FIELD OF THE INVENTION

The invention relates to a drill bit meant for drilling into a ground or rock.

BACKGROUND OF THE INVENTION

A drill bit meant for drilling into a ground or rock, either in vertical direction or a horizontal direction, or in any direction between the vertical direction and the horizontal direction, comprises a shank forming a body of the drill bit and a drill head.

In a drill bit the shank and the drill head form one uniform part. Because of the drill head being the part of the drill bit that substantially first meets the material which it is drilled into, the drill head wears out faster than the shank of the drill bit. Because of the uniform structure of the drill bit, the drill bit must be discarded even if the shank of the drill bit would still be operational.

In another drill bit the shank and the drill head are separate parts that are detachably fastened to each other, whereby a worn-out drill head may be replaced with a new one to provide an operational drill bit with reusable shank of the drill bit. The drill bit like this is economical because of the reutilization of the shank of the drill bit. A problem with the drill bit like this is, however, a decoupling of the drill head from the shank because of the dill head having become rammed very tightly to the shank during the drilling operation.

BRIEF DESCRIPTION OF THE INVENTION

An object of the present invention is to provide a novel drill bit comprising a shank and a drill head as well as a novel method for aiding the detachment of the drill head from the shank.

The invention is characterized by the features of the independent claims.

The invention is based on the idea of supplying pressurized detaching medium flow into the volume of the drill bit comprising the fastening means for fastening the shank and the drill head to each other, therefore intended to cause a pressure effect directed to the fastening means for aiding the detachment of the drill head from the shank.

During drilling the fastening means fastening the shank and the drill head of the drill bit to each other may become rammed very tightly. The disclosed solution causes the contact between the fastening means to loosen, thereby aiding the detachment or releasing of the drill head from the shank.

Some embodiments of the invention are presented in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in greater detail by means of preferred embodiments with reference to the accompanying drawings, in which

Figure 1 shows schematically an exploded view of a drill bit;

Figure 2 shows schematically a side view of a first shank and a first drill head;

Figure 3 shows schematically a side view of the shank and the drill head of Figure 2 in cross-section;

Figure 4 shows schematically a side view of the shank and the drill head of Figures 2 and 3 in cross section and separated from each other;

Figure 5 shows schematically a side view of a second shank and a second drill head in cross-section; and

Figure 6 shows schematically a side view of a third shank and a third drill head in cross-section; and

Figure 7 shows schematically a side view of a fourth shank and a fourth drill head in cross-section.

For the sake of clarity, the figures show some embodiments of the invention in a simplified manner. Like reference signs identify like elements in the figures.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 shows schematically an exploded view of a drill bit 1 meant for drilling into a ground. Figure 1 and the drill bit 1 shown therein refers to a drilling application, wherein the drill bit 1 is arranged to pull with it an impact shoe 40 and a protective casing 50 into a hole being drilled as the drilling is proceeding. The protective casing 50 may be used when ramming pipe piles, for example. The protective casing 50 may also be used, for example, to support the walls of a hole drilled in a soft ground so that the hole walls do not collapse inside the hole being drilled. The protective casing 50 may also be used as an installation channel, for example, for wires, pipes, cables etc. to be placed underground.

The drill bit 1 of Figure 1 comprises a shank 10, a pilot bit 20 and a ring bit 30. The pilot bit 20 forms or provides a drill head of the drill bit 1 of Figure 1. The shank 10 and the pilot bit 20 are detachably fastened to each other by a screw joint, as discussed in more detail later. The ring bit 30 is, in turn, detachably fastened to the pilot bit 20. The casing 50 and the impact shoe 40 to be fastened to the casing 50 do not form part of the drill bit 1.

The shank 10 forms or provides a body or a stem of the drill bit 1, by means of which the drill bit 1 may be connected to a drill rod of a drilling device. For reasons of clarity, the figures do not show said drilling device or drill rod. The drilling device may comprise a rotating device to rotate the drill rod and a pushing device to push the drill rod forward, whereby the drill rod is adapted to transmit the rotational movement of the rotating device to the drill bit 1 for the purpose of rotating the drill bit 1 around its centre axis as well as a force to push the drill bit 1 forward. The drilling device may also comprise a percussion device to direct a percussive motion to the drill rod, whereby the drill rod is adapted to transmit to the drill bit 1 the rotational movement of the rotating device for the purpose of rotating the drill bit 1, the force pushing the drill bit 1 against the ground or rock being drilled, and the percussive motion of the percussion device to strike the drill bit 1 against the ground or rock being drilled. Alternatively, if a down-the-hole drilling is applied, the percussion device is arranged to direct the percussive motion straight to the shank 10 of the drill bit 1.

In the drilling application referred to in Figure 1, the impact shoe 40 is fastened, typically by welding, to the casing 50, and the pilot bit 20 is arranged into contact with the impact shoe 40 through the casing 50 so that the drill bit 1 pulls the casing 50 into the hole being drilled as the drilling is proceeding. The ring bit 30, however, remains outside the casing 50 to allow the drilling of a hole with a sufficient large diameter to receive the casing 50. Because of the ring bit 30 remaining outside the casing 50, in vertical drilling the ring bit 30 will leave in place at the bottom of the drilled hole at the end of the casing 50 when the shank 10 and the pilot bit 20 are pulled out of the drilled hole so that the casing 50 is left in place in the drilled hole. In horizontal drilling, in turn, the ring bit 30 may be retrieved if the said end of the casing 50 becomes visible, as it takes place when drilling through a bench, for instance.

In another embodiment of the drill bit to be applied in the drilling application referred to in Figure 1 and wherein the solution disclosed herein may also be applied, the ring bit 30 may be omitted and the pilot 20 may be arranged to comprise one or more reamer blade wings which are arranged, when the drill bit is rotated in the intended drilling direction, to move outwards and extend past the largest outer diameter of the pilot bit 20 to enlarge the hole being drilled, and as the drill bit is rotated in the opposite direction, to return back inside the largest outer diameter of the pilot bit 20 in order to allow a pull of the shank 10 and the pilot bit 20 out from the drilled hole. In this drill bit the reamer blade wings thus provide the effect of the omitted ring bit 30.

The solution disclosed herein may also be applied in other type of drill bits, i.e., in drill bits applied in drilling applications, wherein the hole is to be drilled into the ground or rock without any intent to install the protective casing 50 into the drilled hole. The drill bits for this purpose typically comprise only the shank 10 and an appropriate drill head, which for example in rock drilling applications are different kind of rock drill heads.

Figure 2 shows schematically a side view of a first shank 10 and a first pilot bit 20, Figure 3 shows schematically a side view of the shank 10 and the pilot bit 20 of Figure 2 in cross-section along the cross-section line A - A shown in Figure 2, and Figure 4 shows schematically a side view of the shank 10 and the pilot bit 20 of Figures 2 and 3 separated from each other and in cross section along the crosssection line A - A shown in Figure 2. The cross-sectional lineation is omitted in Figures 2, 3 and 4 for the sake of clarity.

The shank 10 comprises a first end 10a to be directed towards a drill rod or the percussion device of the drilling device, i.e., away from the pilot bit 20, and a second end 10b directed towards the pilot bit 20. A direction between the first end 10a and the second end 10b forms an axial direction of the shank 10. Between the first end 10a and the second end 10b there is a side 10c of the shank 10, which determines a periphery or an outer circumference of the shank 10.

On the periphery of the shank 10, in a vicinity of the second end 10b of the shank 10, there is an external thread 11 extending along the periphery of the shank 10. The external thread 11 forms or provides one kind of fastening means in the shank 10 to fasten the shank 10 detachably to the pilot bit 20. The external thread 11 extends at a portion of the side 10c of the shank 10 from a point at a distance from the second end 10b of the shank 10 towards the first end 10a of the shank 10. Alternatively, the external thread 11 could also extend from the second end 10b of the shank 10 towards the first end 10a of the shank 10. The external thread 11 extends towards the first end 10a of the shank 10 substantially up to a shoulder 12 formed on the side 10c of the shank 10 at a distance from the second end 10b of the shank 10. In the embodiment of Figures 2 to 4, the shoulder 12 has a form of a bevelled shoulder, having a sloping contact surface 12a at least partly facing towards the second end 10b of the shank 10. The contact surface 12a may also be a straight horizontal surface in case of the shoulder 12 being straight. The shank 10 may also be implemented without any shoulder 12.

The shank 10 further comprises, substantially at its centre axis C, an internal flushing medium channel 13 extending through the shank 10 from the first end 10a of the shank 10 up to the second end 10b of the shank 10 substantially in the axial direction of the shank 10. Through the flushing medium channel 13 flushing medium, such as air or water, may be supplied to the drill bit 1 from the drilling device, the purpose of the flushing medium being to carry drilling waste away from the hole being drilled.

The pilot bit 20 comprises a first end 20a to be directed towards the shank 10, i.e., away from the hole to be drilled, and a second end 20b directed away from the shank 10, i.e., towards the hole to be drilled, the second end 20b of the pilot bit 20 forming or providing a face of the pilot bit 20. A direction between the first end 20a and the second end 20b forms an axial direction of the pilot bit 20. Between the first end 20a and the second end 20b there is a side 20c of the pilot bit 20, which determines a periphery or an outer circumference of the pilot bit 20.

On the periphery of the pilot bit 20 there are stroke shoulders 21 that impact on the impact shoe 40 during drilling, thereby causing the drill bit 1 to pull the casing 50 into the hole being drilled. The projections 21 may also be omitted if the pulling of the casing 50 into the hole being drilled is implemented by some other means.

At the second end 20b of the pilot bit 20, on the side of the pilot bit 20, there are a number of grooves 22 and projections 23 that form means for fastening the ring bit 30 to the pilot bit 20 releasably. The grooves 22 and the projections 23 may fasten the ring bit 30 to the pilot bit 20 both in the axial direction and the direction of the rotation of the pilot bit 20. Alternatively, the grooves 22 and the projections 23 may fasten the ring bit 30 to the pilot bit 20 only in the direction of the rotation of the pilot bit 20.

The pilot bit 20 further comprises a substantially cylindrical recess 24 extending from the first end 20a of the pilot bit 20 towards the second end 20b of the pilot bit 20 up to a distance from the second end 20b of the pilot bit 20, the cylindrical recess 24 having a closed bottom surface 24a. A centre axis C of the pilot bit 20, that being also a centre axis of the recess 24, will substantially unite with the centre axis C of the shank 10 when the shank 10 and the pilot bit 20 are fastened to each other. The purpose of the recess 24 is to receive a part of the shank 10, as is described in more detail below, for fastening the pilot bit 20 to the shank 10. A rim 25 surrounding the recess 24 comprises at the first end of the pilot bit a sloping contact surface 25a at least partly facing towards the first end 20a of the pilot bit 20. An angle of the contact surface 25a of the rim 25 in the pilot bit 20 is preferably formed such that the contact surface 25a of the rim 25 in the pilot bit 20 can provide a mating surface for the contact surface 12a of the shoulder 12 in the shank 10 when the shank 10 and the pilot bit 20 are fastened to each other. The contact surface 25a in the pilot bit 20 is, naturally, straight in case of the shoulder 12 in the shank 10 being straight.

On an inner circle of the recess 24, there is an internal thread 26 extending along the inner circle of the recess 24, the internal thread 26 corresponding to the external thread 11 in the shank 10. The internal thread 26 forms or provides one kind of fastening means in the pilot bit 20 to fasten the pilot bit 20 detachably to the shank 10. The internal thread 26 extends, at a portion of the inner circle of the recess 24, from a point at a distance from the first end 20a of the pilot bit 20 towards the bottom surface 24a of the recess 24, i.e., towards the second end 20b of the pilot bit 20. Alternatively, the internal thread 26 could also extend from the first end 20a of the pilot bit 20 towards the bottom surface 24a of the recess 24. The internal thread 26 extends towards the bottom surface 24a of the recess 24 up to a point at a distance from the bottom surface 24a of the recess 24 towards the first end 20a of the pilot bit 20. Alternatively, the internal thread 26 could also extend from the first end 20a of the pilot bit 20 up to the bottom surface 24a of the recess 24.

The pilot bit 20 further comprises, substantially at its centre axis C, a flushing medium channel 27 extending from the bottom surface 24a of the recess 24 towards the second end 20b of the pilot bit 20. When the shank 10 and the pilot bit 20 are fastened to each other, the flushing medium channel 1 in the pilot bit 20 substantially unites with the flushing medium channel 13 in the shank 10.

According to an embodiment of the pilot bit 20 disclosed in Figures 2 to 4, the flushing medium channel 27 in the pilot bit 20 extends in the pilot bit 20 up to a point at a distance from the second end 20b of the pilot bit 20 towards the first end 20a of the pilot bit 20. The second end 20b of the pilot bit 20 may then comprise flushing connections, not shown in the figures for reasons of clarity, extending towards the periphery of the pilot bit 20 for removing drilling waste from the front of the pilot bit 20 towards the periphery of the pilot bit 20. Additionally, or alternatively, the flushing medium channel 1 in the pilot bit 20 may extend up to the second end 20b of the pilot bit 20, or the pilot bit 20 may comprise one or more flushing connections extending from the flushing medium channel 1 up to the second end 20b of the pilot bit 20. The drilling waste removed from the front of the pilot bit 20 flows backwards in the hole past the pilot bit 20 via flushing grooves 28 remaining between the projections 21 on the side 20c in the drill bit 20.

The drill bit 1 is assembled by setting the second end 10b of the shank 10 at the recess 24 in the pilot bit 20 and turning the shank 10 and the pilot bit 20 relative to each other into a direction causing the external thread 11 in the shank 10 to turn into contact with the internal thread 26 in the pilot bit 20. The portion of the shank 10 comprising the external thread 11 and a depth of the recess 24 in the pilot bit 20 are preferably dimensioned so that when the drill bit 1 is assembled, the second end 10b of the shank 10 does not meet the bottom 24a of the recess 24 but the contact surface 12a of the shoulder 12 in the shank 10 will meet the contact surface 25a of the rim 25 in the pilot bit 20, whereby an impact directed to the shank 10 by the percussion device will go forward to the pilot bit 20 through the mating contact surfaces 12a, 25a but not through the bottom surface 24a of the recess 24, thereby preventing possible damages in the bottom surface 24a of the recess 24 or in the face of the pilot bit 20. This provides that the forces affecting between the shank 10 and the pilot bit 20 are not directed only to the threaded portions in the shank 10 and the pilot bit 20, thereby preventing the threads 11, 26 being destroyed and allowing the detachment of the pilot bit 20 from the shank 10 for replacing the worn-out pilot bit 20 with a new one. The detachment of the pilot bit 20 from the shank 10 is provided by turning the shank 10 and the pilot bit 20 relative to each other into a direction causing the external thread 11 in the shank 10 to turn away from the contact with the internal thread 26 in the pilot bit 20.

The embodiment of Figures 2 to 4 further comprises in the pilot bit 20 at least one detaching medium flow channel 60 extending from the side 20c of the pilot bit 20, i.e., from the periphery of the pilot bit 20, up to the internal thread 26 in the recess 24 through a wall of the pilot bit 20 between the side 20c of the pilot bit 20 and the recess 24. The detaching medium flow channel 60 has a first end 60a at the side 20c of the pilot bit 20, i.e., at the periphery of the pilot bit 20, and a second end 60b at a threaded portion on the inner circle of the recess 24. Other implementations of the detaching medium flow channel 60 in the pilot bit 20 are also possible so that the first end 60a of the detaching medium flow channel 60 opens towards an exterior of the pilot bit 20. One example of this kind of alternative implementation of the detaching medium flow channel 60 in the pilot bit 20 is shown schematically in Figure 7, wherein at least one detaching medium flow channel 60 extends from the first end 20a of the pilot bit 20 up to the internal thread 26 in the recess 24 through a wall of the pilot bit 20 between the side 20c of the pilot bit 20 and the recess 24 in the pilot bit 20. The second end 60b of the detaching medium flow channel 60 opens towards the fastening means 11, 26 that fasten the pilot bit 20 to the shank 10. For the sake of clarity, the cross-sectional lineation is omitted in Figure 7.

During drilling the external thread 11 in the shank 10 and the internal thread 26 in the pilot bit 20 may become rammed very tightly. This may hamper the detachment of the pilot bit 20 from the shank 10. The detaching medium flow channel 60 allows a pressurized detaching medium flow to be supplied through the detaching medium flow channel 60 into a volume between the external thread 11 in the shank 10 and the internal thread 26 in the pilot bit 20. The flow of the pressurized detaching medium into the volume between the external thread 11 in the shank 10 and the internal thread 26 in the pilot bit 20 causes a pressure effect directed to, i.e. affecting to, the external thread 11 in the shank 10 and the internal thread 26 in the pilot bit 20, causing the external thread 11 in the shank 10 to contract and the internal thread 26 in the pilot bit 20 to expand, whereby a diameter of the threaded portion in the shank 10 decreases and a diameter of the threaded portion in the pilot bit 20 increases, thus causing the contact between the external thread 11 in the shank 10 and the internal thread 26 in the pilot bit 20 to loosen and thereby aiding the detachment or releasing of the pilot bit 20 from the shank 10.

Referring to the embodiment shown in Figure 3, the first end 60a of the flow channel 60 comprises a coupling arrangement 61, including for example a connector 62, for connecting an external pressure source 63, such as a pump, by an external flow channel 64, such as a hose, a pipe, or like, to the first end 60a of the flow channel 60 for supplying the flow of the pressurized detaching medium flow into the flow channel 60 from an external tank 65 or like reserved for the detaching medium. The pressure source 63 external to the drill bit 1, as well as the flow channel 64 and the tank 65 also external to the drill bit 1 are disclosed very schematically only in Figure 3. The tank 65 for the detaching medium may be integrated with the pressure source 63, as shown in Figure 3, or it may be external to the pressure source 63.

The pressure provided by the pressure source 63 causes the detaching medium to become pressurized and to flow through the external flow channel 64 into the flow channel 60 in the pilot bit 20 and further into the volume between the external thread 11 in the shank 10 and the internal thread 26 in the pilot bit 20, whereby the external thread 11 in the shank 10 will contract and the internal thread 26 in the pilot bit 20 will expand. The actual detachment of the pilot bit 20 from the shank 10, as provided by turning the shank 10 and the pilot bit 20 relative to each other into the direction that causes the external thread 11 in the shank 10 to turn away from the contact with the internal thread 26 in the pilot bit 20, may be implemented in a specific opening device or by utilizing a torque provided by the drilling device.

The medium to be used as a pressurized detaching medium may for example be oil, lubricating oil, or any other applicable liquid. Alternatively, the medium to be used as a pressurized detaching medium may for example be grease, lubricating grease, or any other applicable medium that has substantially high viscosity but is still running medium. A selection of the medium to be used may for example be based on shape and/or dimensions of the threads 11, 26, shape and/or dimensions pressurized medium flow channel 60 and/or connector 62, characteristics of the external pressure source 63 and/or characteristics of possible sealing between the shank 10 and the pilot bit 20.

The pressure level of the pressurized detaching medium to be applied into the volume between the external thread 11 in the shank 10 and the internal thread 24 in the pilot bit 20 may for example be 10 MPa or more. The applied pressure of the pressurized detaching medium may for example depend on elasticity of the material of the shank 10 and the pilot bit 20 or on torsional capacity of the device applied for detaching the pilot bit 20 from the shank 10. The said pressure effect for aiding the detachment of the drill head from the shank is directed to the fastening means when the drilling is not in progress.

The embodiment of Figures 2 to 4 may further comprise a sealing arranged between the shank 10 and the drill bit 20 for preventing a leakage of the pressurized detaching medium away from the contact with the fastening means between the pilot bit and the shank, thereby ensuring for its part the pressurized detaching medium to cause a pressure effect directed to the threads 11, 26 in the volume between the external thread 11 in the shank 10 and the internal thread 26 in the pilot bit 20 for aiding the detachment of the pilot bit 20 from the shank 10.

In the embodiment of Figures 2 to 4 there is a first gasket 71 between the contact surface 12a of the shoulder 12 in the shank 10 and the contact surface 25a of the rim 25 in the pilot bit 20.

In the embodiment of Figures 2 to 4 there is also a second gasket 72 between a non-threaded portion at the end of the external thread 11 next to the shoulder 12 in the shank 10 and a non-threaded portion at the end of the internal thread 26 next to the first end 20a of the pilot bit 20.

In the embodiment of Figures 2 to 4 there is also a third gasket 73 between a non-threaded portion at the end of the external thread 11 next to the second end 10b of the shank 10 and a non-threaded portion at the end of the internal thread 26 next to the bottom surface 24a of the recess 24 in the pilot bit 20.

In the embodiment of Figures 2 to 4 there is also a fourth gasket 74 between the second end 10b of the shank 10 and the bottom surface 24a of the recess 24 in the pilot bit 20.

In the embodiment of Figures 2 to 4 the sealing is thus arranged by a number of gaskets arranged between the shank 10 and the drill bit 20. In the event of a tightness of the assembly of the shank 10 and the pilot bit 20 provided by the mating surfaces in the shank 10 and the drill bit 20 being high enough, one or more of the gaskets 71, 72, 73, 74, or even all the gaskets 71, 72, 73, 74 may be omitted.

Figure 5 shows schematically a side view of an assembly of a second shank 10 and a second pilot bit 20 in cross-section. For the sake of clarity, the cross- sectional lineation is omitted in Figure 5.

The embodiment of Figure 5, as well as the embodiment of Figure 7, is substantially similar to the embodiment of Figures 2 to 4, the difference being that in the embodiment of Figure 5 and in the embodiment of Figure 7 the recess 24 in the pilot bit 20 extends in the axial direction of the pilot bit 20 through the pilot bit 20, i.e., from the first end 20a of the pilot bit 20 up to the second end 20b of the pilot bit 20. The shank 10 is, in turn, dimensioned so that the second end 10b of the shank 10 extends out of the recess 24 in the pilot bit 20. In response to that, the second end 10b of the shank 10 may then comprise flushing connection, not shown in the figures for reasons of clarity, extending towards the periphery of the shank 10 and/or towards the second end 10a of the shank 10 for removing drilling waste from the front of the shank 10. Furthermore, because of the shank 10 extending completely through the pilot bit 20, the fourth gasket 74 disclosed above is omitted. The detachment of the pilot bit 20 from the shank 10 by using the pressurized detaching medium flow is similar to that disclosed in the embodiment of Figures 2 to 4.

Figure 6 shows schematically a side view of an assembly of a third shank 10 and a third pilot bit 20 in cross-section. For the sake of clarity, the cross-sectional lineation is omitted in Figure 6.

The embodiment of Figure 6 is substantially similar to the embodiment of Figures 2 to 4, the difference being that in the embodiment of Figure 6 the detaching medium flow channel 60 is arranged in the shank 10 instead of the pilot bit 20.

In the embodiment of Figure 6 the detaching medium flow channel 60 extends from the flushing medium channel 13 of the shank 10 up to the external thread 11 in the shank 10 and has a first end 60a at the flushing medium channel 13 and a second end 60b at a threaded portion on the periphery of the shank 10. The first end 60a of the detaching medium flow channel 60 comprises a coupling arrangement 61, including for example a connector 62, for connecting through the flushing medium channel 13 an external pressure source 63 by an external flow channel 64 to the connector 62 at the first end 60a of the flow channel 60 for supplying the flow of the pressurized detaching medium flow into the flow channel 60 from an external tank 65 or like reserved for the detaching medium and further into the volume between the external thread 11 in the shank 10 and the internal thread 26 in the pilot bit 20 as discussed above in connection with the embodiment of Figures 2 to 4. Other implementations of the detaching medium flow channel 60 in the shank 10 are also possible.

The embodiment of Figure 6 thus discloses a drill bit comprising a shank, a drill head, and fastening means for detachably fastening the drill head to the shank, wherein the shank comprises at least one detaching medium flow channel extending up to the fastening means for supplying the at least one pressurized detaching medium flow to cause the pressure effect directed to the fastening means for aiding the detachment of the drill head from the shank.

In the embodiments above, the drill bit 1 comprises the detaching medium flow channel 60 either in the shank 10 or in the pilot bit 20 but alternatively, the drill bit may comprise at least one detaching medium flow channel 60 both in the shank 10 and in the pilot bit 20.

In the embodiments above, the drill bit 1 comprises a single detaching medium flow channel 60 either in the shank 10 or in the pilot bit 20 but alternatively, the drill bit may also comprise two or more detaching medium flow channels 60 in the shank 10 and/or in the pilot bit 20.

In the embodiments above, the fastening means for fastening the pilot bit to the shank detachably are implemented with compatible threads arranged in the pilot bit and the shank. Alternatively, the detachable fastening of the pilot bit to the shank could also be implemented with one or more bayonet attachment between the shank 10 and the pilot bit 20, or with a taper shank, whereby the pressurized detaching medium flow is arranged to direct the pressure effect to the re- spective attachment for aiding the detachment of the pilot bit 20 from the shank

10. Other types of fastening means are also possible.

It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.