Abstract:
The present invention relates to an apparatus for sharpening a circular blade. The sharpening apparatus is adapted to be positioned adjacent a power-driven sharpening wheel at an angle. The sharpening apparatus includes an angularly adjustable tool holder for angularly positioning the circular blade against the power-driven sharpening wheel. The sharpening apparatus of the present invention also includes a blade holder that quickly and easily locks the circular blade into place for sharpening and releases the blade after sharpening is complete. The present invention provides a reasonably safe and efficient sharpening apparatus for circular blades that provides uniform, high quality sharpening of one-sided and two-sided blades of varying circumferences.

Description:
FIELD OF THE INVENTION 
   The present invention generally relates to an apparatus for sharpening a circular blade. More particularly, the invention relates to a sharpening apparatus that includes an adjustable tool holder for angularly positioning the circular blade against a power-driven sharpening wheel and a blade holder that allows for reasonably safe and efficient loading and removal of the circular blade that is being sharpened. 
   BACKGROUND OF THE INVENTION 
   Various apparatus for sharpening circular blades are known in the art. For example, U.S. Pat. No. 2,528,193 to Van Allen et al. entitled “Automatic Disk Blade Grinder” discloses a machine for grinding disk-type blades that is adjustable and power-operated for grinding the edge of a disk-type blade to a predetermined bevel and throughout the entire circumference of the blade. 
   In an apparatus for sharpening a circular blade, the part of the apparatus that holds the circular blade may be angularly adjustable in relation to the sharpening wheel. This is because circular blades having different circumferences require different angular positioning in relation to the power-driven sharpening wheel to ensure uniform sharpening, and a user wants to be able to use the same sharpening apparatus to sharpen circular blades of many different sizes. 
   Also, a sharpening apparatus for circular blades needs to be safe. A user engaged in blade sharpening attempts to sharpen circular blades as quickly and efficiently as possible, but circular blades are very sharp, requiring the user to take special precautions. Specifically, precautions should be taken when loading the blade onto the sharpening apparatus, when running the power-driven sharpening wheel during sharpening, and when removing the blade from the sharpening apparatus. 
   Additionally, the moving parts of a circular blade sharpening apparatus should be easy to manipulate so that a user can sharpen circular blades in an efficient manner. For example, if a user wants to sharpen one side of a two-sided circular blade and immediately switch to sharpening the other side of the blade, a sharpening apparatus should be provided with a blade holder or a blade loading and release mechanism that easily enables the user to remove the blade, turn it over, and quickly begin sharpening the second side. 
   Thus, a need exists in the art for a sharpening apparatus for circular blades wherein the moving parts of the apparatus are easy to manipulate so that the circular blade may be loaded onto and removed from the sharpening apparatus quickly and efficiently. A further need exists for a sharpening apparatus that is safe, where the user&#39;s hands and fingers come into contact with the blade as little as possible. The sharpening apparatus of the present invention addresses these and other needs. 
   SUMMARY OF THE INVENTION 
   The present invention relates to an apparatus for sharpening a circular blade. The sharpening apparatus includes: a platform and base assembly; a slidable standard that is capable of forward and rearward movement along the platform and base assembly; an adjustable tool holder carried by the slidable standard where the adjustable includes a rotatable shaft supported for rotation and a main body that is angularly adjustable; a blade holder for releasably locking the circular blade onto the apparatus in a plane perpendicular to a longitudinal axis of the rotatable shaft of the tool holder; and a power-driven sharpening wheel. 
   The sharpening apparatus of the present invention may be used to sharpen both one-sided and two-sided blades. For example, a one-sided circular blade used in a typical pizza cutter may be sharpened using the apparatus of the present invention. 
   The slidable standard slides along one or more rails mounted on the platform and base assembly. The slidable standard of the apparatus may be driven forward and rearward relative to the power-driven sharpening wheel either manually or mechanically. In embodiments where the slidable standard is mechanically driven toward and away from the power-driven sharpening wheel, the slidable standard may be driven by a motor, by hydraulics, or the slidable standard may be air-driven. 
   The angular positioning of the adjustable tool holder allows the sharpening apparatus of the present invention to sharpen blades of many different circumferences. While using the apparatus of the present invention for sharpening a circular blade, a handle attached to the rotatable shaft of the adjustable tool holder is turned, either manually or mechanically, to rotate the circular blade and thereby ensure that the entire circumference of the circular blade is sharpened uniformly. In embodiments where the handle attached to the rotatable shaft is turned mechanically during sharpening, a motor may be attached to the handle for turning the handle. 
   The blade holder of the apparatus present invention may include a threaded blade-centering pin that is used to load and lock the circular blade onto the sharpening apparatus. The blade holder may, alternatively, include a slidable locking cam with an inclined or wedged surface that engages a blade-centering pin and locks the blade-centering pin and the circular blade onto the sharpening apparatus. 
   The power-driven sharpening wheel employed in the present invention may be, for example, a grinding wheel, a honing wheel, a polishing wheel, a diamond wheel, a leather wheel, an aluminum oxide wheel, a rubber wheel, a composite wheel, or a CBN wheel. In various embodiments of the present invention, a power-driven sharpening wheel may be used that contains two wheels, one on the left side and one on the right side. For example, a power-driven sharpening wheel may be employed where the right wheel is a grinding wheel that creates a larger burr and the left wheel is a grinding wheel that creates a smaller burr, or vice versa. Typically, a “burr” is considered the rough protuberance, ridge, or area left on a metal blade after sharpening. A user of the sharpening apparatus of such embodiments may use the right grinding wheel first to sharpen the chosen blade and obtain a larger burr and then refine the blade using the left grinding wheel that creates a smaller burr. 
   Generally, the sharpening apparatus of the present invention can be described as comprising: a platform and base assembly; a slidable standard capable of forward and rearward movement along the platform and base assembly; an adjustable tool holder carried by the slidable standard, where the tool holder comprises a rotatable shaft supported for rotation, and a main body that is angularly adjustable; a locking member, where the locking member includes a removable blade-centering pin having an enlarged head on its remote end and a compressible member, and where longitudinal force is applied to the blade-centering pin so that the enlarged head of the blade-centering pin compresses the compressible member against an outer surface of the circular blade for securely holding the circular blade on the adjustable tool holder in a plane perpendicular to a longitudinal axis of the rotatable shaft of the tool holder; and a power-driven sharpening wheel. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A full and enabling disclosure of this invention, including the best mode known to one of ordinary skill in the art, is set forth in this specification. The following Figures illustrate certain preferred embodiments of the present invention, wherein: 
       FIG. 1  shows a left, front perspective view of a sharpening apparatus in accordance with a preferred embodiment of the present invention; 
       FIG. 2  shows a right, front perspective view of the sharpening apparatus of  FIG. 1 , where the slidable standard is shown being loaded and unloaded from the platform and base assembly of the apparatus; 
       FIG. 3  shows a left, side view of the slidable standard and the adjustable tool holder of an alternative embodiment of a sharpening apparatus of the present invention; 
       FIG. 4  shows a right, front perspective view of the sharpening apparatus of  FIG. 1 ; 
       FIG. 5  shows a left, side, exploded view of parts of the slidable standard, the adjustable tool holder, and the blade holder of the sharpening apparatus of  FIG. 1 ; 
       FIG. 6  shows two enlarged views of the blade holder, the circular blade to be sharpened, and the adjustable tool holder of the sharpening apparatus of  FIG. 1 ; 
       FIG. 7  shows a left, side view of a sharpening apparatus in accordance with a preferred embodiment of the present invention, where the power-driven sharpening wheel is provided with a safety eyeshield; 
       FIG. 8  shows a left, rear perspective view of the sharpening apparatus of  FIG. 1  in motion; 
       FIG. 9  shows a left, front perspective view of a sharpening apparatus in accordance with an alternative preferred embodiment of the present invention; 
       FIG. 10  shows a left, side, enlarged view of the standard, the adjustable tool holder, and the blade holder of the sharpening apparatus of  FIG. 9 , along with an inset enlarged view of the blade holder of the sharpening apparatus of  FIG. 9 ; 
       FIG. 11  shows a left, front perspective view of the sharpening apparatus of  FIG. 9 , where the standard is mounted on the right mounting area of the horizontally extending slidable base of the platform and base assembly; 
       FIG. 12  shows a left, side, exploded view of parts of the standard, the adjustable tool holder, and the blade holder of the sharpening apparatus of  FIG. 9 ; 
       FIG. 13A  shows a cross-sectional view of the parts of the blade holder of the sharpening apparatus of  FIG. 9 , where the blade holder is in an unlocked position; and 
       FIG. 13B  shows a cross-sectional view of the parts of the blade holder of the sharpening apparatus of  FIG. 9 , where the blade holder is in a locked position. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Reference now will be made to various embodiments of the present invention. Each embodiment is provided by way of explanation of the invention, not as a limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in this invention without departing from the scope or spirit of the invention. 
     FIG. 1  shows a first preferred embodiment of a sharpening apparatus in accordance with the present invention. The sharpening apparatus of  FIG. 1  includes a platform and base assembly A. Specifically, platform and base assembly A is provided with: a platform  1 OA, which may be flat; left rail  12 A and right rail  14 A, which extend lengthwise along the left and right sides of platform  10 A; and left stop  16 A and right stop  18 A. Platform  10 A, rails  12 A and  14 A, and stops  16 A and  18 A may be constructed out various materials including metals and plastics. More specifically, the parts of platform and base assembly A may be constructed of aluminum, bronze, brass, graphite, a rigid plastic, or the like. 
   The sharpening apparatus of  FIG. 1  further includes slidable standard B. The bottom portion of slidable standard B comprises a bearing. This bearing is configured so that slidable standard B can be loaded and unloaded, from the rear of platform  10 A, onto either of left rail  12 A or right rail  14 A and so that slidable standard B is able to slide along either rail  12 A or  14 A. For example, as shown in  FIG. 2 , the bottom portion of slidable standard B comprises a bearing having a modified “C-shape” that complements the modified “C-shape” of left rail  12 A and right rail  14 A. The arrows of motion in  FIG. 2  show how slidable standard B may be loaded or unloaded onto left rail  12 A or right rail  14 A. 
   It should be noted that even though  FIGS. 1 and 2  depict a slidable standard having a bearing with a modified “C-shape,” the bearing of the bottom portion of slidable standard B can be any linear bearing, including but not limited to, a round rail bearing, a square rail bearing, a wheel and channel bearing, a dovetail bearing, or a gothic arch bearing. Likewise, the left and right rails of platform and base assembly A can be any linear rail, including but not limited to, a round rail, a square rail, a wheel and channel-type rail, a dovetail-type rail, or a gothic arch rail. 
   As seen in  FIG. 2 , left stopping screw  20 A, which is threaded through left stop  16 A, will serve to stop slidable standard B from sliding too far along left rail  12 A into the power-driven sharpening wheel E. Similarly, if slidable standard B were being loaded onto right rail  14 A, right stopping screw  22 A, which is threaded through right stop  18 A, would serve to stop slidable standard B from sliding too far along right rail  14 A into power-driven sharpening wheel E. 
   Referring back to  FIG. 1 , slidable standard B may include, in certain embodiments, a bifurcated upper portion  30 B that provides a space between two vertically extending legs  32 B and  34 B. This bifurcated upper portion  30 B may also be described as yoke-shaped or y-shaped. In  FIG. 1 , the space that is provided between vertically extending legs  32 B and  34 B of bifurcated upper portion  30 B of slidable standard B houses an adjustable tool holder C. Specifically, adjustable tool holder C has a main body  40 C that fits into the space between vertically extending legs  32 B and  34 B. Main body  40 C of adjustable tool holder C is permanently secured in the space between vertically extending legs  32 B and  34 B by a pin that extends through hole  36 B (shown on leg  32 B), through main body  40 C, and through a hole (not shown in  FIG. 1 ) on leg  34 B that is the mirror image of hole  36 B. 
   It should be noted that in certain embodiments of the present invention, the upper portion of slidable standard B is not bifurcated. For example, as shown in  FIG. 3 , main body  40 C of adjustable tool holder C may be permanently secured in a space beside one vertically extending leg  34 B of upper portion  30 B of slidable standard B by a pin that extends through main body  40 C and through leg  34 B. 
   Referring to  FIG. 4 , main body  40 C of adjustable tool holder C may be angularly positioned relative to power-driven sharpening wheel E by pivoting through a range of motion established by hole  38 B on leg  34 B. Specifically, knob  42 C is attached to a screw that extends through hole  38 B and into a threaded hole running through main body  40 C. Knob  42 C is loosened to allow main body  40 C to be angularly positioned relative to power-driven sharpening wheel E, through upward and downward movement, depending on the circumference of the circular blade to be sharpened. Knob  42 C is tightened to secure main body  40 C in the desired angular position. 
   In certain preferred embodiments of the present invention, guide marks  44 C are provided on main body  40 C of adjustable tool holder C, as shown in FIG.  1 . For example, such guide marks  44 C may be added to main body  40 C by laser inscribing or the like. In such embodiments, the guide marks aid the user in angularly positioning main body  40 C so that a specific angle (for example, a 30° angle) is established for main body  40 C of adjustable tool holder C relative to power-driven sharpening wheel E, depending on the diameter of the circular blade to be sharpened. 
   Still looking to  FIG. 1 , main body  40 C of adjustable tool holder C contains a bore that extends longitudinally through main body  40 C. This bore allows rotatable shaft  46 C to extend through main body  40 C of adjustable tool holder C.  FIG. 5  provides an exploded view of some of the parts of the sharpening apparatus of the embodiment of  FIG. 1 , particularly slidable standard B and adjustable tool holder C. Specifically  FIG. 5  shows the combination of bushings  48 C and retaining rings  50 C that ensures that rotatable shaft  46 C does not move forwards or backwards inside the bore of main body  40 C. This combination of bushings  48 C and retaining rings  50 C also allows shaft  46 C to rotate freely within the bore of main body  40 C. Specifically, retaining rings  50 C fit into grooves  51 C on rotatable shaft  46 C to prevent forwards and backwards movement of rotatable shaft  46 C inside the bore of main body  40 C. It should be noted that in other embodiments of the present invention, snap rings are used in place of retaining rings  50 C, and in such embodiments, there is no need for rotatable shaft  46 C to contain grooves  51 C. 
   Referring back to  FIG. 1 , rotatable shaft  46 C of adjustable tool holder C is rotated using handle  52 C. Specifically, in preferred embodiments of the present invention, a user will turn handle  52 C clockwise throughout the entire time of blade sharpening to rotate shaft  46 C which in turn rotates the circular blade being sharpened and allows for uniform sharpening of the entire circumference of the circular blade. It should be noted that in certain embodiments of the present invention, handle  52 C is rotated manually by a user, while in other embodiments, handle  52 C is rotated mechanically, for example, by a motor. 
   The top of shaft  46 C of adjustable tool holder C is affixed to a blade-receiving member  54 C. This blade-receiving member  54 C may be generally cylindrical in shape with its bottom or rear portion having a reduced diameter as shown in  FIG. 1. A  smooth, flat surface of blade-receiving member  54 C is where the circular blade  60  to be sharpened will be loaded for sharpening. For example, the enlarged view shown in  FIG. 6  illustrates the smooth, flat surface  56 C of blade-receiving member  54 C where circular blade  60  to be sharpened will be loaded for sharpening. 
   Another facet of the sharpening apparatus of the present invention is blade holder D. Referring to  FIG. 6 , in certain preferred embodiments, blade holder D may be a removable, blade-centering pin that includes: a head  7 OD; a shoulder  72 D, where the diameter of shoulder  72 D corresponds to or fits the inside diameter (I.D.) of circular blade  60  to be sharpened; and a threaded portion  74 D. In some preferred embodiments, the center portion of head  70 D of blade holder D may be color coded to match some identifying color located on circular blade  60  to be sharpened or on the packaging of such circular blade  60 . This color coordination scheme allows a user to ensure quickly and easily that the correct sized blade holder is being used with the particular circular blade to be sharpened. 
   Still looking to  FIG. 6 , when loading circular blade  60  onto a sharpening apparatus in accordance with the present embodiment, the user can allow blade  60  to rest on shoulder  72 D of blade holder D while inserting threaded portion  74 D of blade holder D into hole  58 C that extends inside blade-receiving member  54 C. As seen in  FIG. 6 , hole  58 C is partially threaded to receive threaded portion  74 D of blade holder D. 
   In certain preferred embodiments, a standard fiber washer  76 D is provided as part of blade holder D. In such embodiments, standard fiber washer  76 D rests on shoulder  72 D of blade holder D, between the underside of head  70 D and circular blade  60  to supply proper friction or tension to blade  60  while sharpening and thereby prevent blade  60  from slipping while sharpening. It should be noted that instead of standard fiber washer  76 D, a rubber gasket, a lock washer, a foam washer, or the like could be used to provide friction and prevent blade  60  from slipping while sharpening. 
   As threaded portion  74 D of blade holder D is inserted into hole  58 C, the user holds head  70 D steady with one hand (for example, with the user&#39;s left hand) while turning handle  52 C clockwise (for example, with the user&#39;s right hand) until circular blade  60  rests against smooth, flat surface  56 C of blade-receiving member  54 C and the fit is hand-tight. 
   Thus, to summarize the above-described embodiment of the present invention with reference to  FIGS. 1 and 6 , a sharpening apparatus is shown where a user loads circular blade  60  onto blade-receiving member  54 C of adjustable tool holder C and locks circular blade  60  into place using blade holder D. Adjustable tool holder C is held by slidable standard B, which slides forward and rearward along either of rails  12 A or  14 A affixed to platform and base assembly A. Once the combination of slidable standard B, adjustable tool holder C, circular blade  60 , and blade holder D slides toward power-driven sharpening wheel E and once circular blade  60  is angularly positioned relative to power-driven sharpening wheel E, circular blade  60  is ready to be sharpened. 
   Looking back to  FIG. 1 , power-driven sharpening wheel E is provided for sharpening the circular blade, and wheel E and sits upon platform  10 A. In certain preferred embodiments, sharpening wheel E is secured to platform  10 A by locating pins (for example,  80 E). As mentioned above, power-driven sharpening wheel E comes into contact with circular blade  60  by way of the forward sliding movement of slidable standard B and by way of the angular positioning of adjustable tool holder C. 
   In certain preferred embodiments, power-driven sharpening wheel E may be provided with two wheels for working with circular blade  60 . For example, in  FIG. 1 , power-driven sharpening wheel E is shown as having left wheel  82 E, which might be a grinding wheel, as well as right wheel  84 E, which might be a finishing or polishing wheel. Additionally, in certain preferred embodiments, power-driven sharpening wheel E may be provided with certain safety features, such as an eyeshield  88 E, as shown in  FIG. 7 , a left side view of a sharpening apparatus in accordance with certain preferred embodiments of the present invention. Eyeshield  88 E protects the user&#39;s eyes while sharpening circular blades. Two mounting areas  86 E are shown in  FIG. 1  for mounting such an eyeshield. 
   Looking to  FIG. 8 , there is shown a left rear perspective view of a sharpening apparatus in accordance with the embodiment of the present invention depicted in FIG.  1 .  FIG. 8  includes arrows of motion which represent the clockwise rotation of handle  52 C, which causes the rotation of circular blade  60 . As stated above, the constant rotation of circular blade  60  (caused by the constant rotation of handle  52 C either manually or mechanically) while sharpening helps to ensure that the entire circumference of circular blade  60  will be sharpened uniformly. Note that during sharpening, a user might firmly hold slidable standard B steady in a forward direction to ensure that slidable standard B does not travel rearward along left rail  12 A. 
   Thus, referring to  FIG. 8  (but also generally) a user may turn on power-driven sharpening wheel E, angularly position adjustable tool holder C according to the size of circular blade  60  to be sharpened, slide the slidable standard B toward power-driven sharpening wheel E, allow circular blade  60  to come into contact with power-driven sharpening wheel E for sharpening, and immediately begin turning handle  52 C to ensure uniform sharpening all the way around the circumference of circular blade  60 . 
     FIG. 9  shows an alternative preferred embodiment of a sharpening apparatus in accordance with the present invention. Like the sharpening apparatus shown in  FIG. 1 , the sharpening apparatus of  FIG. 9  also includes a platform and base assembly A, where assembly A is provided with platform  10 A, left rail  12 A, right rail  14 A, left stop  16 A, right stop  18 A, left stopping screw  20 A, and right stopping screw  22 A. Platform and base assembly A of the apparatus depicted in  FIG. 9  also includes left rear stop  17 A, and right rear stop  19 A. 
   Furthermore, platform and base assembly A includes a horizontally extending slidable base AA. Slidable base AA slides along left and right rails  12 A and  14 A, and bearings  13 A and  15 A are provided for base AA so that it slides easily along rails  12 A and  14 A. Left rear stop  17 A and right rear stop  19 A mounted on platform  10 A limit the rearward movement of slidable base AA. 
   The sharpening apparatus depicted in  FIG. 9  also includes a standard B. In certain embodiments, standard B has a bifurcated upper portion  30 B, which provides a space between two vertically extending legs  32 B and  34 B that houses adjustable tool holder C. However, in other embodiments, the upper portion of standard B is not bifurcated (as depicted with regard to a previous embodiment in FIG.  3 ). 
   Looking to  FIG. 10 , an enlarged view of standard B is included, where standard B has a base  31 B that includes an extended lip  33 B and a receiving hole  35 B. Base  31 B of standard B, with its extended lip  33 B and receiving hole  35 B, allows standard B to be secured on either of two mounting areas of slidable base AA. For example, referring back to FIG.  9 . standard B is shown mounted on a left mounting area of slidable base AA, while right mounting area  10 AA is left open. Specifically in  FIG. 9 , standard B has been placed on the left mounting area of slidable base AA with its extended lip  33 B fitting securely under a left lip receiver  37 B. Once extended lip  33 B is fit under left lip receiver  37 B, a left knob  27 B is tightened so that a screw fits snugly into the receiving hole located at the back of base  31 B of standard B. 
     FIG. 11  shows an alternative embodiment of the sharpening apparatus of  FIG. 9 , where standard B is mounted on the right mounting area of slidable base AA. In  FIG. 11 , standard B has been placed on the right mounting area of slidable base AA with its extended lip  33 B fitting securely under a right lip receiver  39 B. As extended lip  33 B of standard B is fit under right lip receiver  39 B, right knob  29 B is tightened so that a screw fits snugly into the receiving hole located at the back of base  31 B of standard B. 
     FIG. 9  shows left stopping screw  20 A, which is threaded through left stop  16 A, and which will serve to stop the combination of standard B and slidable base AA from sliding too far along rails  12 A and  14 A into the power-driven sharpening wheel E when standard B is mounted on the left mounting area of slidable base AA. Similarly, as shown in  FIG. 11 , if standard B is mounted on the right mounting area of slidable base AA, right stopping screw  22 A, which is threaded through right stop  18 A, will serve to stop the combination of standard B and slidable base AA from sliding too far along rails  12 A and  14 A into power-driven sharpening wheel E. 
   Returning to  FIG. 10 , the space that is provided between vertically extending legs  32 B and  34 B of bifurcated upper portion  30 B of standard B houses adjustable tool holder C. Just as described in detail above with regard to previous embodiments, adjustable tool holder C has a main body  40 C that fits into the space between vertically extending legs  32 B and  34 B. Also, as described above, main body  40 C of adjustable tool holder C is permanently secured in the space between vertically extending legs  32 B and  34 B by a pin that extends through hole  36 B (shown on leg  32 B), through main body  40 C, and through a hole (not shown in  FIG. 10 ) on leg  34 B that is the mirror image of hole  36 B. Main body  40 C may be angularly positioned relative to power-driven sharpening wheel E by loosening and tightening knob  42 C as described in detail above. In the present embodiment, guide marks  44 C may be provided on main body  40 C of adjustable tool holder C to aid a user in angularly positioning main body  40 C at a specific angle, depending on the diameter of the circular blade to be sharpened. 
   Like the embodiments of the present invention shown in FIG.  1  and described above,  FIG. 10  shows that main body  40 C of adjustable tool holder C contains a bore that extends longitudinally through main body  40 C and that allows rotatable shaft  46 C to extend through main body  40 C. In the embodiment of  FIG. 10 , a combination of bushings and retaining rings ensures that rotatable shaft  46 C cannot move forwards or backwards inside the bore of main body  40 C and allows shaft  46 C to rotate freely within the bore of main body  40 C. 
   During sharpening, a user will turn handle  52 C to rotate shaft  46 C and thereby allow for uniform sharpening of the entire circumference of the circular blade beirig sharpened. In some preferred embodiments, handle  52 C is rotated manually by a user during sharpening, while in other embodiments, handle  52 C is rotated mechanically. 
   Still looking to  FIG. 10 , the top of shaft  46 C of adjustable tool holder C is affixed to blade holder D, a blade holder that differs from the blade holder described above with regard to the embodiments of the present invention depicted by  FIGS. 1-8 . Generally, blade holder D of  FIG. 10  includes a slidable locking cam  92 D that allows for efficient loading and removal of the circular blade  60  to be sharpened. The major components of blade holder D, as shown in FIG.  10  and its inset, include: a cam guide disc  90 D; a slidable locking cam  92 D; a retaining disc  94 D; and a removable blade-centering pin  96 D, all of which work together to hold circular blade  60  in place on the apparatus while sharpening. 
   Looking to  FIG. 12 , there is shown an exploded view of parts of standard B, adjustable tool holder C, and blade holder D. With regard to the parts of blade holder D, cam guide disc  90 D contains a slot  91 D for receiving slidable locking cam  92 D. Slot  91 D on cam guide disc  90 D contains center hole  100 D as well as two locating pins  102 D. Locating pins  102 D create a sideways range of motion through which slidable locking cam  92 D moves from an unlocked position to a locked position (described in more detail below). Cam guide disc  90 D is also provided with holes  104 D to receive the screws used to secure retaining disc  94 D and slidable locking cam  92 D to cam guide disc  90 D. 
   Still looking to  FIG. 12 , slidable locking cam  92 D is placed into slot  91 D of cam guide disc  90 D using locating pins  102 D as a guide. Slidable locking cam  92 D is secured to the blade holder assembly by retaining disc  94 D and socket head screws  106 D that permanently fasten retaining disc  94 D to cam guide disc  90 D via holes  104 D. 
   Circular blade  60  may then be loaded onto removable blade-centering pin  96 D. A compressible washer  112 D may rest on the shoulder of blade-centering pin  96 D to supply friction or tension between circular blade  60  and the underside of the head of blade-centering pin  96 D, thereby preventing circular blade  60  from slipping during sharpening. Compressible washer  112 D may be made of a rubberized material or the like. 
   The combination of blade-centering pin  96 D, compressible washer  112 D, and circular blade  60  is then loaded onto the sharpening apparatus. Specifically, removable blade-centering pin  96 D is inserted through the center hole of retaining disc  94 D, through a circular hole in slidable locking cam  92 D and into center hole  100 D of cam guide disc  90 D. This constitutes an unlocked position for circular blade  60  on the sharpening apparatus of the present embodiment. 
     FIGS. 13A and 13B  are included to provide more detail on how slidable locking cam  92 D is used to hold circular blade  60  in a locked position on the sharpening apparatus. Specifically,  FIG. 13A  depicts the unlocked position, described above, wherein the combination of blade-centering pin  96 D, compressible washer  112 D, and circular blade  60  has been loaded onto the sharpening apparatus by inserting removable blade-centering pin  96 D through the center hole of retaining disc  94 D, through the circular hole in slidable locking cam  92 D and into the center hole of cam guide disc  90 D. 
   As shown in  FIG. 13A , slidable locking cam  92 D includes a rear inclined surface  114 D as well as two flanges  110 D that allow a user to grasp slidable locking cam  92 D and slide it from the unlocked to a locked position (and vice versa). As a user grasps flanges  110 D of slidable locking cam  92 D and slides cam  92 D upward, rear inclined surface  114 D of slidable locking cam  92 D engages a portion of blade-centering pin  96 D, pulling blade-centering pin  96 D rearward and locking blade-centering pin  96 D into the locked position shown in FIG.  13 B. In the locked position, slidable locking cam  92 D retains the rear portion of blade-centering pin  96 D, thereby securing blade  60  to the apparatus for sharpening. A safety feature of the apparatus of the present embodiment involves flanges  110 D of slidable locking cam  92 D being positioned so that they extend away from circular blade  60  rather than toward circular blade  60 . 
   In other embodiments of the present invention, a sharpening apparatus is provided where the forward and rearward movement of the circular blade to be sharpened, toward and away from the power-driven sharpening wheel, is accomplished by the forward and rearward movement of the rotatable shaft through the bore inside the main body of the adjustable tool holder. For example, in  FIG. 1 , rather than slidable standard B moving forward and rearward, toward and away from power-driven sharpening wheel E, slidable standard B would be held stationary on either left rail  12 A or  14 A, and rotatable shaft  46 C would move circular blade  60  toward and away from power-driven sharpening wheel E by sliding through the bore contained in main body  40 C of adjustable tool holder C. Likewise, in  FIG. 9 , rather than horizontally extending slidable base AA moving forward and rearward, toward and away from power-driven sharpening wheel E, horizontally extending slidable base AA would be held stationary on rails  12 A and  14 A, and rotatable shaft  46 C would move circular blade  60  toward and away from power-driven sharpening wheel E by sliding through the bore contained in main body  40 C of adjustable tool holder C. 
   It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only and is not intended as limiting the broader aspects of the present invention.