SAW CHAIN CUTTER LINK

Abstract: A cutting link (18) having a cutter portion (36), a depth gauge portion (38), and a guide edge (48;148) extending between the depth gauge peak (40;140) and cutter portion for guiding a file (52) to sharpen the cutting edge (24) of the cutter portion. In the process of sharpening the cutting edge, the cutter portion is abraded away along a line (46) that extends the guide edge and thereby continues the guiding of the file to properly file the cutting edge.

Description: The invention relates to a cutting link having a gullet including an elongate sloped guide surface that accommodates a file having a non-abrading guide portion for guiding an abrading portion thereof to sharpen the cutting edge of the cutting link. Since saw chain for chain saws was first developed, a major concern has been maintaining the cutting edges. Many inventions have been directed to making the job of sharpening the saw chain easier, faster and more accurate. The present invention provides a further step in this development of means for simplifying the sharpening process. A saw chain cutting link can consist of a body portion, an outwardly extended cutter portion formed into a C or L shape with a leading cutting edge, and a second outwardly extended portion in front of and spaced forward of the cutter portion to form a depth gauge. The depth gauge is essentially a blunted, leading, outer "peak" that limits the ability of the cutting edge of the cutter portion to penetrate the wood surface. This peak is positioned substantially forward of the cutting edge. The space between the cutter portion and depth gauge portion is referred to as a gullet. The cutter portion is elongate so that, as the cutting edge dulls, it can be repeatedly sharpened. This shortens the cutter portion length and increases the gullet spacing until further sharpening is no longer feasible, a point at which the cutting link reaches "end-of-life". Typically, the cutting edge is sharpened with a round file positioned at the appropriate angle and depth within the gullet. The file is maintained in that relative position as it is drawn across the edge of the cutter. A variety of file guide accessories have been developed to assist in locating and maintaining the relationship during sharpening. The most pertinent prior art is believed to be disclosed in U.S. Patent 3,380,496 to E.H. Hill which illustrates a depth gauge peak and a trailing guide surface terminating at the base of the cutting edge. A file is provided with a smooth guide surface. A base line establishes the desired removal of the cutter portion. The guide surface, cutter portion and file are coordinated to initially guide the file properly for filing, but as soon as any material is removed, the guide surface is no longer effective as a guide for the file. Furthermore, the base line does not encompass the full cutter portion. Because the cutter portion of a typical cutting link is laterally offset to provide side relief, the portion of the offset that is below the true line and which is not removed during sharpening, after several sharpenings, produces interference. (In the context of this invention, the cutter portion as differentiated from the body portion is considered to be delineated by the side relief offset.) In accordance with the invention, a straight edge following the peak, referred to as a guide edge, is angled rearwardly and inwardly from the depth gauge to the base of the cutter portion, i.e. below the cutting edge thereof, and the cutter portion is designed to be abraded and thereby worn away by sharpening at a rearwardly and inwardly directed angle that coincides with or approximates to the angle of the guide edge. The line that is followed in abrading away the cutter portion is referred to as the base line. The gullet is defined as that space between the cutting edge and depth gauge peak, above said guide edge. Also in accordance with the invention, a file is configured with a flat guide surface that, when mated to the straight edge preceding the cutter portion, presents an abrading surface that abrades away the entire cutter portion and thereby extends the guide edge along the base line of the cutter portion. The abrading surface concurrently sharpens the cutting edge. The present invention thus resides in a change in the configuration of the cutter portion, depth gauge, gullet and of the link, and of the file, all of which are coordinated to provide for guide-assisted sharpening, but eliminating the need for a file guide accessory. The present invention is an improvement over that of U.S. 3,380,496 in providing a continuation of the guide edge and a substantially total removal of the cutter portion, both due to the novel coordination of the elements of the cutter portion (e.g. the base line), the guide edge of the depth gauge, and the file configuration. Because the guide surface of the file is flat, the leading surface of the file removes only the cutter portion above the base line. The guide edge is contained along a substantially straight line, generating the desired cutting edge configuration. The process is simple and convenient and eliminates the need for an accessory file guide. The invention is further described below, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a side view of a cutting link of a saw chain in accordance with the invention; Fig. 2 is a perspective view from one side of the cutting link of Fig. 1; Fig. 3 is a perspective view from the other side of the cutting link of Fig. 1; Fig. 4 is an end view of the cutting link; Fig. 5 is a sectional view taken on section lines 5-5 of Fig. 1; Fig. 6 is a plan view of the cutting link of Fig. 1; Figs. 7a-7e show in cross section various sharpening tools of different shapes positoned for sharpening a cutting link in accordance with the invention; Fig. 8 illustrates a cutting chain including cutting links in accordance with the present invention; and Fig. 9 is a side view of an alternative form of cutting link in accordance with the invention. Reference may first be made to Fig. 8 which illustrates a series of links making up a saw chain 10. The links comprise pairs of side links interconnecting to centre links in repeating sequence. The centre links are drive links 12 having drive tang portions 14 shaped to ride in the groove of a guide bar, a portion 16 of which is illustrated by broken line. Certain pairs of the side links comprise a cutting link 18 mated on the opposite side with a tie strap 20. It will be noted that the cutting links 18 alternate from side to side and are either right or left hand cutters which are mirror images of each other as is common in such saw chains. Other pairs of side links comprise pairs of tie straps 20. Reference is now made to Figs. 1-6 which illustrate a left hand cutting link 18 in a variety of views. The cutting link includes a lower body portion 32 which generally simulates the configuration of atie strap in having rivet openings 30 located above front and rear foot portions 28 that slide on the guide bar as shown in Fig. 8. An upper body portion 34 is shaped into the desired form which includes a cutter portion 36 with a cutting edge 24, and a depth gauge portion 38 terminating in an outer peak 40. The cutter portion 36 is bent first outwardly and then sharply across the body of the cutting link to form a side plate 44 and a top plate 42. As will be noted particularly from Fig. 5, the side plate 44 projects laterally outwardly from the upper body portion 34 and is delineated by a bend or base line 46, best seen in Fig. 2. The bend line 46 is preferably generated by a coining operation to specifically establish the portion thereabove as the cutter portion 36 of the cutting link. As is typical for cutting links, relief angles are established including a top relief angle "a" (Fig. 1) and a side relief angle "b" (Fig. 6). An angle "c" (Fig. 4) is also typical. What is not typical is the relationship of the guide edge 48 of the depth gauge portion 38 and the cutter portion 36, whereby the guide edge 48 forms an extension of bend line 46 or vice versa. To accomplish these desired relationships, several factors must be coordinated. The height differential between the top edge of cutting edge 24 and the peak 40 of the depth gauge 38 is the depth gauge setting and must be established to ensure the desired penetration of the cutter during the cutting operation. The bend line 46 in relation to the side plate and top plate must be consistent so that an appropriately configured file, as shown in Figs. 7a-7e, will remove the cutter portion above line 46 while also maintaining a continuation of the guide edge 48. As explained below, the file should be configured with a non-abrading lower guide surface that cooperates with the guide edge 48 while sharpening the cutting edge 20 so that the file removes the top plate and at the same time generates a continuation of the guide edge 48. Because sharpening lowers the height of the cutting edge 24, as is typical, the peak 40 of the depth gauge must be filed down (also thereby drawing it back along guide edge 48) to retain the desired height differential. This is illustrated in Fig. 1 in broken lines and by parts indicated by numbers with prime marks, i.e. 50′ indicates the depth gauge setting or height relationship between cutting edge 24′ and the reduced peak 40′ at end-of-life. The slope of lines 46 & 48 as viewed in Fig. 1 in part dictates the spacing front to back between the cutting edge 24 and the peak 40. The other factors are the height of the top plate cutting edge 24 from the base line 46 and the desired depth gauge setting or differential 50. The relationship can be described by a mathematical formula as follows. The lengthwise distance between cutting edge 24 and peak 40 is determined by the difference between the height of the cutter portion (edge 24 to line 46) and the depth gauge setting, divided by the slope of the guide surface 48. The length of the cutter portion when new, which determines the life of the cutting link, is determined by the length of the cutting link less this spacing between the cutting edge 24 and the depth gauge peak 40. In a specific example, a cutting link 18 is about 18.3 cm. (.72 inch) in length (e.g. for a .95 cm. (3/8 inch) pitch chain), the height of the cutting edge 24 above the base line 46 is about .19 cm. (.075 inch) and the desired depth gauge setting is .08 cm. (.030 inch). Providing an angle "a" of about 10 degrees generates a slope of about 8 to 1 for base line 46 and guide 48. Peak 40 is then spaced forwardly of cutting edge 24 by the amount equaling .075 times 8 times .19 - .08 .19 (.075-.030/.075). The spacing between edge 24 and peak 40 is thus about .91 cm. (.36 inch). That is about half of the length of the link and thus the length of the cutter portion 36 at beginning of life is also .91 cm. (.36 inch). Reference is now made to Figs. 7a-7e which illustrate files 52 of various cross-sectional configurations. The different shapes of the files 52 accommodate different cutting edge shapes. In each case, the file 52 has a flat non-abrading guide surface 54 that slides on the guide edge 48 of the cutting link, and an abrading edge surface 56 that engages the cutter portion to sharpen the edge 24. The cutter portion above base line 46 is removed in the process which extends the guide edge 48. Broken lines in Fig. 1 indicate the configuration of the cutter after a number of sharpenings. Continuation of the guide edge 48 rearward along the base line 46 can be difficult to achieve precisely. However, a small variation is tolerable. In general, there is a tendency to bend the direction of the guide edge slightly upwardly from the guide line during the sharpening process. This tendency can be accommodated by slightly bending the baseline upwardly from true alignment with the indicated guide edge. In a modification of the link 18, there is provided an initial elevated depth gauge peak 140, as illustrated in Fig. 9. The guide edge 148 is stepped down from the peak 140 in the initial or start-of-life condition of the link. As the top plate 42 is abraded back along the base line 146, the peak 140 is continuously lowered until eventually it merges with the guide edge 148. Such a configuration complicates somewhat the production of the cutting link but relaxes the geometric relationship as described for the link 18. It should be appreciated that the sharpening process is not accomplished without the use of some skills in matching the angle of the file to the cutting edge shape. Thus whereas the guide edge 48 guides the file at the appropriate height and lateral angle, the filer will have to maintain the desired rearward slope of the file as he draws the file across the cutting edge. It is common to provide the file guide previously used with a guideline to assist in establishing this angle. In accordance with the present invention, guidelines 58 are provided on the top plate 42 to assist the filer in establishing the proper filing angle. Whereas others having skill in the art will conceive of variations to the embodiments herein described, the invention is to be considered to encompass such variations within the scope of the following claims.

Claims: 1. A cutting link for a saw chain comprising a depth gauge peak (40; 140) and a trailing guide edge (48; 148) for a sharpening file which terminates at the base of a trailing cutting edge (24), which cutter link comprising a cutter portion (36) including a top plate (42) providing the cutting edge (24), and a depth gauge portion (38) providing the depth gauge peak (40; 140) and the guide edge (48; 148), characterised in that the top plate and the guide edge (48; 148) extend rearwardly and downwardly at substantially the same angle to the direction of movement of the link. 2. A cutting link comprising a lower body portion (32) having means for accommodating pivotal interconnection with preceding and following links in a saw chain, and an upper body portion configured into a cutter portion (36) and a depth gauge portion (38), the cutter portion including a top plate (42) having a leading cutting edge (24), the top plate extending downwardly and rearwardly at a predetermined angle from the cutting edge toward the lower body portion, and the depth gauge portion having a depth gauge peak (40; 140) that is lower in height than the cutting edge by a predetermined distance, thereby establishing a depth gauge setting, and a guide edge (48; 148) extending from the depth gauge peak toward the cutting edge at substantially the same angle as the top plate angle, the guide edge being arranged to guide a file (52) having a non-abrading guide surface (54) and an abrading surface (56) for sharpening the cutting edge and for substantially abrading away the cutter portion along a path substantially paralleling inclination of the top plate and guide edge. 3. A cutting link as claimed in claim 1 or 2 wherein the top plate (42) and the depth gauge portion (38) each occupy about half the length of the cutting link, at start-of-life. 4. A cutting link as claimed in claim 1, 2 or 3 wherein the cutter portion (36) is delineated by a base line (46), and the guide edge (48; 148) extends from the base line below the cutting edge (24) to the depth gauge peak (40; 140). 5. A cutting link as claimed in claim 3 or 4 wherein the guide edge angles define a guide edge slope and the lengthwise distance between the cutting edge (24) and the depth gauge peak (40; 140) is determined by the difference between the height of the cutter portion (36) and the depth gauge setting, divided by the guide edge slope. 6. A cutting link as claimed in claim 3, 4 or 5 wherein the height of the top plate cutting edge (24) above the base line is about .19 cm. (.075 inch), the depth gauge setting is about 0.076 cm. (.030 inch) and the angle of the base line from the horizontal is about 10 degrees. 7. A cutting link as claimed in claim 3 wherein the guide edge (148) extends to a step extending upwardly to the depth gauge peak (140). 8. A cutting link as claimed in any preceding claim wherein guide lines (58) are provided on the top plate (42) to assist guiding the file during sharpening.

Inventors: DAY, KENNETH R., GIBSON, DUANE MICHAEL, HUNTINGTON, KENT L., PETROVICH, MICHAEL V.
Applicants: BLOUNT, INC.
Application year: 1988
Main classification: B27B33
IPC codes: B27B33, B23D63