WO2002052123A1 - Drill bit - Google Patents

Drill bit Download PDF

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Publication number
WO2002052123A1
WO2002052123A1 PCT/AU2001/001671 AU0101671W WO02052123A1 WO 2002052123 A1 WO2002052123 A1 WO 2002052123A1 AU 0101671 W AU0101671 W AU 0101671W WO 02052123 A1 WO02052123 A1 WO 02052123A1
Authority
WO
WIPO (PCT)
Prior art keywords
drill bit
annular portion
central
central portion
annular
Prior art date
Application number
PCT/AU2001/001671
Other languages
French (fr)
Inventor
Ian Graeme Rear
Original Assignee
Ian Graeme Rear
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Ian Graeme Rear filed Critical Ian Graeme Rear
Publication of WO2002052123A1 publication Critical patent/WO2002052123A1/en

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Classifications

    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B10/00—Drill bits
    • E21B10/62—Drill bits characterised by parts, e.g. cutting elements, which are detachable or adjustable

Definitions

  • This invention relates to drill bits and in particular relates to drill bits. Which are used in rock drilling.
  • Examples of the form of drill bit referred to above are disclosed in AU-B-81327/91 , AU-B- 71288/91 and JP2574705.
  • Each of the abovementioned specifications disclose an arrangement whereby the drill bit is formed of a number of segments which are capable of radial movement with respect to the central axis of the drill bit in order to vary the cutting diameter of the drill bit. Due to the harsh working conditions for such drill bits, a drill bit which is formed in segments and has a form of articulated connection between the main body of the hammer and the drill bit to facilitate the movement of those segments, creates a significant difficulty in that the segments and their interconnection may present a weakness in the structure of the drill bit particularly when drilling in certain ground conditions or formations.
  • a drill bit comprising a body adapted to be supported from a hammer assembly and having an outer portion which provides the cutting face of the drill bit said outer portion having an integral central portion having an outer axial end face and a cylindrical side face, the outer portion further comprising an annular portion which is removably receivable over the central portion, a locking means adapted to retain the annular portion in position on the central portion at which position the end face of the central portion and the outer face of the annular portion co-operate to provide the cutting face.
  • the annular portion is threadably receivable over the central portion.
  • the central portion is concentrically located with respect to the central longitudinal axis of the drill bit.
  • the annular portion has a central bore which is eccentrically located with respect to the outer perimeter of the annular portion.
  • the degree of eccentricity can be varied to vary the drilling diameter of the drill bit.
  • the degree of eccentricity is effected by utilising a set of annular portions of varying eccentricities from which one can be selected according to the desired drilling diameter.
  • the central portion is eccentrically located with respect to the central longitudinal axis of the drill bit.
  • the annular portion has a central bore which is eccentrically located with respect to the outer perimeter of the annular portion and the central portion is eccentrically located with respect to the central longitudinal axis of the drill bit and the degree of eccentricity of the central bore of the annular portion substantially corresponds to the degree of eccentricity of the central portion from the central longitudinal axis of the drill bit.
  • the degree of eccentricity can be varied to vary the drilling diameter of the drill bit.
  • the degree of eccentricity is effected by utilising a set of annular portions of varying eccentricities from which one can be selected according to the desired drilling diameter.
  • the locking means comprises a locking member which is supported in the central portion or annular portion to be capable of resilient radial movement with respect to the respective portion wherein the annular portion or central portion respectively is formed with a recess which is positioned to become aligned with the locking member on the annular portion becoming fully engaged with the central portion.
  • the recess has a circumferential extent to allow for some relative rotation between the annular portion and central portion when the locking member is engaged in the recess.
  • the circumferential extent of the recess corresponds to the degree of rotation of the annular portion with respect to the central portion corresponding to the minimum and maximum cutting diameter of the cutting face.
  • the annular portion is threadably received upon the central portion.
  • said threadable engagement comprises a first thread on the central portion or the annular portion which is threadably engagable by a second thread on the annular portion or central portion respectively whereby when the annular portion is fully received on the central portion the annular portion is in a first position, a third thread provided on the central portion or the annular portion said third thread being threadably engagable by the second thread whereby when so engaged and when the annular portion is fully engaged on the central portion the annular portion is in a second position, wherein when the annular portion is in the first position the outer periphery of the annular portion is concentric with the central longitudinal axis of the drill bit and when the annular portion is in the second position the outer periphery of the annular portion is eccentric to the central longitudinal axis of the drill bit.
  • the first and third threads are angularly offset from each other by 180°.
  • Figure 1 is a sectional elevation of drill bit according to the first embodiment
  • Figure 2 is an end elevation of the cutting face of the drill bit of Figure 1 ;
  • Figure 3 is an end elevation of the annular portion of the first embodiment
  • Figure 4 is an end elevation of the drill bit showing the central portion of the drill bit according to the embodiment and without the annular portion;
  • Figure 5 is a side elevation of the drill bit according to the first embodiment without the annular portion
  • Figure 6 is a sectional elevation of a drill bit according to the second embodiment
  • Figure 7 is an end elevation of the cutting face of the drill bit of the second embodiment
  • Figure 8 is a sectional elevation of a drill bit according to the third embodiment illustrating the annular portion in the concentric position
  • Figure 9 is an end elevation of a cutting face of a drill bit of the third embodiment illustrating the annular portion in the concentric position
  • Figure 10 is a sectional elevation of a drill bit according to the third embodiment illustrating the annular portion when the other threaded formation of the annular portion is engaged with the central portion and the annular portion is in the eccentric position and fully engaged with the shoulder of the drill bit;
  • Figure 11 is an end elevation of a cutting face of a drill bit of the third embodiment illustrating the annular portion in the eccentric position according to Figure 10;
  • Figure 12 is a sectional elevation of a drill bit according to the third embodiment illustrating the annular portion when the other threaded formation of the annular portion is engaged with the central portion and the annular portion is in the concentric position and spaced from the shoulder of the drill bit;
  • Figure 13 is an end elevation of a cutting face of a drill bit of the third embodiment illustrating the annular portion in the concentric position according to Figure 12;
  • Figure 14 is a part sectional elevation of the thread provided on the annular portion of the third embodiment.
  • Each of the embodiments relate to a drill bit which can be used with a downhole hammer in which the drill bit comprises a main body which is mounted to a downhole hammer assembly in the conventional manner where the drill bit has an outer cutting face where the cutting face is defined by a central portion which is formed as an integral part of the main body of the drill bit and an annular portion which is removably mounted to the central portion.
  • the outer portion provides the gauge cutting elements of the drill bit and will suffer from the greatest degree of wear.
  • the first embodiment is illustrated at Figures 1 , 2 and 3 comprises a drill bit 11 having a shank 13 which is adapted to be supported in a downhole hammer assembly in a conventional manner and a head portion 15 which extends from the hammer assembly and which provides the cutting face 17 of the drill bit.
  • the cutting face is defined by a central portion 19 and an annular portion 21 which are each provided with a cutting face 23 and 25 respectively which co-operate to provide the cutting face 17 of the drill bit.
  • the central portion 19 provides the cutting face 23 at its axial outer end and extends from the head portion 15 of the drill bit to define a central extension of substantially cylindrical configuration where the diameter of the central portion is less than the diameter of the head 15 of the drill bit in order to provide a shoulder 27 on the head portion 15 at the inner most end of the central portion 19.
  • the annular portion 21 is threadably received from the central portion 19 such that when it is fully engaged with the central portion 19 its innermost axial face 29 abuts with the shoulder 27 of the head portion 15 at which position its cutting face 25 provides a continuation of the cutting face 23 of the central portion.
  • the threaded engagement of the annular portion 21 on the central portion 19 is provided through a helical groove 31 which is of substantially semi circular profile and which is provided on the inner radial face of the annular portion 21.
  • the side face of the central portion 19 is provided with a helical formation (as shown at Figure 5) which comprises a helical array of semi-hemispherical recesses 33 where the helical array of recesses 33 is of a corresponding pitch to the helical groove 31 provided on the annular portion 21.
  • the recesses 33 are intended to provide support for spherical locking members which are to be jointly supported by the recess 33 and the opposed portion of the helical thread 31. If desired the locking members can have a shape other than spherical (i.e. cylindrical, ellipsoid or the like).
  • each of the recesses 33 have a spherical locking member located in position in them and the annular portion is then threadably engaged on to the helical formation created by the helical array locking members supported in the recesses 33.
  • the central portion is engaged with the annular portion whereby the outermost recess 33 in the central portion 19 is located adjacent the entry into the helical groove 31 on the annular portion and whilst in that position a spherical locking member is located in position in the recess.
  • the drill bit is then sequentially lowered and caused to rotate relative to the annular portion whereby as succeeding recesses 33 come into engagement with the entry to the helical formation 31 a spherical locking member is located in position in the respective recess.
  • a locking means is provided in the form of a locking pin 37 which is slidably received in a radial passageway formed in the side wall of the central portion 19.
  • the locking pin is associated with a spring 41 which resiliently biases the locking pin to an outwardly extending position from the passageway 39 to extend beyond the side wall of the central portion 19.
  • the locking pin is associated with a radial aperture 43 provided in the annular portion 21 which will become aligned with the passageway 39 accommodating the locking pin 37 when the annular portion 21 is fully engaged with the central portion 19.
  • the locking pin 37 is able to move radially outwardly into engagement with the passageway 43 provided in the annular portion 21.
  • the outer end of the annular passageway 43 in the annular portion 21 is provided with a plug 45 which closes the passageway.
  • the annular portion 21 is threadably engaged onto the central portion 19 and the locking pin 37 is depressed to enable the annular portion 21 to move to the fully engaged position.
  • the annular portion 21 is at the fully engaged position it is positively locked in that position through the action of the locking pin 37.
  • the plug 45 is removed from the radial passageway 43 in the annular portion 21 and the locking pin 27 is depressed to enable the annular portion 21 to be threadably disengaged from the central portion 19 and to permit the location of a new or refaced annular portion 21.
  • the first embodiment has application (although it is not restricted to such application) for use with large diameter bits and reduces the need for replacement of a complete drill bit as a result of the gauge of the drill bit having been worn to a condition at which the drill bit is no longer effective.
  • the second embodiment as shown at Figures 6, 7, 8 and 9 is of a similar form to that of the first embodiment in that it comprises a drill bit 111 having a shank 113 and a head portion 115 which provides a cutting face 117 which is provided jointly by a cutting face 123 of a central portion 119 and a cutting face 125 of an annular portion 121 where the annular portion 121 is threadably engaged upon the central portion 119 to facilitate the separation of the annular portion 121 for replacement when the gauge row of the cutting face 117 has been worn to a condition at which the drill bit is no longer efficient.
  • a locking pin 137 is received in a radial passageway 139 within the central portion 119 and is associated with a biasing spring 141 which biases the pin to an outwardly extended position from the central portion 119 while the annular portion 121 is provided with a radial passageway 143 which is closed by a plug 145 at its outer end and which will become aligned with the radial passageway 139 in the central portion 119 when the annular portion 121 is fully engaged with the central portion 119.
  • the annular portion 121 is eccentric in that the central axis A of the inner bore is offset from the central axis B of the outer periphery of the annular portion 121.
  • the eccentric nature of the annular portion 121 enables the cutting diameter of a drill bit of the first embodiment to be increased by applying to the central portion 119 of the bit an eccentric annular portion 121 of the form described above in relation to the second embodiment. Therefore it is possible to effect the drilling of a borehole utilising a substantially standard assembly whereby the diameter of the boreholes can be varied in accordance with the degree of eccentricity of the annular portion 121.
  • the threadable engagement of the annular portion 121 to the central portion 119 is of a corresponding form to that described in relation to the first embodiment.
  • the third embodiment as illustrated at Figures 8, 9, 10 and 11 is of a similar form to that of the second embodiment in that the annular portion 221 is eccentric.
  • the central portion 219 is also eccentrically mounted on the head portion 215 of the drill bit 211.
  • the degree of eccentricity of the central portion 219 with respect to the central axis of the drill bit corresponds the degree of eccentricity of the annular portion 221.
  • the drill bit 211 is capable of varying its cutting diameter between a minimum diameter which corresponds to the cutting diameter of the drill bit as shown at Figures 8 and 9 when the outer periphery of the annular portion 221 is concentric with the central longitudinal axis of the drill bit.
  • the cutting diameter of the drill bit is at its maximum when the central axis of the outer periphery of the annular portion 221 corresponds to the central longitudinal axis of the central portion 219 as shown at Figures 10 and 11.
  • the threaded engagement of the annular portion 221 on the central portion 219 is effected through use of two thread profiles 251 and 253 (see Figure 14) which are formed on the inner face of the annular portion 221 where the entries to the threaded portions 251 and 253 are offset by 180°.
  • the threaded formation which is provided on the central portion 119 is threadably engagable with one or the other of the threaded formations 251 and 253 of the annular portion 221.
  • the locking of the annular portion 221 to the central portion 219 is effected by utilisation of a locking pin 237 which is slidably received in a radial aperture 239 provided in the central portion 219.
  • the locking pin is resiliently biased by a spring 241 to an outwardly extended position.
  • the annular portion 221 is provided with a pair of radial passageways 243a and 243b which are angularly offset by 180° from each other.
  • the second radial passageway 243b in the annular portion 221 intersects the other threaded formation 253 in the annular portion 221 which is provided with a zone of enlarged depth along the helical formation for an angular distance of approximately 180°.
  • the zone of enlarged depth receives the outer end of the locking pin to provide for some limited relative rotation of the annular portion away from the fully engaged position (as shown at Figure 10) and provides two end shoulders which can be engaged by the locking pin 239 to define the limits of the relative rotation between the annular portion and the central portion.
  • the presence of the enlarged portion of the thread provides for limited relative rotation between the annular portion 221 and the central portion from a fully engaged position as shown at Figures 10 and 11 at which the annular portion 221 is in its eccentric position and is fully engaged with the central portion 219 and a second position as shown at Figures 11 and 12 at which the annular portion 221 is in a concentric position in relation to the drill bit but is not fully engaged with the shoulder 227.
  • the presence of the enlarged zone portion of the grove enables the drill bit to be readily changed between a concentric position at which it is able to pass through a bore casing of a diameter corresponding to the diameter of the concentric drill bit and an eccentric position at which the cutting diameter of the drill bit is maximised.
  • the annular portion When in the eccentric position the annular portion will be caused to remain in that position as a result of the clockwise rotation of the hammer assembly during the drilling procedure.
  • the drill bit 211 can be caused to rotate in an anti-clockwise direction with respect to the annular portion 221 to cause relative rotation therebetween until the locking pin 237 reaches the other end of the enlarged zone at which position the annular portion is in its concentric position and is able to be withdrawn through the bore casing.
  • the drill bit of the invention and having a cutting face of the form described in relation to each of the above embodiments may be of a form which is used with drilling systems which don't utilise downhole hammers.

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Abstract

A drill bit (11) comprising a body (13) adapted to be supported from a hammer assembly and having an outer portion (15) which provides the cutting face (17) of the drill bit said outer portion having an integral central portion (19) having an outer axial end face (23) and a cylindrical side face, the outer portion further comprising an annular portion (21) which is removably receivable over a central portion, a locking means (37) adapted to retain the annular portion in position on the central portion at which position the end face of the central portion and the outer face of the annular portion co-operate to provide the cutting face.

Description

Title: "Drill Bit"
Field of the Invention
This invention relates to drill bits and in particular relates to drill bits. Which are used in rock drilling.
Background
According to conventional practice downhole drilling is conducted utilising a single integral drill bit and due to the drilling action such drill bits suffer their most significant wear at the outer perimeter or "gauge" of the drill bit. As a result it is not unknown for drill bits to have completed their efficient working life as a result of significant wear of the outer portions of the cutting face of the outer portion of the drill bit and yet the central face of such drill bits are relatively unworn. In the case of large diameter drill bits the disposal of such drill bits can prove to be quite wasteful.
It is an object of this invention to provide a drill bit whereby the portion of the drill bit which can suffer the most significant wear can be replaced. It is preferred object of the invention that the portion may, if desired and appropriate, be replaced by one which is of a differing diameter. Alternatively the portion may, if desired and appropriate, be replaced by one having a different form and/or array of cutting elements to accommodate for variations in ground conditions. In addition the portion may, if desired and appropriate, be replaced several times before it becomes necessary to discard the entire drill bit due to adverse wear of the central zone of the cutting face or it becomes necessary to reface the central zone.
In addition in downhole drilling it is often the circumstance that it becomes necessary to increase the diameter of a borehole at one or more positions intermediate for a section of the length of the borehole. This can often be the case where the borehole is being lined during the drilling action due to the nature of the ground being encountered. It is therefore necessary to drill a larger diameter borehole to enable the casing to pass through that zone immediately behind the drill bit. In the past systems have been proposed for providing drill bits whereby the cutting diameter of the drill bit can be increased. In order to facilitate the extraction of such drill bits from the borehole subsequent to drilling or alternatively to continue drilling the borehole with the previous diameter on the particular adverse ground conditions having been traversed it is necessary that the drill bit also be capable of being reduced in its cutting diameter. Examples of the form of drill bit referred to above are disclosed in AU-B-81327/91 , AU-B- 71288/91 and JP2574705. Each of the abovementioned specifications disclose an arrangement whereby the drill bit is formed of a number of segments which are capable of radial movement with respect to the central axis of the drill bit in order to vary the cutting diameter of the drill bit. Due to the harsh working conditions for such drill bits, a drill bit which is formed in segments and has a form of articulated connection between the main body of the hammer and the drill bit to facilitate the movement of those segments, creates a significant difficulty in that the segments and their interconnection may present a weakness in the structure of the drill bit particularly when drilling in certain ground conditions or formations.
The preceding discussion of the background to the invention is intended only to facilitate an understanding of the present invention. It should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was part of the common general knowledge in Australia as at the priority date of the application.
Disclosure of the Invention
Accordingly the invention resides in a drill bit comprising a body adapted to be supported from a hammer assembly and having an outer portion which provides the cutting face of the drill bit said outer portion having an integral central portion having an outer axial end face and a cylindrical side face, the outer portion further comprising an annular portion which is removably receivable over the central portion, a locking means adapted to retain the annular portion in position on the central portion at which position the end face of the central portion and the outer face of the annular portion co-operate to provide the cutting face. According to a preferred feature of the invention the annular portion is threadably receivable over the central portion.
According to one embodiment the central portion is concentrically located with respect to the central longitudinal axis of the drill bit.
It is a further preferred object of the invention, although not an essential object of the invention, that the cutting diameter of the drill bit can be varied selectively whilst the drill bit is in service.
According to a preferred feature of the invention the annular portion has a central bore which is eccentrically located with respect to the outer perimeter of the annular portion.
According to a preferred feature of the previous feature of the invention the degree of eccentricity can be varied to vary the drilling diameter of the drill bit. According to one embodiment of the invention the degree of eccentricity is effected by utilising a set of annular portions of varying eccentricities from which one can be selected according to the desired drilling diameter.
According to an alternative embodiment the central portion is eccentrically located with respect to the central longitudinal axis of the drill bit.
According to a preferred feature of the annular portion has a central bore which is eccentrically located with respect to the outer perimeter of the annular portion and the central portion is eccentrically located with respect to the central longitudinal axis of the drill bit and the degree of eccentricity of the central bore of the annular portion substantially corresponds to the degree of eccentricity of the central portion from the central longitudinal axis of the drill bit.
According to a preferred feature of the previous feature of the invention the degree of eccentricity can be varied to vary the drilling diameter of the drill bit. According to one embodiment of the invention the degree of eccentricity is effected by utilising a set of annular portions of varying eccentricities from which one can be selected according to the desired drilling diameter.
According to a preferred feature of the invention the locking means comprises a locking member which is supported in the central portion or annular portion to be capable of resilient radial movement with respect to the respective portion wherein the annular portion or central portion respectively is formed with a recess which is positioned to become aligned with the locking member on the annular portion becoming fully engaged with the central portion. According to a preferred feature of the invention the recess has a circumferential extent to allow for some relative rotation between the annular portion and central portion when the locking member is engaged in the recess. According to a preferred feature of the invention the circumferential extent of the recess corresponds to the degree of rotation of the annular portion with respect to the central portion corresponding to the minimum and maximum cutting diameter of the cutting face.
According to a preferred feature of the invention the annular portion is threadably received upon the central portion. According to one embodiment said threadable engagement comprises a first thread on the central portion or the annular portion which is threadably engagable by a second thread on the annular portion or central portion respectively whereby when the annular portion is fully received on the central portion the annular portion is in a first position, a third thread provided on the central portion or the annular portion said third thread being threadably engagable by the second thread whereby when so engaged and when the annular portion is fully engaged on the central portion the annular portion is in a second position, wherein when the annular portion is in the first position the outer periphery of the annular portion is concentric with the central longitudinal axis of the drill bit and when the annular portion is in the second position the outer periphery of the annular portion is eccentric to the central longitudinal axis of the drill bit. According to a feature of the embodiment the first and third threads are angularly offset from each other by 180°.
The invention will be more fully understood in the light of the following description of several specific embodiments. Brief Description of the Drawings
The description is made with reference to the accompanying drawings of which:
Figure 1 is a sectional elevation of drill bit according to the first embodiment;
Figure 2 is an end elevation of the cutting face of the drill bit of Figure 1 ;
Figure 3 is an end elevation of the annular portion of the first embodiment;
Figure 4 is an end elevation of the drill bit showing the central portion of the drill bit according to the embodiment and without the annular portion;
Figure 5 is a side elevation of the drill bit according to the first embodiment without the annular portion;
Figure 6 is a sectional elevation of a drill bit according to the second embodiment;
Figure 7 is an end elevation of the cutting face of the drill bit of the second embodiment;
Figure 8 is a sectional elevation of a drill bit according to the third embodiment illustrating the annular portion in the concentric position;
Figure 9 is an end elevation of a cutting face of a drill bit of the third embodiment illustrating the annular portion in the concentric position;
Figure 10 is a sectional elevation of a drill bit according to the third embodiment illustrating the annular portion when the other threaded formation of the annular portion is engaged with the central portion and the annular portion is in the eccentric position and fully engaged with the shoulder of the drill bit;
Figure 11 is an end elevation of a cutting face of a drill bit of the third embodiment illustrating the annular portion in the eccentric position according to Figure 10; Figure 12 is a sectional elevation of a drill bit according to the third embodiment illustrating the annular portion when the other threaded formation of the annular portion is engaged with the central portion and the annular portion is in the concentric position and spaced from the shoulder of the drill bit;
Figure 13 is an end elevation of a cutting face of a drill bit of the third embodiment illustrating the annular portion in the concentric position according to Figure 12; and
Figure 14 is a part sectional elevation of the thread provided on the annular portion of the third embodiment.
Detailed Description of the Specific Embodiments
Each of the embodiments relate to a drill bit which can be used with a downhole hammer in which the drill bit comprises a main body which is mounted to a downhole hammer assembly in the conventional manner where the drill bit has an outer cutting face where the cutting face is defined by a central portion which is formed as an integral part of the main body of the drill bit and an annular portion which is removably mounted to the central portion. In the case of each of the embodiments the outer portion provides the gauge cutting elements of the drill bit and will suffer from the greatest degree of wear. As a result once the outer annular portion has worn to a condition at which it is no longer efficient in its cutting operation the outer annular portion can be removed and replaced by a fresh annular portion which has been remanufactured or alternatively refaced in order that the central portion which will not have suffered the same degree of wear and can co-operate with the new annular portion.
The first embodiment is illustrated at Figures 1 , 2 and 3 comprises a drill bit 11 having a shank 13 which is adapted to be supported in a downhole hammer assembly in a conventional manner and a head portion 15 which extends from the hammer assembly and which provides the cutting face 17 of the drill bit. The cutting face is defined by a central portion 19 and an annular portion 21 which are each provided with a cutting face 23 and 25 respectively which co-operate to provide the cutting face 17 of the drill bit.
The central portion 19 provides the cutting face 23 at its axial outer end and extends from the head portion 15 of the drill bit to define a central extension of substantially cylindrical configuration where the diameter of the central portion is less than the diameter of the head 15 of the drill bit in order to provide a shoulder 27 on the head portion 15 at the inner most end of the central portion 19.
The annular portion 21 is threadably received from the central portion 19 such that when it is fully engaged with the central portion 19 its innermost axial face 29 abuts with the shoulder 27 of the head portion 15 at which position its cutting face 25 provides a continuation of the cutting face 23 of the central portion.
The threaded engagement of the annular portion 21 on the central portion 19 is provided through a helical groove 31 which is of substantially semi circular profile and which is provided on the inner radial face of the annular portion 21. The side face of the central portion 19 is provided with a helical formation (as shown at Figure 5) which comprises a helical array of semi-hemispherical recesses 33 where the helical array of recesses 33 is of a corresponding pitch to the helical groove 31 provided on the annular portion 21. The recesses 33 are intended to provide support for spherical locking members which are to be jointly supported by the recess 33 and the opposed portion of the helical thread 31. If desired the locking members can have a shape other than spherical (i.e. cylindrical, ellipsoid or the like).
In mounting the annular portion 21 to the drill bit each of the recesses 33 have a spherical locking member located in position in them and the annular portion is then threadably engaged on to the helical formation created by the helical array locking members supported in the recesses 33.
As an alternative the central portion is engaged with the annular portion whereby the outermost recess 33 in the central portion 19 is located adjacent the entry into the helical groove 31 on the annular portion and whilst in that position a spherical locking member is located in position in the recess. The drill bit is then sequentially lowered and caused to rotate relative to the annular portion whereby as succeeding recesses 33 come into engagement with the entry to the helical formation 31 a spherical locking member is located in position in the respective recess.
In order to positively retain the annular member in its fully engaged position a locking means is provided in the form of a locking pin 37 which is slidably received in a radial passageway formed in the side wall of the central portion 19. The locking pin is associated with a spring 41 which resiliently biases the locking pin to an outwardly extending position from the passageway 39 to extend beyond the side wall of the central portion 19. The locking pin is associated with a radial aperture 43 provided in the annular portion 21 which will become aligned with the passageway 39 accommodating the locking pin 37 when the annular portion 21 is fully engaged with the central portion 19. When the annular portion 21 is at its fully engaged position and the passageways 43 and 39 in the annular portion 21 and the central portion 19 respectively become aligned the locking pin 37 is able to move radially outwardly into engagement with the passageway 43 provided in the annular portion 21. The outer end of the annular passageway 43 in the annular portion 21 is provided with a plug 45 which closes the passageway.
In use the annular portion 21 is threadably engaged onto the central portion 19 and the locking pin 37 is depressed to enable the annular portion 21 to move to the fully engaged position. When the annular portion 21 is at the fully engaged position it is positively locked in that position through the action of the locking pin 37. When it becomes necessary to re-service the bit by replacement of the annular portion 21 , the plug 45 is removed from the radial passageway 43 in the annular portion 21 and the locking pin 27 is depressed to enable the annular portion 21 to be threadably disengaged from the central portion 19 and to permit the location of a new or refaced annular portion 21.
The first embodiment has application (although it is not restricted to such application) for use with large diameter bits and reduces the need for replacement of a complete drill bit as a result of the gauge of the drill bit having been worn to a condition at which the drill bit is no longer effective.
The second embodiment as shown at Figures 6, 7, 8 and 9 is of a similar form to that of the first embodiment in that it comprises a drill bit 111 having a shank 113 and a head portion 115 which provides a cutting face 117 which is provided jointly by a cutting face 123 of a central portion 119 and a cutting face 125 of an annular portion 121 where the annular portion 121 is threadably engaged upon the central portion 119 to facilitate the separation of the annular portion 121 for replacement when the gauge row of the cutting face 117 has been worn to a condition at which the drill bit is no longer efficient. In addition a locking pin 137 is received in a radial passageway 139 within the central portion 119 and is associated with a biasing spring 141 which biases the pin to an outwardly extended position from the central portion 119 while the annular portion 121 is provided with a radial passageway 143 which is closed by a plug 145 at its outer end and which will become aligned with the radial passageway 139 in the central portion 119 when the annular portion 121 is fully engaged with the central portion 119.
In a case of the second embodiment the annular portion 121 is eccentric in that the central axis A of the inner bore is offset from the central axis B of the outer periphery of the annular portion 121. The eccentric nature of the annular portion 121 enables the cutting diameter of a drill bit of the first embodiment to be increased by applying to the central portion 119 of the bit an eccentric annular portion 121 of the form described above in relation to the second embodiment. Therefore it is possible to effect the drilling of a borehole utilising a substantially standard assembly whereby the diameter of the boreholes can be varied in accordance with the degree of eccentricity of the annular portion 121.
The threadable engagement of the annular portion 121 to the central portion 119 is of a corresponding form to that described in relation to the first embodiment.
The third embodiment as illustrated at Figures 8, 9, 10 and 11 is of a similar form to that of the second embodiment in that the annular portion 221 is eccentric. In the case of the third embodiment however the central portion 219 is also eccentrically mounted on the head portion 215 of the drill bit 211. The degree of eccentricity of the central portion 219 with respect to the central axis of the drill bit corresponds the degree of eccentricity of the annular portion 221. As a result the drill bit 211 is capable of varying its cutting diameter between a minimum diameter which corresponds to the cutting diameter of the drill bit as shown at Figures 8 and 9 when the outer periphery of the annular portion 221 is concentric with the central longitudinal axis of the drill bit. The cutting diameter of the drill bit is at its maximum when the central axis of the outer periphery of the annular portion 221 corresponds to the central longitudinal axis of the central portion 219 as shown at Figures 10 and 11.
In addition in the case of the third embodiment the threaded engagement of the annular portion 221 on the central portion 219 is effected through use of two thread profiles 251 and 253 (see Figure 14) which are formed on the inner face of the annular portion 221 where the entries to the threaded portions 251 and 253 are offset by 180°. The threaded formation which is provided on the central portion 119 is threadably engagable with one or the other of the threaded formations 251 and 253 of the annular portion 221. Therefore if the first threaded formation 251 of the annular portion 221 is engaged with the treaded formation on the central formation 119 (as shown at Figures 8 and 9) the threaded engagement is such that when the annular portion 21 is fully engaged with the central portion 219 it occupies the concentric position as shown at Figures 8 and 9 at which the drill bit has the minimum diameter.
When the other threaded formation 253 is engaged with the threaded formation on the central portion 219 (as shown at Figures 10, 11 , 12 and 13) the annular portion 121 occupies the eccentric position as shown at Figures 10 and 11 when the annular portion 221 is fully engaged with the central portion 219.
As in the case of the previous embodiments the locking of the annular portion 221 to the central portion 219 is effected by utilisation of a locking pin 237 which is slidably received in a radial aperture 239 provided in the central portion 219. The locking pin is resiliently biased by a spring 241 to an outwardly extended position. In addition the annular portion 221 is provided with a pair of radial passageways 243a and 243b which are angularly offset by 180° from each other. When the annular portion 221 is in the concentric position as shown at Figures 8 and 9 and when it is fully engaged on the central portion 219 the first radial passageway 243a in the annular portion 221 becomes aligned with the radial passageway 239 in the central portion 219 to positively retain the annular portion 221 in its concentric position.
When the annular portion 221 is in its eccentric position and fully engaged on the central portion 219 as shown at Figures 10 and 11 the second radial passageway 243b in the annular portion 221 becomes aligned with the radial passageway 239 in the central portion 219.
In addition the second radial passageway 243b in the annular portion 221 intersects the other threaded formation 253 in the annular portion 221 which is provided with a zone of enlarged depth along the helical formation for an angular distance of approximately 180°. The zone of enlarged depth receives the outer end of the locking pin to provide for some limited relative rotation of the annular portion away from the fully engaged position (as shown at Figure 10) and provides two end shoulders which can be engaged by the locking pin 239 to define the limits of the relative rotation between the annular portion and the central portion. The presence of the enlarged portion of the thread provides for limited relative rotation between the annular portion 221 and the central portion from a fully engaged position as shown at Figures 10 and 11 at which the annular portion 221 is in its eccentric position and is fully engaged with the central portion 219 and a second position as shown at Figures 11 and 12 at which the annular portion 221 is in a concentric position in relation to the drill bit but is not fully engaged with the shoulder 227. The presence of the enlarged zone portion of the grove enables the drill bit to be readily changed between a concentric position at which it is able to pass through a bore casing of a diameter corresponding to the diameter of the concentric drill bit and an eccentric position at which the cutting diameter of the drill bit is maximised. When in the eccentric position the annular portion will be caused to remain in that position as a result of the clockwise rotation of the hammer assembly during the drilling procedure. When it becomes necessary to cease drilling and withdraw the drill bit from the hole through the bore casing the drill bit 211 can be caused to rotate in an anti-clockwise direction with respect to the annular portion 221 to cause relative rotation therebetween until the locking pin 237 reaches the other end of the enlarged zone at which position the annular portion is in its concentric position and is able to be withdrawn through the bore casing.
According to further embodiments of the invention the drill bit of the invention and having a cutting face of the form described in relation to each of the above embodiments may be of a form which is used with drilling systems which don't utilise downhole hammers.
It should be appreciated that the scope of the present invention need not be limited to the scope of the embodiment described above.
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.

Claims

ClaimsThe claims defining the invention are as follows:
1. A drill bit comprising a body adapted to be supported from a hammer assembly and having an outer portion which provides the cutting face of the drill bit said outer portion having an integral central portion having an outer axial end face and a cylindrical side face, the outer portion further comprising an annular portion which is removably receivable over a central portion, a locking means adapted to retain the annular portion in position on the central portion at which position the end face of the central portion and the outer face of the annular portion co-operate to provide the cutting face.
2. A drill bit as claimed at claim 1 or 2 wherein the central portion is concentrically located with respect to the central longitudinal axis of the drill bit.
3. A drill bit as claimed at claim 1 , 2 or 3 wherein the annular portion has a central bore which is eccentrically located with respect to the outer perimeter of the annular portion.
4. A drill bit as claimed at claim 4 wherein the degree of eccentricity can be varied to vary the drilling diameter of the drill bit.
5. A drill bit as claimed at claim 5 wherein a set of annular portions of varying eccentricity are provided from which one can be selected to vary the degree of eccentricity according to the desired drilling diameter of the drill bit.
6. A drill bit as claimed at claim 1 or 2 or any one of claims 4, or 5 or 6 as dependant from claim 1 or 2 wherein the central portion is eccentrically located with respect to the central longitudinal axis of the drill bit.
7. A drill bit as claimed at claim 1 or 2 wherein the annular portion has a central bore which is eccentrically located with respect to the outer
7. A drill bit as claimed at claim 1 or 2 wherein the annular portion has a central bore which is eccentrically located with respect to the outer perimeter of the annular portion and the central portion is eccentrically located with respect to the central longitudinal axis of the drill bit and the degree of eccentricity of the central bore of the annular portion substantially corresponds to the degree of eccentricity of the central portion from the central longitudinal axis of the drill bit.
8. A drill bit as claimed at claim 8 wherein the degree of eccentricity can be varied to vary the drilling diameter of the drill bit.
9. A drill bit as claimed at claim 9 wherein a set of annular portions of varying eccentricity are provided from which one can be selected to vary the degree of eccentricity according to the desired drilling diameter of the drill bit.
10. A drill bit as claimed at any one of the preceding claims wherein the locking means comprises a locking member which is supported in the central portion or annular portion to be capable of resilient radial movement with respect to the respective portion wherein the annular portion or central portion respectively is formed with a recess which is positioned to become aligned with the locking member on the annular portion becoming fully engaged with the central portion.
11. A drill bit as claimed at claim 11 wherein the recess has a circumferential extent to allow for some relative rotation between the annular portion and central portion when the locking member is engaged in the recess.
12. A drill bit as claimed at claim 12 wherein the circumferential extent of the recess corresponds to the degree of rotation of the annular portion with respect to the central portion corresponding to the minimum and maximum cutting diameter of the cutting face.
13. A drill bit as claimed at any one of the preceding claims wherein the annular portion is threadably receivable over the central portion.
14. A drill bit as claimed at claim 13 wherein said threadable engagement comprises a first thread on the central portion or the annular portion which is threadably engagable by a second thread on the annular portion or central portion respectively whereby when the annular portion is fully received on the central portion the annular portion is in a first position, a third thread provided on the central portion or the annular portion said third thread being threadably engagable by the second thread whereby when so engaged and when the annular portion is fully engaged on the central portion the annular portion is in a second position, wherein when the annular portion is in the first position the outer periphery of the annular portion is concentric with the central longitudinal axis of the drill bit and when the annular portion is in the second position the outer periphery of the annular portion is eccentric to the central longitudinal axis of the drill bit.
15. A drill bit as claimed at claim 14 wherein the first and third threads are angularly offset from each other by 180°.
16. A drill bit substantially as herein described with reference to the accompanying drawings.
PCT/AU2001/001671 2000-12-22 2001-12-21 Drill bit WO2002052123A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AUPR2269 2000-12-22
AUPR2269A AUPR226900A0 (en) 2000-12-22 2000-12-22 Drill bit

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WO2002052123A1 true WO2002052123A1 (en) 2002-07-04

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2017004666A1 (en) * 2015-07-09 2017-01-12 Fero Group Pty Ltd Two part drill bit assembly
WO2018158503A1 (en) * 2017-03-01 2018-09-07 Robit Oyj A drill bit for percussive drilling, a drill bit assembly, and a method for manufacturing such a drill bit

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2643414A1 (en) * 1989-02-21 1990-08-24 Vennin Henri Rotary single-piece boring trepanning tool
DE3941609C1 (en) * 1989-12-16 1991-10-24 Johannes 4130 Moers De Radtke Boring head for mining - has head and shaft provided with fluid flushing channels and tapering surface on head
WO1994012760A1 (en) * 1992-12-03 1994-06-09 Jaervelae Jorma Drilling apparatus

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2643414A1 (en) * 1989-02-21 1990-08-24 Vennin Henri Rotary single-piece boring trepanning tool
DE3941609C1 (en) * 1989-12-16 1991-10-24 Johannes 4130 Moers De Radtke Boring head for mining - has head and shaft provided with fluid flushing channels and tapering surface on head
WO1994012760A1 (en) * 1992-12-03 1994-06-09 Jaervelae Jorma Drilling apparatus

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2017004666A1 (en) * 2015-07-09 2017-01-12 Fero Group Pty Ltd Two part drill bit assembly
EP3320169A4 (en) * 2015-07-09 2019-03-27 Fero Group Pty Ltd Two part drill bit assembly
WO2018158503A1 (en) * 2017-03-01 2018-09-07 Robit Oyj A drill bit for percussive drilling, a drill bit assembly, and a method for manufacturing such a drill bit
KR20190124249A (en) * 2017-03-01 2019-11-04 로비트 피엘씨 Drill bits, drill bit assemblies and methods for manufacturing such drill bits for impact drilling
US11008812B2 (en) 2017-03-01 2021-05-18 Robit Oyj Drill bit for percussive drilling, a drill bit assembly, and a method for manufacturing such a drill bit
KR102595404B1 (en) 2017-03-01 2023-10-27 로비트 피엘씨 Drill bits for impact drilling, drill bit assemblies and methods for manufacturing such drill bits

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