Abstract:
An apparatus for sharpening blades, such as those used for mowing. A rotary grinder is mounted within an extensible, retractable, and rotatable support assembly. Lockable, rotational adjustment of the position of the grinder about three axes, and translational movement along one axis is thereby provided. A spring attached to one end of the assembly counter-balances the weight of the grinder. An adjacent blade holding fixture maintains the workpiece at a predetermined angle for grinding. A toggle clamp, edge alignment keepers, and a registration pin secure the blade in place. An adapter fixture, including a toggle clamp and an alignment recess, attaches to one end of the blade holding fixture. The adapter fixture has an angled shelf to orient and secure smaller, contoured blades requiring a different edge grinding angle. Once the support assembly is adjustably secured, the grinder is moved along the cutting edge of the blade for sharpening.

Description:
PRIORITY CLAIM 
     Pursuant to the provisions of 35 U.S.C. §119(e)(1), Applicant claims the priority of U.S. Provisional Patent Application Ser. No. 61/849,653, filed Jan. 30, 2013. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to improvements in devices for sharpening blades that are used for cutting grass, sod, or other plant matter. More particularly, the invention pertains to an apparatus incorporating an extensible, retractable, and rotationally adjustable multi-axis support assembly for a rotary grinder, and a blade holding fixture that maintains the workpiece at a predetermined angle for grinding. 
     2. Description Of the Prior Art 
     The prior art includes a number of approaches directed toward the task of sharpening mower blades. For example, U.S. Pat. No. 7,918,715, issued to Clark et al., discloses a Device And Method For Sharpening Blades. A fixture in the &#39;715 Patent, holds the blade to be sharpened in the desired position. An elevated horizontal shaft is slidably coupled by a handle bar whose end adjustably supports a rotary grinder. 
     In U.S. Pat. No. 6,761,623, granted to Baker, an Apparatus And Method For Sharpening Blades At A Predetermined Angle, are disclosed. Included in Baker&#39;s apparatus are a blade retention and positioning mechanism, a blade sharpening mechanism, and a guide rod for directing the blade sharpening mechanism laterally across the width of the apparatus. 
     Yet another Blade Sharpener employing a rotary grinder is shown in U.S. Pat. No. 7,967,666, issued to Messner. Messner&#39;s sharpener employs a blade support, a sharpener guide mounted to the blade support, and a sharpener mount. A rotary grinder is mounted on the end of the sharpener mount, so that the sharpener mount and the grinder may pivot about a sharpening axis to provide the desired sharpening angle on the blade, while allowing translational movement along the sharpening axis for sharpening the full extent of the cutting edge of the blade. 
     And, in U.S. Pat. No. 7,329,172, issued to Dieck et al., a Rotary Mower Blade Sharpener Having Movable Grinding Wheels is illustrated. The mower blade is mounted on a base plate. Grinding head assemblies are mounted on carriages slidably mounted on a respective rail. The rails are parallel to each other, and located on either side of the blade. The carriages are driven by an endless chain that moves them and the grinding assemblies in unison, so that the two opposing cutting edges of the blade can be simultaneously sharpened. 
     Another approach to sharpening mower blades is to maintain the grinding apparatus stationary, and then move the cutting edge of the mower blade into and out of engagement with the abrasive wheel of the grinding apparatus. Representative of this approach is the device shown in U.S. Pat. No. 6,786,806, granted to Maus, Jr. The &#39;806 Patent discloses a Rotary Mower Blade Sharpener using a conventional bench grinder in combination with a mower blade holder. As shown in  FIGS. 1 and 2 , the subject blade is slid into and out of engagement with the grinder&#39;s wheel. 
     Similarly, in U.S. Pat. No. 6,471,569, granted to Bernhard, a Rotary Mower Blade Grinder includes an adjustable support for receiving a rotary mower blade. The position of the blade is movable and adjustable, axially and transversely, to engage a grinding wheel  4 . 
     U.S. Pat. No. 4,736,544, issued to Greenquist, teaches a Blade Holder For Sharpening Lawnmower Blades. Grinder  52  is fixed in position, and the blade support plate  12  is movable, as explained in column 4, lines 5-9 of this reference. 
     An Apparatus For Sharpening Implements is disclosed in U.S. Pat. No. 5,218,787, granted to Rice. A conventional grinder  12  is mounted on a support post  34 . The apparatus has a movable carriage for holding the blade by means of a clamping wrench, so the blade can selectively be moved into engagement with a grinding wheel  22 . 
     Issues regarding the performance of prior art blade sharpening devices include inadequate means for precisely adjusting and maintaining the angle of the grinding wheel during the grinding process. Known prior art blade sharpening devices also lack features for securely maintaining the subject blade at a selected predetermined angle, so the cutting edge can be faithfully restored to manufactured specifications. And, such prior art devices do not include simple and reliable means for positioning, locking, and releasing blades in a blade holding fixture, specifically designed for sharpening a blade having either two opposing cutting edges, or a blade having a single edge with a complex cutting edge contour. 
     Therefore, it is an object of the apparatus disclosed herein to sharpen blades used for mowing, having different angles and contours for their cutting edges. 
     It is a further object herein, to mount and utilize a conventional rotary grinder within a rotatable, extensible, and retractable support assembly. 
     It is also an object herein to support a rotary grinder adjustably about three axes and along one axis for extension and retraction. 
     It is also an object herein detachably to position and secure a mower blade at a number of different predetermined angles, for sharpening the cutting edge properly. 
     These and other objects will become apparent in the specification and the detailed description of the preferred embodiment, to follow. 
     SUMMARY OF THE INVENTION 
     The apparatus herein is useful for sharpening blades, such as those used for mowing grass or cutting other plant material. A frame or base, generally horizontal to the ground, is maintained at a convenient work height by downwardly extending legs. The frame or base may also be mounted on a workbench, to provide identical utility in a more permanent setting. 
     A grinder support assembly includes a support member having a lower end attached to the frame, and extending upwardly therefrom. The grinder support assembly also includes a three-way pivot, having a fixed portion mounted to the upper end of the support member. The three-way pivot allows rotation and adjustment of the position of its movable portion, about a generally horizontal first axis, second axis perpendicular to the first axis, and third axis perpendicular to the second axis. The three-way pivot also includes means for selectively locking its movable portion to the extent and manner necessary to undertake a grinding operation. 
     The grinder support assembly also includes an elongated grinder support arm. The grinder support arm has a first end mounted to the movable portion of the three-way pivot. A grinder mount is secured to a second end of the grinder support arm, remote from the three-way pivot. The grinder support arm is extensible and retractable along its axis, providing for movement of the grinder mount, relative to the cutting edge of a blade to be sharpened. 
     A conventional hand grinder, having a rotatable grinding disk, is detachably secured within the grinder mount. The hand grinder may easily be removed from the grinder mount for servicing, or for use in another application. A dedicated grinder may also be used in lieu of the removable hand grinder. 
     The apparatus herein also includes a blade holding fixture, for securing the blade during the grinding process, at a selected predetermined angle. The blade holding fixture includes an inclined plate supported by a post mounted on the frame. The plate may include a registration pin, to assist in the alignment and positioning of a blade having a central hole, such as a lawn mower blade. The plate also includes means for detachably securing the blade over the plate, such as toggle clamps. After one cutting edge of a lawn mower blade is sharpened, the blade is released from the blade holding fixture, flipped around end for end, and secured in place, so the other cutting edge can be sharpened. 
     An adapter fixture is also provided, for securing smaller blades having only one cutting edge to be sharpened. Such blades may also have a complex contour to the cutting edge, resembling a ramp or curve in a portion of the cutting edge. The adapter fixture includes a toggle clamp and edge alignment keepers to secure the blade. The adapter fixture may conveniently be attached to one end of the blade holding fixture, and its shelf may also be angled so that blades requiring a different edge grinding angle than a conventional blade, may be sharpened. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the grinding apparatus of the present invention; 
         FIG. 2  is a perspective view of the grinding apparatus with a typical rotary lawn mower blade secured in place on the blade holding fixture; 
         FIG. 3  is a perspective view as in  FIG. 2 , showing the grinder in position for engaging the blade and resurfacing the cutting edge through extension and retraction of the grinder support arm; 
         FIG. 4  is a close-up perspective of the front side of the three-axis pivot of the grinder support assembly; 
         FIG. 5  is a close-up perspective of the rear side of the three-axis pivot, showing rotational adjustment of the grinder support arm about a generally horizontal, first axis; 
         FIG. 6  is a view as in  FIG. 4 , showing rotational adjustment of the grinder support arm about a second axis, perpendicular to the first axis; 
         FIG. 7  is a view as in  FIG. 4 , showing rotational adjustment of the grinder support arm about a third axis, perpendicular to the second axis; 
         FIG. 8  is a fragmentary side elevational view of the rear side of three-axis pivot, showing rotational adjustment of the grinder support arm about the first axis; 
         FIG. 9  is a fragmentary end elevational view of the three-axis pivot, showing rotational adjustment of the grinder support arm about the third axis; 
         FIG. 10  is a fragmentary top plan view of the three-axis pivot, showing rotational adjustment of the grinder support arm about the second axis; 
         FIG. 11  is an exploded, fragmentary perspective view of the blade holding fixture, the adapter fixture, and the single cutting edge blade with a complex contour; and, 
         FIG. 12  is a fragmentary perspective view of the adapter fixture holding the single edge blade, mounted on one end of the blade holding fixture. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning now to the drawings, and in particular, to  FIG. 1 , the apparatus  11  for sharpening blades is disclosed. The apparatus  11  includes a frame  12 , preferably in the form of a plate. The frame  12  may include a plurality of legs  13 , to maintain the frame  12  in spaced relation from the ground or floor at a convenient working height. Alternatively, legs  13  may be eliminated entirely if it is desired to mount frame  12  directly upon a workbench, or other work surface. It should also be noted that before any grinding operations are undertaken, it is generally advisable to level frame  12  to enhance the ease and accuracy of using the apparatus  11 . 
     The apparatus  11  further includes a grinder support assembly  14 , shown in its entirety in  FIG. 1 . Grinder support assembly  14  includes a vertically extending support member  16  having a lower end  17  attached to the upper surface  15  of frame  12 . 
     Support assembly  14  also includes a three-way pivot  18 , having a fixed portion  19  mounted to an upper end  21  of support member  16 . A bolt  22  passes through an aperture in upper end  21 , and is secured on the rear side of member  16  by fixed portion  19 , including a rear nut  23  and a locking nut  24 . The threaded shaft  26  of bolt  22 , passes through and is threadably engaged by nuts  23  and  24 , defining a first horizontal axis  27  of rotation for the pivot  18 . 
     Being capable of rotation about its axis  27 , bolt  22  is the first element of movable portion  28  of three-way pivot  18 . Rear nut  23  may be adjusted for tightness against upper end  21 , providing the desired amount of resistance to rotation of bolt  22  about axis  27 . Locking nut  24  may be tightened against nut  23 , when a fixed rotational position for bolt  22  is desired. Locking nut  24  will also keep nut  23  from loosening under vibration. 
     One flat on the side of a transition nut  29  is welded to the head of bolt  22 . A transition bolt  31  has a threaded transition shaft  32  which threadably engages a transition nut  29 . Threaded transition shaft  32  defines a second axis  33  of rotation, which is perpendicular to first axis  27 . A locking nut  34  is also provided on transition shaft  32 , so that when shaft  32  is in the desired rotational position, nut  34  may be tightened against nut  29 , locking shaft  32  in that position. 
     The next element of movable portion  28  is a bar member  36 , preferably oriented on edge for maximum resistance to bending. An edge of one end of bar  36  is welded to the head of transition bolt  31 , as shown most clearly in  FIGS. 8 and 10 . The head of a bar bolt  37  is welded to the same end of bar member  36 , adjacent transition bolt  31 . Bar bolt  37  includes a threaded bar shaft  38 , which threadably engages a bar nut  39 . Threaded bar shaft  38  defines a third axis  41  of rotation, which is perpendicular to second axis  33 . A locking nut  42  is also provided on bar shaft  38 , so that when shaft  38  is in the desired rotational position, nut  42  may be tightened against nut  39 , locking shaft  38  in that position. 
     The lower side of a connection plate  43  is welded to an upper flat on bar nut  39 . A first segment  44  of elongated grinder support arm  46 , is welded to the upper side of connection plate  43 . Connection plate  43  is the last of the elements comprising the movable portion  28  of three-way pivot  18 . 
     It should be apparent to one of ordinary skill in the art that the three-way pivot arrangement just described, can be accomplished in a number of ways without departing from the advantages provided by the disclosed structures. By way of example only, hinged systems, ball and socket combinations, and block and journal bearing constructions could all accomplish the same result with equivalent structures having the same relational features. 
     As shown in  FIG. 1 , first segment  44  is located at a first, or proximate end of grinder support arm  46 . Grinder support arm  46  also has a second, or distal end, at the far terminus of a second segment  47 . Preferably, segments  44  and  47  of support arm  46  are in telescoping relation, so that adjustments in the effective length of arm  46  and the resultant position of the second end may readily be made. In other words, segment  47  may be telescopically extended or retracted with respect to segment  44 . 
     Positioned on the second end of grinder support arm  46 , attached to second segment  47 , is a grinder mount  48 . Grinder mount  48  may comprise a hinged collar, strap, or other clamp arrangement, adapted to secure a conventional hand held grinder  49  in place on the remote end of arm  46 . Grinder mount  48  is preferably designed to allow the quick installation and removal of grinder  49 , so it can be serviced or used for another purpose. It is also apparent that a grinder solely dedicated, and essentially permanently mounted on the end of grinder support arm  46 , will also prove advantageous for some applications. Grinder  49  will typically include an integral handle  51 , which is useful for positioning and for manipulating the movement of the grinder  49 , for the purposes of the apparatus  11  herein. 
     For the purpose of counter-balancing the weight of the grinder  49  mounted on the remote end of the grinder support arm  46 , bias means is applied to other end of bar  36 . Bias means is readily accomplished by interposing a spring  52  between bar  36  and a connection block  53 , mounted on the upper surface  15  of frame  12 .  FIGS. 2 and 3  illustrate that as grinder  49  is moved downwardly, spring  52  stretches slightly, providing downward bias forces on the other end of bar  36 , tending to restore the original position of the grinder support arm  46 . This also makes preliminary adjustments and handling of the grinder during a grinding operation much easier than it would otherwise be. 
     The apparatus  11  also includes a blade holding fixture  54 , supported in spaced relation above frame  12  by a post  56 . Blade holding fixture  54  includes an inclined plate  57  mounted on the upper end of post  56 . Plate  57  is preferably inclined at approximately the same slant, or angle, as the cutting edge of the blade to be sharpened. This inclination is selected so that when a blade is mounted on the blade holding fixture, the cutting edge  55  of the blade  60  will generally be horizontal for the grinding operation. This facilitates ease and accuracy in the grinding operation. 
     The angles of the cutting edges of a typical rotary mower blades may vary to some extent, but generally, they fall within in the range of 25° to 40°, with 30° being a popular and common angle. It is apparent that the connection between the upper end of post  56  and the underside of plate  57  may be a weld, holding the plate  57  at a fixed, standard inclination. Alternatively, an adjustable connection may be provided through a hinge or another rotatable arrangement so that blades having cutting edges of different angles may be accommodated by the apparatus  11 . 
     For alignment with and attachment to a drive shaft, rotary lawn mower blades typically include a centrally positioned shaft aperture. To utilize that aperture advantageously, inclined plate  57  includes a registration pin  58  extending upwardly from the blade supporting surface. The registration pin  58  is sized and configured to provide a snug fit within the blade&#39;s shaft aperture. Inclined plate  57  also includes at least one upwardly extending edge alignment stop  59 , located along a lower edge of plate  57 . Alignment stops  59  are effective to assist in the placement of a blade  60  on inclined plate  57 , as illustrated in  FIGS. 2 and 3 . 
     Inclined plate  57  plate also includes means for detachably securing the blade  60  over the blade supporting surface of the plate. For that purpose, at least one toggle clamp  61  is mounted on plate  57 .  FIG. 1  shows toggle clamp  61  in a raised position, in preparation for the installation of a blade  60  onto inclined plate  57 .  FIGS. 2 and 3  show toggle clamp  61  in a lowered, clamping position, after blade  60  has been installed. 
     After blade  60  has been clamped into place on plate  57 , the adjustment and locking features of the three-way pivot  18  are utilized to place grinding wheel  62  of the grinder  49  in the proper location and at the proper inclination, so that accurate grinding of the cutting edge  55  can take place. After handle  51  is grasped by the user, grinder  49  is actuated and the wheel  62  is moved along the surface and contour of the cutting edge  55  to restore its sharpness and surface. Depending upon the nature of the cutting surface  55 , movement of the grinder  49  inwardly or outwardly, through the feature of the telescoping grinder support arm  46 , is made possible. See.  FIG. 3 . Also, a user of the apparatus  11  may prefer one direction of movement of the grinder  49 , through relative extension or retraction of the support arm  46 , to be more comfortable or easier to control. After a pass across a cutting edge  55  is made, the direction of movement of the grinder  49  may be reversed, or the grinder  49  may be lifted so that another pass along the same direction may be made. 
     With one cutting edge  55  on one end of the blade  60  sharpened, the blade  60  is flipped end for end, so the cutting edge  55  on the other end can be sharpened. In that process, the toggle clamp  61  is released, and the blade  60  is flipped around, repositioned on the inclined plate  57 , and re-clamped in place by clamp  61 . Then, grinding of the other cutting edge  55  can be undertaken, as just described. 
     There are other mower blades that differ in size and configuration from the typical rotary lawn mower blade  60 , described above. For example, certain mowers used at golf courses and elsewhere where extremely low and accurate cutting is required, use a plurality of short blades having a single, but complex cutting edge, instead of a single blade having cutting edges at both ends.  FIGS. 11 and 12  show such a short mower blade  63 , and the special adapter fixture  64  designed to accommodate its features. 
     Blade  63  includes an attachment bore  66  and a complex, contoured cutting edge  67 . It should be noted that cutting edge  67  includes a ramp-like inflection  68 , approximately midway along its length. It is this inflection  68 , that makes sharpening blade  63  so difficult, because the surface of the cutting edge  67  effectively rises when passing from right to left. The current practice known to Applicant, is simply to discard such blades  63 , after they become dull. However, through the use of adapter fixture  64 , blades  63  can successfully be re-sharpened, providing even greater utility to the apparatus  11 . 
     Adapter fixture  64  includes a blade support plate  69 , which has several features worth noting. One end of plate  69  includes holes  71 , so that bolts  72  can pass through the holes and be threadably attached to an end of inclined plate  57 . These bolts, including edge alignment stop  59 , maintain the adapter fixture  64  securely in place with proper alignment. The other end of plate  69  includes a wedge plate  73 , which effectively adds another 3 to 5 degrees of inclination to the other end of plate  69 . This is done because the angle of the cutting edge  67  of blade  63 , is 3 to 5 degrees or so, greater than that of the cutting edge of the standard rotary mower blade. Secured over the wedge plate  73  is an alignment keeper  74 . The placement and configuration of alignment keeper  74  defines a recess  76  having a 90° corner to accommodate and maintain the alignment registration of blade  63 . 
     Adapter fixture  64  also includes a toggle clamp  76  which operates in exactly the same fashion as the previously described toggle clamp  61 . As shown in  FIGS. 11 and 12 , toggle clamp  76  is raised to allow the placement of blade  63  within recess  76 , and then lowered to secure blade  63  in place for sharpening. 
     Blade  63  is sharpened in essentially the same way as blade  60 , except that the user must raise or lower the grinder  49  at the appropriate time during the grinding pass, so that the grinding wheel  62  follows the complex contour and inflection  68  of cutting edge  67 . The adaptability and adjustability of the apparatus  11  fitted with the adapter fixture  64 , ensures that a factory-like sharpened edge can be restored to blade  63 . 
     It should be noted that, as shown in the drawings, both blade  60  and blade  63  are designed for counter-clockwise rotation about their drive shaft or drive mechanism. However, some mower blades are designed for clockwise rotation, placing the cutting edge  55  or the cutting edge  67 , on the opposite side of the blade. For the purpose of sharpening such clockwise rotation blades, a simple modification can be made to the apparatus  11 , to make the position and orientation of the blade holding fixture  54  adjustable. 
     At the foot of post  56 , a transverse plate (not shown) is welded. A pair of holes may be drilled in the plate, in spaced relation, on either side of the post. Two pairs, and preferably three, pairs of corresponding bores are drilled through upper surface  15  of frame  12 . One set of the bores is selected for grinding blades designed for counter-clockwise rotation. Bolts and nuts in conjunction with the holes and bores, are used to secure the transverse plate to the frame  12 . 
     If it is desired to sharpen blades designed for clockwise rotation, the bolts and nuts are removed, and the blade holding fixture  54  is rotated 180°. The fixture  54  is then remounted to the frame  12 , through one of the other sets of bores. A particular set of bores is selected to place the post  56  and the fixture  54  in the proper spaced relation from the grinder  49 . The other set of bores allows the fixture  54  to accommodate wider blades, and maintain optimum spacing between the fixture  54  and the grinder  49  during the grinding process.