Tool holder and a runout correcting tool for a tool holder

Abstract: Even when a position of a tip end 18 of a tool 17 is laterally shifted to deviate from a rotation center Ca of a tool holder 10, the position of the blade edge 18 of the tool 17 is made to coincide with the rotation center Ca of the tool holder 10 by rotating a screw member 24. The tool holder 10 comprising an attaching portion 12 which is disposed on a basal side of a shaft 13, and which is to be attached to a rotary part of a working machine and a holding portion 14 which is used for holding the tool 17, and which is disposed in a tip end side of said shaft 13, wherein, in an outer peripheral portion of said shaft 13, a first contact portion 26 and a second contact portion 27 are set in positions which are separated from each other in a longitudinal direction of said shaft 13, and runout correcting means 20 for, between said contact portions 26 and 27, generating a force by rotating the screw member 24 is disposed between said contact portions 26 and 27, said force causing an axis C of the tip end side of said shaft 13 to be displaced.

Description: FIELD OF THE INVENTION The present invention relates to a tool holder which is used with being attached to a rotary part of a working machine, and more particularly to a tool holder which is used with attaching the basal side of a shaft of the tool holder to a rotary part of a working machine, which has a holding portion for holding a tool such as a cutting tool, in the tip end side of the shaft, and which can correct runout of a tip end portion of the tool such as a cutting tool attached to the holding portion. BACKGROUND OF THE INVENTION When a hole is to be opened in a workpiece or the inner face of a hole is to be ground by using a working machine or the like, a tool such as a cutting tool is attached to the tip end side of a tool holder mounted on a rotary part of the working machine. The tool in the tip end side of the tool holder is rotated at a high speed by rotating the rotary part of the working machine, whereby desired working can be performed on the workpiece for a short time period. As described above, the tool holder is used in a high speed state. When the tip end of the tool attached to the tip end of the tool holder deflects even at a small degree as a result of the high speed rotation, there arises a problem in that the dimensional accuracy of the hole is lowered or the inner peripheral face of the hole is roughened to disable the hole from being accurately worked. In order to solve the problem, conventionally, means for correcting vibrations of a shaft of a tool holder is disposed on the tool holder (see Japanese published unexamined Patent application No. 11-104931). Fig. 7 shows the conventional art example. With reference to the figure, the conventional art example will be described. In a tool holder 1, the basal side 2 of a shaft 3 is formed as a shank portion 2 which is tapered as well known in the art, in order to fit the basal side into a tapered hole 1b of the main shaft 1a of a working machine which is not shown and has a well-known configuration. A holding portion 4 for a tool 4a is disposed in the tip end side of the shaft 3. (Usually, in order to fasteningly fix the tool 4a an example of which is a cutting tool such as a drill, a chuck 4 having a clamping hole which is expandable and contractable is disposed as the holding portion 4. In a well-known configuration, the cutting tool 4a may be attached directly integrally to the shaft 3 in the position of the chuck 4.) A large-diameter flange 5 which is used in the case where a grasping operation is to be performed by a grasping portion of a robot as well known in the art is formed on the outer periphery of the shaft 3 and on the side of the shank portion 2. The reference numeral 5a denotes a groove for engagement. In the tool holder 1 shown in Fig. 7, plural radial holes 6 are threadedly formed in a bottom of the groove 5a of the flange 5, and a male screw 7 which is a screw member serving as a mass is screwed into each of the holes 6. A hexagonal hole 8 for a hexagonal wrench is formed in the head of each of the male screws 7. Each male screw 7 is adjusted so as to advance or retract in the corresponding hole 6 by using a wrench, so that, when the tool holder 1 is rotated at a high speed, the positional change in a radial direction appears as a change of the mass, whereby vibrations of the shaft 3 of the tool holder 1 can be corrected. Even when vibrations of the shaft are corrected in a portion of the shaft 3 of the tool holder 1, the shaft center may sometimes deflect in a position closer to the tool attaching portion 4 in the tip end. Therefore, male screws 9 which similarly serve as a mass are attached to a tip end portion 3a so as to be advanceable and retractable, so that vibrations of the shaft in the tip end portion 3a can be corrected by advancing or retracting each of the male screws 9. In the conventional art described above, however, the means for correcting vibrations of a shaft can correct vibrations of the shaft, only in a place where the correcting means is disposed and in the vicinity of the place. In the case of a long tool such as a drill 4a which protrudes by a large distance from the tool attaching portion 4, the portion where correction of runout of the shaft center with respect to the rotation center is required at the highest degree is a blade edge 4b which is in the tip end of the drill. In the conventional art described above, however, it is impossible to correct runout of the shaft center with respect to the rotation center in a portion which largely protrudes from the tool attaching portion 4, such as the blade edge 4b in the tip end of the drill. US-A-5,286,042 refers to a tool holder for a machine tool. The tool holder comprises a grooved collar and an annular flange spaced apart from each other by means of an annular groove. Three screws are tightened into the flange (generally parallel to the axis of the tool holder body) such the cone point of each screw seats in a conical depression in the face of the body accessing the groove. US-A-4,218,068 discloses a similar arrangement. In this case, four screws are provided for adjusting the runout of the shaft. These screws act on flanges of the shaft. In particular, two flanges are provided which are separated by means of a groove. The gap between the two flanges is narrowed or widened using the screws. EP-A-0187647 discloses a tool holder having two separated flanges extending from a shaft. The runout of a shaft is adjusted by tightening a screw which serves to adjust the distance between the two flanged portions of the shaft. CH-A-237045 refers to means for adjusting the runout of a tool holder, comprising a rotatable ring and a second rotatable ring which is inserted into the first rotatable ring. The inner ring comprises a slit into which a pressure roll is inserted. Holes for turning the ring by means of a corresponding tool are provided. The rings and the pressure roll form a device which is used for achieving an elastic deformation of the tool holder. For this purpose the ring is rotated such that the pressure of the roll applies a bending torque on the shaft. US-A-5,249,895, which forms the preamble of claim 1, refers to a tool holding fixture comprising a clamping ring arrangement for adjusting the shaft runout. A rotatable clamping ring is mounted on a shaft. Two sliding blocks are seated inside the clamping ring. An axially directed pressure screw presses on one of the sliding blocks. Accordingly, a pressure is exerted on a sliding block with the screw. This in turn applies a tensile force on the shaft and transmits the pressure to the holding body by means of the clamping ring. In particular, the tensile force is transmitted to the shaft by means of the raised surface on the front face of the clamping ring. Accordingly, a bending torque is exerted on the shaft and the clamping ring slightly tilts. The invention in defined in claim 1. A tool is attached to a holding portion at a tip end portion of a shaft. In the case where a drilling or cutting work is to be conducted, even when the position of the tip end of the tool is laterally shifted to deviate from the rotation center of a tool holder, a screw member is rotated to generate a force of displacing the axis of the tip end side of the shaft, between two contact portions of the tool holder, whereby the position of a blade edge of the tool can be easily moved toward the rotation center of the tool holder so as to coincide therewith. According to this configuration, it is possible to attain an effect that, in the case where a drilling or cutting work is to be conducted by rotating the tool holder at a high speed, precision working can be accurately performed. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a section view of a tool holder having runout correcting means of an embodiment of the invention; Fig. 2 is a section view taken along the line II-II of Fig. 1, (A) shows an example in which a screw member is disposed in four places, (B) shows an example in which a screw member is disposed in three places, and (C) shows an example in which a screw member is disposed in six places; Fig. 3 is an enlarged view of the runout correcting means shown in Fig. 1; Fig. 4 is a partially cutaway view showing a state where a cutting edge of a tool deflects; Fig. 5 is a partially cutaway view showing a state where the runout of the cutting edge is corrected; Fig. 6 is a partial section view showing runout correcting means of another embodiment; and Fig. 7 is a view illustrating a runout correcting tool of the conventional art. DETAILED DESCRIPTION Hereinafter, an embodiment of the invention will be described with reference to the accompanying drawings. Fig. 1 is a section view of a tool holder 10 which is a first embodiment of the invention, and (A) of Fig. 2 is a section view taken along the line II-II of Fig. 1. In Fig. 2, (B) and (C) are views showing examples in which the number of screw members 24 is changed. Fig. 3 is an enlarged view of the runout correcting means shown in Fig. 1. Although a configurations of components denoted by reference numerals 10 to 18 in Figs. 1 to 5 are well known in the same manner as a tool holder 1 shown in Fig. 7, the configurations will be described below. As well known in the art, the tool holder 10 comprises a shaft 13 having a hollow portion 13a serving as a main unit. A flange 11 is disposed on an outer periphery of the shaft 13. A tapered shank portion 12 which protrudes in a rearward direction or toward a basal portion is disposed in back of the flange 11. The portion 12 serves as an attaching portion which is to be attached to a rotary part of a working machine. In a front position with respect to the flange 11, a diameter of the shaft 13 is very smaller than that of the flange 11 (occasionally, the shaft may be larger in diameter than the flange 11). A step 11b is formed in front of the flange 11. As well known in the art, the shaft 13 is formed into a slender hollow cylindrical shape (occasionally, the shaft may be solid). A holding portion 14 for holding a tool 17 is disposed in a tip end side of the shaft. The holding portion 14 is a portion which is well known as a chuck, and as well known fasteningly fixes a basal portion of a drill 17 which is an example of a cutting tool inserted into a center hole 14a of the holding portion 14, by using a collet chuck 15a, a clamp ring 15, etc. In the holding portion 14, the thickness as a whole is not even because of the thickness of the shaft in the holding portion 14, and production errors of the collet chuck (contract ring) 15a, the clamp ring 15, etc. As a result, a position of a tool tip end 18 is laterally shifted with respect to a rotation center Ca of the tool holder 10 to deviate from the rotation center Ca of the tool holder. When the drill 17 is rotated at a high speed under such a state, the blade edge 18 at the tip end of the drill 17 deflects. This state of runout is such a state that the blade edge 18 at the tip end of the drill 17 deflects in both a direction of an arrow S in Fig. 1 and a direction of depth in Fig. 1 when the blade edge 18 is rotated around the rotation center Ca centering around the center Ca. In such runout state, precision working becomes disabled. In the embodiment, therefore, a runout correcting tool 20 is detachably disposed on the outer peripheral face of the shaft 13. The runout correcting tool 20 has a main unit which is made of a metal material having substantial thickness and weight, and which is configured as a ring-like member (annular member) 21 so as to be fittable onto the outer periphery of the shaft 13. Screw members 24 are screwed advanceably and retractably with tapped holes 23 which are formed from an outer periphery of the annular member 21 to an inner periphery. The screw members 24 configured by male screws are passed by the whole length through the tapped hole 23 via a well-known operation groove disposed in a head 24b. The tapped holes are formed in three or more places in a circumferential direction of the periphery of the shaft (see (B) and (C) of Fig. 2). Since these holes are respectively formed in uniform positions, adjustment of "nmout" of the center of the tip end 18 of the tool can be performed very easily and rapidly. An abutting portion 28 which is to abut against a first contact portion 26 disposed in the outer periphery of the shaft 13 is formed on one side face of the annular member 21. The first contact portion 26 is formed in the step 11b. Namely, the one side face 28 of the annular member 21 is caused to abut against the front wall face 26 of the flange. A tip end 29 of the screw member 24 can abut against a second contact portion 27 which is disposed in a position separated in the longitudinal direction from the first contact portion 26. The second contact portion 27 is configured by cuttingly forming an annular U-groove 22 in the outer peripheral face of the shaft 13. The two contact portions (26 and 27) are pressurized by rotating the screw member 24 to generate a force F of displacing the axis C of the tip end side of the shaft 13, between the portions. When the tip end portion 29 of the screw member is in press contact with the shaft 13, a reaction force of the shaft 13 causes the end face 28 of the annular member 21 and the side end face 26 of the flange 11 to be in press contact with each other, so that the annular member 21 and the shaft 13 are firmly fixed to each other. In the embodiment, as shown in Fig. 3, when the flange side end face 28 of the annular member 21 abuts against the end face 26 of the flange 11, i.e., in the press contact state in which the annular member 21 cannot be moved toward the flange 11, the through hole 23 is positioned so that its center is slightly deviated from a center 22a of the U-groove 22 toward the holding portion 14. When the screw member 24 is screwed and the tip end portion 29 of the screw member enters the U-groove 22, therefore, the screw tip end portion 29 abuts against only the inclined face (second contact portion) 27 of the U-groove 22 on the side of the holding portion 14, and does not abut against an inclined face on the side of the flange 11. As a result, when the screw member 24 is screwed into the tapped hole 23 to perform a fastening operation, the screwing force (in Fig. 3, the force directed toward the shaft center C of the tool holder 10) is caused by the function of the inclined face 27 to have a force in the direction indicated by F in Fig. 3, i.e., a component of force which bends the portion of the shaft 13 on the side of the holding portion 14 in the direction of the arrow Fa. The reference numeral 30 denotes an annular cover which is placed on the outer periphery of the annular member in order to prevent the screw member 24 from jumping out. An end portion of the cover is detachably fixed to the shaft 13. The reference numeral 31 denotes an operation hole which has a diameter smaller than the screw head 24b, and which is positioned in the outer peripheral side of the screw head 24b. In the case where the drill 17 is attached to the thus configured tool holder 10 and then rotated, when the position of the blade edge 18 of the drill deviates from the rotation center axis Ca as shown in Fig. 4, the center portion of the tip end 18 of the tool 17 is made coincident with the rotation center Ca of the tool holder. In this case, as shown Figs. 3 and 5, the shaft 13 is bent by adjusting the fastening force (the press contacting force on the inclined face 27) of each of the three (or more) screw members 24 shown in Fig. 2, to displace the axis C in the direction of the arrow Fa, thereby making the position of the blade edge 18 coincident with the rotation center axis Ca. In the tool holder of the conventional art shown in Fig. 7, even when a screw 7 of the correcting tool is fastened, only the mass which is immediately below the screw can be changed. Therefore, it is difficult to correct runout of the shaft center which occurs on the side of the drill with respect to a correcting place. By contrast, in the embodiment, the fastening force exerted on the screw 24 causes the shaft 13 to be bent, so that the force can be applied toward the holding portion 14 as the force F shown in Fig. 3. Therefore, runout between the rotation center of the tip end 18 of the tool and the rotation center Ca of the tool holder 10 can be easily corrected. As described above, the runout correcting tool 20 of the embodiment can correct runout which occurs on the side of the tool 17 with respect to the correcting tool 20. This is realized by the function of the inclined face 27. When the inclination angle of the inclined face 27 is changed, the direction of the force F can be directed more closely to the drill. However, the necessary force (the force of fastening the screw 24) must be increased in accordance with the change. Fig. 6 shows a tool holder 10 of a second embodiment of the invention in which runout of the blade edge 18 at the tip end of the drill can be corrected at a higher degree. The embodiment is different from the first embodiment in that the attaching position of the runout correcting tool 20 is set to be closer to the drill 17. When the runout correcting tool 20 is closer to the drill as described above, it is not required to reduce the inclination angle of the inclined face 27, and runout of the tip end 18 of the drill can be corrected by a smaller fastening force. In the above description, the runout correcting means of the tool holder 10 shown in Figs. 1 to 6 corrects "runout" of the tool holder 10 after the runout correcting tool 20 which is configured so as to be attachable and detachable with respect to the tool holder 10 is attached to the tool holder 10. As described above, the runout correcting means 20 may be an independent component which is detachably configured. Alternatively, the means may be configured by previously attaching the annular member 21 to the outer peripheral face of the shaft in a step of producing the tool holder 10. In Fig. 6, components which seem to be functionally identical or equivalent to those of Figs. 1 to 5 described above are denoted by the same reference numerals as those used in Figs. 1 to 5, and letter "e" is affixed to the reference numerals in order to distinguish the numerals from those used in the figures. Therefore, the configuration of the components can be easily realized, and duplicated description is omitted. In the above-described embodiment of Figs. 1 to 6, one inclined face of the U-groove 22 is used as the second contact portion of the runout correcting tool 20. It is requested only that an engagement structure for receiving the second abutting portion 29 exists correspondingly and scatteringly in the circumferential direction of the shaft 13. The second contact portion is not required to be formed as a U-groove. In Fig. 3, the screw member 24 is opposed to the second contact portion 27. Alternatively, the U-groove 22 may be formed in the first contact portion 26, and the screw member 24 may be configured so as to be advanceable and retractable with respect to the U-groove. In the alternative also, the force F shown in Fig. 3 can be similarly generated. As many apparently widely different embodiments of this invention may be made without departing from the scope thereof as defined by the appended claim, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claim.

Claims: A tool holder (10) comprising an attaching portion (12) to be attached to a rotary part of a working machine and disposed on a basal side of a shaft (13), and a holding portion (14) for holding a tool (17) at a tip end side of said shaft (13), wherein at an outer peripheral portion of said shaft (13) a first contact portion (26) and a second contact portion (27) are set at positions separate from each other in a longitudinal direction of the shaft; said first contact portion (26) is formed of a front wall face (26) of a flange (11) of the shaft (13); said second contact portion (27) is formed of an inclined face (27) around the shaft (13); an annular member (21) is disposed around an outer periphery of said second contact portion (27) of said shaft (13); a side face of said annular member (21) is an abutting portion (28) adapted to abut against said first contact portion (26); a female screw hole (23) is disposed in said annular member (21) from an outer peripheral side to an inner periphery of the annular member (21), and a screw member (24) is threadedly engaged with said female screw hole (23), so as to be advanceably and retractably movable toward said inclined face (27) serving as said second contact portion (27); the advance positions of tip end portions (29) of said screw member (24) are set toward said inclined face (27) so that by rotating and advancing said screw member (24), said abutting portion (28) abuts against said first contact portion (26), and a force (Fa) is generated between said first contact portion (26) and said second contact portion (27), said force (Fa) causing an axis (C) of said tip end side of said shaft (13) to be displaced by bending in relation to said basal side end of said shaft (13); characterized in that female screw holes (23) are provided at least at three uniform positions around the periphery of said annular member (21) and screw members (24) are threadedly engaged with said female screw holes (23), respectively; and by advancing and rotating said screw members (24); said tip end portions (29) are caused to abut against said inclined face (27) and press said inclined face (27). .

Inventors: ISHIKAWA HITOSHI, ISHIKAWA, HITOSHI, Ishikawa, Hitoshi, c/o NT TOOL Kabushiki Kaisha
Applicants: NT TOOL KK, NT TOOL KABUSHIKIKAISHA
Application year: 2000
Main classification: B23Q11
IPC codes: B23Q3, B23Q11, B23B31