Abstract:
A portable combined clamp and bit guide assembly guides a bit, turned by a power driver, into the exact center between the opposing faces of the clamp. The clamp is designed to hold workpieces having substantially parallel edges and a substantially linear centerline on their upper surfaces, and provides a drill path perpendicular to that centerline. An optional incline adapter supports the clamp and bit guide at an angle to the workpiece, while also aiding in support of the workpiece itself. The entire assembly may be carried in a single case with a power driver and bits.

Description:
BACKGROUND OF INVENTION 
   This invention has to do with the art of cutting by the use of a rotating, axially-moving tool, such as a drill, the art of work holders, and the art of geometrical instruments. 
   Drilling a straight hole through a precise spot in a workpiece at a precise angle requires careful and rigid positioning of the drill bit and the workpiece. A hand-held power driver drills holes quickly, but the entry point of the bit and the bit direction may meander. A common solution, where it can be used, is a drill press. In a drill press, the spinning chuck assembly is held and moved along a single, usually vertical, axis through bearings that are fixed in a heavy mount. A drill or other bit is mounted in the chuck and is advanced downward into the work by a rack that can move only up and down. Before drilling, the workpiece is carefully positioned beneath the bit and held or clamped in place so that the bit will enter the work precisely where desired and advance through the work in a precise direction relative to the workpiece. The location and direction of the drilling is usually measured and marked in advance on the workpiece so that it may be seen clearly by the operator. 
   Over many years, various levels of sophistication have been added to the drill press concept, usually to improve speed and efficiency as well as precision in manufacturing operations. These include devices for automated positioning of the work and the employment of multiple cutters moving along multiple axes. Milling machines, for example, have been developed which permit machining coordinates to be entered from digitally-rendered drawings, and the cutters and the workpiece are moved automatically relative to one another along a computed set of coordinates by mechanical positioners until all surfaces and holes are properly cut into the workpiece. 
   No such sophisticated device is economically available to hand driver users. One simple device, however, for improving the precision of a hand drill is U.S. Pat. No. 4,669,926 to Wilcox, Jr. It describes a guide for a hand drill incorporated into a vise. A tube, with an internal diameter sized to slip fit around a particular drill bit, is positioned by hinged arms over a point centered between the faces of the vise. The vise holds the workpiece, and the tube limits the amount of meandering the bit can do as it is pushed downward into the workpiece. 
   Geometrical instruments are a separate class of art in which physical representations of geometric entities (points, lines, planes, and solids) are employed to define other geometric entities. (For example, two straightedges may be laid across each other to define a point.) U.S. Pat. No. 5,437,105 to Work exemplifies this type of device. It describes a mechanical device for finding the center of an elongate workpiece having a flat upper surface and straight, but not necessarily parallel, sides. Two straight arms with tracks within them are aligned with the sides of the workpiece. Cross arms which intersect at their centers have ends that ride in the tracks. The intersection of the cross arms will always lie centered between the sides of the workpiece. At that intersection is a scribing pin to mark a point equidistant between the sides of the workpiece. 
   The above mentioned patent to Wilcox, Jr., combines the art of geometrical instruments with those of cutting and work holding. It allows the user to drill a fairly precisely located hole through the center of a workpiece held by a vise, but being incorporated into the vise, it does not adequately provide for portability. It also relies on a cylindrical drill guide, a tube having a diameter matched to the drill bit being used with it. Such a guide allows some play in the position of the drill bit tip and the angle of drilling. Moreover, a separate drill guide must be used with each different size of drill bit, and such guides may not be used with bits that have an end diameter larger than the shank. 
   There is also a need for a device, capable of holding both the work and the driver, which will also permit precise drilling at an angle other than vertical. 
   Another need not met by the prior art is to provide a precise guide for a portable power driver that can be moved around on a large surface with little effort. 
   SUMMARY OF INVENTION 
   This invention provides a portable combined clamp and bit support that guides a bit, turned by a power driver, into the exact center between the opposing faces of the clamp. The clamp is designed to hold workpieces having substantially parallel edges and a substantially linear centerline on their upper surfaces, and provides a drill path perpendicular to that centerline. An incline adapter is also provided to support the clamp and bit guide at an angle to that centerline, while also aiding in support of the workpiece itself. The entire assembly may be carried in a single case with a power driver and bits. 
   An object of this invention is to provide a portable clamp for workpieces which holds both a workpiece and a power driver such as a drill in a fixed relative orientation so that the rotating tool moves along a fixed and precise axial path into the workpiece. It is a further object of this invention to place such path in the centerline between the clamp jaws. Another object of the invention is to allow precise drilling at an angle to the surface of the workpiece. Another object of the invention is to provide a precise guide for a portable power driver that can be moved around on a large surface, for example to drill multiple precise holes in a large tabletop in a curved path or in a line parallel to one of the tabletop edges. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a perspective view of a subassembly comprising half of the clamping portion of the invention. 
       FIG. 2  is a perspective view of two subassemblies from  FIG. 1  joined in sliding relation to form the clamping portion of the invention. 
       FIG. 3  is a perspective view of the clamping portion of the invention with crossbar attached. 
       FIG. 4  is a perspective view of the complete first embodiment of the invention. 
       FIG. 5  is a perspective view of the first embodiment with a power driver in place. 
       FIG. 6  is a different perspective view of the clamping portion of the invention with a workpiece in position, illustrating the self-centering feature of the invention. 
       FIG. 7  is a perspective view of the clamping portion of the invention with a workpiece and a shim in the clamp. 
       FIG. 8  is a perspective view of the clamping portion of the invention with a cylindrical workpiece in place. 
       FIG. 9  is a perspective view of the clamping portion of the first embodiment of the invention, clamping the end of an elongate workpiece. 
       FIG. 10  is a perspective view of the clamping portion of the second, preferred, embodiment of the invention. 
       FIG. 11  is a perspective view of the preferred embodiment clamping the end of an elongate workpiece. 
       FIG. 12  is a close-up view of  FIG. 11 . 
       FIG. 13  is a perspective view of an incline accessory to either embodiment of the invention. 
       FIG. 14  is a perspective view of the first embodiment of the invention being used with the incline accessory. 
       FIG. 15  is a perspective view of a fence accessory for the invention. 
   

   DETAILED DESCRIPTION 
     FIG. 1  is a perspective view of a first subassembly  1  comprising half of the clamping portion of the invention. It consists of a vertical slide rod  15 , a slide rail  2 , and a clamp iron  3 , all fixed rigidly together at mutual right angles. The slide rod  15  is preferably of a round cross-section, the slide rail  2  is preferably of a rectangular cross-section, and the clamp iron  3  is preferably of an L-shaped cross-section, commonly referred to as “angle iron”. At the end of the clamp iron proximal to the junction point  4  of these three parts and rigidly connected to the upper surface of the clamp iron  3  is a sleeve  5  forming a slot  6 . Rigidly affixed to the clamp iron  3  near its distal end  7  is a rigid slot bar  8 , extending in the same direction from the clamp iron  3  as slide rail  2 , and parallel to slide rail  2 . Some length of clamp iron  3  is allowed to protrude to the right of slot bar  8  to provide additional support for a cooperating subassembly described below. Slot bar  8  has a butt end  16 , flush with the rear edge  17  of clamp iron  3 . 
   Slide rail  2  also passes through proximal end  9  of sliding arm  10 , so that sliding arm  10  can function like the sliding arm of a bar clamp well known in the clamping arts. Like the sliding arm of a typical bar clamp, sliding arm  10  has at its distal end  11  a clamp screw  12  which may be turned by a handle  13 , moving a swivel pad  14  along an axis parallel to slide rail  2 . 
     FIG. 2  is a perspective view of two subassemblies from  FIG. 1  joined in sliding relation to form the clamping portion of the invention. A second subassembly  1 ′, identical to first subassembly  1  in  FIG. 1 , is slidably attached to subassembly  1  by passing first slot bar  8  through second slot  6 ′, and second slot bar  8 ′ through first slot  6 . Pad  14  is thus located near butt end  16 ′ of slot bar  8 ′, and conversely located is pad  14 ′. Note that the material from which the slot bars and the slots are made is of approximately the same width and thickness as one of the legs of the angle iron. Note also that to maintain the best collimation of the two subassemblies, slide rails  2  and  2 ′, slots  6  and  6 ′, and slot bars  8  and  8 ′ are all at the same height just above clamp irons  3  and  3 ′. This assures that both slide rails and both slot bars will be parallel and coplanar, and helps assure that both slide rods  15  and  15 ′ will be maintained parallel in the vertical direction. It also allows slide rails  2  and  2 ′ to rest upon the distal ends  7 ′ and  7  of clamp irons  3 ′ and  3 , respectively, providing the entire structure with additional rigidity. 
     FIG. 3  is a perspective view of the clamping portion of the invention with rigid crossbar  30  slidably attached to the subassemblies  1  and  1 ′. Slide rod  15  is put through first bushing  31  rigidly fixed in first hole  32 , and slide rod  15 ′ is pushed through second bushing  31 ′ rigidly fixed in second hole  32 ′. The bushings  31  and  31 ′ slip fit the rods  15  and  15 ′. If the slide rods are made of steel, the bushings should preferably be made of Babbitt metal or other low friction material to allow a tight tolerance yet low friction on the fit between the slide rods and the bushings. The crossbar assembly should ride easily up and down along the slide rods. In the exact center of crossbar  30  is placed a bearing  33 . The centerline A of bearing  33  must be parallel with both slide rods  15  and  15 ′ 
     FIG. 4  is a perspective view of the complete first embodiment of the invention. Note chuck assembly  40  set rotatably in bearing  33 . Chuck assembly  40  has a chuck  41  at its lower end to grip a bit, and a shank  42  at its upper end to be turned by a power driver (not shown). Optionally on each slide rod  15  and  15 ′ is a set clamp  43  and  43 ′, respectively, to limit the lowest position of the crossbar  30 , and a spring  44  and  44 ′, respectively, to raise the crossbar up after it is pushed down during use. 
     FIG. 5  is a perspective view of the first embodiment with a power driver  50  and a drill bit  51  in place. 
     FIG. 6  is a different perspective view of the clamping portion of the invention with a workpiece in position, illustrating the self-centering feature of the invention. A workpiece  60  with a flat upper surface  61  has been placed between opposing clamp irons  3  and  3 ′, and seated firmly upwardly against slide rails  2  and  2 ′ and slot bars  8  and  8 ′. The workpiece  60  is clamped firmly in place by tightening swivel pads  14  and  14 ′ against butt ends  16 ′ and  16  using handles  13  and  13 ′ to turn screws  12  and  12 ′ respectively. As happens with conventional bar clamps, the reactions of sliding arms  10  and  10 ′ cause them to bind against slide rails  2  and  2 ′, compressing the clamp irons  3 ′ and  3  against the workpiece  60 . 
   It is taken for granted that the center of any diagonal line between two parallel lines will always lie on the centerline between the parallel lines, but here is a proof. The following geometric construction shows that a drill bit moving vertically along the chuck bearing centerline A (at the center of crossbar  30 , not shown) will always pass through the centerline B between the parallel edges  62  and  62 ′ of clamp irons  3  and  3 ′. The first step in the geometric construction is to draw a diagonal line segment C, representing crossbar  30 , between the ends of slide rods  15  and  15 ′. Crossbar  30  is constructed so that the chuck bearing centerline A is at its center, so line A bisects diagonal line segment C by definition, forming equal line segments C 1  and C 1 ′. Lines parallel to the true workpiece centerline B are then drawn through the ends of segments C 1  and C 1 ′ (D and D′ respectively). These lines are of course also parallel to each other. The next step is to use the plane geometry theorem that the interior and exterior angles formed by a diagonal crossing two parallel lines must be equal. Thus angles x and x′ are equal. Finally, line segment E, perpendicular to the parallels D and D′, is drawn through the intersection of A and C. That point divides line E into two segments E 1  and E 1 ′. Because E is perpendicular to D and D′, angles y and y′ are both right angles and therefore equal. Triangles B-C 1 -E 1  and B′-C 1 ′-E 1 ′ thus have equal angles x and x′, two equal right angles, and equal sides C 1  and C 2 . Another geometric theorem says that triangles having two equal angles and one equal side are congruent. Therefore E 1  and E 1 ′ are equal. Now, slide rods  15  and  15 ′ are each welded in place the same distance F from edges  62  and  62 ′ on clamp irons  3  and  3 ′. If distance F is subtracted from the lengths E 1  and E 1 ′ just shown to be equal, equal lengths G and G′ remain, defining the perpendicular distance of the vertical chuck centerline A from clamp iron edges  62  and  62 ′. The chuck centerline is thus shown to be equidistant from the clamp iron edges, so it must therefore lie on the centerline between the clamp iron edges, no matter how far apart the clamp iron edges are and no matter what the value of angles x and x′. 
     FIG. 7  is a perspective view of the clamping portion of the invention with a workpiece and a shim  70  in the clamp alongside the workpiece  60 . Placement of a shim of known thickness T as shown moves chuck centerline A a distance T closer to one side of the workpiece  60  if desired. 
     FIG. 8  is a perspective view of the clamping portion of the invention with a cylindrical workpiece  80  in place. (Crossbar  30  in the other views is omitted for visibility of the other parts) As is well known in the art, starting a drill into a convex metal surface such as a pipe wall can be daunting because the bit tip tends to meander away from the highest point, especially when the drill is hand-held with no other support. In this invention, skirts  81  and  81 ′ depending from clamp irons  3  and  3 ′ allow a cylindrical workpiece to be clamped in place. Thus, the invention permits a power driver to be used to drill through the center of workpiece  80  without the drill bit tip meandering away from the center point. 
     FIG. 9  is a perspective view of the clamping portion of the first embodiment of the invention, clamping an elongate workpiece  90 , such as a table leg. Note that this workpiece is too narrow at the end  91  to seat upwardly against the slot bars  8  and  8 ′. A modification is desirable, as shown in the next figure, to better control the position of such workpieces. 
     FIG. 10  is a perspective view of the clamping portion of the second, preferred, embodiment of the invention. Small stock stops  100  and  100 ′ have been added, being slidably secured to clamp irons  3  and  3 ′ respectively by screws  101  and  101 ′ respectively. 
     FIG. 11  is a perspective view of the preferred embodiment clamping the end of the elongate workpiece  90 , showing stops  100  and  100 ′ in use. 
     FIG. 12  is a close-up view of  FIG. 11 . Curved edges  120  and  120 ′ on stops  100  and  100 ′ permit at least a small portion of workpiece end  91  to be restrained from upward motion within the clamp. Slots  121  and  121 ′ allow stops  100  and  100 ′ to be moved in or out depending on how much of their length is needed. 
     FIG. 13  is a perspective view of an incline accessory  180  to either embodiment of the invention, for use in drilling holes through a workpiece at an off-vertical angle. It consists of left and right clamp plates  130  and  130 ′, each having lower flanges  131  and  131 ′, respectively. Front and rear bolts  132  and  133 , and wing nuts  134  and  135 , respectively, are used to tighten flanges  131  and  131 ′ against a workpiece  136 . Left and right inclined guides  137  and  137 ′ are fixed to the inclined front edges of plates  130  and  131 , respectively. Guides  137  and  137 ′ have track slots  138  and  138 ′ running lengthwise along them. An upper clamping bolt  139  is also disposed between the clamp plates  130  and  130 ′. It is used to adjust the space between the upper ends of guides  137  and  137 ′. An adjusting lock wheel  140 , threaded at its center, can be run along threads on bolt  139  to urge guides  137  to a position to accept the track slots (not shown) of either embodiment of the invention (see  FIG. 14 ). 
     FIG. 14  is a perspective view of the first embodiment of the invention being used with the incline accessory  180 . To drill a hole at an angle in a workpiece  136 , clamp plates  130  and  130 ′ are opened sufficiently to allow accessory  180  to rest on the upper surface  141  of workpiece  136 . Wing nuts  134  and  135  (out of sight behind plate  130 ′) may be tightened slightly to restrain accessory  180  from leftward or rightward motion along the workpiece  136 . The first embodiment of the invention  45  (for example) is then placed with its left end on top of the workpiece at H, with clamp irons  3  and  3 ′ on either side of the workpiece. At the same time, depending skirts  81  and  81 ′ at the right ends of clamp irons  3  and  3 ′ are placed into track slots  138  and  138 ′ of inclined guides  137  and  137 ′, respectively. Accessory  180  and embodiment  45  are then moved left or right and embodiment  45  moved towards or away from accessory  180  so as to position the centerline A of chuck  41  at the correct position and angle relative to drill point j. Then handle  13  is tightened slightly to pinch the workpiece  136  between clamp irons  3  and  3 ′. Wing nuts  134  and  135  (not visible) are then tightened fully to secure accessory  180  to workpiece  136 . Lock wheel  140  is then adjusted to spread guides  137  and  137 ′ to frictionally engage skirts  81  and  81 ′ in track slots  138  and  138 ′, respectively. Handles  13  and  13 ′ are then fully tightened to secure embodiment  45  to both the workpiece  136  and the accessory  180 . 
     FIG. 15  is a perspective view of a fence accessory  150  for the invention. It has a base  151  rigidly attached to an arm  152 , which is in turn connected through extension clamps  153  to fence assembly  154 . Base  151  is shaped to fit between clamp irons  3  and  3 ′ in previous drawings. Wood blocks  155  are shown built into base shell  156  to provide rigidity, although any other means of making the base capable of withstanding the clamping of irons  3  and  3 ′ is equally satisfactory. A hole  157  is cut into base shell  156  to permit the drill bit in either of the embodiments of the invention to pass through to the underlying workpiece  158 . Depending on how far drill axis A needs to be placed from workpiece edge  161 , a piece of wood  160  of suitable length can be inserted through extension clamps  159  and  159 ′, and secured in place using extension clamp bolts  162  and  162 ′. If it is desired to drill plural holes along line K–K′, wing nut  163  is tightened so as to position flat  164  of fence assembly  154  against edge  161  of workpiece  158 , and the entire apparatus slid along edge  161  to position drill axis A over the selected drill locations. If it is desired to drill plural holes along circular arc L–L′, fence assembly  154  is turned around 180 degrees from the position shown about bolt  165 , so that cavity  166  can be placed over workpiece edge  161  so far as to place bolt  165  against edge  161 . Moderate tightening of wing nut  163  will then cause assembly  154  to grip edge  161  while allowing the entire accessory  150  to swivel about bolt  165 . Drill axis A will now be able to be positioned at any point along arc L–L′.