Tension device for a chain in a chain saw

When moving the guide bar on a chain saw in order to adjust the chain tension, the following procedure is applied. Through the guide bar runs a shaft (19) having a slot for a screw driver as well as a shape of a cog-wheel (18) on the inside of the guide bar. The hole in the guide bar is the ordinary hole for a tension pin. The cover (11) above the clutch also keeps the guide bar in place and has an oval opening (23) providing accessibility to the above shaft in all its positions. Inside the guide bar, in the saw body, there is a suitable oblong cavity (16) to make room for the cog-wheel part of the shaft. That cavity has on its lower edge the form of a straight toothed section (17) adapted to the cog-wheel part.

BACKGROUND AND SUMMARY 
The present invention relates to an arrangement for setting the position of 
a guide bar on a chain saw relatively to the saw body. 
The guide bar attachment on a chain saw is generally so designed that the 
guide bar can be displaced in its longitudinal direction within a limited 
setting area before the position is locked by means of guide bar bolts. In 
the Swedish Patent Specification SE-P-7401345.9 there is described a means 
for displacing the guide bar forwards and in that way effect a stretching 
of the saw chain on the guide bar. The arrangement thus known comprises a 
rack attached to the guide bar. Moreover, it comprises a tooth wheel 
projecting on the outside of the guide bar attachment and being in 
engagement with the rack. It is also rotatably mounted on one of the guide 
bar bolts. The arrangement is principally located in the cover above the 
guide bar attachment and shall thus be fitted against the guide bar 
mounted on the bolts. The application of the cover is therefore by many 
saw operators considered unnecessarily troublesome and time wasting as it 
involves a careful adaptation of several parts. It is therefore considered 
important to redesign the arrangement so that its components are located 
in a saw body. In doing so, the arrangement and the guide bar form a unity 
when the cover is to be put on. 
The solution of the problem presented by the present invention is based on 
the principle to move the guide bar in its attachment by means of a 
cog-wheel and a straight toothed section. Such a principle offers in this 
case a simpler construction and a better location compared with that of 
the prior art. Other advantages of it are good accessibility in respect of 
the adjustment unit, rapid displacement of the guide bar without any 
pre-positioning of the same when it is fitted. Those advantages are 
obtained when the arrangement is made according to the characteristics of 
claim 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A guide bar attachment 10 is located on the right side of the saw body and 
is covered by a cover 11 kept in place by two guide bar bolts 12 with nuts 
13. The inner end of a guide bar 14 is in its fitted position secured 
between the cover and a guide bar plate 15 on the side of the saw body. 
Under the two bolts 12 on that side there is a long narrow groove 16 
carried out when the saw body was manufactured. The lower long side of the 
groove has the shape of a toothed section 17, while the upper long side is 
flat. Between the long sides there is a space for a cog-wheel 18 provided 
with a shaft 19 having a screw driver slot 20. If the wheel is rotated in 
the groove, it can be moved thanks to the teeth between the two ends of 
the groove. 
The shaft 19 passes through an elongated groove 21 in the guide bar plate 
15 and also through a round hole 22 in the guide bar as well as through an 
elongated hole 23 in the cover 11. The end of the shaft with the screw 
driver slot 20 can thus be reached with a screw driver on the outside of 
the cover. When rotating the shaft with the screw driver, the shaft is 
moved between the ends of the grooves 21 and 23. The hole 22 surrounds the 
shaft which thus drives the guide bar when being moved. The guide bar has 
an oblong hole 24 around the bolts 12 and is, when setting the chain 
tension by means of the shaft and the screw driver, loosely supported in 
the guide bar attachment and follows consequently the movement of the 
shaft as long as that one is turned by the screw driver. After the 
setting, the guide bar is fastened by means of the guide bar bolts. As a 
brake against a possible self-rotation during the setting and for 
maintaining the setting, the shaft has been provided with a cup spring 24 
located between the cog-wheel and the guide bar plate. When tightening the 
nuts 13, the cup spring is compressed and locks in this way the cog-wheel 
(and the guide bar) in the set position. As disclosed in FIG. 2, the cup 
spring is placed in an elongated countersink 26 around the groove 16 in 
the saw body. As the periphery of the cup spring presses against the top 
edge of the countersink, the cog-wheel ist constantly kept in good contact 
with the toothed section.