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CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application Ser. No. 62/171,025 filed on Jun. 4, 2015, the entire contents of which are incorporated herein by reference. 
     
    
     FIELD 
       [0002]    This invention relates generally to backreamers, and specifically fluid flow mechanisms for backreamers. 
       SUMMARY 
       [0003]    The invention is directed to a reamer comprising a tubular shaft and a body. The tubular shaft is symmetric about a bit axis and has a radially extending fluid passage. The body is supported on the shaft and forms a plurality of layers. The body comprises a distributor layer and a spaced pair of boundary layers. The distributor layer is penetrated by an internal void having uniform cross-sectional dimension and communicating with the fluid passage. The spaced pair of boundary layers contact each side of the distributor layer and form side walls that enclose major portions of the internal void. 
         [0004]    The invention is also directed to a bit comprising a central shaft, a first layer, a second layer and a distributor layer. The central shaft defines a longitudinal axis and has a radial fluid passage. The first layer is disposed about the central shaft and has a nozzle formed through the first layer and substantially parallel to the longitudinal axis. The second layer is disposed about the central shaft. The distributor layer is disposed about the central shaft and has a cutaway portion disposed to create an internal void in fluid communication with the radial fluid passage and the nozzle. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a diagrammatic representation of a backreaming operation using the backreamer of the present invention. 
           [0006]      FIG. 2  is a front isometric partially exploded view of a backreamer for use with the present invention. 
           [0007]      FIG. 3  is a front isometric view of the backreamer of  FIG. 2 . 
           [0008]      FIG. 4  is a front isometric view of an alternative embodiment of a backreamer device. 
           [0009]      FIG. 5  is an exploded view of a plate assembly for use with the backreamer device of  FIG. 4 . 
           [0010]      FIG. 6  is an isometric view of an alternative backreamer device. 
           [0011]      FIG. 7  is a back isometric view of an alternative backreamer device. 
           [0012]      FIG. 8  is a sectional view along line A in  FIG. 6  of plates for use with the backreamers of  FIGS. 6 and 7 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0013]    With reference to  FIG. 1 , the invention is directed to a stacked-plate backreamer  10 . The reamer  10  is attached at a terminal end of a drill stem  100 . In backreaming operations, a horizontal directional drill  102  drills a pilot bore into the subsurface  104 . This pilot bore exits the subsurface  104  at an exit point. The reamer  10  is then placed at the terminal end of the drill stem  100 . A wider product pipe  106  is attached to the reamer  10 , and the reamer  10  is pulled back through the subsurface  104  by the drill stem  100 , widening the borehole. 
         [0014]    In operations as described in  FIG. 1 , drilling fluid, such as drilling mud or lubricant, is pumped down the drill stem into the reamer  10  and distributed within the borehole to promote cutting by the reamer during hole opening/backreaming operations. While the operations discussed herein are referred to “hole opening” or “backreaming” operations, they should be understood to include “swabbing” operations—that is, using reamer  10  to clean the pilot bore of debris without significantly expanding the radius of the borehole. 
         [0015]    With reference now to  FIG. 2 , shown therein is an embodiment of the reamer  10 . The reamer  10  comprises a central shaft  12 , a first plate  14 , a second plate  16 , a distributor plate  18 , and a cutter plate  20 . The first plate  14 , second plate  16 , distributor plate  18 , and cutter plate  20  are each disposed about the central shaft  12 . A second cutter plate  22  may also be disposed about the central shaft  12 . In order from closest to the HDD machine  102  ( FIG. 1 ) to the furthest, the stacked plates are ordered cutting plate  20 , first plate  14 , distributor plate  18 , second plate  16 , second cutter plate  22 . 
         [0016]    Each of these plates may be welded or otherwise integrally connected to the central shaft  12  and to each other. Upon welding the plates together as in  FIG. 3 , they form a body  23  of multiple layers. External welds may connect the adjacent layers, causing the body  23  to be non-homogenous at the places that the plates are welded to make layers. 
         [0017]    The central shaft  12  is attached at one end to the drill stem  100  ( FIG. 1 ) and may be translated and rotated through operation of the drill stem. Each of the plates of the reamer  10  rotates integrally with the rotation of the central shaft  12 . The central shaft  12  defines a central fluid flow passage  28  and at least one radially disposed fluid flow port  30 . The central shaft  12  of  FIG. 2  has three fluid flow ports  30  disposed 120 degrees apart on an outer surface of the central shaft. 
         [0018]    The distributor plate  18 , when disposed about the central shaft  12 , defines an interior cutaway portion  34  and has a uniform cross-sectional dimension. As shown, there are three interior cutaway portions  34  disposed proximate each of the radial fluid flow ports  30  of the central shaft  12 . The distributor plate  18  preferably does not extend beyond an external periphery  36  of the second plate  16  and the first plate  14 . Fluid from the fluid flow ports  30  flows into into the cutaway portion  34  of distributor plate  18 . The distributor plate  18  may be covered in hardfacing material (not shown) on its periphery to protect it from wear due to interaction with the subsurface. 
         [0019]    The first plate  14  has a plurality of longitudinal bores or nozzles  40 . When assembled, the nozzles  40  are positioned next to the cutaway portion  34 . In this way, fluid flow is directed from ports  30 , through the cutaway portion  34 , and into the nozzles  40 . Each nozzle  40  preferably has a longitudinal axis that is parallel to the central shaft  12 . In  FIG. 2 , the nozzles  40  direct fluid in the direction the reamer  10  is being pulled by the drill stem  100  (FIG.  1 ). The first plate  14  and second plate  16  form a pair of boundary plates on each side of the distributor plate  18 , covering the cutaway portion  34  creating an internal void within the body of the reamer  10  with the nozzles  40  as the only outlets. 
         [0020]    With reference now to  FIG. 3 , the cutter plate  20  comprises an outer surface  50 . A plurality of teeth  52  are disposed on the outer surface  50  of the cutter plate  20  and oriented in the direction of rotation. As shown, the teeth  52  extend in the clockwise direction from the outer surface  50 . The outer surface  50  is shaped such that the teeth  52  extend radially beyond the external periphery  36  of the first  14  and second  16  plates. The teeth  52  therefore engage the subsurface as the reamer  10  is translated and rotated. As shown, the first cutter plate  20  comprises three teeth  52 , though other numbers of teeth may be utilized. Preferably, the number of teeth  52  corresponds to the number of nozzles  40 . As shown, the nozzles  40  incorporate a flow restrictor  54  to restrict the cross-sectional area of the nozzles  40  and thus increase the velocity of fluid expelled from the nozzles. 
         [0021]    The second cutter plate  22  is similarly formed to the first cutter plate  20 , and may be identically formed. The second cutter plate  22  comprises an outer surface  60  and a plurality of teeth  62  disposed on the outer surface. The teeth  62  similarly engage the subsurface. 
         [0022]    The second plate  16 , as shown in  FIG. 2 , does not comprise nozzles. While nozzles may optionally be included on the second plate  16 , fluid directed by nozzles  40  of the first plate  14  provide sufficient fluid to enhance hole opening by softening the subsurface. The second cutter plate  22  will be moved through this softened subsurface as the reamer  10  is pulled through the pilot hole. As a result, directing fluid through nozzles  40  in the direction of reamer  10  travel will enhance the cutting of both the first  20  and second  22  cutter plates. 
         [0023]    The teeth  52  of the first cutter plate  20  and the teeth  62  of the second cutter plate  22  are shown in substantially the same angular positions relative to a longitudinal axis  63  of the central shaft. However, teeth  52  may also be angularly offset from teeth  62 . Additionally, further plates may be added in addition to the first cutter plate  20  and the second cutter plate  22  to provide more layers. 
         [0024]    The central shaft  12  may comprise a connection point  70 . The connection point  70  facilitates torque transmitting connection between the reamer  10  and the drill stem  100  ( FIG. 1 ). This may be a threaded inner surface, pins, splines, geometrical features or other known torque transmitting features. The outer surface  72  of the central shaft  12  comprises a plurality of flat surfaces  74  to promote ease of connection and disconnection of the reamer  10  from the drill stem  100  ( FIG. 1 ). 
         [0025]    The reamer  10  additionally comprises a pullback feature  80  for connection to the product pipe  106  ( FIG. 1 ). As shown in  FIG. 3 , the pullback feature  80  comprises a towing eye  82 . The pullback feature  80  may be connected to the reamer  10  through a swivel assembly (not shown) or other means to enable pullback without imparting rotational forces from the reamer  10  to the product pipe  106  ( FIG. 1 ) 
         [0026]    With reference now to  FIG. 4 , an alternative reamer  200  is shown. The reamer  200  comprises a first plate assembly  201 , which comprises a first plate  202 , a distributor plate  204 , and a second plate  206 . The first plate  202  comprises a plurality of nozzles  208 . The first plate assembly  201  is disposed about a central shaft  210  of the reamer  200  at an acute angle. The second plate  206  comprises a plurality of cutting teeth  212  for enlarging a pilot bore by disrupting the subsurface as the first plate assembly  201  is rotated and pulled by the drill stem  100  ( FIG. 1 ). 
         [0027]    The reamer  200  also comprises additional plates  220  and  222 , each also disposed about the central shaft  210  at an acute angle relative to the central shaft. As shown, two additional plates  220  are offset by 120 degrees from the first plate assembly  201 , one clockwise, one counter-clockwise about axis  223 . The additional plates  220 ,  222  may not have teeth, but rather a hard-facing material (not shown) disposed around the periphery of the plates. 
         [0028]    The first plate assembly  201  is preferably the furthest “front” relative to the direction that the reamer  200  is pulled by the drill stem  100 . In this way, fluid conveyed through the central shaft  210  through radial ports (not shown) to the distributor plate  204  for use by all the plates  201 ,  220 ,  222  of the reamer  200  to wash cuttings from proximate the reamer  200 . The nozzles  208  are directed away from the direction of travel of the reamer  200 , into the page in  FIG. 4 . This will place fluid in the path of the plates  220 ,  222 , as well as the back end of the second plate  206 . 
         [0029]    With reference to  FIG. 5 , the first plate assembly  201  is shown in exploded view. When attached to the second plate  206 , the distributor plate  204  defines a cavity  230  for receiving fluid flow from radial ports (not shown) formed in the central shaft  210  ( FIG. 4 ). The cavity  230  comprises two bays  232  corresponding to the nozzles  208  formed in the first plate  202 . As shown, there are three nozzles  208  corresponding to each of the two bays  232 . One of skill in the an will appreciate that other cavities may be considered, as well as other nozzle patterns, without departing from the spirit of the invention. The second plate  206  has no nozzle and thus provides a closed wall surface  234  for enclosing the cavity  230 . A nozzle may optionally be placed in the second plate to provide fluid to the from side of the first plate assembly  201 . 
         [0030]    With reference now to  FIG. 6 , shown therein is a stacked-plate reamer  300  with an alternative configuration. The reamer  300  comprises a plurality of ported plates  302  and a plurality of unported plates  304  disposed about a central shaft  306 . The central shaft  306  comprises a connection point  308  for connection to the drill stem  100  ( FIG. 1 ). As shown, the connection point  308  comprises threads  310 . The reamer  300  comprises a pullback feature  312  such as a towing eye to pull a product pipe  106  ( FIG. 1 ). The central shaft  306  comprises radial ports  314  formed in a periphery of the shaft. As shown in  FIG. 6 , at least some of the radial ports  314  are uncovered by plates  302 ,  304 . The unported plates  304  and ported plates  302  each comprise teeth  316 . As shown, the teeth  316  are mounted on a shelf  318  formed on a face of the plates  302 ,  304  and extend beyond a periphery of the preceding plates. Radially aligned nozzles  320  are formed in the ported plates  302  for providing fluid proximate the cutting teeth  316  during reaming operations. 
         [0031]    A plurality of untoothed plates  322  may be provided in the “back” of the reamer  300  relative to the direction of travel (to the right in  FIG. 6 ). These untoothed plates  322  smooth and clean the borehole without generating substantial additional cuttings. As shown, each of the plates  302 ,  304 ,  322  define a number of grooves  324  and cutout sections  326  in their peripheries to allow fluid and cuttings to pass behind the reamer  300  as it is pulled through the ground. 
         [0032]    With reference now to  FIG. 7 , an alternative reamer  301  having many of the same component parts as the reamer  300  of  FIG. 6  is shown. Reamer  301  comprises more plates  302 ,  304 ,  322  than the reamer of  FIG. 6 , but the ultimate design is similar. In  FIG. 7 , at least some of the untoothed plates  322  comprise nozzles  320 . The reamer  301  has a product pipe connection point  330  disposed at its rear end (the right side in  FIG. 7 ) for connection to a swivel or similar structure of a product pipe  106  ( FIG. 1 ). The connection point  330  may be freely exchanged for the pullback feature  312  of  FIG. 6 . 
         [0033]    With reference to  FIGS. 6 and 7 , upon connection of the various plates  302 ,  304 ,  322  through welding or other means, the plates each form a layer of a body  303 . The layers may be formed such that the teeth  316  are positioned helically along an outside periphery of the body  303  as shown in the Figures, though artisans may conceive of other tooth orientations without departing from the scope of the invention. 
         [0034]    With reference to  FIG. 8 , an internal cross-section of the reamer  300  is shown at line A of  FIG. 6 . The ported plate  302  encircles but does not contact the central shaft  306 . A hollow region  350  is defined by an internal surface of the ported plate  302 , the external surface of the central shaft  306 , and the neighboring unported plates  304 . Fluid flows into the aperture  350  from the central shaft  306  through fluid ports  314  ( FIG. 6 ). The fluid then move through radial nozzles  320  to the external surface of the body  303 . The nozzles  320  are located proximate the teeth  316  to aid in hole opening and cleaning operations. 
         [0035]    One of skill in the art will appreciate that in all of the embodiments disclosed herein, multiple alternative teeth, configurations of teeth and configurations of layers may be utilized. For example, adjacent layers may comprise offset nozzles. Adjacent layers may be welded or bolted together. Hardfacing is typically used on reamers such as those disclosed herein to assist with boring operations and protect components from wear. The particular arrangement of such features and hardfacing should not be construed as a departure from the present invention. While the preferred embodiments of the invention are disclosed in the figures and specification herein, one of skill in the art will appreciate that various modifications to the embodiments above can be made without departing from the spirit of the disclosed invention.

Summary:
A stacked-plate system for a backreamer. The backreamer has a set of plates disposed about a central shaft for providing fluid for use in reaming operations. A distributor plate forms a cavity within a plate assembly for receiving fluid from the central shaft through radial fluid ports. Fluid from the cavity is then expelled through nozzles that overlay the cavity in a separate plate. The direction of fluid flow at the nozzles is axial, rather than toward the sidewall of the enlarged bore.