FIELD OF THE INVENTION
The present invention is directed to the field of saws, machines for cutting or abrading material and replaceable teeth therefore.
BACKGROUND
A variety of devices exist for cutting or abrading materials including masonry, concrete, metal, glass, wood and stone. These devices can employ various implements for cutting or abrading including chain and rotary blades.
In the timber industry, wood is cut, for example, using chain saws and timber harvesters. The particular chain that is used depends on the area and condition of the wood being cut. Normally, steel cutting links having sharp edges are used to cut wood. However, when there is a danger of the chain impacting metal articles in the wood costly carbide tips can be soldered onto the steel cutting links of the chain. This enables the chain to withstand contact with metal articles in the wood without becoming excessively dull. On the other hand, the soldered carbide tips can become dislodged from the steel cutters upon impact with metal articles in the wood.
The sharp edges of all cutting links of saw chain and rotary blades undergo expected wear over time. In the case of chain saws, worn chain is sharpened in the field or replaced with new or sharpened chain, leading to costly down time during the cutting operation or hazard to the worker sharpening the cutting links by hand.
Some attempts have been made to construct chains with removable cutting inserts of various designs typically from steel. These efforts have generally been unsuccessful. Saw chain having removable cutting inserts is currently not used extensively, if at all. U.S. Pat. No. 2,583,243 discloses saw chain including removable teeth wedged into a slot of a head of a link of the chain. U.S. Pat. No. 2,852,048 discloses saw chain with removable teeth having a T-shaped recess that contacts a T-shaped element of a link of the chain. U.S. Pat. No. 3,547,167 discloses a removable cutting sleeve having a recess that receives a stud of a link of the chain.
Cutting links for wood cutting typically are constructed of stamped and machined metal (e.g., steel) and are permanently affixed to other links of the chain. Previously proposed removable cutting inserts were retained on the cutting links using screws or other means. However, so far as the present inventor is aware, such chains do not employ a safety device, apart from cumbersome fasteners or particular engagement between the cutting inserts and cutting links, for avoiding the dangerous condition of the teeth becoming dislodged during operation of the saw.
Another safety hazard posed by cutting links on a saw chain is what is commonly known as kickback. This refers to what happens when a cutting portion on a saw chain digs excessively into the wood as the cutting link moves over the nose of the saw. Under these conditions, the relationship between the cutting tooth, depth gauge and wood surface may cause the tooth to dig deeply into to the uncut surface. When this happens, the cutter link is thrust in a reactionary backwardly motion causing chain movement to stop momentarily. The energy from the moving chain is then thrust upwardly and rearwardly, so as to propel the saw chain guide bar toward the operator.
Various attempts have been made to prevent the problem of kickback, which are disclosed in the prior art. U.S. Pat. No. 4,425,830 provides for a safety link to be disposed between each cutter link to prevent the cutter link from cutting deeply into the wood when coming around the nose of a saw bar. U.S. Pat. No. 4,133,239 provides a saw chain comprising a safety link having an upstanding cam portion with an upstanding and rearwardly inclined leading edge and a rearwardly projecting tail which pivots outwardly as the chain rounds the nose of a saw blade to provide a reduced effective depth gauge for the cutter link to follow.
The proposed preventative solutions are aimed at providing modified safety links before a cutter link that will allegedly stop the cutter from digging deeply into wood. However, it has yet to be contemplated to prevent the actual rollback movement by the cutter tooth itself, and particularly in a saw chain with replaceable cutter teeth. Therefore, it is desirable to provide a saw chain with easily replaceable teeth that is designed with built in safety features, particularly, preventing chain kickback.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present disclosure, an anti-kickback saw chain including a plurality of links each having an upstream end and a downstream end relative to a direction of travel of the chain is provided. The anti-kickback saw chain comprises a holding link having a first side and a second side, a replaceable tooth adapted to be removably mounted on the downstream end of the holding link, and a safety drive link. The upstream end of the safety drive link is pivotally connected to the downstream end of the first side of the holding link. The safety drive link includes a safety lobe effective to prevent the tooth from being dislodged from the holding link during chain travel, and a substantially flat upper edge.
In accordance with another aspect of the present disclosure, a saw chain including a plurality of links is provided. The saw chain comprise a plurality of holding links each having an upstream end and a downstream end relative to a direction of travel of the chain and a first side and a second side, a plurality of replaceable teeth that include a cutting surface, the teeth being adapted to be removably retained on the downstream end of the holding link, and a plurality of safety drive links comprising a straight back edge. The straight back edge is adapted to limit rollback movement of the tooth and prevent kickback of the saw chain.
In accordance with yet another aspect of the present disclosure, a method of preventing kickback in a saw chain with replaceable cutting teeth is provided, including a plurality of links each having an upstream end and a downstream end in a direction of travel of the chain. The method includes the steps of removably mounting a tooth to a holding link having a first side and a second side; pivotally connecting the upstream end of a safety drive link to the first side of the downstream end of the holding link, the safety drive link comprising a straight top edge, and obstructing rollback movement of the holding link with the straight top edge of the safety drive link to maintain a generally flat cutting plane.
In accordance with another aspect of the present disclosure, a powdered metal rivet is provided. The powdered metal rivet includes a first end having a head portion, a second end opposite the first end and comprising a cylindrical tail portion with a uniform diameter, and a doughnut shaped bearing surface positioned between the first end and the second end. The bearing surface of the rivet comprises powdered metal.
In accordance with another aspect of the present disclosure, a method for preventing kickback in a saw chain comprising a plurality of links, each having an upstream end and a downstream end according to a direction of travel of the chain is provided. The method includes removably mounting a removable tooth to a holding link, providing a safety drive link with a generally semi-circularly shaped rivet hole, the rivet hole including a “V” shaped protrusion extending therein, the protrusion having a first angle, molding a powdered metal rivet having a diameter less than the rivet hole, the rivet having a semi-circular shape with a “V” shaped section missing therefrom, the section having a second angle, and pivotally connecting the upstream end of a safety drive link to the holding link, wherein the “V” shaped portion limits the rotation of the holding link.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of saw chain constructed in accordance with one aspect of the present invention;
FIG. 2 is an exploded view of the saw chain of FIG. 1;
FIG. 3 is a side elevational view of the saw chain of FIG. 1;
FIG. 4 is a top plan view of the saw chain as seen along the lines and arrows designated 4-4 in FIG. 3;
FIG. 5 is a vertical cross-sectional view as seen along the lines and arrow designated 5-5 in FIG. 3;
FIG. 6 is a perspective view of one of the holding links and teeth;
FIG. 7 is a side elevational view of the saw chain of FIG. 1 showing how a safety lobe of an upstream link can be rotated out of the path of a tooth for removal and replacement of the tooth;
FIG. 8 is a perspective view showing another aspect of the inventive saw chain wherein the safety links include rakers;
FIG. 9 is an exploded view of the saw chain shown in FIG. 8;
FIG. 10 is a side elevational view of a portion of the saw chain shown in FIG. 8;
FIG. 11 is a perspective view of a portion of saw chain featuring another aspect of the present invention wherein one of the links includes a safety lobe that retains the tooth on the holder;
FIG. 12 is an exploded view of the components of the chain shown in FIG. 11;
FIG. 13 is a side elevational view of the saw chain shown in FIG. 11;
FIG. 14 is a side elevational view of the saw chain shown in FIG. 13 showing how the safety cam and safety lobe are rotated out of the path of the tooth permitting its removal and replacement;
FIG. 15 is perspective view of a saw chain according to another embodiment having a safety link with a straight back edge;
FIG. 16 is a perspective view of the straight back preventing rotation by the replaceable tooth;
FIGS. 17
a & b are opposing side views of a traditional saw chain without anti-kickback protection;
FIG. 18 illustrates a side by side comparison between the anti-kickback saw chain and a saw chain without the anti-kickback feature;
FIGS. 19-23 illustrate various angled views of the features of the replacement teeth used on the present saw chain.
FIG. 24
a illustrates a side view of a holding link having an anti-kickback tab;
FIG. 24
b illustrates a front view of the anti-kickback tab blocking the rotation of the safety drive link;
FIG. 25(
a) illustrates a side view of a safety drive link having a rotation blocking rivet hole'
FIG. 25(
b) illustrates a cross sectional view of a rivet bearing surface having a rotation blocking “V” shaped portion;
FIG. 25(
c) illustrates a cross sectional view of a mated rotation limiting rivet and rivet hole according to one aspect of the present disclosure; and
FIG. 25(
d) illustrates a cross sectional view of the rivet bearing surface according one aspect of the present disclosure.
DETAILED DESCRIPTION
Referring now to FIGS. 1-7 of the drawings, one embodiment is directed to safety saw chain 10 including a plurality of links 12 each having an upstream end 14 and a downstream end 16 relative to a direction of travel of the chain (shown by the arrow) around the bar of a saw in a known manner. A plurality of replaceable teeth 18 are each adapted to be removably retained on one of a plurality of holding links 20. The combination of holding link 20 and replaceable tooth 18 functions as a conventional one-piece cutting link. The chain includes a plurality of safety links 22 each being located upstream of one of the holding links. Each safety link 22 includes a safety lobe 24 extending in proximity to a tooth effective to prevent the tooth from being dislodged from the holding link during travel of the chain. The holding link includes a depth gauge or raker 26 located upstream of the tooth. Other links in the chain of this particular design are contemplated in the invention. For example, drive links or drivers 28 engage the chain saw sprocket and optional sprocket at the end of the guide bar in a conventional manner. Drive links 28 and safety links 22 include surfaces 29 for engaging a sprocket of the saw.
The safety links, holding links, drive links and other links of the chain, each include a pair of rivet holes 30. Connector or tie straps 34 along the chain each include a pair of rivet holes 30. Rivets 32 are disposed in aligned rivet holes of the holding links, safety links, drive links, and other links, and the connector straps, which pivotally connect the links together.
The holding links and safety links are used with other links of the chain in any standard wood-cutting or other chain design (e.g., plastic or metal cutting). For example, in wood cutting the cutting links (i.e., the holding links of the invention) may be used in full compliment, semi-skip (half skip) and full skip chains, referring to the number of tie straps between cutting links. The 2003 website by Manufacturer's Supply Inc., which is incorporated herein by reference in its entirety, describes the chain designs as follows: full compliment chain has a first cutter, tie strap and another cutter (e.g., right cutter, tie strap, left cutter, tie strap, right cutter, etc.); semi-skip chain has alternating one and two tie-straps after cutters (e.g., right cutter, tie strap, left cutter, two ties straps, right cutter, etc.); and full skip chain has two tie straps after cutters (e.g., right cutter, two tie straps, left cutter, two ties straps, right cutter, etc.). The inventive holding link is suitable for all chain pitches (defined as the distance between three consecutive rivets divided by two), including ¼, 0.325, ⅜, ⅜ extended, 0.404, % and 0.750 inch pitches. The particular chain shown in FIGS. 1-14 is particularly suitable for use on chain saws. The chain may be used on a variety of other saws as well including, but not limited to a timber harvester, a rescue saw, a buck saw and a saw for cutting wood pallets.
The holding links 20 each include a holding or key member 36 having at least one seating surface. The key member 36 shown in FIGS. 2 and 6 has an inverted-L shape and includes a top surface 38, a long side surface 40, first and second short side surfaces 42, 44, and front and back surfaces 46,48. Each tooth 18 includes a recess 50 configured and arranged to receive the key member 36. The recess can have an inverted-L shape that corresponds to the inverted-L shaped holding member and includes a top recess surface 52, a long side recess surface 54, first and second short side recess surfaces 56, 58, and a front recess surface 60. The recess includes at least one seating surface. Seating surfaces are surfaces of the tooth and holding member that contact each other. Between the short side recess surfaces 56 and 58 is seating surface 61 extending along the length of the tooth. The seating surface 61 engages seating surface 39 of the holder. The L-shaped recess is open at a back surface 62 of the tooth and at a bottom tooth surface 63. It will be appreciated by those of ordinary skill in the art in view of this disclosure that the figures show but one example of a suitable design for the holding member and tooth. The tooth could include a stud and the holding member could include a recess that receives the stud. The key member and tooth recess could include other shapes such as a T-shape. These and many other variations in the design of the teeth and holding members are possible and contemplated to be within the scope of the present invention.
The teeth are inserted onto the chain by pushing each tooth so that the holding member moves into the tooth recess. The holding member front surface 46 may engage the front tooth recess surface 60 (FIG. 3), which prevents the tooth from moving in the direction opposite to the chain travel direction. The seating surfaces of the holding member and tooth engage each other when the tooth is disposed on the holding member during operation of the saw.
A function of the saw chain of the present invention is to enable material to be cut or abraded using teeth that are quickly replaceable and yet safe. In this regard, the teeth advantageously engage the holding members without the need for fasteners (e.g., screws). The teeth can be held in place on the holding members in various ways as would be appreciated by those skilled in the art reading this disclosure. The seating surfaces of the holding members and teeth (e.g. seating surface 39 of the holding member and seating recess surface 61) can be tapered as disclosed in the U.S. patent application Ser. No. 10/780,323, which is incorporated herein by reference in its entirety. These “wedge and taper” surfaces inhibit the tooth from moving in a direction opposite to the chain travel direction. The wedge and taper also inhibit movement of the tooth in the chain travel direction. When the teeth are retained on the holding members with the interacting wedge and taper feature, a specialty tool or hammer is used to remove them in the chain travel direction.
The present invention is not limited to the wedge and taper or other design of holding member and teeth. In fact, in one aspect of the invention the holding members do not prevent movement of the teeth in the chain travel direction. Movement of the teeth 18 in the chain travel direction is prevented entirely by the safety lobes 24. This enables very fast replacement of the teeth without the need for a tool (e.g., specialty tool or hammer) which would otherwise be used to remove teeth held in place on the holding members by engagement of tapers and wedges as described in the 10/780,323 patent application.
The teeth 18 alternate right- and left-handed along the chain (i.e., left-handed tooth, right-handed tooth, left-handed tooth, etc.). Referring to FIG. 4, the chain 10 has a central axis C along the chain travel direction. The left-handed teeth 18a have cutting edges 64 that extend from the central axis C outwardly on a left side L of the chain; and the right-handed teeth 18b have cutting edges 64 that extend from the central axis C outwardly on a right side R of the chain. The cutting edges 64 are adapted to cut various materials. One material that the teeth are ideally suited to cut is wood. Alternatively, the cutting edges 64 are designed for abrasion of material. Abrading teeth can have various compositions tailored to the particular material being abraded (e.g., masonry, concrete or other refractory material).
The features of the replacement teeth 18 used on the saw chain of FIGS. 1-7 are shown in FIGS. 19-23. The sharp cutting edge 64 penetrates wood fibers or other material being cut (e.g., plastic). The top surface 66 of the tooth affects the width of the saw kerf. The tooth has side surfaces 70 that extend at angle p (e.g., 3°). The tooth has an angle a, which is in the range of, for example, 0 to 90°. In this exemplary design of FIGS. 20-23 the chisel angle a is 60°. A front surface 72 of the tooth forms the cutting edge 64 at an upper location. The front surface includes upper and lower surfaces 200,202. The upper surface 200 is chamfered or concave. The concave surface has a certain radius of curvature r for a given chain pitch that is proportional to a radius of about 0.25 inch for a chain pitch of 0.750 inch. That is, about 0.25 inch is the radius of curvature for a large 0.750 pitch chain. The radius of curvature of the upper front surface 200, and in particular, of all geometries of the teeth and holding member, would be smaller for smaller pitch chains. The radius of curvature r may vary, such as being smaller than about 0.25 inch for a chain pitch of 0.750 inch. The right side of this particular tooth includes an upper surface 204 and a lower surface 206.
The upper surface 204 extends generally vertically and the lower surface 206 extends inwardly at an angle γ of, for example, 5°, for providing clearance of the tooth as it cuts through material (e.g., wood). The seating tooth recess surface 61 is tapered in this particular design, e.g., at angle δ (e.g., 3.000 to 3.125 degrees), which engages the correspondingly tapered seating surface 39 on the holder as disclosed in the 10/780,323 application. Any of the surfaces of the holding member and tooth recess may be tapered as disclosed in the Ser. No. 10/780,323 application.
The teeth and/or holding links can be formed of any suitable cutting, abrading or wear-resistant materials. One suitable material is sintered and compacted particulate material, known as powdered metal as disclosed in the Ser. No. 10/780,323 patent application or known to those of ordinary skill in the art. One suitable material for forming abrading teeth is ceramic such as silicon carbide.
Referring to FIGS. 3 and 4, a left side connector strap 34a has a downstream hole 30a aligned with an upstream hole 30b of a drive link 28a and with a downstream hole 30a of a right-handed holding link 20a. The links are secured with a rivet 32a. The drive link 28a is sandwiched between the connector strap 34a and the right-handed holding link 20a. The upstream hole 30b of that left side connector strap 34a is aligned with the downstream hole 30a of a safety link 22a and with an upstream hole 30b of the right-handed holding link 20a. The links are secured with a rivet 32b. The safety link 22a is sandwiched between the left side connector strap 34a and the right-handed holding link 20a. The upstream hole 30b of the safety link 22a is aligned with downstream holes 30a of a pair of connector straps 34b and secured by rivets 32c. The upstream holes 30b of the connector straps 34b are aligned with a downstream hole 30a of a drive link 28b and secured by rivets 32d. The downstream hole 30a of the next right side connector strap 34c is aligned with an upstream hole 30b of the drive link 28b and with a downstream hole 30a of a left-handed holding link 20b. The links are secured by a rivet 32e. The drive link 28b is sandwiched between the connector strap 34c and the left-handed holding link 20b. The upstream hole 30b of that connector strap 34c is aligned with a downstream hole 30a of the next safety link 22b and with an upstream hole 30b of the left-handed holding link 20b. The links are secured with a rivet 32f. The safety link 22b is sandwiched between the left-handed holding link 20b and the right connector strap 34c. An upstream hole 30b of the safety link 22b is aligned with downstream holes 30a of a pair of connector straps 34d. The safety link 22b is sandwiched between the connector straps 34d. The links are secured with a rivet 32g. An downstream hole 30a of the drive link 28a is aligned with upstream holes 30b of the pair of connector straps 34d. The drive link 28a is sandwiched between the connector straps 34d. The links are secured by a rivet 32h (FIG. 1). The sequence of components of the chain repeats in this or a similar fashion depending on the chain design (e.g., full compliment, semi-skip (half skip) and full skip chains).
Referring to FIG. 3, the safety link 22a includes an imaginary reference line B that intersects the centerpoints of the upstream and downstream rivet holes 30b, 30a of the safety link. The body of the safety link has a height h1 along the arrow at a location perpendicular to the reference line B and intersecting a centerpoint of the upstream hole 30b of the safety link 22a. The safety lobe 24 of the safety link extends to a height h2 along the arrow perpendicular to the reference line B and intersecting the centerpoint of the downstream hole 30a of the safety link 22a. The safety lobe 24 is located in a region in the chain travel direction between the line h2 and a line h3 extending perpendicular to the reference line B at the most downstream end surface 73 of the safety link. The height h2 is greater than the height hi. The central portion of the body of the safety link has a height h4 perpendicular to the reference line B at the midpoint between lines h1 and h2. h2<h1<h4. In other words, the safety lobe 24 extends to a maximum height of the safety link (height h2) that is higher than the upstream portion of the safety link (height hi), which extends higher than the central portion of the safety link (height h4) that is approximately at a minimum height of the safety link.
In a method of safely operating saw chain of the first embodiment, the saw is operated to move the chain by powering the motor to rotate the chain upon engagement of the drive links of the chain with the chain saw sprocket and optional sprocket at the end of the guide bar (not shown) in a known manner. Initially the teeth are all new, sharpened or contain a maximum amount of cutting or abrasion material (e.g., sharpened teeth). The saw is used to cut or abrade the intended material. During operation of the saw, at which time the chain rotates around the bar, dislodging of the teeth from the holders in the chain travel direction is prevented by the safety lobes. This ensures safe operation in that the dangerous condition in which whole teeth are dislodged in the chain travel direction is avoided. Breakage of portions of the teeth may be unavoidable, as occasionally occurs in the breakage of soldered tips from steel teeth. However, this condition can be accounted for with proper safety goggles and other conventional safety equipment and procedures. The saw is operated (e.g., shut off) to stop movement of the chain.
Once it is determined by the user that one or more teeth should be replaced, such as due to damage or wear of the teeth, the safety link is pivoted out of a path of an adjacent tooth needing replacement. Referring to FIG. 7, safety link 22b is pivoted downward out of the path of the tooth 18 (in the clockwise direction of arrow 73). This enables the tooth 18 to be removed from the holding member 36b in the direction shown by arrow 75 and replaced with a new or replacement tooth 18 in the direction opposite to arrow 75. The tooth may need to be struck from behind to loosen the tooth from the holding link's wedge. The chain is pivoted back to an operational position. That is, the safety link 22b is pivoted in the counterclockwise direction. The tooth may be replaced while the chain is still on the bar and only loosened to allow movement of the links. This entire operation can be done quickly and economically compared to sharpening teeth or replacing the entire chain. In addition, cutting or abrading is performed safely despite the use of the quickly replaceable teeth.
The saw chain of the present invention may include various modifications that would be apparent to those of ordinary skill in the art in view of this disclosure. In this disclosure like components are given like reference numbers throughout the several views. As shown in FIGS. 8-10, one modification compared to the chain shown in FIGS. 1-7 is that the depth gauges or rakers 80 are disposed on the safety links instead of on the holding links 20. This design is suitable for automated saws, despite kickback that occurs when cutting wood near the end of the bar, in that such saws present fewer safety concerns for the operator.
Referring to FIG. 10, the safety link 82 includes an imaginary reference line B that intersects the centerpoints of the upstream and downstream rivet holes 30b, 30a of the safety link. The body of the safety link has a height h5 along the arrow at a location perpendicular to the reference line B and intersecting a centerpoint of the upstream hole 30b of the safety link 82. The safety lobe 84 of the safety link extends to a height h9 along the arrow perpendicular to the reference line B at the most downstream end surface 86 of the safety link. The safety lobe 84 is located in a region in the chain travel direction between the line h9 and a line h8 extending perpendicular to the reference line B at an intersection of the centerpoint of the downstream hole 30a. The central portion of the body of the safety link has a height h6 perpendicular to the reference line B at the midpoint between lines h5 and h8 from the hole centerpoints. The raker 80 extends to a height h7 along the arrow perpendicular to the reference line B located approximately at a midpoint between lines h6 and h8. h7<h9<h5. In other words, the raker 80 extends at a maximum height (h7) of the safety link, the upstream portion extends to a minimum height (h5) and the safety lobe 84 (height h9) extends at an intermediate height between heights h7 and h5.
Referring to FIGS. 11-14, in other embodiment the link that is downstream of the holding link (e.g., a drive link 90 as shown in FIG. 11) has its upstream end 92 pivotably fastened to the downstream end 94 of the left side holding link 20b. The link 90 is also a safety link and includes a cam-shaped or arcuate surface 96 at its upstream end, which is received in a cam-shaped or arcuate recess 98 formed in a lower surface of a corresponding tooth 100 (FIG. 12). The arcuate surface 96 and arcuate recess 98 may have other shapes and sizes as would be appreciated by one of ordinary skill in the art reading this disclosure. This safety feature ensures that the teeth are seated against the front of the keys 36 and limits tooth movement during operation of the saw especially when no means for retaining the teeth is employed on the holding members (e.g., no wedge and taper).
In the design shown in FIGS. 11 and 12, the drive link 90 and the safety link 22 can be the same link. However, the drive and safety links can be separate links on the chain depending on the number of links between holding links. In addition, it might be desirable to provide the upstream safety link 22 with one design and the downstream link 90 with a different design. The safety cam member 96 is usable alone, or in conjunction with the safety lobe 102 and/or means on the holding members for retaining the teeth. If the teeth and holding members have the corresponding wedge and taper design, or some other means for retaining the teeth on the holding members, the cam safety member 96 and cam recess 98 alone, without the upstream safety lobe 102, may be sufficient to prevent movement of the teeth on the holders in the direction of chain travel. Even without the wedge and taper design or other means on the holder for retaining the teeth in position, in which case the teeth can move freely on the holding members, the safety cams 96 and cam recesses 98 alone may be sufficient to retain the teeth on the holding members without the need for the upstream safety lobe 102. However, those of ordinary skill in the art will appreciate in view of this disclosure the benefit of having multiple safety features: the combination of the upstream safety lobe 102 of safety link 103 and the safety cam 96/cam recess 98, whether on the same or different links. This combination of safety features can be used with or without the wedge and taper design or other means for retaining the teeth in place on the holders.
In the tooth replacement procedure shown in FIGS. 13 and 14, the chain is removed from the saw. The tooth 100 can be removed by rotating the link 90 counterclockwise along arrow 101 such that the cam surface 96 does not engage the cam recess 98. If the safety lobe 102 is also used as shown in FIG. 14, the safety link 103 is rotated clockwise along arrow 105 so that the safety lobe 102 does not obstruct movement of the tooth 100 in the chain travel direction. The tooth 100 is then removed from the holding member in the direction of arrow 107. If the tooth is retained using the wedge and taper, it is removed with a suitable tool. A replacement tooth is installed in a direction opposite the arrow 107. The links 90 and 103 are rotated clockwise and counterclockwise, respectively, and the chain is re-installed on the saw.
FIGS. 15-16 illustrate another modification of the presently claimed saw chain. Similar to previous embodiments, the chain links according to this modification include a plurality of replaceable teeth 18 removably retained on one of a plurality of holding links 20 and tie straps 34, pivotally connecting the links together. This embodiment provides an additional safety feature in which modifying the shape of the safety links 22 described above to form safety drive links 25, which prevent dangerous saw chain kickback caused by digging into wood with the nose of the saw bar.
Saw chain kickback most frequently occurs when depth gauge or raker 26 and/or tooth 18, positioned at the upper quadrant of the bar nose, dives too deeply into a piece of wood, suddenly transferring power forward. The tooth 18 is then caused to roll backward, stopping the rotation of the chain, which violently transfers energy and momentum of the saw toward the operator of the saw chain. The present embodiment prevents such movement by limiting the backward movement of tooth 18. As displayed in FIG. 15, safety drive links 25 are similar in shape to safety links 22, but include a straight back edge 27, rather than a dip as is customarily seen in the art. Typical links, such as safety link 22 in the above referenced Figures, include dips in the upper back edge that allow the tooth a much greater range of motion, thereby permitting the tooth to roll back in such an unrestricted manner that causes the nose of the saw to kickback toward the operator.
Particularly, in FIG. 17a, a view from the holding link side of the saw chain displays the way in which the holding link and tooth assembly is generally free to rollback until the holding link is blocked by the tie strap. This provides the holding link with a large range of motion that could cause the chain to stop moving and kickback. With the present modification, shown in FIG. 16, straight back edge 27 of safety drive link 25 blocks the rollback upwardly movement of the tooth 18, thereby keeping the cutting plane of the saw generally flat and reduces the risk of the chain experiencing the dangerous kickback. From the safety link side view displayed in FIG. 17b, it is apparent that the tooth does not encounter the safety link in typical standard chains.
Additionally, FIG. 18 illustrates a comparison between the present anti-kickback saw chain 300 and a saw chain without the anti-kickback feature 310. Both the safety drive links 303(a) and 303(b) are illustrated in the parallel position. However, the cutter of saw chain 310 is able to rock back without contacting the top of safety drive link 303(b). In contrast, the cutting link of anti-kickback saw chain 300 is unable to roll back without being blocked by the top of the next safety drive link 303(a). Additionally, the safety lobe 315 of the anti-kickback saw chain 300 extends past the nose of the holder link. This configuration further reduces chain breakage and prevents kickback.
FIG. 24(
a) and (b) illustrate another aspect of the present disclosure, including an additional feature provided to prevent kickback from the saw chain. According to this embodiment, a tab 320 is provided on the rear edge of the holding link 20 on the same side that the holding link is attached to the safety drive link. The tab 320 may be stamped on the holding link 20 and extends from the link on the same side as the inverted-L shaped key member 36. See FIG. 24(b). The tab 320 is located on the holding link to contact the top of the safety drive link 25 as the holding link 20 begins to rock backward. The tab 320 works to limit the backward rotation of the holding link 20 and prevents the violent transfer of energy and momentum of the saw toward the operator of the saw chain.
Alternatively, or in addition to the above anti-kickback mechanisms, the safety drive link 25 may include a pair of rivet holes and corresponding rivets adapted to further limit the rotation of the holding link. Rather than the traditional circular holes 30, the rivet hole 322 that connects the safety drive link to the holding link, may be generally semi-circular shaped with a “V” shaped portion protruding into the hole. (See FIG. 25(a)). As illustrated in FIG. 25(b), a complementary rivet 324 may also include a generally semi-circular shape, with a generally “V” shaped slice missing from the circle. The rivet 324 is preferably an oil-less powdered metal rivet that is impregnated with oil. A lubricant (molybdenum, graphite, oil, etc.) can be added into a powdered metal mix before the rivet is molded. The rivet may be shaped such that a head is formed on one side and a generally cylindrical tail with a uniform diameter, as opposed to current designs which have a smaller diameter on each end and a larger “bearing surface” in the middle. The bearing surface of the present rivet resembles a donut and is made of powdered metal. The bearing surface 326 may be pressed, shrunk fit, or slip fit onto the new rivet with the already formed head. This method saves time by forming one side of the rivet when assembling the saw chain and proving an easier assembly of the chain. Additionally, the powdered metal bearing surface 326 is inherently porous and will accept oil, grease, or resin impregnation. When the chain is assembled, the second rivet is formed and will seal the impregnation material inside the bearing cage of the safety drive link. When the chain is in use, the oil lubricates the bearing surface and inside the bearing cage. Impregnating the powdered metal eliminates many steps in making a rivet and allows for the use of extremely high strength alloys that are nearly impossible to form using the current widely practiced method of “cold heading or hot heading”. The rivet may also be molded in one piece with the rotation limiting “V” shaped slice already in the bearing surface of the rivet. This feature is illustrated in FIG. 25(d), which shows a lengthwise view of rivet 324 with “V” slices provided in the bearing surface. The hidden lines represent the location the semi-circle begins.
The present rivet formation method is environmentally friendly in that oil does not have to be continuously fed into the rivet. As the rivet warms up, small amounts of oil are placed exactly where they are supposed to be. Previously, channels have been stamped into the links to allow oil to get to the captured area between the barrel of the rivet and the matching hole in the safety drive link. Allowing oil to reach this area is one argument for having larger clearances between the barrel and the hole in the safety drive link.
An additional advantage of powdered metal rivets is that the particle hardness of the material can be very high (about 50-65 Rockwell C), while the apparent hardness may remain low (about 30-45 Rockwell C), the later which lends itself to the forming process of making a rivet head.
The rotation limiting “V” portion in rivet 324 comprises an angle θ1 that is greater than angle θ2 of the generally triangular portion in rivet hole 322. Additionally, it is preferred that rivet hole 322 comprise a larger diameter than the rivet 324, to include clearance for the rivet to rotate. Generally, the best clearance, or tolerance, that current methods can achieve in cold or hot heading is 0.003-0.004 thousandths of an inch. To achieve tighter clearances and therefore less chain wear for traditional rivets, the entire rivet would require machining. However, the rivet 324 presented herein provides a clearance (tolerance) of within 0.001 thousandths of an inch. Therefore, when rivet 324 is inserted into rivet hole 322, the rivet is allowed limited rotation, but the available rotation is less than 360 degrees. FIG. 25(c) illustrates one example of the angle differences between θ1 and θ2, such that angle θ1 comprises a larger angle than the θ2. The angle θ1 of the rivet may be adjusted to make for a larger angle, which allows more rotation of the holding link 20, or the angle θ1 may be lessened to further limit rotation. The rivet hole 322 may be oriented on the safety drive link 25 to limit the rotation of the holding link 20 backward without limiting the rotation of the holding link 20 around the nose of the saw bar.
It is further provided that an anti-kickback saw chain including a plurality of links each having an upstream end and a downstream end relative to a direction of travel of the chain is provided that includes a holding link, a replaceable tooth adapted to be removably mounted on the downstream end of the holding link, and a safety drive link having a generally semi-circularly shaped rivet hole, wherein the upstream end of the safety drive link is pivotally fastened to the downstream end of the holding link by a rivet. The rivet is adapted to limit rotational movement of the holding link. The rivet hole further includes a generally “V” shaped protrusion extending into the rivet hole comprising a first angle. The rivet comprises a generally semi-circular shape with a “V” shaped section missing from the circle. The slice comprises a second angle, wherein the second angle is greater than the first angle. The rivet hole has a greater diameter than the rivet to provide rotational clearance (tolerance), which may be about 0.001 thousands of an inch. The rivet includes a head portion, a tail portion, opposite the head portion, and a bearing disposed between the head and tail portions. The bearing is generally doughnut shaped and includes a bearing surface. The bearing surface comprises powdered metal. The bearing surface is designed to accept at least one of oil, grease, and resin impregnation. The anti-kickback saw chain further includes a second rivet capable of sealing the oil in the bearing. The rivet preferably comprises a particle hardness of about 50-65 Rockwell C and an apparent hardness of about 30-45 Rockwell C.
Many modifications and variations of the invention will be apparent to those of ordinary skill in the art in light of the foregoing disclosure. Therefore, it is to be understood that, within the scope of the appended claims, the invention can be practiced otherwise than has been specifically shown and described
Patent Application
20110120280
