Tool holder

Abstract

To provide a tool holder capable of stabilizing deflection accuracy of a cutting tool.SOLUTION: A tool holder (1) includes: a collet chuck body (10) including a taper hole (17) and a straight hole (18) formed in an inner periphery of a tip and a male screw (16); a collet (20) including a tool insertion hole (23) for inserting a tool, a taper surface (21), and a straight surface (22) and configured to fit into the taper hole (17) and the straight hole (18); and a cylindrical fastening member (30) including a female screw (31) which threadedly engages with the male screw (16) and a protruding portion (33) protruding in an inner diameter direction. A difference in diameter between the straight hole (18) and the straight surface (22) is formed so as to be very small, and an apical surface (27) and the protruding portion (33) are formed so as to contact with each other.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a tool holder, and more particularly to a tool holder for gripping the shank of a cutting tool. [Background technology]

[0002] Generally, a tool holder for gripping the shank of a cutting tool has a structure in which a nut is screwed onto the collet chuck body, and the collet is forced into a tapered hole in the collet chuck body to reduce its diameter, allowing a tapered collet to grip the shank portion.

[0003] Known examples of documents disclosing such technology include Japanese Utility Model Application Laid-Open Publication No. 7-027712 (Patent Document 1). Patent Document 1 discloses that the tapered collet is a double tapered collet that further includes a tapered surface tapered toward the tip in addition to a main tapered surface that fits into the collet chuck body, and that a bearing is interposed in the annular space formed between them. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Utility Model Application Publication No. 7-027712 Summary of the Invention [Problem to be solved by the invention]

[0005] In the collet chuck of Patent Document 1, since a bearing is interposed between the nut and the workpiece, the outer diameter of the nut becomes large, and there is a risk of interference with the workpiece during machining. Therefore, a technique is known in which the outer diameter is reduced by using a nut without a bearing. However, since a bearing is not provided, it may not be possible to achieve concentricity between the taper of the nut and the tapered hole of the tapered collet chuck body, and the runout accuracy of the cutting tool may become unstable.

[0006] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a tool holder that can stabilize the runout accuracy of a cutting tool. [Means for solving the problem]

[0007] For this purpose, a tool holder according to one aspect of the present invention comprises a collet chuck body including a tapered hole and a straight hole formed on the inner periphery of the tip portion and continuing in sequence from the tip portion in the axial direction, and a male thread formed on the outer periphery of the tip portion; a tool insertion hole formed on the inner periphery of the tip portion for inserting a tool; a collet including a tapered surface and a straight surface formed on the outer periphery of the tip portion and continuing in sequence from the tip portion in the axial direction, the collet fitting into the tapered hole and the straight hole; and a cylindrical fastening member which is located closer to the tip than the collet chuck body and which protrudes inwardly toward the rear end, and which reduces the diameter of the tool insertion hole of the collet by screwing the female thread into the male thread and pressing the collet against the tapered hole, and which is formed so that the difference in diameter between the straight hole of the collet chuck body and the straight surface of the collet is extremely small, and after the collet is attached to the fastening member, the front end face of the collet and the rear end face of the fastening member abut against each other when the fastening member is attached to the collet chuck body.

[0008] Preferably, the boundary between the straight hole and the tapered hole of the collet chuck body has a shape including a circular arc portion and a pair of chamfered portions formed on both sides of the circular arc portion. Effect of the Invention

[0009] According to the present invention, it is possible to stabilize the run-out accuracy of a cutting tool. [Brief description of the drawings]

[0010] [Figure 1] 1 is a side view showing a tool holder according to an embodiment of the present invention; [Diagram 2]1 is an exploded side view of a tool holder according to an embodiment of the present invention; [Diagram 3] FIG. 2 is a cross-sectional view of a collet chuck body. [Figure 4] FIG. 4 is an enlarged view of a portion IV in FIG. [Diagram 5] FIG. [Figure 6] FIG. [Figure 7] FIG. [Figure 8] FIG. 2 is an enlarged view of a portion VIII in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference characters and their description will not be repeated.

[0012] A tool holder according to an embodiment of the present invention will be described with reference to Figures 1 to 8. In Figures 1 and 2, the dashed dotted line O is an axis, the arrow T indicates the front side in the axial direction (also referred to as the tip side), and the opposite direction of the arrow T indicates the rear side in the axial direction (also referred to as the rear end side).

[0013] 1 in particular, tool holder 1 according to this embodiment is for chucking cutting tool 60, such as a very small diameter blade having an outer diameter of φ15 mm or less, and is attached to a spindle 100 of a machine tool. Tool holder 1 includes, as its main components, a collet chuck body 10, a collet 20 attached to the axial front side of collet chuck body 10, and a fastening member 30 attached to the axial front side of collet 20. When these components are assembled, tool holder 1 grips cutting tool 60.

[0014] 2 to 4, the collet chuck body 10 includes a shank portion 11, a flange 12 formed on the tip side of the shank portion 11, a cylindrical portion 13 extending from the flange 12 to the tip side, and a tool attachment portion 14 extending from the cylindrical portion 13 to the tip side for gripping a cutting tool 60 (FIG. 1). The collet chuck body 10 also has a through hole that communicates from the rear end side to the tip side along the axial direction.

[0015] First, the outer peripheral surface of the collet chuck body 10 will be described. The shank portion 11 is a portion that is attached to a spindle 100 (FIG. 1) of a machine tool. The shank portion 11 extends from a flange 12 toward the rear end along the O-axis. The outer peripheral surface 11a is a tapered surface whose diameter decreases from the flange 12 toward the rear end.

[0016] The flange 12 is a part that is gripped when replacing a cutting tool 60 (FIG. 1). The flange 12 is the collar portion that protrudes most outward in the collet chuck body 10, and protrudes radially outward further than the shank portion 11, the cylindrical portion 13, and the tool attachment portion 14. The cylindrical portion 13 is located in the axial center of the collet chuck body 10. The cylindrical portion 13 extends from the flange 12 toward the tip side along the O-axis.

[0017] The tool mounting portion 14 is an end portion of the collet chuck body 10 located opposite the shank portion 11. An annular step 15 is provided at the boundary between the tool mounting portion 14 and the cylindrical portion 13. Therefore, the outer diameter of the tool mounting portion 14 is smaller than the outer diameter of the cylindrical portion 13. A male thread 16 is formed at the tip portion of the tool mounting portion 14.

[0018] Next, the inner peripheral surface of the collet chuck body 10 will be described. As described above, the collet chuck body 10 has a through hole that communicates from the rear end side to the front end side along the O axis. Specifically, the inner peripheral surface on the rear end side is formed at its axial center with a fluid passage 11b for circulating cutting fluid supplied through the spindle 100 of the machine tool. The inner peripheral surface on the front end side is formed with a tapered hole 17 and a straight hole 18 that are successively formed from the front end in the axial direction.

[0019] The tapered hole 17 extends from the front end to the rear end, and the inner diameter gradually decreases toward the rear end. The straight hole 18 extends parallel to the O axis, connects to the rear end of the tapered hole 17, and connects to the front end of the fluid passage 11b.

[0020] As shown in Fig. 4, the boundary 19 between the tapered hole 17 and the straight hole 18 has a shape including an arc portion 19a and a pair of chamfered portions 19b, 19c located at both axial ends of the arc portion 19a. The arc portion 19a and the pair of chamfered portions 19b, 19c extend in the circumferential direction and have approximately the same axial length. In Fig. 4, the boundary between the arc portion 19a and the chamfered portions 19b, 19c is indicated by a dashed line.

[0021] A collet 20 is detachably inserted into the tapered hole 17 and the straight hole 18 of the collet chuck body 10. The collet 20 directly holds a cutting tool 60 (FIG. 1). The collet 20 will be described in detail with reference to FIGS. 5 and 6.

[0022] Collet 20 includes a tapered surface 21 and a straight surface 22, which are successively connected from the axial tip. Collet 20 is cylindrical, and has a tool insertion hole 23 formed on the inner circumference of the tip along the axial direction. Tool insertion hole 23 extends from the tip to the rear end, penetrating collet 20 in the axial direction.

[0023] The tapered surface 21 is located on the tip side with the axial center as the boundary, and the straight surface 22 is located on the rear end side. As shown in Figures 1 and 5, the outer diameter of the tapered surface 21 increases toward the tip side, and the tapered surface 21 abuts against the tapered hole 17 of the collet chuck body 10 described above. At the boundary between the tapered surface 21 and the straight surface 22, a minute annular step is provided that is coaxial with the axis.

[0024] The straight surface 22 extends parallel to the axis O. The straight surface 22 abuts against the inner peripheral surface of the straight hole 18 of the collet chuck body 10 described above. The axial dimension of the straight surface 22 is about 20 to 40 percent of the axial dimension of the collet 20, typically about 30 percent. The difference between the inner diameter dimension D1 (FIG. 3) of the straight hole 18 and the outer diameter dimension D2 of the straight surface 22 is formed to be extremely small.

[0025] The extremely small difference in diameter between the straight hole 18 and the straight surface 22 means that the difference in diameter is smaller than that of conventional products, specifically, that the difference is less than 0.1 mm, and more preferably less than 0.01 mm.

[0026] The difference in diameter between the straight hole and the straight surface in a conventional product and in this embodiment will be taken as an example. In the conventional product, the inner diameter dimension of the straight hole in the collet chuck body is φ9 mm, with a tolerance of ±0.2 mm. In contrast, the outer diameter dimension of the straight surface of the collet is φ7.5 mm, with a tolerance of ±0.03 mm. In the conventional product, the difference in diameter between the straight hole and the straight surface is about 1.5 mm, and a gap is formed between the straight hole and the straight surface when the collet is attached to the collet chuck body.

[0027] In contrast, in this embodiment, the inner diameter dimension D1 of the straight hole 18 of the collet chuck body 10 is φ7.6 mm, and the tolerance is +0.005 mm or more and +0.013 mm or less. In contrast, the outer diameter dimension D2 of the straight surface 22 of the collet 20 is φ7.6 mm, and the tolerance is -0.005 mm or more and -0.001 mm or less. Thus, in this embodiment, the difference in diameter between the straight hole 18 and the straight surface 22 (D1-D2) is less than 0.1 mm.

[0028] In this way, the tool holder 1 of this embodiment can reduce the gap between the straight hole 18 and the straight surface 22 compared to conventional products, making it possible to integrate the collet chuck body 10 and the collet 20.

[0029] As shown in Fig. 5, a flange 25 and a constricted portion 26 are formed on the tip end 27 side of the collet 20. The flange 25 is located on the outer diameter side of the tool insertion hole 23 and protrudes most outwardly from the tapered surface 21. The constricted portion 26 is formed on the rear end side of the flange 25. The constricted portion 26 has a smaller diameter than the tip side of the tapered surface 21 and the flange 25. The collet 20 engages with the tool insertion side end of the fastening member 30 at the constricted portion 26 so as to be relatively rotatable. In addition, it is preferable that the corners on the rear end side of the collet 20 are not sharp but are rounded.

[0030] As shown in Fig. 5, slits 24 are provided extending in the axial direction from the axial center of straight surface 22 to tip end 27 of tapered surface 21. As shown in Fig. 6, a plurality of slits 24 are provided at equal intervals in the circumferential direction, specifically, four slits 24 are provided. By compressing slits 24, the diameter of collet 20 can be reduced.

[0031] As described above, the collet 20 has the tool insertion hole 23 formed on its inner circumferential surface for holding the cutting tool 60. The tool insertion hole 23 penetrates the collet 20 in the axial direction from the rear end to the front end. An end of the cutting tool 60 is inserted into the tool insertion hole 23 from its front end side.

[0032] The fastening member 30 is for reducing the diameter of the collet 20 to tightly and firmly grip the cutting tool 60 in the collet chuck body 10. As shown in Figures 3 and 7, the fastening member 30 is a cylindrical member, and is fitted onto the outer periphery of the collet chuck body 10 so as to be rotatable and to be movable in the axial direction of the tool attachment portion 14.

[0033] The fastening member 30 is a cylindrical nut, and a female thread 31 is formed on the inner peripheral surface of the rear end side from the axial center toward the rear end side. Furthermore, on the inner peripheral surface of the front end side of the fastening member 30, a first protruding portion 32 protruding toward the inner diameter side, a recessed portion 34 recessed toward the outer diameter side from the first protruding portion 32, and a second protruding portion 35 protruding toward the inner diameter side are formed in this order from the axial front end toward the rear end. Here, the first protruding portion 32 has a rear end side end face 33 which is a surface facing the axial rear end side. The rear end side end face 33 is a ring-shaped flat surface perpendicular to the axis. The rear end side end face 33 faces the front end portion 27 of the collet 20 described above, and abuts against the front end portion 27 when the tool holder 1 is assembled.

[0034] Furthermore, as shown in FIG. 1, when the tool holder 1 is assembled, the recess 34 receives the flange portion 25 of the collet 20 described above, and the second protrusion 35 abuts against the narrowed portion 26 of the collet 20 described above.

[0035] Next, the procedure for chucking the tool holder 1 will be described with reference to FIGS.

[0036] 8, the tip portion 27 of the collet 20 is abutted against the rear end surface 33 of the fastening member 30, and the flange portion 25 of the collet 20 is inserted into the recess 34, and in a reduced diameter state, the flange portion 25 is inserted into the second protrusion 35 of the fastening member 30. Thereafter, the flange portion 25 returns to its original outer diameter, whereby the constricted portion 26 engages with the second protrusion 35, and the collet 20 is attached to the fastening member 30 so as to be capable of relative rotation.

[0037] 1, the straight surface 22 of the collet 20 is inserted into the straight hole 18 of the collet chuck body 10, and the tapered surface 21 of the collet 20 is inserted into the tapered hole 17 of the collet chuck body 10. The female thread 31 of the fastening member 30 is screwed into the male thread 16 of the collet chuck body 10, and the fastening member 30 is temporarily fastened to the collet chuck body 10.

[0038] Next, the shank portion of the cutting tool 60 is inserted into the tool insertion hole 23 of the collet 20. Here, the shank portion of the cutting tool 60 is inserted from the tip side of the fastening member 30. In this provisionally fastened state, the collet 20 has hardly contracted in diameter, so the shank portion of the cutting tool 60 can be easily inserted into the tool insertion hole 23.

[0039] Furthermore, the fastening member 30 is further rotated to further rotate (screw) the male thread 16 and the female thread 31 relatively to each other, and the fastening member 30 is finally fastened to the collet chuck body 10. As a result, the tapered surface 21 is pressed into the tapered hole 17 of the collet chuck body 10, and the collet 20 is reduced in diameter, chucking the shank portion of the cutting tool 60. In this chucked state, the tip portion 27 of the collet 20 and the rear end surface 33 of the fastening member 30 come into contact with each other, so that the collet 20 and the fastening member 30 are integrated together. Furthermore, since the difference between the outer diameter dimension D2 of the straight surface 22 and the outer diameter dimension of the straight hole 18 is extremely small, the collet chuck body 10 and the collet 20 are integrated together.

[0040] In the tool holder 1 of the embodiment, the difference in diameter between the straight hole 18 of the collet chuck body 10 and the straight surface 22 of the collet 20 is extremely small, so that the contact area between the collet chuck body 10 and the collet 20 can be increased. Furthermore, the rear end face of the first protrusion 32 of the fastening member 30 presses the tip portion 27 of the collet 20, so that the contact area between the fastening member 30 and the collet 20 can be increased. Therefore, the tool holder 1 of the embodiment can stabilize the runout accuracy of the cutting tool 60.

[0041] Furthermore, in conventional tool holders, if the boundary 19 between the straight hole 18 and the tapered hole 17 of the collet chuck body 10 is formed as a corner, when the collet 20 is inserted into the collet chuck body 10, the collet 20 may come into contact with the corner of the collet chuck body 10, causing the collet 20 to tilt.

[0042] In contrast, in the present embodiment, the boundary portion 19 between the straight hole 18 and the tapered hole 17 in the collet chuck body 10 is shaped to have an arc portion 19a and a pair of chamfered portions 19b, 19c formed on both sides of the arc portion 19a, thereby allowing the collet 20 to be smoothly pushed into the collet chuck body 10.

[0043] Furthermore, the corner where the outer circumferential surface and the side wall intersect at the rear end of the collet 20 may be formed with a radius. This, in combination with the shape of the boundary portion 19 described above, allows the collet 20 to be pushed into the collet chuck body 10 more smoothly.

[0044] Although the embodiment of the present invention has been described above with reference to the drawings, the present invention is not limited to the illustrated embodiment. Various modifications and variations can be made to the illustrated embodiment within the same scope as the present invention or within an equivalent scope. [Industrial Applicability]

[0045] The present invention is advantageously used in machine tools. [Explanation of symbols]

[0046] 1 tool holder, 10 collet chuck body, 14 tool attachment portion, 16 male thread, 17 tapered hole, 18 straight hole, 19a arc portion, 19b, 19c chamfered portion, 20 collet, 21 tapered surface, 22 straight surface, 23 tool insertion hole, 27 tip portion, 30 fastening member, 31 female thread, 33 rear end surface, 60 cutting tool, 100 spindle.

Claims

1. a collet chuck body including a tapered hole and a straight hole formed on an inner periphery of a tip portion and successively connected from the tip portion in the axial direction, and a male screw formed on an outer periphery of the tip portion; a collet including a tool insertion hole formed on an inner periphery of the tip portion, for inserting a tool, and a tapered surface and a straight surface formed on an outer periphery of the tip portion, which are successively connected from the tip portion in the axial direction, the collet being fitted into the tapered hole and the straight hole; a cylindrical fastening member including a female thread formed on an inner periphery of a rear end portion thereof and screwed into the male thread of the collet chuck body, and a rear end surface located on the tip side of the female thread, protruding inwardly toward the rear end side, the female thread being screwed into the male thread to press the collet against the tapered hole, thereby reducing a diameter of a tool insertion hole of the collet, The difference in diameter between the straight hole of the collet chuck body and the straight surface of the collet is formed to be extremely small, a tool holder formed so that after the collet is attached to the fastening member, the tip surface of the collet and the rear end surface of the fastening member abut against each other when the fastening member is attached to the collet chuck body.

2. 2. The tool holder according to claim 1, wherein a boundary between the straight hole and the tapered hole of the collet chuck body includes an arcuate portion and a pair of chamfered portions formed on both sides of the arcuate portion.

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