Abstract:
A workpiece indexing and clamping system for machining the workpiece. Spherical or narrow cylindrical heads of index pins extend from holes in a base plate into workpiece holes to align and index the workpiece. The pin portions in the base plate holes can be expanded to lock them to the base plate. Each pin has relief flats parallel to the pin axis. Clamps engage workpiece edges with thread-like angled grooves on a cam surface to force workpiece edges against the base plate during machining of the workpiece. A central clamp has a pin extending from the base plate into a workpiece hole. Angled grooves in a cam surface are brought into contact with the hole sides to force the workpiece toward the base plate and hold the central area in place during machining. In another version, a combined index and clamp pin has a head that fits within a workpiece hole and an extension that fits within a base plate hole. Setscrews and tapered threaded holes cooperate to expanding the head and extension into clamping contact with the respective holes.

Description:
This application is a continuation-in-part, of U.S. patent application Ser. No. 08/811,243, filed Mar. 3, 1997, now U.S. Pat. No. 6,039,312 which is a continuation-in-part of U.S. patent application Ser. No. 08/613,808, filed Mar. 6, 1996 now U.S. Pat. No. 5,961,107. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates in general to the clamping of workpieces to a surface and, more specifically, to a system for indexing and clamping a workpiece to a base plate that leaves the opposite surface free for machining or the like. 
     When raw material or preforms are to be machined it is necessary that the workpiece be tightly clamped to a base plate or an intermediate sub-plate to hold the workpiece stable at a precise position while resisting the forces on the workpiece produced by the machining operation. Typically, such machining includes drilling, boring, honing, grinding and milling. 
     In numerical controlled machining, a machine tool, such as a milling head, is programmed to follow a very precise path. The workpiece must be located extremely precisely relative to certain machine datum points and/or datum planes from which the machining path is related or measured. 
     A number of different indexing and clamping systems have been developed to permit a workpiece to be positioned at a specific location on the support plate. Generally, the clamps have fingers and straps or other means that extend over the side of the workpiece opposite the supporting surface. While generally effective, these upper surface clamps must be carefully positioned to avoid interference with the movement of the machine tool, such as a milling head, across the workpiece. 
     Insufficient clamping-pressure, or the use of too few clamps, may allow the workpiece to shift during machining, resulting in wasted, out-of-tolerance products. Further, errors in clamp placement may allow the machine tool cutter to run against the tool, resulting in damaged clamps and serious damage to the machining tool and/or to the machine itself and could be a safety hazard to nearby personnel. 
     A wide, generally flat workpiece that is clamped to a support plate around the edges may lift slightly at the center due to machining forces. Thus, the central dimensions of the product may be thinner and out-of-tolerance. 
     It is absolutely essential, especially with numerical controlled machining, that the workpiece be positioned precisely relative to datum points or planes on the support plate. Failure to establish and maintain the precise workpiece position will result in an improperly machined and rejected parts. 
     A variety of components have been used to accurately locate workpieces. Among these are index pins mounted on or in the support plate and extending into precisely located holes in the workpiece. Round pins inserted into round workpiece holes may have problems such as lack of the necessary concentricity, a hole that has an axis that is slightly off the pin axis (angularly or otherwise), pins that tend to interfere or be loose in productions holes with variable diameters, etc. These problems, and others, largely keep full round index pins from having the necessary overall accuracy and flexibility. 
     Thus, there is a continuing need for improved indexing and clamping systems for workpieces to be machined, systems that have improved reliability, accuracy and versatility and do not extend over or obstruct the workpiece surface being machined, generally the surface opposite the surface in contact with a support or base plate and hold the workpiece firmly in place during machining. 
     SUMMARY OF THE INVENTION 
     The above-mentioned problems, and others, are overcome in accordance with this invention by an improved workpiece clamping and locating system for use in machining, in particular numerical control machining. The clamping system basically includes at least one index pin for locating a workpiece on a base plate, and edge clamping arrangement and a central clamping pin. The indexing and clamping pin may cooperate with other clamping devices that clamp workpiece edges to the base plate, etc. Typically an edge clamping portion may basically include a plurality of clamps, each having a simple clamp arm pivotally mounted on a support block that can be fastened to a base plate and preferably is longitudinally movable or adjustable on top of the base plate surface toward and away from a side of a workpiece supported on the base plate. Each clamp arm has a cam surface adjacent to the axis of rotation with the cam surface configured to move towards and away from an adjacent workpiece side as the arm is pivoted. The clamp arm includes means for pivoting the arm about the axis, preferably an extended handle for manual pivoting or a powered gear segment engageable with a powered drive for exact automatic movement toward and against the workpiece. 
     In the invention as claimed in this application, a workpiece is precisely positioned on a base plate by one or more indexing and clamping pins fastened to the base plate. Each pin has a head at the pin distal end extending above the base plate and an extension at the pin proximal end extending into a corresponding hole in the base plate. Each pin preferably has a generally spherical head with at least two radially spaced flats on the head, the flats lying generally perpendicular to the base plate when the index pin is installed on the base plate. The workpiece is positioned by lowering holes in the workpiece over correspondingly sized pin heads. The pins preferably have 2-4 spaced flats. In an optimum embodiment, two pairs of contiguous flats are provided, with the pairs on opposite sides of the head, so that the head has a generally diamond shaped plan view. While the spherical head is optimum for ease of insertion and accurate indexing, if desired the head could be cylindrical. 
     The index and clamping pin has an axial hole therethrough, a more narrow threaded hole in the extension and a wider threaded hole in the head. At least two, preferably four, equally spaced axial slots extend from the distal end of the head through the head to approximately the base of the head. Similarly, two or preferably four, equally spaced axial slots extend from the proximal end of the extension to almost the base of the head, with out intersecting the head slots. 
     The threaded holes in the head and extension receive setscrews, sized to expand the diameters of the head and extension as detailed below to bring the head and extension into forceful contact with the workpiece and base plate, respectively. 
     In a preferred embodiment, the head (where cylindrical) and/or extension have a plurality of protuberances extending outwardly toward the workpiece and base plate to press against and indent the hole walls and further secure the index/clamping pin in place against any forces tending to lift the workpiece above the base plate. The plural protuberances may have any suitable shape. For best results, the protuberances are shaped as normal bolt threads. The tips may spiral as in a bolt thread or may be circular, Optimally, the thread angle will be approximately 90° on the thread side toward the pin distal end and an a lesser angle toward the pin proximal end for best engagement with hole walls. 
     As an aid in remotely clamping a workpiece, an eccentric central index clamping pin may be provided if desired. 
     Any suitable base plate may be used with the clamping system of this invention. 
     Depending on the size of the workpiece, at least two index/clamping pins are used. If desired in particular circumstances the other clamping means as disclosed in this application may be used with those index/clamping pins. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     Details of the invention, and of preferred embodiments thereof, will be further understood upon reference to the drawing, wherein: 
     FIG. 1 is a plan view of the clamping system, here including four edge clamps and a central clamp and several kinds of index pins; 
     FIG. 2 is a section view taken on line  2 — 2  in FIG. 1; 
     FIG. 3 is a detail perspective view of one index pin embodiment; 
     FIG. 4 is a plan view of the pin shown in FIG. 3; 
     FIG. 5 is a section view taken on line  5 — 5  in FIG. 4; 
     FIG. 6 is a view of the lower end of the pin shown in FIG. 3; 
     FIG. 7 is a perspective view, partially cut-away, of one combination central index/clamping pin; 
     FIG. 8 is a detail perspective view of one edge clamp arm; 
     FIG. 9 is an plan view of another locating pin embodiment; 
     FIG. 10 is a side elevation view of the pin of FIG. 9; 
     FIG. 11 is a perspective view of an index/clamping pin having a generally spherical head; 
     FIG. 12 is a section view taken generally along the axis of the index/clamping pin of FIG. 11; 
     FIG. 13 is a plan view of the pin of FIG. 11; 
     FIG. 14 is a view looking upwardly at the lower end of the pin of FIG. 11; 
     FIG. 15 is a perspective view of an alternative embodiment of the index/clamping pin having a generally cylindrical head; 
     FIG. 16 is a perspective view of an index/clamping pin embodiment as seen in FIG. 11 but with side protuberances on the extension; 
     FIG. 17 is a perspective view of an index/clamping pin embodiment having a spherical head and side protuberances on the head and extension; and 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to FIG. 1, there is seen a base plate assembly  10  made up of a lower plate  12  and an upper plate  14 . A workpiece  16  to be machined is installed on upper plate  14 . 
     Four edge clamp assemblies  18 , as seen in FIGS. 1 and 8, are located on opposite sides of workpiece  16 . Depending on the size, complexity and particular machining operations to be accomplished, from two to a larger number of clamp assemblies  18  may be used in various clamp sizes. 
     Each clamp assembly  18  includes a support block  20  secured to lower plate  12  by cap screws  22 . Cap screws  22  are near the ends of slot  21  in support block. The spaced arrangement provides maximum strength, with some range of adjustment of the position of support block  20  toward and away from workpiece  16 . An arm  24  is mounted on each support block  20  by a shoulder screw  26  that permits the arm to pivot about an axis centered on screw  26 . Each arm  24  has a cam surface  28  around each axis with a continuous varying diameter. When an arm  24  is moved in the direction indicated by arrow  30 , the cam diameter increases, increasing clamping pressure on the edge of workpiece  16 . In three of the arms  24  shown, an extended handle  32  is provide with which the arm is manually moved between clamped and unclamped positions. The other arm  24 , seen to the lower right in FIG. 1, shows an alternate embodiment where, in place of handle  32 , a gear segment  34  is provided that engages a gear in a power drive  36 , typically a small electrical gear motor, to automatically move the upper portion of arm  24  between clamped and unclamped positions. 
     As seen in FIGS. 1,  2  and  5 , grooves  37  similar to screw threads are provided along cam surface  28 . Preferably, the cam surface  28  and power drive surface  34  are suitably hardened or heat treated for strength and durability. Grooves preferably have sharp apexes and are slanted so that as the grooves engage and move along the edge of workpiece  16  the grooves force the workpiece tightly down against upper plate  14 , as well as horizontally in two additional directions against opposing index pins, bars and the like and other opposing clamps as shown in FIGS. 1 and 2. Since clamp assemblies  18  do not extend above the upper surface of workpiece  16 , machining tools, such as mills, can traverse the entire upper surface without interference from, or impact against, clamps as would be the case with conventional clamping systems. 
     Generally, workpiece  16  must be precisely located on base plate  10  to align with the machining tools, especially in the case of Numerical Control (N/C) machining. As seen in FIGS. 1 and 3, a novel and more effective index pin system is provided to correctly locate the workpiece. 
     Three types of ball index pins are shown, a diamond-shaped ball pin  38 , a triangular-shaped ball pin  40  and a square-shaped ball pin  42 . Each of these pins is secured to upper base plate  14  and slip fits precisely in a hole  44  of suitable diameter, precisely located in the workpiece. Thus, workpiece  16  is exactly located relative to the pins for machining. Each type of ball pin may be used in conjunction with other conventional pins and locators, with particular pin types selected to meet specific conditions and needs. 
     The diamond ball pin  38  embodiment is shown in perspective in FIG.  3  and in orthographic view in FIGS. 4,  5  and  6 . The upper portion  39  of each of the pins  38 ,  40  and  42  is basically spherical before final machining of flats on the sides. Each pin has a head of different configuration on a base flange  46  and extension  48  for insertion into a correspondingly slip fit hole  47  in upper plate  14 . Each pin has the desired number of flats  50  machined into the spherical surface  49  along planes parallel to the vertical axis of the pin, ultimately perpendicular to the surface of upper plate  14 . Diamond ball pin  38  has two pairs of contiguous flats  49 , arranged on opposite sides of the pin to provide a diamond-like appearance in a plan view. Thus, the two opposed remaining spherical surfaces  50  are the only “tangent line” portions of the pin that contact the interior of a hole  44 , providing accurate positioning in two opposed directions, at desired minimum contact, while providing exceptional relief in the remaining directions, thus guaranteeing absolute minimum hole and pin interference. Similarly, triangular pin  40  has three equally spaced flats  49 , providing three equally spaced spherical surfaces  50  and square pin  42  has four equally spaced flats  49  and four equally spaced spherical surfaces  50 . Pins  40  and  42  are designed to replace existing full size pins for more accurate indexing and alignment with minimum interference. The diamond ball pin configuration is considered optimum, and equally spaced spherical surfaces  50  are preferred for most versatile indexing ability, especially when several planes are involved at complex or compound angles toward each other. 
     If desired, the surfaces  50  could be rounded to provide essentially a line contact with a workpiece. Further, if desired a different number of flats could be provided, spaced apart other than equally. Clear advantages of pins  38 ,  40  and  42  include precise yet simple and quick index capability in complex set-ups with additional tolerance benefits. Preferably the ball pins  38 ,  40  and  42  are suitably hardened or heat treated and otherwise processed for strength, durability and longevity. 
     For installing and removing pins  38 ,  40  and  42 , an aperture  54  is provided in the upper end to receive a tool, such as a screwdriver, Allen wrench or the like to rotate a setscrew  52  threaded into a narrow lower portion of aperture  54 . The interior of aperture  54  bears threads  53 , which taper to a narrower lower end of aperture  54 . Extension  48  has two or four axial slots  55 . Thus, as setscrew  52  is threaded downwardly, extension  48  between slots  55  is forced outwardly to engage the interior wall of hole  47 . Since the pin extension  48  is a slip fit in hole  47 , an expansion of extension  48  of only 0.001 to 0.003 inch is generally sufficient to hold the pin securely in the hole. The pin is easily removed by simply inserting an Allen wrench into a hexagonal hole in setscrew  52  or a screwdriver into a corresponding slot in the setscrew to move the setscrew back up threads  53 . 
     Two flats  57  are preferably included on opposite sides of flange  46  so that the head can be held in the proper orientation with a conventional wrench while the setscrew is being tightened. 
     Large, thin, or flat workpieces  16  often tend to lift at central areas during milling. A central clamp  58  as shown in FIGS. 1 and 7 may be used if desired, alone or in conjunction with the index/clamping pins as shown in FIGS. 11-16 as described below. Central clamp  58  basically comprises a threaded extension  60  on which a cylindrical, coaxial, base or locator section  63  is secured, with a cylindrical head  62  mounted on the base  63 , with the axis of extension  60  and base or locator section  63  offset from the axis of head  62 . The offset head  62  is sufficiently eccentric to provide a cam action of the head when rotated about the axis of threaded extension  60  and base  63 . Locator section  63  is a close slip fit with hole  65  in plate  14  to assure precise location. Central clamp  58  is threaded into upper plate  14 , but not tight against upper plate  14 . 
     Workpiece  16  has a hole  64  that fits over central clamp  58  and is sized so that as the clamp is rotated by means of a conventional Allen wrench or the like engaging hexagonal opening  68  in head  62  the cam head  62  moves into engagement with the wall of hole  64  when rotated in one direction and out of engagement when rotated in the opposite direction. In order to provide the clamping action, forcing workpiece  16  against upper plate  14 , angled grooves, preferably conventional threads  66 , either right-handed or left-handed, as desired, are provided on the outer cam surface of head  62 . Thus, when the cam surface is rotated into pressure contact with the wall of hole  64 , threads  66  will engage the wall and drive the workpiece  16  against upper plate  14  in the same manner as the grooves  37  on clamp arm  24 . Preferably, central clamp pin  58  is suitably hardened, heat treated or otherwise processed for strength, durability and longevity. If desired, a threaded bushing could be used in lower plate  12  rather than directly threading the lower plate opening and a guide bushing could be provided in the opening in upper plate  14  to surround the locator section  63 . 
     A tool receiving opening  68  is provided in the end of head  62  to permit central clamp  58  to be rotated in the manner described by any suitable tool, such as an Allen wrench, screwdriver or the like. 
     Another embodiment of a locator pin suitable for use with the overall system of this invention is illustrated in FIGS. 9 and 10. In this case, base  46 , extension  48 , slot(s)  55  and expansion setscrew  52  are the same as discussed above in conjunction with FIGS. 3-6. In this embodiment, however, upper portion  72  is initially machined as a cylinder rather than as a sphere, then is machined to provide a narrow cylindrical band. Finally, two or more flats  74  are machined to provide a diamond shaped, square, triangle, or other desired configuration, as discussed above. 
     A flange  46  is provided between said upper portion  72  and extension  48  to engage the base plate surface when the pin is in place thereon. Two flats  57  may be provided on opposite sides of flange  46  to be engaged by a conventional wrench while the central setscrew is moved. 
     This embodiment is particularly suitable where the locating hole  44  in which the pin is inserted is parallel to the pin axis, yet minimum index contact is guaranteed with minimum interference. Where the pin axis and hole may be at an angle to each others, the spherical upper portion embodiments are preferred, since this makes a complex set-up simple and easy to work with, at minimum cost. 
     Several embodiments of combined indexing and clamping pins  100  are shown in FIGS. 11-16. With this combined function, each clamping pin  100  would replace both an indexing pin  38 ,  40  or  42  and a clamp  58 . 
     As seen in FIG. 11, the basic components of a pin  100  are a head  102 , which can be spherical as shown with flats  104 , a base  106  with two opposite flats  108  for gripping with a wrench and a generally cylindrical extension  110 . Extension  110  is sized to fit into a precisely located hole in a base plate (not shown). Head  102  is sized to fit into a hole in a workpiece to be indexed relative to the base plate. 
     A circular cross section aperture  112  extends axially through head  102 , base  106  and extension  110  as best seen in FIGS. 11-13. The portion  114  in head  102  of this aperture  112  has a greater diameter than portion  116  in extension  110 . Each of these aperture portions  114  and  116  taper to a narrower diameter toward the distal end of extension  110 . Each portion  114  and  116  is threaded to receive a setscrew. First setscrew  118  is configured to thread into the narrower aperture portion  116  in extension  110  and easily slips through the wider aperture portion  114  in head  102 . Second setscrew  120  threads into tapered threaded aperture  114  in head  102 . 
     At least one, preferably two, equally spaced, axial slots  122  are provided through head  102 . Similarly, at least one axial slot  124  is provided through extension  110 . Thus, when extension  110  is placed in a corresponding base plate hole and setscrew  118  is threaded down into aperture portion  116 , the narrowing taper through extension  110  will expand the extension into clamping contact with the wall of the base plate hole. Then, when a workpiece is placed with a hole fitted over head  102  and setscrew  120  is threaded down into aperture portion  114 , the taper will cause the head to expand into clamping contact with the walls of the workpiece hole. 
     An alternate embodiment of pin  100  with a different head  102  configuration is illustrated in FIG.  15 . Here head  126  has a cylindrical outside shape, sized to fit into a workpiece hole. The other components of pin  100  are otherwise the same as the embodiment of FIGS. 11-14. Head  126  preferably has four equally spaced axial slots  122  as described above, although any other suitable number of slots  122  may be used. Head  126  preferably has several flats around the circumference, so that a portion of the cylindrical surface remains between each pair of adjacent slots  122 . As a setscrew  120  is threaded into aperture portion  114 , the head expands into clamping contact. 
     As shown in the embodiments of FIGS. 16 and 17, to maximize clamping effectiveness, circumferential thread-like serrations may be provided on extension  110  and/or head  102 . As seen in FIG. 16, if desired, serrations  130  may be provided only on extension  110  to increase clamping effectiveness to the base plate. While each serration may have any suitable cross section, preferably they will have an angle to the pin axis of from about 80 to 120 degrees on the side towards base  106  to provide maximum resistance to withdrawal from the base plate hole. 
     If desired, serrations may be used on only extension  110 , only on head  102  or on both of them, as shown in FIG.  17 . Serrations  130  are the same as shown in FIG.  16 . Serrations  132  on head  102  may be formed in any suitable manner. Typically, a narrow cylindrical surface may be turned on spherical head  102 , serrations  132 , typically by conventional threading methods forming a spiral, bolt-like thread, or circular threads may be turned, then flats  104  are milled as desired. Similar serrations  132  may be formed on the cylindrical head embodiment of FIG.  15 . 
     For optimum engagement between head  102  and a workpiece, the serrations on both extension  110  and head  102  will have an angle to the pin axis of from about 80 to 120 degrees on the side towards base  106 . 
     The pins  100  as described may be used with any suitable base plate and workpiece having any suitable shape, including workpiece shapes having high peripheral areas (such as an open box-like shape) which are particularly difficult to clamp with prior clamping systems. 
     While certain specific relationships, materials and other parameters have been detailed in the above description of preferred embodiments, those can be varied, where suitable, with similar results. Other applications, variations and ramifications of the present invention will occur to those skilled in the art upon reading the present disclosure. Those are intended to be included within the scope of this invention as defined in the appended claims.