Abstract:
Underground drilling operation often requires connecting a drill tool (e.g., drill bit, backreamer, etc.) to a drill string. It is desirable to connect the drill tools to a drill string in a manner that facilitates quick and easy assembly and disassembly. Low torque coupling, commonly referred to as “torque-less” connection, can provide such functionality. The useful life and strength of such connections can be improved upon. The present disclosure provides a low torque coupling with improved strength and durability.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 13/380,168 filed on Jun. 26, 2012, which is a National Stage Application of PCT/US2011/062356 filed on Nov. 29, 2011, which claims priority to U.S. Provisional Patent Application Ser. No. 61/418,783, filed Dec. 1, 2010 and U.S. Provisional Patent Application Ser. No. 61/435,689, filed Jan. 24, 2011, which applications are incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure provides a coupling for connecting a drill tool to a drill string and related methods. 
     BACKGROUND 
     Underground drilling operation often requires connecting a drill tool (e.g., drill bit, backreamer, etc.) to a drill string. It is desirable to connect the drill tools to a drill string in a manner that facilitates quick and easy assembly and disassembly. Low torque coupling, commonly referred to as “torque-less” connection, can provide such functionality. The useful life and strength of such connections can be improved upon. The present disclosure provides a low torque coupling with improved strength and durability. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a schematic illustration of a drilling machine in operation; 
         FIG. 2  is a perspective view of a coupling according to the principles of the present disclosure; 
         FIG. 3  is a cross-sectional view of a portion of the coupling of  FIG. 2 ; 
         FIG. 4  is a cross-sectional view of an alternative embodiment of the coupling shown in  FIG. 3 ; 
         FIG. 5  is a side view of a portion of the coupling of  FIG. 2  shown in a fully engaged position; 
         FIG. 6  is a cross-sectional view along line  6 - 6  of  FIG. 5 ; 
         FIG. 7  is an enlarged view of a portion of  FIG. 6  labeled  7 ; 
         FIG. 8  is an enlarged view of a portion of  FIG. 6  labeled  8 ; 
         FIG. 9  is a view of the subject matter of  FIG. 7  with the coupling shown in a partially engaged position; 
         FIG. 10  is a cross-sectional view of an alternative embodiment of the coupling of  FIG. 2 ; 
         FIG. 11  is a cross-sectional view of an alternative embodiment of the coupling of  FIG. 2 ; 
         FIG. 12  is a mass-sectional view of the coupling of  FIG. 11  along lines  12 - 12 ; 
         FIG. 13  is a side view of a portion of the coupling of  FIG. 11 ; and 
         FIG. 14  is a side view of an alternative embodiment of the portion of the coupling shown in  FIG. 13 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1  a drilling machine  10  is shown driving a drill string  20  into the ground. The distal end of the drill string includes a drill tool assembly  100 . The coupling between an end of the drill string  20  and the drill tool assembly  100  is shown in greater detail in  FIGS. 2-9 . 
     Referring generally to  FIGS. 2-9 , a coupling between a starter rod  12  and a sonde housing  14  is shown. The starter rod  12 , also referred to as a pilot rod or generically a first member, is threadly connected to the distal most (down hole most) drill rod  16  via a torque connection. The sonde housing  14  is configured to house a sonde therein and supports a drill bit (not shown) at its distal end  24 . 
     In the depicted embodiment an adaptor  18  is threadly connected in the proximal end  22  of the sonde housing  14  via a torque connection. The adaptor  18  and sonde  14  are also referred to herein generically as a second member. A collar  26  is provided to slide over a distal end  28  of the starter rod  12  and a portion of the adaptor  18  to prevent relative rotation between the starter rod and adaptor (and hence also prevent relative rotation between the starter rod  12  and the sonde housing  14 ). 
     In the depicted embodiment an inner surface of the collar  26  is configured to engage external structural features on the distal end  28  of the starter rod  12  and on the exterior surface of the adaptor  18 . In the depicted embodiment the collar includes internal flats  30  that engage flats  32  on the distal end  28  of the starter rod  12  and flats  68  on the exterior of the adaptor  18 . The connection between the distal end  28  of the starter rod  12  and the proximal end  36  of the adapter  18  is described in greater detail below. 
     In the depicted embodiment the coupling includes first member including a driving end and a driven end. In the depicted embodiment, the first member is shown as the starter rod  12 . The drive end is shown as the distal end  28  and the driven end is shown as the proximal end  34 . The proximal end  34  is threadly connected to the down hole most drill rod  16  via a torque connection. 
     In the depicted embodiment the driving end of a first member (e.g., the distal end  28  of the starter rod  12 ) includes a tapered portion (recess  36  shown in  FIG. 3  or protrusion  38  shown in  FIG. 4 ) including threads thereon. The driving end includes a first land  40  ( FIG. 6 ) adjacent a distal end of the tapered portion (e.g., the protrusion  38  or recess  36  and a second land  42  ( FIG. 6  adjacent a proximal end of the tapered portions (protrusion  38  or recess  36 ). 
     In the depicted embodiment the second member (adaptor  18 ) includes a drive end  44  and a driven end  46 . The drive end  44  includes a threaded connection for attaching to a cutting tool (e.g., a sonde housing  14  supporting a drill bit). The driven end  46  is adapted for connection with the driving end  28  of the first member  12 . The driven end  46  includes a tapered portion (e.g., recess  48  shown in  FIG. 4  or protrusion  50  shown in  FIG. 6 ) including threads thereon. The driven end  46  includes a third land portion  52  ( FIG. 6 ) adjacent a distal end of the tapered portion (e.g., recess  48  or protrusion  50 ). The drive end  46  also includes a fourth land portion  54  adjacent a proximal end of the tapered portion. 
     In the depicted embodiment the first land  40  is configured to engage the fourth land  54  and the second land  42  is configured to engage the third land  52  when the tapered threads on the first member  28  are engaged with the tapered threads on the second member  18 . In the depicted embodiment the clearance between the first land  40  and fourth land  54  and the clearance between the second land  42  and the third land  52  is sufficient to allow a user to slidably engage the first and second members by hand. In the depicted embodiment the first land and the fourth land are cylindrical having diameters that are at least 0.003 inches different from each other (for example, within 0.003 inches to 0.006 inches (0.076 to 0.150 millimeters) of each other). In other words, the clearance between the surfaces of the lands in a radial direction (radial clearance) is between 0.0015 to 0.003 inches (0.038 to 0.076 millimeters). It should be appreciated that in alternative embodiment the lands could be of different geometric configurations and have different clearance therebetween. 
     In some embodiment the peaks  58  of the threads on the tapered portion of second member and valleys  60  of the threads of the first member are offset by at least 0.030 inches (0.76 millimeters) even when the threads are engaged. In the depicted embodiment the pitch diameter between the threaded portions on the first and second members are offset by at least 0.030 inches. On a tapered thread like the ones shown the pitch diameter at a given position on the thread axis is the diameter of the pitch cone at that position. It should be appreciated that when the crest of the thread is truncated beyond the pitch line, the pitch diameter and pitch cylinder or pitch cone would be based on theoretical extension of the threaded flanks. 
     As discussed above, the second member is depicted as an adapter  18 . However, it should be appreciated that in alternative embodiments the first member can be different components including, for example, a drill bit or a sonde housing. 
     In the depicted embodiment the threads on the tapered recess and threads of the tapered protrusions are asymmetric having a tooth width W to height H ratio between 1.25 to 3.0 ( FIG. 9 ). The asymmetric short threads facilitate self-alignment and maintain the above-described offset between peaks and valleys of corresponding threads. 
     In the depicted embodiment the first member  28  includes structure that abuts structure on the second member  18  to limit the offset between the peaks of the threads on the tapered recess and valleys of the threads of the tapered protrusions. The structure on the first member is shown as front face  62  and the structure on the second member is shown as an annular shoulder  64 . 
     In the depicted embodiment, a portion  66  ( FIG. 8 ) of the tapered recess at its distal end is enlarged and does not include threads thereon. In the depicted embodiment, a portion of the tapered recess at its proximal end is also enlarged (portion  67  of  FIG. 7 ) and does not include threads thereon. These portions are configured to receive foreign matter (e.g., rock and dirt) and thereby prevent the matter from jamming the connection between the first and second members, in addition, these portions also act as stress relief zones that distribute load at the transition, thereby avoiding stress concentrations, which increases the durability of the coupling  18 . In the depicted embodiment the enlarged portion comprises an annular notch that is part of the tapered recess. It should be appreciated that in alternative embodiments the enlarged portion (e.g., notch) can be part of the tapered protrusion or both a part of the tapered recess and the tapered protrusion. It should also be appreciated that alternative embodiment may be configured without these enlarged portions. 
     In the depicted embodiment the proximal end of the coupling  18  (e.g., adaptor) which is shown threaded to the sonde housing  14  includes a tapered threaded portion configured to engage mating threads of a sonde housing to toque level in excess of 50 foot pounds. As discussed above, the distal end includes a tapered portion between a first unthreaded portion and a second unthreaded portion. The first and second unthreaded portions include a constant maximum cross-sectional dimension. As discussed above, the coupling includes a stop that engages an end face of the first member to prevent full engagement of the threads (i.e., maintains the above define offset). The stop is positioned on a predetermined location on the second unthreaded portion such that it ensures an offset of at least 0.030 inches between the peaks on the threads of the tapered threaded portion with the valleys on threads that the taper threaded portion is configured to engage. In the depicted embodiment the pitch diameter between the threaded portions on the first and second members are offset by at least 0.030 inches. 
     The present disclosure also provides a method of connecting a drill tool to a drill rod. The method includes the steps of: contacting threads located at a proximate end of a drill tool member with threads located at a distal end of a drill rod member; threading the drill tool member to the drill rod member by relatively rotating the drill rod member and the drill tool member; and aligning structural features on an external surface of the drill tool member with structural features on an external surface of the drill rod member. In the depicted embodiment the step of aligning the structural features includes counter rotating the drill rod assembly relative to the drill tool between one to ninety degrees. 
     The method further includes the step of sliding a collar over a portion of the drill tool member and drill rod member, wherein the collar is configured to engage the structural features on the external surface of the drill tool member and drill rod member thereby preventing relative rotation between the drill tool member and the drill string member. 
     In the depicted embodiment the step of threading the drill tool member to the drill rod member simultaneously inserts a boss on the distal end of the drill tool member with an aperture on the drill rod member and inserts a boss on the proximal end of the drill tool member with an aperture on a distal end of the drill rod member. The method also includes the step of maintaining at least 0.030 inch (0.76 millimeters) offset between a peak of the threads located on the proximate end of the drill tool member and a valley of the threads located at a distal end of the drill rod member at least when structural features on the external surface of the drill tool member are aligned with the structural features on the external surface of the drill rod member. In the depicted embodiment the pitch diameter between the threads on the drill tool and mating threads on the drill rod are offset by at least 0.030 inches. 
     In the depicted embodiment the threading step is accomplished by rotating the drill tool member while holding the drill rod member stationary. It should be appreciated that alternatively the drill rod could be rotated while the drill tool is held stationary. In the depicted embodiment, the threading step includes relatively rotating the drill rod member and drill tool member between one to blur full revolutions. In alternative embodiments the threading step may include more or fewer revolutions. 
     In the depicted embodiment the toque needed to unthread the drill rod assembly from the drill tool assembly is less than 50 foot pounds. The step of threading the drill tool assembly to the drill rod assembly includes rotating the drill tool member until a portion of the drill tool member (e.g., annular shoulder) abuts a portion of the drill rod member (e.g., end face) and limits further rotation. In the depicted embodiment at least 0.030 inches offset is maintained when the portion of the drill tool assembly abuts the portion of the drill string assembly. The at least 0.030 inches offset is maintained even if as much as 50 foot pounds of torque are applied to the connection between the drill rod member and drill tool member during the threading step. 
     In the depicted embodiment the boss on the distal end of the drill tool includes a maximum cross-sectional dimension that is within 0.0015 to 0.03 inches (0.038-0.76 millimeters) of a maximum cross-sectional dimension of the aperture of the drill rod assembly. 
     Referring to  FIG. 10 , an alternative embodiment is shown. The depicted embodiment is similar to the above-described embodiment, however, the threads on the tapered protrusion and aperture are removed. Instead, pins  100 ,  102  secure the tapered protrusion within the tapered aperture and resist tension forces between the adapter  18  and the starter rod  12 . The pins  100 ,  102  extend through a portion of the distal end  28  of the starter rod and driven end  46  of the adapter  18 . The collar  26  slides over the end of the pins and retains them in place. 
     Referring to  FIGS. 11-13 , another alternative embodiment is shown. In the depicted embodiment the tapered aperture  124  and protrusion  126  are not threaded. Instead, the tapered protrusion  126  includes grooves  106 ,  108 ,  110  that engage pins  112 ,  114 ,  116 ,  118 ,  120 ,  122 , which are retain in pin receiving apertures that extend through a portion of the tapered aperture  124 . The above described pin configuration secures the tapered aperture  124  to the protrusion  126  against tension forces applied to the connection during operation (e.g., as the drill string is pulled back through the hole). In the depicted embodiment the pins can be removed after removal of the collar  26  via driving a punch through smaller apertures that extend to the back side of the pin receiving apertures. It should be appreciated that although the tapered aperture and protrusion are shown with a gradual taper they could alternative have a stepped profile or the taper could be non-linear. 
     Referring to  FIG. 14 , another alternative embodiment is shown. In the depicted embodiment the tapered protrusion  130  includes a spiral groove  132  that is configured to mate with locking pins similar to those shown in  FIGS. 11-13 , which are retained in pin receiving apertures that extend through a portion of the tapered aperture  124  in a manner to intersect the spiral groove. In this embodiment the groove  131  acts as a single enlarged thread member that secures the tapered aperture and tapered protrusion together. This configuration provides a quick connection and disconnection between the tapered protrusion and tapered aperture. The locking pins that mate with the spiral grooves on the tapered aperture and the receiving apertures in the aperture  124  resist tension forces applied to the connection. The collar  26  prevents the tapered protrusion from rotating relative to the tapered aperture. 
     It should be appreciate that many more alternative embodiments are possible. For example, although the embodiment shown in  FIGS. 10-14  are shown to include annular stress relief zone recess into the tapered protrusion similar to those described above with reference to  FIGS. 7 and 8  (portions  66  and  67 ). Some alternative embodiment do not include stress relieve zones. 
     The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.