Patent Publication Number: US-2004040751-A1

Title: Directional drilling apparatus

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] THIS INVENTION relates to directional drilling equipment and more particularly to directional drilling equipment utilised for forming generally horizontal passages in the ground, (usually 1 to 10 metres from the surface) for electrical or telephone cables, gas or water pipes, etc. Such directional drilling equipment is known per se. The drilling equipment is directional in the sense that the drill can be, in effect, steered to allow it to be navigated along streets or roads, for example, or under roads and rivers, without striking the foundations of buildings or water mains, gas mains or sewers.  
       [0003] 2. Description of Related Art  
       [0004] Such systems are known and utilise, for example, a drill bit which is not rotationally symmetrical about its axis and/or has asymmetrically disposed fluid flushing outlets, so that material can be removed preferentially from one side of the bore being drilled whereby, in use, the end of the bore being drilled can deliberately be made to drift to one side or the other of the axis of the regions of the bore further from the end whereby the drill can be “steered”. WO97/49889 discloses one example of a directional drilling arrangement. The primary mechanism for deviation in known directional drilling equipment is the out-of-balance transverse force component acting on the drill bit, and hence the drill string, caused where there is no rotation of the drill string and the bit is being forced into the medium being drilled. There is some additional nonsymmetric flushing causing preferential removal of debris from one side of the bore-hole which can also assist deviation in certain softer formations.  
       [0005] This transverse force component effectively causes deviation or steering of the drill and drill string in the particular azimuth direction required when the drill string is not rotating. When uniform rotation is recommenced, there is no further effective transverse force component and the drill string continues along a new straight axis (which is then a different axis from the previous one). This operation can be carried out fairly frequently to effect the desired rate of change of direction, or steering.  
       [0006] In conventional drilling equipment, the drilling bit has a splined shank which is received in the correspondingly splined end of an endmost tubular element (or chuck) of the drilling string, the cooperating splines preventing relative rotation between the drill bit and the chuck. Normally manufacturing techniques and convenience dictate that in such known arrangements, the arrangement of splines on the drill bit shank and the chuck is rotationally symmetrical.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007] According to one aspect of the invention, there is provided drilling apparatus including a drill string terminating in a drill chuck and a drill bit detachably fitted in the drill chuck, the drill bit having a shank received in the drill chuck, the drill chuck and the drill bit shank having cooperating spleens thereon and the distribution of the said splines about the axis of the drill chuck and bit being irregular so that the drill bit can be fitted in the drill chuck in only one orientation.  
       [0008] Preferably the drill string incorporates a pneumatically operable hammer arranged to apply axial impact forces to the drill bit, the apparatus including first passageways for supplying compressed air to such hammer mechanism and separate second passages for applying fluid to the drill bit.  
       [0009] In the last-noted arrangement, separate air exhaust ports and drilling fluid discharge ports are provided on the bit.  
       [0010] According to yet another aspect of the invention there is provided drilling apparatus including a drill string terminating in a drill chuck and a drill bit detachably fitted in the drill chuck, the drill bit having a shank received in the drill chuck, the drill bit shank having a first splined region adjacent a head position of the drill bit and having splines cooperating with grooves between splines of an internally splined complementary portion of said chuck wherein the drill bit has a second splined region adjacent its rear end and has a spline-free band located between said first and second splined regions, and the apparatus includes a liner, adjoining the chuck and having an internal axial passage which is splined in correspondence with the second splined region, over an axial extent less than that of said spline-free band, the axial passage in said liner having, immediately behind the splined region of the liner, a region which is free of splines and has an internal diameter greater than the external diameter of the second splined region of the drill bit shank, said liner being rotatable between an angular position in which the splines thereon are in axial alignment with those in the second splined region of the chuck and an angular position in which they are out of such alignment, whereby the drill shank can be inserted in the passages of complementary cross section in the chuck and the liner, with the spleens of the chuck and liner aligned with the corresponding splines of the drill bit shank, until said second splined region of the drill bit shank is within the splineless region of the liner and the end splined region of the liner is within the spline-free band of the drill bit shank, and the liner thereafter rotated so as to move its splines out of axial alignment with those of said second splined region of the drill shank, thereby preventing axial removal of the drill bit.  
       [0011] According to yet another aspect of the invention there is provided drilling apparatus comprising a series of elongate sections releasably interconnected end to end by interengaging screw threads, orienting means for ensuring that a first component carried by a first said section adopts a predetermined orientation with respect to a second component carried by, or forming part of, an adjoining second said section when the first and second section are screwed together, wherein said first component is rotatable with respect to said first section and wherein the first section carries a member, herein referred to for convenience as an azimuth member, which is rotatable with respect to said first section but is non-rotatable with respect to said first component, and wherein the second section carries a reference member which is fixed against rotation relative to said second component and is engageable with said azimuth member in a predetermined angular orientation relative to the azimuth member as said first and second sections are screwed together end to end, and wherein, when so engaged relative rotation about the axis of said sections, between said azimuth member and said reference member is precluded by such engagement, and wherein one of said azimuth member and said reference member is resiliently displaceable away from the other as said first and second section are screwed together, whereby during an initial phase of screwing said first and second sections together the resiliently displaced member can be displaced axially, to counteract the progressive approach of said first and second sections, as the latter are screwed together, whilst rotating relative to the other said member, until said predetermined angular orientation of the reference member with respect to the azimuth member is reached, allowing the azimuth member and reference member to engage and thereby prevent further relative rotation between the two, whereby the azimuth member, and said first member coupled thereto, will maintain said predetermined orientation relative to said second component despite further rotational movement between said first and second section during completion of the screwing together of said first and second sections.  
       [0012] According to a still further aspect of the invention there is provided percussion drilling bit operable when accorded only a limited range of angular movement about a longitudinal axis of the bit, and wherein the bit comprises cutting tips or inserts arranged in a series of rings or tiers concentric with said longitudinal axis, such that for a predetermined angle of rotation of the bit about said axis, the zone of action of each cutting tip or insert in each said ring or tier overlaps that of at least the adjoining cutting tips or inserts in the same ring or tier.  
       [0013] In the preferred embodiments.of the invention, a sensing and transmitting apparatus is incorporated in the drill string, adjacent to the drill chuck, to sense and transmit to the surface information about the position and orientation of the drill bit or other drilling equipment. This apparatus can relay back to the surface readings of depth, position and angular position of the drill string. This infonnation, inter alia, allows the angular position of the drill bit to be determined and allows the bit to be positioned at the required angle for steering in the desired direction. Sensing and transmitting apparatus capable of operating as described above is herein referred to, for convenience, as a “sonde” or as a data transmitter.  
       [0014] Preferably the sonde is mounted in the drill string via a resilient suspension arrangement to isolate the sonde from mechanical shocks. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0015] An embodiment of the invention is described below by way of example with reference to the accompanying drawings, in which:  
     [0016]FIGS. 1A and 1B are respective parts of a view in axial section through a drill bit, chuck and associated parts of a first form of drilling assembly in accordance with the invention,  
     [0017]FIG. 2 is a view in cross section along the line II-II in FIG. 1,  
     [0018]FIG. 3 is a view in cross section along the line III-III of FIG. 1,  
     [0019]FIG. 4 is a perspective view of the shank of the drilling bit,  
     [0020]FIG. 5 and FIG. 6 are respectively a perspective view and an enlarged longitudinal section view of a stem body forming part of the apparatus of FIG. 1,  
     [0021]FIG. 7 is a fragmentary view in longitudinal section of the outer cylinder and chuck of the apparatus of FIG. 1 to  6 ,  
     [0022]FIG. 8 is a view in longitudinal section view of a cylinder liner of the assembly, FIG. 8 showing above the longitudinal axis a section in one axial plane and below the axis a section in a different axial plane,  
     [0023]FIG. 9 is an end elevation view of the liner of FIG. 8,  
     [0024]FIGS. 10 and 11 are diagrammatic side elevation views of another form of drilling apparatus in accordance with the invention;  
     [0025]FIG. 12 is an end view of a drilling bit in accordance with another aspect of the invention;  
     [0026]FIG. 13 is a side view of the drilling bit of FIG. 12;  
     [0027]FIGS. 14A and 14B are respective parts of a partial axial section view, to an enlarged scale as compared with FIG. 1, of part of the assembly of FIG. 1 having a sonde;  
     [0028]FIGS. 15 and 16 are corresponding sectional view of corresponding parts of the drilling apparatus of FIGS. 10 and 11 respectively, and  
     [0029]FIG. 17 is a schematic perspective view of a hammerless drilling device which may alternatively be used with the sonde housing illustrated in FIGS. 14A and 14B. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0030]FIGS. 1A and 1B show what is in effect the operative or active portion of the drilling assembly. This is adapted to be attached, by the tapered screw-threaded stub  50  shown at the left hand side of FIG. 1A, to a so-called drill string which normally comprises a series of tubular sections connected together end to end by complementary coarse pitch screw-threaded stubs and sockets, the string, at its end remote from the drill bit, being connected, in manner known per se, to means for supplying energy to the drill bit. The drilling assembly in the embodiment under discussion is adapted to operate percussively rather than, (or as well as) rotatively and the energy supply is provided by compressed air, which is supplied down the hollow drill string and operates a piston hammer arrangement, to be described below, acting on the drill bit.  
     [0031] In the apparatus illustrated in FIGS  1 A and  1 B, the drill bit comprises a head portion  20  and a shank  22 . The head portion is of asymmetrical form, known per se in directional drilling apparatus, and is shown somewhat schematically in FIG. 1B. By way of example, apart from a series of ports, for the discharge of drilling fluid and/or air, or flutes or grooves disposed around the rearward part of the head portion and hard buttons or inserts of the kind conventional in percussive rock drills, (none of which features is shown in FIG. 1B), the head portion may have the general form of a body of revolution about the bit axis from which a portion has been sectioned along a plane oblique to the bit axis, defining a flat  30  extending to the front end of the drill bit and imparting a deliberate asymmetry to the bit. A passage  34  for air extends axially along the bit shank  22  from the rear (i.e. upper) end of the latter, and communicates, in the head of the bit, with passageways leading to discharge ports  35 ,  35 A on the surface of the drill bit head, as shown. The effect of such asymmetry is that when the bit is being driven through material by blows applied by a hammer (see below) to the rear end of the drill bit, the asymmetrical configuration of the drill head results in a progressive deviation of the bore being drilled to one side or the other, depending on the orientation of the drill bit about its axis. Other forms of asymmetrical drill bit may be used, for example a drill bit which has the general form of an axially short cylinder with a domed end surface concentric with that cylinder, but with that short cylinder and domed end having their common axis of curvature arranged eccentrically with respect to the central axis of the drill bit shank, although generally parallel therewith. Such eccentric drill bits are known per se. The head could, of course, take other, e.g. convex, shapes.  
     [0032] The apparatus shown in FIGS. 1A and 1B has provision for supplying both compressed air and drilling fluid to the drill bit and so the drill bit  20 ,  22  illustrated in FIG. 1B has separate passages (see below) for supplying compressed air and drilling fluid to the bit, the compressed air passage opening onto a port  35  on the bit head and the drilling fluid passage opening onto drilling fluid ports  35 A on the head of the drill bit. These ports are also arranged asymmetrically about the drill bit head. Thus, when the bit is being used to drill in fluid-erodable material, such as soil or other granular material, the drilling fluid under pressure or exhaust air from the hammer supplied to the bit removes material preferentially from one side of the axis of the hole being bored, assisting the deviation or steering of the bit to that side. By controlling the orientation of the bit and selective supply of fluid in this way, the route of the drilled hole can be controlled.  
     [0033] It will be understood that the shape of the drill bit head is represented in simplified schematic form in FIG. 1B.  
     [0034] Referring again to FIGS. 1A and 1B, the drill bit shank  22  is received within a component referred to herein as a chuck  40  which is simply the forward end of an integral tubular cylindrical casing or sleeve  46  which effectively forms the forwardmost portion of the drill string. As best shown in FIG. 7, this sleeve  46  is internally screw-threaded at its rear (i.e. upper) end to receive an externally screw-threaded portion of a plug or adaptor  43 , the rear (upper) end of which is provided with an internally screw-threaded socket to receive, in turn, a sonde section  48  of the apparatus, the sonde section  48  in turn having, at its rear (upper) end, the tapered, screw threaded stub  50  referred to above, which connects with the adjoining section (not shown) of the drill string. In this specification the “rear” or “upper” end of a part of the apparatus is that end which is furthest from the drill bit head.  
     [0035] The shank  22  of the bit has a series of longitudinal splines  36  (see FIGS. 2 and 4) thereon and is received in a correspondingly internally splined passage or socket ( 46   b —see FIG. 2) in a chuck  40  at the end of the drill string, whereby the drill bit is constrained against rotation relative to the chuck and drill string. As shown in the cross-sectional view which forms FIG. 2, the spleens  36  are not completely regularly distributed around the axis of the bit, and since the grooves between the splines  46   b  of the chuck are arranged in the same way as the splines  36  on the shank  22 , the shank  22  can be slid into the chuck in only one angular orientation. Thus, in the preferred arrangement illustrated in FIG. 2, the splines  36  are spaced apart at 35° intervals around the axis of the shank apart from the spline indicated at  36   b  which is spaced 40° from the adjoining splines  36  on either side. It will be understood that in variants, the angular spacing between splines may have any desired value and the splines may be in any desired number. Indeed, the drill bit and chuck need not be splined, specifically, but could, for example, be of polygonal cross-section. However, the complementary cross-sectional forms of the drill bit shank and the chuck should be such that the drill bit can be inserted in the chuck in only one angular orientation about the axis of the drill string. As shown in FIG. 4, an unsplined shank portion  37  is provided between the head portion  24  (shown only schematically in FIG. 4) and the beginning of the splines  36 . As shown, the portion of the drill shank aft of the splines  36  is of stepped construction, comprising a plain cylindrical bearing part  38  of the diameter as small as or smaller than the diametral dimension measured across the grooves between splines  36 , (although for manufacturing reasons or to assist in clearing debris, the surface of bearing part  38  may be interrupted by grooves as shown in FIG. 4), and comprising a second plain cylindrical part  39  aft of the part  38  and of still smaller diameter and which extends rearwardly to an axially short splined rear end part  41  of somewhat greater diameter than part  39  but still of smaller diameter than, or of the same diameter as, plain cylindrical bearing part  38  of the drill shank. As will appear below, the portion  38  and the further forward plain portion  37  of the drill bit shank constitute bearing surfaces.  
     [0036] Mounted within the sleeve  46  in substantially sealing relationship therewith, is a tubular, generally cylindrical liner  54  which forms the working cylinder for an annular-section piston  56  which acts as a hammer and, in operation of the apparatus in its percussion mode, repeatedly strikes the rear end of the drill bit shank to drive the drill bit into the material being drilled. The piston or hammer  56 , in operation of the apparatus, is reciprocated by compressed air supplied alternately to opposite ends of the piston by a valving system which includes an arrangement of ports extending through the wall of the liner  54  and communicating with grooves on the exterior of the latter, in manner known per se, which grooves in turn define, with the adjoining surface of the cylinder  46 , ducts for the compressed air which is supplied to said valving system from an annular chamber  57  just forward of adapter  43 . The compressed air passes, via ports in a flange  63  of an upper fluids tube  74 , via ports in a stem body  64 , and via adjoining ports  58  in the liner  54 , (FIG. 8) through a said longitudinal duct defined between the liner  54  and the sleeve  46 , and through ports  59  in the liner  54  into an annular chamber  56 A defined between the liner  54  and a central waisted portion of the piston  56 . The piston  56  and the ported liner  54  together act as a kind of spool valve such that with the piston in its forwardmost position, (i.e. nearest the drill bit), the chamber  56 A communicates with a port in the liner  54  which leads via a respective duct, to the forward end of the working cylinder, whilst with the piston  56  in its rearwardmost position, the chamber  56 A communicates with a port in the liner  54  which leads, via a respective duct to the rearward end of the working cylinder. The stem body  64  has a forwardly projecting externally cylindrical and smooth spigot  65  which engages sealingly in the axial bore through piston  56  in the rearwardmost position of the latter to seal off the rear end of the working cylinder from the axial passage  66  through the piston, but which spigot is withdrawn from said axial passage  66  in the forwardmost position of the piston to allow air from the chamber at the rear end of the working cylinder to exhaust through axial passage  66  and through the central passage  34  in the drill bit and thence via ports  35  to the borehole being drilled. A bush  60  which is sealingly received within an enlarged end portion of the bore  34  extends axially rearwardly from the drill bit stem and engages sealingly in the axial passage  66  through piston  56  in the forwardmost position of the piston, to seal off the front end of the working cylinder from the axial passage  66  and from the bore  34  through the bit. In the rearwardmost position of the piston, the piston is clear of the bush  60 , to allow air from the front end of the working cylinder to exhaust through the bush  60  and the bore  34 .  
     [0037] In the arrangement illustrated in FIG. 1 provision is made for the supply of drilling fluid for the drill bit, such provision including a drilling fluid supply tube  32  which extends axially from the spigot  65 , (which in this case is hollow to receive the tube  32 ), and which tube  32  extends with clearance through the bush  60  and the main part of passage  34  and at its forward end is a close sliding fit with a reduced diameter forward end portion of passage  34  connecting via a drilling fluid duct or ducts with a drilling fluid discharge port or ports  35 A on the drill bit. Where no provision is to be made for the supply of drilling fluid to the drill bit, the tube  32  may be dispensed with the spigot  65  made solid.  
     [0038] The bearing portions  37  and  38  of the drill shank are spaced apart significantly in the axial direction to resist as effectively as possible lateral tilting movement of the drill bit in the chuck.  
     [0039] The stem body  64  is fixed against rotation in casing  46  (for a purpose described below) by a projection or key  64 A at a predetermined location around its periphery which key  64 A engages in a corresponding keyway or longitudinal groove  46 A formed along the internal surface of the casing  46  adjacent the rear end of the latter (FIG. 7). The liner  54  is also fixed against rotation relative to the body  64  by a peg  55  projecting therefrom at a predetermined location around its periphery and which engages in one of several corresponding keyways or longitudinal grooves  51  formed along the internal surface of liner  54  adjacent the rear end of the latter. (FIG. 8). The body  64  thus prevents the liner  54  from rotating relative to casing  46 . It is possible, by means of a special tool (not shown), to rotate the liner  54  about its axis within casing  46  through al limited angular range, when the adapter  43 , fluids tube  74  and stem body  64  are removed, for a purpose to be explained below. Sealing means, such as an O-ring  55  etc., around the stem body  64 , seals the latter with respect to the rear end of the liner  54 .  
     [0040] As shown in FIG. 8, the end of the cylinder liner  54  adjacent the drill bit is provided with a radially inwardly directed flange which is interrupted at intervals by axially extending grooves to define five equally spaced splines  67 . The splined rear end portion  41  of the drill bit shank (see FIGS. 1B and 4) is formed with five equally spaced, complementary outwardly projecting splines which correspond in cross-sectional size and shape with the grooves between the internal splines  67  at the end of the cylinder liner  54 . That is to say, in the splined region  41  and in the region of the splines  67 , the drill bit shank and the passage through the end of the cylinder liner  54 , respectively, are of complementary cross-sectional form so that, with the splines at the end of the drill bit shank aligned with the spaces between the splines  67  at the end of the cylinder liner  54 , the end of the drill bit shank can be extended axially into the end of the cylinder liner, with the splines on the portion  41  of the drill bit shank passing between respective adjoining splines  67  in the interior of the cylinder liner  54 , the radially inner surfaces of the spleens  67  of the cylinder liner  54  cooperating closely with the cylindrical surface  39  of the drill shank end. A rotation of the cylinder liner  54 , within member  46 , through an angle, about its axis, corresponding to half the pitch between splines  67  will thereafter place the splines  67  in angular registry with the splines in region  41  of the drill bit shank, thereby thereafter preventing withdrawal of the drill bit shank and without a corresponding rotational movement in the reverse direction of the cylinder liner, (since the splines  36  further down the drill bit shank cooperate with the correspondingly splined region  46 B (cf. FIG. 8) closely adjacent the forward end of the chuck  40 , thereby preventing rotation of the drill bit relative to the chuck  40 ). Fitting of the drill bit in the manner described, and the indicated rotation of liner  54  within member  46  are carried out with member  46  unscrewed from adapter  43  and with fluids tube  74  and stem body  64  removed. The rotation of liner  54  referred to is effected by a tool which is extended through the rear end casing  46 , and into the rear end of liner  54 , the tool having lateral projections or ribs to engage in the grooves  51  in the liner. One of the grooves  51  will, of course, align with the internal groove  46 A when the liner is in its position in which the splines  67  are in register with the splines on bit portion  41 , and thus fully out of register with the grooves between splines of portion  41  and thus, because pin  55  is in alignment with key  64 A on stem body  64 , insertion of stem body  64  after such positioning of the liner locks the liner in position against rotation within casing  46 .  
     [0041] It will, of course, be appreciated that the number of splines provided on any of the complementarily splined components described herein is of no particular significance and that numbers other than those specifically recited herein by way of example may be used. For example, if the bit shank has  12  splines, the number of locking grooves could be 6, 4, 3, or 2.  
     [0042] Because, as explained above, the drill bit shank can be inserted in the chuck  40  in only one orientation, the drill operator can keep a track of the orientation of the drill bit by keeping track of the orientation of a sonde mounted in sonde section  48  because, as explained below, the orientation of the sonde, about the drill string axis, relative to the casing  46 , and thus chuck  40 , is assured. The sonde is a device, known per se, which incorporates sensors, including sensors for sensing the orientation of the sonde, e.g. relative to the vertical and/or relative to the earth&#39;s magnetic field, and which also incorporates means for transmitting to the surface signals indicating the quantities sensed by the sensors, including signals indicating the orientation of the sensor. Thus, the sonde, (also referred to herein as a “data transmitter”, transmits to the surface, by radio or some other means, (e.g. by ultrasonics) information as to the position, depth and orientation with respect to the vertical.  
     [0043] In the embodiment illustrated in FIG. 1 and featuring the drilling fluid supply tube  32 , the tube  32  is sealingly engaged at its rear end in the hollow spigot  65  and in stem body  64 . The bore through spigot  65  is part of an axial bore extending entirely through stem body  64  which communicates directly with an axial bore through upper fluids tube  74 . The tube  74  has, formed integrally therewith, the aforementioned flange  63  which has, as shown in FIGS. 1A and 3, like stem body  64 , longitudinal passages displaced laterally from the axis of the drill string, for thee supply of compressed air from chamber  57  to the liner  54 .  
     [0044] Referring to FIGS. 1A and 3, the flange  63 , which also fits closely within the rear end of sleeve  46 , has key  63 A projecting radially from its circumference, which also is received in keyway  46 A (FIG. 7) and thus locates the fluids tube  74  in a predetermined angular position in sleeve  46  about its longitudinal axis.  
     [0045] Referring to FIG. 1, compressed air is supplied, through the drill string, to the chamber  56 , via an annular passage  61  defined between the axial bore in the sonde section  48  and the exterior of a valve member  47  which is mounted on the fluids tube  74  for limited axial sliding movement and is rearwardly spring biased to engage a valve seat provided within sonde section  48  around the axial passage therethrough. The valve member  47  with said valve seat, thus forms a check valve for the compressed air supply to the bit. This check valve could, of course, be placed elsewhere in the assembly.  
     [0046] The sonde section  48  also acts as a housing for sonde  100 , (see below). The sonde section  48 , with the components contained therein is herein referred to as the sonde section, or the data transmitter section, of the drill string. The sonde section  48  is so contrived as to allow passage of compressed air from an axial passage through connector to at the rear end of sonde section  48 , past the sonde, to the aforementioned check valve, (and also, where provision is made for the supply of drilling fluid, for the supply of drilling fluid from the rear end of sonde section  48  to the fluids tube  74  and thence to the tube  32 ). Thus, in the arrangement of FIGS. 1A and 1B in which a drilling fluid supply is also provided, the adapter  49  has central drilling-fluid supply tube extending from the stub  50  and is so contrived as to provide a fluid passageway, separate from that provided for compressed air, extending from the last-noted drilling fluid supply tube to the axial bore through member  74 . Similarly, each other section (not shown) of the drill string includes a central tube or passage for drilling mud, and a generally concentric passageway for compressed air defined generally between such central tube and the outer structure or casing of that section. Each said other section of the drill string further includes spider-like structures supporting the respective central tube from the exterior structure. It will be understood that the rearward end of each drill string section may thus be configured similarly to the rear end of the assembly shown in FIG. 1A and that the forward end of each such drill string section may have central drilling mud tube contrived for sealing engagement with the drilling fluid tube at the rear end of the sonde section  48  or the corresponding component of the rear end of the adjoining drill string section, whereby a drilling fluid passage and a separate compressed air passage extend through the hole length of the drill string.  
     [0047] Where no provision is made for drilling fluid, the members  65  and  74  may be made solid, rather than as tubes, and the configuration of the internals of sonde section  48  may be correspondingly simplified.  
     [0048] It should be appreciated that the sonde section of the apparatus between the tube  74  and the threaded spigot  50  and including the sonde, and sonde housing, are shown only schematically in FIGS. 1 and 2, and, in particular, are shown as being much shorter than is actually the case.  
     [0049] Referring to FIGS. 10 and 11, instead of utilising a drill bit which has a head which is in some way asymmetrically disposed in relation to the longitudinal axis of the drill shank, for example being of “duck bill” form, as shown in FIG. 1B, or being eccentric with respect to the drill shank axis, the drilling apparatus may be made steerable by incorporating a slightly bent section  69  in the drilling string adjacent to, but spaced from the drill bit. By way of example, this bent section may be placed either at the rear of the hammer section/drill section assembly, as shown in FIG. 10, or between the hammer section  46  and the transmitter or sonde section  48 , as shown in FIG. 11.  
     [0050] In FIGS. 10 and 11, the drill bit head is referenced  20 A and the rearward (upper) part of the drill string is referenced  25 . During drilling, the whole assembly may, for example, be rocked through, for example,  60  degrees to either side of the direction in which it is desired to steer.  
     [0051] In the arrangement of FIG. 10 or FIG. 11, since the bent section  69  is responsible for the steering, the drill bit need not be configured asymmetrically and need only be designed for the task of creating the hole. Attention in drill bit design can thus be concentrated on the minimisation of the drill bit snag. FIGS. 12 and 13 show a drill bit according to another aspect of the invention in which this has been achieved, creating a drill bit that presents cutting tips (eg. insets) to all the rock at the end of the bore, despite the limited rotation applied to the drill. On ordinary rock drilling bits, in order to present cutting tips to all the rock at the end of the bore, the drill bit must be rotated 360 degrees. The drill bit shown in FIGS. 12 and 13, however, has the following features:  
     [0052] (a) The drill bit  20 A is designed such that, within the given arc or rocking motion, cutting tips (provided, for example, by hard inserts  23 ) are present to all the rock to be removed. Thus, for example, if the drill bit is to be rocked through 90 degrees to each side of the direction of steer, the drill bit is designed in two segments about a centre (diametral) axis; each segment being provided with enough cutting tips  23  to remove all the rock in its arc of rocking. For rocking 60 degrees to each side of the steering direction the bit is designed in three segments, as illustrated in FIG. 12, and so on.  
     [0053] (b) As shown in FIG. 12, the bit is formed with its cutting tips  23 , (provided, in the usual way, by hard carbide inserts) arranged in a series of concentric rings or tiers, with the inserts  23  of each row overlapping, i.e. being angularly displaced, about the central longitudinal axis of the drill bit, with respect to the insets of the adjacent tiers or rows. This allows a more progressive entry of the bit into the rock and reduces the propensity of the bit to snag in the impression left by the bit in the rock.  
     [0054] (c) The drill bit is designed with one or more waisted regions  112  (FIG. 13) disposed rearwardly of the front face of the bit, and cutting tips or inserts  23  are provided also around the forwardly facing shoulders on the bit surface at the back of each such waisted portion, these cutting tips or inserts likewise being arranged to overlap, in angular position about the drill bit axis, the inserts of the adjacent tier of inserts to the front and/or to the rear. Furthermore, the bit has air exhaust ports  25  (corresponding in function with the ports  35  in FIG. 1B) which are located at the bottoms, (i.e. the radially innermost regions) of the respective waistings  112  of the bit, so that these ports are shielded from occlusion by the wall of the bore being drilled, by the wider portion of the drill bit in front, and are thus not easily blocked. Correspondingly located discharge ports for liquid drilling fluid, eg. drilliung mud may be similarly located.  
     [0055] It will be understood that whilst the inserts  23  closest to the centre on the end face of the bit  20 A in principle should pass through the whole extent of the respective sector (which is the minimum angle through which the bit is designed to be rocked, in use), the inserts  23  further from the centre are more closely spaced angularly and thus each of these will, in use, sweep through a corresponding sector which will, however, also overlap substantially the corresponding sectors of adjacent inserts  23  in the same ring or tier.  
     [0056] Since, in the arrangement of FIGS.  10  to  13 , the orientation of the drill bit is not a factor in determining the direction in which the drill steers, it is not necessary to ensure any particular angular orientation of the drill bit in the drill chuck, and thus there is no need for the irregular distribution of cooperating splines discussed above in relation to asymmetrical steerable drill bits.  
     [0057] Likewise, it will be understood that the mechanism described above for drill retention in the chuck, utilizing partial rotation of liner  54  in sleeve  64 , may also be employed in the arrangements of FIGS.  10  to  13 , whether irregularly distributed drill shank splines are used or not, and may also be employed in non-steerable, non-directional drilling apparatus, and so in apparatus without the irregularly distributed bit shank splines. This allows the percussive tool, i.e. the pneumatic hammer, to continue running, even when it has been thrust with too much force into softened materials, or predrilled rock.  
     [0058]FIGS. 14A and 14B are adjacent parts of a partial view, in axial section, and to an enlarged scale as compared with FIGS. 1A and 1B, showing the sonde section  48  in more detail, in a practical embodiment, corresponding to the arrangement described with reference to FIGS. 1 and 9. FIGS. 14A and 14B each show the respective part of the drill string extending from the circumference on one side to the central axis and part of the remainder from the central axis toward the other side. Thus FIGS. 14A and 14B are each slightly more than “half-axial” section views.  
     [0059]FIG. 14A shows a portion of sonde section  48  and associated parts closer to the drill bit and FIG. 14B shows a portion of sonde section  48  and associated parts further from the drill bit. For convenience FIGS. 14A and 14B are together referred to below as “FIG. 14”.  
     [0060] Referring to FIG. 14, the complexity of the structure shown is largely due to the fact that a multi-component construction is appropriate from the point of view of ease of construction. In essence, however, in the arrangement shown in FIG. 14, the components  101  and  104  are, in use, substantially permanently fixed with respect to each other and may be regarded as forming the outer wall of the sonde section  48  of FIG. 1 which is releasably screwed into the adaptor  43  of FIG. 1A. Likewise, components  110 ,  12 , to be referred to are, in use, normally permanently fixed with respect to the components  101  and  104 .  
     [0061] The upper part  101 ,  104 , is connected with the part of the drill string above it by a conventional coarse pitch screw such as is used conventionally to connect adjoining cylindrical or tubular sections of a conventional drill string together for rapid connection and disconnection, and the sonde section  101 ,  104 , is likewise connected to the adapter  43  by a similar coarse pitch thread. (The representation of the components  48 ,  43  in FIGS. 1A and 1B thus does not show accurately, or indeed to scale, the arrangement shown in more detail in FIGS. 14A and 14B. The upper part  101 ,  104  and the components within it may conveniently form a sonde or data-transmitter section  48  of the drill string quickly detachable, by means of the coarse-pitch threaded connections referred to, from the hammer/bit section  46  below and from the drill string parts immediately above.  
     [0062] This data-transmitter or sonde section  48  of the drill string defines:  
     [0063] (a) a central space within which is accommodated a sonde assembly described below,  
     [0064] (b) a passage for compressed air from the upper end of the data-transmitter or sonde section to the lower end, which passage extends alongside the region of the adapter accommodating the sonde and  
     [0065] (c) (where there is provision for the supply of drilling fluid (drilling mud)) a similar passage for drilling fluid from the upper end of the data-transmitter or sonde section to the lower end which drilling fluid passage likewise is laterally displaced from the region of the adapter accommodating the sonde and is separate from the passage for the compressed air.  
     [0066] In addition, the arrangement to be described serves to maintain the sonde or data-transmitter in a predetermined rotational orientation, about the longitudinal axis of the assembly, with respect to the fluids tube member  74 . It will be recollected that the member  74 , like the stem body  64 , has a collar or flange  63  which fits closely within the upper end of the sleeve  46  and is fixed in a predetermined angular position therein.  
     [0067] As shown in FIG. 14B, the component  101  provides the outer housing part and coarse-threaded connector  50  at the upper end of the sonde section (data-transmitter section) of the drill string. A drilling fluid tube  110 , fixed within component  101 , is adapted to connect with the central drilling fluid tube of he next rearward part of he drill string and provides a central fluid passage, closed at its lower end and communicating with a laterally displaced longitudinal duct  103  through an intermediate part  104  of the sonde or data-transmitting section, at the lower end of which the passage  103  connects via a lateral port  106 , with an annular groove around an insert  112  fixed within part  104 , and, via radial holes through the wall of insert  112  in the base of this groove, with a corresponding annular groove around an azimuth shaft  114 . The last-noted groove communicates, via a port in shaft  114 , with an axial bore in shaft  114  for the supply of drilling fluid to the fluids tube  74 . The forward end of this axial bore in shaft  114  is counterbored to receive as a snug sliding fit, the rear end of fluids tube  74  and has an internal annular groove accommodating a sealing ring for sealing engagement with the rearward end of tube  74 . A zenith pin  98 , fitted in the forward end of shaft  114 , projects radially into the outer counterbore for engagement in a longitudinally extending slot in a collar on tube  74 , which collar is received in that counterbore as a free sliding fit. The pin  98  and the slot receiving it are part of the system provided for ensuring angular orientation of the sonde (see below).  
     [0068] Compressed air is supplied to the sonde or transmitter section  48  of the drill string via an annular space  62  defined between component  101  and the exterior of tube  110  and through an offset longitudinal duct  105  in component  104  (different from the duct carrying drilling fluid) and through a radial bore, (indicated at  107 ) into an annular space  96  defined within a bore  132  in a forward (i.e. lower) portion of intermediate part  104 , between the wall of bore  132  and the azimuth shaft  114  passing through part  104 , and thence passes to the next section of the drill string.  
     [0069] The azimuth shaft  114  has a collar  130  which is a sliding fit within the bore  132  in the forward (lower) end portion of component  104  and the compressed air from annular space  96  passes through longitudinally extending apertures in collar  130 , to the check valve having valve member  47 . The azimuth shaft  114  further has an elongated generally cylindrical stem portion which extends as a close sliding fit within a complementary axial bore in component  112 . Azimuth shaft  114  is urged forwardly by a compression spring  115  acting between a further collar  111  on shaft  114  and a forward end face of component  112 , forward axial movement of the component  114  being limited by abutment of the collar  130  with a circlip engaged in an internal groove at the forward end of bore  132 . As noted above, the intermediate part  104  is screwed via a coarse-pitch thread, into the rear (upper) part  43 , of the next (lower) drill string section, i.e. of the hammer/drill bit section. The part  43 , inter alia, provides the valve seat with which valve  47  (see also FIG. 1) cooperates.  
     [0070] Received within a cylindrical central bore  150  in intermediate part  104  is a cylindrical tubular sonde housing casing  109 , for example of plastics, which in turn receives, as a rotating and sliding fit, a cylindrical tubular sonde carriage  116  containing the sonde  100 . The various components of the sonde are housed in a cylindrical casing or body which fits closely within sonde carriage  116 . These components include, for example, the sensors, electronic circuitry, power supply battery, etc. making up the sonde. Such sondes are known per se and the sonde is therefore not described in detail herein. The tubular sonde carriage is closed at either end by respective plugs  154 ,  156  between which the sonde  100  is located. The plugs  154 ,  156  each comprise a respective tubular extension  157 ,  158 , of reduced diameter with respect to the sonde carriage  152 , extending axially therefrom, each such extension having an axial blind bore extending from its free end remote from the sonde and which receives as a free axial sliding fit, a respective cylindrical shaft  160 ,  161 . In the case of the plug  154  at the end of the sonde carriage further from the drilling head, this cylindrical shaft, referenced  160 , is provided by or fixed to the component  110  and the plug  154  is rotatable therein about the drill string axis whilst in the case of the plug  156  nearer to the drill bit, the shaft  161  received slidably therein is a rearward extension of the azimuth shaft  114 . Because the assembly comprising the sonde carriage  116 , sonde  100  and plugs  154 ,  156 , is, in principle, axially slidable on the shafts  160 ,  161 , the plugs  154 ,  156 , are also referred to herein as slides, and the plug  156 , for a reason which will become evident, specifically as the zenith slide. This sonde assembly is biased towards a central position, midway along the sonde housing  109  by compression springs  164 ,  166 , at either rend, the compression spring  164  acting between the sonde assembly and an annular shoulder provided at the rearward end of component  112 , around the bore through which the component  114  extends, and the spring  168  acting between the rearward end of he sonde assembly and an annular shoulder provided at the junction of the shaft  160  with the adjoining portion of component  110 . The housing  109  is located axially within the bore  150  by, at the forward end of said bore, a rearward portion of component  112  fitted sealingly within the housing  109  and, at the rearward end of bore  150 , by a forward end portion of component  110  likewise fitting closely within the housing  109 . The resilient mounting of the sonde assembly within the housing  109  serve to minimise the transmission of possibly harmful shocks to the sonde assembly. If desired, a measure of gas or fluid damping for longitudinal movement of the sonde assembly in the housing  109  may be provided by a gas (e.g. air) or liquid contained within the housing  109  around the sonde assembly between the components  110  and  112 . Alternatively, or additionally, damping may be provided by friction between the sonde carriage  116  and the casing  109 . Longitudinal grooves or passages may be provided on the exterior surface of the sonde carriage  116  or on the internal surface of the bore in housing  109  to allow controlled transfer of fluid from behind the sonde assembly to in front of it and vice versa in order to dissipate energy. Instead of the sonde carriage being in the form of a tubular body encompassing the sonde in its entirety, the function of the sonde carriage could be fulfilled by two end caps, each placed over a respective end of the sonde.  
     [0071] Because the sonde is sensitive to its orientation with respect to the vertical, as well as to its depth (since it senses and relays these parameters to a receiver at the surface), it is important that reliable means be provided for fixing the orientation of the sonde, about the longitudinal axis of the drill string, relatively to the corresponding angular position of the drill bit. It will be recollected that the fluid tube  74  has an annular collar  63  from which projects radially, in the same way as the key  64 A projects from the annular collar on the stem body  64 , a key  63 A which fixes the angular orientation of the fluid tube  74  with respect to the drill bit. As noted above, the zenith pin  98  at the forward end of shaft  114  is received in a longitudinally extending slot or keyway in the end portion of tube  74 , whereby the angular orientation of the component  114  with respect to the drilling bit is maintained. Likewise, the rear end  161  of shaft  114 , slidably received within the axial bore in zenith slide  156 , is provided with a longitudinal slot or keyway receiving a zenith pin  170  fixed in the tubular part of the zenith slide  156  and projecting rearwardly inwardly into said keyway.  
     [0072] Accordingly, the angular orientation of the zenith slide about the longitudinal axis of the drill string is fixed with respect to the drill bit. Finally, the sonde body itself is provided, at its end adjoining slide  156 , with a radially extending slot or recess which receives an off-set longitudinally extending zenith pin  172 , to ensure the angular orientation of the sonde itself with respect to the plug or zenith slide  156  forming the respective end of the sonde carriage. It will be understood, of course, that orientation of the shaft  114  with respect to tube  74 , or of the shaft  114  relative to zenith slide  156 , need not be achieved specifically by pins and slots but could be by means of any complementary formations which allow interengagement in only a single orientation about the axis of the drill string. In addition to being slidable longitudinally along the sonde housing  109 , the sonde carriage  116  is also rotatable, in the sonde housing  109 , about the longitudinal axis of the drill string.  
     [0073] The provision made for longitudinal sliding movement of the azimuth shaft  114  relative to component  104  (and thus relative to sonde section  48  as a whole) is provided to allow the shaft  114  to be displaced resiliently rearwardly by the rear end of the tube  74  as the sonde/transmitter section of the drill string is screwed into the rear (upper) end  43  of the hammer section of the drill string, until the zenith pin  98  comes into angular alignment with the keyway or slot in the rear end of tube  74 , at which point, of course, the spring  115  urges the shaft  114  forwardly and thus urges the zenith pin along the slot in tube  74 . Because the shaft  114  is rotatable about its longitudinal axis with respect to the part  104 , and hence with respect to the whole casing  104 ,  101  of the sonde/transmitter drill string section (albeit that such rotation is resisted by significant frictionally forces), during screwing together of the part  104  and the part  43 , after the zenith pin  98  has engaged in the longitudinal slot in the end of tube  74 , the shaft  114 , and with it the zenith slide  156  and the sonde carriage  116 , with the sonde itself, are fixed rotationally with respect to tube  74  and rotate within housing part  104  as the hammer section of the drill string is screwed onto the sonde/transmitter section (or alternatively remain stationary with the hammer section as the sonde/transmitter section is screwed onto the hammer section). By this means, it is ensured reliably and automatically that the sonde  100  has a predetermined orientation, about the drill string axis, with respect to the drill bit, (since the tube  74  has a predetermined angular orientation, about the longitudinal axis of the drill string, with respect to the housing  46  and the bit has a predetermined angular orientation with respect to housing  46 ).  
     [0074] It will be understood that, where no provision is to be made for the supply of drilling fluid, the arrangement may be simplified, with the shaft  114  being made solid, the annular space  106 , bore  103  and the rearward tubular extension of component  110  omitted. In this case, also, the fluids tube  74  will be replaced by a solid reference member. (The tube  74  forms a reference member with respect to shaft  114  which forms an azimuth member).  
     [0075] The sonde arrangement described above may be used also in directional drilling devices not incorporating a hammer, such as may be used, for example, in directional drilling in materials which can readily be displaced or eroded by jets of high pressure liquid. Thus, for example, FIG. 17 illustrates schematically a hammerless directional drilling bit or device of the last-noted character which is adapted to be screwed directly onto the sonde section  48  in place of the housing  46 , hammer assembly, and drilling bit  20  of FIGS.  1  to  14 B. Thus the device of FIG. 17 comprises a generally cylindrical body  200  having an oblique flat  202  extending along one side to the front end of the device and a fluid jetting port  204  (illustrated schematically in broken lines) opening onto the front end face at a location spaced from the oblique flat. At its rear end, the device of FIG. 17 has a configuration corresponding substantially to the rear end of the housing  46  and adapter  43  and carriers, internally, components corresponding to components  47  and  74  in the embodiment of FIGS.  1  to  14 B, for similar engagement with the complementary components at the front end of the sonde section  48 , the fluid tube  74  or its counterpart in FIG. 17, thus having a collar with a longitudinally extending azimuth slot to receive the zenith pin  98  in the forward end of shaft  114  in the sonde section  48 . Since the device of FIG. 17 is hammerless, compressed air is not required to operate a hammer and thus the device of FIG. 17 need not have internal passages communicating with the compressed air passages in the sonde section  48 . Alternatively, where supply of compressed air to the front end of the drilling device of FIG. 17 may assist in excavation of the material to be drilled, such compressed air passages may be provided and may open onto corresponding ports at the front end of the drilling device.  
     [0076]FIGS. 15 and 16 are sectional views illustrating the application of automatic alignment arrangements in accordance with the invention to the variants illustrated in FIGS.  10  to  13  utilising a so-called “bent sub” instead of an asymmetrical drill bit. In such variants, of course, it is the orientation of the bend or angle in the bent sub with respect to which the sonde  100  is required to adopt reliably a predetermine orientation. Thus, referring to FIG. 16, in which components corresponding in function to components in FIGS. 14A and 14B have like references, an alignment finger  74  fixed in the hammer section which incorporates (below the region holding the finger  74 —i.e. nearer the drill bit than the region holding finger  74 ) the sub bend  69 , cooperates with azimuth shaft  114  which, as in FIG. 14A, has a grooved stem  161  slidable in, but non-rotatable in a zenith slide  156  of the sonde carriage  116 , which again is rotatable in the sonde housing  109 . The azimuth shaft  114  is again rotatable, against significant frictional resistance, in the sonde or data transmitter housing  48 . An alternative arrangement is shown in FIG. 15, in which the bent section  69  is located above, (rearwardly of), the sonde section  48  and the hammer section. In this case an alignment or reference member  74 , again carried by and non-rotatable with respect to the bent section  69  provides a tube or socket which extends downwardly (forwards), to receive a solid plug or spigot portion  115  of an azimuth shaft  114  extending upwardly into that socket. The portion  115  has a longitudinal groove receiving a pin projecting radially inwardly into the socket of the alignment or reference member  74  so that, again, when the azimuth member  114  is fully engaged with the reference member  74 , the azimuth member is slidable longitudinally with respect to the reference member  74  but is non-rotatable with respect thereto. The sonde carriage, disposed below the azimuth shaft  114  again ahs zenith slide  156  located, in this case, at its upper end and again cooperating non-rotatably with the shaft  161 , (downwardly-projecting, in this case), of the azimuth shaft, the azimuth shaft  114  and sonde carriage  116  again being rotatable in the casing  109  and hence in the outer housing of the sonde section  48  of the drill string. In this arrangement, simply by way of illustration, the azimuth shaft is not significantly movable axially in the sonde section of the drill string, but is fixed in the end of the sonde housing  109  and the alignment or reference member  74 , whilst being non-rotatably supported in the bent section  69 , is displaceable therealong, against the force of a biasing spring  117  along the longitudinal axis of the sonde section, (i.e. along the axis of the lower part of the bent section  69  which screws onto the sonde section  48  below). It will be understood that in FIGS. 14 and 16 likewise, the element  74  could be displaceable axially against spring pressure but non-rotatable, with the azimuth shaft  114  being rotable without being axially displaceable. Likewise, in these embodiments, the member  74  might provide a socket to receive the end of the azimuth shaft instead of the latter providing a socket to receive the reference member  74 .  
     [0077] In each of the arrangements of FIGS. 15 and 16, compressed air to operate the hammer is led through the section  48 , past the sonde housing, through longitudinal passages  105  offset from the central axis of the section  48 , just as in the arrangement of FIG. 14 and the reference member  74  in FIGS. 15 and 16 has ports to allow air to pass into (in the case of FIG. 16), the section downstream of (below) section  48  or, (in the case of FIG. 15), from the section upstream of (above) the section  48 . As in FIG. 14, corresponding provision may be made for the supply of drilling mud or other drilling fluid to the bit, in a manner similar to that described in relation to FIG. 14.