AU2013201024A1 - Drilling System - Google Patents

Abstract

Abstract A drill bit comprising a body having an outer surface, and at least one cutting element attached to the outer surface, wherein the cutting element is adapted for selective displacement between an extended condition and a contracted condition. There is also provided a drilling tool and a drill comprising a drill bit and a drive means for transferring rotary and/or percussive movement to the drill bit, the drill bit comprising a body having an outer surface, and a cutting element attached to the outer surface, wherein the cutting element is adapted for selective displacement between an extended condition and a contracted condition as well as a method for installing a rock bolt in a rock formation.

Description

P/00/0 11 28/5/91 Regulation 3.2 AUSTRALIA Patents Act 1990 ORIGINAL COMPLETE SPECIFICATION STANDARD PATENT Name of Applicant: Matthew David McLaren Actual Inventor Matthew David McLaren Address for service is: WRAYS Ground Floor, 56 Ord Street West Perth WA 6005 Attorney code: WR Invention Title: Drilling System The following statement is a full description of this invention, including the best method of performing it known to me: 1 TECHNICAL FIELD [0001] The present invention relates to drilling tools. [0002] The invention has been devised particularly, although not necessarily solely, in relation to a drill tool used for installing rock bolts in rock formation for stabilization of the rock formations. BACKGROUND ART [0003] 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. [0004] The purpose of the following description of the background art is to provide an understanding of a possible application of the embodiments of the invention described in the present specification. The possible application relates to a method for stabilising rock formations 10 using a stabiliser system 12. [0005] Figures 1 to 3 show a rock formation 10 being stabilised using the stabiliser system 12. In particular, figure 1 shows a cross-sectional view of a rock formation 10 having a hole 28 which incorporates a stabiliser system 12. Figures 2 and 3 show the stabiliser system 12. The stabiliser system 12 secures the hole 28 of the rock formation 10 to avoid collapse of the rock formation. [0006] The stabiliser system 12 comprises a rock bolt 14 and a bearing plate 16. The rock bolt 14 comprises a tube 18 having a tapered end 20 and a flanged head 22. The tube 18 has a slot 19 along its length. The bearing plate 18 comprises a support area 24 and an opening 26. The opening 26 is adapted to receive the rock bolt 14. The flanged head 22 impedes release of the bearing plate 18 from the rock bolt 14 during installation and during use of the stabiliser system 12. After the stabilising system 12 has been installed, the support area 24 of the bearing plate abuts the rock formation (see figure 1). Also, the tube 18 when installed exerts radial pressure against the rock over tis full length. This arrangement secures the rock formation surrounding the hole 28.

[0007] The stabiliser system 12 is typically used for supporting the rock formations of tunnels or shafts drilled during underground mining procedures. In particular, the stabiliser system 12 is suited for supporting the roofs of the mine tunnels or mine shafts. For supporting a roof of a mine tunnel a plurality of stabiliser system are installed in the roof. Typically, a relative large number of stabiliser systems need to be installed in order to properly support a roof of a mine tunnel. Installation of the plurality of stabiliser system 12 typically is a cumbersome and expensive procedure. [0008] The process for installing a stabiliser system 12 consists of drilling a hole 28 in the rock formation 10. The diameter of the hole 28 is of slightly less diameter than the diameter of the tube 18 such that the slot 19 narrows as the tube 18 is inserted into the hole 28. Typically, the hole 28 is drilled with a drilling equipment incorporating a drill bit. After drilling of the hole 28, the drill bit is extracted from the hole 28 to allow installation of the stabiliser system 12. The procedure for installing the stabiliser system 12 consists of fixing the bearing plate 26 to the rock bolt 14. This is accomplished by inserting the tube 18 of the rock bolt 14 into the opening 26 of bearing plate 16 and sliding the bearing from the tapered end 20 of the rock bolt to the flanged head 22 of the rock bolt 14. Subsequently, the tube 18 is inserted in the hole 28 of the rock formation 10 such that the support area 24 of the bearing plate 16 abuts the rock formation 10. [0009] Installing the stabiliser system 12 requires several operations performed using a different tool at each stage of installation. As explained above in relation to the procedure for installing the stabiliser system, installing a single stabiliser system 12 requires at least two steps. The first step is to drill the hole 28. The second step consists of inserting the tube 18 the rock bolt 14 in the hole 18. This two-step installation process makes installation of a relative large quantity of stabiliser systems 12 time consuming and cumbersome and, therefore, expensive. [0010] It is against this background that the present invention has been developed. SUMMARY OF INVENTION [0011] According to a first aspect of the invention there is provided a drill bit comprising a body having an outer surface, and at least one cutting element attached to the outer surface, wherein the cutting element is adapted for selective displacement between an extended condition and a contracted condition.

[0012] Preferably, the cutting element is in the extended condition when at least a portion of the cutting element protrudes from the outer surface and wherein the cutting element is in the contracted condition when the cutting element is substantially flush in relation to the outer surface of the body. [0013] Preferably, the body comprises an opening adapted to slideably receive the cutting element wherein the cutting element is slideably attached within the opening to allow displacement of at least a portion of the cutting element out of the opening to locate the cutting element in the extended condition and to allow displacement of at least the portion into the opening to locate the cutting element in the extended condition. [0014] Preferably, the cutting element is slideably located within the opening such that the cutting element is biased towards the contracted condition. In this manner, the cutting element is in the contracted condition unless a force is applied to the cutting element for displacement of the cutting element from the contracted condition to the extended condition. [0015] Preferably, the cutting element comprises an inner end and an exterior end, at least a portion of the exterior end protruding from the exterior surface when the cutting element is located in the extended condition and the inner end being adapted for receiving a force for displacing the cutting element from the contracted condition to the extended condition. [0016] Preferably, the cutting element is tapered. [0017] Preferably, the body comprises a hollow body defining an inner portion adapted to receive a distal end of a drill rod. [0018] Preferably, the opening incorporating the cutting element traverses the body of the drill bit such as to define a passage extending from the inner portion of the body to the outer surface of the body, the cutting element extending through the passage such that the inner end of the cutting element is located at least partially within the inner portion of the body when the cutting element is in the contracted condition. [0019] Preferably, the distal end of the drill rod is adapted to engage the inner end of the cutting element in order to apply the force to the cutting element for displacing the cutting element from the contracted condition to the extended condition.

[0020] Preferably, the drill rod is releasable attached to the drill bit. [0021] Preferably, the drill rod comprises a threaded outer surface and the inner portion of the body of the drill bit comprises an inner threaded inner surface to allow screwing of the drill rod to the drill bit. [0022] Preferably, the cutting element is displaced from the contracted condition to the extended condition during screwing of the drill rod into the body of the drill bit [0023] Preferably, the cutting element is displaced from the extended condition to the contracted condition during unscrewing of the drill rod from the body of the drill bit. [0024] In an arrangement, the drill bit comprises a plurality of cutting elements. [0025] Preferably, the plurality of cutting elements are located around the periphery of the body of the drill bit spaced apart with respect to each other. [0026] Preferably, the body of the drill bit comprises an upper end and a lower end, the upper end comprising the plurality of cutting elements and the lower end comprising an aperture to allow access of the drill rod into the inner portion of the body of the drill bit. [0027] According to a second aspect of the invention there is provided a drilling tool comprising a drill bit and a drive means for transferring rotary and/or percussive movement to the drill bit, the drill bit comprising a body having an outer surface, and a cutting element attached to the outer surface, wherein the cutting element is adapted for selectively displacement between an extended condition and a contracted condition. [0028] Preferably, the drive means comprise a drill rod adapted to be attached to the drill bit. [0029] Preferably, the drill rod is adapted to receive a rock bolt. [0030] Preferably, the drill rod comprises a flange adapted to abut the rock bolt for transferring the percussive movement of the drill rod to the rock bolt. [0031] Preferably, the drill rod comprises a spacer located between the flange and the rock bolt to avoid transference of the rotary movement of the drill rod to the rock bolt.

[0032] According to a third aspect of the invention there is provided a drill adapted to receive a drilling tool comprising a drill bit and drive means for transferring the rotary and/or percussive movement of the drill to the drill bit, the drill bit comprising a body having an outer surface, and cutting element attached to the outer surface, wherein the cutting element is adapted for selectively displacement between an extended condition and a contracted condition. [0033] According to a fourth aspect of the invention there is provided a method for installing a rock bolt in a rock formation, the method comprises the step of: mounting the rock bolt on a drilling tool in accordance with the second aspect of the invention; displacing cutting element of the drill bit from an contracted condition to a extended condition; drilling a hole in the rock formation using the drilling tool; displacing the cutting element of the drill bit from the extended condition to the contracted condition; retrieving the cutting tool from the hole to leave the rock bolt in the hole. [0034] Preferably, displacing the at least one cutting element of the drill bit from the contracted condition to the extended condition comprises the step of screwing a drill rod into the drill bit to apply a force to the cutting element to displace the cutting element from the contracted condition to the extended condition. [0035] Preferably, displacing the at least one cutting element of the drill bit from the extended condition to the contracted condition comprises the step of unscrewing a drill rod at least partially the drill bit to release a force applied to the cutting element which maintains the cutting element in the contracted condition allowing to displace the cutting element from the extended condition to the contracted condition. BRIEF DESCRIPTION OF THE DRAWINGS [0036] 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 a cross-sectional view of a rock formation incorporating a stabiliser system; Figure 2 is a side view of a rock bolt of the stabiliser system shown in figure 1; Figure 3 is a top view of a bearing plate of the stabiliser system shown in figure 1; Figure 4 is a cross-sectional schematic view of a drill bit according to a first embodiment of the invention; Figure 5 is a cross-sectional schematic view of the drill bit and the distal end of the drill rod prior to attachment of the drill rod to the drill bit; Figure 6 is a cross-sectional schematic view of the drill bit and the distal end of the drill rod during attachment of the drill rod to the drill bit; Figure 7 is a cross-sectional schematic view of the drill bit and the distal end of the drill rod secured to the drill bit; Figure 8 is a side view of a drilling tool in accordance with the present embodiment of the invention incorporating a rock bolt prior to installation of the rock bolt; and Figure 9 is a side view of a drilling tool in accordance with the present embodiment of the invention incorporating a rock bolt during installation of the rock bolt. DESCRIPTION OF EMBODIMENTS [0037] Figures 4 to 7 show a drilling bit 30 in accordance an embodiment of the invention. As will be described with reference to the method of operation of the drill bit 30, the drill bit 20 is particular useful for installing rock bolts 14 in a rock formation for stabilizing the rock formation. Figure 8 shows a drilling tool in accordance with the present embodiment of the invention. Figure 9 shows the process for installing a rock bolt 14 in a rock formation. In particular, figure 8 shows a drill bit 30 in accordance with the present embodiment of the invention mounted on a percussion drill 34. The percussion drill 34 comprises a drill rod 36 for transferring rotary movement and percussive movement of the drill 34 to the drill bit 30. As will be described below, the drill bit 30 is adapted to be attached to the drill rod 36 to define a drill bit 30 and drill rod 36 assembly. In this manner, rotary movement and percussive movement is transferred from the drill 34 to the drill bit 30. The rock bolt 14 is installed in the rock formation by drilling a hole 28 into the rock formation using the drill bit 30. Figure 9 shows the initial process of drilling of the opening in the rock formation. For installation of the rock bolt 14 the drilling of the hole 28 proceeds until the rock bolt 14 is fully confined within the hole 28 (see figure 1). At this stage, the drill bit 30 together with the drill rod 36 is extracted from the opening in such a manner that the rock bolt 14 is left within the drilled opening 28. [0038] The drill bit 30 in accordance with the present embodiment of the invention is adapted to be extracted from the hole 28 through the rock bolt 14. For this, as will be described below, the drill bit 30 comprises a plurality of cutting elements 40 that can be located from a contracted condition to an extended condition and vice versa. (see figure 4). [0039] Figure 4 shows a drill bit 30 in accordance with an embodiment of the invention. The drill bit 30 comprises a body 32. In the arrangement shown in figure 4, the body is of cylindrical configuration. [0040] The body 32 comprises a distal end 42 and a proximal end 44. The distal end 42 comprises a top portion 46. The distal end 42 comprises a plurality of cutting elements 40 and 48. The cutting elements 40 are arranged around the sides of the top portion 46. The cutting elements 48 are arranged on the top portion 46. As will be described below, the cutting elements 40 in accordance with the present embodiment of the invention are adapted to be selectively displaced between an extended condition and a contracted condition. [0041] A plurality of apertures 50 are disposed around the outer surface of the top portion 46 of the body 32. Each aperture 50 is adapted to slideably receive one of the cutting elements 40. In this manner, the cutting elements 40 can slide from a contracted condition (see figure 4 or 5) to an extended condition (see figure 7). In the extended condition the cutting elements 40 protrude outward from the outer surface of the body 30. In the extended condition, the cutting elements 40 allows cutting of the rock formation during drilling of the hole 28. In the contracted condition, the cutting elements 40 are confined at least partially inside the outer surface of the body 32 of the drill bit 30 and, thus, flush with the outer surface of the body 32. As will be described with reference to the method of operation of the drill bit 30, the fact that the cutting elements 40 may be confined at least partially inside the outer surface of the body 32 of the drill bit 30 allows drilling the hole 28 using the drill bit 32 and drill rod 36 assembly having the rock bolt 14 mounted on the drill bit 32 and drill rod 36 assembly. The reason for this is that the extraction of the drill bit 30 and the drill rod 36 from the hole 28 can be conducted through the rock bolt 14 without the rock bolt 14 exiting hole 28. After the drill bit 32 and the drill rod 36 has been extracted from the hole 28 the rock bolt 14 is maintained within the hole 28. [0042] The at least one cutting element 40 is slideably located within the opening such that the at least one cutting element 40 is biased towards the contracted condition. In this manner, the at least one cutting element 40 is in the contracted condition unless a force is applied to the at least one cutting element 40 for displacement of the at least one cutting element 40 from the contracted condition to the extended condition. [0043] In the arrangement shown in the figures, the cutting elements 40 are of tapered configuration. The fact that the cutting elements 40 are of tapered configuration is particularly advantageous because it impedes the cutting elements 40 from exiting the aperture 50 during displacement of the cutting elements 40 from the contracted condition to the extended condition. [0044] Referring to now figure 5, the body 32 of the drill bit 32 is a hollow body including an internal thread 50. The internal thread 51 allows releasably attaching the drill rod 36 to the drill bit 30. For this, the proximal end 44 of the body 32 comprises an aperture 52 adapted to receive the drill rod 36. [0045] The drill rod 36 comprises a distal end 54 and a proximal end 56 (see figure 8 or 9). The distal end 54 comprises an exterior threaded circumference 58. The exterior threaded circumference 58 is a counterpart thread with respect to the thread of the inner surface of the drill bit 32. This allows releasable attaching the drill rod 36 to the drill bit 30. [0046] Referring now to figure 6, the drill rod 36 is releasably attached to the drill bit 32 by screwing the drill 36 into the aperture 52 of the proximal end 44 of the drill bit 30.

Prior to drilling of the hole 28 in the rock formation the drill rod 36 is screwed into the drill bit 30 such that the distal end 54 of the drill rod 36 enters in contact with the cutting elements 40 (see figure 7) and pushes the cutting elements 40 out of the top portion 46 of the drill bit 30. The drill rod 36 is screwed into the drill bit 32 until the cutting elements 40 are in the extended condition and the drill rod 36 is secured within the body 32 of the drill bit 32 to allow transferring the rotary and percussive movement of the drill rod 36 to the drill bit 32 (see figure 7). At this stage, installation of the rock bolt may commence. [0047] The drill rod 36 comprises a flange 60. The flange 60 is located such that the rock bolt 14 abuts the flange 60 when the rock bolt 46 is mounted on the drill rod 36. The flange 60 transfers the percussive movement of the drill rod 36 to the rock bolt 14. In an arrangement, a spacer may be located between the flange 60 and the rock bolt 14. The presence of the spacer impedes that the rotary movement of the drill rod 36 be transferred to the rock bolt 14. [0048] As mentioned before, for installing the rock bolt 14 into the rock formation, the rock bolt 14 is mounted on the drill bit 30 and drill rod 36 assembly. Mounting of the rock bolt 14 onto the drill bit 30 and drill rod 36 assembly is accomplished prior to locating the cutting elements 40 in the extended condition. Thus, the rock bolt 40 is mounted on the drill bit 30 and drill rod 36 assembly prior securing the drill rod 36 to the body 32 of the drill bit 30. For example, the rock bolt 14 may be mounted on the drill bit 30 and drill rod 36 assembly when the drill rod 36 is partially mounted in the drill bit 30 and the cutting elements 40 are still in the contracted condition. (see figure 6). This allows the drill bit 30 together with the drill rod 36 to slide into the rock bolt 14 without being obstructed by the cutting elements 40. [0049] After having mounted the rock bolt 14 onto the drill bit 30 and drill rod 36 assembly, the drill rod 36 is secured within the body 32 of the drill bit 30 by screwing the distal end 54 of the drill rod 36 further into the body 32 such that the cutting elements 40 are displaced from the contracted condition to the extended condition. [0050] After having placed the cutting elements 40 in the extended condition, the drill bit 30 and drill rod 36 assembly is delivered to the location of the rock formation where the rock bolt 36 is to be installed. At the location, the hole 28 is drilled using the drill bit 30 and drill rod 36 assembly having the rock bolt 14 mounted thereon (see figure 9). The hole 28 is drilled to a depth such that the rock bolt 14 is fully confined within the hole 28 (see figure 1). After the hole 28 is drilled to the desired depth, the drill bit 30 and drill rod 36 assembly is extracted from the hole 28, by the sliding the drill bit 30 and drill rod 36 assembly through the rock bolt 14. Extraction of the drill bit 30 and drill rod 36 assembly through the rock bolt 14 is accomplished by initially displacing the cutting elements 40 from the extended condition to the contracted condition. Displacement of the cutting elements 40 to the contracted condition is accomplished by unscrewing at least partially the drill rod 36 from the body 32 of the drill bit 30. By unscrewing at least partially the drill rod 36 from the drill bit 30, the cutting elements 40 return to the contracted condition. This is because the distal end 54 of the drill rod 36 provides support for maintaining the cutting elements in the extended condition (see figure 7). The cutting elements 40 return to the contracted condition as the drill rod 36 is unscrewed from the drill bit 30 such that the distal end 54 of the drill rod 36 distances itself from the top portion 46 of the drill bit 32 (see figure 6). [0051] It is evident that the drill bit in accordance with present embodiment of the invention is particularly useful for installing a rock bolt 14 into a rock formation. As mentioned before, drill bit 30 and the drill rod 36 assembly may be extracted from the hole 28 through the rock bolt 14 such that the rock bolt 14 stays within the hole 28 while the drill bit 32 and the drill rod 36 is extracted from the hole 28. Thus, the rock bolt 14 may be installed in a single step process. [0052] Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention. [0053] Further, it should be appreciated that the scope of the invention is not limited to the scope of the embodiment disclosed. For example, the cutting elements may be cutting elements that are adapted to change its configuration such as to change the cutting elements from the contracted condition to the extended condition and vice versa. [0054] Throughout this 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 (28)

1. A drill bit comprising a body having an outer surface, and at least one cutting element attached to the outer surface, wherein the cutting element is adapted for selective displacement between an extended condition and a contracted condition.

2. A drill bit according to claim 1 wherein the cutting element is adapted such that at least a portion of the cutting element protrudes from the outer surface to locate the cutting element in the extended condition and wherein the cutting element is adapted such that the cutting element is substantially flush in relation to the outer surface of the body to locate the cutting element in the extended condition.

3. A drill bit according to claims I or 2 wherein the body of the drill bit comprises an opening adapted to slideably receive the cutting element, the cutting element being slideably attached within the opening to allow displacement of at least a portion of the cutting element out of the opening to locate the cutting element in the extended condition and to allow displacement of at least the portion of the cutting element into the opening to locate the cutting element in the extended condition.

4. A drill bit according to any one of the preceding claims wherein the cutting element is slideably located within the opening such that the cutting element is biased towards the contracted condition.

5. A drill bit according to any one of the preceding claims wherein the cutting element comprises an inner end and an exterior end, at least a portion of the exterior end protruding from the exterior surface when the cutting element is located in the extended condition and the inner end being adapted for receiving a force for displacing the cutting element from the contracted condition to the extended condition.

6. A drill bit according to any one of the preceding claims wherein the cutting element is tapered.

7. A drill bit according to any one of the preceding claims wherein the body of the drill bit comprises a hollow body defining an inner portion adapted to receive a distal end of a drill rod.

8. A drill bit according to claim 7 wherein the opening incorporating the cutting element traverses the body of the drill bit such as to define a passage extending from the inner portion of the hollow body to the outer surface of the body of the drill bit, the cutting element extending through the passage such that the inner end of the cutting element is located at least partially within the inner portion of the hollow body when the cutting element is in the contracted condition.

9. A drill bit according to claim 8 wherein the distal end of the drill rod is adapted to engage the inner end of the cutting element to apply a force to the cutting element for displacing the cutting element from the contracted condition to the extended condition.

10. A drill bit according to any one of claims 7 to 9 wherein the drill rod is releasable attached to the drill bit.

11. A drill bit according to claim 10 wherein the drill rod comprises a threaded outer surface and the inner portion of the body of the drill bit comprises an inner threaded inner surface allowing screwing of the drill rod into the hollow body of the drill bit.

12. A drill bit according to claim 11 wherein the drill rod is adapted to screw into the hollow body of the drill bit to apply the force to the inner end of the cutting element in order to displace the cutting element from the contracted condition to the extended condition during screwing of the drill rod into the hollow body of the drill bit.

13. A drill bit according to claims 11 or 12 wherein the drill rod is adapted to be unscrewed at least partially from the body of the drill bit to remove the force applied to the inner end of the cutting element to displace the cutting element from the extended condition to the contracted condition.

14. A drill bit according to any one of the preceding claims wherein the drill bit comprises a plurality of cutting elements.

15. A drill bit according to claim 14 wherein the plurality of cutting elements are arranged around the periphery of the body of the drill bit in a spaced apart relationship with respect to each other.

16. A drill bit according to any one of the preceding claims wherein the body of the drill bit comprises an upper end and a lower end, the upper end comprising the at least one cutting element and the lower end comprising an aperture to allow access of the drill rod into the body of the drill bit.

17. A drilling tool comprising a drill bit and drive means for transferring rotary and/or percussive movement to the drill bit, the drill bit comprising a body having an outer surface, and a cutting element attached to the outer surface, wherein the cutting element is adapted for selective displacement between an extended condition and a contracted condition.

18. A drilling tool according to claim 17 wherein the drive means comprise a drill rod adapted to be attached to the drill bit.

19. A drilling tool according to claim 18 wherein the drill rod is adapted to receive a rock bolt.

20. A drilling tool according to claim 19 wherein the drill rod comprises a flange adapted to abut the rock bolt for transferring the percussive movement of the drill rod to the rock bolt.

21. A drilling tool according to claim 20 wherein the drill rod comprises a spacer located between the flange and the rock bolt to avoid transference of the rotary movement of the drill rod to the rock bolt.

22. A drill adapted to receive a drilling tool comprising a drill bit and drive means for transferring rotary and/or percussive movement of the drill to the drill bit, the drill bit comprising a body having an outer surface, and cutting element attached to the outer surface, wherein the cutting element is adapted for selectively displacement between an extended condition and a contracted condition.

23. A method for installing a rock bolt in a rock formation, the method comprises the step of: mounting the rock bolt on a drilling tool in accordance with claim 17; displacing the at least one cutting element of the drill bit from an contracted condition to an extended condition; drilling a hole in the rock formation using the drilling tool to allow the rock bolt to enter the hole; displacing the at least one cutting element of the drill bit from the extended condition to the contracted condition; retrieving the cutting tool from the hole to leave the rock bolt in the hole.

24. A method according to claim 23 wherein the step of displacing the at least one cutting element of the drill bit from the contracted condition to the extended condition comprises the step of screwing a drill rod into the drill bit to apply a force to the cutting element to displace the cutting element from the contracted condition to the expanded condition.

25. A method according to claims 23 or 24 wherein the step of displacing of the at least one cutting element of the drill bit from the extended condition to the contracted condition comprises the step of unscrewing a drill rod at least partially from the drill bit to release at least partially a force applied to the cutting element which maintains the cutting element in the extended condition in order to displace the cutting element from the extended condition to the contracted condition.

26. A drill bit as herein described with reference to the figures of the accompanying drawings.

27. A drilling tool as herein described with reference to the figures of the accompanying drawings.

28. A method as herein described with reference to the figures of the accompanying drawings.