Abstract:
A hole coring system is provided that greatly stabilizes a tubular core drill bit for drilling into concrete or other materials enabling large diameter holes to be drilled with a handheld tool. The drill bit is guided by a mandrel which is attached to the concrete. The mandrel serves as a central guidepost that ensures that a relatively large diameter, tubular core drill bit remains precisely centered relative to the guide mandrel. This enables the operator to use a commonly available tool to rotate the drill and apply drill pressure only. The motor may rotate the drill bit via a gear box. The gear box may have a lever arm which may be used to resist any torquing action of the gear box due to the friction between the drill bit and the concrete. Additionally, in the event the motor&#39;s housing is not fixed to the gearbox and allowed to rotate, a brace may be attached to the lever arm which may be used to resist any torquing action of the motor&#39;s housing due to the friction between the drill bit and the concrete.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation in part application of U.S. patent application Ser. No. 11/646,761, which claims the benefit of Provisional Patent Application Ser. No. 60/759,594 filed Jan. 17, 2006. The entire contents of both U.S. patent application Ser. No. 11/646,761 and Prov. Pat. App. Ser. No. 60/759,594 are expressly incorporated herein by reference. 
     
    
     STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT 
       [0002]    Not Applicable 
       BACKGROUND 
       [0003]    1. Field of the Invention 
         [0004]    The present invention relates to a tool designed to drill holes in concrete and other materials. 
         [0005]    2. Description of the Prior Art 
         [0006]    Holes have been drilled in concrete using masonry drill bits for many years. One problem that has persisted, especially when relatively large-diameter holes are drilled into concrete using a cylindrical, annular core drill bit, is that it is sometimes difficult to maintain the drill bit precisely centered so as to drill a completely circular and aligned large diameter hole into concrete, fiberglass, plastic, and other materials. The problem arises due to the tendency for one edge of the drill to make contact before another edge. Consequently, the drill tries to walk sideways erratically. There is a tendency for the drill bit to wobble or vibrate in a lateral direction, rather than stay precisely centered on the intended drill bit axis. As a result, it is difficult to drill holes in concrete, particularly large diameter holes, with portable equipment. 
         [0007]    One prior system that has been developed to attempt to stabilize a drill bit is available under the trade designation “Core Drill Rig”. This device operates somewhat in the manner of a drill press. However, unlike a drill press, there can be no stabilizing table beneath a workpiece when drilling into concrete. This is because the concrete structure into which a hole is drilled is always much too thick and expansive to lend itself to stabilization by a table located beneath the drill. 
         [0008]    The Core Drill Rig employs a relatively large diameter, annular drill bit mounted on a drill held by a stanchion to one side of a frame. It is necessary to bolt the frame of the Core Drill Rig to the concrete surface to be drilled or hold it in place by suction in order to provide resistance to the drill bit so that the drill bit can penetrate the concrete. If the drill supporting frame is not bolted or otherwise secured to the concrete floor, the drill bit tends to lift off the concrete surface being drilled. 
         [0009]    The supporting frame is provided with bolt holes and bolts that must be attached to the concrete structure into which the relatively large diameter hole is to be drilled. First, relatively small diameter holes must be drilled in the concrete at the bolt locations to allow the Core Drill Rig frame to be secured to a concrete floor or wall into which a large diameter hole is to be drilled. Once the frame is bolted to the surface it provides the drill bit with much greater stability than can be achieved using a hand-held drill. However, since the Core Drill Rig must be bolted to the surface, the holes that are used to attach the bolts that secure the frame to the concrete surface must later be filled. Also, considerable effort is required to bolt the frame to the surface to be drilled. 
         [0010]    The Core Drill Rig can be configured with a vacuum device that creates a suction to draw the drill frame down to the concrete floor. However, it is difficult to achieve a sufficient suction force to prevent the frame from lifting off the floor and breaking the vacuum if one attempts to operate the drill with high torque. To the contrary, in conventional systems such as the Core Drill Rig, the large diameter drill bit can only be operated at a relatively low speed with a high torque in order for the hole drilled to be circular within acceptable tolerances. 
         [0011]    Furthermore, conventional concrete core drills that employ stabilizing frames, such as the Core Drill Rig, are very bulky, heavy, and expensive. They cannot be conveniently packed in a small carry case. They also require a considerable volume of space for transportation in a truck or other work vehicle. 
         [0012]    Another conventional annular drilling arrangement is the common hole saw. This is used primarily for cutting holes in wood. The hole saw incorporates a pilot drill fixed in the center of an annular strip of saw blade. The drill bit is simply attached to a chuck driven by a hand drill motor and the pilot drill makes a smaller hole to start off with. As the depth of drilling process progresses the larger annular drill bit engages. At this time the smaller hole acts as a guide for the larger drill. 
         [0013]    Although this drilling system has been around for many years it is unsatisfactory for many materials, including concrete. The desirable features of the cutting action for the smaller pilot bit are not the same as those for the cutting action of the larger hole saw. For substances like concrete a percussion action is ideal for drills up to approximately one inch in diameter using carbide tips shaped to pulverize their way through the material with the percussion action. This action is not practical for the larger diameter, thin walled core bit that a hand held drill motor can practically hammer and rotate. Similarly a high rotational speed is more suited to the small pilot drill bit but these speeds may exceed the optimum speed for the large core bit, thus causing overheating and failure of the bit or melting of the material to be cut. In addition, the pilot drill is not aligned in an orientation that can be checked for accuracy before commencing the drilling of the larger hole. Also, the guiding tolerance does not remain constant since the pilot drill tends to “oval” the pilot hole with continued rotation thus causing irregular holes, variable location and misalignment. 
       BRIEF SUMMARY 
       [0014]    A system has been devised that permits relatively large diameter holes to be drilled in a hard material like concrete, plastic, or fiberglass with a high degree of control in keeping the drill bit centered, but without the disadvantages of prior conventional systems. Specifically, one or more relatively small diameter anchor holes may be first bored into the concrete at or about the center at which a larger diameter hole is to be drilled using current conventional percussion tools or developed in the future. Once the anchor hole(s) has been drilled, a mandrel is secured to the concrete and aligned via a stabilizing plate. At this point, the mandrel extends upwardly and serves as a stabilizing guidepost for a relatively large diameter, hollow drill bit drive shaft. 
         [0015]    The large diameter, hollow drill bit has a central, axial opening therein that receives a long, hollow, tubular sleeve of a drive shaft assembly. This sleeve fits over the mandrel and has a lower, hollow coupling which is internally lined with bearings near its lower extremity. A drill motor coupling is provided at the upper end of the tubular sleeve and is equipped with an appropriate fitting for connection to a handheld drill motor. The drill motor, through a suitable chuck arrangement, turns the hollow drive shaft assembly at a high speed in rotation about the anchored mandrel. The drill motor that is coupled to the drive shaft assembly and which turns the drive shaft assembly can be any one of a number of different power sources that are widely utilized in the industry. 
         [0016]    The hollow, tubular core drill bit is coupled to the drive shaft assembly and is rotated about the anchored mandrel at a high speed by the hollow drive shaft assembly. The drive shaft assembly is maintained centered, turning in driving rotation in coaxial alignment relative to the mandrel. Internal bearing sleeves at the lower end of the drive shaft assembly reside in longitudinal sliding and rotational sliding contact with the anchored mandrel, thereby ensuring that the drive shaft assembly remains in precise, coaxial alignment with the anchored mandrel. Since the drive shaft assembly carries the tubular core drill bit at its lower end, the tubular core drill bit is likewise held in precise coaxial alignment with the anchored mandrel. As the tubular core drill bit advances into the concrete, the bearing sleeves at the lower end of the drive shaft assembly advance longitudinally along the outer surface of the anchored mandrel, as well as in high speed rotation relative thereto. 
         [0017]    By utilizing the superior guidance provided by the mandrel and attached drill, high speed rotation can be achieved without vibration. This high speed enables the same or more power to be developed by the system with the lower pressure that can be applied by a manual operation. 
         [0018]    By employing the stabilizing, anchored, mandrel and the hollow drive shaft assembly, the operator can precisely locate and drill a precision hole in a variety of materials using a hand operated portable tool. 
         [0019]    In part because the drill is operated at high speeds, it is highly desirable, if not necessary, to supply cooling water both to cool the tubular core drill bit, as well as the bearings interposed between the drive shaft assembly and the anchored mandrel, and to flush out the concrete debris as it is drilled away. The coupling at the upper end of the drive shaft assembly is preferably equipped with some means to supply water to the cutting teeth of the hollow, tubular core drill bit. In some arrangements water is provided through a water swivel. Because the drive shaft assembly is rotated at a relatively high speed, the cooling water may be supplied down the center of the hollow drive shaft assembly either from a water feed drill motor or by means of a water swivel that conducts a flow of water radially inwardly toward the drive shaft assembly and down through its hollow center. The cooling water flows downwardly in the annular space between the inner surface of the tubular drive shaft assembly and the outer surface of the anchored mandrel and as a film between the bearing sleeves and the anchored mandrel guidepost. Below the bearing sleeves the water flows down into the circular, annular opening being drilled by the tubular core drill bit so as to cool the drill bit teeth and wash away the concrete debris as drilling progresses. 
         [0020]    In one broad aspect, an apparatus for drilling holes in concrete may comprise: a central, cylindrical mandrel having an upper end, a lower anchoring and a smooth cylindrical intermediate, outer surface therebetween; a hollow, cylindrical annular drive shaft disposed axially about the mandrel and having an upper end with a drive motor coupling and an opposite driven end; at least one bearing mounted to the driven end of the annular, hollow drive shaft and residing in rotational and longitudinal sliding surface contact with the mandrel, whereby the drive shaft is freely rotatable about the mandrel and is also movable longitudinally relative to the mandrel; and a hollow, tubular core bit drill at the lower end of the drive shaft which has a lower annular, serrated edge with cutting teeth thereon. 
         [0021]    A further preferred feature involves a system for releaseably engaging the mandrel with the hollow drive shaft. This feature is particularly advantageous in drilling holes through concrete slab floors in the upper stories of a multistory building. In such a situation the mandrel, together with the cylindrical block or “doughnut” of concrete in which it is embedded will otherwise drop to the story below as the teeth of the annular drill bit break through the final structure of the concrete floor. The falling cylindrical block of concrete with the mandrel embedded therein at the very least will shatter into debris upon which workmen can slip. More importantly, the falling block of concrete could cause serious damage to objects in the space below. When it falls it can also cause serious bodily injury, or even death to a person below. 
         [0022]    To prevent such a dangerous situation the mandrel may be provided with a releasable latching mechanism while the hollow, cylindrical, annular drive shaft is provided with an internal catch located below its driving end. As a result, the latching mechanism engages the internal catch once the driving end of the drive shaft is moved longitudinally relative to the anchoring support end of the mandrel and arrives at a predetermined engagement position relative thereto. 
         [0023]    In an aspect of the hole coring system, the motor&#39;s housing may be fixedly attached (e.g., bolted, etc.) to the drill motor coupling (e.g., gearbox). In this manner, a torque reaction imposed on the motor&#39;s housing is resisted by the fixed attachment between the motor&#39;s housing and the drill motor coupling. 
         [0024]    In an aspect of the hole coring system, a torque arm may be attached to the drill motor coupling (e.g., gearbox) to assist in resisting the torque reaction imposed on the drill motor coupling. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    These and other features and advantages of the various embodiments disclosed herein will be better understood with respect to the following description and drawings, in which like numbers refer to like parts throughout, and in which: 
           [0026]      FIG. 1  is a side elevational view illustrating the mandrel of the hole coring system in isolation. 
           [0027]      FIG. 2  is a side elevational view of the mandrel stabilizing washer shown in isolation. 
           [0028]      FIG. 3  is a top plan view of the mandrel washer shown in  FIG. 2 . 
           [0029]      FIG. 4  is an elevational view showing the mandrel anchored in an anchor bore in a slab of concrete. 
           [0030]      FIG. 5  is a sectional elevational detail showing the lower coupling for the lower end of the drive shaft in isolation. 
           [0031]      FIG. 6  is an elevational detail showing one embodiment of an upper coupling for the upper end of the drive shaft, shown in isolation. 
           [0032]      FIG. 7  is a sectional elevational view showing the drive shaft assembly in which the couplings of  FIGS. 5 and 6  are engaged on the drive shaft, disposed upon the upper end of the mandrel of  FIG. 1 . 
           [0033]      FIG. 8  is an elevational view, partially broken away in section, of the tubular core drill bit shown in isolation. 
           [0034]      FIG. 9  is an exploded sectional detail illustrating the threaded connection and bearing sleeves at the lower end of the drive shaft assembly in preparation for engagement with the tubular core drill bit collar. 
           [0035]      FIG. 10  is a sectional elevational view showing the hole coring system with components assembled and in operation. 
           [0036]      FIG. 11  is an elevational detail illustrating a different upper drive shaft end threaded connection employing a water swivel. 
           [0037]      FIG. 12  is an alternative embodiment of the connection illustrated in  FIG. 11 . 
           [0038]      FIG. 13  illustrates another alternative embodiment of a mandrel employed according to the system. 
           [0039]      FIG. 14  is a sectional elevational view showing the hollow drive shaft assembly with a core drill bit engaged thereon being lowered onto the mandrel of  FIG. 13 . 
           [0040]      FIG. 15  illustrates retraction of the latching mechanism of the mandrel in the embodiment of  FIG. 14 . 
           [0041]      FIG. 16  illustrates engagement between the latching and catch mechanisms of the embodiment of  FIG. 14 . 
           [0042]      FIG. 17  is a sectional elevational view illustrating an alternative embodiment employing different types of catch and latching mechanisms. 
           [0043]      FIG. 18  is a top plan detail of the biasing spring and catch pin employed in the embodiment of  FIG. 17 , shown in isolation. 
           [0044]      FIG. 19  is a sectional elevational view showing the catch and latching mechanisms of the embodiment of  FIG. 17  engaged and illustrating removal of a concrete core from a concrete slab from which it has been extracted. 
           [0045]      FIG. 20  is an exploded, sectional elevational view illustrating another alternative embodiment. 
           [0046]      FIG. 21  is an elevational view, partially in section, showing the operation of the embodiment of  FIG. 20 . 
           [0047]      FIG. 22  is an enlarged elevational detail, partially in section, of a portion of the embodiment of  FIG. 21 . 
           [0048]      FIG. 23  is a top plan diagrammatic view showing the operating components illustrated in  FIG. 22 . 
           [0049]      FIG. 24  is a cross sectional view of an alternative embodiment. 
           [0050]      FIG. 24A  is an enlarged cross section of the embodiment shown in  FIG. 24 . 
           [0051]      FIG. 25  is a perspective view of the embodiment shown in  FIGS. 24 and 24A  during use. 
       
    
    
     DETAILED DESCRIPTION 
       [0052]      FIG. 10  illustrates a hole coring system  10 . The hole coring system  10  includes a mandrel  12 , an anchor mechanism  14  attached to the lower end of the mandrel  12 , a shoulder washer  16  for stabilizing the mandrel  12 , a drive shaft assembly  18 , and a hollow, tubular core drill bit  20 . The mandrel  12  is a long, solid steel rod having an upper engagement end  13  of hexagonal cross section and an externally threaded lower anchoring support end  24 . The mandrel  12  has a smooth, cylindrical, intermediate, outer surface  17  between its upper end  13  and its lower end  24 . The diameter of the lower mandrel end  24  is smaller than the diameter of the cylindrical outer surface  17 . The mandrel  12  is shown in isolation in  FIG. 1 . 
         [0053]    As shown in  FIG. 4  the lower, anchoring support end  24  is provided with an expansion anchor mechanism  14 . The anchor mechanism  14  is an expansion anchor that provides a rigid connection between the concrete material to be drilled, indicated at  22 , and the mandrel  12 . The anchor mechanism  14  in the illustration of  FIG. 4  has radially expanding wings  15  and an internally threaded neck that is threadably engaged on the externally threaded lower anchoring support end  24  of the mandrel  12 . As the threaded end  24  is advanced into the anchor mechanism  14 , the lower ends of the wings  15  of the expansion anchor mechanism  14  are forced radially outwardly, thereby firmly lodging the anchor mechanism  14  in a relatively small diameter anchor bore  26  previously drilled into the concrete  22  using a conventional, small diameter masonry drill. In alternative embodiments, the anchor mechanism  14  may be, for example and not limitation, a toggle bolt, a glue-on system, or a glue-in system. 
         [0054]    Before inserting the lower end  24  of the mandrel  12  into the anchor mechanism  14 , the mandrel washer  16  is interposed between the anchor mechanism  14  and the larger, downwardly facing shoulder  28  at the lower end  24  of the mandrel  12 . The shoulder  28  is illustrated in  FIG. 1 . Beneath the shoulder  28  the mandrel  12  is provided with a neck  30  just slightly larger in diameter than the externally threaded tip of the lower mandrel end  24 , but smaller in diameter than the smooth, cylindrical, intermediate, outer surface  17 . The neck  30  is of an axial length just long enough to receive the shoulder washer  16 , shown in isolation in  FIGS. 2 and 3 . 
         [0055]    The shoulder washer  16  is an annular disc-shaped structure which may have a thickness of 0.20 inches and an outer diameter of 1.750 inches and serves as an annular, stabilizing plate. The shoulder washer  16  has a frustoconical surface  32  that tapers slightly from the outer diameter of the shoulder washer  16  up to a flat, annular bearing face  34 , which has an outer diameter of 1.250 inches. The diameter of the central aperture  36  of the shoulder washer  16  may, for example, be 0.625 inches. 
         [0056]    To install the mandrel  12  in the concrete slab  22 , the small diameter, cylindrical anchor bore  26  is first drilled with a masonry drill. The diameter of the bore  26  is of a size corresponding to the outer diameter of the expansion anchor mechanism  14  in its unexpanded state. The anchor mechanism  14  is then inserted into the bore  26  with a force fit against the walls thereof. It may be necessary to pound the anchor mechanism  14  into the position illustrated in  FIG. 4 . Thereafter, the shoulder washer  16  is inserted onto the lower end of the mandrel  12  oriented perpendicular thereto and disposed about the neck  30 . The threaded tip of the lower end  24  of the mandrel  12  is then advanced into the expansion anchor mechanism  14 , thereby forcing its expansion wings  15  radially outwardly against the cylindrical wall of the cylindrical anchor bore  26  so that the anchor mechanism  14  is tightly lodged in the bore  26 . The mandrel  12  may be advanced downwardly using a wrench to engage the hexagonal upper end  13 . 
         [0057]    The mandrel and washer are attached to the concrete. The mandrel  12  is tightened against the washer  16 , which has a considerably wider base. Eventually, the washer may be pulled against the concrete surface by the anchor mechanism. The mandrel  12  is tightened with sufficient tension so as to form a connection which provides a considerable degree of resistance to bending moment from the proper orientation of the mandrel  12  relative to the concrete slab  22 . In this way a stiff and accurate guide is provided for the core drill at some distance from the surface to be drilled. 
         [0058]    It is contemplated that the washer  16  be glued to the surface to be drilled, preferably by a fast setting glue. It is also contemplated that the washer  16  may have an adjustable angle for applications requiring a hole to be drilled at an angle to the surface to be drilled. 
         [0059]    The lower, externally threaded end  24  of the mandrel  12  is fully advanced into the anchor mechanism  14  until the shoulder  28  bears tightly downwardly to squeeze the mandrel washer  16  against the exposed, flat, horizontal upper surface of the concrete slab  22 . The lower extremity of the mandrel  12  is thereby lodged in the anchor mechanism  14 , which, in turn, is wedged tightly into the bore  26 . The portion of the mandrel  12  above its lower end  24  thereby forms a very firm, upright stabilizing and centering post for the drive shaft assembly  18 . The mandrel  12  is oriented perpendicular to the upper surface of the concrete slab  22 , as illustrated in  FIGS. 4 and 7 . 
         [0060]    The drive shaft assembly  18  is formed of a hollow, tubular, cylindrical annular drive shaft  38  having an externally threaded, hollow lower drill bit coupling  40  inserted into its lower extremity and an externally threaded drive motor coupling  42  inserted into its upper extremity. The lower coupling  40  is illustrated in section and in isolation in  FIG. 5 . The lower coupling  40  is provided with a barrel-shaped body with an externally threaded nipple  43  at its lower end. The nipple  43  may be provided with a 11/4-12 Class 3B thread. Above the nipple  43  the lower coupling  14  is provided with a radially outwardly tapered region  47  that terminates in a drive shaft seat  44  that defines an upwardly facing annular shoulder  46 . The shoulder  46  is of a diameter slightly greater than the outer diameter of the tubular drive shaft  38  so as to seat the lower edge of the drive shaft  38  which resides in abutment thereon, as shown in  FIGS. 7 and 9 . The lower coupling  40  is provided with a pair of diametrically opposed, internally threaded, radially directed fastener bores  48 , as illustrated in  FIG. 5 . The fastener bores  48  receive the externally threaded shanks of a pair of diametrically opposed shear pins  50 , as illustrated in  FIG. 10 . It is contemplated that the hollow drive shaft  38  may have a circular configuration or polygonal configuration (e.g., hexagonal, etc.). 
         [0061]    The interior of the lower coupling  40  has a smooth cylindrical wall  51  throughout most of its length but terminates at a reduced diameter collar  52  at its upper extremity. The smooth wall bore  51  through the lower coupling  40  accommodates at least one, and preferably a pair of cylindrical, annular Oil Lite bearing  54 . These are annular bronze sleeve-shaped bearings  54  formed of porous powdered metal and vacuum impregnated with oil that lasts the useful life of the bearings  54 . The pair of bearings  54  are visible in  FIGS. 7 and 10  and are illustrated in greater detail in the exploded view of  FIG. 9 . The internal diameter of the bearings  54  just fits over the outer diameter of the cylindrical intermediate outer surface  17  of the upwardly projecting shaft portion of the mandrel  12 . 
         [0062]    The nipple  43  of the lower coupling  40  is threadably engageable in the internally tapped collar  56  attached to the tubular core drill bit  20 , as indicated in  FIG. 9 . The collar  56  is internally chamfered and has a elevated, frustoconical band  57  at its upper extremity. The band  57  is elevated a distance of 0.010 inches above the chamfered region  57 ′ located beneath and radially inwardly from the band  57 . That is, the outer annular band  57  is raised a small distance up from the inner chamfered surface  57 ′. The reason for providing the frustoconical band  57  on the internal engagement surface of the collar  56  is to provide a stabilizing bearing surface that resists torsional forces acting in a vertical plane that passes through the axis of alignment of the drive shaft assembly  18 . 
         [0063]    The collar  56  is internally threaded at  59 , as shown in  FIG. 9 . Due to the necessary tolerances that are required between the threaded nipple  43  and the internal threads  59  in the collar  56 , bending forces exist that would otherwise tend to bend the drive shaft assembly  18  out of precise coaxial alignment with the collar  56 . However, by providing the elevated frustoconical band  57  radially outboard as far as possible from the axis of alignment of the drive shaft assembly  18  and the collar  56 , the complete, tightened engagement of the threads of the nipple  43  with the internal threads  59  provides centering and alignment forces at the interface between the two matched, inclined surfaces  57  and  47 . The result is that the drive shaft assembly  18  is clamped tightly to the core drill bit  20  so that the drive shaft assembly  18  and the core drill bit  20  are held in tight, nearly perfect alignment. These forces correct the “play” that would otherwise occur between the male threads of the nipple  43  and the female threads  59  of these two key components, namely the lower coupling  40  and the collar  56 . 
         [0064]    The collar  56  includes a radial, annular flange  58  that provides a seat for the upper edge of the relatively large diameter, cylindrical, annular portion  60  of the tubular core drill bit  20 , as illustrated in  FIG. 8 . The core drill bit  20  has an opposite, annular lower edge  21  that is serrated and has a multiplicity of industrial diamond concrete cutting teeth thereon. 
         [0065]    At its upper end extremity the drive shaft assembly  18  is provided with an upper coupling member, which may be the drill bit coupling  42  illustrated in  FIGS. 6 and 10 . The coupling member  42  has a hollow, cylindrical duct  62  defined axially down its center, as shown in  FIGS. 7 and 10 . The duct  62  is provided to receive water from a conventional water feed drill motor equipped with its own cooling water supply (not shown). The upper, hollow extremity of the upper drill bit coupling  42  terminates in an externally threaded male tip  64  that is engaged in a female socket in the conventional water-feed drill motor. The upper coupling  42  is rigidly attached to the upper extremity of the tubular drive shaft  38  by means of a pair of diametrically opposed shear pins  66  that have shanks that extend into radial bores defined in the wall structure of the upper coupling  42 , as illustrated in  FIGS. 7 and 10 . 
         [0066]    Once the mandrel  12  has been installed in the concrete  22  so that its upper extremity extends upwardly in the manner of an upright guidepost, as illustrated in  FIG. 4 , the male connector  64  of the upper coupling  42  is threaded into the internally threaded female socket in the water-cooled drill motor, while the nipple  43  at the lower coupling  40  is threaded into the collar  56  of the tubular core drill bit to which it is rigidly connected, as indicated in  FIG. 9 . The hole coring assembly  10  is then lowered down onto the mandrel  12 , with the bearings  54  residing in contact with the outer surface  17  of the mandrel  12  to ensure precise, coaxial alignment of the drive shaft  38  of the drive shaft assembly  18  relative to the mandrel  12 , as shown in  FIG. 10 . 
         [0067]    Once the teeth at the lower edge  21  of the tubular core drill bit  20  reach the upper surface of the concrete slab  22 , the drill motor is operated, thereby rotating the entire drive shaft assembly  18  in rotation about the stationary mandrel  12 . The permanently lubricated bearing sleeves  54  allow high speed rotation-of the drive shaft assembly  18  relative to the mandrel  12 . For example, where the outer diameter of the tubular core drill bit  20  is four inches, the drive shaft assembly  18  can be rotated at a speed of 6000 RPM. In contrast, the same drill bit of a conventional Core Drill Rig can only be rotated at a maximum speed of about 600 RPM. The ability to rotate the core drill bit  20  at high speed allows the operator to manage the same horsepower with less torque reaction. As a result the force applied to the cutting surfaces is lower and the cutting speed of the diamond teeth used is closer to optimum cutting speed. This allows the system to cut as fast as a drill rig of similar power. 
         [0068]    Furthermore, in the hole coring system, the bearings  54  are located much closer to the upper surface concrete material  22  than the bearings of a conventional tubular core drill bit assembly. By stabilizing the drive shaft  38  closer to the surface of the concrete slab  22 , greater stability and precise centering of the tubular core bit assembly  20  relative to the stationary mandrel  12  is achieved. The relatively long overall lengths of about three inches of the tandem mounted bearings  54  within the lower coupling  40  aid in stabilizing the drive shaft assembly  18 , so that it remains perpendicular to the concrete slab  22 . 
         [0069]    The hole coring system  10  may be utilized to drill large holes such as holes having a diameter greater than three (3) inches. For drilling holes having a diameter of between three inches and eight inches, the anchor bore  26  preferably has a diameter of about one-half inch. For drilling holes having a diameter significantly greater than eight inches, the anchor bore  26  may preferably be replaced with a group of two or more anchors at a generally central area of the hole to be bored. 
         [0070]    Once the drive shaft assembly  18  with the tubular core drill bit assembly  20  attached thereto has been lowered onto the mandrel  12  and centered relative thereto by the bearings  54 , the cooling and flushing water is turned on, and the motor is actuated to turn the drive shaft assembly  18 . Rotation of the core bit assembly  20  starts when the lower edge of the core drill bit  20  is just above the surface of the concrete  22  to be cut. The core drill bit  20  is then pushed gently downwardly with a force sufficient to overcome the water pressure of the cooling water that is entrapped between the mandrel  12  and the core drill bit  20 . 
         [0071]    The mandrel  12  is an accurately sized piece of high strength steel. The mandrel  12  forms a guide and axle about which the cylindrical, annular, saw blade  60  spins at high speed. The drive shaft assembly  18  serves the dual function of connecting the motor power for turning the core drill bit  20 , and also guiding the core drill bit  20  by means of the internal bearing sleeves  54  that run on the mandrel  12 . Depending upon the depth of the large diameter hole to be cut, it may be necessary to withdraw the core drill bit  20 , break off the concrete core that has been cut, and then drill further using the hole that has been cut that far as a guide for further drilling. 
         [0072]    During the drilling process, cooling and flushing water flows from the water supply within the drill motor down through the central duct  62 , down through the hollow drive shaft  38 , and into the annular space between the inner surface of the drive shaft  38  and the outer surface  17  of the mandrel  12 . The cooling water flows through the neck at the upper end of the lower coupling  40  and past the bearings  54  which provide sufficient clearance for the passage of liquid. The cooling water flows downwardly into the cylindrical, annular cavity between the mandrel  12  and the inner wall surface of the core bit  20 , and down into the cylindrical, annular groove or channel cut by the industrial diamond teeth at the lower edge  21  of the core bit assembly  20  into the concrete  22 . Water is flushed downwardly below the lower cutting teeth of the core bit  20  and back upwardly alongside the outer surface of the core bit  20  to flush powdered concrete granular material radially outwardly away from the hole coring system  10  and across the flat upper surface of the concrete slab  22 . 
         [0073]    It is to be understood that numerous variations and modifications of the components of the hole coring system are possible. For example, the particular adapter or lower drill bit coupling  42  is designed for use with an electric drill motor having its own water supply.  FIG. 11  illustrates an alternative embodiment in which the upper coupling  142  is an adapter for a drill chuck without a water supply. The coupling  142  is provided with a water swivel  144  having a radial port  146  through which water is directed radially inwardly and then down alongside the shank  148  of the adapter  142 . 
         [0074]      FIG. 12  illustrates still another embodiment in which an electric grinder adapter  242  is also provided with a water swivel  144  having radial water input apertures  146 . The adapter  242  differs from the adapter  142  in that the adapter  142  includes a stepped shank having an upper, larger diameter portion and also a narrower, lower small diameter portion. In the embodiment of  FIG. 12  the shank  248  of the adapter  242  has a uniform diameter throughout. 
         [0075]    Once the core has been cut, the mandrel  12  can be used as a handle to remove the concrete core from the concrete slab  22 . The freshly cut concrete core can be dislodged from the mandrel  12  so that the mandrel can be reused. 
         [0076]    Different mandrels are available and may be utilized. For example, a self-drilling mandrel may be utilized if the material to be drilled is plastic, rather than concrete. Also, mandrel anchors may be provided as either disposable items or reusable structures. Reusable anchors are preferably provided for the larger diameter anchor holes. 
         [0077]    The drill motor that drives the drive shaft can be any one of a multitude of power drill motors that are available in the construction industry. Also, while water is preferably supplied in the drilling process as the preferred cutting fluid, other liquids such as oil or some other fluid may be utilized instead. 
         [0078]    As previously explained, a very advantageous feature involves the releasable latching of the hollow drive shaft to the mandrel.  FIGS. 13-16  and illustrate one such embodiment employing a hollow mandrel  120  which may be releaseably engaged by the hollow drive shaft  180 . The hollow mandrel  120  is illustrated in isolation in  FIG. 13  and defines a mandrel cavity  122  of circular cross-section therewithin. The mandrel  120  has an upper engagement end  123  and a lower anchoring end  124  while an upper internal bearing ledge  127  ( FIG. 16 ) is located a short distance below the upper engagement end  123 . A lower internal bearing ledge  126  is located above the anchoring support end  124 . The lower internal bearing ledge  126  serves as a delineation in the mandrel cavity  122  between an intermediate cylindrical cavity portion  128  and a lower cylindrical cavity portion  130 . The upper bearing ledge  127  delineates the intermediate cylindrical cavity portion  128  from an upper cylindrical cavity portion  129 . The intermediate cylindrical cavity portion  128  is greater in diameter than the lower cylindrical cavity portion  130 , while the upper cylindrical cavity portion  131  is slightly greater in diameter than the intermediate cylindrical cavity portion  128 . 
         [0079]    A longitudinally extending, elongated slot  132  is defined diametrically through the mandrel  120  and extends radially between the smooth, cylindrical intermediate outer surface  17  thereof and the lower cylindrical cavity portion  130  therewithin. The elongated slot  132  is located beneath the bearing ledge  126 . 
         [0080]    Diametrically opposed, circular, radial latching lug openings  134  are defined a short distance beneath the upper engagement end  123  in the hollow mandrel  120 . The latching lug openings  134  extend between the smooth, cylindrical, intermediate, outer surface  17  of the hollow mandrel  120  and the upper, cylindrical cavity portion  128  therewithin. 
         [0081]    A piston  150  is provided which has a circular cross-section and a shoulder  152  which divides the piston  150  into a cylindrical, enlarged diameter upper portion  154  and a cylindrical, reduced diameter lower portion  156 . The piston  150  is mounted for reciprocal movement within the mandrel cavity  122 . 
         [0082]    A transverse latch release lever  158  passes diametrically through the reduced diameter lower portion  156  of the piston  150  and through the slot  132  to project radially outwardly behind the cylindrical outer surface  17 . The latch release lever  158  provides a means for manually moving the piston  150  in reciprocal nature within the cavity  122  in the hollow mandrel  120 . The bearing ledge  126  limits the downward movement of the shoulder  152  of the piston  150  within the hollow mandrel  120 , while the upward movement of the piston  150  is limited when the latch release lever  158  reaches the top of the elongated slot  132 . 
         [0083]    A piston head  160  is located atop the piston  150  and is illustrated in greater detail in  FIGS. 14-16 . The piston head  160  has a cylindrical, annular upper portion  162  that slides smoothly within the smooth wall of the upper cylindrical cavity portion  129  of the mandrel cavity  122 . At its lower extremity the piston head  160  is necked down to form as part of its structure a lower, reduced diameter latching lug receiving neck  164 . 
         [0084]    A pair of diametrically opposed latching lugs in the form of a pair of small spheres  166  are located in the mandrel  120  within the diametrically opposed radial latching lug openings  134  therein. The mouth apertures of the transverse, radial latching lug receiving openings  134  at the outer surface  17  of the mandrel  120  are very slightly smaller in diameter than the transverse, radial openings  134  and the spherical lugs  166  therein. Consequently, while the radial outermost surfaces of the spherical latching lugs  166  can protrude radially outwardly behind the outer diameter of the smooth, cylindrical outer surface  17 , as illustrated in  FIG. 13 , the spherical lugs  66  remain entrapped by the structure of the mandrel  120 . 
         [0085]    A coil spring  168  is located within the upper cavity portion  129  of the hollow, cylindrical cavity  122  within the mandrel  120  atop the piston head  160 . The coil spring  168  is compressed against the top of the piston head  160  by an annular plug  170 . The coil spring  168  thereby biases the piston head  160  and the piston  150  in a downward direction toward the anchoring support end  124  of the mandrel  120 . This biasing action normally pushes the latching lug receiving neck  164  out of radial alignment with the spherical latching lugs  166 . As a consequence, under the normal actions of the biasing spring  168 , the upper portion  162  of the piston head  160  pushes the latching lugs  166  radially outwardly so that their outer surfaces protrude slightly radially beyond the outer surface  17  of the mandrel  120 , as illustrated in  FIG. 13 . 
         [0086]    The hollow, cylindrical annular drive shaft  180  differs in construction from the drive shaft  18 . Specifically, the interior diameter of the interior wall surface  183  of the intermediate portion of the drive shaft  180  above the lower coupling  40  is smaller than the interior diameter of its lower end. The lower end of the drive shaft  180  thereby forms an internal socket  181  that receives the lower coupling  40  therewithin. However, the diameter of the interior wall surface  183  is slightly greater than the interior diameter of the bearing  54  so that it provides clearance for the outer surface of the spherical lugs  166 , as illustrated in  FIG. 16 . Also, an internal, radial annular channel  182  of even greater diameter is defined just above the socket  181  that receives the lower coupling  40 . The channel  182  is located within the drive shaft  180  and below the wall surface  183  of the interior intermediate portion of the drive shaft  180  between the driving end thereof (not visible) and the bearings  54 . 
         [0087]    In operation the drive shaft  180  is disposed coaxially about the mandrel  120  and lowered in coaxial alignment therewith, as illustrated in  FIG. 14 . However, due to the force of the biasing spring  168 , the piston head  160  and the piston  150  are pushed downwardly so that the shoulder  152  of the piston  150  resides in abutment against the internal bearing ledge  126  within the mandrel  120 . When the piston head  160  is forced downwardly in this manner, the latching lug receiving neck  164  is located within the mandrel  120  at a level lower than the latching lugs  166 , so that downward movement of the hollow drive shaft  180  is limited by the interference between the lowermost cylindrical bearing  54  and the radially outwardly protruding portions of the latching lugs  166 . 
         [0088]    When the hollow drive shaft  180  is lowered to the position depicted in  FIG. 14 , the user lifts upwardly on the latch release lever  158 , thereby overpowering the spring  168  and pushing the piston  150  upwardly within the mandrel cavity  122 , as illustrated in  FIG. 15 . When the latch release lever  158  resides in abutment against the upper edge of the longitudinally elongated slot  132 , the latching lug receiving neck  164  of the piston head  160  resides in longitudinal registration and in radial alignment with the spherical latching lugs  166 . This allows the spherical latching lugs  166  to be pushed radially inwardly by the weight of the drive shaft  180  and the annular core drill bit  20 , which can then be lowered downwardly toward the surface of the concrete  22 , as indicated in  FIG. 15 . 
         [0089]    The drill motor is then coupled to the upper end of the drive shaft  180  and operated, thereby driving the drive shaft  180  in rotation about the hollow mandrel  120 . As the annular core drill bit  20  progresses downwardly the lower coupling  40  and the lower end of the drive shaft  180  also move downwardly, as illustrated in  FIG. 15 . Once the lower coupling  40  advances downwardly past radial alignment with the piston head  160 , its upper edge clears the spherical latching lugs  166 , as illustrated in  FIG. 16 . Without radial resistance against the spherical latching lugs  166  applied by the bearings  54  within the lower coupling  40 , the force of the spring  168  is sufficient to push the piston head  160  and the piston  150  back downwardly thereby forcing the upper portion  162  of the piston head  160  into longitudinal registration with the spherical latching lugs  166 . This movement forces the spherical latching lugs  166  radially outwardly and into the gap that exists at the radial, annular channel  182  defined near the lower end of the hollow, cylindrical annular drive shaft  180  just above the lower coupling  40 . 
         [0090]    Clearance also exists between the radially extended latching lugs  166  and the drive shaft interior wall surface  183  as the drill bit  20  descends further into the concrete slab  322 . When this occurs the spherical latching lugs  166 , which form the engageable part of the latch mechanism of this embodiment, have sufficient clearance with respect to the interior wall surface  183  to allow continued downward movement of the drive shaft  180  about the hollow mandrel  120 . This downward movement continues until the annular drill bit  20  cuts completely through the slab of the concrete  322 . 
         [0091]    At this point the mandrel  120 , together with the “doughnut” of concrete in which is embedded tend to drop downwardly relative to the drive shaft  180 . However, once the mandrel  120  drops sufficiently so that the spherical latching lugs  166  meet the upper edge of the lower coupling  40 , further downward movement is arrested. This is because the upper portion  162  of the piston head  160  has a large enough diameter so that the spherical latching lugs  166  cannot be pushed radially inwardly within the openings  134  a sufficient distance to clear the internal diameter of the upper end of the lower coupling  40 . As a consequence, the spherical latching lugs  166  are lodged in the internal, radial, annular channel  182  in the hollow drive shaft  180 , so that they releaseably couple the mandrel  120  to the hollow drive shaft  180 . The mandrel  120  remains engaged with the hollow drive shaft  180  until the latch release lever  158  is again purposely forced upwardly in the slot  132  to overcome the biasing spring  168  and bring the piston head neck  164  into longitudinal registration with the spherical latching lugs  166 . This allows the mandrel  120  to be withdrawn from the drive shaft  180 . 
         [0092]      FIGS. 17 ,  18  and  19  illustrated a further, preferred embodiment in which the mandrel  212  is formed as a solid rod like the mandrel  12 , but is provided with a releaseable latching mechanism in the form of a reduced diameter latching neck  222  located just below the hexagonal shaped upper mandrel end  13 . The cylindrical, hollow annular drive shaft  280  is provided with a radially disposed catch pin  282 . The drive shaft  280  has a radial catch pin receiving opening defined at its lower end through its cylindrical annular wall to receive the catch pin  282 . Corresponding, aligned radial openings are also formed through the lower coupling  240  and the uppermost bearing  254  located radially within the confines of the lower coupling  240 . 
         [0093]    The catch pin  282  is secured to a generally horseshoe-shaped clip spring  284 , illustrated in isolation in  FIG. 18 , and projects radially inwardly therefrom. The feet  286  of the spring clip  284  embrace the outer surface of the drive shaft  280  so that the arcuate portion  285  of the clip  284  is normally slightly elastically deformed when the inner tip of the catch pin  282  bears radially inwardly pressed into contact with the cylindrical outer surface  17  of the mandrel  212 , as illustrated in  FIG. 17 . The spring clip  284  resiliently biases the catch pin  282  radially inwardly, urging it against the cylindrical outer surface  17  of the mandrel  212 . 
         [0094]    The catch pin  282  is radially movable within the catch receiving opening defined in the outer wall of the drive shaft  280  and the aligned apertures through the lower coupling  240  and the upper, cylindrical bearing  254 . The hollow drive shaft  280  is normally longitudinally movable relative to the mandrel  212 , as well as rotatable at high-speed rotation relative thereto. Therefore, as the large diameter core drill bit  20  drills an annular channel or groove into the concrete slab  322 , the hollow drive shaft  280  moves longitudinally toward the lower, anchored end  24  of the mandrel  212 . 
         [0095]    Once the core drill bit  20  cuts completely through the thickness of the concrete slab  322  the mandrel  212  and the chunk of concrete  324  within the circumference of the core drill bit  20  will tend to drop vertically downwardly from the position show in  FIG. 17 , free from the concrete slab  322 . However, the descent of the mandrel  212  and the “doughnut”  324  is halted when the latching neck  222  drops vertically to the level of the catch pin  282 . This occurs when there is sufficient relative longitudinal movement between the hollow, cylindrical annular drive shaft  280  and the mandrel  212  to bring the catch pin  282  into longitudinal registration with the latching neck  222 . That is, when the mandrel  212  drops downwardly far enough, the bias of the spring  284  pushes the catch pin  282  radially inwardly into engagement with the latching neck  222 , thereby longitudinally immobilizing the mandrel  212  relative to the drive shaft  280 . 
         [0096]    The drive shaft  280  can then be lifted vertically, carrying the mandrel  212  and the concrete “doughnut”  324  with it, as illustrated in  FIG. 19 . By releaseably coupling the mandrel  212  to the drive shaft  280 , damage or injury in the area beneath the concrete slab  322  is avoided. Once the drive shaft  280  and the mandrel  212  have been raised upwardly, as illustrated in  FIG. 19 , the mandrel  212  can be released by pressing laterally inwardly against the sides of the spring clip  24  which bows the arcuate portion  285  of the spring clip  284  radially outwardly, away from the mandrel  212 . This action pulls the catch pin  282  radially out from engagement with the latching neck  222 . 
         [0097]      FIGS. 20-23  illustrate a further preferred embodiment especially suitable for use in drilling larger diameter bores. As shown in  FIG. 20 , the mandrel  412  may have an upwardly projecting engagement end  413  which may be externally threaded. In this embodiment, the anchoring end  414  of the mandrel  420  may be attached to plate or washer  416 . The plate or washer  416  may be bolted to the concrete slab  322  by concrete bolts  415 . The bolts  415  may be tightened until the plate or washer  416  is tightly pushed against the concrete slab  322 . The angle of the madrel  412  to the concrete slab  322  may determine the angle of the hole to be drilled. 
         [0098]    The lower, coupling end  481  (see  FIG. 21 ) of the hollow, tubular drive shaft  480  may be permanently and rigidly secured to the tubular, annular core drill bit  420 . The upper driving end portion  483  (see  FIG. 20 ) of the drive shaft  480  has a hexagonal, outer surface cross-sectional configuration. A cylindrical, annular Oil Lite sleeve bearing  54  (see  FIG. 21 ) is force fitted into the lower end portion  481  of the hollow drive shaft  480 . The sleeve bearing  54  assists in allowing the drive shaft  480  and drill bit  420  to remain centered on the mandrel  412  while rotating about the mandrel  412 . The sleeve bearing  54  aids in maintaining the drive shaft  480  and core drill bit  420  in precise coaxial alignment relative to the mandrel  412  during the cutting operation. 
         [0099]    A power transmission gearbox  430  is shown in  FIG. 21  and transmits rotational energy from a motor  492  to the drive shaft  480 . The gearbox  430  may be disposed about the upper driving end  483 , of the hollow, annular drive shaft  480 . The gearbox  430  contains a power input shaft  491  at its power input end which is journaled within the gearbox  430  for rotation of an output sleeve  497  (see  FIG. 22 ) and driven by a high-speed motor  492 . The motor  492  may be a conventional motor of the type utilized to rotate a saw blade for sawing concrete, electric saw, gas powered chop saw, etc. and may be provided with a saw blade guard  489 . However, when utilized, the saw blade is optionally removed and instead the saw motor  492  receives the upwardly projecting end of the power input shaft  491  that protrudes from the top of the gearbox  430 , as shown in  FIG. 21 . The motor  492  may also be fixedly attached to the gearbox  430  such that the motor  492  does not rotate relative to the gear box  430 . By way of example and not limitation, the housing of the motor  492  may be bolted to the gear box  430 . 
         [0100]    The gearbox  430  contains gears  493  and  494  and a chain drive system  495 ,  496 . These power transmission elements reduce the speed and increase the torque of power delivered from the motor  492 . The chain drive system  495 , 496  rotates the power output sleeve  497  that has an internal axial opening of hexagonal cross-sectional configuration, as shown in  FIG. 23 . The sleeve  497  fits smoothly about the outer, hexagonal cross-sectional surface of the driving end  483  of the drive shaft  480  to drive it in rotation therewith. 
         [0101]    The sleeve  497  rotates freely within bearings provided in the gearbox  430 , but is entrapped by upper and lower retaining ledges  498  and  499  (see  FIG. 22 ) so that it is retained and longitudinally confined within the gearbox  430 . The drive shaft  480  and the power output sleeve  497  may interlock with each other such that rotation of the power output sleeve  497  operates to rotate the drive shaft  480 . By way of example and not limitation, as discussed above, the outer surface cross sectional configuration of the drive shaft  480  may be hexagonal. Similarly, the inner surface cross sectional configuration of the power output sleeve  497  may have a corresponding hexagonal shape. They  480 ,  497  may have a uniform cross section throughout in an axial direction, so that free longitudinal movement of the sleeve  497  relative to the drive shaft  480  parallel to the axis of the mandrel  412  is possible. During operation, the power output sleeve  497  may be disposed about the drive shaft  480 . The size of the inner surface cross sectional configuration of the power output sleeve  497  may be sized such that the power output sleeve  497  may slide onto the drive shaft  480  and yet rotate the drive shaft  480  upon rotation of the power output sleeve  497 . 
         [0102]    Atop the drive shaft  480  there is a hollow, annular thrust bearing  500  (see  FIG. 21 ) at its upper extremity with an internal diameter slightly larger than the outer diameter of the threaded upper end  413  of the mandrel  412 . A hollow, cooling water delivery collar  502  is located directly above the thrust bearing  500  and has a cooling water inlet line  504  connected thereto to receive cooling water as indicated by the directional arrow  506  (see  FIG. 21 ). The collar  502  may be elongate to allow the advancement nut  508  to displace the drill bit  420  to a predetermined depth or until the drill bit  420  has penetrated the entire thickness of the substrate. The thrust bearing  500  permits relative rotation of the upper driving end  483  of the drive shaft  480  relative to the cooling water delivery collar  502 . Immediately above the cooling water delivery collar  502  there is a drill bit advancement nut  508  that is threadably engaged with the threaded upper end  413  of the mandrel  412 . A drill crank advancement arm  510  is secured by welding to the drill bit advancement nut  508  and projects radially therefrom. A vertically extending crank handle  512  projects perpendicularly upwardly from the radial outboard end of the crank arm  510 . The operator may turn the drill bit advancement nut  508  to traverse the drill bit  420  into the concrete slab  322 . 
         [0103]    The power transmission gearbox  430  is disposed about the drive shaft  480  and is located longitudinally between the drill bit advancement nut  508  and the anchoring support end  414  of the mandrel. Prior to drilling, the plate or washer  416  is first secured to the upper surface of the concrete slab  322  by means of the concrete bolts  415  (see  FIGS. 20-21 ). The upper driving end  483  of the drive shaft  480  is then inserted through the hexagonal opening in the power output sleeve  497  that is entrapped within the gearbox  430 . The drive shaft  480 , with the core drill bit  420  rigidly secured thereto, is then lowered onto the mandrel  412  with the hollow, tubular upper driving end  483  of the drive shaft  480  disposed coaxially about the mandrel  412  and in spaced separation therefrom. The threaded upper end  413  of the mandrel  412  thereby projects up through the gearbox  430  and the drive shaft  480  and through the hollow thrust bearing  500 , as shown in  FIG. 21 . 
         [0104]    The cooling water delivery collar  502  is then lowered onto the exposed tip of the upper end  413  of the mandrel  412  and the drill advancement nut  508  is then threaded onto the upper extremity of the upper end  413  of the mandrel  412  and advanced downwardly toward the mandrel base  414  until the teeth of the annular saw blade of the core drill bit  420  exert a light downward pressure against the upper, exposed surface of the concrete slab  322 . 
         [0105]    Prior to interlocking the power output sleeve  497  and the drive shaft  480 , the power input shaft  491  of the gearbox  430  may be coupled to the motor  492 . By way of example and not limitation, the spindle of the motor  492  may be coupled to the power input  491  Also, the motor  492  may be fixedly attached to the gear box  430 . After all of the components are assembled, the motor  492  is then started, thereby causing the power input shaft  491  to rotate and to drive the sleeve  497  in rotation at reduced speed and increased torque. The motor  492  does not rotate with respect to the gear box  430  because the housing of the motor  492  may be fixedly attached to the gearbox. However, the gearbox  430  and the motor  492  may be urged in an opposite direction compared to the drill bit rotation due to the frictional forces caused by the drill bit  420  and the substrate. The operator may hold the gear box  430  and the motor  492  in place. 
         [0106]    At the same time, cooling water is fed into the cooling water delivery collar  502  and flows down through the hollow drive shaft  480  alongside the mandrel  412 . The flow of cooling water is forced downwardly due to the fluid pathway formed in the cooling water delivery collar  502 . From there the water flows laterally upon the surface of the concrete slab  322 , and down into the annular groove being drilled by the annular core drill bit  420 . The cooling water flows through the annular channel formed by the cutting teeth of the core drill bit  420  and flushes the particulate concrete grit created outwardly across the upper surface of the concrete slab  322  and outward away from the drill bit  420 . 
         [0107]    As drilling progresses the operator rotates the crank handle  512  in an orbital path about the upright mandrel  412  to advance the drill advancement nut  508  slowly toward the base  414  of the mandrel  412 . This creates a downward force against the annular thrust bearing  500  at the top of the drive shaft  480  and presses the cutting edge of the annular core drill bit  420  into the concrete slab  322 . The advancement nut  508  may be advanced downward. Also, coaxial alignment of the drive shaft  480  and the core drill bit  420  relative to the mandrel  412  is maintained. 
         [0108]    As the drilling proceeds, the operator slowly advances the handle  512  in rotation about the mandrel  412  to continually press the cutting edge of the core drill bit  420  downwardly into the annular channel created as the drill bit teeth (i.e., cutting edge) bite into the concrete slab  322 . As the drive shaft  480  is forced downwardly, the motor  492  and the gearbox  430  are also moved down with the drive shaft  480 . 
         [0109]    Rotation of the drive shaft  480  by the power input from the motor  422  continues in this fashion while maintaining continuous downward pressure upon the teeth of the drill bit  420  by continuous advancement of the core drill bit advancement nut  508 . Drilling continues until the annular channel created by the rotating teeth of the drill bit  420  cuts the concrete slab  322  to a predetermined depth or completely through to the far side of the slab  322 . [0110] Referring now to  FIGS. 24-25 , a hole coring system  10  for producing a large diameter hole in a substrate  550  is shown. The substrate  550  may be a concrete slab  22 ,  322  or some other material such as plastic, wood, etc. In  FIG. 24 , the substrate  550  may define a generally horizontal ground surface  552 . It is contemplated that the hole coring system  10  may be utilized to drill holes in a vertical surface, angled surface or a ceiling. To begin preparation for drilling a large hole in the substrate  550 , a mandrel  554  may be secured to the surface  552  of the substrate  550 . As discussed previously, the mandrel  554  may be secured to the substrate  550  with a concrete anchor or other attachment mechanism. By way of example and not limitation, the mandrel  554 , and more particularly, the plate or washer  416  may be attached to the surface  552  with concrete bolts  415 , as shown in  FIG. 24A . 
         [0110]    With the mandrel  554  attached to the surface  552 , the drill bit  420  and the attached drive shaft  480  may be disposed about the mandrel  554 . More particularly, the mandrel  554  may comprise a distal end portion  556  (i.e., guide post) having a smooth cylindrical configuration and a proximal end portion  558  having threads. The proximal and distal end portions  558 ,  556  may be coaxially aligned to each other. The drive shaft  480  may have a sleeve bearing  54  (see  FIG. 24A ) attached within the drive shaft  480 . The sleeve bearing  54  coaxially aligns the drive shaft  480  and the drill bit  420  to the longitudinal axis  560  of the mandrel  554 . Additionally, the sleeve bearing  54  permits the drive shaft  480  and the drill bit  420  to rotate about the longitudinal axis  560  of the mandrel  554  while maintaining coaxial alignment between the mandrel  554  and the drill bit  420 . Additionally, the sleeve bearing  54  may be independently slid longitudinally along the distal end portion  556  of the mandrel  554  to guide the drill bit  420  into the substrate. The drill bit  420  is operative to form a hole in the substrate  550  via (1) rotation of the drill bit  420  about the longitudinal axis  560  of the mandrel  554  and (2) pressure applied to the surface  552  of the substrate  550  by a cutting edge  562  of the drill bit  420 . With the application of pressure and rotation of the drill bit  420 , the drill bit  420  produces an annular groove in the substrate  550 . The drill bit  420  is rotated and pressure applied to the substrate  550  until the drill bit  420  has penetrated the substrate  550  to a predetermined depth or until the drill bit  420  has formed a hole through the substrate  550  (see  FIG. 24 ). 
         [0111]    The drill bit  420  may be rotated under a power of a motor  564 . The motor  564  may be an electric drill, hand held radial saw, gas powered chop saw (see  FIG. 25 ) or other device for producing a rotating shaft. The motor  564  may be coupled to the drive shaft  480  via a gearbox  430 . More particularly, the drive shaft  480  may have a proximal end portion  568 . The proximal end portion  568  of the drive shaft  480  may have a polygonal outer surface configuration (e.g., hexagonal). The gearbox  430  may have a power output sleeve  497  defining an inner surface. The cross sectional configuration of the inner surface of the power output sleeve  497  may have a corresponding configuration to the outer surface cross sectional configuration of the proximal end portion  568  of the drive shaft  480 . The proximal end portion  568  of the drive shaft  480  may be inserted into the power output sleeve  497  to interlock the power output sleeve  497  and the drive shaft  480 . Upon rotation of the power output sleeve  497 , the drive shaft  480  and the drill bit  420  may also be rotated. 
         [0112]    Below a distal end portion of the drive shaft  480 , a shoulder  570  (see  FIG. 24A ) may be formed. The shoulder  570  may be a snap ring fitted within a groove of the drive shaft  480  and attached to the drive shaft  480 . The shoulder  570  may be gapped or spaced apart from the proximal surface  572  of the drill bit  420 . The drive shaft  480  is inserted into the power output sleeve  497  until the power output sleeve  497  contacts the shoulder  570 . Accordingly, the gearbox  430  is gapped above the drill bit  420 . 
         [0113]    Prior to interlocking the power output sleeve  497  and the drive shaft  480 , the motor  564  may be attached to a power input shaft  491  of the gearbox  430 . The power input shaft  491  may protrude from the gearbox  430  away from the substrate  550 , as shown in  FIG. 24 . Moreover, the power input shaft  491  may have a threaded hole  574 . Typically, the motor  564  will have a rotating threaded stud  576 . The threaded stud  576  may be threaded into the threaded hole  574 . To assist in the engagement of the threaded hole  574  of the power input shaft  491  to the threaded stud  576  of the motor  564 , the gearbox  430  may additionally have a rotateable shaft  578  (see  FIG. 24 ). The rotateable shaft  578  may have a wrenching surface that permits an operator to turn the shaft  578  in the clockwise or counter-clockwise direction with a wrench. Upon rotation of the shaft  578 , the power inputs shaft  491  also rotates. To thread the threaded stud  576  of the motor  564  into the threaded hole  574  of the power input shaft  491  of the gearbox  430 , the distal end of the threaded stud  576  may be aligned against the threaded hole  574 . The user may rotate the rotateable shaft  578  in the appropriate direction via a wrench in order to threadingly engage the threaded stud  576  into the threaded hole. The user continues to rotate the shaft  578  until the threaded stud  576  is secured to the threaded hole  574 . The housing of the motor  564  may be unsecured to the gear box  430 . Alternatively, it is contemplated that housing of the gearbox may be secured to the gearbox  430 , as previously described. With the motor  564  attached to the gearbox  430 , the power output sleeve  497  may be disposed around the proximal end portion  568  of the drive shaft  480 . The gearbox  430  is stopped by the shoulder  570  such that the distal end  580  of the rotateable shaft  578  does not interfere with the drill bit  420 . This may be particularly problematic when the radius of the drill bit  420  is equal to or greater than the distance between the power output sleeve  497  and the rotateable shaft  578 . The shoulder  570  helps to lift or gap the gearbox  430  away from the drill bit  420  such that the rotateable shaft  578  does not contact or interfere with the drill bit  420 . 
         [0114]    After the gearbox  430  is mounted to the drive shaft  480 , a collar  582  may be disposed about the mandrel  554 , and more particularly, a proximal end portion  558  of the mandrel  554 . The distal end of the collar  582  may have a thrust bearing that interfaces with the proximal portion of the drive shaft  480 . The thrust bearing located at the distal end portion of the collar  582  permits rotation of the drive shaft while the collar  582  does not rotate and generally remains stationary. The proximal end portion of the collar  582  may also have a thrust bearing. On top of the collar  582 , an advancement nut  508  may be threaded onto the threaded proximal end portion  558  of the mandrel  554 . The advancement nut  508  engages the thrust bearing at the proximal end portion of the collar  582 . As the advancement nut  508  is advanced along the proximal end portion  558  of the mandrel  554 , a force is transferred through the collar  582 , drive shaft  580  and the drill bit  420  such that the cutting edge  562  of the drill bit  420  applies pressure onto the surface  552 . 
         [0115]    In summary, the motor  564  rotates the drill bit  420  via the gearbox  430 . The advancement nut  508  transmits a downward cutting force to the drill bit and into the substrate  550 . 
         [0116]    The collar  582  may be fitted with a liquid inlet line  504 , as shown in  FIG. 24A . The inlet line  504  may be tapped into the distal end portion of the collar  582 . An upper seal  616  disposed above the inlet line  504  may form a water seal between the mandrel  554  and the collar  582 . As fluid is injected into the inlet line  504 , the fluid enters the collar  582  and flowed downward between the drive shaft  480  and mandrel  554  then into the interior of the drill bit  420 . The fluid also enters the annular groove or channel created by the drill bit in the substrate  550  and exits outside of the drill bit  420 . The fluid may serve two purposes, namely, a lubricating function and a cooling function. The fluid may lubricate and cool the sleeve bearing  54  on the distal end portion  556  of the mandrel  554 . Moreover, the fluid may remove frictionally generated heat between the cutting edge  562  and the wall of the drill bit  420  with the substrate  550 . 
         [0117]    Referring now to  FIG. 25 , the gearbox  430  may have a lever arm  600 . The lever arm  600  may be bolted to and extend away from the gearbox  430 . Preferably, the lever arm  600  is telescoping such that the operator may adjust the length of the lever arm to resist any torsional rectional forces caused by the rotation of the drill bit  420  into the substrate  550 . Instead of holding the lever arm  600  manually with a hand, a brace  602  may be attached to an adjacent structure or the surface  552  (see  FIG. 25 ). The brace  602  may be sufficiently tall such that the lever arm  600  will contact the brace  602  at the start of the cutting operation. The brace  602  may additionally have a front surface  604  which may be generally parallel to the longitudinal axis  560  of the mandrel  554 . In this manner, as the drill bit  420  penetrates the substrate  550 , the gearbox  430  as well as the lever arm  600  will approach the surface  552 . The lever arm  600  may slide against the front surface  604  as the drill bit  420  penetrates the substrate  550 . 
         [0118]    Additionally, a second brace  606  may be slideably attached to the lever arm  600 . The second brace  606  prevents rotation of the handle of the motor  564 . Since the input shaft  491  may be attached to various types of motors having handles of various lengths, the second brace  606  may be adjustably positioned on the lever arm  600 . In use, the motor  564  is attached to the gearbox  430 . The housing of the motor  564  may still rotate with respect to the gearbox  430 . The second brace  606  is positioned on the lever arm  600  such that the handle of the motor  564  will contact the second brace  606  during operation. 
         [0119]    Preferably, the lever arm  600  is a plurality of successively smaller square tubes  618 ,  620 . Each of these smaller tubes is slideably disposed within the subsequent larger tube. The tubes may be fixed to each other by a locking thumb screw  622  threaded into the larger tube  618  and wedgeable against the inner smaller tube  620 . Similarly, the second brace  606  may have an extension  608  and a square tube  624  that may be disposed about the tubes  618 ,  620  of the lever arm  600 . A thumb screw  626  may be threaded into the tube  210  and pressed against the lever arm  600  to fix the position of the second brace  606  on the lever arm  600 . 
         [0120]    To set up the hole coring system  10 , the drill bit  420 , gearbox  430 , collar  582  and the advancement nut  508  may be mounted to the substrate  550  as discussed above. Moreover, the gearbox  430  may have a lever arm  600  attached thereto. The brace  602  may also be positioned adjacent the lever arm  600  to prevent rotation of the lever arm  600  during the cutting operation. It is also contemplated that the substrate or a nearby fixture may be used to stop the lever arm. Hence, in certain situations, the brace  602  is unnecessary. Moreover, the second brace  606  may be positioned on the lever arm  600  to prevent rotation of the motor during the cutting operation. It is also contemplated that the motor&#39;s housing may be fixed to the gearbox  430 . Hence, in this situation, the brace  606  would not be necessary. 
         [0121]    More particularly, as the drill bit  420  rotates, the drill bit  420  and the substrate  550  produce an opposite torquing force through the drive shaft  480  and gearbox  430 . The opposing torquing force kicks the handle of the motor towards the second brace  606  in direction of arrow  612 . Fortunately, the second brace  606  stops any further rotation of the motor&#39;s handle. Moreover, the frictional forces between the drill bit  420  and the substrate  550  causes the gearbox  430  as well as the lever arm  600  to rotate in a direction of arrow  614 . Fortunately, the brace  602  blocks any further rotation of the gearbox  430  and the lever arm  600  such that all rotational forces may be applied to the substrate  550 . As the drill bit  420  penetrates the substrate  550 , the lever arm slides down the front surface  604  of the brace  602 . 
         [0122]    In an aspect of the system, the rotateable shaft  578  may also be used to manually rotate the drill bit  420  during the drilling process. For example, during the drilling process, the drill bit  420  may become locked into the substrate  550 . In this situation, the user or operator may shut off the motor  462  and manually turn the drill bit  420  via the rotateable shaft  578  in reverse direction to loosen the drill bit  420  from the substrate  550 . 
         [0123]    In an aspect of the system, it is also contemplated that the proximal end portion of the mandrel may be internally threaded instead of externally threaded as shown in  FIGS. 20-24 . Moreover, the advancement nut may be replaced with an advancement bolt. The flange of the bolt head may be operative to push the drive shaft toward the substrate through the use of a collar or spacer. 
         [0124]    The above description is given by way of example, and not limitation. Given the above disclosure, one skilled in the art could devise variations that are within the scope and spirit of the invention disclosed herein, including various ways of attaching the mandrel to the substrate (i.e., concrete). Further, the various features of the embodiments disclosed herein can be used alone, or in varying combinations with each other and are not intended to be limited to the specific combination described herein. Thus, the scope of the claims is not to be limited by the illustrated embodiments.