DEVICE FOR SHARPENING SAW CHAIN
FIELD OF THE INVENTION The invention is related to a device for sharpening a saw chain on a bar, the device comprising a frame adapted to be placed on the bar from above and including clamping means in the branches extending on both sides of the bar for attaching the frame to the bar, a motor attached pivotally to the frame, and a sharpening stone connected to the motor for sharpening the teeth of the chain by moving a tooth to the sharpening place and by guiding the sharpening stone to sharpen the tooth.
BACKGOUND OF THE INVENTION US patents 2792724, 4254673, 4319502, 4463630, 4658677 and 4762027 present such devices in which the chain is moved by hand and the next tooth to be sharpened is set at the sharpening place by means of a pawl, strip or equivalent means which may be spring loaded and is turned or bent behind the tooth. In this solution, the user of the device must make sure, e.g. by pushing the chain backwards, that the tooth is set against said means defining the sharpening place. In the devices like those described above, a further problem is how to support laterally the tooth to be sharpened, so that tilting and vibration of the tooth is prevented. In US patents 4463630 and 4762027, for example, the tooth is supported at the sharpening place by sturdy jaws extending along the whole length of the tooth but only up to the rivets because said pawl or strip is working on top of the jaws.
SUMMARY OF THE INVENTION An object of the invention is to provide in a device for sharpening a saw chain according to the definition of the field of the invention a solution for moving the chain and setting a tooth at the sharpening place which is better than the known solutions. To achieve this object, a device according to the invention for sharpening a saw chain the device comprising a frame adapted to be placed on the bar from above and including clamping means in the branches extending on both sides of the bar for attaching the frame to the bar, a motor attached pivotally to the frame, and a sharpening stone connected to the motor for sharpening the teeth of the chain by moving a tooth to the sharpening place and by guiding the sharpening stone to sharpen the tooth, is characterised in that the frame is adapted to be set against and on the saw chain before tightening it against the bar and that the device comprises in the frame a slide movable in the direction of the chain with gripping means attached to the slide for gripping the chain and moving it and a mechanism for moving the chain with one movement a certain distance into the direction opposite to its rotation direction for setting the next tooth to be sharpened at the sharpening place. The mechanism for moving the chain may include a turning lever and means for transmitting the turning movement of the lever into the movement of the slide in the direction of the chain. The mechanism for moving the chain includes advantageously also means for setting the start and/or end point of the movement and accordingly said certain distance. The device may further include a surface provided with an abrasive coating settable from above against the teeth of the chain for sharpening the teeth from above during the movement. The abrasive coating may be a diamond mix coating. The device includes advantageously also means for setting the position of the surface vertically. An advantage of the device of the invention is, firstly, that there is no need to touch the saw chain by hand during the sharpening. Furthermore, the device may be set on and against the chain because the chain is moved backwards in relation to the surface which is against it with as well the front part of the frame as the slide during its return, and so it does not get stuck to the surface. At the same time, additional sharpening or grinding from the top may be accomplished in connection with the movement. As the alignment of the tooth to be sharpened happens in the moving arrangement which is at a certain distance from said tooth, the supporting of the tooth to be sharpened may be accomplished better than with the devices in which the alignment is made at the tooth to be sharpened itself.
BRIEF DESCRIPTION OF THE DRAWINGS The invention and some embodiments thereof are described in further detail in the following with reference to the accompanying drawings, in which: Figs. 1 to 3 present schematically in side view an embodiment of the device according to the invention and its operation; Fig. 4 presents isometrically the device of Figs. 1 to 3 without the motor, the sharpening stone and some other parts; Figs. 5 and 6 present the frame parts of the device of Figs. 1 to 3 in front and rear view, respectively, and without some parts included in Figs. 1 to 3; and Figs. 7 to 9 present a preferred embodiment of the device according to the invention. DETAILED DESCRIPTION OF THE INVENTION A possible realisation of the device according to the invention is described in the following with reference to Figs. 1 to 6. Fig. 1 presents a bar 1 of a chain saw or a harvester and a saw chain 2 on it. A device for sharpening the saw chain includes a main frame 4 to which a frame part 6 in the front below, a frame part 5 in the rear below, and a frame part 7 on the top are attached. A motor 8 which is provided with grips and adjustment means is attached pivotally to the frame part 7, and a sharpening stone 9 is connected to the motor for being rotated by it. The motor may be turned into oblique sharpening positions at both sides for either left-hand or right-hand teeth. A usual turning angle is 35 degrees. The sharpening itself is preferably carried out by tilting the motor and the sharpening stone to side and down. Then, the angle between the stone and the tooth is the same during the whole sharpening motion. As far as the motor and the sharpening stone are concerned, this kind of sharpening devices are known, and there is no need to describe their structure and operation in further detail here. The device is set to lie on and against the saw chain. The top edge of the bar and the chain as well as the frame of the device are depicted here as straight, but in practice the top edge of the bar is a little curved and therefore there must be an angle of 2 to 3 degrees between the surfaces of the frame parts 5 and 6 lying against the chain. The sharpening is made in the front on the side of the rotation direction R of the chain. For supporting the chain and the tooth to be sharpened during the sharpening, jaws 10 have been attached to the front frame part 6 the inner surfaces of the jaws being shaped according to the type of the chain, so that there are grooves 34 adapted for the rivets of the chain and oblique upper surfaces 35 adapted for the dimensions of the teeth (Fig. 5). One of the jaws (the right-hand jaw in Fig. 5) is attached steadily to the frame part 6 by screws 33. The jaw of the other side is released and tightened by an arrangement including eyelet screws 30, an eccentric grip 29 and springs (not shown) pressing the jaw. As shown in Figs. 1 and 3, the jaws 10 ascend backwards from the sharpening place and thereby provide enhanced support on the tooth. As to the branches of the rear frame part 5 extending on both sides of the bar, there is a clamping screw 23 with a turning lever 24 in one of them and a setting screw in the other by means of which the device may be set and tightened according to the thickness of the bar, so that the bar and the chain are laterally properly aligned in relation to the device (Fig. 6). The slide 12 is moving in the frame part 5 on side rails 14 in the direction of the chain. At the end of the slide there are gripping pawls 13 projecting a little from it the pawls being attached pivotally to the frame 25 at 31 and being provided with suitable springs (not shown in the drawings) pressing them towards each other. On the frame 4 above the slide, a gear 15 is mounted on an axle mounted with bearings on supports 16, the axle being provided with a turning lever 18 and the gear being coupled to the slots 17 in the frame 25 of the slide corresponding to the cogs of the gear. The device is operating as follows. As the device is set on the saw chain, the eccentric grip 29 is turned into the position releasing the jaw 10 and the lever 18 is turned into the uppermost position. The device being mounted, it is moved a little into the rotating direction of the chain, so that the gripping pawls are opened and set against the both sides of the chain. The gripping place is selected to be between a depth gauge and the next link of chain. The device is set and tightened on the bar by means of the setting and tightening screws 32 and 23. In Fig. 1, the tooth 26 at the sharpening place PO is sharpened and the lever 18 turned thereafter up into the starting position as indicated by arrow Ml. The slide 12 and the gripping pawls 13 with it have been moved on the chain 2 without moving the chain into gripping place Pl between the depth gauge of the tooth 27 and the next link of the chain. In Fig. 2, turning of the lever 18 is started, as indicated by arrow M2, and the chain is moved backwards, as indicated by arrow S. In Fig. 3, the lever is turned into its final position and the pawls 13 have moved the gripping place into point P2 the distance of which from the starting point Pl of the movement is the distance D between two successive teeth of the chain (see at the right in Fig. 1). The next tooth 28 from the tooth 26 is moved into the sharpening place PO and may now be sharpened by turning first the motor 8 with the stone 9 into the other sharpening position and then by tilting it to accomplish the sharpening. The start and end points of the movements of lever 18 and the gripping pawls 13 are set by adjusting screws 20 and 22 in lugs 19 and 21 (presented only in Figs. 1 to 3). The adjustment is accomplished in such a way that at the final point of the movement one of the teeth to be sharpened (the tooth 28 in Fig. 3) is at the sharpening position PO and that the length of the return movement is the distance D between two successive teeth to be sharpened. The adjustment of the start and end points is necessary because the teeth to be sharpened of course wear down with the sharpening and both those and the depth gauges wear down as the chain is used. Sharpening of the teeth from above during the movement may be easily added to the device according to the invention. Figs. 7 to 9 present an embodiment of that. A plate 36 is placed between the frame 4 and the frame part 6 and a strip 38 extending backwards from the front edge is separated by cuts in the plate. For attachment, the plate is provided with openings 39 which are aligned with screws placed in recesses 41. The front edge 37 of the plate is bent a little upwards so that sticking of the teeth is definitely prevented. A thin strip 40 coated with diamond mix provided for grinding is attached to the underside of the strip this kind of diamond strips being available as ready-to-fix with adhesive on the other side. A screw 42 is placed at the front edge of the frame in alignment to and extending against the strip whereby the position of the strip may be adjusted vertically, so that it may be brought in touch with worn teeth, for example. Some examples of the realisation of the invention have been presented above but it is clear that the invention may be realised in many other ways within the scope of the accompanying claims.
