5 10 15 20 25 30 35 Date Regue/Date Received 2024-03-07 1 A tool body including a damping apparatus and a machin¬ ing tool having such a tool body TECHNICAL FIELD OF THE INVENTION The present invention relates to a tool body including a damping apparatus for damping vibrations in a machining tool as well as a machining tool having such a tool body. The invention is not restricted to tool bodies and machining tools for any particular type of machining, and the tool body may for instance have members with cutting edges secured thereto in the form of cutting inserts for chip-removing machining of a work piece by turning, milling, drilling, or boring. Thus, the tool body may be designed to receive a cutting head including cutting edges or seats for cutting inserts. Both rotating and non-rotating ma¬ chining tools are comprised. Neither is the invention restricted to any size of such machining tools, but these may for instance have a diameter of 500 millimetres and a length of 6 metres or be as small as having a diameter of only 10 millimetres. The tool body is provided with such a damping apparatus for damping radial and tangential forces applied on the tool body by the machining action and by that improving the accuracy of the machining operation and prolonging the lifetime of cutting edges of the machining tool. The damping effect of such a damping ap¬ paratus is a result of an interaction between the damper mass body, which is of a high density material such as lead, and the machining tool member provided with a cutting edge through any type of resilient element. The frequency by which the damper mass body will swing upon machining will depend upon the mass of the damper mass body and the spring constant of said resilient element. This frequency will increase with an increasing said spring constant and de¬ crease with an increasing mass of the damper mass body. The5 10 15 20 25 30 35 Date Regue/Date Received 2024-03-07 2 frequency needed for appropriate damping of self-induced vibra¬ tions in a machining tool will depend upon the design of the ma¬ chining tool, such as the ratio of the length/diameter of the tool body, and weight distribution of the machining tool. BACKGROUND ART A tool body of the type defined in the introduction is known through WO 92/14947 and the resilient element of the damping apparatus of that tool body is provided by elastomer rings sur¬ rounding the central tube, which is secured to the damper mass body and moves with this as being an integral part therewith. These elastomer rings are rather soft, which results in a low spring constant and a low damping frequency for a given mass of a damper mass body restricting the range of possible shapes and dimensions of tool bodies and machining tools for which appro¬ priate damping may be obtained. Furthermore, the elastomer ma¬ terial may not withstand the high temperatures which may occur during certain machining operations desired, so that excessive cooling will be required or the efficiency of the machining opera¬ tion has to be lowered for keeping the temperature down. The properties of such elastomer material will also change over time due to aging. SUMMARY OF THE INVENTION The object of the present invention is to provide a tool body of the type defined in the introduction being improved in at least some aspect with the respect to such tool bodies already known. Thus, by rigidly connecting the central tube at both ends thereof to a tool body fixed part and making the central tube of a material with a spring property allowing the damper mass body to oscillate in the internal room perpendicularly to the longitudinal extension of the central tube said resilient element will be provided by the5 10 15 20 25 30 35 Date Regue/Date Received 2024-03-07 3 central tube without any elastomer rings needed therefor. By us¬ ing the central tube as resilient element substantially higher tem¬ peratures may be allowed and the problems with ageing of the elastomer material will be avoided. The term tool body fixed part is to be understood as part of the tool body which is to be rigid or stiff with respect to a said member 3 with at least one cutting edge to be secured to the tool body, such as for example parts of the tool body casing or parts rigidly secured thereto. Furthermore, the spring constant of the resilient element in the form of the central tube may be varied within a wide range by the choice of diameter and wall thickness of the central tube. This means that substantially higher damping frequencies than by elastomer rings may be obtained when desired. But it is pointed out that low damping frequencies are still possible to obtain by embodiments of the invention. According to an embodiment of the invention the central tube is made of steel or carbon fibre. These are suitable materials with spring properties for obtaining spring constants of desired mag¬ nitudes. According to an embodiment of the invention the central tube is a machining tool cooling tube, which may transport any coolant to a member carrying out chip-removing machining of a said machin¬ ing tool, for example a coolant liquid such as water or a gas mix¬ ture as air. According to an embodiment of the invention the through bore has at at least one end thereof a length portion with larger cross-sec¬ tion dimensions than the central tube leaving a space between the damper mass body and the central tube, and an element is arranged to bridge this space between the central tube and the damper mass body at a location along the central tube. The ar¬ rangement of such an element supporting the central tube with5 10 15 20 25 30 35 Date Regue/Date Received 2024-03-07 4 respect to the damper mass body will influence the spring con¬ stant of the damper apparatus. The choice of the location of this bridging element will then also influence the magnitude of the spring constant and accordingly be used to obtain the spring con¬ stant desired. According to an embodiment of the invention said element is rigid, and according to other embodiments of the invention this element has elastic properties and it may be in the form of an O-ring of rubber. The choice of the material of this bridging element will also influence the magnitude of the spring constant. According to an embodiment of the invention said element is mov¬ able along the central tube between different said locations so as to change the spring constant of the central tube. It is then espe¬ cially advantageous if the through bore has a said length portion and a said element at both ends of the through bore. A frequency tuning can then be implemented by these movable elements, and the spring constant may be adjusted for one and the same damp¬ ing apparatus, so that this may be used for machining tools with different lengths by allowing the spring constant to be adjusted to be appropriate for each such length. According to an embodiment of the invention the damper mass body has a circular cylindrical shape with the through bore ex¬ tending according to the centre axis of the cylinder so formed. This results in a uniform damping of the vibrations of a machining tool in operation. According to an embodiment of the invention the internal room of the tool body contains a damping fluid, such as oil, in an annular cavity separating the damper mass body radially from internal walls defining the internal room. Such a damping fluid improves the damping action of the damping apparatus.5 10 15 20 25 30 35 Date Regue/Date Received 2024-03-07 5 The invention also relates to a machining tool having a tool body according to the invention and a use of such a tool body to damp vibrations in a machining tool in operation. Other advantageous features as well as advantages of the pre¬ sent invention appear from the description following below. BRIEF DESCRIPTION OF THE DRAWINGS With reference to the appended drawings, below follows a specific description of embodiments of the invention cited as examples. In the drawings: Fig. 1 is a perspective view of a machining tool including a tool body according to the present invention with a damping apparatus for damping vibrations in the ma¬ chining tool and a member with a cutting insert, Fig. 2 is a view in the direction of the arrow II in fig. 1 of the tool body shown in fig. 1 without the member with a cutting insert, Fig. 3 is a cross section view according to Ill-Ill in fig. 2 of a tool body according to fig. 1, and Fig. 4 is a view similar to that of fig. 3 of a tool body according to a second embodiment of the invention. DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVEN¬ TION Fig. 1 illustrates a machining tool 1 for turning having besides a tool body 2 according to an embodiment of the invention a mem¬ ber 3 with a cutting insert 4 for chip-removing machining in the form of turning secured at an end 5 of the tool body. The tool body5 10 15 20 25 30 35 Date Regue/Date Received 2024-03-07 6 may just as well be used in a machining tool for other types of machining, such as milling, drilling, or boring, and a correspond¬ ing member with at least one cutting edge for chip-removing ma¬ chining is then to be secured to the end 5 of the tool body. The tool body includes a damping apparatus 6 for damping vibra¬ tions in the machining tool caused by machining operation, and this damping apparatus is arranged in an internal room 7 (see fig. 3) of the tool body defined by a casing 8. The damping apparatus comprises a damper mass body 9 with a circular cylindrical shape of a high density material, such as of lead, with an axial through bore 10. The internal room 7 contains a damping fluid, such as oil, in an annular cavity 22 separating the damper mass body 9 radially from internal walls of the casing 8 defining the internal room. A central tube 11 extends through the through bore 10 and is rigidly secured to the damper mass body 9 inside the through bore. The central tube 11 is at both ends 12, 13 thereof rigidly connected to a tool body fixed part 14, 15, i.e. a part of the tool body which is to be rigid or stiff with respect to a said member 3 with at least one cutting edge to be secured to the tool body, in this case end pieces. The central tube 11 is made of a material with a spring property, such as steel or carbon fibre with this prop¬ erty, allowing the damper mass body 9 to oscillate in the internal room 7 of the tool body perpendicularly to the longitudinal exten¬ sion of the central tube 11. The damping frequency of the damp¬ ing apparatus will be proportional to the square root of k/m, in which k is the spring constant of the spring formed by the central tube with a spring property and m is the mass of the damper mass body 9. The spring constant will depend upon the diameter and the wall thickness of the central tube as well as the material cho¬ sen for that tube, so that said frequency may be selected to match the frequency of the vibrations to be damped by appropriately choosing these characteristics of the central tube. Embodiments of the invention will by this without any problem allow to obtain such a frequency in the range of 300 Hz to 1 100 Hz, and fre¬ quencies outside this range are also conceivable.5 10 15 20 25 30 35 Date Regue/Date Received 2024-03-07 7 The through bore 10 of the damper mass body 9 has at each end thereof a length portion 16, 17 with larger cross section dimen¬ sions than the central tube leaving a space 18, 19 between the damper mass boy 9 and the central tube 11. The choice of length of these length portions will also influence the spring constant of the central tube 11. Fig. 4 is a view similar to fig. 3 of a tool body according to a second embodiment of the invention differing from that shown in fig. 3 by an arrangement of an element 20, 21 bridging the re¬ spective space 18, 19 between the damper mass body 9 and the central tube 11. These elements 20, 21 will form a support of the central tube 11 with respect to the damper mass body and will influence the spring property of the central tube 11. The elements 20, 21 may be chosen to be rigid or to have elastic properties, such as being O-rings surrounding the central tube 11. The prop¬ erties chosen for these elements 20, 21 will also influence the magnitude of the spring constant of the central tube 11. Further¬ more, the elements 20, 21 are preferably movable along the cen¬ tral tube between different locations so as to change the spring constant of the central tube. This makes it possible to use the same tool body or identical tool bodies for obtaining appropriate damping of vibrations in machining tools of different types and/or dimensions generating vibrations of different frequencies by the machining operation thereof. The invention is of course not restricted to the embodiments thereof described above, but many possibilities to modifications thereof would be apparent to a person with skill in the art without departing from the scope of the invention. The length portions with larger cross-sections dimensions of the through bore of the damper mass body may have other lengths than shown in the figures or not be there at all. It is of course also possible to have the elements bridging the space between the8 central tube and the damper mass body immovably arranged or only one of them movable or having only one such element. Date Regue/Date Received 2024-03-07