Patent Publication Number: US-2022212275-A1

Title: Chainsaw Cutting Link, A Saw Chain Comprising Such a Cutting Link, A Method for Manufacturing of a Cutting Link, and a Method of Grinding a Cutting Link

Description:
FIELD OF THE INVENTION 
     The present invention relates to the field of chain saws, and more particularly, to a chainsaw cutting link, a saw chain comprising such a cutting link, a method for manufacturing of a cutting link, and a method of grinding a cutting link. 
     BACKGROUND OF THE INVENTION 
     Chain saws are commonly used to cut timber or to perform other rigorous cutting operations. Chain saws are typically relatively robust hand-held machines which include a housing containing a driving device, e.g. a motor powered by gasoline or an electric motor. A guide bar extends from the housing, and a saw chain is driven by the driving device around the perimeter of the guide bar at a relative high speed. The saw chain may include different types of links arranged in different configurations. Some of the links included in the saw chain may be cutting links having a sharpened portion for cutting through a medium to be cut, e.g. wood. 
     U.S. Pat. No. 2,774,396 describes an exemplary cutting link for a saw chain to be used in a chainsaw. There is however always a need for even further improvements to the safety aspect for people working with chainsaws. 
     SUMMARY 
     It is an object of the present invention to solve, or at least mitigate, parts or all the above-mentioned problem. To this end, according to a first aspect there is provided a chainsaw cutting link comprising a base portion provided with two rivets holes for pivotal inter-connection with adjacent links, each of said rivet hole defining a respective pivot axis; and a cutting tooth extending away from the base portion, wherein the cutting tooth comprises a top plate and a side plate defining an angle to form an L-shaped cutting edge facing in a cutting direction in which the chainsaw cutting link is configured to move during cutting, the L-shaped cutting edge comprising a top plate cutting edge arranged on the top plate, and a side plate cutting edge arranged on the side plate, wherein the top plate cutting edge is sharper than at least a portion of the side plate cutting edge. Thereby, the cutting link will be less prone to cut through protective workwear, while maintaining a good ability to cut through the material to be cut. Typically, the top plate cutting edge and the side plate cutting edge may be integrally formed of a single piece of metal, such as steel sheet. According to further embodiments, the entire cutting tooth may be integrally formed of a single piece of metal, and optionally, the cutting tooth may be integrally formed with the base portion of a single piece of metal. The top plate may extend along the direction of the pivot axes defined by the rivet holes, and may e.g. extend along a plane which is substantially parallel or slightly inclined relative to a plane comprising the pivot axes. The side plate may extend transverse to said pivot axes, for example along a plane which is substantially perpendicular to the pivot axes. The cutting direction may be substantially parallel to the plane comprising said pivot axes, and perpendicular to said pivot axes. 
     The purpose of the top plate cutting edge is to shave off a chip from the material to be cut, whereas the purpose of the side plate cutting edge is to cut off e.g. any fibres within the material, which fibres may be parallel to the top plate cutting edge such that they are not cut off by the top plate cutting edge, to obtain a clean cut without tearing. In a newly sharpened saw chain according to prior art, the top plate cutting edge and the side plate cutting edge typically have the same sharpness. As the chain wears, the top plate cutting edge is exposed to more wear than the side plate cutting edge, and thereby becomes blunt faster. Once the chain has become blunt, both the top plate cutting edge and the side plate cutting edge are sharpened in a single sharpening operation, using a round file. 
     When a brand new saw chain of conventional prior art type is used for the first time, the top plate cutting edge and the side plate cutting edges are typically very sharp, and there is a risk that the saw chain will cut through the protective pants typically worn by the user, and thereby injure his/her leg(s). If at least a portion of the side plate cutting edge is less sharp than the top plate cutting edge, the cutting link will not as easily cut off filaments in the protective pants, since some filaments will engage with said at least a portion. The filaments engaging with the relatively duller portion of the side plate cutting edge may thereby be pulled out from the protective padding of the trousers by the cutting tooth, and follow the cutting tooth to the chainsaw housing. Once reaching the chainsaw housing, the filaments of the protective garment will get stuck in the driving wheel and thereby stop the chain from rotating, which reduces the risk of the user cutting through the protective pants into his/her leg(s). 
     According to an embodiment, at least 25% of a length, as projected on a plane perpendicular to the cutting direction, of the side plate cutting edge is less sharp than the top plate cutting edge. Thereby, a substantial engagement with the filaments of the protective trousers may be reached. Even though only a small portion of the length of the side plate cutting edge needs to be less sharp than the top plate cutting edge to protect the cutting link from cutting through the protective pants to a certain degree, according to further embodiments, at least 50% or at least 80% of the length of the side plate cutting edge may be less sharp than the top plate cutting edge. 
     According to an embodiment, the cutting tooth may have a cutting tooth height above the base portion, in an outwards direction perpendicular to the cutting direction, wherein an outermost end of said at least a portion of the side plate cutting edge is located at a height above the base portion of at least 40% of the cutting tooth height. According to further embodiments, the outermost end of said at least a portion of the side plate cutting edge is located at a height above the base portion of at least 50% or at least 60% of the cutting tooth height. 
     According to an embodiment, the side plate cutting edge may comprise an outermost side plate cutting edge portion, arranged nearest to the top plate, which side plate cutting edge portion is as sharp as the top plate cutting edge. Thereby, a good cutting efficiency for cutting off fibres integrated in a solid material to be cut, such as wood fibres, is maintained. As noted above, the top plate provides a shaving function of the cutting link, whereas the outermost cutting edge portion of the side plate, arranged closest to the top plate, will cut off fibres to release the chip from the object being cut. Both those portions should preferably be sharp to get a good cutting capacity of the cutting link. The top plate and the side plate may define an angle of about 90°, as seen in a cross-section perpendicular to the cutting direction, and may meet at a cutting corner. 
     According to an embodiment, the cutting tooth has a cutting tooth height above the base portion, in an outwards direction perpendicular to the cutting direction, wherein a lowermost end of said outermost side plate cutting edge portion is located at a height above the base portion of at least 40% of the cutting tooth height. According to further embodiments, the lowermost end of said at least a portion of the side plate cutting edge is located at a height above the base portion of at least 50% or at least 60% of the cutting tooth height. 
     According to an embodiment, said at least a portion of the side plate cutting edge comprises a trailing, relative to the cutting direction, portion of the side plate cutting edge. The trailing portion is the rearmost portion of the side plate cutting edge when the cutting tooth moves in the cutting direction. When cutting in the protective pants, the filaments tom from the pants will, as they are tightened by the motion of the chain, tend to move to the trailing portion of the side plate cutting edge, and accumulate there. It is therefore preferred that the trailing portion be made dull to maximize the safety of the cutting link. 
     According to an embodiment, the at least a portion of the side plate cutting edge may have a dull edge radius of curvature, as seen in a cross-section extending substantially parallel to a plane comprising pivot axes defined by the rivet holes, said dull edge radius of curvature being greater than 0.015 mm. Typically, a sharp cutting edge has a radius of curvature of 0.015 mm or less. A radius of curvature greater than 0.015 mm is generally considered dull for the purpose of cutting wood using a chainsaw. According to a further embodiment, the dull edge radius of curvature may be greater than 0.030 mm. In fact, the at least a portion of the side plate cutting edge may even be a straight edge which is parallel to the pivot axes, i.e. corresponding to an infinite radius of curvature. It is pointed out that in the present disclosure, the radius of curvature of the cutting edge is used as a measure of sharpness of the respective cutting edges. However, it will appreciated that there are other ways of measuring sharpness, all of which are intended to be covered by the independent claims. 
     According to an embodiment, the top plate cutting edge may have a top plate cutting edge radius of curvature, as seen in a cross-section extending in a plane substantially perpendicular to the cutting direction, said top plate cutting edge radius of curvature being less than 0.015 mm. According to a further embodiment, the top plate cutting edge radius of curvature may be less than 0.010 mm. 
     The respective radii of curvature the cutting edge may be obtained by grinding the respective cutting edges to different respective levels of sharpness. 
     According to an embodiment, the at least a portion of the side plate cutting edge may comprise a concave portion, wherein an upper end of the concave portion begins at a distance below a top face the top plate. 
     The concave portion may be formed by a cutout in the side plate cutting edge, which cutout may be formed by punching during manufacture of the cutting link. This cutout may be shaped not to engage with the tools used for grinding the edge, so as to become dull compared to the top plate cutting edge. By way of example, the cutout may have a shape which prevents fully reaching into the cutout using a circular-cylindrical file having a diameter of 4.8 mm, as such files are generally used for sharpening the cutting tooth. The concave portion may begin e.g. less than 5 mm, preferably 2-3 mm, and most preferably 0.5-1 mm, below a top face of the top plate to obtain an optimal balance between safety and cutting efficiency of the cutting link. The concave portion may be arcuate but other concave shapes are possible, such as a V-shape, as long as a relatively dull trailing portion of the cutout is formed. 
     According to an embodiment, the side plate cutting edge may further comprise a convex portion arranged between the top plate and the concave portion of the side plate cutting edge. The convex portion, which may be at the interface between said at least a portion of the side plate cutting edge which is less sharp, and a sharp outermost side plate cutting edge, may have any substantially convex shape, i.e. it may be curved or form a sharp angle. When the cutting link becomes too dull to be used for cutting, a file may be used for grinding of the top plate cutting edge and the side plate cutting edge. The convex portion may prevent a circular-cylindrical file of the type generally used for sharpening the cutting link from fully reaching into and sharpen the bottom, i.e. trailing portion, of the convex portion while sharpening the top plate cutting edge. 
     According to an embodiment, the at least a portion of the side plate cutting edge, as seen in a cross-section parallel to a plane comprising the pivot axes defined by the rivet holes, may have a straight front edge extending substantially parallel to said pivot axes. When making the link by punching, a straight front edge of the at least one portion of the side plate cutting edge may obtained; this straight front edge may be at least partly maintained when sharpening the side plate cutting edge. The cutting link may be formed of sheet metal having a sheet metal thickness, and the straight edge may have a width, along the pivot axes, that at least corresponds to 5%, preferably at least 15%, most preferred at least 50% of the sheet metal thickness. If the trailing portion of the side plate cutting edge is formed by punching a cutout, the width of the trailing portion may correspond to the thickness of the material from which the cutting link is formed, minus whatever may be grinded off when grinding the side plate cutting edge. 
     According to a second aspect, parts or all the above mentioned problems are solved, or at least mitigated, by a saw chain for a chainsaw, the saw chain comprising a plurality of cutting links according to any embodiment of the first aspect defined above. The saw chain may be a new saw chain, which may be packaged in a sales package such as a sealed plastic bag and/or a cardboard box. 
     The saw chain may comprise a plurality of drive links that each includes a portion thereof that is configured to ride in a channel around a periphery of a guide bar of a chain saw. Each drive link may be attached to an adjacent pair of tie links by rivets that extends perpendicular to the longitudinal length of the chain. A rivet can be provided at the front portion of each drive link to attach the drive link to the rear portion of a pair of preceding tie links. Another rivet may be provided at the rear portion of each drive link to attach the drive link to the front portion of a subsequent pair of tie links. Each pair of tie links may connect to opposing lateral sides of the drive link. The connections may be repeated in an alternating fashion to complete an endless loop of alternating drive links and tie links. For some pairs of the tie links, one of the tie links may be formed as a cutting link according to any embodiment of the first aspect above. When cutting with such a saw chain, the risk of the user getting cut in his/her leg(s) may be reduced, especially when the saw chain is new. 
     According to a third aspect, there is provided a method of cutting with a chainsaw in chainsaw protective wear, such as a pair of chainsaw protection trousers, the chainsaw protective wear being provided with chainsaw protective filler material configured to be released from the chainsaw protection wear to engage with a drive sprocket of the chainsaw when cutting the chainsaw protective wear, the method comprising cutting in the chainsaw protective wear using a chain as defined above such that the chainsaw protective filler material engages with said at least a portion of the side plate cutting edge. 
     According to a fourth aspect, the use of a chainsaw cutting link or a saw chain as defined above reducing the ability of cutting through a chainsaw protective padding of chainsaw protective wear. 
     According to a fifth aspect, there is provided a combination of a saw chain as defined above and a chainsaw protective wear provided with chainsaw protective padding. The chainsaw protective wear and the saw chain may be combined together and sold as a safety kit. 
     According to a sixth aspect, parts or all the above mentioned problems are solved, or at least mitigated, by a method of manufacturing a cutting link, comprising: 
     punching a piece of material to form a cutting link blank comprising a top plate portion and a side plate portion, the side plate portion having a cutout; 
     bending the top plate in relation to the side plate to form an L-shaped edge; and 
     grinding a side plate cutting edge with a grinding tool that does not mate with the cutout, such that the cutout is sharpened less than a portion of the side plate cutting edge adjacent to the cutout. 
     According to an embodiment, the method may further comprise grinding a top plate cutting edge with the same grinding tool, simultaneously with grinding the side plate cutting edge. 
     These methods require less grinding of the link compared to prior art links and thus the link may be less expensive to manufacture. Moreover, the cutout may define an area which is less prone to cutting off, and thereby more prone to getting entangled with, filaments of protective trousers. 
     According to a seventh aspect, there is provided a method of grinding a cutting link, the method comprising sharpening, using a grinding tool, a top plate cutting edge; sharpening, using a grinding tool, a side plate cutting edge; and blunting, using a grinding tool, at least a portion of the sharpened side plate cutting edge to make the at least a portion of the side plate cutting edge less sharp than the top plate cutting edge. The method may be performed during manufacture of a cutting link, as well as when re-sharpening a cutting link in the field. 
     According to an embodiment, the sharpening of the top plate cutting edge and the side plate cutting edge may be made in a single step, using a single grinding tool. According to an example, the grinding tool used for sharpening may have a curved profile corresponding to a radius of curvature of about 2.4 mm, so as to be compatible with the most typical commercially available cutting chains. 
     According to an embodiment, the blunting of the at least a portion of the side plate cutting edge may be made using a grinding tool which is separate from that used for sharpening the side plate cutting edge. According to an example, the grinding tool used for blunting may have a profile corresponding to a radius of curvature of less than about 2.3 mm, such that when blunting a cutting chain of the most typical commercially available type, an outermost side plate cutting edge portion may be left unblunted. 
     According to an embodiment, the blunting step may comprise refraining from blunting an outermost side plate cutting edge portion. 
     It is noted that embodiments of the invention may be embodied by all possible combinations of features recited in the claims. Further, it will be appreciated that the various embodiments described for the cutting link are all combinable with the methods and devices as defined in accordance with the third, fourth, fifth, sixth, and seventh aspects of the present invention, and vice versa. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and non-limiting detailed description of preferred embodiments of the present invention, with reference to the appended drawings, where the same reference numerals will be used for similar elements, wherein: 
         FIG. 1A  is a side view of a chainsaw; 
         FIG. 1B  is a front view of a pair of chainsaw protective trousers; 
         FIG. 2  is a side view illustrating a front portion of a guide bar of the chainsaw of  FIG. 1 a   , the guide bar being provided with a saw chain; 
         FIG. 3A  is a side view of a cutting link of the saw chain of  FIG. 2  as seen from a first side; 
         FIG. 3B  is a side view of the cutting link of  FIG. 3A  as seen from a second side opposite to the first side; 
         FIG. 3C  is a schematic view in perspective illustrating the cutting link of  FIGS. 3A-B  as seen approximately from the cutting direction. 
         FIG. 4  is a schematic view in section of a top plate cutting edge of the cutting link of  FIGS. 3A-C , the section being taken along a plane indicated by the line IV-IV in  FIG. 3C ; 
         FIG. 5  is a schematic view in section of a side plate cutting edge of the cutting link of  FIGS. 3A-C , the section being taken along a first plane indicated by the line V-V in  FIGS. 3B and 3C ; 
         FIG. 6  is a schematic view in section of a side plate cutting edge of the cutting link of  FIGS. 3A-C , the section being taken along a second plane indicated by the line VI-VI in  FIGS. 3B and 3C ; 
         FIG. 7  is a schematic view in section of a side plate cutting edge of the cutting link of  FIGS. 3A-C , the section being taken along a third plane indicated by the line VII-VII in  FIGS. 3B and 3C ; 
         FIG. 8  is a schematic view in section of a side plate cutting edge of a cutting link according to an alternative embodiment, the section being taken along either of the planes indicated by the lines VI-VI and VII-VII in  FIGS. 3B and 3C ; 
         FIG. 9A  is a schematic side view of a cutting link blank for forming the cutting link of  FIGS. 3A-C , and illustrates a bending step during manufacturing the cutting link of  FIGS. 3A-C ; 
         FIG. 9B  is a schematic side view corresponding to that of  FIG. 9A , and illustrates a grinding step during manufacturing the cutting link of  FIGS. 3A-C ; 
         FIG. 10  is a flow chart illustrating a method of manufacturing the cutting link of  FIGS. 3A-3C ; 
         FIG. 11  is a flow chart illustrating a method of grinding a cutting link; 
         FIG. 12A  is a schematic side view of a cutting link, and illustrates a sharpening step during manufacturing the cutting link; and 
         FIG. 12B  is a schematic side view of the cutting link of  FIG. 12A , and illustrates a blunting step performed after the sharpening step of  FIG. 12A . 
     
    
    
     All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary to elucidate the embodiments, wherein other parts may be omitted. 
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
       FIG. 1A  illustrates a handheld chainsaw  1  comprising a drive unit  3 , a guide bar  5  and a saw chain  7  configured as an endless loop, guided along the guide bar  5 , between a drive sprocket (not illustrated) and a nose sprocket  8 . The drive unit  3  comprises battery  11  and an electric motor (not illustrated), powered by the battery  11 . A handle  2  is provided with a trigger  4  for operating the electric motor. The saw chain  7  is configured to be driven around the guide bar  5  responsive to operation of the motor to enable the chainsaw  1  to cut lumber or other materials. 
       FIG. 1B  schematically illustrates, as an example of a chainsaw protective wear, a pair of chainsaw protection trousers  10  to be worn by a user of the chainsaw  1  of  FIG. 1A . The chainsaw protective trousers  10  are provided, on a front side thereof, with chainsaw protective padding  12  in the manner well known in the art, and described in e.g. WO17050373A1. The padding  12  comprises chainsaw protective filler material which, if the user of the chainsaw  1  of  FIG. 1A  accidentally cuts the trousers  10 , is configured to be released from the chainsaw protective trousers  10  to engage with the drive sprocket of the chainsaw  1 . The protective filler material comprises long fibres of high strength material such as para-aramid (e.g. Kevlar(R)), ballistic nylon, high performance filament yarn made of PET (Poly Ethylene terephtalat), PP (Polypropylene) or PE (Poly Ethylene), PA (Poly Amide) (for example materials such as Dyneema(R) or Vectran(R) etc) which are loosely arranged, usually in multiple layers. When a sawchain contacts the trousers, the outer layer is immediately cut through but the loose fibres of the filler material are drawn out and entangled by the blade so that they wrap around the chainsaw&#39;s drive sprocket, locking it solid and halting the chain, and so limiting damage to the operator&#39;s leg. Chainsaw protective trousers in the EU must comply with EN381-5 and are classified in three classes and three types, depending on the quantity and arrangement of the filler material. Class 1, 2 and 3 trousers are rated for use with chainsaws running at speeds up to 20 m/s, 24 m/s and 28 m/s respectively, with the requisite level of protection typically being provided by about 3 to about 12 or even more layers of filler material. 
       FIG. 2  illustrates a portion of the saw chain  7  disposed on the guide bar  5 , driven around the nose sprocket  8 , as seen in  FIG. 1A . For clarity of illustration, the assembly is illustrated with a side plate of the guide bar broken away, to illustrate how the saw chain  7  is guided within the guide bar. The saw chain  7  comprises a plurality of drive links  13 , each of which includes a guide tooth  27  that rides in a channel  15  along a periphery of the guide bar  5  and engages with the teeth of the nose sprocket  8 . The leading end  13   a , with respect to a direction of travel B of the saw chain  7 , of each drive link  13  is pivotally connected to leading pair  16  of tie links  17 , a trailing end of which sandwich the leading end  13   a  of the drive link  13  between them. The pivotal connection is formed by a rivet  19   b , which penetrates the tie links  17  and the drive link  13 , and defines a pivot axis extending in a direction perpendicular to the direction of travel B of the chain  7  during cutting. Similarly, the trailing end  13   b  of each drive link  13  is pivotally connected, again via a rivet  19   a , to a trailing pair  18  of tie links  17 , a leading end of which sandwich the trailing end  13   b  of the drive link  13  between them. The connections between drive links  13  and tie links  17  are repeated in an alternating fashion to complete an endless loop around the guide bar  5 . For some pairs  16  of tie links  17 , one of the tie links  17  is formed as a cutting link  21 . Moreover, each drive link immediately preceding a cutting link  21  may be provided with a bumper  13   c . The direction of travel B of the saw chain will, in the following, be referred to as the cutting direction. 
       FIG. 3A  illustrates a cutting link  21  as seen from a first side,  FIG. 3B  illustrates the cutting link  21  as seen from a second side, and  FIG. 3C  illustrates the cutting link  21  as seen substantially from the cutting direction. Starting with  FIG. 3A , the cutting link  21  includes a base portion  29  with a leading end  29   a  and an opposing trailing end  29   b . The cutting link  21  has a first side face  31 , visible in the view of  FIG. 3A , and an opposite second side face  33 , as seen in  FIG. 3B . A leading end rivet hole  20   a  and a trailing end rivet hole  20   b  each extends between the first side face  31  and the second side face  33 . Each of the rivet holes  20   a ,  20   b  is configured to receive a respective rivet  19   a ,  19   b  ( FIG. 2 ) for connection to a respective drive link  13  and a respective tie link  17 . A bottom face  14  of the base portion  29  rides on the periphery of the guide bar  5  ( FIG. 2 ). 
     The cutting link  21  further includes a cutting tooth  35 . The cutting tooth  35  is disposed at the trailing end  29   b  of the base portion  29  and extends from the base portion  29 , when carried on a guide bar  5  ( FIG. 2 ), in an outwards direction perpendicular to the cutting direction B, away from the guide bar, to a height H ( FIG. 3B ) above the base portion  29 . Typical values of the height H may be, for example, between 2 mm and 6 mm. The cutting link  21  also includes a depth gauge  37 , disposed at the leading end  29   a  of the base portion  29 , which depth gauge also extends away from the base portion  29  in the outwards direction. The cutting tooth  35  and the depth gauge  37  portion are separated from each other by a depth gauge gap  39 , the bottom  40  ( FIG. 3B ) of which defines the upper edge of the base portion  29 . The depth gauge gap  39  may grow over time, as the cutting tooth  35  is worn out due to use, and grinded to remain sharp. 
     The cutting tooth  35  comprises a top plate  41  and a side plate  43 , which meet at an angle defining an L-shape, as seen from the cutting direction ( FIG. 3C ). The top plate  41  extends along the direction of the pivot axes C 1 , C 2  defined by the rivet holes  20   a ,  20   b , while the side plate  43  extends along a plane which is substantially perpendicular to the pivoting axes C 1 , C 2 . The cutting direction B of the cutting link  21  is substantially parallel to a plane P comprising the pivot axes C 1 , C 2 , and perpendicular to the pivoting axes C 1 , C 2 . The cutting link  21  is integrally formed of steel sheet having a thickness d. Typical values of the thickness d may be, for example, between 0.5 mm and 2 mm. 
     The top plate  41  comprises a top plate cutting edge  45 , which is inclined relative to the cutting direction B as well as to the pivot axes C 1 , C 2 , and the side plate  43  comprises a side plate cutting edge  47 . The top plate and side plate cutting edges  45 ,  47  are formed at the leading edge of the cutting tooth  35 , such that they face the depth gauge portion  37 . The top plate  41  and the side plate  43  meet in a cutting corner  49  forming an angle, as seen from the cutting direction B ( FIG. 3C ), of about 90°. The side plate cutting edge  47  extends from the cutting corner  49  to the bottom  40  of the depth gauge gap  39 , and has a length L, as seen in a projection on a plane perpendicular to the cutting direction B, which corresponds to the height H of the cutting tooth. The side plate cutting edge  47  may be straight or, as in the illustrated embodiment, curved. 
     When the cutting link  21  is used for cutting wood, the top plate cutting edge  45  shaves off material to form chips, whereas the side plate cutting edge  47  cuts off the fibres of the wood material, thereby releasing the chips from the material being cut. The height of the depth gauge portion  37  relative to the height H of the cutting tooth  35  determines the maximum cut (chip thickness) for each cutting link  21 . 
       FIG. 4  illustrates the top plate  41  as seen in the cross-section IV-IV indicated in  FIG. 3C . The top plate cutting edge  45  is sharp and may, for example, have a radius of curvature r 1 , as seen in a cross-section extending in a plane substantially perpendicular to the pivot axes C 1 , C 2  ( FIG. 3C ), that is less than 0.015 mm, and preferably less than 0.007 mm. 
     Referring back to  FIG. 3A , the side plate cutting edge  47  comprises an outermost side plate cutting edge portion  51 , arranged nearest to the top plate cutting edge  45 , which side plate cutting edge portion  51  is as sharp as the top plate cutting edge  45 . This outermost side plate cutting edge portion  51  may, for example, extend from the cutting corner  49  along a length L 2 , as projected on a plane perpendicular to the cutting direction B, of about 0.5-2 mm; in the illustrated embodiment, the outermost side plate cutting edge portion  51  has a length L 2  of about 40% of the total side plate cutting edge length L. The side plate cutting edge  47  also comprises a portion  53  which is less sharp, or blunter, than the top plate cutting edge  45 . The less sharp portion  53  of the side plate cutting edge  47  extends from a lower end of the outermost, sharper, side plate cutting edge portion  51  to the bottom  40  of the depth gauge gap  39 , and includes the rearmost, trailing, portion  55  of the side plate cutting edge  47 . The less sharp portion  53  has a length L 1 , as projected on a plane perpendicular to the cutting direction B, of about 60% of the total side plate cutting edge length L. 
       FIGS. 5, 6 and 7  illustrate three different cross-sections taken in respective planes which are parallel to the plane P comprising the two pivot axes C 1 , C 2 . Each cross-section illustrates the sharpness of the side plate cutting edge at a different respective distance from the cutting corner  49  ( FIG. 3A ). 
       FIG. 5  illustrates the side plate cutting edge  47  at the height of the outermost side plate cutting edge portion  51 . The outermost cutting edge  51  is as sharp as the top plate cutting edge  45  ( FIG. 3C ), and may, for example, have a radius of curvature r 2 , as seen in the illustrated cross-section extending in a plane parallel to the plane P ( FIG. 3A ), that is less than 0.015 mm, and preferably less than 0.007 mm. 
       FIG. 6  illustrates a first section of the less sharp portion  53  of the side plate cutting edge  47 . Even though partly sharpened at an inclined edge  54 , the less sharp portion  53  of the side plate cutting edge  47  has a straight leading edge extending substantially parallel to the pivot axes C 1 , C 2 , i.e. substantially perpendicular to the cutting direction B. Thereby, the leading edge of the less sharp portion  53  has, as seen in the illustrated section, an infinite radius of curvature r 2 , even though functionally, the radius of curvature may rather correspond to a finite radius of curvature r 3  of a few tenths of the material thickness d. 
       FIG. 7  illustrates the trailing portion  55  of the side plate cutting edge  47 . As is apparent from the cross-section, the leading edge of the trailing portion  55  is very blunt and has, again, an infinite radius of curvature r 2 , even though the functional radius r 3  may correspond to about twice that of the section of  FIG. 6 . In the illustrated embodiment, the straight leading edge of the trailing portion  55  of the side plate cutting edge  47  has a width that corresponds the entire thickness d of the material that forms the cutting link  21 . According to other embodiments, it may have another width, such as 5% or 50% of the material thickness. 
       FIG. 8  illustrates an alternative embodiment of the less sharp portion  53 . The less sharp portion may have substantially the same sharpness along its entire length, such that the section of  FIG. 8  may correspond to the section of  FIG. 6  as well as that of  FIG. 7 . In the embodiment of  FIG. 8 , the leading edge of the trailing portion  55  has a radius of curvature r 2  which is greater than the radius of curvature r 1  of the top plate ( FIG. 4 ). By way of example, the radius of curvature r 2  may be greater than 0.015 mm, for example, between 0.015 and 0.15 mm, and preferably greater than 0.05 mm. The different levels of sharpness of the top plate and side plate cutting edges  45 ,  47  may be obtained by sharpening the two edges  45 ,  47  separately, and to a different extent. 
     Only a small portion of the length of the side plate cutting edge  47  needs to be less sharp to protect the cutting link  21  from cutting through the protective trousers  10  ( FIG. 1B ) but in practice, it may be easier to manufacture a cutting link  21  in which at least 80% of the length of the side plate cutting edge  47  will be less sharp than the top plate cutting edge  45 . An exemplary manufacturing method will now be described with reference to  FIGS. 9A and 9B , following the method steps of the flow chart in FIG.  10 . The exemplary manufacturing method may result in a side plate cutting edge in accordance with the sections illustrated in  FIGS. 5-7 . 
     In a punching step  101  ( FIG. 10 ), a piece of steel sheet is punched to form a cutting link blank  21   a , which is illustrated in  FIG. 9A . The cutting link blank  21   a  comprises a top plate portion  41   a  having a top plate edge  45   a  which is to become the top plate cutting edge  45  ( FIG. 3A ), and a side plate portion  43   a . The side plate portion  43   a  has a side plate edge  47   a  which is to become the side plate cutting edge  47  ( FIG. 3A ). A The side plate edge  47   a  comprises a concave cutout  57   a , which meets a substantially straight edge portion  51   a  between the cutout  57   a  and the top plate edge  45   a  at a convex side edge portion  59   a . After punching, the cutting link blank  21   a  may be deburred, for example by barrel polishing. 
     In a bending step  103  ( FIG. 10 ), the top plate portion  41   a  is bent in relation to the side plate portion  43   a  along a bending line  60 , in the direction illustrated by the arrow in  FIG. 9A , such that the top plate edge  45   a  and the side plate edge  47   a  together define the L-shape described with reference to  FIG. 3A . 
       FIG. 9B  illustrates a grinding step  105  ( FIG. 10 ), in which the top plate edge  45   a  ( FIG. 9A ) and the side plate edge ( FIG. 9A ) are sharpened into the respective top plate and side plate cutting edges  45 ,  47 . The top plate and side plate cutting edges  45 ,  47  are sharpened in the same grinding step using a circular-cylindrical grinding tool  70  that does not fully enter into or mate with the cutout  57 , such that the cutout  57  is sharpened less than a portion  51  of the side plate cutting edge  47  between the top plate cutting edge  45  and the cutout  57 . Thereby, the manufacturing cost of the cutting link  21  may be less than for a cutting link according to prior art, since less material needs to be ground off from the side plate cutting edge  47 . According to an embodiment, only the side plate cutting edge may be grinded in step  105 , and the top plate may be grinded in a separate step  107  ( FIG. 10 ), which may take place before or after grinding the side plate cutting edge. 
     The blunt, concave portion  57  of the cutting edge  47  may, for example, meet the outermost, sharp, side plate cutting edge portion  51   a  at a convex portion  59  of the side plate cutting edge about 0.5-2 mm from the top plate cutting edge  45 , such that a good balance between fiber cutting capability and safety is obtained. The convex portion  59  may be arcuate, as illustrated in  FIG. 9B , may form a sharp corner, or may have another shape. 
     In an alternative to the manufacturing method above, the cutting link may first be manufactured in accordance with prior art, i.e. without the cutout  57   a  such that the grinding tool  70  sharpens the top plate cutting edge and the entire length L of the side plate cutting edges  47  to the same sharpness. Thereafter, a portion, such as the trailing portion  55 , of the side plate cutting edge  47  may be blunted by grinding it blunt using a smaller grinding tool. The grinding method is illustrated by the flow chart of  FIG. 11 , and with reference to the drawings of  FIGS. 12A and 12B . In a sharpening step  201 , illustrated in  FIG. 12A , the top plate cutting edge  45  and the side plate cutting edge  47  are sharpened, using a grinding tool  70  having a radius of curvature of about 2.4 mm (i.e. for a circular cylindrical file, corresponding to the conventional file diameter of 4.8 mm), to substantially the same sharpness. Thereafter, in a blunting step  203 , illustrated in  FIG. 12B , a portion  53  of the sharpened side plate cutting edge  47  is blunted, using a grinding tool  72  having a smaller radius of curvature than the tool  70  of  FIG. 12A , to be less sharp than the top plate cutting edge  45 . In the illustrated example, after blunting, the blunted portion  53  comprises the trailing portion  55  of the side plate cutting edge  47 . In the illustrated example, the blunted portion  53  is blunted by grinding the leading edge of the blunted portion  53  to be straight, in accordance with what&#39;s illustrated in the cross-section of any of  FIGS. 6 and 7 . An outermost side plate cutting edge portion  51  is left unblunted. 
     The cutting links of a brand new saw chain according to prior art are generally very sharp. This is of course a highly desired property, but it also poses a potential safety risk, since the chain may be sharp enough to cut through the protective padding of chainsaw protection wear  10  ( FIG. 1 ). Thanks to the cutting link  21  defined herein, a saw chain  7  with increased safety may be obtained. Referring back to  FIG. 3A , the rearmost, trailing portion  55  of the side plate cutting edge  47  is less sharp than the outermost portion  51  of the side plate cutting edge  47 . If accidentally cutting in work wear, such as chainsaw protection pants or trousers  10 , filaments from the protective padding of the protection pants will engage with the rearmost, trailing, portion  55  of the side plate cutting edge  47 , and be pulled out from the protective padding of the trousers  10 . The filaments pulled out of the protective padding will eventually follow the chain  7  to the drive sprocket driving the saw chain  7 , get entangled with the drive sprocket, and stop the saw chain  7  from rotating. 
     As the cutting link  21  is exposed to wear and becomes dull, it is regularly re-sharpened by the user of the chainsaw, typically using a circular-cylindrical file having the shape and dimensions of the grinding tool  70  of  FIG. 9B . The convex portion  59  together with the concave cutout  57  thereby prevents the file from grinding the trailing portion  55  ( FIG. 3A ) of the side plate cutting edge  47 . However, as the material of the cutting link  21  wears away due to repeated sharpening, the bluntness of the trailing portion  55  of the side plate cutting edge decreases (i.e. the trailing portion  55  becomes sharper) with the life time of the cutting link  21 . If the user wishes to keep the rearmost portion  55  of the side plate cutting edge  47  less sharp than the top plate cutting edge  45 , the user may blunt the cutting edge of the trailing portion  55  with a smaller file from a different angle. 
     In an example embodiment, the cutting link  21  may be formed of hardened steel or other suitable material by stamping, grinding and combinations thereof with or without other techniques also being employed. Some of the surfaces of the cutting link  21  may be coated or plated. For example, some surfaces different from the cutting edges  45 ,  47  may be chrome-plated. 
     The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims. For example, in each of the illustrated embodiments, the side plate cutting edge comprises one relatively sharper portion  51  and one relatively less sharp portion  53 . Alternatively, the side plate cutting edge may comprise two or more relatively sharper cutting edge portions separated by one, two, or more relatively less sharp cutting edge portions. 
     In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality.