Replaceable drill bit head

Abstract

A down-hole hammer drill tool, the drill tool comprising a percussive piston, a drive sub, a drill bit shank comprising a rearward external annular shoulder and a drill bit head, wherein the drill bit shank and the drill bit head are threadably connected.

Description

Replaceable Drill Bit HeadTECHNICAL FIELD

[0001] The present invention relates to a down-hole hammer drill tool. More specifically, the drill tool of the present invention comprises a releasable drill bit head.BACKGROUND ART

[0002] The following discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.

[0003] In the field of rock drilling, two prominent techniques are practised, top hammer drilling and down-the-hole drilling. In top hammer drilling, a surface based hammer produces a percussive force on the drill rods. The force is transmitted through the rods to the drill bit. In down-the-hole drilling, the percussive force is applied in the hole adjacent the drill bit.

[0004] A down-hole hammer drill tool typically comprises a backhead assembly and a drill head assembly. The drill head assembly is provided at the working end of the drill tool and retains the drill bit. The drill bit typically comprises a drill bit head defining a cutting face and a shank extending from the drill bit head away from the cutting face. The backhead assembly comprises an air-operated percussive hammer which provides percussive blows to the drill bit. The drill bit head assembly further comprises a drive sub, where the drill bit is retained in the drive sub. Typically, splines are provided on the shank of the drill bit which cooperate with counterpart splines on the drive sub. In this manner, rotational torque applied to the drive sub is transmitted to the drill bit through the mating splines while allowing reciprocatory movement of the drill bit in response to percussive blows delivered by the percussive hammer. A retaining sleeve may be provided to retain their coupling. The rearward end of the drive sub is then rotatably connected to an outer casing.

[0005] Drill bits are known to break or become worn over time. Replacing drill bits is time consuming and costly. It is not possible to simply remove the worn or damaged drill bit head. To replace the drill bit, it is necessary to unthread the drive sub from the outer casing thereby releasing the drive sub, the retaining sleeve and the drill bit with the elongate shaft. All of these components are then discarded despite only the head of the drill bit being worn. Such waste constitutes a significant expense. Additionally, each time the drive sub and drill bit assembly is removed and reassembled it increases the likelihood of injury to the fitter that changes the drill bit out. Attempts to separate the drill bit head and the shank have to date been unsuccessful. Various methods have been attempted including the use of Oil Field threads both fine and course pitch without success.

[0006] Mobile drilling units comprise a pivotable mast mounted onto a platform. A drill string is mounted onto the mast for drilling into the earth. The drill sting comprises a drilling tool and a plurality of drill rods. The drill rod(s) connect the drilling tool to a source of rotation. During drilling, additional drill rods may be added as required.

[0007] Replacement of a drill bit requires cessation of the drilling operation and retrieval of the drilling tool to the surface. The drilling tool is threadably connected to the drill rod and is manually removed and replaced. In the drill and blast sector of exploration and mining it is not permissible in some jurisdictions for a drill rig operator to change a drill bit on a drill rig but has to engage the services of a specialist to change the bit and hammer. As this is a time consuming and tedious process, many operators have adopted the practice of drilling to the destruction of the drill bit. As can be appreciated, this has the cascading effect of decreasing efficiency in drill penetration rate, increase in fuel consumption with drill bit wear resulting in extra wear on the drill rig itself and its drivetrain.

[0008] It is against this background that the present invention has been developed.

[0009] The present invention seeks to overcome, or at least ameliorate, one or more of the deficiencies of the prior art mentioned above, or to provide the consumer with a useful or commercial choice.

[0010] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. Theinvention includes all such variation and modifications. The invention also includes all of the steps, features, formulations and compounds referred to or indicated in the specification, individually or collectively and any and all combinations or any two or more of the steps or features.

[0011] Each document, reference, patent application or patent cited in this text is expressly incorporated herein in their entirety by reference, which means that it should be read and considered by the reader as part of this text. That the document, reference, patent application or patent cited in this text is not repeated in this text is merely for reasons of conciseness.

[0012] Any manufacturer’s instructions, descriptions, product specifications, and product sheets for any products mentioned herein or in any document incorporated by reference herein, are hereby incorporated herein by reference, and may be employed in the practice of the invention.

[0013] The present invention is not to be limited in scope by any of the specific embodiments described herein. These embodiments are intended for the purpose of exemplification only. Functionally equivalent products, formulations and methods are clearly within the scope of the invention as described herein.

[0014] The invention described herein may include one or more range of values (e.g. size, displacement and field strength etc). A range of values will be understood to include all values within the range, including the values defining the range, and values adjacent to the range which lead to the same or substantially the same outcome as the values immediately adjacent to that value which defines the boundary to the range.

[0015] Other definitions for selected terms used herein may be found within the detailed description of the invention and apply throughout. Unless otherwise defined, all other scientific and technical terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which the invention belongs.

[0016] Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

[0017] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications. The invention also includes all of the steps, features, compositions and compounds referenced to or indicated in the specification, individually or collectively and any and all combinations or any two or more of the steps or features.

[0018] The present invention is not to be limited in scope by the specific embodiments described herein, which are intended for the purpose of exemplification only. Functionally equivalent products, compositions and methods are clearly within the scope of the invention as described herein. The entire disclosures of all publications (including patents, patent applications, journal articles, laboratory manuals, books, or other documents) cited herein are hereby incorporated by reference.SUMMARY OF INVENTION

[0019] In accordance with present invention, there is provided a down-hole hammer drill tool, the drill tool comprising a percussive piston, a drive sub, a drill bit shank comprising a rearward external annular shoulder and a drill bit head, wherein the drill bit shank and the drill bit head are threadably connected.

[0020] In use, the piston applies percussive force to the rearward external annular shank shoulder and the shank transmits said percussive force to the drill bit head.

[0021] Preferably, the drill bit shank and the drill bit head are threadably connected such that an annular gap is provided about the periphery of the drill tool between the shank and the head.

[0022] Advantageously, the gap between the shank and the head prevents energy transmitted by the piston to be transmitted to the periphery of the drill bit head.

[0023] Advantageously, energy transmitted by the piston to the shank is directed to the centre of the drill head.

[0024] Advantageously, the annular gap controls the formation of a fulcrum point when drilling.

[0025] The presence of the annular gap enables for degrees of flex in the drilling to be compensated.

[0026] Preferably, the annular gap is no more than 10 mm wide.

[0027] In one form of the invention, the annular gap is about 1 mm wide. In an alternate form of the invention, the annular gap is about 2 mm wide. In an alternate form of the invention, the annular gap is about 3 mm wide. In an alternate form of the invention, the annular gap is about 4 mm wide. In an alternate form of the invention, the annular gap is about 5 mm wide. In an alternate form of the invention, the annular gap is about 6 mm wide. In an alternate form of the invention, the annular gap is about 7 mm wide. In an alternate form of the invention, the annular gap is about 8 mm wide. In an alternate form of the invention, the annular gap is about 9 mm wide.

[0028] In one form of the invention, the annular gap is less than 50 mm deep. In an alternate form of the invention, the annular gap is less than 40 mm deep. In an alternate form of the invention, the annular gap is less than 30 mm deep. In an alternate form of the invention, the annular gap is less than 20 mm deep. In an alternate form of the invention, the annular gap is less than 15 mm deep. In an alternate form of the invention, the annular gap is less than 10 mm deep. In an alternate form of the invention, the annular gap is less than 5 mm deep.

[0029] In one form of the invention, the annular gap is about 50 mm deep. In an alternate form of the invention, the annular gap is about 40 mm deep. In an alternate form of the invention, the annular gap is about 30 mm deep. In an alternate form of the invention, the annular gap is about 20 mm deep. In an alternate form of the invention, the annular gap is about 15 mm deep. In an alternate form of the invention, the annular gap is about 10 mm deep. In an alternate form of the invention, the annular gap is about 5 mm deep.

[0030] In one form of the invention, the annular gap comprises a percussive dampener.

[0031] It will be appreciated that a central bore extends though the drill tool as is known in the art. Said bore facilitates fluid communication between the piston, the shank and the head.

[0032] It will be appreciated that the annular gap circles the central bore.

[0033] In one form of the invention, the hammer drill is a conventional hammer drill. In an alternate form of the invention, the hammer drill is a reverse circulation hammer drill.

[0034] The drill tool may further comprise a hammer casing. The forward end of the hammer casing may be threadably connected to the rearward end of the drive sub.

[0035] The rearward end of the hammer casing may be provided with a radially outwardly facing thread to engage a drill rod as is known in the art.

[0036] The head is provided with a forward end adapted to engage the earth. The forward end is provided with a cutting face.

[0037] The drill bit head is provided with a rearward end adapted to engage the shank.

[0038] In one form of the invention, the rearward end of the head is provided with a recess to engage the shank. The recess preferably comprises a radially inwardly facing thread.

[0039] The base of the recess comprises an inner annular ring.

[0040] Preferably, the shank is provided with a forward end adapted to engage the head. Preferably, the forward end comprises a radially outwardly facing thread.

[0041] The forward end of the shank provides a forward annular face.

[0042] The radially outwardly facing thread of the shank is adapted to engage the radially inwardly facing thread of the head.

[0043] The threaded portions of the head and the shank are dimensioned such that threading of the head and the shank together creates an annular ring between the head and the shank. That is, when the shank is screwed into the head until the forward face of the shank abuts the inner annular ring of the head, there remains a gap between the peripheral surfaces of the shank and the head.In one form of the invention, the forward end of the shank is provided with a recess to engage the head. The recess preferably comprises a radially inwardly facing thread.

[0044] The base of the recess comprises an inner annular ring.

[0045] Preferably, the head is provided with a rearward end adapted to engage the shank. Preferably, the rearward end comprises a radially outwardly facing thread.

[0046] The rearward end of the head provides a rearward annular face.

[0047] The radially outwardly facing thread of the head is adapted to engage the radially inwardly facing thread of the shank.

[0048] The threaded portions of the head and the shank are dimensioned such that threading of the head and the shank together creates an annular ring between the head and the shank. That is, when the head is screwed into the shank until the rearward face of the head abuts the inner annular ring of the shank, there remains a gap between the peripheral surfaces of the shank and the head.

[0049] In one form of the invention, the rearward end of the head is provided with a recess and the forward end of the shank is provided with a recess and the drill tool is further provided with a coupler adapted to engage both the shank recess and the head recess.

[0050] The head recess comprises radially inwardly facing threads. The shank recess comprises radially inwardly facing threads.

[0051] The base of the head recess comprises an inner annular ring. The base of the shank recess comprises an inner annular ring.

[0052] The coupler is provided with a first radially outwardly facing thread adapted to engage the recess of the head. The coupler is provided with a second radially outwardly facing thread adapted to engage the recess of the shank.

[0053] In one form of the invention, the first and second radially outwardly facing threads are provided as two discrete threads. In an alternate form of the invention, the first and second radially outwardly facing threads are contiguous. In an alternate for of the invention, the first and second radially outwardly facing threads are continuous.

[0054] The coupler is provided with a forward annular face adapted to engage the inner annular ring of the recess.

[0055] The coupler is provided with a rearward annular face adapted to engage the inner annular ring of the shank.

[0056] The threaded portions of the coupler, the head and the shank are dimensioned such that threading of the coupler and the head and threading of the coupler and the shank creates an annular ring between the head and the shank. That is, when the coupler is screwed into the head until the forward face of the coupler engages the inner annular ring of the head and when the coupler is screwed into the shanks until the rearward face of the coupler engages the inner annular ring of the shank, there remains a gap between the peripheral surfaces of the shank and the head.

[0057] The head may be provided with an axially extending sleeve at its rearward end. The axially extending sleeve may have a narrower diameter than the diameter of the head at the cutting face. Said narrower diameter may form an annular shoulder on the head.

[0058] The rearward end of the head terminates in an annular ring.

[0059] In one form of the invention, the drill bit head is provided in two parts. Where two parts are provided, the first part comprises at least a portion of the sleeve and the second part comprises the remainder of the head. It will be appreciated that the second part may also comprise a portion of the sleeve. Where two parts are provided, they are preferably threadably connected.

[0060] Preferably, the thread of the threadable connection of the drill bit head and the drill bit shank is the opposite direction to the direction of rotation of the drill tool.

[0061] The rearward end of the shank comprises an annular shoulder, adapted to engage the percussive piston.

[0062] The shank terminates with a piston guide. It will be appreciated that the piston guide is rearward of the annular shoulder.

[0063] Preferably, the shank comprises a plurality of axially outwardly extending splines.

[0064] It will be appreciated that the drive sub is the rotary transmission component of the drill tool. The drive sub preferably partially encases the shank.

[0065] The drive sub preferably comprises a plurality of axially internally extending splines. The splines on the shank and the splines on the drive sub are adapted to engage each other as is known in the art to facilitate transfer of rotational drive from the drive sub to the head via the shank.

[0066] The rearward end of the drive sub comprises as radially outwardly facing thread. The radially outwardly facing thread is adapted to engage a corresponding radially inwardly facing thread at the leading end of the hammer casing.

[0067] The forward end of the drive sub is provided in the form of an annular face. In use the annular face of the drive sub abuts the annular shoulder of the drill bit head.

[0068] The percussive piston comprises a forward end comprising a strike face and a rearward end.

[0069] The strike face is adapted to engage the rearward annular shoulder of the shank for the transmission of percussive force.

[0070] The forward end of the percussive piston overlays the piston guide of the shank.

[0071] The percussive piston is mounted within the hammer casing for reciprocating movement as is known in the art.

[0072] In accordance with the present invention, there is provided a drill bit head replacement apparatus for replacing a drill bit head of a drill tool, the apparatus comprising a drill bit head carousel, the carousel comprising a plurality of receptacles, each receptacle adapted to receive a drill bit head and means to align a drill bit head with the central axis of a drill tool hammer, wherein the drill tool comprises a compressive piston, a drive sub, a drill bit shank comprising a rearward external annular shoulder and a drill bit head comprising an inner annular ring, wherein the drill bit shank and the drill bit head are threadably connected and wherein in use, the piston applies percussive force to the shank shoulder and the shank transmits said percussive force to the inner annular ring of the drill bit head.

[0073] It will be appreciated that the carousel is operable in a loading position and a storage position.

[0074] Preferably, the means to align a drill bit head are means to move the carousel, including by way of sliding and / or rotating.

[0075] Preferably, the carousel is operable remotely.

[0076] Preferably, there are provided means to crack the drill bit head from the shank, loosening the threaded tension between the head and the shank.

[0077] Each receptacle preferably comprises a retaining means to inhibit rotational movement of the drill bit head.

[0078] In one form of the invention, the carousel is mounted to a drill platform. In an alternate form of the invention, the carousel is mounted to a drill mast.BRIEF DESCRIPTION OF THE DRAWINGS

[0079] Further features of the present invention are more fully described in the following description of a non-limiting embodiment thereof. This description is included solely for the purposes of exemplifying the present invention. It should not be understood as a restriction on the broad summary, disclosure or description of the invention as set out above. The description will be made with reference to the accompanying drawings in which:Figure 1 is an exploded side view of a drilling tool in accordance with an embodiment of the present invention;Figure 2 is a side view of the drilling tool of Figure 1 ;Figure 3 is a cross-sectional view of a drilling tool in accordance with an embodiment of the present invention;Figure 4 is an exploded cross-sectional view of a head and shank in accordance with an embodiment of the invention;Figure 5 is an exploded cross-sectional view of a head and shank in accordance with an alternate embodiment of the invention;Figure 6 is an exploded cross-sectional view of a head and shank in accordance with an alternate embodiment of the invention;Figure 7 is an upper perspective view of a carousel for use with a drilling tool of the present invention.DESCRIPTION OF EMBODIMENTS

[0080] In Figure 1 there is shown a drill tool 10 in accordance with an embodiment of the present invention. The drill tool 10 comprises a substantially hollow cylindrical hammer casing 12 comprising an axially rearward end 14 and an axially forward end 16. A drive sub 18 is threadably connected to the forward end 16 of the casing 12. The drive sub 18 comprises an axially rearward end 20 and an axially forward end 22. The rearward end 20 of the drive sub 18 comprises a thread 24 adapted to engage an internal thread (not shown) on the forward end 16 of the casing 12. The drive sub 18 comprises a plurality axially internally extending splines (not shown).

[0081] The drill tool further comprises a drill bit shank 30 comprising an axially rearward end 32 and an axially forward end 34 partially encased by the drive sub 18. The forward end 34 comprises a radially outwardly facing thread 36. The radially outwardly facing thread 36 terminates in a leading face 38 in the form of an annular ring. The rearward end 32 comprises an annular shoulder 40. The shank 30 terminates with a foot valve 42. The shank 30 comprises a plurality of axially extending splines 44.

[0082] A drill bit head 50 comprising an axially rearward end 52 and an axially forward end 54 engages the shank 30. The rearward end 52 comprises a recess 55. The base of the recess comprises an annular ring 60.

[0083] The splines on the shank 30 slidably engage the splines on the drive sub 18. The drill bit head 50 can move axially, relative to the drive sub 18 during percussive movement.

[0084] The recess 55 further comprises a radially internally facing thread 62 adapted to engage the radially outwardly facing thread 36 on the shank 30. The forward end 54 of the head 50 comprises a plurality of tungsten carbide cutting teeth 64 as is known in the art. The rear end of the head terminates in an annular ring 66.

[0085] The leading face 38 of the shank 30 is adapted to abut the annular ring 60 base of the head recess 55. That is, when the head 50 and the shank 30 are threadably connected, the leading face 38 of the shank 30 and the base 56 of the recess 55 of the head 50 should abut.

[0086] The drill tool 10 further comprises a percussive piston 80 comprising an axially rearward end 82 and an axially forward end 84. The forward end 84 of the piston 80 is adapted to engage the annular shoulder 40 of the shank 30. The forward end of the piston 80 overlays the piston guide 42 of the shank 30. The piston 80 is mounted for reciprocating movement within the hammer casing 12 as is known in the art.

[0087] A bit ring 90 and a bit bearing 92 are provided at the rearward end of the shank. A retaining sleeve (not shown) may be provided to retain their coupling.

[0088] The present invention facilitates the simple separation of the head and the shank and does not require removal of the shank or drive sub from the drill tool.

[0089] In Figure 4 there is provided an exploded cross-sectional view of a shank 30 and head 50 in accordance with an embodiment of the invention. The embodiment in Figure 4 is substantially the same as that depicted in Figures 1 and 3.

[0090] The shank 30 comprises a radially outwardly facing thread 36 at its forward end 34. An annular shoulder 94 is provided at the end of the thread 36. The head 50 comprises a radially inwardly facing thread 62 in its recess 55. The shank 30 and the head 50 screw together until the leading face 38 abuts in annular ring 60, best seen in Figure 4c. In this configuration, an annular gap 96 is provided between the annular ring 66 and the annular shoulder 94.

[0091] In Figure 5 there is provided an exploded cross-sectional view of a shank 100 and head 110 in accordance with an embodiment of the invention.

[0092] The rearward end 112 of the head 110 comprises a radially outwardly facing thread 114. The radially outwardly facing thread 114 terminates in a leading face 116 in the form of an annular ring 116. An annular shoulder 118 is provided at the end of the thread 114.

[0093] The shank 100 comprises a recess 120. The base of the recess 120 comprises an annular ring 122. The recess 120 further comprises a radially internallyfacing thread 124 adapted to engage the radially outwardly facing thread 114 on the head 110. An annular ring 126 is provided at the forward end of the shank 100.

[0094] The shank 100 and the head 110 screw together until the leading face 116 abuts the annular ring 122, best seen in Figure 5c. In this configuration, an annular gap 130 is provided between the annular ring 126 and the annular shoulder 118.

[0095] In Figure 6 there is provided an exploded cross-sectional view of a shank 150, a head 160 and coupler 162 in accordance with an embodiment of the invention.

[0096] The rearward end 164 of the head 160 comprises a recess 166. The base of the recess 166 comprises an annular ring 168. The recess 166 further comprises a radially internally facing thread 170. An annular ring 172 is provided at the rearward end of the head 160.

[0097] The shank 150 comprises a recess 180. The base of the recess 180 comprises an annular ring 182. The recess 180 further comprises a radially internally facing thread 184. An annular ring 186 is provided at the forward end of the shank 100.

[0098] The coupler 162 is provided with a forward end 190 and a rearward end 192. The forward end 190 terminates in annular face 194 and the rearward end 192 terminates in annular face 198.

[0099] The shank 150 and the coupler 162 screw together until the leading face 196 abuts the annular ring 182, best seen in Figure 6c. Similarly, the head 160 and the coupler 162 screw together until the leading face 194 abuts the annular ring 168, best seen in Figure 6c. In this configuration, an annular gap 200 is provided between the annular ring 172 and the annular ring 186.

[0100] Down-the-hole drilling uses high pressure air to drive the piston to engage the rotating drill bit. Under repeated impacts at high frequency, the drill bit is subjected to significant force at piston impact ultimately resulting in failure of the drill bit. The present invention directs the piston impact to the inner portion of the drill bit head rather than the outer skirt thereof, decreasing the likelihood and / or frequency of failure.

[0101] Figure 7 shows a perspective view of a rotatable drill bit head carousel 300 adapted to hold up to three replacement drill bit heads (not shown) in four corresponding receptacles 302 in accordance with an embodiment of the presentinvention. The carousel is rotatable to bring it into alignment with the central axis of the hammer and may be angled for angular drilling or arranged for vertical drilling. The operator can disengage the drill bit head remotely and replace it with a fresh drill bit head. The carousel 300 may comprise three replacement drill bit heads thereby providing an empty receptacle 302 for a used drill bit head.

[0102] The four receptacles may be rotated such that any one of them is in a presentation position for loading a used head into an empty receptacle or loading a new head onto a drill string.

[0103] The carousel is pivotable about a hydraulic pivoting arm 303 from a disengaged configuration to a loading configuration. In the disengaged configuration, the carousel is safely away from the activity of the drill. In the loading configuration, the carousel is ready to remove a used head or attach a new head. In the loading configuration, the receptacle is collinear with and directly below the drill rod.

[0104] Protrusions 304 adapted to mate with air passages on the drill bit head are provided to inhibit rotation of the drill bit head when held in a carousel receptacle 302. Rotation of the hammer casing and rods can then engage or disengage a drill bit head.

[0105] To remove a used or failed drill bit head, the following steps may be undertaken: a. Rotate the carousel with an empty receptacle such that the empty receptacle is in the presentation position; b. Lower the hammer and drill assembly so as to engage the bit in the receptacle; c. Momentarily engage the air so as to cycle the hammer; d. Uncouple the drill head from the shank by rotating in an uncoupling rotation; e. Lift the hammer assembly to separate from the drill head; f. Pivot the carousel from the disengaged configuration to the loading configuration;g. Lower the hammer assembly and engage with a fresh drill head h. Raise the hammer assembly with the new head engaged.

Claims

CLAIMS1 . A down-hole hammer drill tool, the drill tool comprising a percussive piston, a drive sub, a drill bit shank comprising a rearward external annular shoulder and a drill bit head, wherein the drill bit shank and the drill bit head are threadably connected.

2. A down-hole hammer drill tool in accordance with claim 1 , comprising an annular gap about the periphery of the drill tool between the shank and the head.

3. A down-hole hammer drill tool in accordance with claim 2, wherein the annular gap comprises a percussive dampener.

4. A down-hole hammer drill tool in accordance with any one of the preceding claims wherein the rearward end of the head is provided with a recess to engage the shank.

5. A down-hole hammer drill tool in accordance claim 5, wherein the recess comprises a radially inwardly facing thread.

6. A down-hole hammer drill tool in accordance with any one of the preceding claims wherein the forward end of the shank comprises a radially outwardly facing thread.

7. A down-hole hammer drill tool in accordance with any one of claims 1 to 3, wherein the forward end of the shank is provided with a recess to engage the head.

8. A down-hole hammer drill tool in accordance with claim 7, wherein the recess comprises a radially inwardly facing thread.

9. A down-hole hammer drill tool in accordance with claim 7 wherein the rearward end of the head comprises a radially outwardly facing thread.

10. A down-hole hammer drill tool in accordance with any one of claims 1 to 3, wherein the rearward end of the head is provided with a recess and the forward end of the shank is provided with a recess.

11. A down-hole hammer drill tool in accordance with claim 10 wherein the head recess comprises a radially inwardly facing thread and the shank recess comprises a radially inwardly facing thread.

12. A down-hole hammer drill tool in accordance with claim 10, further comprising a coupler.

13. A down-hole hammer drill tool in accordance with claim 12, wherein the coupler comprises a first radially outwardly facing thread adapted to engage the recess of the head and second radially outwardly facing thread adapted to engage the recess of the shank.

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