Abstract:
Apparatus for boring a hole from an inside of a casing outwardly at an angle relative to a longitudinal axis of the casing comprises a drill shoe having a longitudinal axis and being positionable in the casing, the shoe having first and second passageways which converge into a third passageway exiting the shoe, a torsional load transmitting element and a cutting element connecting to one end of the torsional load transmitting element, the torsional load transmitting element and cutting element being positioned in the first passageway during non-use and in the third passageway during use, and a fluid conduit and a nozzle connected to one end of the fluid conduit, the fluid conduit and nozzle being positioned in the second passageway during non-use and in the third passageway during use.

Description:
RELATED APPLICATIONS 
     This application is divisional of application Ser. No. 09/761,985 filed Jan. 17, 2001 now U.S. Pat. No. 6,412,578 issued Jul. 2, 2002 which is a continuation-in-part of my application Ser. No. 09/643,306 filed Aug. 22, 2000 now U.S. Pat. No. 6,378,629 which is hereby incorporated by reference herein as if fully set forth in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates broadly to the boring of a hole through the wall of a tube from the inside of the tube outwardly at an angle to a longitudinal axis of the tube. More specifically, this invention relates to apparatus for drilling through an oil or gas well casing at an angle to the longitudinal axis of the casing and into the earth strata surrounding the well casing. More particularly, this invention relates to an improved such drilling apparatus and to a means of transporting, deploying and retrieving the drilling apparatus. 
     BACKGROUND OF THE INVENTION 
     Oil and gas wells are drilled vertically down into the earth strata with the use of rotary drilling equipment. A tube known as a casing is placed down into the well after it is drilled. The casing is usually of made of mild steel and is in the neighborhood of 4.5 inches to 8 inches in external diameter (4 inches in internal diameter and up) and defines the cross-sectional area of the well for transportation of the oil and gas upwardly to the earth surface. However, these vertically extending wells are only useful for removing oil and gas from the terminating downward end of the well. Thus, not all of the oil and gas in the pockets or formations in the surrounding earth strata, at the location of the well depth, can be removed. Therefore, it is necessary to either make additional vertical drillings parallel and close to the first well, which is costly and time consuming, or to provide some means to extend the original well in a radial direction relative to the vertical longitudinal axis of the casing horizontally into the surrounding earth strata. 
     The most common means for horizontal extension of the well has been to drill angularly through the well casing at a first 45° angle for a short distance and then to turn the drill and drill at a second 45° angle thereby making a full 90° angular or horizontal cut from the vertically extending well. These horizontal drills have proved useful for extending the well horizontally but have proved to be relatively expensive. 
     Another solution to the problem is disclosed in U.S. Pat. Nos. 5,413,184 and 5,853,056, both of which are hereby incorporated by reference herein as if fully set forth in their entirety. In these patents there is disclosed an apparatus comprising an elbow, a flexible shaft or so-called “flex cable” and a ball cutter attached to the end of the flexible shaft. The elbow is positioned in the well casing, and the ball cutter and flexible shaft are passed through the elbow, turning 90°. A motor rotates the flexible shaft to bore a hole in the well casing and surrounding earth strata with the ball cutter. The flexible shaft and ball cutter are then removed and a flexible tube with a nozzle on the end thereof is passed down the well casing, through the elbow and is directed out of the casing through the hole therein. Water pumped through the flexible tube exits the nozzle at high speed and bores further horizontally into the earth strata. 
     Prototype testing of the device disclosed in U.S. Pat. Nos. 5,413,184 and 5,853,056 has proven less than satisfactory. In particular, a number of problems plague the device disclosed in U.S. Pat. Nos. 5,413,184 and 5,853,056. For example, the disclosed ball cutter is inefficient at best and ineffective at worst in cutting through the well casing. The inherent spherical geometry of a ball cutter causes it “walk” or “chatter” during rotation as it attempts to bore through the well casing which greatly increases the amount of time required to bore through the casing. Ball cutters are best utilized for deburring, and/or cutting a radius in an existing hole or slot for example and are simply not suitable for drilling holes. 
     Another problem is the torsional flexibility of the flexible shaft or flex cable. Rather than transmitting rotational displacement to the ball cutter at 100% efficiency the flex cable tends to “wind up” or exhibit “backlash,” thus reducing the already inefficient cutting efficiency of the ball cutter even more. 
     Yet another problem is the tendency of the elbow to back away from the hole in the casing during drilling with the ball cutter. Such backing away causes the elbow outlet to become misaligned with the hole in the casing thereby preventing smooth introduction of the nozzle and flexible tube into the hole in the casing. 
     Still another problem is the large amount of torsional friction generated between the elbow passageway and the flex cable which of course increases the horsepower requirements of the motor required to rotate the flex cable. The addition of balls, separated by springs, to the flex cable, in an effort to alleviate the resistance of the apparatus to being rotated, has not remedied this problem. 
     A further problem is the closed nature of the apparatus of U.S. Pat. Nos. 5,413,184 and 5,853,056. which prevents its being taken apart, inspected, cleaned and repaired as needed. 
     The invention of my application Ser. No. 09/643,306 overcomes the deficiencies of the apparatus disclosed in U.S. Pat. Nos. 5,413,184 and 5,853,056. That invention is apparatus for boring a hole from an inside of a tube outwardly perpendicular to a longitudinal axis of the tube. The apparatus comprises a drill shoe having a longitudinal axis and being positionable in the tube, the shoe having an inlet, an outlet perpendicular to the shoe longitudinal axis and a passageway connecting the inlet and outlet, a torsional load transmitting element having no torsional flexibility in relation to its bending flexibility, having a longitudinal axis and being disposed in the passageway, the torsional load transmitting element being movable relative to itself about first and second perpendicular axes both of which are perpendicular to the longitudinal axis of the torsional load transmitting element, a hole saw connected to one end of the torsional load transmitting element and a motor rotatably connected to the other end of the torsional load transmitting element. Rotation of the torsional load transmitting element by the motor rotates the hole saw to bore through the tube from the inside of the tube outwardly perpendicular to the longitudinal axis of the tube. 
     Further improvements in boring technology are nonetheless desired. For example, the invention of U.S. Pat. Nos. 5,413,184 and 5,853,056 is inefficient and time consuming to operate in that after the cutting tool has bored through the well casing the drilling operation must be interrupted so that the entire drilling apparatus can be retrieved to the earth surface in order to remove the well casing cutting tool and to install the earth strata boring water nozzle. The drilling apparatus must then be lowered back down into the well casing to resume the drilling operation. 
     SUMMARY OF THE INVENTION 
     The invention includes apparatus for boring a hole from an inside of a casing outwardly at an angle relative to a longitudinal axis of the casing. The apparatus comprises a drill shoe having a longitudinal axis and being positionable in the casing, the shoe having first and second passageways which converge into a third passageway exiting the shoe a torsional load transmitting element and a cutting element connected to one end of the torsional load transmitting element, the torsional load transmitting element and cutting element being positioned in the first passageway during non-use and in the third passageway during use, and a fluid conduit and a nozzle connected to one end of the fluid conduit, the fluid conduit and nozzle being positioned in the second passageway during non-use and in the third passageway during use. 
     The third passageway may exit the shoe at any desired angle of between 0° and 90° relative to the longitudinal axis of the drill shoe. The angle may be, for example, 75° or 90°. The apparatus may include an exit insert installable in the shoe to provide variability in the exit angle. 
     The torsional load transmitting element has a longitudinal axis, and preferably has no torsional flexibility in relation to its bending flexibility and is movable relative to itself about first and second perpendicular axes both of which are perpendicular to the longitudinal axis of the torsional load transmitting element. The torsional load transmitting element may be freely movable relative to itself about the first and second perpendicular axes. The torsional load transmitting element may be pivotable relative to itself about the first and second perpendicular axes. The torsional load transmitting element may be freely pivotable relative to itself about the first and second perpendicular axes. 
     The cutting element may be a hole saw. The apparatus may further comprise a drill bit connected to the end of the torsional load transmitting element centrally of the hole saw. The drill shoe may be fabricated in halves. The torsional load transmitting element may comprise a plurality of interconnected universal joints. The shoe may include an angled end surface adapted to cooperate with a matingly angled end surface of a drill shoe depth locator for locating the shoe at a selected depth in the casing such that an angular orientation of the shoe relative to the casing is establishable by positioning the depth locating device at an angular orientation relative to the casing. 
     A drill shoe depth locator for locating a drill shoe at a selected depth in a casing comprises a housing, at least one locking arm pivotally connected to the housing and an actuator for selectively pivoting the arm. The arm is pivotable to and between a retracted non-locking position in the housing and an extended locking position wherein at least a portion of the arm projects out of the housing and is adapted to contact a wall of the casing. 
     The actuator for selectively pivoting the arm may comprise a firing mechanism which fires a charge that propels the arm to the extended locking position. The firing mechanism may include a chamber adapted to accept a charge cartridge, a gas path between the chamber and the pivoting arm and a firing pin which is selectively activatable to strike the charge cartridge. The housing may include an angled end surface adapted to cooperate with a matingly angled end surface of the drill shoe such that an angular orientation of the drill shoe relative to the casing is establishable by positioning the depth locator at an angular orientation relative to the casing. 
     A tool for deploying a drill shoe depth locator in the casing comprises a housing, at least one locking arm pivotally connected to the housing and an actuator for selectively pivoting the arm. The arm is pivotable to and between a retracted non-locking position in the housing and an extended locking position wherein at least a portion of the arm projects out of the housing and is adapted to engage a surface of the drilling apparatus depth locator. 
     The actuator may comprise a rod movable longitudinally relative to the housing which cooperates with a cam surface on the pivoting arm to thereby move the arm. 
     A tool for retrieving a drill shoe depth locator from a casing comprises a housing, at least one locking arm pivotally connected to the housing and a resilient member normally biasing the locking arm to an extended locking position yet permitting upon application of sufficient force the locking arm to move to a retracted non-locking position. The arm is pivotable to and between the retracted non-locking position in the housing and an extended locking position wherein at least a portion of the arm projects out of the housing and is adapted to engage a surface of the drill shoe depth locator. 
     A mobile drilling apparatus comprises a wheeled trailer having a trailer bed, a drill shoe, a mast mounted on the trailer bed for suspending therefrom the drill shoe, a first reel rotatably mounted on the trailer bed for paying out and taking up a cable connected to the drill shoe, the cable supported by the mast, a second reel rotatably mounted on the trailer bed for paying out and taking up a first length of tubing which communicates fluid from a fluid source to a fluid motor in the drill shoe, the tubing supported by the mast, and a third reel rotatably mounted on the trailer bed for paying out and taking up a second length of tubing which communicates fluid from a fluid source to a fluid nozzle in the drill shoe, the tubing supported by the mast. 
     The mast may be pivotally mounted to the trailer bed for pivoting movement to and between an upright operable position and a lowered inoperable position. The mast may be mounted to a work platform and the work platform may be mounted to the trailer bed for movement transverse to a longitudinal axis of the trailer bed. The apparatus may further comprise a catwalk extending the length of the trailer bed on one side thereof and mounted to the trailer bed for pivoting movement to and between an upright inoperable position and a lowered operable position wherein the catwalk extends the width of the trailer bed. The catwalk may include a set of steps secure thereto such that when the catwalk is in the lowered operable position an operator may climb the steps from a ground surface to the trailer bed. 
     The apparatus may further comprise a motor rotatably driving each of the first, second and third reels, a brake mounted to each of the first, second and third reels, a sensor mounted to each of the first, second and third reels for sensing an angular velocity of each of the first, second and third reels and a controller which controls the brakes in response to signals received from the sensors. The apparatus may further include a sensor mounted on the mast for sensing a depth traversed by the drill shoe. 
     These and other advantages of the present invention will become more readily apparent during the following detailed description taken in conjunction with the drawings herein, in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS OF THE INVENTION 
     FIG. 1 is a side view of a drill shoe of the invention; 
     FIG. 2 is an enlarged sectional side view of a portion of the drill shoe of FIG. 1; 
     FIG. 3 is a side view in partial cross section of the cooperatingly matingly angled end surfaces of the drill shoe and drill shoe depth locator; 
     FIG. 4 is an enlarged view of the end of the drill shoe with angle locating surface; 
     FIG. 5 is a side cross-sectional view of a device for locating the drill shoe at a selected depth in the casing, and a tool for deploying the drill shoe depth locator: 
     FIG. 6 is a view similar to FIG. 5 with the drill shoe depth locator fixed in position in the casing and the deploying tool being withdrawn from the casing; 
     FIG. 7 is a view similar to FIG. 5 but of a tool for retrieving the drill shoe depth locator engaging the drill shoe depth locator; 
     FIG. 8 is a view similar to FIG. 7 of the retrieving tool and drill shoe depth locator being withdrawn from the casing; 
     FIG. 9 is a side view of the mobile drilling apparatus of the invention; and 
     FIG. 10 is a top view of the mobile drilling apparatus of FIG.  9 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring first to FIG. 1 a boring apparatus  10  according to the principles of the present invention is illustrated. During use apparatus  10  is positionable inside a well casing  12  in the earth strata  14  (FIG.  3 ). The boring apparatus  10  includes a hollow carbon steel drill shoe  20 . Drill shoe  20  has a longitudinal axis which when inserted into casing  12 , is generally parallel to a longitudinal axis of the well casing  12 . Drill shoe  20  may preferably be fabricated in halves  20   a ,  20   b  securable together via bolts  22 . Drill shoe  20  may be connected to a ½ inch diameter 6×25 IWRC wire rope  24  which is utilized to lower drill shoe  20  down into casing  12 . 
     A fluid motor  26  imparts rotation to a motor coupling  28  which is connected to a drill bit shaft  30  itself connected to a plurality of interconnected universal joints  32  which terminate in a hole saw  34  with central pilot hole drill bit  36 . Above motor  26  is a motor locator  38 ; motor locator  38  and drill shoe  20  include cooperating structure (not shown; see U.S. patent application Ser. No. 09/643,306 for same) rotatably fixing the motor locator  38  and hence motor  26  relative to the shoe  20  thereby preventing relative rotation between motor  26  and shoe  20  during operation of motor  26 . 
     Shoe  20  further includes a first passageway  40 , a second passageway  42  and a third passageway  44 . The universal joints  32 , hole saw  34  and drill bit  36  reside in first passageway  40  during nonuse and in third passageway  44  during use. Similarly, a flexible fluid conduit  46  with a nozzle  48  connected to its end is positioned in the second passageway  42  during nonuse and in the third passageway  44  during use. Motor  26  may be suspended from and supplied with liquid through a ½ inch diameter 0.049 inch wall thickness 316L stainless steel tubing  50 . Similarly, fluid conduit  46  may be suspended from and supplied with liquid through a ⅝ inch diameter 0.049 inch wall thickness 316L stainless steel tubing  52 . 
     Third passageway  44  may exit the shoe  20  at any desired angle of between 0° and 90° relative to the longitudinal axis of the shoe  20 , depending on the drilling application. Preferably, the angle is in the general range of about 75° to 90°. To provide convenient variability and versatility in the exit angle of the third passageway  44  one of a number of exit angle inserts  54  may be utilized, each of which inserts would include a different exit angle. For example, two exit inserts  54  may employed, one of which is at 75° (FIG. 4) and the other of Which is at 90° (FIG. 3) thereby providing an operator with a ready means of quickly changing the exit angle depending on drilling conditions etc. Exit insert  54  may be removably installable in the shoe  20  via screws  56 . 
     Referring to FIGS. 1-4, shoe  20  may include an angled end surface  58  formed as part of an angular locator  60  secured to a lower end of shoe  20  with a bolt  62  and locating pin  64 . Angled end surface  58  is adapted to cooperate with a matingly angled end surface  66  of a drill shoe depth locator  68  (discussed in more detail below) for locating the shoe  20  at a selected depth in the casing  12 . An angular orientation of the shoe  20  relative to the casing  12  Is establishable by positioning the depth locator  68  at an angular orientation relative to the casing  12 . The matingly angled end surfaces  58  and  66  automatically determine the angular orientation of the shoe  20  to locator  68  and thus shoe  20  to casing  12 . The use thereof will be described below in more detail. 
     Referring now to FIGS. 3,  5  and  6 , the drill shoe depth locator  68  is illustrated which locates the drill shoe  20  at a selected depth in the casing  12 . The depth locator  68  comprises a housing  70  and may preferably comprise a pair of locking arms  72  pivotally connected to the housing  70  as by pivots  74 . The arms  72  are pivotable to and between a retracted non-locking position in the housing (FIG. 5) and an extended locking position wherein at least a portion of the arms  72  project out of the housing  70  and is adapted to contact the wall of the casing  12 . An actuator  76  may be included for selectively pivoting the arms  72 . The actuator  76  may comprise a firing mechanism, which fires a charge that propels the arms  72  to the extended locking position, which comprises a chamber  78  adapted to accept a charge cartridge  80 , a gas path  82  between the chamber  78  and each pivoting arm  72  and a firing pin  84  which is selectively activatable to strike the charge cartridge  80  thus releasing combustion gases which force the arms  72  upwardly into a locking position relative to the casing  12 . Gas vent paths  86  bleed excess gas out of housing  70 . Preferably the firing mechanism actuator  76  of the device  68  would be activated as the device  68  is being lowered into the casing  12 ; when the device  68  reaches the desired depth as indicated by, for example, a rotary encoder, the mechanism  76  is fired propelling the arms  72  upwardly into engagement with the casing  12 , the downward momentum of the device  68  further assisting in locking the arms  72  into the wall of the casing  12 . In the alternative, the charge cartridge  80  and firing pin  84  could be eliminated; the locking arms  72  can be forced upwardly into engagement with the casing  12  by simply lowering locator  68  at a sufficient velocity such that water in casing  12  moves forcefully up chamber  80  through paths  82  and into contact with arms  72  forcing them upwardly. 
     Firing pin  84  is spring loaded via compression spring  85  positioned within firing pin housing  87 . A firing pin blocking plate  89  normally blocks firing pin  84  from upward movement. Firing pin blocking plate  89  is maintained in its blocking position via a release rod  91 . Upon upward movement of release rod  91  aperture  93  in blocking plate  89  centers around firing pin  84  thereby freeing firing pin  84  to move upwardly under force of compression spinrg  85 . 
     As mentioned briefly above, the depth locator  68  preferably includes an angled end surface  66  which cooperates with the matingly angled end surface  58  of the drill shoe  20 . Once the device  68  is in position in the casing  12 , a plurality of radially extending horizontal borings can be made into the earth strata by adjusting the angular position of the angular locator  60  relative to the shoe  20 , it being contemplated that the shoe  20  and locator  60  would have a plurality of locating pins  64  positioned at, for example 5° to 10° increments. Thus, with each 5° or 10° readjustment of locator  60  relative to shoe  20 , the shoe  20  can bore a new radial path radially outwardly from the casing  12  but at a known increment relative to the previous boring. If desired, the shoe  20  and locator  60  can be repeatedly readjusted to drill radially outwardly from the well casing  12  in a full 360° circle. 
     Referring still to FIGS. 5 and 6, there is illustrated a tool  100  for deploying the drill shoe depth locator  68  in the casing  12 . The tool  100  comprises a housing  102  and a pair of locking arms  104  pivotally connected to the housing  102  as by pivots  106 . The locking arms  104  are pivotal to and between a retracted non-locking position (FIG. 6) generally within the periphery of the housing  102  and an extended locking position (FIG. 5) wherein at least a portion of the arms  104  project out of the housing  102 , and are adapted to engage a surface  110  of the depth locator  68 . An actuator  112  selectively pivots the arms  104  to and between the retracted non-locking position (FIG. 6) and the extended locking position (FIG.  5 ). The actuator preferably comprises a rod  114  which is movable longitudinally relative to the housing  102  and which cooperates with a cam surface  116  on each pivoting arm  104  to thereby move the arms  104 . Thus, to lower the depth locator  68  in the well casing  12 , the tool  100  is engaged with the depth locator  68  in that the rod  114  is in a downward position forcing arms  104  outwardly so as to engage underneath surface  110  of the device  68 . Once the depth locator  68  is at the desired depth in the casing  12 , the rod  114  is pulled upwardly thereby permitting upward force on the tool  100  to force the pivoting arms  104  inwardly and free of surface  110  thus permitting the tool  100  to be withdrawn from the casing  12 . 
     Referring now to FIGS. 7 and 8 there is illustrated a tool  200  for retrieving the depth locator  68  from the casing  12 . The tool  200  comprises a housing  202  and a pair of locking arms  204  pivotally connected to the housing  202  as by pivots  206 . The locking arms  204  are pivotable to and between a retracted non-locking position (FIG. 7) generally within the periphery of the housing  202  and an extended locking position (FIG. 8) wherein a portion of the arms  204  project out of the housing  202  and are adapted to engage the prior mentioned surface  110  of the depth locator  68 . A resilient member  210  normally biases the locking arms  204  to the extended locking position, yet permits upon application of a sufficient force the locking arms  204  to move to the retracted non-locking position, i.e. during initial insertion of housing  202  and locking arms  204  into depth locator  68  (FIG.  7 ). 
     Referring to FIGS. 9 and 10 a mobile drilling apparatus  300  is illustrated. The apparatus  300  comprises a wheeled trailer  302  having a trailer bed  304 , the prior described drill shoe  20 , a mast  308  mounted on the trailer bed  304  for suspending therefrom the drill shoe  20 , a first reel  310  rotatably mounted on the trailer bed  304  for paying out and taking up cable  24  connected to the drill shoe  20 , the cable  24  being supported by the mast  308 , a second reel  314  rotatably mounted on the trailer bed  304  for paying out and taking up the first length of tubing  50  which communicates fluid from a fluid source (not shown) to the fluid motor  26  in the drill shoe  20 , the tubing  50  supported by the mast  308 , and a third reel  318  rotatably mounted on the trailer bed  304  for paying out and taking up the second length of tubing  52  which communicates fluid from the fluid source to the fluid nozzle  48  in the drill shoe  20 , the tubing  52  supported by the mast  308 . Reels  310 ,  314  and  318  may be five feet in diameter and capable of storing up to ten thousand feet of wire rope or tubing. 
     The mast  308  is preferably mounted to a work platform  340 . Work platform  340  is preferably mounted to the trailer bed  304  for pivoting movement of the mast  308  to and between an upright operable position and a lowered inoperable position, and is also mounted to the trailer bed  304  for movement transverse to a longitudinal axis of the trailer bed  304  thereby providing transverse alignment of drill shoe  20  to casing  12 . Hydraulic cylinder  342  may be operable between the trailer bed  304  and mast  308  to pivot the mast  308  relative to the bed  304 . Hydraulic cylinder  344  may be operable between the work platform  340  and trailer bed  304  to move the work platform  340  transversely to the longitudinal axis of the trailer bed  304 . 
     Trailer  302  may additionally comprise a catwalk  350  extending along the trailer  302  on one side thereof and mounted to the trailer bed  304  for pivoting movement to and between an upright inoperable position and a lowered operable position wherein the catwalk  350  extends the width of the trailer bed. A hydraulic cylinder  352  may be operable between the bed  304  and catwalk  350  to pivot the catwalk  350  and between the upright inoperable and lowered operable positions. Catwalk  350  may include a set of steps  354  secured thereto such that when the catwalk  350  is in the lowered position an operator may climb the steps from a ground surface to the trailer bed  304 . 
     With reference to FIG. 10 the apparatus may further preferably comprise hydraulic motors  400 ,  402  and  404  rotatably driving each of the reels  310 ,  314  and  318  respectively at up to 8 rpm. hydraulic disk brakes  410 ,  412  and  414  mounted to each of the reels  310 ,  314  and  318  respectively and sensors  420 ,  422  and  424  mounted to each of the reels  310 ,  314  and  318  respectively for sensing an angular velocity of each of the reels  310 ,  314  and  318 . A controller  450  is operable to control the brakes  410 ,  412  and  414  in response to signals received from the sensors  420 ,  422  and  424  to insure that the cable  20  and tubing  50  and  52  all pay out and are taken back up at the same rate. Controller  450  also includes manually manipulable controls for the reels and brakes. To monitor the distance drill shoe  20  is being lowered into the casing  12  a sensor  460  may be mounted atop mast  308  to sense a depth traversed by the drill shoe  20 . Sensors  420 ,  422 ,  424  and  460  may take the form of, for example optical rotary encoders. A diesel engine driven 15,000 psi water pump and hydraulic fluid pump  470  supplies high pressure water to motor  26  and nozzle  48  and hydraulic fluid pressure to motors  400 ,  402 ,  404 , brakes  410 ,  412 ,  414  and cylinders  342 ,  344 ,  352 , respectively. 
     Those skilled in the art will readily recognize numerous adaptations and modifications which can be made to the present invention which will result in an improved boring apparatus, yet all of which will fall within the spirit and scope of the present invention as defined in the following claims. Accordingly, the invention is to be limited only by the scope of the following claims and their equivalents.