Cutting tool sharpener

Method (300) and apparatus (100) for sharpening a cutting tool (114, 132, 204, 210, 216). A flexible abrasive belt (116, 116A, 116B, 162, 172) with a selected linear stiffness and an abrasive surface (128A, 128B) of selected abrasiveness level is driven (304) in a selected direction along a selected plane between a first support (122) and a second support (118). In some embodiments, the cutting tool is presented (306, 308) in contacting engagement against the abrasive surface to induce torsion of the belt (140, 144, 148) out of the selected plane to conform to a cutting edge (138, 168, 178, 207, 208, 213, 214, 215) of the cutting tool. In further embodiments, presentation of the cutting tool against the abrasive surface of the belt (306, 308) induces bending of the belt out of said selected plane at a radius of curvature (169, 179) determined in relation to said linear stiffness to shape a side surface (164, 166, 174, 176) of the cutting tool with said radius of curvature.

BACKGROUND

Cutting tools are used in a variety of applications to cut or otherwise remove material from a workpiece. A variety of cutting tools are well known in the art, including but not limited to knives, scissors, shears, blades, chisels, machetes, saws, drill bits, etc.

A cutting tool often has one or more laterally extending, straight or curvilinear cutting edges along which pressure is applied to make a cut. The cutting edge is often defined along the intersection of opposing surfaces (bevels) that intersect along a line that lies along the cutting edge.

In some cutting tools, such as many types of conventional kitchen knives, the opposing surfaces are generally symmetric; other cutting tools, such as many types of scissors, have a first opposing surface that extends in a substantially normal direction, and a second opposing surface that is skewed with respect to the first surface.

More complex geometries can also be used, such as multiple sets of bevels at different respective angles that taper to the cutting edge. Scallops or other discontinuous features can also be provided along the cutting edge, such as in the case of serrated knives.

Cutting tools can become dull over time after extended use, and thus it can be desirable to subject a dulled cutting tool to a sharpening operation to restore the cutting edge to a greater level of sharpness. A variety of sharpening techniques are known in the art, including the use of grinding wheels, whet stones, abrasive cloths, etc. A limitation with these and other prior art sharpening techniques, however, is the inability to precisely define the opposing surfaces at the desired angles to provide a precisely defined cutting edge.

SUMMARY

Various embodiments of the present invention are generally directed a method and apparatus for sharpening a cutting tool.

In accordance with some embodiments, a method generally comprises driving a flexible belt in a selected direction along a selected plane between a first support and a second support, the flexible belt comprising an abrasive surface. The method further generally comprises presenting a cutting tool in contacting engagement against the abrasive surface to induce torsion of the belt out of the selected plane to conform to a cutting edge of the cutting tool.

In accordance with other embodiments, the method generally comprises driving a flexible belt in a selected direction along a selected plane between a first support and a second support, the flexible belt comprising an abrasive surface and having a selected linear stiffness. The method further generally comprises presenting a cutting tool in contacting engagement against the abrasive surface to induce bending of the belt out of said selected plane at a radius of curvature determined in relation to said linear stiffness to shape a side surface of the cutting tool with said radius of curvature.

In accordance with other embodiments, the method generally comprises driving a flexible belt in a selected direction along a selected plane between a first support and a second support, the flexible belt comprising an abrasive surface and having a selected linear stiffness. The method further generally comprises presenting a cutting tool in contacting engagement against the abrasive surface to induce torsion of the belt out of the selected plane to conform to a cutting edge of the cutting tool and to induce bending of the belt out of said selected plane at a radius of curvature determined in relation to said linear stiffness to shape a side surface of the cutting tool with said radius of curvature.

DETAILED DESCRIPTION

FIGS. 1A and 1Bgenerally depict an exemplary cutting tool sharpener system100(“sharpener”) constructed in accordance with various embodiments of the present invention. The sharpener100is configured to sharpen a number of different types of cutting tools in a fast and efficient manner.

The sharpener100includes a main drive assembly102with a housing104which encloses a drive assembly (generally denoted at105). The drive assembly105can take any suitable configuration depending on the requirements of a given application. Preferably, the drive assembly105includes an electric motor which rotates at a selected rotational rate.

Suitable gearing or other torque transfer mechanisms can be used to provide a final desired rotational rate. In some embodiments, the rate and/or the direction of rotation can be adjusted, either automatically or manually by the user, for different sharpening operations. User control switches are generally depicted at106.

The sharpener100further generally includes a sharpening assembly108coupled to the drive assembly. The sharpening assembly108preferably includes a substantially triangularly-shaped guide housing110with opposing sharpening guides112extending therein. The guides112enable a particular cutting tool, such as a kitchen knife114, to be alternately presented to the sharpener100from opposing sides.

FIG. 2provides another view of the sharpener100ofFIGS. 1A and 1B. InFIG. 2, the guide housing110has been removed to reveal a continuous, flexible abrasive belt116which is routed around rollers118,120and122. The roller118is characterized as a drive roller which is powered by the aforementioned drive assembly. The roller120is a fixed idler roller, and the roller122is a spring biased idler roller with an associated tensioner assembly124.

The tensioner assembly124preferably includes a coiled spring126or other biasing mechanism which applies an upwardly directed tension force upon the belt, as generally depicted inFIG. 3. The rollers118,120and122are preferably crowned to maintain centered tracking of the belt116, as generally represented inFIG. 4A, although guide rollers can additionally or alternatively be used, as generally represented inFIG. 4B. While a substantially triangular path for the belt116is preferred, such is not necessarily required as any number of other arrangements can be used as desired.

For example, in an alternative embodiment the belt116is routed around just two rollers rather than the three shown inFIG. 3. The rollers can be the same diameter to provide a substantially oval shaped path, or a larger roller can be used in lieu of the two lower rollers shown inFIG. 3to maintain a substantially triangular path. More than three rollers can also be used to provide other path configurations. It will be appreciated that in each of these embodiments, the system can be characterized as aligning the belt along a first selected plane between first and second supports (e.g., such as on the left hand side ofFIG. 3), and aligning the belt along a second selected plane between a third support and the first support (e.g., such as on the right hand side ofFIG. 3).

The belt116nominally rotates at a speed and direction around the rollers118,120,122as determined by the operation of the drive assembly. It is contemplated that a population of belts will be supplied for use with the sharpener100, each belt having different physical characteristics and each being easily removable from and replaceable onto the sharpener100in turn.

By way of illustration,FIGS. 5A and 5Bprovide respective side and top views of a first belt116A. The belt116A preferably includes a layer of abrasive material128A affixed to a backing (substrate) layer130A. The abrasive layer can take any number of forms, such but not limited to diamond particles, sandpaper material, etc., and will have a selected abrasiveness level (roughness). The backing layer130A can similarly be selected from a wide variety of materials, such as cloth, plastic, paper, etc.

In the present example, the first belt116A is contemplated as having an abrasiveness level on the order of about 400 grit. It is contemplated that the relative width, thickness and roughness of the first belt116A will make the belt suitable for initial grinding operations upon the cutting tool in which relatively large amounts of material are removed from the tool.

FIGS. 6A and 6Bshow a second exemplary belt116B. The second belt116B also has an abrasive layer128B and a backing layer130B. The abrasive layer128B is contemplated as comprising a finer grit than that of the first belt116A, such as order of about 1200 grit. The exemplary second belt116B is contemplated as being generally more flexible than the first belt116A.

The second belt116B is shown to be narrower than the first belt116A, to demonstrate that the sharpener100can be readily configured to accommodate different widths of belts. However, in preferred embodiments, all of the belts utilized by the sharpener100will have nominally the same width and length dimensions. Further, for reasons that will be discussed below, it is preferred that belts of coarser grit (such as the first belt116A) will be configured to have successively higher levels of linear stiffness, whereas belts of finer grit (such as the second belt116B) will be configured to have successively lower levels of linear stiffness.

As used herein, the term “linear stiffness” generally relates to the ability of the belt to bend (displace) along the longitudinal length of the belt (i.e., in a direction along the path of travel) in response to a given force. Generally, a belt with a higher linear stiffness will provide a larger radius of curvature as it is deflected by an object, since the belt has a relatively lower amount of flexibility along its length. Conversely, a belt with a lower linear stiffness, due to its relatively higher level of flexibility, will provide a smaller radius of curvature as it is deflected by the same object.

Accordingly, the second belt116B is particularly suited for subsequent grinding or honing operations upon the cutting tool in which relatively smaller amounts of material are removed from the tool. It will be appreciated that the relative dimensions represented inFIGS. 5-6are merely exemplary in nature and are not limiting. For example, all of the belts may be of the same general thickness with different flexibilities established by other characteristics, such as the material used to form the belts, the composition of the backing layers, etc. Also, any number of additional belts can be provided with other dimensions and levels of abrasiveness, including belts with a grit of 40 or lower, belts with a grit of 2000 or higher, etc.

It is contemplated that all of the belts will have generally the same circumferential length, but this is also not necessarily required as at least some differences in belt length can be accommodated via the tensioner124. Indeed, as will now be explained beginning withFIGS. 7A-7B, a number of factors including the tensioner force and the belt length, width, thickness and stiffness are preferably selected to provide specifically controlled amounts of linear and torsional deflection of the belt during sharpening.

FIGS. 7A and 7Bprovide schematic representations of the sharpener100to illustrate preferred operation of a selected belt116during a sharpening operation upon a cutting tool132.FIG. 7Ashows the cutting tool132prior to engagement with the belt116, andFIG. 7Bshows the cutting tool132during engagement with the belt116.

For reference, the cutting tool132is shown in a canted orientation, and for purposes of the present example the cutting tool is characterized as a conventional kitchen knife with handle134, blade136and curvilinearly extending cutting edge138.

As shown inFIG. 7B, the belt116preferably twists out of its normally aligned plane, as indicated by torsion arrow140, in the vicinity of the knife132as the cutting edge138is drawn across the belt116. More specifically, the user preferably grasps the handle134and pulls the knife132back in a substantially linear fashion, as indicated by arrow141. The moving belt116will undergo localized torsion (twisting) to maintain a constant angle of the abrasive layer128against the blade136irrespective of the specific shape of the cutting edge136. In this way, a constant and consistent grinding plane can be maintained with respect to the blade material.

The amount of torsional displacement of the belt along a particular cutting edge can vary widely in relation to changes in the curvilinearity of the cutting edge. A typical amount of twisting may be on the order of 30 degrees or more out of plane. In extreme cases such as when the distal tip of a blade passes across the belt, twisting of up to around 90 degrees or more out of plane may be experienced. The torsion is generally a function of the length of the extent of the belt presented to the tool in comparison to the belt width, as well as a function of the tension applied to the belt applied by the tensioner assembly124. Thus, it is contemplated that, generally, each of the belts respectively installed onto the sharpener100will undergo substantially the same amount of torsion irrespective of the abrasiveness or linear stiffness of the belt.

The direction of belt twist will be influenced by the relation of the cutting edge138to the belt116. InFIG. 8A, a first portion142of the cutting edge138at the base of the blade136adjacent the handle134is generally concave with respect to the belt116. This will generally induce torsion in a counter-clockwise direction, as indicated by arrow144, as that portion of the blade passes adjacent the belt116.

InFIG. 8B, a second portion146of the cutting edge138near the point of the blade136is generally convex with respect to the belt116. Passage of the second portion146adjacent the belt will generally induce torsion in the opposite clockwise direction, as indicated by arrow148.

In a preferred embodiment, the retraction of the knife132across the belt116is controlled by the aforementioned sharpening guides112in the guide housing108(FIG. 1). One of the guides112is generally depicted inFIG. 9. A slot is formed by facing surfaces150,152and a base surface154, although other configurations can be used, including angled surfaces that form a v-shape. During the sharpening steps ofFIGS. 8A and 8B, the knife132is inserted into the slot above the belt116and moved downwardly until the base of the cutting edge138(portion142inFIG. 8A) comes into contacting abutment against the base surface154(also referred to as a cutting edge guide surface).

While maintaining a small amount of downward pressure upon the handle134, the user slowly draws the knife132back (i.e., direction141inFIGS. 8A-8B) so that the cutting edge138remains in contact with, and slides against, the base surface154. Preferably, the blade136is also lightly pressed against the vertical guide surface152so as to slidingly pass in contacting engagement with the surface152during the sharpening operation.

Although not shown inFIG. 9, a suitable retention feature, such as a spring clip or a magnet, can be incorporated into the guide112to maintain the knife132in contacting engagement with the surfaces152,154. The knife132is preferably passed across the belt several times in succession, such as 3-5 times, to sharpen a first side of the blade136. The knife132is then preferably moved to the other guide (seeFIG. 1) and these steps are repeated to sharpen the other side of the blade136.

In some embodiments, the belt continues to rotate in a common rotational direction so that the belt moves “downwardly” with respect to the cutting tool on one side and “upwardly” with respect to the cutting tool on the other side. In other embodiments, the belt rotational direction is changed so as to pass downwardly on both sides, thereby drawing material down and past the cutting edge on both sides of the blade. Such change in belt rotational direction is not required in order to achieve effective levels of “razor” sharpness of the tool, but may be nevertheless be found to be beneficial in some applications. In such case, it is contemplated that the alternative directions of belt rotation can be manually set by the user, or automatically implemented by the sharpener100such as, for example, from the incorporation of a pressure switch or a proximity switch in each of the guides112to sense the presence of the cutting tool therein.

FIGS. 10A-10Cgenerally illustrate a preferred sharpening sequence upon a blade160. As will be recognized by those skilled in the art, the ability to obtain a superior sharpness for a given cutting tool will depend on a number of factors, including the type of material from which the tool is made. It has been found that certain types of processed steel, such as high grade, high carbon stainless steel, are particularly suitable to obtaining sharp and strong cutting edges. It will be appreciated, however, that the sharpener100can be readily adapted to provide extremely sharp cutting edges for any number of materials, including relatively lower grades of steel, high quality Damascus steel, ceramic blades, tools made of other metallic alloys or non-metallic materials, etc.

As set forth byFIGS. 10A-10C, the sharpener100generates a novel, convex grind surface geometry.FIG. 10Ashows the blade160in conjunction with a first belt162which, when alternately applied to opposing sides of the blade160, provides continuously extending, substantially convex surfaces164,166which converge and intersect along a cutting edge168. The first belt162is characterized as having a relatively coarse abrasive level, and relatively high linear stiffness characteristics.

FIG. 10Bshows a subsequent grinding operation upon the blade160using a second belt172that forms opposing surfaces174,176and a cutting edge178.FIG. 10Cis a side view depiction of the blade160at the conclusion of the operation ofFIG. 10B. It will be appreciated that due to the torsional operation of the respective belts162,172, the cross-sectional geometries represented inFIGS. 10A-10Bare nominally consistent along the entire longitudinal length of the blade (e.g., from substantially the tip of the blade to a position adjacent the handle).

The sharpening operation ofFIG. 10Awith the first belt162constitutes a relatively coarse, first stage grinding operation upon the blade material, and provides a relatively large radius of curvature upon the opposing sides164,166of the blade160. This radius of curvature (denoted as R1at169) is primarily established as a result of the relatively higher linear stiffness of the belt162. Substantially this same radius of curvature is applied along the entire extent of the blade160. (It will be appreciated that the length of the radius R1is relatively large with respect to the scale ofFIG. 10A, and therefore the origin of the radius does not fit on the page).

While the sharpening geometry ofFIG. 10Acan produce an extremely sharp cutting edge168, a limitation that may be experienced with this particular sharpening geometry is the fact that the blade160is relatively thin for a substantial extent of the width of the blade160. This can result in an undesirably weak blade that will deform, dull or break relatively easily if large forces are applied to the cutting edge168.

Accordingly, it is contemplated that at the conclusion of this first stage of the sharpening operation, the first belt162is preferably removed from the sharpener100and the second belt172is installed, as depicted inFIG. 10B. The blade160is once again presented to the sharpener100and the second belt172applies a relatively fine (honing) grind upon the blade160. This results in a correspondingly smaller radius of curvature (R2at179) upon each of the surfaces174,176due to the reduced linear stiffness of the second belt172.

As before, the second belt172undergoes torsion as the blade160is drawn across the belt so that the smaller radius of curvature shown inFIG. 10Bis consistently applied along the extent of the blade160. As noted above, the respective belts162,172will preferably undergo substantially the same amounts of torsion during the respective grinding operations.

The smaller radius of curvature established by the more flexible second belt172generally localizes the honing operation to the vicinity of the end of the blade160. The new cutting edge178(and the opposing surfaces174,176) result from the removal of material inFIG. 10Bover what was present at the conclusion of the operation ofFIG. 10A.

The effects of this localized honing operation in the vicinity of the cutting edge178are depicted inFIG. 10C. Generally, score (scratch) marks180may be present on the blade as a result of the relatively more aggressive abrasive of the first belt162. The ends of these score marks180, however, may be honed out of the blade in the vicinity of the final cutting edge178as a result of the secondary sharpening operation.

An advantage of the secondary sharpening process set forth byFIG. 10Bis that the blade160now has the slicing advantages provided by the first surfaces164,166ofFIG. 10A, as well as greater blade strength due to the greater thickness in the vicinity of the cutting edge178resulting from the greater curvature of the second surfaces174,176.

While two belts have been discussed above, it will be appreciated that such is merely illustrative and not limiting. For example, sharpening can be accomplished using any number of belts of various abrasiveness and stiffness that are successively installed onto the sharpener100and utilized in turn. Conversely, sharpening operations can be effectively carried out using just a single belt of selected abrasiveness and stiffness.

For example, once the blade160has become dulled due to moderate use, all that may be required to restore the blade160to the sharpness ofFIGS. 10B and 10Cwould be to re-present the blade160for sharpening against the second belt172, thereby realigning the material along the cutting edge178. Conversely, if greater wear or damage is incurred, the sharpness of the blade160can be restored by application of both belts162,172to the blade.

The two belt sharpening process ofFIGS. 10A-10Cis particularly suitable for relatively harder materials such as laminated and/or high carbon steels, or other materials with a relatively high Rockwell Hardness level (such as on the order of e.g., 60 or higher). Such materials are sufficiently strong and hard to be able to transition from the relatively coarse grinding provided by the first belt162to the relatively fine grinding provided by the second belt172without undergoing deformation or other effects that would cause deviation from the displayed geometries.

Indeed, subjecting such relatively hard material to just the second belt172would ultimately result in the cutting edge178, although such may require an extended period of time since the finer abrasiveness of the second belt will generally take longer to remove the requisite material from the blade to arrive at this final configuration. The use of multiple belts of varying abrasiveness is thus preferred for purposes of efficiency, but is not necessarily required. Similarly, it may be desirable to apply just the coarse grind ofFIG. 10Afor certain applications.

Softer materials such as lower grade steels with relatively lower Rockwell Hardness (such as on the order of, e.g., 45-50) may benefit from the use of higher numbers of sequential grinding stages. For example, a sequence of three different belts of 400 grit, 800 grit and 1200 grit may be respectively used in turn. This would tend to reduce the transitions between different belts, thereby reducing the risk of undesirably inducing folding or other deformations of the blade material in the vicinity of the cutting edge. Indeed, any number of belts, including 5-10 different belts or more, and belts of upwards of 2000 grit or more, can be progressively used as desired, depending on the requirements of a given application.

While the geometries set forth byFIGS. 10A-10Bare symmetric, similar geometries can readily be established for asymmetric blades, such as an exemplary blade200shown inFIG. 11. The asymmetric blade200is typical of certain types of cutting tools such as pocket or utility knives with scallops (serrations) along a portion thereof (not separately shown), as well as some types of shears, scissors, etc.

The blade200has a first surface201that extends in a substantially vertical direction, and an opposing second surface202that curvilinearly extends to provide a convex grind surface similar to the surface174inFIG. 10B. It will be appreciated that the asymmetric blade200can be readily sharpened simply by applying the aforementioned sharpening sequence to just the second surface202.

FIGS. 12A-12Bprovide further examples of tools that can be readily sharpened using the aforementioned sharpening sequence.FIG. 12Ashows a first style of utility knife204with a blade205and handle206. The blade205includes opposing, curvilinearly extending cutting edges207and208. The cutting edge207further includes a concave recess209useful, for example, in cutting fibrous materials such as a rope. The knife204can be sharpened by the sharpener100simply by applying the sequence ofFIGS. 10A-10Bwhile the knife204is in the orientation ofFIG. 12A(to sharpen edge207), flipping the knife over, and repeating (to sharpen edge208). The aforementioned torsional and bending characteristics of the respective belts are readily capable of providing so-called “razor” sharpness to the entire extents of the edges207and208.

FIG. 12Bshows a second type of utility knife210with blade211and handle212. The blade211has a complex geometry with a lower curvilinear edge213, a straight cutting edge214, and scallops (localized serrations)215. The cutting edges213and214can be readily sharpened as set forth above. In many cases scallops such as215can also be sharpened, albeit in a manner similar to that shown inFIG. 11. It will be noted, however, that the torsional stiffness and width of the belts may need to be adjusted in relation to the relative size of the scallops215in order to maintain substantially the same initial geometries of the scallops at the conclusion of the sharpening operation.

It will be noted at this point that complex geometries such as depicted inFIGS. 10-12with maximum levels of sharpness can generally be obtained only to the extent that the sharpening angle (i.e., the angle between the tool and the abrasive) is maintained within close tolerances during each sharpening pass. Too much variation in the sharpening angle from one pass to the next can actually result in a cutting edge becoming duller as a result of the sharpening operation, since the variations prevent formation of the desired intersection of the respective opposing surfaces. This constitutes a major drawback with most prior art sharpeners.

Even state of the art sharpeners that employ multiple stages of guides and rotating grinding wheels to provide highly controlled sharpening operations are not immune to such variability. Such sharpeners will often require the user to rotate the tool as the tool is drawn back so that the tool takes a curvilinear path to match the curvilinear extent of the cutting surface. While such sharpeners may produce high levels of sharpness, it will be immediately apparent that variations will occur to the extent that the user does not (and cannot) draw the curved blade back at the exact same angle during each pass.

It will thus be seen that the sharpener100advantageously provides highly repeatable and controllable sharpening angles for substantially any shape cutting edge, since the sharpening angle is established and maintained by the adaptive torsion of the belt as it reacts to the differences in curvilinearity of the cutting edge. It has been found that sharpeners constructed in accordance with the exemplary sharpener100disclosed herein readily achieve levels of sharpness that exceed what is sometimes generally referred to in the art as “scary sharpness” (razor sharp, scalpel sharp, etc.) even for cutting tools with less-than superior metallic constructions.

While the various embodiments discussed above have been configured for the sharpening of bladed cutting tools, such as knives, which can be inserted into the guides112, it will be appreciated that any number of different types and styles of tools can be sharpened using the sharpener100by removal of the guide housing110(FIG. 3) and presentation of the tool to the respective exposed extents of the belt116. Accordingly, any number of other styles and types of cutting tools, such as lawn mower blades, machetes, scissors, swords, spades, rakes, etc. can be effectively sharpened by the sharpener100in like manner to that discussed above.

An alternative embodiment for the sharpener100is generally depicted inFIG. 13, which uses an alternative drive configuration and belt path for the belt116. Unlike the symmetric arrangement ofFIG. 3, the alternative arrangement ofFIG. 13provides an asymmetric triangular path for the belt. As before, the belt passes over rollers118,120,122and is tensioned by the tensioner124.

The arrangement ofFIG. 13provides only a single side of the belt for sharpening, such as for a cutting tool216characterized as a set of pruning shears. The shears216include spring biased handles218,220which, when closed, bring a blade portion222with cutting edge224into proximity with a shear portion226.

As further shown inFIG. 14, the configuration of the shears is such that the cutting edge224lies in close relation to the intersection with the shear portion226, making the shears difficult to sharpen in this vicinity using conventional processes such as a grinding wheel, due to the lack of clearance. However, generally the only limiting factor with the sharpener100is the thickness of the belt116, so that substantially the entire extent of the cutting edge224can be sharpened without the need to disassemble the tool216. That is, in both the embodiments of FIGS.3and13-14, sufficient clearance is provided behind the belt116to provide a bypass clearance to enable a portion of the tool to be disposed behind the belt.

FIG. 15provides a flow chart for a SHARPENING OPERATION routine300, generally illustrative of steps carried out in accordance with various preferred embodiments of the present invention. It will be appreciated thatFIG. 15generally summarizes the foregoing discussion.

Initially, at step302a first abrasive flexible belt (such as116A inFIGS. 5A-5Bor162inFIG. 10A) is selected and installed onto the sharpener100. This first abrasive belt will have a selected abrasiveness level and a selected linear stiffness as discussed above. Once installed, the first belt is driven at step304via the drive assembly105(FIG. 1A) in a selected direction along a selected plane between a first support and a second support (such as between the rollers122and118inFIG. 3).

At step306, a cutting tool (such as114,132,204,210,216, etc.) is presented in contacting engagement against the abrasive surface of the belt. This induces torsion of the belt out of the selected plane to conform to the cutting edge of the cutting tool (as generally depicted inFIGS. 7-8) and/or bending of the belt out of the selected plane at a radius of curvature determined in relation to said linear stiffness to shape a side surface of the cutting tool with said radius of curvature (as generally depicted inFIGS. 10A-10C).

At this point it will be noted that while preferred embodiments configure the belt to both deflect in a torsional mode to follow changes in the contour of the cutting edge and to deflect in a bending mode to provide a desired radius of curvature to the formed cutting edge, both deflection modes are not necessarily required. That is, while both modes are preferably utilized together, each has separate utility and can be implemented without the other. For example and not by way of limitation, a given tool may be rotated as the tool is drawn back across the belt, thereby removing the advantageous torsional operation of the belt upon the cutting edge. Indeed, the sharpener could be readily configured to support the belt and prevent such torsion, as desired. Accordingly, the flow ofFIG. 15shows that torsion and/or bend modes of deflection are induced during presentation of the tool.

Preferably, the sharpening operation is applied to opposing sides of the tool, such as depicted inFIGS. 10A-10C, soFIG. 15applies the foregoing step to the other side of the tool at step308. The operations at steps306and308can be carried out via the sharpening guides112, or can be carried out on the belt116with the guide housing removed, as depicted in FIGS.2and13-14.

A determination is made at decision step310as to whether additional sharpening operations are desired; if so, a new belt is installed onto the sharpener at step312and steps304through310are repeated using the new belt. Preferably, the new belt has a finer abrasiveness level (e.g., 1200 grit v. 400 grit, etc.) and less linear stiffness than then first belt. This sequence will generally result in the generation of a new cutting edge along the cutting tool, as depicted inFIGS. 10B-10C. Once all of the desired sharpening stages have been completed, the routine ends as shown at step314.

While step312sets forth the removal of an existing belt and the installation of a new replacement belt onto the sharpener100, it will be appreciated that such is not necessarily limiting to the scope of the claimed subject matter. Rather, the sharpener100can be readily adapted to concurrently operate multiple belts so that the tool is merely moved from one belt to another during the above sequence.

Any number of sharpener configurations can be employed as desired. As noted previously, the respective bending and twisting modes are dependent on a number of factors relating to the configuration, speed and tension force upon a given abrasive belt.

For purposes of reference, it has been found in preferred embodiments to utilize relatively narrow abrasive belts with lengths on the order of about 12 inches to 18 inches and widths of about 0.5 inches. The distance (journal length) between adjacent supports (e.g., such as the distance along the belt from rollers118,122inFIG. 3) can preferably vary from as low as around 2 inches to up to about 6 inches or more. The linear speed of the belt can also vary, with a preferred range being from about 1,500 feet/minute (ft/min) to about 5,000 ft/min. A preferred tension force supplied to the belt (such as via the tensioner spring126) is on the order of around 4 pounds (lbs), with a preferred range of from about 0.5 lbs to upwards of about 10 lbs. It will be appreciated that the foregoing values and ranges merely serve to illustrate preferred embodiments and are not limiting.