Abstract:
An improved back reamer for horizontal directional drilling is provided with multiple components which can be assembled and disassembled before and after the back reaming process. The reamer includes a main shaft connectable to the drill string, a reamer head removably mounted on the main shaft, and a pull tab removably attached to the main shaft. Faceted couplings between the reamer shaft and head, and between the reamer head and pull tab preclude rotation between the components.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119(e) to provisional application Ser. No. 61/041,967 filed Apr. 3, 2008, herein incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to a back reamer for horizontal directional drilling, and particularly, to a multi-piece, sectional back reamer which can be quickly and easily assembled and disassembled in a safe manner by an operator. 
     BACKGROUND OF THE INVENTION 
     Utility lines for water, electricity, gas, telephone, and cable television are often run underground for reasons of safety and aesthetics. Sometimes, the underground utilities can be buried in a trench that is subsequently back filled. However, trenching can be time consuming and can cause substantial damage to existing structures or roadways. Consequently, alternative techniques such as horizontal directional drilling (HDD) are becoming increasingly more popular. 
     A typical horizontal directional drilling machine includes a frame on which is mounted a drive mechanism that can be slidably moved along the longitudinal axis of the frame. The drive mechanism is adapted to rotate a drill string about its longitudinal axis. The drill string comprises a series of drill pipes threaded together. Sliding movement of the drive mechanism along the frame, in concert with the rotation of the drill string, causes the drill string to be longitudinally advanced into or withdrawn from the ground. 
     In a typical horizontal directional drilling sequence, the horizontal directional drilling machine drills a hole into the ground at an oblique angle with respect to the ground surface. To remove cuttings and dirt during drilling, drilling fluid is pumped by a pump system through the hollow drill string, over a drill head (e.g., a cutting or boring tool) at the end of the drill string, and back up through the hole. After the drill head reaches a desired depth, the drill head is then directed along a substantially horizontal path to create a horizontal hole. Once the desired length of hole has been drilled, the drill head is then directed upwards to break through the ground surface, completing a pilot bore. Alternatively, the drill head may terminate in a trench. 
     The diameter of the pilot bore so constructed typically must be enlarged. To accomplish this, a reamer (sometimes called a back reamer) is attached to the drill string which is pulled back along the path of the pilot hole, thus reaming out the hole to a larger diameter. The reamer usually includes a reaming or cutting surface on which is mounted cutting teeth or other cutting or grinding elements. It is also common to attach a utility line or other conduit product to the reamer so that the product is pulled through the hole behind the reamer as the reamer enlarges the hole. 
     A back reamer, then, may perform several functions including: mechanically cutting, grinding and loosening the soil to enlarge the pilot hole diameter, directing drilling fluid to assist in the cutting action, mixing the loosened soil with the drilling fluid such that the resulting slurry is a consistency that will flow out of the bore when displaced by whatever product is to be pulled in, and transferring the longitudinal force required to pull the product through the hole. 
     The back reamer is normally constructed of heavy duty steel, and comes in many different sizes to create a bore which accommodates the utility product. The back reamer also has many different configurations according to the type of soil being drilled. 
     Once the pilot hole is completed, a person removes the drilling head and installs the back reamer. This manual operation is dangerous, since the person typically stands in front of or straddles over the top of the reamer in order to install the reamer on the drill string. 
     Communication errors are known to occur, with a resulting premature actuation of the back reamer while the installer is still preparing the reamer, thus causing serious injury, and even death, to the installer. The heavy weight of the reamer also results in back problems for the installer, both during attachment of the reamer and detachment of the reamer after the utility hole is formed. Furthermore, attachment and detachment of the reamer normally requires the use of large and heavy wrenches, which also may cause injuries if the wrenches are dropped or slipped. 
     Therefore, a primary objective of the present invention is the provision of an improved back reamer having components which can be quickly and easily assembled and disassembled by one person. 
     Another objective of the present invention is the provision of an improved back reaming method of horizontal directional drilling using a back reamer having separable components. 
     Another objective of the present invention is the provision of an improved back reamer having a main shaft, a reamer head, and a pull tab, each of which include faceted faces to prevent rotation relative to one another after the components are assembled. 
     Another objective of the present invention is the provision of a back reamer having separable components having faceted surfaces to prevent rotation of the components relative to one another. 
     A further objective of the present invention is an improved back reamer which can be quickly and easily mounted and dismounted from the drill pipe. 
     A further objective of the present invention is the provision of a method of horizontal directional drilling wherein the back reamer has components which are fixed against rotation relative to one another. 
     Still another objective of the present invention is an improved method of horizontal directional drilling which minimizes risk of injury to the operator, while effectively and efficiently enlarging the diameter of a pre-drilled pilot hole. 
     These and other objectives will become apparent from the following description of the invention. 
     SUMMARY OF THE INVENTION 
     The sectional back reamer of the present invention is intended for use in horizontal directional drilling, and comprises three components which can be assembled and disassembled quick and easily by an operator at each end of the drilling operation. The reamer includes a main shaft connectable to the drill string or pipe, a reamer or cutting head mountable on the main shaft, and a pull tab mountable to the reamer. The connections between the main shaft and the reamer cutting head, and between the cutting head and the pull tab include faceted surfaces to preclude rotation of the components relative to one another. The components are assembled sequentially by the installer in the trench or on top of the ground. The smaller size and weight of the components, as compared to the prior art one-piece back reamers, simplifies and greatly improves the safety to the operator driving the attachment and detachment of the reamer&#39;s components to and from the drill pipe. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a conventional horizontal directional drilling operation. 
         FIG. 2  is a perspective view of one configuration of a prior art back reamer. 
         FIG. 3  is a schematic view of the reamer of  FIG. 2  installed on the drill pipe for horizontal directional drilling. 
         FIG. 4  is a perspective view of another configuration of a conventional back reamer. 
         FIG. 5  is a schematic view showing the back reamer of  FIG. 4  installed on the drill pipe for horizontal directional drilling. 
         FIG. 6  is an exploded view of the sectional back reamer of the present invention. 
         FIG. 7  is a perspective view of the assembled sectional reamer of the present invention. 
         FIG. 8  is a rear end view of the assembled reamer of the present invention. 
         FIG. 9  is a side elevation view of the reamer of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows a conventional horizontal directional drilling machine  10  having a drill string or pipe  12  to form a pilot hole  14  extending to a trench  16 . The back reamer  18  is attached to the forward end of the drill string  12  in the trench and then pulled backwardly through the pilot hole  14  to enlarge the hole. 
     Two conventional configurations of back reamers  14 A and  14 B are shown in  FIGS. 2 and 4 . As seen in  FIGS. 3 and 5 , a utility product  15  is attached to the reamer  14 A,  14 B via a swivel coupling  16  so as to be pulled through the enlarged hole as the reamer  14 A,  14 B is pulled by the drilling machine  10 . 
     Each of the conventional reamers  14 A,  14 B include a front pipe  20  having internal threads  21  for threadable coupling with the forward end of the drill pipe  12 . The cutting head or body  22  of the reamer  14 A,  14 B includes cutting tools or bits  24  and fluid jets  26 . The rear end of each reamer  14 A,  14 B includes a pulling tab  28  to which the swivel coupler  16  is attached, which in turn connects to the utility product  15 , as seen in  FIGS. 3 and 5 . 
     The conventional reamers  14 A,  14 B are heavy duty, one piece construction with diameters up to 36 inches. The size and weight of these reamers makes their handling and installation difficult and dangerous. 
     The improved multi-piece, sectional reamer  30  of the present invention is shown in  FIGS. 6-9  and includes a main shaft  32 , a reamer head or body  34 , and a pull tab  36  which can be quickly and easily assembled and disassembled to and from one another. More particularly, the main shaft  32  is hollow and includes external threads  33  on the forward end for threadable coupling to the forward end of the drill pipe  12  and an open opposite end  35 . Alternatively, the reamer shaft  32  may have internal threads on the forward end for coupling to the drill pipe  12 , as in the prior art. 
     The cutting head  34  has a hollow hub  38  which slides on to the rearward end of the main shaft  32 . The head  34  includes a cylindrical shroud  41  surrounding the hub  38  and connected to the hub  38  by a plurality of spokes  43 . The pull tab  36  is slidably received in the rearward end of the hub  38  and includes threads  37  for threaded coupling with the rearward end of the reamer shaft  32 . Preferably, the main shaft  32 , the hub  38  of the cutting head  34 , and the pulling tab  36  each include one or more facets  40  for mating coupling which precludes rotation of the components relative to one another. The components of the reamer  30  can be removably secured to one another in any convenient manner, such as by a bolt  50  extending through bolt holes  42 ,  45  on the head  34  and tab  36 , respectively. Thus, the pull tab  36  is fixed to both the main shaft  32  and to the head  34  so as to lock the three components together. The main shaft  32  and/or hub  34  also include a plurality of fluid jets  44  for ejecting fluid to carry the cut soil and material out of the drilled hole. A plurality of cutting teeth or bits  46  are welded or otherwise mounted on the shroud  41 , and a plurality of teeth or cutting bits  48  are similarly attached to the spokes  43 . 
     In use, after the pilot hole  14  is drilled, the reamer  30  is mounted to the pipe  12 . More particularly, the reamer components are sequentially assembled so as to minimize the weight required to be handled by the installer at any given time. The first step in the assembly sequence is to threadably mount the reamer shaft  32  to the end of the drill pipe  12 . Then, the reamer head or body  34  is slid over the end of the shaft  32 . The pull tab  36  is then inserted into the open end of the head  34 , and the end  37  of the tab  36  threaded onto the main shaft  32 . The bolt  50  is then inserted through the hole  42  on the head  34  and threaded into the hole  45  on the pull tab  36 . As seen in  FIGS. 6 and 9 , the faceted surfaces  40  on the shaft  32 , the tabs  36 , and the hub  38  are aligned for assembly of the reamer  30 . 
     After the pilot hole  14  has been enlarged by the back reamer  30 , the back reamer components  32 ,  34 ,  36  can be quickly and easily disassembled in the reverse sequence. The smaller, lighter, components of the reamer  10  allow the installer to assemble and disassemble the unit with substantially reduced risk of injury, with reduced coupling forces, and lighter weight tools. Thus, the multi-piece improved back reamer  30  of the present invention inherently improves the safety for the installer or operator, as compared to heavy duty, one-piece prior art reamers. 
     The invention has been shown and described above with the preferred embodiments, and it is understood that many modifications, substitutions, and additions may be made which are within the intended spirit and scope of the invention. From the foregoing, it can be seen that the present invention accomplishes at least all of its stated objectives.