This invention relates to an arrangement for a motordriven hand tool such as a chain saw the tool comprising at least two parts that are removably secured to one another by means of a screw joint comprising two elements, the first element relating to the first part whereas the second element abuts the second part.

As the links in the cutting chain of a chain saw wear with use the chain stretches and becomes loose on the guide bar. Many methods exist to move the guide bar longitudinally away from the chain saw body and the drive sprocket to take the slack out of the links of the cutting chain to ensure that the links of the chain remain seated and ride in a peripheral channel in the guide bar. In order to make a longitudinal adjustment of the guide bar with respect to the chain saw body the operator usually has to untighten a nut which is fastened to a bar bolt fixed to the chain saw body and clamping for instance a clutch cover and the guide bar between the nut and the chain saw body and to re-tighten the nut again when the longitudinal position of the guide bar has been adjusted. However, due to the play between the bar bolt and the opening through which the bolt extends through the clutch cover it might occur that the clutch cover does not become exactly positioned with respect to the brake of the chain saw or that the clutch cover moves slightly when being exposed to forces.

The purpose of this invention is to create a simple arrangement that eliminates the disadvantages mentioned above and which automatically fixes the clutch cover in the right position when the guide bar nut is tightened. This is achieved by means of a device having the characteristics mentioned in the claims.

An embodiment of the invention will now be described with referense to the accompanying drawings on which Fig. 1 shows a partly broken side view of a chain saw wheras Fig. 2 is front a perspective view of a clutch cover assembly for the saw with a tightening mechanism for the guide bar clamping means, Fig 3 is a perspective view of said clutch cover without the tightneing mechanism, Fig. 4 is a perspective view of a part of the tightening mechanism, Fig 5 and 6 are two embodiments of the invention shown in section.

Fig. 1 shows a chain saw body 10 having two handles 11 and 12 and a saw guide bar 13 on which an endless chain 14 is arranged. The chain is driven by a sprocket

wheel hidden under a clutch cover 15. The clutch cover is provided with a circular recess 16, see Fig. 3, having a bottom part 17 that has a central opening 18. The end of the opening 18 facing the recess 16 is provided with a seat 19 that is shaped as a truncated cone.

The clutch cover 15 clamps the guide bar 13 at the body 10 by means of a tightening arrangement, see Fig. 4, comprising a bar bolt 20, that is firmly secured to the body 10, and a nut 21 that is integrated with a tubular means 22 having a non-circular outer periphery. The tubular means supports a toothed wheel 23 that is used to tighten or untighten the clamping arrangement. The wheel 23 has a hub part 24 with an inner tubular opening whose shape corresponds to the outer shape of the tubular means 22 and the hub is arranged to slide on the tubular means 22 such that the wheel can be moved between two positions. In the first position the wheel is inserted in the recess 16 and locked against turning motion by a ridge 25 placed on the inner periphery of the recess 16. In the second position the wheel 23 is placed partly outside the recess such that the wheel and consequently the nut 21 can be turned with respect to the bar bolt 20.

The outer periphery 26 of the nut 21 is shaped as a truncated cone having mainly the same geometrical design as the seat 19, see Fig. 5. The nut can of course also be adjusted by a separate tool provided an ordinary clutch cover is used.

Fig. 6 shows another embodiment in which the saw body 10 is provided with a threaded bore 27. A bolt 28 is inserted in the bore 27 and extends through the guide bar 14 and the clutch cover 15. The bolt 28 is provided with a collar 29 having an outer surface 30 that is shaped as a truncated cone and abuts the seat 19 of the clutch cover 15. At the end of the bolt there is a head 31 that can be integrated with a tightening arrangement shown in Figs. 1-5 or be separately adjusted by a tool.

According to the two embodiments described above the truncated conical surface of the seat 19 and on the nut 21 or bolt 28 automatically co-operate to centre the clutch cover 15 with respect to saw body 10 when the screw-nut arrangement is tightened thereby avoiding any movement between these two parts during use.

It should in this connection be mentioned that it is also possible to use an arrangement where solely one of the co-operating surfaces 19 and 26 or 19 and 30 are conical whereas the other surface is mainly shaped as an annular surface. It is also possible to use co-operating surfaces that to some degree are toothed in order to avoid loosening of the details with respect to one another. With regard to the chain saw arrangement described above it should be pointed out that instead of having an

intermediate element such as a clutch cover which is clamped against the guide bar the nut or screw could act directly on the guide bar provided that the co-operating surfaces are shaped in accordance with the following claims.