Abstract:
A powered sharpening system utilizing a turntable to rotate reversible, interchangeable platters carrying different grades of abrasive for grinding, polishing and lapping woodworking and other edge tools to be sharpened that are secured in a tool holder that contacts a reference surface on a tool rest to facilitate formation of bevels and micro-bevels at desired angles. Use of a platter of a first thickness followed by a thinner platter enables automatic formation of a micro-bevel without any adjustment in the tool holder, tool rest or sharpening technique. The turntable is rotated by an electric motor that also rotates a conventional abrasive wheel or a conventional narrow abrasive belt. The motor is mounted in a base within which a duct is located for coupling to a vacuum system for removing, through ports in the duct, abrasive and metal particles produced in grinding and sharpening. Blades on the underside of the turntable induce airflow through the base to cool the motor and other components.

Description:
FIELD OF THE INVENTION 
     This invention relates to methods and devices for sharpening woodworking tools, including chisels, plane blades, carving tools, and knives. It relates, in particular, to rotating grinding, buffing, lapping, and polishing wheels and belts and other powered tool sharpening apparatus. 
     BACKGROUND OF THE INVENTION 
     Most woodworking hand tools require sharpening, especially new tools. Chisels, plane blades, carving tools, axes, drawknives, and other tools all need to be prepared for use by grinding and polishing two intersecting surfaces to create a keen cutting edge or arris. Tool use dulls and sometimes damages this arris, making periodic re-sharpening necessary. Many tool sharpening devices and techniques have been developed, but tool sharpening and re-sharpening remains difficult for many tool users because of the substantial practice, skill and time needed to utilize many sharpening devices and techniques successfully. Additionally, widespread unfamiliarity with well-sharpened tools makes it difficult for many tool users to accurately judge the quality of sharpening results. 
     All relevant sharpening techniques involve abrading tool surfaces with abrasive materials, such as natural or man-made stones, or with abrasive particles deposited on another substrate. Among existing products intended for sharpening woodworking hand-tools are high-speed, “dry” grinding wheels that do not use lubrication and low-speed “wet” wheels that use lubrication on the wheel surface, typically water. Some of these products utilize relatively large diameter vertical wet or dry grinding or honing wheels, where the wheel edge is the principal working surface. Others utilize horizontal wheels where one face of the wheel is the principal working surface. A variety of abrasive “stones” usually having flat surfaces are available for manual sharpening. 
     One of the challenges associated with use of all abrasive wheels and manual stones is wheel or stone surface shape. Wear during use invariably causes stone or wheel surfaces to become uneven, requiring dressing of those surfaces to restore the desired shape and often resulting in changes in the distances between such surfaces and associated tool guides and rests. These changes in system geometry as a result of stone wear, and shortcomings of existing tool guides and rests make it extremely difficult or impossible with most existing devices to achieve reproducible sharpening geometries that produce reproducible sharpening angles on the tools being sharpened. Depending on the type of tool, the way it was manufactured, the materials from which it was manufacture and its intended use, certain specific bevel angles are required for the cutting edge. Once a specific, successful bevel angle is achieved, the user will want to reproduce that same angle as closely as possible when the tool requires resharpening. 
     Additionally, existing sharpening products have no provision for grinding and polishing both surfaces of many cutting tools such as plane blades and chisels, because they have no provision or only inadequate provisions for grinding and polishing or “lapping” the back of such tools, which is required successfully to sharpen such tools. 
     To be practical and effective, any abrasive operation like tool sharpening must use several grades of abrasives to progress from shaping and forming of the tool&#39;s surface to the desired level of surface finish. The more highly polished the surface finish needs to be, the more abrasive steps are required. Typical tool sharpening requires a broad range of abrasive grades because sharpening starts with formation of the principal bevel or back surface by grinding and ends with polishing to a mirror finish. 
     SUMMARY OF THE INVENTION 
     Among other desiderata that result from the considerations mentioned above, a sharpening system desirably should provide: 
     a wide range of abrasive grades 
     a highly functional tool holding and guiding system 
     controllable, reproducible system geometry, particularly relative to the relationship between the tool holder and guide (and therefore the tool being sharpened) and the abrasive surface; 
     an absolutely flat abrasive surface 
     easily renewable abrasive surfaces 
     flexibility in accommodating a wide range of tool sizes and shapes 
     modest generation of heat in the tool to avoid metallurgical damage 
     safe operation 
     speed. 
     These and other desirable objectives associated with tool sharpening are achieved by this invention. 
     This sharpening system combines a relatively slowly rotating horizontal turntable and, alternatively, either a rotating vertical grinding wheel or belt. The belt and/or wheel may be used for grinding, shaping, and in some cases, sharpening, a wide variety of woodworking tools in a relatively conventional manner. The rotating turntable is topped, during use, by a platter to which abrasive has been attached by bonding a plastic or fabric sheet coated with abrasive or a disk of cloth charged with abrasive. Abrasive may be positioned on both sides of the platter, making the platter reversible, and multiple platters may be used. Relatively slow turntable rotation limits heat buildup during use. 
     A tool such as a plane blade or chisel to be sharpened (and already having a properly lapped back) is secured in a tool holder that rests and travels against a repositionable tool rest or tool guide fixed in position relative to the turntable in order to form a main bevel on the tool at a desired angle. That bevel is formed utilizing a first grade of abrasive affixed to a platter having a particular thickness and that is mounted on the turntable. A second, thinner platter having a finer grade abrasive is then mounted on the turntable. Contact between the tool and the abrasive on the second platter (without changing any other aspect of the system or tool holder geometry) then automatically produces a micro-bevel to complete tool sharpening because the tool contacts the abrasive on the thinner platter at a slightly greater angle. Thus, abrasion occurs only at the very front of the bevel adjacent to the arris where it is needed to hone the cutting edge or arris. This minimizes the amount of abrasion required, and consequently lengthens the working life of the abrasive and reduces the time needed for sharpening. 
     The back of a tool such as a plane blade or chisel may be lapped flat against an appropriate grade of abrasive mounted on a platter positioned atop the rotating turntable. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the sharpening system of this invention shown with a vertical grinding wheel and cover mounted on the right side of the device and with a chisel being sharpened. 
     FIG. 2 is a perspective view of the system shown in FIG. 1 with an abrasive belt attachment substituted for the vertical grinding wheel and its cover shown in FIG.  1 . 
     FIG. 3 is a perspective view of the underside of the system shown in FIG.  2 . 
     FIG. 4 is an exploded perspective view of the sharpening system of this invention shown with the components for use of either a grinding wheel or a grinding belt. 
     FIG. 5 is exploded perspective view of the belt grinder assembly shown in place on the system in FIG.  2 . 
     FIG. 6 is an exploded perspective view of the turntable bushing and components that hold the turntable in place on the sharpening system of this invention. 
     FIG. 7 is an elevation view of the turntable. 
     FIG. 8 is a perspective view of the tool holder of this invention shown holding a bench chisel. 
     FIG. 9 is a perspective view of the tool holder of this invention being used with the blade projection-setting jig of this invention. 
     FIG. 10 is a perspective view of positioning of a skew chisel on the body of the tool holder shown in FIGS. 8 and 9. 
     FIG. 11 is an end elevation view of the turntable and tool rest portion of the system shown in FIGS. 1-4 with a bench chisel being positioned in the tool holder shown in FIGS. 8 and 9. 
     FIG. 12 is an enlarged side elevation view of a portion of a reversible platter for use on the turntable of the sharpening system of this invention with abrasive sheets on both sides. 
    
    
     DETAILED DESCRIPTION 
     As will be appreciated by reference to the Figures, the sharpening system  20  of this invention utilizes a base  22  that may be a generally hollow structure cast, fabricated, formed or molded of a variety of materials including suitable plastics, cast iron and aluminum. 
     Base  22  holds a horizontal drive shaft  24  (visible in FIG. 3) that is driven by a motor  26  mounted inside base  22 . Numerous alternatives could be used for coupling the motor  26  to the drive shaft  24 , including round or vee-shaped belts, gears and other coupling means, but a single flat belt  28  provides a compact, efficient method for coupling motor  26  to shaft  24 . Shaft  24  drives a horizontal turntable  30  on the left side of base  22  and, on the right side of base  22 , alternatively, either a vertical grinding wheel  32  (illustrated in FIG. 1) or a narrow abrasive belt  34  illustrated in FIG.  2 . 
     When using the grinding wheel alternative, the grinding wheel  32  is secured to drive shaft  24  with washers  36  and a nut  38  (visible in FIG. 4) and is covered with a guard  40  and eye shield  42 . 
     Alternatively, a belt drive wheel  44  may be mounted on shaft  24  while other components of the belt assembly  46  are mounted on the base  22 . Generally, these components include a stanchion  48  that is secured to the base  22  and that supports belt idler wheel  50  over which abrasive belt  34  runs. Belt idler wheel  50  runs on a shaft  52  secured in an idler yoke  54  that is pivotally connected to stanchion  48  by a pin  56 . Yoke  54  is urged to pivot upward by spring  58  between the stanchion  48  and yoke  54  to thereby tension belt  34  around idler wheel  50  and drive wheel  44 . Idler wheel shaft  52  is secured in a round hole in the right side  60  of idler yoke  54  and in a slot  62  in the left side  64  of idler yoke  54  so that the end  66  of idler shaft  52  in slot  62  may be moved up and down by a screw  68  attached to yoke  54  and threaded into the end  66  of shaft  52 . Thus, adjustment of screw  68  tilts shaft  52  and idler wheel  50  in order to cause belt  34  to run true. Belt  34  bears against a spring steel belt platen shoe  70  that clips on the face of stanchion  48  platen  72 . A flat platen shoe  70  is illustrated, but a convex shoe can also be used so that hollow grinding can be accomplished against belt  34 . A vertical grinder tool rest assembly  31  provides positioning for tools relative to either the grinding wheel  32  or belt  34 . 
     Drive shaft  24  also rotates the turntable  30 , which may be cast aluminum or other suitable materials, including other metals and alloys and plastics and composites. As is illustrated in FIG. 6, a bronze bushing  74 , such as an Oilite® flange bushing, is press fit in turntable  30 , which has air fins or blades  76  on its underside that draw air for cooling purposes through filter  78  mounted in the back of base  22  into the interior of base  22 , through openings  80  in base  22  under turntable  30 , and out between safety pins  82  in base  22 , as well as through the clearance between the underside of the turntable  30  and the close adjacent cast projections assign number assign number in base  22 . Pins  82  prevent a user&#39;s fingers from contacting fins  76  on the underside (see FIG. 7) of turntable  30 . The positive air flow emanating between turntable  30  and base  22  aids in preventing abrasive particles from entering the rotating drivetrain components (bushings and bearings). 
     Stub axle post  84  is received in bearing  74  in turntable  30 , so that turntable  30  can rotate. Through clearance between the stub axle  84  and bearing  74 , turntable  30  can also rock slightly on post  84  to insure firm contact with wheels  108 ,  110 , and  112  and accommodate uneven wear of those wheels. 
     In some aspects of operation of the system  20 , such as when a shaped-edge felt wheel is mounted on turntable  30 , upward pressure is exerted on platen  30 , thus making it desirable that turntable  30  be mounted in a manner that resists such upward pressure. Firm contact with drive wheel  112  is also desirable. As may be seen in FIG. 6, this contact and retention is accomplished by placing turntable  30  with bushing  74  around stub axle post  84  and then securing turntable  30  in place using screw  86  passing through washer  88 , spring washer  90  and keyed to tab washer  92 . Keyed washer  92  is received on axle post  84 , which carries a key way. Disk  94 , essentially a thick metal washer, is secured above axle post  84  in the center of turntable  30  with screws  96 . A threaded center hole  98  in Disk  94  receives a threaded post  100  on platter thumb screw  102 , which post  100  passes through center hole  104  in interchangeable abrasive-bearing platter  106  and thereby secures platter  106  to turntable  30 . 
     Turntable  30  rests on three wheels  108 ,  110 ,  112 , each of which wheels is shod with a resilient tire  114 , that may be an o-ring of neoprene, rubber, nitrile (Buna-N, a copolymer of butadiene and acrylonitrile), silicone, EPDM, Butyl or other suitable material. As will be appreciated by reference to FIGS. 3,  4  and  7 , wheel  112  is positioned on drive shaft  24  so that its tire  114  contacts a smooth, flat portion  115  of the underside of turntable  30  and imparts rotational motion to turntable  30  when drive shaft  24  is rotating. Wheels  108  and  110  ride on axles  109  that mount on base  22 . Rotational speed of turntable  30  is a function of the speed of drive shaft  24 , wheel  112  diameter, and the distance from the center of turntable  30  to the point where wheel  112  contacts the underside  115  of turntable  30 . A turntable speed of approximately 650 revolutions per minute works well. 
     Rotational speed of grinding wheel  32  or belt drive wheel  44  is a function of the speed of drive shaft  24 . A drive shaft  24  speed of approximately 1750 revolutions per minute facilitates use of grinding wheel  32  or belt  34  with less heat buildup and a consequently smaller risk of tool damage than when using a conventional wheel grinder that normally operates at about 3600 revolutions per minute. 
     Each side of each interchangeable platter  106  may be topped with a pressure sensitive adhesive-backed abrasive sheet  116 , such as 3M® Imperial™ microfinishing film in a grade such as 100 microns, 60 microns, 40 microns, or 9 microns (polyester film backing coated with resin-bonded micron-graded mineral particles that are electrostatically oriented). Coarser abrasives may also be used such as 80, 120 or 180 zirconia abrasive disks, which are typically manufactured with a fabric substrate. Alternatively, a platter  106  may be topped with a layer of fabric, such as woven cotton broadcloth bonded to the platter  106  with rubber cement. This cloth may then be charged with abrasive compound such as Veritas® blade honing compound (containing chromium oxide) available from Lee Valley Tools, Ltd. 
     Platters  106  should be of a specific thickness and as flat as possible so that when laid on a surface plate and checked with a precision measuring instrument such as a dial indicator, the distance from the highest to the lowest spot on any one side of a platter  106  is no more than 0.005″. Platters  106  could be formed of solid metals, such as steel or aluminum, and could be plastic or plastic composites. Such platters may also be structures having multiple laminations. For instance, as illustrated in FIG. 12, platters  106  may have a thermoplastic core  180  bonded between two aluminum skins  182  (e.g., 0.020 inch gauge aluminum sheets) and sold under the name AlucoBond®, available from Alusuisse Composites, Inc., 55 West Port Plaza, Ste. 625, St. Louis, Mo. 63146. FIG. 12 is an enlarged elevation view of a portion of the edge of a platter  106  with sheets of abrasive  116  and  116 ′ on each side. A first sheet of coated abrasive  116  is bonded to one side of platter  106  and a second sheet  116 ′ is bonded to the opposite side. 
     By use of platters  106  of differing thicknesses, slight grinding angle changes may automatically be achieved. For instance, a first platter  106  four millimeters thick and having a courser abrasive  116  (e.g., 100 micron abrasive) may be used to produce a principal bevel on a woodworking tool, such as bevel  164  on chisel  120 . After producing bevel  164 , a second platter  106 , three millimeters in thickness and preferably having a finer grade abrasive  116  (e.g., 9 micron abrasive), may be substituted on top of platen  30 . This will cause chisel  120  to contact abrasive  116  at a slightly greater angle, producing a micro-bevel without changing any apparatus settings. 
     A tool, such as chisel  120 , to be sharpened utilizing system  20  is locked in a tool holder  122  by clamping the tool blade  124  between the holder body  126  and a holder bar  128  by tightening thumb nuts  130 , as illustrated in FIG.  8 . Concavities  132  in feet  134  of tool holder body  126  rest and slide against a horizontal semi-cylindrical surface  136  of a tool guide or tool rest  138 . A rest holder yoke  140  positioned atop a tool rest post  142  supports tool rest  138 . It is important that tool rest  138  be parallel to the surface of platter  106  when mounted on turntable  30  so that a tool blade such as blade  124  will be properly ground when the blade  124  is secured on tool holder  122  and the holder is used as described below in contact with tool rest  138 . Accordingly, it is desirable that tool rest  138  be adjustably attached to rest holder yoke  140  so that such a parallel relationship can be established and maintained. This can be accomplished, for instance, by securing rest  138  to yoke  140  with screws  141  (see FIG. 11) that pass through elongated holes or slots in rest  138  and into yoke  140 , allowing the position of rest  138  to be adjusted before the screws  141  are tightened. 
     The position of tool post  142  in hole  144  in base  22  is adjustable, and the projection of post  142  (and therefore the height of tool rest  38  relative to turntable  30  and platter  106 ) is indicated by indicia  146  on post  142  (as further described below). Post  142  may have a bottom section  148  separated from post  142  by oblique surfaces  150 . Post  142  is locked in hole  144  in base  22  by drawing section  148  upward utilizing a threaded rod (not shown) manipulated by handle  152 , a structure like that used for securing a bicycle handlebar post to the front forks. Predetermining alternative positioning of post  142  may be facilitated by receiving a spring-loaded pin  154  positioned in base  22  in detents (not shown) in the back of post  142   
     Reproducible predetermined grinding angles may be achieved by controlling the height of tool rest surface  36  and the projection of a blade or cutter to be sharpened from tool holder  122 . Positioning a tool such as chisel  120  in tool holder  132  and securing it with proper projection of the blade  123  may be understood by reference to FIGS. 8-11. As can be well understood by reference to FIG. 8, blade  123  is secured in tool holder  122  by clamping the blade between the lower surface  156  of tool holder body  126  (see FIG. 10) and the upper surface  158  of holder bar  128  by tightening thumb screws  130  to draw bar  128  toward body  126 . In some instances, such as when a skew chisel (such as skew chisel  121  shown in FIG. 10) is being secured in tool holder  122 , it is desirable to have pins for the chisel  121  to bear against. These may be provided by positioning screws  158  having cylindrical heads in surface  156 , of tool holder body  126 , as illustrated in FIG.  10 . When not in use, such screws  158  can be positioned on body  122  as shown in FIGS. 8 and 9, where they are out of the way. 
     A chisel  120  having a cutting arris  160  that is square to the blade  123  and can be positioned square in the holder  122  by positioning one side  145  of the blade  123  against a registration surface  143  (visible in FIG. 10) of the holder  122  body  126 . 
     A select predetermined projection of blade  123  from tool holder  128  is virtually always desired. Among other ways, such predetermined projection may be achieved as follows. 
     In order for a tool such as blade  123  to be properly positioned in tool holder  122 , it is necessary for the existing (or desired) cutting arris  160  to be parallel to the front edge  162  of tool holder body  126  and a predetermined distance from body  126 , and, more specifically, a predetermined distance from the arcuate surfaces  132  of feet  134  of tool holder  122  that ride on tool rest surface  36 . Such projection may be achieved by positioning the arcuate surfaces  132  in a predetermined location and adjusting blade  123  until arris  160  is at a location a predetermined distance from the arcuate surfaces  132 . This may be accomplished as illustrated in FIG. 11 by positioning post  142  of tool rest  138  a predetermined projection from base  22 , positioning tool holder  122  with arcuate surfaces  132  on tool rest  138 , and then adjusting the position of blade  123  in tool holder  122  until cutting arris  160  contacts the knob  162  on thumbscrew  102 . After blade  123  projection from holder  122  has been set, the height of tool rest  138  can be adjusted to achieve different desired grinding and sharpening angles, which may be read from indicia  146  on tool rest post  142 . 
     A second technique for positioning the projection of a tool to be sharpened, such as blade  123  of chisel  120 , utilizes a positioning jig  168 . Such a jig  168  may be formed of extruded aluminum so that a convex arcuate surface  174  is provided to receive concave arcuate surfaces  132  of jig  122  feet  134 . Arcuate surface  174  is fixed in relation to a first step  170  and second step  172 . As is illustrated in FIG. 9, the arris  160  of a blade  123  is positioned against step  170  with the feet  134  of tool holder  122  positioned on arcuate surface  174 , and the blade is then locked in place by rotating thumb screws  130  to clamp the blade  123  with bar  128 . Blades having shorter projection can be positioned instead by reference to step  172 , which will provide a different grinding angle for a particular position of tool rest  138 . However, most desired grinding angles can still be achieved by raising or lowering tool rest  138 . 
     As will be understood by those skilled in the art in light of the description above and the accompanying drawings, other tool holders can be fabricated for holding other tools to be sharpened utilizing the system  20  of this invention. For instance, tool holders can be made to grasp considerably wider or longer blades such as, for instance, planer blades or jointer knives. 
     Similarly, alternative jigs and methods can be utilized for setting the projection of blades from tool holder  122  or alternative tool holders. Additionally, alternative tool rests can easily be substituted for the tool rest  138  illustrated and described herein by, for instance, fabricating different tool rest structures that attach to post  142  received in posthole  144  in base  22 . 
     Alternatives to platters  106  may also be attached to and used on turntable  30 . For instance, a felt buffing wheel can be mounted on turntable  30  by passing a bolt through a washer and the wheel (and through a buffing wheel bushing if needed) and into the threaded hole  98  in disk  94 . A spacer may be desirable between turntable  30  and the buffing wheel in order to raise the buffing wheel above the turntable and thereby make the edge of the buffing wheel more accessible. 
     Particles and debris from sharpening and grinding can be drawn from the turntable  30  area into ports  181  in base  22  (see FIG. 4) below tool rest  138  and from the grinding wheel  32  or belt  34  into a grinder port  189  in the base  22  adjacent to the wheel  32  or belt  34 . Such a grinder port  189  may be located, as shown in a broken line in FIG. 3, on the backside of upstanding portion  190  (indicated in FIG. 4) of base  22 . When the grinding wheel  32  or belt  34  is in use, ports  181  may be covered by shutters  182  that may be made of sheet metal such as brass or other appropriate materials. Ports  181  and the grinder port  189  communicate with a duct formed within base  22  by duct cover  184  (see FIG. 3) to which a vacuum system, such as a vacuum cleaner, shop vacuum or dust collector, may be attached at vacuum opening  186  in base  22  (see FIGS.  1  and  4 ). The duct under cover  184  also ensures that abrasive laden air remains isolated from the airflow created by turntable  30  blades  76  and described above for motor cooling and drivetrain cleanliness purposes. Vacuum opening  186  can be closed by a cap  188  when not in use. 
     As will be readily understood by reference to the forgoing description, the accompanying drawings and following claims, numerous other modifications can be made in the power sharpening system of this invention without departing from the spirit of the invention or the scope of the following claims.