Boring head and boring tool assembly

Abstract

A boring head (101) for securing a boring tool (102) to a rotatable tool holder, wherein the boring tool is intended for chip removal machining of a workpiece when the boring tool is rotated about an axis of rotation defining an axial direction (Z), the boring head comprising: - a main body (103) mounted to the rotatable tool holder; - a piston (104) for holding the boring tool, the piston being accommodated within a guiding cavity (105) of the main body and being movable in a radial direction (X) relative to the main body, wherein a circumferential surface of the piston comprises a flat face (106) extending parallel to the radial direction; - positioning means (110) for radial positioning of the piston within the guiding cavity; - combined orientation and fixation means (120) for orienting and fixing the piston relative to the main body, the combined orientation and fixation means comprising: o a blind sleeve fixedly mounted in the main body, a flexible end wall of the blind sleeve facing the flat face of the piston; and o a fixation screw configured for threaded engagement with the blind sleeve, wherein the combined orientation and fixation means are configured such that, when the fixation screw is tightened, the flexible end wall is pressed against the flat face of the piston, 20 thereby pressing the piston against the main body for simultaneous orientation and fixation of the piston relative to the main body.

Description

TECHNICAL FIELD

[0001] The present invention relates to the field of accessories for machine tools for boring operations. In particular, the present invention relates to a boring head for securing a boring tool to a rotatable tool holder, and to a boring tool assembly. The boring tool is intended for cutting a workpiece when the boring tool is rotated around an axis of rotation. In particular, but not exclusively, the workpiece can be a metal workpiece. The boring head and the boring tool assembly are particularly suitable for manufacturing precise holes with high tolerance requirements in terms of geometry and size of the hole. BACKGROUND

[0002] Boring heads allowing precise positioning of exchangeable boring tools for high-precision control of the cutting diameter are known, wherein the exchangeable boring tool is mounted on the boring head. Such boring heads can comprise a movable piston on which the boring tool is mounted, and a positioning device in the form of a micrometer screw. The positioning device is used to move the piston in order to adjust the cutting position of the boring tool, and thus the cutting diameter. After adjustment of the cutting position, the piston has to be fixed relative to the body of the boring head so that the stiffness of the boring head is not compromised during machining.

[0003] US 8 322 952 discloses a boring head of the above-mentioned type. The boring tool in the form of a blade holder and an exchangeable cutting blade has a contact flange which is intended to ensure the stiffness of the boring tool assembly by abutting a corresponding contact surface of the body of the boring head. It thus also orients the boring tool relative to the boring head. The boring head comprises a spring-loaded fastening device which is adapted to pull the blade holder towards the body before the boring head is positioned in the desired cutting position. The boring head further comprises an indirect fastening device for fixing the position of the piston. The boring head offers the possibility of adjusting the cutting diameter with high precision.

[0004] However, in order to meet the requirements for even narrower machining tolerances, an improved solution for fixing the boring tool in the desired cutting position with even higher precision is desirable. SUMMARY

[0005] It is a main object of the present invention to realize a boring head and a boring tool assembly which are at least in some respect improved relative to known boring heads and boring tool assemblies. In particular, it is an object of the present invention to provide a boring head and a boring tool assembly which allow precise positioning of the boring tool in the correct orientation for precision boring applications. It is a further object to realize a boring head and a boring tool assembly whose cutting diameter can be adjusted smoothly with little friction.

[0006] The at least main objects are achieved by a boring head according to claim 1 and a boring tool assembly according to claim 9.

[0007] According to a first aspect of the present application, there is provided a boring head for securing a boring tool to a rotatable tool holder, wherein the boring tool is intended for chip-removing machining of a workpiece when the boring tool is rotated about an axis of rotation defining an axial direction. The boring head comprises:

[0008] - a main body configured to be mounted to the rotatable tool holder;

[0009] - a piston for holding the boring tool, said piston being accommodated within a guiding cavity of the main body and being movable in a radial direction of the boring tool relative to the main body, wherein a circumferential surface of the piston comprises a flat surface extending parallel to the radial direction;

[0010] - positioning means for radial positioning of the piston within the guiding cavity;

[0011] - a combined orientation and securing means for orienting and securing the piston relative to the main body, the combined orientation and securing means comprising:

[0012] o a blind sleeve having an internal thread and being fixedly mounted in the main body such that a flexible end wall of the blind sleeve faces the flat surface of the piston, and

[0013] o a securing screw configured for threaded engagement with the blind sleeve,

[0014] wherein the combined orientation and securing means is configured such that, when the securing screw is tightened, the flexible end wall is pressed against the flat surface of the piston, thereby pressing the piston against the main body in order to simultaneously orient and secure the piston relative to the main body.

[0015] The proposed boring head uses only a combined orientation and fixation device to simultaneously orient and fix the piston in a desired position relative to the body, thereby also orienting and fixing the boring tool attached to the piston in a desired position relative to the body. Thus, a single device is provided for orienting and fixing the piston with or without the boring tool attached in a desired cutting position. This has the advantage that a non-overdetermined balanced system is achieved, by which a very fine adjustment of the cutting diameter can be achieved with a correctly and predictably oriented boring tool. Compared to boring heads in which separate devices are provided for the orientation and fixation of the piston and / or the boring tool, a boring head is achieved in which there is no risk of the orientation of the boring tool changing when the piston is fixed relative to the body. Furthermore, no direct contact between the surface of the boring tool and the respective surface of the body is required to correctly orient the boring tool in the cutting position, which direct contact could otherwise change the orientation of the boring tool. In particular for precision boring, the absence of such direct contact improves the cutting diameter resolution. For such applications, the cutting forces are typically small enough that the stiffness achieved between the boring tool and the body without direct contact is sufficient.

[0016] When the fastening screw of the combined orientation and fixation device is loosened, the pressure exerted by the flexible end wall on the flat face of the piston decreases. Thereby, the piston is allowed to slide within the guide cavity, but a minimum gap is provided between the piston on the one hand and the flexible end wall and the guide cavity on the other hand.

[0017] The term boring tool as used herein, the boring tool can be a solid boring tool which is monolithic, or more preferably, the boring tool can be a cartridge in which a replaceable cutting insert is mounted. In the latter case, no direct contact is present between the body on the one hand and the cutting insert and the cartridge on the other hand. Thus, the cartridge does not need to be in contact with the body of the boring head to achieve sufficient stiffness of the boring tool and the boring head.

[0018] The radial direction of the boring tool, and by definition also of the boring head, is perpendicular to the axial direction. By using a positioning device to position the piston radially within the guide cavity, the cutting diameter of the boring tool can thereby be adjusted. The positioning device can for example be in the form of a positioning screw, such as a micrometer screw. The radial positioning of the piston is thus understood as an adjustment of the position of the piston in the radial direction of the boring tool. The piston can typically extend with its central axis in the radial direction of the boring tool. The radial positioning of the piston thus corresponds to a translational movement of the piston along its own central axis.

[0019] The piston comprises a mounting interface for fixing the boring tool to the piston, for example by screw mounting.

[0020] In the body is provided a hole, for example a bore, for receiving a blind sleeve. The hole opens into a guide cavity in which a piston is accommodated. The blind sleeve has a flexible end wall which, when the blind sleeve is mounted in the hole, faces a flat face of the piston. By "flexible" is meant here elastically deformable, so that, when the tightening screw is loosened so that the pressure on the flexible end wall is removed, the flexible end wall springs back and no longer presses against the piston. Advantageously, the tightening screw can be a round head screw, i.e. have a round head, for pressing against the flexible end wall of the blind sleeve. Alternatively, the tightening screw can be a flat head screw, i.e. have a flat head, for pressing against the flexible end wall.

[0021] Optionally, the circumferential surface of the piston comprises a rounded surface portion opposite the flat face, which rounded surface portion is configured to press against a corresponding rounded surface of the guide cavity when the tightening screw is tightened. A rounded surface which can preferably have a constant radius of curvature ensures that the piston does not rotate within the guide cavity when the tightening screw is tightened. Thereby, the cutting diameter resolution can be improved.

[0022] Optionally, the guide cavity has a cylindrical shape, i.e. it has a circular cross section. The piston is preferably of substantially cylindrical shape, with a diameter which is slightly smaller than the guide cavity, and the flat face is provided in a circular recess in the piston. Thereby, a frictionless sliding within the guide cavity can be achieved when the tightening screw is loosened.

[0023] Optionally, the piston comprises a mounting interface for fixing the boring tool to the piston, wherein the mounting interface is provided at a front end of the piston, and wherein the positioning device is provided at an opposite rear end of the piston. The circumferential surface of the piston extends between the front end and the rear end of the piston. In this embodiment, the boring head can be referred to as a radial boring head, which is generally understood as a boring head which can be used for boring with a relatively large cutting diameter which is larger than the width of the boring head. During the boring operation, the boring head can thus be located within the boring hole being formed.

[0024] Optionally, the blind sleeve is glued to the body. The glue should be chosen so as to achieve a non-elastic fixation of the blind sleeve within the body, so as to ensure a correct orientation of the piston when the piston is fixed in the desired radial position of the boring tool using the combined orientation and fixation device.

[0025] Optionally, during the installation of the blind sleeve in the body, the blind sleeve is pivotably adjustable, i.e. the central axis of the blind sleeve is adjusted relative to the longitudinal axis of the bore in which the blind sleeve is installed. After the pivot adjustment, the central axis of the blind sleeve and the longitudinal axis of the bore can not be parallel. For example, when fixed, the central axis of the blind sleeve can deviate from the longitudinal axis of the bore by ± 2° or ± 1.5° or less. After the installation of the blind sleeve in the body, the blind sleeve can thus be adjusted in its exact orientation relative to the piston before the blind sleeve is finally fixed to the body. Manufacturing defects of the combined orientation and fixation device itself, the piston and / or the body can thus be compensated for, which would otherwise result in misalignment of the piston.

[0026] When correctly oriented after the pivot adjustment, the blind sleeve should be fixed in said correct orientation by, for example, gluing the blind sleeve to the body. To orient and fix the blind sleeve during the first assembly of the boring head, the blind sleeve is inserted into the bore of the body, glue is applied and the flexible end wall of the blind sleeve is faced towards the flat face of the piston. When the flexible end wall contacts the flat face of the piston, it will self-align with the flat face by the pivot adjustment of the blind sleeve. Thereafter, the glue dries, thereby irreversibly fixing the blind sleeve in its self-aligned position. Thereafter, when the boring head is to be used in a boring operation, the fixation screw is tightened in the blind sleeve by applying a tightening torque which is sufficient to firmly press the flexible end wall of the blind sleeve against the flat face of the piston. For example, a tightening torque can be applied which is about 5-15 times the tightening torque used to orient the blind sleeve during the first assembly. Thus, the piston is allowed to slide when the fixation screw is not pressing on the flexible end wall, but a minimum gap is provided between the piston on the one hand and the guide cavity and the flexible end wall on the other hand.

[0027] Optionally, the blind sleeve further comprises external threads which threadedly engage with the screw hole of the body, wherein one of the external threads of the blind sleeve and the internal threads of the screw hole has a thread depth which decreases in a direction towards the flexible end wall, i.e. in the inward direction of the screw hole. In this way, the blind sleeve is configured to allow for the pivot adjustment of the blind sleeve during the installation in the body as described above.

[0028] Optionally, the other one of the external threads of the blind sleeve and the internal threads of the screw hole has a constant thread depth. For the ease of manufacturing the components of the boring head, the screw hole of the body is preferably of constant thread depth, while the external threads of the blind sleeve have a thread depth which decreases towards the flexible end wall. This is advantageous for manufacturing, since the thread depth of the external threads is easier to control during thread machining.

[0029] According to a second aspect, there is provided a boring tool assembly comprising a boring head according to the first aspect and a boring tool configured to be mounted to the boring head. The advantages and advantageous embodiments of the boring tool assembly largely correspond to the advantages and advantageous embodiments of the boring head according to the first aspect, and will therefore not be described in detail. It should be understood that all embodiments of the boring head described in connection with the first aspect also apply to the boring tool assembly according to the second aspect, and vice versa.

[0030] Using the positioning device, the cutting diameter of the boring tool assembly can be adjusted within a cutting diameter range between a minimum cutting diameter and a maximum cutting diameter.

[0031] Optionally, the boring tool assembly is configured such that the boring tool, when mounted to the piston, can move within the cutting diameter range without contacting the body of the boring head. The piston with the mounted boring tool can thereby be moved in the radial direction of the boring tool between the minimum cutting diameter and the maximum cutting diameter without any friction between the boring tool and the body.

[0032] Optionally, the boring tool assembly is configured such that, when the boring tool is mounted to the piston and the piston is oriented and fixed using the combined orientation and fixation device, there is no contact between the boring tool and the body within the cutting diameter range. A clearance of e.g. at least 0.1-0.7 mm can be provided between the boring tool and the body. In this way, an overstatic orientation of the piston and the boring tool in any cutting position is avoided, since the orientation is only defined by the contact of the piston with the body and the flexible end wall of the blind sleeve, and not by any contact between the boring tool and the body.

[0033] Optionally, the boring tool comprises a blade holder configured to be removably mounted to the piston, and a cutting blade configured to be removably mounted to the blade holder. The cutting blade can be mounted to the blade holder e.g. by clamping the cutting blade to the blade holder or by threadably mounting the cutting blade to the blade holder. Alternatively, a one-piece boring tool can be used, i.e. a boring tool in which the cutting edge and the mounting interface for fixing the boring tool to the piston are provided in the same component.

[0034] Optionally, the boring tool is mounted at the front end of the piston, opposite the positioning device. In this embodiment, the boring tool assembly is configured as a so-called radial boring tool, in which the cutting diameter of the boring tool is larger than the width of the body of the boring head. During the boring operation, the boring head can thus be positioned inside the formed hole.

[0035] Further advantageous features and advantages of the present application will appear from the detailed description below. BRIEF DESCRIPTION OF DRAWINGS

[0036] Embodiments of the present application will be described below by way of example with reference to the accompanying drawings, in which:

[0037] Figure 1 is a perspective view showing a boring tool assembly according to an embodiment of the present application,

[0038] Figure 2 is a perspective view of a boring head according to an embodiment of the present application,

[0039] Figures 3a-3b is Figure 2 is a side view of a boring head with a boring tool mounted therein,

[0040] Figures 4a-4b shows a cross-section along the line IVa-IVa in Figure 3a and the line IVb-IVb in Figure 3b

[0041] Figure 4c is a detailed view of Figure 4b

[0042] Figure 4d is a detailed view of Figure 4a and

[0043] Figure 5 shows a cross-section along the line V-V in Figure 4a

[0044] The drawings are schematic and not necessarily to scale. Details can have been omitted for clarity. DETAILED DESCRIPTION

[0045] Figure 1 shows a rotatable tool holder 200, on which two boring tool assemblies 100, 100' according to embodiments of the present application are mounted. The rotatable tool holder 200 extends along a rotation axis A defining an axial direction Z, about which the tool holder 200 is rotatable in a direction R. The rotatable tool holder 200 has a rear end comprising an adapter 201 configured for mounting the rotatable tool holder 200 in, for example, a machine spindle, a drive sleeve, a chuck or a socket. At a front end of the rotatable tool holder 200, a bridge 202 is provided, on which the boring tool assemblies 100, 100' are in turn mounted. Each boring tool assembly 100, 100' comprises a boring head 101, 101' and a boring tool 102, 102'. The boring tools 102, 102' are intended for cutting machining of a workpiece when the rotatable tool holder 200 is rotated about the rotation axis A.

[0046] ​​​Of course, depending on the boring application, the rotatable tool holder 200 can have many different configurations. The bridge 202 can also have different configurations and dimensions depending on the desired cutting diameter and the intended boring application. Also, the boring tool assemblies 100, 100' can be identical or different, or only one boring tool assembly 100 can be provided and the counterbalance weight is mounted opposite the boring tool assembly. For example, if two boring tool assemblies are provided, one of the boring tool assemblies can be configured for rough boring (not shown) and the other boring tool assembly is configured for precision boring. Both tool assemblies 100, 100' shown here are intended for precision boring applications.

[0047] Reference is now made to Figures 2-5 a boring head 101 is shown in more detail. Figure 2 The boring head 101 is shown without a boring tool 102, whereas Figures 3a-5 The boring head 101 is shown with a boring tool 102 mounted.

[0048] The boring head 101 comprises a main body 103 configured to be mounted to the bridge 202 by means of a fastening member. The boring head 101 further comprises a piston 104 accommodated within a guide cavity 105 of the main body 103 and movable relative to the main body 103 in a radial direction X perpendicular to the axial direction Z. The piston 104 has a generally cylindrical shape with a central axis extending in the radial direction. The guide cavity 105 also has a cylindrical shape. A circumferential surface of the piston comprises a flat face 106 extending parallel to the radial direction X. The flat face 106 is provided on a circularly shaped recess of the piston 104.

[0049] A positioning device 110 in the form of a micrometer screw is provided for radial positioning of the piston 104 within the guide cavity 105, i.e. in the radial direction X. To achieve this radial positioning, the piston 104 is thus translated along its own central axis. The positioning device 110 is located at a rear end of the piston opposite a front end at which a mounting interface 111 is provided for securing the boring tool 102 to the piston by means of a fastening member. Using the positioning device 110, the cutting diameter of the boring tool assembly 100 can be adjusted within a cutting diameter range between Figure 3a and Figure 4a the minimum cutting diameter shown and Figure 3b and Figure 4b the maximum cutting diameter shown.

[0050] In the shown embodiment, the boring tool 102 comprises a replaceable cutting insert 112 and an insert holder 113 to which the cutting insert 112 is removably attached.

[0051] The boring head 101 further comprises a combined orientation and fixation device 120 for orienting and fixing the piston 104 relative to the body 103 by indirect fastening. The combined orientation and fixation device 120 comprises a blind sleeve 121 having an internal thread and fixedly mounted in a screw hole of the body 103 leading into the guiding cavity 105. A flexible end wall 122 of the blind sleeve 121 thus faces the flat face 106 of the piston 104 located in the guiding cavity 105. The combined orientation and fixation device 120 further comprises a fastening screw (not shown) configured for threadedly engaging the internal thread of the blind sleeve 121 so as to, when fully engaged, press against the flexible end wall 122. Thus, when the boring tool 102 is in the desired cutting position, the flexible end wall 122 is pressed against the flat face 106 of the piston 104 and the piston 104 is thus pressed against the body 103 so as to simultaneously orient and fix the piston 104 relative to the body 103.

[0052] Since the piston 104 has a substantially cylindrical shape, the circumferential surface of the piston 104 comprises a rounded surface portion opposite the flat face 106 which is pressed against a corresponding rounded surface of the guiding cavity 105 when the fastening screw is tightened. The piston 104 is thereby automatically aligned within the guiding cavity 105.

[0053] The blind sleeve 121 of the combined orientation and fixation device 120 is fixed to the body 103 so as to always ensure correct orientation of the piston 104 and the boring tool 102 mounted to the piston 104 in all possible cutting positions and so as to provide a minimum clearance between the piston 104 and the flexible end wall 122 allowing translational movement of the piston 104 whenever the fastening screw does not exert a pressure on the flexible end wall 122. In the shown embodiment, the blind sleeve 121 is mounted and fixed to the body 103 using a combination of thread engagement and glue. To this end, the blind sleeve 121 is provided with an external thread having a slightly conical shape, i.e. having a thread depth decreasing in a direction towards the flexible end wall 122. The screw hole in the body 103 has a constant thread depth so that, when the blind sleeve 121 is engaged in the screw hole, the blind sleeve 121 is allowed to pivot slightly in the screw hole. To fix the position of the blind sleeve 121 relative to the body 103 during first assembly of the boring head 101, the blind sleeve 121 is engaged with the screw hole of the body 103, e.g. by a fastening screw, so that the flexible end wall 122 is brought into contact and alignment with the flat face 106 of the piston 104 by the pivot adjustment of the blind sleeve 121. The glue applied between the external thread of the blind sleeve 121 and the internal thread of the screw hole of the body 103 dries and fixes the blind sleeve 121 and orients its central axis correctly relative to the flat face 106. Thus, in use, the blind sleeve 121 is firmly and irreversibly fixed to the body 103.

[0054] When the boring head is to be used for boring operations, the boring tool 102 is mounted to the mounting interface 111 of the piston 104. The tightening screw of the combined orientation and fixation device 120 is loosened, so that the piston 104 is allowed to slide in the radial direction X. Thereafter, the desired cutting diameter is set using the positioning device 110. Subsequently, the tightening screw is tightened to press against the flexible end wall 122 of the blind sleeve 121, whereby the piston 104 is locked / fixed at the set cutting diameter. Since a minimum gap is provided between the piston 104 and the flexible end wall 122, the orientation of the piston 104 does not change when the tightening screw is tightened.

[0055] The boring tool assembly 100 is configured such that the boring tool 102, when mounted to the piston 104, can move over the entire range of cutting diameters without contacting the body 103 of the boring head 101. A small gap is always provided between the boring tool 102 and the body 103. Furthermore, when the boring tool 102 is mounted to the piston 104 and the piston 104 is oriented and fixed using the combined orientation and fixation device 120, there is no contact between the boring tool 102 and the body 103 over the entire range of cutting diameters. This can be clearly seen in Figure 4d , Figure 4d is Figure 4a a detailed view showing the minimum cutting diameter in which the boring tool 102 only partly protrudes from the boring head 101. As can be seen, a small gap d is provided between the body 103 and the boring tool 102. Since a minimum gap is provided between the piston 104 and the flexible end wall 122 when the tightening screw of the combined orientation and fixation device 120 is not tightened, the gap d does not change significantly when the tightening screw is loosened / tightened.

[0056] The present invention is of course not limited to the embodiments disclosed but can be varied and modified within the scope of the appended claims. For example, the boring head and boring tool assembly can be configured for use with many different types of tool shanks and machine adapters. In other embodiments, the boring tool can be of the type that extends mainly in the axial direction of the boring tool, i.e. a so-called axial boring tool, instead of the radial boring tool described above. In such an axial boring tool, the cutting diameter of the boring tool is smaller than the width of the body of the boring head.

Claims

1. A boring head (101) for securing a boring tool (102) to a rotatable tool holder (200), wherein the boring tool (102) is intended for chip removal machining of a workpiece when the boring tool (102) is rotated about an axis of rotation (A) defining an axial direction (Z), the boring head (101) comprising: - a main body (103) configured to be mounted to the rotatable tool holder (200); - a piston (104) for holding the boring tool (102), the piston (104) being received within a guiding cavity (105) of the main body (103) and movable relative to the main body (103) in a radial direction (X) of the boring tool (102), wherein a circumferential surface of the piston (104) comprises a flat face (106) extending parallel to the radial direction (X); - a positioning device (110) for radial positioning of the piston (104) within the guiding cavity (105); - a combined orientation and fixation device (120) for orienting and fixing the piston (104) relative to the main body (103), the combined orientation and fixation device (120) comprising: o a blind sleeve (121) having an internal thread and fixedly mounted in the main body (103) such that a flexible end wall (122) of the blind sleeve (121) faces the flat face (106) of the piston (104), and o a tightening screw configured for thread engagement with the blind sleeve (121), wherein the combined orientation and fixation device (120) is configured such that, when the tightening screw is tightened, the flexible end wall (122) is pressed against the flat face (106) of the piston (104), thereby pressing the piston (104) against the main body (103) so as to simultaneously orient and fix the piston (104) relative to the main body (103), and the blind sleeve (121) further comprises an external thread threadedly engaging a screw hole of the main body (103), wherein one of the external thread of the blind sleeve (121) and the internal thread of the screw hole has a thread depth that decreases in a direction towards the flexible end wall (122).

2. The boring head of claim 1, wherein, The circumferential surface of the piston (104) comprises a rounded surface portion opposite the flat face (106), the rounded surface portion being configured to be pressed against a corresponding rounded surface of the guiding cavity (105) when the tightening screw is tightened.

3. The boring head of claim 1 or 2, wherein, The piston (104) comprises a mounting interface (111) for securing the boring tool (102) to the piston (104), wherein the mounting interface (111) is provided at a front end of the piston (104), and wherein the positioning device (110) is provided at an opposite rear end of the piston (104).

4. The boring head of any one of claims 1-2, wherein, The blind sleeve (121) is glued to the body (103).

5. The boring head of any one of claims 1-2, wherein, During mounting of the blind sleeve in the body (103), the blind sleeve (121) is pivotably adjustable.

6. The boring head of claim 1 wherein, The other one of the outer thread of the blind sleeve (121) and the inner thread of the screw hole has a constant thread depth.

7. The boring head of any one of claims 1-2, wherein, The guiding cavity (105) has a cylindrical shape.

8. A boring tool assembly (100) comprising a boring head (101) according to any one of the preceding claims, and a boring tool (102) mounted to the boring head (101).

9. A unit consisting of the boring tool assembly according to claim 8 and a rotatable tool holder (200), wherein The boring head is mounted to the rotatable tool holder (200), and wherein a cutting diameter of the boring tool assembly (100) is adjustable using the positioning device (110) within a cutting diameter range between a minimum cutting diameter and a maximum cutting diameter.

10. The unit of claim 9, wherein, The boring tool assembly is configured such that the boring tool (102) is movable within the cutting diameter range without contacting the body (103) of the boring head (101) when mounted to the piston (104).

11. The unit of claim 9 or 10, wherein, The boring tool assembly (100) is configured such that, when the boring tool (102) is mounted to the piston (104) and the piston (104) is oriented and fixed using the combined orientation and fixation device (120), there is no contact between the boring tool (102) and the body (103) within the cutting diameter range.

12. The unit of any of claims 9-10, wherein, The boring tool (102) comprises a blade holder (113) removably mounted to the piston (104) and a cutting blade (112) removably mounted to the blade holder (113).

13. The unit of any of claims 9-10, wherein, The boring tool (102) is mounted at a front end of the piston (104) opposite the positioning device (110).

Images