Boring head and boring tool assembly

Abstract

The invention relates to a boring head for holding a boring tool for metal cutting. The boring head includes a body including a support surface (25) and a graduation surface. The boring head further comprises a plunger (6) and a fine tuning screw (19), the plunger (6) comprising a boring tool interface for carrying the boring tool in a fixed manner, the plunger (6) being arranged in the body so as to be movable along a positioning axis (y). The fine adjustment screw (19) is arranged in the body and coupled to the plunger (6) such that when the fine adjustment screw (19) is rotated, the plunger (6) moves along the positioning axis to an extended or retracted position of a plurality of extended positions. The fine adjustment screw (19) comprises a head (21) which abuts against the support surface (25), and the head (21) comprises a radially outer head surface (26), the head surface (26) being provided with a first indexing mark (23). The scale surface is provided with a second indexing mark (29), and the second indexing mark (29) is aligned with the first indexing mark (23) so as to provide a reading of the axial position of the plunger (6). The scale surface is a convexly rounded beveled surface (28) at the head surface (26), the beveled surface (28) having an arcuate edge (32).

Description

Technical Field

[0001] The present invention relates to a boring head for holding a boring tool for metal cutting, and to a boring tool assembly including the boring head. Background Art

[0002] As is known, boring heads allow precise positioning of a replaceable boring tool mounted on the boring head in order to control the cutting diameter with high precision. Such boring heads may comprise a plunger on which the boring tool is mounted and a fine adjustment screw operable to move the plunger together with the mounted boring tool relative to the body of the boring head. By this, the cutting position of the cutting edge of the boring tool can be adjusted so as to vary the cutting diameter when the boring head is mounted on a rotatable spindle. A scale on the fine adjustment screw is aligned with a scale on the body to provide a reading of the cutting position. A problem with known boring heads of this type is that a free view of the scale is obstructed, making reading and thereby precise positioning difficult. Summary of the invention

[0003] The object of the present invention is to at least partially eliminate the above-mentioned problems. According to the invention, this object is achieved by means of a boring head according to claim 1 and a boring tool assembly according to claim 13 .

[0004] A boring head of the present invention for holding a boring tool for metal cutting comprises: a body extending along the positioning axis from an axially outer end to an axially inner end and comprising a support surface and a graduated surface, a plunger comprising a boring tool interface for carrying the boring tool in a fixed manner when the boring tool is held in the boring head, wherein the plunger is arranged in the body to be movable along the positioning axis into a retracted position axially inwards and into a plurality of advanced positions axially outwards from the retracted position, a fine adjustment screw arranged in the body and coupled to the plunger so that when the fine adjustment screw is rotated, the plunger moves along the positioning axis to one of the extended positions or the retracted position, in - the fine adjustment screw comprises a head which abuts against the support surface and comprises a radially outer head surface which is provided with first graduation markings, and - the graduated surface is provided with a second graduation mark which is aligned with the first graduation mark to provide a reading of the axial position of the plunger, Wherein the graduated surface is a convexly rounded beveled surface at the head surface, the beveled surface having an arcuate edge.

[0005] Therefore, the second graduation mark of the body is arranged on the surface shaped as a convex rounded bevel. In contrast, in commonly used known boring heads, the second graduation mark is arranged on a surface in the same plane as the support surface against which the head of the fine-tuning screw abuts, or in other words, on a surface perpendicular to the axis of the fine-tuning screw. In such known boring heads, the operator has to look along the axis of the fine-tuning screw to obtain an accurate reading. However, in many applications, this view is obstructed when the boring head is mounted in the machine, which is why the operator often needs to see the two scales from a certain angle. As a result, the graduation marks of the scale may be difficult to see, or the viewing angle introduces parallax errors.

[0006] Due to the bevel of the graduated surface of the invention, the graduation marks can be viewed vertically or nearly vertically, even if the viewing is from the side of the boring head rather than along the axis of the fine adjustment screw. Thereby, an unobstructed viewing is achieved, wherein parallax errors are avoided or at least reduced. Furthermore, due to the rounded shape of the beveled surface with arcuate edges at the head surface of the screw head, the second graduation mark is more accurately aligned against the angled section of the first graduation mark. Thus, a more accurate reading is achieved, thereby improving the positioning accuracy of the plunger and any boring tool with cutting edges retained therein compared to devices of the prior art.

[0007] The boring head and boring tool assembly of the present invention are intended to be used as an accessory of a machine tool (e.g., a CNC machine tool, i.e., a machine tool with computer numerical control) in a boring operation. Therein, the boring head is configured to hold a boring tool and fix the boring tool to a rotatable spindle. The boring tool is suitable for cutting a workpiece when the boring tool rotates around an axis of rotation. The workpiece can be particularly, but not exclusively, a metal workpiece. The boring head and the boring tool assembly are suitable for enlarging a prefabricated hole to a hole having a diameter greater than that of the prefabricated hole. The boring head is particularly suitable for producing enlarged holes with high requirements in terms of geometry and size. In addition, the boring head and the boring tool assembly of the present invention are particularly advantageous for small diameter holes, wherein the diameter of the enlarged finished hole is a maximum of 350 mm, preferably a maximum of 150 mm, and more preferably a maximum of 114 mm.

[0008] The boring tool may be a solid boring tool, wherein the cutting edge and the holder are in one piece, or more preferably, the boring tool may comprise an insert holder and a replaceable and optionally indexable cutting insert mounted to the insert holder.

[0009] The boring head comprises a body, preferably in the form of a housing for components of the boring head.

[0010] A plunger as a component of the boring head is arranged in the body to be movable along the positioning axis. The plunger is operable to move to a retracted position, which is the position furthest inwardly in the axial direction along the positioning axis. In addition, the plunger is operable to move axially outwardly from the retracted position to a plurality of extended positions. Preferably, the extended position can be selected from any position axially outwardly from the retracted position along the positioning axis to a maximum extended position.

[0011] The positioning axis defines an axial direction in the boring head and its components, wherein axially inward is the direction towards the retracted position of the plunger and axially outward is the direction axially opposite to the axially inward direction.

[0012] Preferably, the boring head is configured to be mountable to the spindle for rotating the boring head about an axis of rotation defining an axial direction x in the boring head and its components, wherein the direction x is perpendicular to the positioning axis. The boring tool assembly comprises a boring head and a boring tool, the boring tool being mounted in a boring tool interface of the plunger such that the boring tool is carried in a fixed manner by the plunger. Preferably, when the plunger is in the retracted position, the cutting edge of the boring tool is in a minimum cutting diameter position, and when the plunger is in a maximum forward position of said forward positions, the cutting edge of the boring tool is in a maximum cutting diameter position.

[0013] The plunger is preferably received in a guide cavity in the body so that when the plunger is operated to move along the positioning axis, the plunger slides along the guide cavity with minimal clearance. The plunger preferably extends along a longitudinal axis coinciding with the positioning axis, and the plunger may have any suitable cross-section, such as circular or shaped as a regular polygon, such as a square or rectangle.

[0014] The plunger comprises a boring tool interface, which for example comprises a base or a coupling half. The boring tool interface is adapted to cooperate with a complementary interface of a boring tool to fix the boring tool to the plunger. Preferably, the boring tool is fixed to the plunger in an immovable manner to prevent relative movement. In turn, the plunger carries the boring tool so that the boring tool moves with the plunger. Optionally, the boring head comprises screws and / or clamps for fixing the boring tool in the interface.

[0015] Preferably, the plunger extends along the positioning axis. When the boring tool is mounted in the boring tool interface of the plunger and is carried by the plunger in a fixed manner, at least the cutting edge is located outside the body. Optionally, the plunger or only the boring tool extends from the body through an opening in the body to expose the cutting edge.

[0016] According to one embodiment, the boring tool interface is configured to hold a boring tool having a longitudinal axis, wherein the longitudinal axis optionally extends perpendicular to the positioning axis, parallel to the positioning axis or coincident with the positioning axis. Correspondingly, the opening in the body for exposing the cutting edge may be an elongated slot or channel. Optionally, the boring tool interface is arranged at the axial end of the plunger, or at a distance from both axial ends.

[0017] The fine-tuning screw is another component of the boring head, which is arranged in the body and connected to the plunger. The fine-tuning screw comprises a head and preferably a shaft. The body comprises a support surface, which is, for example, a part of the outer surface of the housing or the surface of a component arranged in the housing, against which the head of the fine-tuning screw abuts. The fine-tuning screw is preferably connected to the plunger via the shaft. In order to convert the rotational movement of the fine-tuning screw into the translational movement of the plunger, the fine-tuning screw interacts directly or indirectly with the plunger when the head abuts against the support surface. To this end, the head preferably comprises an abutment surface facing toward the axis of the fine-tuning screw. The head abuts against the support surface with an abutment surface, wherein the abutment surface slides against the support surface when the fine-tuning screw rotates.

[0018] According to one embodiment, the fine adjustment screw is in threaded engagement with the plunger, for example by means of an external thread on the shaft of the fine adjustment screw engaging an internal thread in the bore of the plunger.

[0019] According to another embodiment, the fine adjustment screw interacts with the plunger via a coupling element, such as, for example, via a gear and a shaft placed in the body.

[0020] The direction of the fine-tuning screw depends on the coupling mode of the fine-tuning screw to the plunger and on the direction of the positioning axis. Preferably, the axis of the fine-tuning screw extends parallel to the positioning axis or coincident with the positioning axis. Thus, the fine-tuning screw can be directly coupled to the plunger without intermediate parts and impart a translational movement thereto, so that advantageously the movement of the plunger is more precise.

[0021] According to one embodiment, the support surface is located at the axially inner end of the body, facing axially inward and orthogonal to the positioning axis. Similarly, the abutment surface of the head faces axially outward and orthogonal to the positioning axis. Preferably, the fine adjustment screw engages the plunger at the axially inner end of the plunger, and the boring tool interface is located at the opposite end of the plunger that is axially outer. This is a simple design that enables high-precision positioning of the plunger when the fine adjustment screw is turned.

[0022] The head includes a radially outer head surface provided with a first graduation mark, and the body includes a graduated surface provided with a second graduation mark. The second graduation mark is aligned with the first graduation mark to provide a reading of the axial position of the plunger.

[0023] The graduated surface is a convexly rounded beveled surface at the head surface, the beveled surface having an arcuate edge. According to an embodiment, the head of the fine adjustment screw is located at a side surface of the body, preferably axially inside, and the graduated surface intersects the side surface as a bevel, wherein the arcuate edge forms an intersection line. In this embodiment, the support surface is close to the intersection line and is in the same plane as the side surface, or in a plane parallel to the side surface. Thus, the head with the radially outer head surface and the graduation marks is adjacent to the graduated surface.

[0024] The convexly rounded beveled surface curves outwardly relative to the interior of the body.

[0025] Preferably, the center of curvature of at least a portion of the arcuate edge is on the rotation axis of the fine adjustment screw, wherein the second graduation mark intersects the arcuate edge or is at an equal distance from the arcuate edge. Thus, the second graduation mark is also at the same distance from the preferably circular edge of the radially outer head surface and the first graduation mark thereon, so that these graduation marks are closely aligned. Due to this design, reliable readings can be obtained.

[0026] According to an embodiment, the second graduation marks are linear and parallel. For example, the first end of each second graduation mark is at the arcuate edge. The second graduation marks are preferably spaced at equal angular distances along the arcuate edge. Thus, advantageously, when viewed vertically toward an oblique angle, the second graduation marks are aligned with the head surface.

[0027] Preferably, the radially outer edge of the head surface has an arcuate shape corresponding to the arcuate edge of the convexly rounded beveled surface, for example a circle with the center of curvature on the rotation axis of the fine adjustment screw. Preferably, the first graduation marks on the head surface are linear, extend in the radial direction, and have equal angular intervals. Preferably, the first graduation marks intersect the edge of the head surface or are at an equal distance from the edge of the head surface.

[0028] According to a preferred embodiment, the first graduation mark 23 and the second graduation mark 29 form a vernier scale, wherein preferably, the first graduation mark is a main mark and the second graduation mark is a vernier mark. Other embodiments may have any suitable type of scale, or may have any suitable type of configuration of graduation marks. Optionally, the first graduation mark and / or the second graduation mark is a groove, a ridge or a colored line.

[0029] Preferably, the convexly rounded beveled surface extends axially outwards from the arcuate edge. This orientation of the beveled surface is suitable for a preferred embodiment in which the support surface is located at the axially inner end of the body, facing axially inwards and orthogonal to the positioning axis. The convexly rounded beveled surface is, for example, a portion of a curved lateral surface of a geometric body having a longitudinal axis, such as the radially outer side surface of a cylindrical segment or a segment of a truncated cone. According to an embodiment, the longitudinal axis extends axially outwards.

[0030] According to an embodiment, wherein the support surface is located at the axially inner end of the body, facing axially inwards and orthogonal to the positioning axis, the bevel surface forms an angle of at least 30° and at most 60°, preferably at least 40° and at most 50°, for example 45° with the positioning axis, as seen in a cross section containing the positioning axis and a center point between the first second graduation mark and the last second graduation mark. Thereby, a direct vertical viewing from a suitable angle is achieved. In embodiments wherein the convexly rounded bevel surface is curved around the longitudinal axis, this angle may be regarded as the angle between the longitudinal axis and the positioning axis.

[0031] The angular distance α of the center point between the first second graduation mark and the last second graduation mark from the axis extending in the direction x, as viewed along the positioning axis, ranges in value from 0° to 90°, preferably at least 30° and at most 70°. This is particularly advantageous when the boring head is mounted in a machine tool with a vertical spindle. In a machine tool with a vertical spindle, the operator is exposed to lubricants or coolants when viewing from below, which is why this arrangement allows viewing directly, perpendicularly, from an angle towards the graduation marks. In an embodiment with a rectangular body, the graduated surface is preferably beveled at a corner, i.e. at a corner of three side surfaces of the body, wherein the head of the fine adjustment screw is located at one of these side surfaces.

[0032] The head surface is at least a part of a top surface or a side surface (e.g. a cylindrical side surface) of the head. Preferably, the head surface is a lateral surface of a truncated cone, preferably a top surface of the head, which is preferably facing axially inwards. According to one embodiment, the cone angle is equal to the angle of the bevel surface. Thus, the graduation marks of the two surfaces can be seen approximately equally well from the same viewing angle.

[0033] The fine adjustment screw is configured to be rotatable by any suitable means, such as by a tool, such as a spanner or a key. Preferably, the head comprises a socket for an Allen key, which is a tool that also allows accessibility and rotation transfer in narrow spaces.

[0034] According to an embodiment in which the support surface is located at the axially inner end of the body, facing axially inwards and orthogonal to the positioning axis, the head comprises an axially outwardly facing abutment surface, wherein the head has an axial thickness from the abutment surface to the head surface at its outer radial edge. Furthermore, the support surface is arranged axially outwards at a distance from the arcuate edge, which distance is equal to the axial thickness. Thus, advantageously, the radially outer edge of the head surface can be arranged flush with the arcuate edge of the convexly rounded bevel surface, which improves the readability of the opposing graduation markings.

[0035] In addition to the boring head and the boring tool held by the boring head, an embodiment of the boring tool assembly also includes a bridge portion configured to be mounted to the spindle. The boring head is mounted on the bridge portion at the first axial end, wherein the positioning axis of the boring head defines the axial direction of the bridge portion. The tool assembly further includes a counterweight, which is mounted on the opposite second axial end of the bridge portion, wherein the head surface of the fine adjustment screw faces axially inward toward the counterweight. In this design, the counterweight blocks the viewing along the positioning axis, which is why the convex rounded bevel surface of the present invention is particularly advantageous. In an alternative embodiment, the tool assembly includes another boring head instead of a counterweight. The other boring head preferably has the same features as the boring head of the present invention, for example, the same as the boring head of the present invention. In other embodiments, the other boring head is a boring head of another type. Furthermore, the boring tools held by the various boring heads may be of the same or of different types, for example one of the boring tools is for fine boring and the other boring tool is for finishing. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In the following, example embodiments will be described in more detail with reference to the accompanying drawings, in which:

[0037] Figure 1 is a perspective view of a rotatable tool holder on which a tool assembly according to a first embodiment of the present invention is mounted;

[0038] Figure 2 is a perspective view of a boring head according to a first embodiment of the present invention;

[0039] Figure 2b is a view along the positioning axis of the boring head according to the first embodiment;

[0040] Figure 3a and 3b The boring head edge according to the first embodiment Figure 2b A view of line III-III in FIG.

[0041] Figure 4 The boring head edge according to the first embodiment Figure 3aA cross-sectional view along line IV-IV shown in FIG.

[0042] Figure 5 is a view of the main body and the mounting structure of the boring head according to the first embodiment along the positioning axis;

[0043] Figure 6 The main body and the mounting structure of the boring head according to the first embodiment are Figure 5 A cross-sectional view along line VI-VI in FIG.

[0044] Figure 7 is a perspective view of a main body and a mounting structure of a boring head according to a first embodiment.

[0045] All the figures are schematic, not necessarily to scale, and generally show only parts which are necessary in order to elucidate the various embodiments, while other parts may be omitted or merely suggested. Unless otherwise stated, the same reference numerals in the different figures refer to the same components. DETAILED DESCRIPTION

[0046] Figure 1 A rotatable tool holder 1 extending along a rotation axis x is shown. In the front end, viewed along the rotation axis x, a tool assembly 3 according to a first embodiment of the invention is mounted. The tool holder can be mounted on a spindle of a CNC machine tool by means of a machine interface in the form of a Capto coupling 4, which is arranged in the rear end, viewed along the rotation axis x.

[0047] The boring tool assembly 3 comprises a bridge 2 and two identical boring heads 5 according to a first embodiment of the invention attached to the bridge 2. Each boring head 5 holds a corresponding boring tool in the form of a blade holder 7 and a replaceable and indexable cutting blade 8, wherein the cutting blade 8 is mounted in the blade holder 7 by means of a mounting screw 15. Figure 1 In the embodiment, each boring head 5 with an associated boring tool is configured for right-hand rotation R. The boring tool is intended for cutting workpieces when the rotatable tool holder 1 is rotated about the rotation axis x in the direction R. In other embodiments, the boring head is configured for left-hand rotation.

[0048] According to another embodiment, the boring tool assembly 3 comprises a boring head 5 according to the first embodiment of the present invention and a counterweight replacing one of the boring heads in the first embodiment.

[0049] exist Figures 2 to 7, a boring head 5 according to a first embodiment is shown. The boring head 5 comprises a mounting structure 10 and a body in the form of a housing 9. In the first embodiment, the mounting structure 10 and the housing 9 are a one-piece integral component. The mounting structure 10 comprises an elongated slot 12 through which a fastening screw 13 can be inserted to attach the boring head 5 to the bridge 2, see Figure 1 Due to the elongated shape of the slot 12, the position of the boring head on the bridge 2 is adjustable. The housing 9 has the basic shape of a square cuboid. In other embodiments, the housing is rounded, for example cylindrical or spherical.

[0050] The plunger 6 is arranged in the housing 9 so as to be movable along the positioning axis y. Figure 3a In FIG. 1 , as seen along the positioning axis, the plunger 6 is shown in an axially inwardly retracted position and in FIG. Figure 3b In the embodiment of the present invention, the plunger 7 is in the first of a plurality of forward positions, wherein all of the forward positions are axially outward from the retracted position as seen along the positioning axis. The positioning axis y defines an axial direction y in the boring head 5, in its components and in the bridge 2 (when the boring head is mounted on the bridge 2). The plunger 6 is received in a guide cavity in the housing 9 so that when the plunger is operated to move along the positioning axis y, the plunger slides along the guide surface 14 of the guide cavity with minimal clearance. The plunger 6 extends along a longitudinal axis coinciding with the positioning axis y and has a circular cross-section. The plunger 6 includes a boring tool interface in the form of a blade holder support surface 16 and a threaded hole 17. The blade holder support surface 16 is suitable for cooperating with a surface of the blade holder 7 to fix the boring tool to the plunger 6 in a stationary manner, wherein the boring tool includes a blade holder 7 with a cutting blade 8 mounted thereon. The boring tool is fixed to the plunger 6 in an immovable manner by means of a fixing screw 18 which is screwed into the bore 17. Thereby, a relative movement between the plunger 6 and the boring tool, which the plunger 6 carries, is prevented so that the boring tool moves together with the plunger 6.

[0051] The boring head further comprises a combined orientation and fixing device 20 for orienting and fixing the plunger 6 relative to the housing 9 of the boring head 5 in the retracted position or in any of the extended positions. In the embodiment shown, the orientation and fixing device comprises a blind sleeve for receiving a tightening screw which, when tightened, forces the flexible bottom of the blind sleeve against the flat surface of the plunger 6. Other embodiments comprise different orientation and fixing devices, such as a device comprising a separate locking screw and a separate orientation screw configured to cooperate with corresponding parts of the plunger.

[0052] The boring head 5 further comprises a fine adjustment screw 19 which is arranged in the housing 9 and is coupled to the plunger 6 by threaded engagement with the plunger 6. The fine adjustment screw 19 comprises a head 21 and a shaft 22. The shaft 22 extends through a through hole 30 in the housing wall of the housing 9 (see FIG. Figure 6 and Figure 7 ), and has an external thread that engages with an internal thread in the bore of the plunger 6 to form the threaded engagement. The longitudinal axis of the shaft 22 of the fine adjustment screw 19 coincides with the positioning axis y and the longitudinal axis of the plunger 6. The shaft 22 of the fine adjustment screw 19 engages with the plunger 6 at the axial inner end of the plunger 6, and the boring tool interface is located at the opposite axial outer end of the plunger 6. The boring tool extends through the axial outer opening in the housing 9, thereby exposing the cutting edge.

[0053] On the axial side of the head 21, the head has an abutment surface 24, which is an annular surface extending radially outward from the shaft 2 to the side surface of the head 21. The abutment surface 24 of the head 21 faces axially outward and intersects the positioning axis y. The abutment surface 24 abuts against a support surface 25 of a component arranged in the housing 9. The support surface 25 surrounds a through hole 30 for the shaft 22 in the housing wall of the housing 9, which is one of the cuboid sides of the housing 9, specifically, the side facing axially inward. The support surface 25 is located at the axial inner end of the housing 9, faces axially inward, and is orthogonal to the positioning axis y.

[0054] The top surface of the head 21 faces away from the shaft 22 and axially inward. A socket 31 for the hexagonal key button 27 is centrally provided in the top surface. The top surface includes a radially outer portion in the form of a head surface 26, which has the shape of a lateral surface of a truncated cone and extends radially outward from the socket 31 to the side surface of the head 21. The head surface 26 is provided with first graduation marks 23. The first graduation marks 23 are linear, extend radially, have equal angular intervals, and intersect with the edge of the head surface 26 at the side surface of the head 21.

[0055] The housing 9 comprises a graduated surface provided with a second graduation mark 29. The second graduation mark 29 is aligned with the first graduation mark 23 to provide a reading of the axial position of the plunger 6.

[0056] The graduated surface is a convexly rounded beveled surface 28 at the head surface 26, which has an arcuate edge 32. The center of the radius of curvature 33 of a portion of the arcuate edge 32 is on the axis of rotation of the fine-tuning screw 19, which corresponds to the positioning axis y. The radius of curvature of the radially outer edge of the head surface 26 is slightly smaller and has the same center on the axis of rotation of the fine-tuning screw. All second graduation marks 29 are arranged at this portion and intersect with the arcuate edge 32. The rounded beveled surface 28 is shaped as the radially outer surface of the cylindrical segment and extends axially outward from the arcuate edge 32. The second graduation marks 29 are linear and parallel, wherein they follow the surface of the cylindrical segment in the direction of the associated longitudinal axis of the cylindrical segment. The second graduation marks 29 are spaced at equal angular distances along the arcuate edge 32.

[0057] At the outer radial edge of the head surface 26, the head has an axial thickness 34 to the abutment surface 24. The support surface 25 in the housing 9 is arranged axially outwardly at a distance from said arcuate edge, which distance is equal to the axial thickness 34. Thus, at the arcuate edge 32, the radially outer end of the first graduation mark 23 is substantially flush with the radially inner end of the second graduation mark 29 and has substantially the same distance from each other.

[0058] The convexly rounded beveled surface 28 is formed at the corner of the housing 9. The rounded beveled surface 20 intersects three of the side surfaces of the rectangular parallelepiped housing 9. As seen along the positioning axis y, the angular distance α between the center point between the first second graduation mark 29 and the last second graduation mark 29 and the axis extending in the rotation direction x is 60°, see Figure 5 .

[0059] As in Figure 6 It can be seen from the cross section of the figure that the cross section includes the positioning axis y and the center point between the first second graduation mark 29 and the last second graduation mark 29, and the convexly rounded beveled surface 28 forms an angle β of 45° with the positioning axis y. This can be understood as the bevel angle of the convexly rounded beveled surface 28.

[0060] refer to Figure 1The tool holder 1 shown has two boring heads 5 mounted on opposite axial ends of the bridge 2. In the tool holder 1, the positioning axis y of the plunger 6 corresponds to the radial direction. The head surface 26 of the fine adjustment screw 19 of one of the two boring heads 5 faces axially inward toward the other boring head of the two boring heads 5. To set the tool holder for the desired final diameter of the hole, the operator must adjust the position of the boring tools of the two boring heads 5. The operator can insert the hexagonal key 27 into the socket 31 of the head 21 of the fine adjustment screw and turn the hexagonal key. Thereby, the fine adjustment screw 19 is rotated. The rotation of the fine adjustment screw 19 is converted into a translational movement of the plunger 6 by the threaded engagement of the shaft 22 with the plunger 6 and by the abutment surface 24 of the head 21 against the support surface 25 in the housing 9. The plunger 6 moves along the positioning axis y, wherein the plunger 6 slides along the guide surface 14 of the guide cavity with minimal clearance. The operator is aware of the axial position of the plunger 6 by reading the first index mark 23 and the second index mark 29. In the present embodiment, the first index mark 23 and the second index mark 29 form a vernier scale, wherein the first index mark 23 is a primary mark and the second index mark 29 is a vernier mark. The tool holder on which the tool assembly 3 is mounted is a smaller tool holder for boring diameters up to 315 mm. Although the opposing boring head 5 blocks the view along the positioning axis 5, the operator is able to read the scale without parallax error due to the convexly curved beveled surface 28 with an arcuate edge 32 at the head surface 26 of the present invention. After the desired diameter has been set, the operator can remove the hexagonal key 27.

Claims

1. A boring head for holding a boring tool for metal cutting, the boring head comprising: - a body extending along a positioning axis (y) from an axially outer end to an axially inner end and comprising a support surface (25) and a graduated surface, a plunger (6) comprising a boring tool interface for carrying the boring tool in a fixed manner when the boring tool is held in the boring head, wherein the plunger (6) is arranged in the body to be movable along the positioning axis (y) into a retracted position axially inwards and into a plurality of extended positions axially outwards from the retracted position, a fine adjustment screw (19) arranged in the body and coupled to the plunger (6) so that when the fine adjustment screw (19) is rotated, the plunger (6) moves along the positioning axis to one of the extended positions or the retracted position, in the fine adjustment screw (19) comprises a head (21) which abuts against the support surface (25) and comprises a radially outer head surface (26) provided with a first graduation mark (23), and - the graduated surface is provided with a second graduation mark (29) which is aligned with the first graduation mark (23) to provide a reading of the axial position of the plunger (6), It is characterized in that The graduated surface is a convexly rounded beveled surface (28) at the head surface (26), the beveled surface (28) having an arcuate edge (32).

2. The boring head according to claim 1, wherein the center of curvature of at least a portion of the arcuate edge (32) is on the rotation axis of the fine-tuning screw (19), wherein all of the second graduation marks (29) of the portion intersect with the arcuate edge (32) or are equidistant from the arcuate edge (32).

3. The boring head according to claim 2, wherein the rounded beveled surface (28) is a radially outer surface of a cylindrical segment.

4. A boring head according to any preceding claim, wherein the second graduation markings (29) are linear and parallel.

5. A boring head according to any preceding claim, wherein the boring head is configured to be mountable to a spindle for rotation of the boring head about an axis of rotation defining an axial direction (x) in the boring head, wherein the direction (x) is perpendicular to the positioning axis (y).

6. A boring head according to claim 5, wherein when viewed along said positioning axis (y), a center point between a first one of said second graduation marks (29) and a last one of said second graduation marks (29) has an angular distance (α) of at least 30° and at most 70° relative to an axis extending in said direction (x).

7. A boring head according to any preceding claim, wherein the support surface (25) is located at the axially inner end, faces axially inwardly and is orthogonal to the positioning axis (y).

8. The boring head according to claim 7, wherein the convexly rounded bevel surface (28) extends axially outwardly from the arcuate edge (32).

9. A boring head according to claim 8, wherein the bevel surface forms an angle (β) of at least 30° and at most 60° with the locating axis (y) when viewed in a cross section including the locating axis (y) and a center point between a first one of the second graduation marks (29) and a last one of the second graduation marks (29).

10. A boring head according to any one of claims 7 to 9, wherein - the head comprises an axially outwardly facing abutment surface (24), wherein the head has an axial thickness (34) at its outer radial edge from the abutment surface (24) to the head surface (26), and - the support surface (25) is arranged axially outwardly from the arcuate edge at a distance equal to the axial thickness (34).

11. A boring head according to any preceding claim, wherein the head surface (26) is a lateral surface of a frustum of a cone.

12. A boring head according to any preceding claim, wherein the fine adjustment screw (19) is in threaded engagement with the plunger (6).

13. A boring tool assembly comprising a boring head according to any preceding claim and comprising a boring tool, wherein the boring tool is mounted in the boring tool interface of the plunger (6) such that the boring tool is carried in a fixed manner by the plunger and is retained in the boring head.

14. A boring tool assembly according to claim 13, wherein the boring head includes the features of claim 5, and wherein when the plunger (6) is in the retracted position, the cutting edge of the boring tool is in a minimum cutting diameter position, and when the plunger (6) is in a maximum forward position in the forward position, the cutting edge of the boring tool is in a maximum cutting diameter position.

15. The boring tool assembly of claim 14, further comprising a bridge portion configured to be mountable to the spindle, wherein - the boring head is mounted on the bridge (2) at a first axial end, wherein the positioning axis (y) of the boring head defines the axial direction of the bridge (2), - the tool assembly comprises a further boring head or counterweight mounted on an opposite second axial end of the bridge portion (2), and wherein - the head surface (26) of the fine adjustment screw (19) faces axially inwardly towards the further boring head or counterweight.

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