Patent Publication Number: US-7708087-B2

Title: Countersink roof bit drill and method for using the same

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a roof bit drill and, more particularly, to a roof bit drill used for imparting within the roof of a mine, counter bores suitable for recessing roof mine bolts. 
     2. Description of Related Art 
     In mine work, such as coal mining, or in underground formations such as tunnels or other excavations, it is necessary to reinforce or support the roof and/or walls of the excavation to prevent rock falls or cave-ins. Among the most common means in use for such support are cable bolts or other suitable elongated members, such as rod bolts, which are inserted into bore holes and exposed to a resin mixture or anchored therein to hold a metal support or bearing plate in tight engagement with a roof or wall surface. With respect to cable bolts, a resin system introduces resin capsules or cartridges into the bore hole and then advances the cables to a blind end of the bore hole by the cable bolt backing the capsules. The spinning of the cable bolt ruptures the capsules and mixes the resin system supplied. 
     Each of these cable bolts or rod bolts utilize either a barrel or wedge assembly or a bolt head, respectively, to secure the metal support or bearing plate against the roof. Therefore, the barrels of the cable bolts extend into the usable walk/crawl or transportation space in a mine as defined by the distance from the floor to the ceiling of the mine tunnel.  FIG. 1  depicts a prior art cable bolt including a wedge assembly  2  and a multi-strand cable  3  secured to a barrel  8  as situated with respect to a roof line in a mine. A drive head, such as a nut  9 , may be attached to a free end of the cable  3 . An exemplary height of the prior art barrel and wedge assembly  2  is approximately 3 inches. Accordingly, several inches (not including the thickness of the prior art bearing plate  6 ) of material extends below the roof line. The prior art barrel and wedge assembly  2  used in connection with typical low clearance tunnels requires that due care be exercised while moving within the tunnel, as the extending bolt head may be engaged by moving equipment or mine personnel. 
       FIG. 2  illustrates another prior art embodiment, wherein a countersunk recess  13 , which may have a generally curved profile, such as substantially semi-spiracle, is formed through a roofline  10  into the roof  11  to accommodate a crater plate or dome plate  14  therein. The crater plate  14  includes a raised portion  16  that substantially corresponds to the shape of the countersink  13 . As a result of the profile of the crater plate  14 , a cable  21  or bolt may be positioned within a top portion  30   a  of the barrel  26  such that the cable bolt/cable rod is significantly recessed within the roof line thereby reducing the obstruction caused by this assembly. The barrel  26  of the bolt cable  21  illustrated in  FIG. 2  has a bottom portion  32  which protrudes below the roof line. 
     However, drilling such a hole may be challenging because there are no drills known to the inventors capable of producing such a countersink and, furthermore, any drill that is capable of producing such a countersink would, in all likelihood, require accessories to collect material removed by the drill and minimize the production of dust. 
       FIG. 3  illustrates a drill bit tool  70  which includes a counter bore bit  72  securely fixed to a first drill shaft  74 . The counter bore bit  72  is sized to create the countersink  13  ( FIG. 2 ) to accommodate a crater plate having a corresponding shape. The counter bore bit  72  may include raised cutting surfaces or protrusions, such as ribs  73 . However, this design makes no provisions for evacuating either dust produced by this operation or larger material removed during this operation. 
     BRIEF SUMMARY OF THE INVENTION 
     One embodiment of the invention is directed to a roof drill bit comprised of a central shaft with a front end and a back end, a base secured about the central shaft proximate to the front end, wherein the base has clearance channels extending radially therethrough; and at least one cutting element arranged on the base in a convex cutting pattern. 
     Another embodiment of the subject invention is directed to a roof bit drill comprised of a central shaft with a front end and a back end, a base secured about the central shaft proximate to the front end, wherein the base has clearance channels extending radially therethrough; at least one cutting element arranged on the base; and a drill depth locator to identify when the drill has been advanced within a mine roof to a predetermined depth. 
     Yet another embodiment of the subject invention is directed to a method of identifying a predetermined depth for the advancement of a roof bit bolt comprising the step of advancing the roof bit bolt within the roof of a mine until a depth indicator signals the proper depth has been reached. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial sectional view of a prior art mine roof support utilizing a cable bolt, wherein the cable bolt protrudes entirely below a roof line; 
         FIG. 2  is a partial sectional view of a prior art mine roof support utilizing a cable bolt recessed within a countersink within the roof thereby minimizing the protrusion of the mine roof support; 
         FIG. 3  is an elevation view of a roof bit drill utilizing a convex base for imparting a dome-shaped counter bore within the roof; 
         FIG. 4A  is a perspective view of a roof bit drill in accordance with a first embodiment of the subject invention; 
         FIG. 4B  is a side view of the roof bit drill illustrated in  FIG. 4A ; 
         FIG. 4C  is a top view of the roof bit drill illustrated in  FIG. 4A ; 
         FIG. 5A  is a perspective view of a roof bit drill in accordance with the second embodiment of the subject invention; 
         FIG. 5B  is a side view of the roof bit drill illustrated in  FIG. 5A ; 
         FIG. 5C  is a top view of the roof bit drill illustrated in  FIG. 5A ; 
         FIG. 6A  is a perspective view of a roof bit drill in accordance with a third embodiment of the subject invention; 
         FIG. 6B  is a side view of the roof bit drill illustrated in  FIG. 6A ; 
         FIG. 6C  is a top view of the roof bit drill illustrated in  FIG. 6A ; 
         FIG. 7A  is a side view of a roof bit drill in accordance with a fourth embodiment of the subject invention with a boot in the extended position; 
         FIG. 7B  is a side view of the roof bit drill illustrated in  FIG. 7A  with the boot retracted; 
         FIG. 7C  is a top view of the roof bit drill illustrated in  FIGS. 7A and 7B ; 
         FIG. 8A  is a side view of a roof bit drill in accordance with a fifth embodiment of the subject invention, wherein a boot is shown in an extended position; 
         FIG. 8B  is a side view of the roof bit drill illustrated in  FIG. 8A  with the boot in a retracted position; 
         FIG. 8C  is a top view of the roof bit drill illustrated in  FIGS. 8A and 8B ; 
         FIG. 9A  is a perspective view of a roof bit drill in accordance with a sixth embodiment of the subject invention; 
         FIG. 9B  is a side view of the roof bit drill illustrated in  FIG. 9A ; and 
         FIG. 9C  is a top view of the roof bit drill illustrated in  FIG. 9A . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Throughout this discussion, the term roof will be utilized. However, it should be understood that the subject invention may also be utilized with mine walls, and the use of the term roof should be understood to apply to walls as well. 
       FIGS. 4A ,  4 B and  4 C illustrate a roof bit drill  100  in accordance with a first embodiment of the subject invention. In particular, the roof bit drill  100  is comprised of a central shaft  105  having a front end  107  and a back end  109 . A base  110  is secured about the central shaft  105  proximate to the front end  107 . The base  110  has clearance channels  115  extending axially through the base  110 . The drill  100  further contains a plurality of cutting elements  120  arranged on the base  110  to define, as best illustrated in  FIG. 4B , a convex cutting pattern  125 . 
     As illustrated in  FIGS. 4A and 4B , the cutting elements  120  are arranged so that the convex Cutting pattern  125  generally defines a dome-shape. As illustrated in  FIG. 4A , the base  110  may be comprised of radially extending members  130  extending from the central shaft  105 . As further illustrated, there is at least one cutting element  120  arranged on each of the radially extending members  130  and together these cutting elements  120  substantially outline the concave cutting pattern  125 . In the present embodiment, the plurality of cutting elements  120  are each comprised of a plug bit which is secured within matching bores in the base  110 . 
     The clearance channels  115  are important for proper operation of the roof drill bit to permit material removed from the roof by the drill to be evacuated. In particular, in the absence of such clearance channels, the drill would be capable of advancing only a very small amount before the newly loosened material, which is now entrapped by the roof bit drill, would act as a physical barrier to further advancement of the drill. Therefore, the clearance channels  115  permit the newly loosened material to be evacuated thereby allowing the cutting elements  120  to act on a new surface. As illustrated in the first embodiment, the radially extending members  130  are fins  138  extending from the central shaft  105 . As illustrated, there are four fins  138  located symmetrically about the central shaft  105 , thereby providing a dynamically balanced configuration. Consistent with providing such a dynamically balanced configuration, it is possible that there may a different number of fins  138  extending from the central shaft  105 . 
     The roof bit drill  100  further includes a vacuum port  140  in the region of the cutting elements  120 . The vacuum port  140  is in fluid communication with a vacuum passageway  143  which extends through the central shaft  105  to a vacuum source (not shown). Dust and small particles removed by the cutting elements  120  may be evacuated through the vacuum port  140  to minimize dispersion of dust and small particles within the environment of the roof bit drill  100 . As illustrated in  FIGS. 4A and 4B , the front end  107  of the shaft  105  is a pilot pin  145  used to locate the drill  100  within a pre-drilled hole in the roof of the mine. 
     At the back end  109  of the shaft  105  is a driven portion  150  adapted to be received by a machine driver (not shown) which imparts rotary motion to the roof bit drill. The central shaft  105  may have a lower shoulder  153  which axially locates the driven portion  150  within the machine driver. 
     The embodiment illustrated in  FIGS. 4A-4C  presented a plurality of cutting elements  120  mounted about radially extending members  130 . In particular, these cutting elements  120  were plug bits  135 . As illustrated in  FIGS. 5A-5C , it is entirely possible for the cutting elements  120  to be comprised of cutting blades  190  which are arranged on each of the radially extending members  130  and which together substantially outline a concave cutting pattern  125 . It should be appreciated that one or more cutting blades  190  may be associated with a particular radially extending member  130 . While four radially extending blades  120  are shown on the drill  100  in  FIGS. 4A-4C  and three radially extending blades  120  are shown on the drill in  FIGS. 5A-5C , it is possible for each of these drills to have a different number of radially extending blades  120 . For example, the drill  100  in  FIGS. 4A-4C , may have three radially extending blades  120  while the drill in  FIGS. 5A-5C  may have four radially extending blades  120 . 
     Optimally, the crater plate  14  adapted to be secured within the countersunk portion of the roof should contact as much of the roof and countersunk portion as possible. Therefore, it is important to drill the counter bore with a certain level of precision so that when the concaved-shaped crater plate  14  is introduced within the counter bore, the top surface of the crater plate  14  will contact the exposed surface of the counter bore within the roof. In order to assist the operator to determine when advancement of the roof drill bit within the roof should cease, the subject invention further includes, as illustrated in  FIGS. 6A-6C , a drill depth locator  155  with at least one protrusion  160  secured at the back surface  112  of the base  110 . As illustrated in  FIGS. 6A-6C , the protrusion  160  is a circular ring  162  secured to the base  110 . 
     In an alternative embodiment, as illustrated in  FIGS. 7A-7C , the drill depth locator  155  is a resilient assembly  165  which signals the depth to which the assembly  165  compresses when the roof bit drill is advanced within a mine roof. In particular, the resilient assembly  165  is a boot  170  surrounding the central shaft  105  and the base  110 . The boot  170  generally conforms to the shape of the base  110 . The boot  170  is axially supported on the central shaft  105  by a spring  175  such that the boot  170  is resiliently displaced in the axial direction when the roof bit drill is advanced within the mine roof. The depth locator  155  signals the drill depth by either the sound the protrusion  160  makes upon contacting the mine roof or the visual appearance of the protrusion  160  as it contacts the roof mine. 
     In the embodiment illustrated in  FIGS. 7A-7C  and each of the other embodiments illustrated herein, the central shaft  105  has an upper shoulder  177  to support the boot  170 . As further illustrated in  FIGS. 7A-7C , the spring  175  is a coil spring  179  which rests upon the upper shoulder  177  and supports the boot  170 . 
     In the alternative, as illustrated in  FIGS. 8A-8C , the resilient assembly  165  is a boot  180  having convoluted walls  182  which resiliently compress in the axially direction when the roof bit drill is advanced within the mine roof. The outermost segments  183  of the convoluted walls  182  may be a different color than the innermost segments  184 , such that when the boot  180  is fully compressed in the axially direction, the compressed boot  180 , as illustrated in  FIG. 8B , appears to be a single color. 
     Briefly returning to  FIGS. 4A and 4B , it should be appreciated that the vacuum port  140  is essentially directly beneath the base  110 . The same relative position of the vacuum port  140  illustrated in  FIGS. 4A-4C  is also present in the embodiments illustrated in  FIGS. 7A-7C  and  FIGS. 8A-8C . However, with attention directed to the  FIGS. 7A-7C  embodiment, the boot  170  conceals the vacuum port  140  while, with respect to the embodiment illustrated in  FIGS. 8A-8C , the boot  180  conceals the vacuum port. Nevertheless, in each of the embodiments illustrated in  FIGS. 7A-7C  and  FIGS. 8A-8C , there is a vacuum port  140  in the region of the cutting elements  120 . The boot  170  may have a flat top  171  just as the boot  180  may have a flat top  181  adapted to seal against the roof of the mine to further ensure that dust and small particles loosened by the roof bit drill are effectively evacuated. The boot  170  may have an air hole  176  while the boot  180  may have an air hole  186  to prevent collapse when the boots  170 ,  180  are subjected to a vacuum and the flat top  171 ,  181  of either is sealed against the roof of the mine. 
     It should be noted that, as illustrated in  FIGS. 7A ,  7 B and  FIGS. 8A ,  8 B, the vacuum port  140  remains within the boot  170 ,  180  throughout the axial travel of the roof bit drill within the roof of a mine. 
     So far discussed and directing attention to the embodiment illustrated in  FIGS. 4A-4C , the roof bit drill  100  has a pilot pin  145  at the front end  107  of the central shaft  105 . Directing attention to  FIGS. 7A-7B , it is entirely possible for the front end  107  of the central shaft  105  to have a pilot drill  195  comprised of a conventional pinning rod system drill bit for which a variety of different types are commercially available. It should be appreciated that the pilot drill  195  would also have associated with it a vacuum source extending through the central shaft  105  to remove dust and small material during the drilling of a pilot hole. 
     In a final embodiment of the subject invention illustrated in  FIGS. 9A-9C , the roof drill bit may further include a rim cutter  196  mounted below the base  110  and extending radially outwardly such that once the cutting element  120  mounted upon the base  110  produces the concave counter bore within the mine roof the roof bit drill may advance further and the rim cutter  196  will cut a ring within the mine roof beyond the perimeter of the cutting elements  120  mounted upon the base  110 . It should be appreciated that by utilizing such a configuration, the roof bit drill may be advanced within the roof of the mine to any desired depth. The outer diameter of the rim  196  is greater than the outer diameter of the rim portion  18  ( FIG. 2 ) of the bearing  18 . As a result, it is entirely possible to completely recess the crater plate  14  with the cable bolt  21  or rod bolt fully within the roof line. 
     The subject invention is also directed to a method for identifying a predetermined depth for the advancement of a roof bit bolt  100  comprising the steps of advancing the roof bit bolt  100  within the roof of a mine until a depth indicator  155  ( FIG. 7B ) signals the proper depth has been reached. In particular, when the roof bit bolt is surrounded by a resilient boot  170  and the roof bit bolt is advanced. At the time the resilient boot  180  is compresses a predetermined amount, advancement of the roof bit drill is stopped. 
     In one embodiment, the boot  170  is supported on the central shaft  105  by a spring  175  and the roof bit bolt is advanced until the spring  175  deflects a predetermined amount, which may be determined visually by the operator of the machine, at which time the roof bit drill advancement is stopped. 
     In accordance with another embodiment, the boot  180  has resilient convoluted walls  182  and the roof bit bolt is advanced until the outer most segments  183  of the convoluted walls  182  are compressed to the point of contacting one another, at which time the roof bit drill advancement is stopped. 
     While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. The presently preferred embodiments described herein are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.