng section 24 teeth 10 are facing straight forward, along sections 22' , 23' forward and obliquely downward, and at the lowest points of sections 22', 25' downward. Due tc the shape of the chain guide as described the saw accordingly acts along the entire nose section, as it is moved forward. The nose section of the chain guide is so dimensioned that its semicircular shape corresponds substantially to half the periphery cf trees of such size as normally cut.

Pig. 1 shows also ho- the unit is attached to casing 1 of the power saw. Legs 22 and 23 of the chain guide are connected in the same plane by means cf a retaining plate 2c with fastening devices 27, 28, 29, 30 appropriately adapted tc chain guide fastening devices on a power saw casing of conventional design. ith the aid of the screwing devices 27, 25 plate 2c is secured to a movable part of the power saw (not shown ^* , as is the case with a conventional chain guide. By means cf an adjusting screw (not shown the movable part with the chain suide can be adjusted in known manner along

slot 30 using pin 29 by way of control element. Thanks to this feature the saw chain can be tensicned as required. Plate 26 is provided with a lubricating point 31 connected via a duct 32 in plate 26 with that part of the guide track which extends along the lower edge of plate 26.

In fig. 2 the power saw illustrated in fig. 1 is shewn schematically as seen from above. The figαre shows that also legs 22, 23 are in relation to the forward direction somewhat bent. This shape is due to the fact that a smooth and as a result frictionless transition is required, on the one hand, to the plane of the driving chain sprocket 11, and, cn the other hand, to chain guide sections 22', 23'. The bent shape is also required inasmuch as the tree trunk shall be able to pass freely when the saw is moved forward along the trunk. Tr.e figαre shows the twist by 80° of the rail within legs 22, which is illustrated by a chain link 3 with saw teeth 10 directed in a horizontal plane substantially halfway between the driving chain sprocket 11 and the transition between leg 22 and section 22'.

Fig. 3 shows a protective device 25 enclosing the saw chain along leg 23 of the chain guide. A corresponding protective device is provided for section 22. The protective device 25 eliminates any risk of direct contact with the saw chain along the corresponding section of the chain guide.

The schematic view cf the chain guide in fig. 3 is rimarily intended tc illustrate the semicircular shape cf the ncse section of the chain guide. For this reason both the saw chain and legs 22, 23 have been omitted and power saw casing 1 has only been marked by dashed lines. Guide track 21 along the edge of the chain guide is marked by a dashed line. In this connection it is pointed cut that the saw chain is not loaded as it passes along leg 22, this being due to the direction in whic it. is driven forward (see fig. 1). It will be appreciated that a saw chain to be able to run along chain guide 2 must be capable of being turned in all lateral directions and about its own longitudinal axis. Such a saw chain is knrwn from the German laid open print 275S3S0. In this specification saw chains are

described, the links of which are held together by means cf ball and socket joints.

A saw chain cf this basic design is shown in fig. 4« The figure shows on the left the saw chain in longitudinal section and cn the right in cross-section along line I-I, including also a cross-section of chain guide 2. Links 3 ^~ & held together ^' z steel rods 4 both ends of which are rotatably fixed by means of ball and socket joints 5 in the corresponding links. Every other link bears a saw tooth 10 and a chip ejector 1C arranged next to it. The cross-sectional view shows guide track 21 in rail 2 of the chain guide. The inner shape of the guide track matches the outer shape of guide lugs 6 thus achieving a suitable sliding fit. So as to prevent the saw chain from sliding out of the guide track each guide lug 6 is provided with a link pin 8 projecting sideways. The side walls of guide track 21 are provided -with longitudinal recesses, with the guide pins engaging the said recesses. The chain guide has a T-shape tapering from the chain links, which counteracts jamming of the chain guide during the sawing operation.