Abstract:
An improved hollow grinder bevel angle control wherein a height-attitude coupling mechanism links the height and attitude motions of an adjustable tool-rest, and a scale on a stationary portion of the grinder cooperates with a pointer on the height-attitude coupling mechanism to indicate a relationship between bevel angle and grinding wheel radius. The coupling mechanism is implemented with a linkage mechanism that provides a wide range of tool-rest adjustment, subject to the height-attitude relationship defined by the linkage. The pointer is mounted for rotation with the linkage mechanism about its fixed pivot point, and is user-adjustable so that a dimension from the fixed pivot point to the tip of the pointer coincides with the radius of the grinder wheel. The bevel angle scale is stationary with respect to movement of the linkage mechanism, and arranged so that the tip of the pointer sweeps across the scale as the linkage mechanism is adjusted through its full range of movement. The indicia on the scale reflect the height-attitude relationship defined by the linkage mechanism, such that the indicia coinciding with the tip of the pointer denotes the achieved bevel angle. A tool-rest lock mechanism selectively couples the linkage mechanism to the grinder housing to maintain a selected heigh/attitude relationship.

Description:
TECHNICAL FIELD 
     This invention pertains to hollow grinding machines, and more particularly to a mechanism for easily and accurately controlling the bevel angle of the grinder. 
     BACKGROUND OF THE INVENTION 
     Hollow grinders are commonly used for sharpening tool blades, and typically include a tool-rest for maintaining a desired orientation of the blade relative to the grinding wheel. This orientation determines the grinding angle (or bevel angle) with respect to the longitudinal axis of the tool blade. 
     The tool-rest is typically adjustable with two or more degrees of freedom to facilitate adjustment of the height and attitude of the tool blade, while maintaining a proper air gap between the tool-rest and the grinding wheel to prevent operator injury. Simultaneously achieving a desired bevel-angle and air-gap can be both difficult and time consuming, and most hollow-grinding machines have no mechanism for determining the bevel angle that will be achieved with a given height-attitude setting. The problem is exacerbated by the fact that the bevel angle not only varies with height-attitude setting, but also with grinding wheel radius, which decreases with use. Thus, the bevel angle obtained for a particular height-attitude setting on one wheel will be different if the tool is ground on a wheel of different radius. Accordingly, what is desired is a hollow grinder with a bevel angle control that is easily adjustable and that provides accurate bevel angle control despite variations in grinding wheel radius. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an improved hollow grinder bevel angle control wherein a height-attitude linkage mechanism restricts the height and attitude motions of an adjustable tool-rest to a prescribed relationship, and a scale on a stationary portion of the grinder cooperates with a pointer on the height-attitude linkage mechanism to indicate a relationship between achieved bevel angle and grinding wheel radius. According to the invention, the linkage mechanism is implemented with a stationary link and three movable links, defining a parallelogram. The first and second movable links are rotatable about fixed pivot points at one end, and the third movable link is coupled to the other (free) ends of the first and second movable links. The fixed pivot point for the first movable link is co-axial with the grinding wheel, and the tool-rest is supported on a shaft coupling the first and third links. The tool-rest is mounted for slidable adjustment parallel to the longitudinal axis of the first link to permit adjustment of the gap between the tool-rest and the periphery of the grinder wheel. 
     The pointer is mounted for rotation with the first link about its fixed pivot point, and is user-adjustable so that the distance from the fixed pivot point to the tip of the pointer coincides with the radius of the grinder wheel. The bevel angle scale is stationary with respect to movement of the linkage mechanism, and arranged so that the tip of the pointer sweeps across the scale as the linkage mechanism is adjusted through its full range of movement. The indicia on the scale reflect the height-attitude relationship defined by the linkage mechanism, such that the indicia coinciding with the tip of the pointer denotes the achieved bevel angle. A tool-rest lock mechanism selectively couples the linkage mechanism to the grinder housing to maintain a selected height/attitude relationship. 
     With the above-described apparatus, achieving a desired bevel angle merely involves adjusting the pointer length based on grinding wheel radius, raising or lowering the tool-rest via the linkage mechanism until the pointer tip coincides with the corresponding indicia on the bevel angle scale, and then locking the tool-rest in place with the tool-rest lock mechanism. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric view of a hollow bevel grinder according to this invention, having a height-attitude linkage mechanism, a tool-rest lock mechanism, and an iso-bevel angle scale. 
     FIG. 2 is a top view of the grinder of FIG.  1 . 
     FIG. 3 is an end view of the grinder of FIG. 1, sectioned through the axis of the grinding wheel. 
     FIGS. 4A and 4B are side views of the grinder of FIG. 1, illustrating different positions of the height-attitude linkage mechanism. 
     FIG. 5 is a side-view of the grinder of FIG. 1, sectioned in part to illustrate operation of the tool-rest lock mechanism. 
     FIG. 6 is a partial exploded view of the grinder of FIG.  1 . 
     FIG. 7 is an enlarged diagram of the iso-bevel angle scale on the grinder of FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings, and particularly to FIGS. 1-3 and  6 , the reference numeral  10  generally designates a hollow bevel grinder according to this invention. The grinding wheel  12  has a bushing  14  pressed into a central axial opening thereof, and a pair of washer bushings  16   a ,  16   b  on either side thereof. A spindle  18  passes through the washer bushings  16   a ,  16   b , supporting the wheel  12  for rotation about the spindle axis. The spindle  18 , in turn, is supported on a pair of flange bushings  20   a ,  20   b  mounted in a spindle support member  22 . A set-screw collar  24  defines an axial gap between the wheel  12  and the support member  22 , and a nut and washer  26  fastened onto the opposite end of spindle  18  clamps the washer bushing  16   a  against the collar  24 , fixing the axial position of the wheel  12 . An arcuate trough  30 , fixed to the spindle support member  22 , envelopes a lower portion of the wheel  12 , and may contain water or another suitable fluid for cooling and clog prevention. 
     As best seen in FIG. 3, the spindle support member  22  is mounted on a base member  32 , which in turn, is mounted on a grinder platform  34 . An electric motor  36 , also mounted on the platform  34 , is geared to rotate a drive pulley  38 , which is coupled via belt  40  to a pulley  42  fixed on the end of spindle  18 . Motor  36  operates at a fixed speed, and the pulleys  38 ,  42  are relatively sized to drive the wheel  12  at a suitable speed, such as 90 RPM. The grinding wheel  12  should rotate away from the operator when cooled by water to prevent water from deflecting off of the top of the tool and onto the operator. Nut  26  and spindle  18  should have right-hand threads for clockwise grinding wheel rotation to prevent loosening with use. 
     A tool-rest  48  has an upper surface  50  for supporting a tool or other article to be ground by wheel  12 . A grinding wheel opening  53  receives the wheel  12 , and the hidden portion of opening  53  may be contoured to prevent said tool-rest bottom from coming into contact with wheel  12  when grinding shallow tool bevels, as shown in FIG.  6 . The contour is determined by the desired minimum bevel-angle of grinder  10 , the grinding wheel diameter and the desired distance (typically, {fraction (1/16)} inch) between the front edge of said grinding wheel opening  53  and wheel  12 . Finally, a tool-rest guide groove  54  is provided as a miter gauge slot to assist in grinding bevels on skewed tools. 
     Tool-rest  48  is mounted on a tool-rest support member  56 , with a box slide interface, generally designated by the reference numeral  58 , that permits adjustment of the spacing between tool-rest  48  and wheel  12  without changing the relative orientation of the tool-rest  48  and wheel  12 . A gib clamp screw  60  is provided for locking the position of tool-rest  48  relative to support member  56  when the tool-rest  48  is positioned as desired. 
     The tool-rest support member  56  is mounted on a shaft  62  and rigidly secured thereon by one or more set-screws  64 . The portion of shaft  62  extending from support member  56  passes through a cylindrical portion  66  of a tongue  68  and is supported by a linkage mechanism  70 , which is described in detail below. A ring portion  72  of tongue  68  is contoured to match the exterior contour of arcuate trough  30 , and the ring portion  72  is laterally retained within a groove  74  defined by a pair of ridges  75 ,  76  formed on the exterior periphery of trough  30 . The tongue  68  is further maintained in position relative to the trough  30  by a clamp pad  78  disposed between the ring portion  72  and an eccentric cam  80 , as illustrated most clearly in FIG.  5 . The cam  80 , in turn, is supported for rotation within the base member  32  on camshafts  82 ,  84 . A user operated handle  86  is rigidly secured to the camshaft  84  to facilitate user rotation of the cam  80  for selectively raising and lowering the clamp pad  78  for respectively locking and unlocking the tongue  68  relative to the trough  30 . Due to the aforementioned connection between shaft  62  and the cylindrical portion  66 , the tongue  68  serves as a coupling for locking and unlocking the tool-rest  48  and linkage mechanism  70 . 
     The linkage mechanism  70  includes a stationary linkage support member  90  mounted on the base member  32 , and first, second and third movable links  92 ,  94  and  96 . A linkage pin  98  rotatably couples the first (upper) link  92  to a flange bushing  100  mounted in support member  90  that is coaxial with the grinder wheel  12 . The second (lower) link  94  is coupled to the camshaft  84 , and the third (vertical) link  96  is coupled between the movable ends of first and second links  92  and  94 . The second and third links  94 ,  96  are coupled via linkage pin  102 , whereas the first and third links are coupled via shaft  62 . Rotation of the shaft  62  with respect to the third link  96  is prevented by the set-screw  104 . The links  92 ,  94 ,  96  are free to rotate at each point of coupling, and snap rings  106 - 116  may be used to secure the links  92 ,  94 ,  96  on the respective pins  98 ,  102  and shaft  62 , as shown in the exploded view of FIG.  6 . 
     The links  92 ,  94  and  96  are sized so that the linkage mechanism resembles a parallelogram. Thus, the first and second links  92 ,  94  are essentially identical, and the third link  96  has an effective length (between pivot points) that corresponds to the distance between the centers of cam shaft  84  and flange bushing  100 . Also, the effective length of the first and second links  92 ,  94  is equal to the mean radius of the ring portion  72  of tongue  68  since the tool-rest  48  is coupled to the cylindrical portion  66 . Finally, the effective length of the third link  96  (and hence, the distance between camshaft  84  and flange bushing  100 ) should be at least as great as the effective length of the first and second links  92 ,  94  in order to avoid interference between the first and second links  92 ,  94 . A handle  122  is affixed to the third link  96 , and the user can move the handle up or down to rotate the first and second links  92 ,  94  in a plane parallel to the front face of linkage support member  90 , while the third link  96  remains perpendicular to the grinder platform  34 . Linkage sticking points caused by all members being collinear are never reached because all bevel-angles between 0 degrees and 90 degrees can be obtained by setting the first and second links  92 ,  94  to an angle less than 90 degrees with respect to the grinder platform  34 . 
     FIGS. 4A and 4B depict the linkage mechanism  70  in two different positions, providing grinding bevel angles of 90 degrees and 50 degrees, respectively. It will be seen that the third link  96  remains perpendicular with respect to the base member  32 , so that the attitude of the tool-rest upper surface  50  with respect to the base member  32  remains unchanged even though its height above base member  32  changes. 
     From the above description, it will be seen that the linkage mechanism  70  serves to couple the height and attitude of the tool-rest  48  in a prescribed relationship while maintaining the tool-rest support member  56  at a fixed distance from the axis of wheel  12 . A pointer  130  passes through the fixed pivot point of first link  92  and serves as a linkage position indicator. As shown in FIG. 6, the pointer  130  passes through openings  132 ,  134  in link  92  and linkage pin  98 . A set-screw  136  threaded into the exposed end of linkage pin  98  can be tightened or loosened to secure or release the pointer  130  for translation along its axis. In use, the extension of pointer  130  is adjusted to correspond to the radius of wheel  12  so that the tip  138  of pointer  130  circumscribes an arc segment corresponding to the wheel radius. See FIGS. 4A and 4B, where the wheel diameter is 10 inches, and the length of pointer  130  has been adjusted accordingly. 
     A scale plate  140  rigidly fastened to the linkage support member  90  is disposed between the pointer  130  and a scale  144  is affixed to the scale plate  140  so that the user can identify a point on the scale  144  corresponding to the position of the pointer tip  138 . Scale  144  is printed or engraved with a series of contour lines  150  representing lines of constant bevel-angle (i.e., iso-bevel lines) and a series of arc lines  152  that are concentric with linkage pin  98 . 
     FIG. 7 shows an example of an iso-bevel scale  144  with contour lines  150  ranging from 10 degrees to 90 degrees and arc lines  152  with radii ranging from 3 inches to 5 inches in ¼ inch increments. 
     When the pointer  130  has been adjusted in accordance with the wheel radius as described above, a desired bevel angle is achieved by adjusting the linkage mechanism  170  until the pointer tip  138  intersects the corresponding iso-bevel line  150 . Stated another way, the intersection of an iso-bevel contour line  150  with an arc line  152  of radius equal to that of grinding wheel  12  indicates the position that the pointer tip  138  must occupy to obtain the bevel-angle corresponding to the respective contour line  150 , when the distance from the centerline of linkage pin  98  to the pointer tip  132  is equal to the radius of wheel  12 . The tool being ground must be placed flat on the top surface  50  of tool-rest  48  to ensure that an accurate bevel-angle is achieved. The iso-bevel contour lines  150  can be constructed geometrically or by plotting the level curves of the equation:          β                   (     x   ,   y     )       =       arcsin        {       [       a        (     x   ,   y     )         r        (     x   ,   y     )         ]          sin   (       arcsin        [     y     r        (     x   ,   y     )         ]       +     arcsin        [           -   x                   δy       r        (     x   ,   y     )           a        (     x   ,   y     )         ]         )       }       -     90      °                              
     where β is the bevel-angle and x, y are Cartesian coordinates whose origin is located at intersection of the centerlines of pointer  130  and linkage pin  98 . The perpendicular distance between the longitudinal axis of said tool-rest support shaft  62  and the upper surface  50  of tool-rest  48  is denoted by the variable δ. The function r(x, y)={square root over (x 2 +L +y 2 +L )} is the radial distance from the origin of the x, y plane to the coordinates x, y at which the bevel-angle is to be calculated, and corresponds to the point of intersection between the centerline of linkage member  92  and the projection of the grinding wheel periphery onto such centerline. Since the tool-rest  48  and scale  144  are on opposite sides of the linkage member  92 , the iso-bevel contours must be calculated at (−x, −y) in order to reflect the 180° offset. The function a (x, y) is simply an intermediate term used to write the equation in compact form, and is defined as follows:          a        (     x   ,   y     )       =       δ                   y   2       +     R   2     +     2      R                 δ                 y                   y         x   2     +     y   2                                      
     In FIGS. 4A and 4B, it can be seen that the tool rest is inclined with respect to base member  32 . With such inclination, the 90° iso-bevel contour falls on a line parallel to base member  32 , as shown. Of course, other inclination angles are also possible, but it is generally desirable to configure the contour lines as shown. In any event, the angle of inclination for any given value of x may be determined by setting β equal to 90°, solving for y, and calculating the inclination angle i from: 
     
       
         i=arcian (y 90 /x 90 ) 
       
     
     where (x 90 , y 90 ) designates any point that lies on the 90° iso-bevel contour line. 
     Iso-bevel contours can be generated by numerical analysis and gridding software and the result imported into computer aided drafting software where labels may be applied. The CAD software can then be used to write plotter or computer numerical control (CNC) code that can be used to directly engrave the image onto scale  144 . The scale can also be photo-etched onto a brass or copper plate. 
     To summarize, achieving a desired grinding bevel angle with the bevel angle control mechanism of this invention simply involves adjusting the pointer  130  in accordance with the wheel radius, adjusting the linkage mechanism until the pointer tip  138  intersects the contour line  150  corresponding to the desired bevel angle, and rotating the handle  86  clockwise to lock the tool-rest  48  in position. Adjustment of the pointer  130  may be conveniently achieved without direct measurement by placing a straightedge against the grinding wheel surface in vicinity of the pointer tip  138 , and extending or retracting pointer  130  until it touches the straight edge. 
     In the manner described above, the bevel angle control mechanism of this invention enables the user to rapidly and accurately position the tool-rest  48  such that a prescribed tool bevel-angle will be obtained when a tool is placed flat on the tool-rest surface  50  and brought into contact with the periphery of grinding wheel  12 . The tool-rest height and attitude with respect to the grinding wheel tangent lines are uniquely defined by the angular position of the parallelogram linkage mechanism  70 , thereby eliminating problems associated with the height-attitude coupling effect on bevel-angle. The position of the linkage mechanism  70  is identified by the pointer  130 , and adjustment of its length based on grinding wheel radius allows a desired bevel angle to be achieved simply by aligning the pointer tip  138  with the corresponding contour line  150  of constant bevel-angle. 
     While the present invention has been described in reference to the illustrated embodiments, it is expected that various modifications in addition to those mentioned above will occur to those skilled in the art. For example, a linkage/scale combination as described herein could be retrofitted to a conventional hollow grinding machine, or a different means of clamping the tool-rest could be used. Thus, it will be understood that mechanisms incorporating these and other modifications may fall within the scope of this invention, which is defined by the appended claims.