METHOD AND SYSTEM FOR SHARPENING TEETH ON SAW CHAINS

Abstract: For users of chain saws it is known that the chain saw teeth should rather often be sharpened by filing in order to keep them well cutting. Traditionally, such a sharpening is effected by means of a straight filing rod moved in a reciprocal manner, but according to the invention it is realized that it is better to arrange the rod as a rotary circular or screw shaped formation, whereby the teeth can be worked in a simplified manner.

Description: Method and system for sharpening teeth on saw chains . The present invention relates to a device for sharpening the teeth of motor chain saws. Users of motor saws are famil- iar with the necessity of sharpening the teeth on the chain at relatively frequent intervals to maintain satisfactory cutting, and are well aware that this procedure is difficult and time-consuming, or is a source of irritation. By its nature, the problem is particularly familiar to forestry work- ers . According to normal standard, the chain saw teeth are filed purely manually by filing with a round file at a filing angle of approximately 30°. Many devices have been developed to facilitate the sharp- ening operation, including control of the file alignment. In general, however, these known devices for controlling the forward and backward movement of the file, or even developing a rotary movement of the file, have not achieved widespread practical use. Also, the use of motor grinding discs has been proposed, with an associtated fixture for holding the respective teeth of the chain. Apart from being troublesome, this method is even dangerous for the teeth themselves, because with a fast running grinding disc this easily results in the teeth being excessively heated, whereby their quality can be drastically reduced. Chain teeth are in several respects very different from ordinary saw teeth, primarily in having not only an outwardly projecting flank portion, but also an outermost, bent-out top portion, which is to be sharpened from below such that the leading edges of both the flank and the top portion are kept sharp. Therefore, the tooth should be affected by a filing or grinding pressure in a direction away from the root of the tooth, in addition to the force against the flank itself. This influence is liable to cause the treated tooth carrying chain link to tilt outwardly from its position rested against the sword edge, and while this can be 'felt' and accepted by a manual filing it will nevertheless incur problems in con- nection with automatic sharpening, inasfar as some backing of the treated tooth is required. Moreover, the tooth carrying chain links also have, at the end opposite to and operatively in front of the respec- tive teeth, an outwardly protruding "rider", which is somewhat less protruding than the tooth and has the purpose of delimiting the intrusion of the tooth into the material being sawn and remove the resulting chips. These riders, arranged rather closely in front of the teeth, will to some degree prevent a grinding disc from entering the teeth in a fully ideal manner, which would be by way of a large disc rotating in a plane parallel with the chain carrying link in front of the tooth; in practice, however, it could be sufficient to operate with an inclined position of the plane of rotation, such that the disc edge will enter into the tooth with the disc just passing over the top of the rider. Finally, the teeth of the saw chains appear with a much longer mutual distance than ordinary saw teeth. Normally there is a number of neutral chain links interposed between the consecutive tooth links, and since the consecutive teeth are layed out (or rather in) to opposite sides, the distance between two similarly oriented teeth will be correspondingly large. Although the chains are made with very high precision, unavoidable tolerances will cause small deviations of the distances referred to. The relevance of this observation will appear from the following. Now, in connection with the present invention, it has been recognized that a more ideal shape of a rotary grinding or filing tool will be a file rod as first referred to, held against the tooth in exactly the same position as by conventional tooth filing, now only rounded up so as to form a relatively large circular element rising upwardly from the tooth and turned into an angular position relative to the saw sword corresponding to the desired filing angle, i.e. an an- gle of the magnitude 3o° from the direction perpendicularly to the sword. In this manner the filing ring element, in the local area immediately in front of the tooth, will appear practically exactly as a conventional file rod, except for a slight curvature thereof, i.e. the ring element will in no way interfere with the said rider in front of the tooth. According to an important aspect of the invention it will then also be possible to arrange for means to excert a hold- ing pressure against the top of the rider belonging to the tooth being filed, whereby the tooth or the entire tooth link can be stabilized against the said tilting in response to the filing/grinding pressure being applied to the tooth, thus without any need of arranging for a support of the tooth at the opposite side thereof. According to the invention, such means for holding down the riders may be provided even on the ring element itself, viz. as a laterally projecting flange which, during the rotation of the ring element, will steadily and slidingly engage the top of the relevant rider and thus stabilize the tooth. Already by these measures the invention, in practice, provides for a sharpening system that will be superior to previous proposals. However, the invention comprises a further and extremely important development, viz. based on the finding that the said circular filing/grinding element, without any significant change in the character of the local engagement with the single tooth, can be changed from a circular shape into three-dimensional screw shape, in which it is able to cooperate, simultaneously, with a number of consecu- tive teeth. As mentioned, the distance between the chain saw teeth is relatively long and the filing angle is relatively large, and it has been found that these two conditions enable the design of a "screw file" having at each place a pitch angle corresponding to the desired filing angle and having a phase length equal to the distance between the teeth, without the diameter of this screw being extremely large or small compared with the chain or sword dimensions, this almost amounting to a "lucky coincidence". The screw file, in being rotated about an axis parallel with the moving direction of the teeth, will thus both sharpen the teeth and urge the teeth forwardly, that is rearwardly relative to their operational movement, in order to sharpen the teeth. The required counter pressure on the teeth for the filing/grinding tool to -effect the desired result may be established already by the inherent resistance against the saw chain being moved along the sword. Hereby an entirely novel perspective is encountered, viz. that the teeth of the saw chain can be sharpened by a conti- nous movement, merely by a rotation of the filing/grinding screw element, when the latter is mounted in holding connection with the sword of the chain saw, with its axis of rota- tion held in parallel with the line of movement of the chain. The screw element may be driven at moderate speed, pressing itself against the front side of the teeth and thus forcing the chain rearwardly. It is a further advantage that the direction of the fil- ing/grinding movement is the preferred one, viz. with and not against the resulting sharp edges. The sharpening screw element, just like the said circular filing or grinding element, may well be provided with the discussed flange member serving to hold down the riders, i.e. the tooth or teeth may be pushed rearwardly without any noticeable tilting, whereby a high quality sharpening is achievable by the fully automatic and continuous operation. A novelty search based on the invention has revealed that it has earlier been proposed to sharpen ordinary saw teeth by means of rotating, screw shaped filing elements, see US-A- 570, 732, published in 1896. However, the teaching of this document is impertinent to the sharpening of chain saw teeth, already because of the above-mentioned fundamental differences between ordinary saws and chain saws . By way of exam- pie, in connection with ordinary saw teeth it would not be possible to operate with a filing angle as large as 30° with this technique, because between the teeth there would not be space enough for the required tool. Besides, the said document does not indicate the possibility of modifying the screw member into a pronounced high pitch member usable for chain saws . Moreover, the said US-A-570, 732 does not take into account the discussed condition with respect to slight varia- tions of the distance between the chain saw teeth. The disclosed apparatus is provided with two counter rotating screw files for engaging, at the same time, two saw teeth as laid out to opposite sides in the usual manner, whereby the two screw members will assist each other in pushing the saw blade (band-saw) in its reverse direction, filing or grinding the two teeth simultaneously. For achieving this result the distance between the two teeth or any pair of two such teeth has to be exactly the same as the operative distance between the two filing or grinding screws, as in case of a slightly larger distance one tooth will be heavily worked while the pressure on the other tooth is relieved and this tooth not worked effectively, while in case of a slightly shorter distance at least one of the teeth and/or one of the filing screws may be mechanically damaged. On this background and in accordance with the present invention, the discussed system should be laid out so as to work only one tooth at a time and as to ensure that the screw element is ready behind the next (or rather second next) tooth when it gets out of engagement with the just worked tooth. Thereafter and preferably only after the working of all of the teeth laid out to the same side, the screw tool for working the remaining teeth is made operative and the first screw tool is made inoperative. In practice, the tools are simply interchanged. Thus, in connection with the invention the problem is not the distance variations between the teeth of opposite layout, but those between the consecutive teeth of the same type. In the following the invention will be described in more detail with reference to the drawing, in which: Fig. 1 is a perspective view of a row of chain saw teeth and different tools for filing or grinding the teeth; Fig. 2 is a lateral view of a saw chain and different sharpening tools; Fig. 3 is a perspective view of a saw chain and a tool according to the invention; Fig. 4 is a perspective view at a preferred tool set according to the invention; Fig. 5 is a lateral view of a chain saw sword with the tool set of Fig. 4 mounted thereon; Fig. 6 is a top view illustrating the more detailed layout of the active part of the tool set; Fig. 7 is a side view of a filing system for operational and concurrent filing of saw teeth laid out to opposite sides; Fig. 8 is a perspective view of a conventional chain tooth; and Figs. 9-10 are similar views of teeth shaped according to the invention. In Fig. 1 is schematically indicated a saw chain 2, ap- pearing with an upstanding saw tooth 4 to be sharpened by filing. Conventionally, this would be effected by working the tooth with a straight round file 6 held at a specific angle relative to the transverse direction of the chain e.g. at an angle of some 30° therewith, by reciprocation of the file 6, though preferably with filing pressure only in strokes with and not against the cutting edge. Each tooth has a bent-out top portion 3, the leading end of which is also sharpened by the filing. Every second tooth, designated 5, is laid out to the opposite side and should be filed by a file 6' under the same filing angle, but with mirrored orientation relative to the file 6, as shown. According to the invention it has been found that it is perfectly possible to imitate the conventional filing by means of a file rod 8 rounded up into a circular shape and moved by a rotary motion, passing the tooth tangentially, whereby its engagement with the tooth will be practically identical with the effect of the straight file rod 6, though now with the improvement that the ring can be moved unidirec- tionally in the correct filing direction as indicated by an arrow A. This is a basic concept of the invention, enabling a convenient, motor driven operation of the ring member 8. The saw chain 2 is shown in more detail in Fig. 2. The teeth 4 and 5 are arranged on link members 10, which are interconnected by three other link members 12, 14 and 16, and in front of the cutting teeth (i.e. to the left) the links 10 are shaped with an upstanding "rider" 18 determining the intrusion depth of the tooth 4, 5 into the material being sawed. The file rods 6 or 8 will not in any way interfere with these riders, but in forcing such rods against the teeth 4.5, this will result in a tilting impact on the entire link 10 about its pivot pin 20 underneath the tooth portion 4.5, whereby the tooth may tilt and thus change the ideal filing conditions . However, as shown to the right in Fig. 2 and in accordance with the present invention, it is possible to combine or provide the filing ring rod 8 with a projecting flange member 22 which, in operation, will serve to prevent any substantial raising of the rider 18, thus also preventing any substantial tilting of the link 10 and therewith the associated tooth 4 or 5. According to a further development of the invention it was found that the rather distance between two consecutive teeth 4 or 5 laid out to the same side could be able to condition that the file ring member 8 could be converted into a screw member 24 which - as shown in Fig. 3 - could extend along the saw chain, with a pitch satisfying the requirements as to the filing angle and also with a winding length corresponding to the distance between two consecutive teeth 4 or 5, without the diameter of this screw member being excessively "small" or "large" . The saw chains were never designed with a view to this criterion, and it is to be regarded as a lucky coincidence that the chain teeth will be sharpenable/- filable/grindable based on the findings of the present invention. In Fig. 3 it is shown that the ring member 8 of Figs. 1 and 2, originally arranged in an oblique plane of rotation corresponding to the desired filing angle, is now converted into a screw rod structure 24 axis-parallel with the saw chain 2 and having a pitch corresponding to the desired fil- ing angle of the teeth as well as a winding length corresponding to the distance between two consecutive, similarly oriented teeth 4 or 5, without the required diameter of the screw rod 24 hereby being excessivlely small or large. The screw rod member 24 is shown connected to a central rotary a shaft 26 by means of radial pins 28. When the shaft is rotated in the direction R, the screw 24 is rotated so as to effect a movement of the chain 2 in the marked direction P, and at the same time the teeth 4 are filed as desired. Fig. 3 merely illustrates the very principle of filing the teeth by means of a screw rod. In practice, of course, a more rigid structure will be required, and besides, as mentioned above, the screw should not be laid out to work more that a single tooth at a time. A practical embodiment of a sharpening apparatus according to the invention is shown in Figs. 4 and 5. The apparatus comprises a fixture member 30 having opposed plate portions 32 which, by means of clamp screws 34, can be secured to the sword 36 of a chain saw, with an intermediate bushing portion 38 rising above the top edge thereof. The portion 38 has a throughhole 40 for receiving a driving shaft 42 of a cylindrical body 44 provided with a screw formation 46 comprising a plate strip 48 and a further raised, undercut rod member 50. In its mounted position as shown in Fig. 5, the cylinder 44 is rotatable e.g. by the chuck 52 of a drilling or screwing machine. It will be readily understood that by such a rotation the filing or grinding rod member 50 will be operable to sharpen the teeth 4 successively pushing the chain rear- wardly of its working direction. Chain saw teeth, unlike ordinary saw teeth, are characteristic in being slightly movable relatively to each other and to the their common carrier structure, inasfar as they are displaceable in all three main directions. For a high quality sharpening, therefore, it is required to stabilize the teeth - or the tooth being worked, and of course also to mount the fixture member 30 very accurately on the sword 36. rt P- 0 0 ø rt CQ tr φ s: P- Hi P 1 0 P 1 cr 0 ' Φ s: P- (i 0 P- tQ 01 Ω 0 rt 01 tr CQ φ P 1 Φ Ω o < CQ ø φ Φ Si P O P- rt SD rt P- P P- Ω SD 0 rt SD 0 P 1 φ ω P 1 ; P- Si P- ø P Φ φ Ω SD rt Ω P- tr 0 0 0 Hi rt tr Φ 3 (D P- 0 Si P- P Φ Ω t . 3 P- ø 0 rt Φ CQ • φ rt ] Ω cr cr P- P rt Hi tr rt ø rt SD P- rt Hi rt SD rt cr cr P O CQ $. 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X 03 P- u P- P P 1 Φ Φ 03 φ Di SD SD P- Ω 0 rr tr 0 Ό Φ ~ rr P O ϋ 03 0 o P- rt P- ø rt rt Hi P i ^ SD P 0 0 03 Φ Ω SD 03 SD Ω rt tr SD cr Si P> 0 P- ø l- 1 rt CQ • 0 O SD tr 3 rt 0 0 rt rt rr Hi 0 P SD Φ SD rt rt Φ o ø CQ 03 φ SD CQ Hi Ω O P- P- 0 cr ^ 0 rt rt SD rt O Pi SD CQ CQ rt p- tr P- P P" rr • P Φ s; Ω 0 ø Φ 0 P- SD Φ P- 03 P Hi rt P- P 0 Φ SD 0 5 > rt SD rt Si rr CQ •d O CQ SD cr SD Φ 03 0 rt Φ ø P- 0 0 SD rt CQ D- SD rr ι-3 P CQ P- 0 P P ^ P cr φ SD p. Hi CQ rt rt σ. SD Ω 03 rr Q rt tr Ω <! rt 03 Φ Ό Hi φ ≤ Φ ' P SD Si Φ P Hi P. P rr CQ Φ. rt P- Φ Φ Ω ø SD rr P P P Φ SD O φ Hi Ω P- rt • : P- P P Φ Φ SD 0 ~ Φ Hi rt Si O rt ø Φ 03 Φ Φ o P P P SD rt 0 tr ø 0 SD Ω Si Si Ω Ω 0 0 rr 03 SD rt rt tr Hi 3 Φ 3 X P> Hi Ω P- ( Q φ rt CQ rt ø rt 0 CQ rt H tr σi Φ rt P φ *d tr P- SD P 1 O rt Φ Hi P- O φ Ω ^ rr SD CQ P- P Φ P- tr oo X SD P 1 P SD O P- 0 CQ 0 S rr P rt 0 $. 0 SD P SD rt SD 3 rt φ < P- 03 <! Φ rt 03 * P- φ P P SD Q Φ 0 ø Φ SD rr P P- CQ 0 P" O tr rt O Φ Di φ 0 - Φ tr rt 0 O rt rt O CQ cr Φ φ rt Hi SD < ϋ - CQ - D. SD SD 1 Hi 03 0 P- P- *- tr p. <! SD Φ SD P- rt 0 03 1 0 ^ Φ Φ ø ϋ rt Si edge. The invention will comprise such chains which are designed particularly for cooperation with the filing system of the invention. Although the invention has been developed for working conventional saw chains it will be understood that the invention is not correspondingly restricted. The system may well be adapted for use with some other kinds of saws, e.g. large band saw blades .

Claims: CLAIMS : 1. A method of sharpening the teeth of a saw chain, whereby a file or grinding rod is caused to be moved axially across the individual teeth at a desired sharpening angle with the saw chain remaining mounted on its associated saw sword, such that the rod effects a sharpening of the leading edged of both the tooth flank projecting from the saw chain and the bent-out top portion of the chain saw tooth, characterized in that the sharpening rod, shaped as a lengthwise rounded structure, is positioned and rotated in a unidirectional manner so as to effect a laterally ori- ented sharpening pressure against the tooth. 2. An apparatus for carrying out the method according to claim 1, characterized in comprising a lengthwise rounded filing or grinding rod, which is rotatable so as to effect, laterally, the desired sharpening of the saw tooth and its associated, bent-out top portion. 3. An apparatus according to claim 2, in which the lengthwise rounded rod structure is a closed ring member, which is operable to engage a chain tooth with the desired sharpening angle in that the plane of ro- tation of the ring member is turned out of the cross plane of the tooth. 4. An apparatus according to claim 2, in which the lengthwise rounded rod structure is shaped as a screw member having an axis of rotation extending in paral- lei with the moving path of the teeth along a selected fraction of the chain passage along the saw sword. 5. An apparatus according to claim 3 or 4 , comprising means for effectively clamping of the saw tooth carrying chain links against local movements during the sharpening of the tooth. 6. An apparatus according to claim 5 in which said clamping means comprise plate portions associated with the rounded rod in such a position thereon that during the operative engagement between a chain tooth and the moving rod, the plate portion will slidingly engage the top of the rider located on the same chain link as the tooth. 7. An apparatus according to claim 6, in which the plate portion is of a moderately grinding nature. 8. An apparatus according to claim 4, in which the length of the screw member is slightly longer than the nominal distance between consecutive teeth to be sharp- ened, and in which the pitch of the screw member is smaller at the end of tooth delivery than at the leading end of the screw member. 9. An apparatus according to claim 4, in which the screw member is arranged on a cylinder, which is rotatably mountable in a fixture member to be fastened to the saw sword, the cylinder being exchangeable with another, mirrored cylinder for sharpening, with opposite direction of rotation, those teeth which are laid out to the opposite side. 10. An apparatus according to claim 4, integrated in the housing of a chain saw as discussed in connection with Fig. 7. 11. A chain saw according to claim 10. 12. A saw chain, the teeth of which are shaped as shown and described with reference to Figs. 9 and 10.

Inventors: SPANG KAARE, SPANG, KAARE
Applicants: SPANG KAARE, SPANG, KAARE
Application year: 1998
Main classification: B23D63
IPC codes: B23D63