Machining tools, machine tools, and machining methods

Abstract

We provide machining tools for precisely creating screw holes. [Solution] The present invention provides a machining tool comprising: a housing that is detachably mounted on a device capable of moving forward and backward relative to a workpiece; a tool holder that is slidably held within the housing in the direction of forward and backward movement; a tap that is detachably attached to the tip of the tool holder; a biasing member that biases the tool holder in the direction to which the tap is attached; and a displacement sensor that detects the amount of movement of the tool holder in the direction of forward and backward movement, wherein when the machined groove of the tap and the screw groove formed in the workpiece become misaligned during tapping, the tool holder slides in the opposite direction to the direction of movement of the device until the machined groove of the tap and the screw groove formed in the workpiece become aligned, and the displacement sensor detects the amount of sliding of the tool holder.

Description

Technical Field

[0001] The present invention relates to a machining tool, and provides a machining tool for precisely forming a screw hole, a machine tool having the machining tool, and a machining method using the machining tool. Background Art

[0002] When performing conventional thread machining, a threading tool (tap) is supported by a holder, and mounted on a device that can move forward and backward relative to a workpiece that is the object to be machined. The tool is moved in parallel while rotating relative to the workpiece, brought into contact with the workpiece, and the workpiece is cut to form a thread groove.

[0003] When performing precise thread machining on a workpiece, for example, in Patent Document 1, a workpiece provided with a prepared hole is first rough-machined using a first tap, and then the hole cut by the first tap is precision-machined using a second tap. Similarly, two types of taps are used for high-hardness machining members and the like. Prior Art Documents Patent Documents

[0004] Patent Document 1 JP 2021-112807 A Summary of the Invention Problems to be Solved by the Invention

[0005] However, Patent Document 1 relates to a method for manufacturing a nut, in which the workpiece is cylindrical, with a first tap arranged at one opening and a second tap arranged at the other opening, so the method can only be applied to form thread grooves in through holes, and cannot be applied otherwise.

[0006] When using two types of taps, the second tap requires alignment, specifically the starting position of the circumferential threads, a process known as "scratch alignment." This alignment is very time-consuming. If the workpiece is highly hard, improper screw alignment can immediately damage the tool.

[0007] This invention was made in view of the above problems, and provides a processing tool, a machine tool, and a processing method for precisely creating screw holes in blind holes and the like of high-hardness members. [Means for solving the problem]

[0008] To solve the above problems, a machining tool in one aspect of the present disclosure comprises a housing detachably mounted on a device capable of moving forward and backward relative to a workpiece, a tool holder slidably held within the housing in the direction of the forward and backward movement, a tap detachably attached to the tip of the tool holder, a biasing member that biases the tool holder in the direction to which the tap is attached, and a displacement sensor that detects the amount of movement of the tool holder in the direction of the forward and backward movement, wherein when the machining groove of the tap and the screw groove formed in the workpiece become misaligned during tapping, the tool holder slides in the opposite direction to the movement of the device until the machining groove of the tap and the screw groove formed in the workpiece become aligned, and the displacement sensor detects the amount of sliding of the tool holder.

[0009] Furthermore, a machine tool in one aspect of the present disclosure includes a device that can move forward and backward relative to a workpiece, a control unit that controls the movement of the device, a first machining tool that forms a screw groove in a pilot hole provided in the workpiece, a housing that is detachably mounted on the device, a tool holder that is slidably held within the housing in the direction of the forward and backward movement, a tap that is detachably attached to the tip of the tool holder, a biasing member that biases the tool holder in the direction to which the tap is attached, and the direction of the forward and backward movement of the tool holder The apparatus comprises a second machining tool having a displacement sensor for detecting the amount of movement, and when the second machining tool is attached to the apparatus and additional tapping is performed with the tap on the pilot hole in which the screw groove has been formed by the first machining tool, if the groove of the tap and the screw groove formed by the first machining tool do not match, the tap slides in the opposite direction to the movement of the apparatus until the groove of the tap and the screw groove match, and the control unit corrects the amount of movement of the apparatus with the amount of sliding of the tool holder detected by the displacement sensor.

[0010] Furthermore, a machining method in one aspect of the present disclosure comprises a housing detachably mounted on a device capable of moving forward and backward relative to a workpiece, a tool holder slidably held within the housing in the direction of the forward and backward movement, a tap detachably attached to the tip of the tool holder, a biasing member that biases the tool holder in the direction to which the tap is attached, and a displacement sensor that detects the amount of movement of the tool holder in the direction of the forward and backward movement, wherein the tool holder has a machining groove of the tap attached to the tool holder during tapping, and the workpiece already formed A machining method for forming a female screw hole in a workpiece, comprising: a pilot hole forming step of forming a pilot hole in the workpiece; a rough machining step of forming the screw groove in the pilot hole provided in the workpiece; and a precision machining step of correcting the machining length of the screw groove using the machining tool and the amount of sliding of the tool holder acquired by the displacement sensor. [Effects of the Invention]

[0011] As is clear from the above explanation, we can provide machining tools, machine tools, and machining methods for precisely creating screw holes in blind holes and the like in high-hardness materials. [Brief explanation of the drawing]

[0012] [Figure 1] This shows a machine tool equipped with a first processing tool and a second processing tool according to the present invention. [Figure 2] A cross-sectional view of the second machining tool is shown. [Figure 3] This is an exploded perspective view of the second machining tool. [Figure 4] A flowchart illustrating a machining method using a machine tool equipped with a second machining tool is shown. [Figure 5] Figure 4 illustrates the processing method shown. [Modes for carrying out the invention]

[0013] Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The embodiments are illustrative and not limiting to the invention, and not all features or combinations thereof described in the embodiments are necessarily essential to the invention. Furthermore, in the following descriptions of embodiments and modifications, the same components will be denoted by the same reference numerals, and redundant descriptions will be omitted as appropriate.

[0014] (Overall view) Figure 1 shows a machine tool 1 according to the present invention. The machine tool 1 is a so-called NC lathe and has a tap synchronous feed function, and can form screw grooves in a pre-drilled hole in the workpiece W, which is the workpiece, thereby forming a female screw hole in the workpiece W.

[0015] The machine tool 1 includes a spindle 6, a spindle rotation drive unit 9, a tool post 5 which is a device that can move forward and backward relative to the workpiece W, a control unit 7, and a first machining tool 10 and a second machining tool 20 fixed to the tool post 5.

[0016] The workpiece W is detachably fixed to a spindle rotation chuck 3 located at the tip of the spindle 6. The spindle 6 is rotationally driven by a spindle rotation drive unit 9, which is a motor. The rotation of the spindle rotation drive unit 9 is controlled by a control unit 7. As the spindle 6 rotates, the workpiece W fixed to the spindle rotation chuck 3 also rotates.

[0017] The tool post 5 is movably mounted on the tool post feed slide 8. The tool post 5 is driven to move by the tool post drive unit 4, which is an actuator. The drive of the tool post drive unit 4 is controlled by the control unit 7.

[0018] The tool rest 5 is arranged to face the main spindle 6. A first machining tool 10 and a second machining tool 20 are detachably fixed to the tip of the tool rest 5, and are arranged to be able to face the workpiece W. The tool rest 5 is capable of moving forward and backward in the rotation axis direction of the main spindle 6. That is, the tool rest 5 can move toward and away from the workpiece W, and as the tool rest 5 moves forward toward the rotating main spindle 6, the first machining tool 10 or the second machining tool 20 abuts on the rotating workpiece W to machine the workpiece W.

[0019] In the present embodiment, the workpiece W is fixed to the rotating main spindle 6, and the tool rest 5 moves forward and backward relative to the rotating workpiece W, but the aspect of the machine tool 1 is not limited thereto. An aspect in which the main spindle 6 moves toward the tool rest 5 is also acceptable. An aspect in which the tool rest 5 moves forward and backward toward the workpiece W while being rotationally driven relative to the fixed workpiece W is also acceptable. As long as the first machining tool 10 and the second machining tool 20 are capable of relative rotational movement and forward / backward movement with respect to the workpiece W, either of them may move, and either of them may rotate.

[0020] The machine tool 1 is movable in two orthogonal axes and can fix a plurality of machining tools. In the present embodiment, the first machining tool 10, the second machining tool 20, and a prepared hole machining tool (not shown) are fixed in parallel to the tool rest 5. As the tool rest 5 moves in the parallel direction (the left-right direction in Fig. 1), the tool that machines the workpiece W is changed.

[0021] The movement direction of the tool rest 5 may be only the forward / backward movement direction toward the workpiece W (uniaxial movement). The movement direction coincides with the rotation axis of the main spindle 6. The tool rest 5 can fix only one tool, and only either the first machining tool 10 or the second machining tool 20 is fixed to the tool rest 5, and the tools are replaced to sequentially machine the workpiece W, which is also an acceptable aspect.

[0022] In the present embodiment, the workpiece W is a high-hardness metal member such as stainless steel, the prepared hole formed in the workpiece W is a blind hole 2 having only one opening, and the depth of the prepared hole is shorter than the length of the workpiece W.

[0023] To form a female screw hole in a workpiece W, the workpiece W is fixed to the spindle chuck 3, and first, a blind hole 2 with a roughly cylindrical shape is formed in the workpiece W as a pilot hole. Next, as a rough machining process, a screw groove is formed in the blind hole 2 with a first machining tool 10. Then, as a precision machining process, a precise screw groove is formed with a second machining tool 20 to adjust the effective screw length, screw pitch diameter, screw thread shape, etc., to the target accuracy.

[0024] Since the workpiece W is a high-hardness material and the screw groove is to be machined into a blind hole 2, by performing a two-stage machining process using not only the first machining tool 10 but also the second machining tool 20, a screw groove of precise effective length can be formed in the blind hole 2.

[0025] The second machining tool 20 has an automatic thread alignment mechanism and a mechanism for automatically adjusting the screw groove length. Thread alignment refers to aligning the starting position of the threads. By aligning the starting position of the threads of the precision machining tap with the starting position of the threads formed by the rough machining tap, a precisely shaped screw groove can be added. By using the second machining tool 20 in the precision machining process, it is possible to automatically align it with the screw groove formed by the first machining tool 10, and to adjust the machining length, i.e., the effective length of the screw groove, thereby forming a precisely shaped screw groove with a high-precision effective length on the workpiece W.

[0026] (2nd tool) Figure 2 is a cross-sectional view of the second machining tool 20. Figure 3 is an exploded perspective view of the second machining tool 20.

[0027] As shown in Figure 2, the second machining tool 20 is detachably held on the tool post 5 of the machine tool 1.

[0028] The second machining tool 20 includes a tap 40 that directly contacts the workpiece W to form a screw groove, and a tool holder 22 that holds it. The tap 40 is detachably held at the tip of the tool holder 22 by a collet chuck mechanism (not shown).

[0029] The tool holder 22 is held within the housing 30 so as to be slidable in the axial direction of the tap 40. When machining the workpiece W, the second machining tool 20 is positioned so that this axial direction coincides with the direction of movement of the tool post 5. An axial hole 30a is formed in the housing 30 along the axial direction, and ball bushings 31, 31 are placed between the axial hole 30a and the tool holder 22, with a dust seal 33 provided at the opening to seal it. The tool holder 22 slides smoothly in the axial direction within the axial hole 30a of the housing 30 via the ball bushings 31, 31.

[0030] Near the base end of the housing 30, a housing shaft hole reduction portion 30b is provided, in which the diameter of the shaft hole 30a is reduced. Corresponding to the housing shaft hole reduction portion 30b, a tool holder reduction portion 22b is provided at the base end of the tool holder 22, in which the diameter of the tool holder 22 itself is reduced.

[0031] As shown in Figure 3, the main body of the tool holder 22 is cylindrical, while the reduced-diameter portion 22b of the tool holder is rectangular. The housing 30 corresponds to this; the shaft hole 30a through which the tool holder 22 is inserted has a circular cross-section, but only the reduced-diameter portion 30b of the housing shaft hole has a rectangular cross-section. As a result, the tool holder 22 does not rotate axially relative to the housing 30, but moves in the axial direction.

[0032] A notch 22c is formed in the reduced diameter portion 22b of the tool holder, and a headless bolt 35 is screwed into a screw hole 30d provided in the housing 30, which penetrates to the reduced diameter portion 30b of the housing shaft hole, with the tip of the screw portion protruding to the housing 30 and secured with a nut 34. As a result, the tool holder 22 is prevented from coming off the housing 30, and is allowed to slide axially by a distance that is the axial clearance between the notch 22c and the headless bolt 35.

[0033] The tool holder 22 has an engagement hole 22a formed along the axial direction. The tap 40 is engaged and fixed to the tip side of the engagement hole 22a. The housing 30 is inserted into and fixed to the base side of the engagement hole 22a, where the contact member 25 is located. The contact member 25 has a rod-shaped engagement portion 25a that engages with the engagement hole 22a and a disc-shaped flange portion 25b. When the engagement portion 25a engages with the engagement hole 22a, the flange portion 25b becomes the flange at the base end of the tool holder 22. When the tool holder 22 moves toward the tip, the flange portion 25b engages with the reduced diameter portion 22b of the tool holder, preventing it from coming loose and preventing the tool holder 22 from falling out of the tip of the shaft hole 30a. Furthermore, when the tool holder 22 retracts, the shoulder portion, which is the boundary between the reduced diameter portion 22b of the tool holder and the main body, abuts against the opening edge of the reduced diameter portion 30b of the housing shaft hole, suppressing excessive retraction.

[0034] A return spring 27 is positioned in the space from the reduced diameter portion 30b of the housing shaft hole to the base end of the shaft hole 30a. As a retaining member for the return spring 27, a plate-shaped spring retaining member 36 is positioned on the ceiling surface of the housing 30, through which the return spring 27 is inserted via a guide hole 36a. Furthermore, a plate-shaped cover member 38 is positioned to hold the return spring 27 in a biased state, and both are fixed to the ceiling surface of the housing 30 by fixing members (not shown). The tool holder 22 is biased toward the tip by the return spring 27.

[0035] A displacement sensor 50 is positioned above the housing 30 to detect the axial movement of the tool holder 22. The displacement sensor 50 has a sensor body 51 and a sensor head 52 which is a pin that is biased by an elastic body (not shown) and protrudes from the body. The sensor head 52 can be retracted into and out of the sensor body 51, and the displacement sensor 50 detects the amount of movement of the sensor head 52, which is movable only in the axial direction.

[0036] The displacement sensor 50 is positioned opposite the contact member 25. The cover member 38 has a through hole 38a in the center. The sensor head 52 is inserted through the through hole 38a of the cover member 38 and the guide hole 36a of the spring holding member 36, passes through the center of the return spring 27, and is positioned in contact with the top surface of the contact member 25.

[0037] The sensor head 52 is positioned in contact with the contact member 25, which is biased toward the tip due to the biasing force of the return spring 27. When the tool holder 22 slides toward the base end, the contact member 25 fixed to the tool holder 22 also slides toward the base end, pushing up the sensor head 52. The displacement sensor 50 measures the amount of movement of the sensor head 52, and the amount of axial movement of the tool holder 22 is determined from the measurement value of the displacement sensor 50.

[0038] In this embodiment, a return spring 27 is used as a biasing member to bias the tool holder 22 that fixes the tap 40 toward the tip, but it is not limited to this, and other elastic bodies may be used, or the housing 30 may be configured to apply pressure in the direction of tap advancement by connecting an air pump to it.

[0039] An optical sensor that uses light to measure distance may be used for the displacement sensor 50 that detects the amount of axial sliding of the tool holder 22. Alternatively, the amount of movement may be calculated from the rotation and feed of the spindle 6 by detecting the time from when the tool holder 22 contacts the workpiece W until it starts moving.

[0040] (Effects and Benefits) The method of use and effects of the second machining tool 20 configured as described above will now be explained. First, a screw groove is formed in the blind hole 2 of the workpiece W by the first machining tool 10, and then the second machining tool 20 is positioned opposite the workpiece W. The machine tool 1 has a tap synchronous feed function, and the spindle 6 is set to a rotational speed corresponding to a predetermined pitch. When the workpiece W is set on the spindle 6 and rotates, the second machining tool 20, which is fixed to the tool post 5 together with the tool post 5, moves forward toward the workpiece W at a speed corresponding to the pitch. The tap 40 comes into contact with the screw groove formed by the first machining tool 10. If the screw groove formed by the first machining tool 10 and the tool groove of the tap 40 do not match in the circumferential direction, the tool holder 22 retracts until the circumferential starting position of the tool groove of the tap 40 matches the circumferential starting position of the machined screw groove (alignment) (automatic alignment function).

[0041] When the tool groove of the tap 40 aligns with the pre-formed screw groove, the tool holder 22 moves forward as the tool post 5 moves forward, advancing through the blind hole 2 along the machined screw groove. When the tap 40 contacts the workpiece W, the tool post 5 moves forward until alignment occurs, but the tool holder 22 retracts. Once alignment is achieved, the tool holder 22 stops retracting and begins to move forward in accordance with the movement of the tool post 5, and the retraction of the sensor head 52 stops. The tool holder 22 slides in the opposite direction to the movement of the tool post 5, but since the tool post 5 continues to move forward, the tool holder 22 appears to remain relatively stationary.

[0042] The displacement sensor 50 measures the amount of axial sliding of the tool holder 22, and the distance D that the contact member 25 pushes the sensor head 52 from the initial state until the sensor head 52 stops moving is fed back to the control unit 7. The control unit 7 adds distance D to the set travel distance of the second machining tool 20. The tool post 5 moves by adding the distance D that the tool holder 22 has moved backward to the set travel distance. As a result, a precise and accurate screw groove with an effective length is formed in the blind hole 2.

[0043] Traditionally, in thread tapping, when creating internal threads in a screw hole, especially when working with hard-to-machine materials such as high-hardness components, multiple types of taps are used, such as a first tap (rough tap) and a second tap (precision tap), to process a single workpiece. However, when rough machining is performed on a pilot hole with a first tap, followed by precision machining with a second tap, it is necessary to align the tool groove of the second tap with the screw groove already formed in the pilot hole before inserting the second tap. When machining with multiple taps using automatic cutting machines such as NC lathes, the pre-machining setup for alignment is time-consuming. In particular, when the workpiece is a high-hardness component and the pilot hole is a blind hole, it is necessary to increase the frequency of tool changes and quality checks, which is time-consuming and costly.

[0044] Therefore, in this embodiment, the tool holder 22 that holds the tap 40 is slidable axially rearward, and the tool holder 22 is biased in the feed direction of the tool post 5 via a contact member 25 by a return spring 27. When the second machining tool 20 is fed by the tool post 5 and contacts the workpiece W while the tool holder 22 is slidable axially, the tool post 5 continues to advance with the rotating workpiece W, and the tool holder 22 that holds the tap 40 retracts until the starting position of the tool groove of the tap 40 matches the starting position of the screw groove formed by the first machining tool 10. When the tool groove of the tap 40 matches the screw groove formed by the first machining tool 10, the tool holder 22 stops retracting and begins to advance integrally with the tool post 5. In this way, the second machining tool 20 automatically aligns its teeth.

[0045] The forward distance of the tool post 5 relative to the workpiece W is set based on the required machining length of the workpiece W (referred to as the specified length RL). However, when alignment is performed automatically and the tap moves in the axial direction, variations occur in the effective length, which is the actual machining length. Therefore, the amount of sliding of the tool holder 22 to which the tap 40 is fixed is detected by the displacement sensor 50, and this is fed back to the control unit 7 that controls the tool post drive unit 4 that moves the tool post 5 to correct the machining length, so that the machining length with the second machining tool 20 becomes the specified length RL. This suppresses variations in thread machining caused by the rearward sliding of the second machining tool 20.

[0046] When performing tap cutting on an NC automatic lathe, using multiple cutting taps requires a lot of time and effort for setup, such as alignment, so it is generally preferable to form the female thread in one go using a single cutting tap. However, this leads to the tap reaching its wear limit after only a few uses, resulting in very high machining costs. In particular, with high-hardness materials like the workpiece W in this embodiment, the wear limit of the tap becomes extremely short.

[0047] When using multiple taps to extend the number of uses, especially when the pilot hole is a blind hole like in workpiece W, it is preferable to use multiple cutting taps to achieve the desired effective thread length. However, as mentioned above, this requires a great deal of setup and effort for alignment.

[0048] By using the second machining tool 20 of this embodiment, the feed rate of the tool post 5 is no longer forced, preventing excessive load on the tap, and increasing the number of uses before the tap reaches its lifespan limit. Furthermore, the workpiece W can be machined precisely with two taps, and by feeding back the measurement values ​​from the displacement sensor 50 to the control unit 7 of the spindle 6, variations in the effective length L are suppressed, enabling the formation of screw grooves with a consistent effective length L with high precision.

[0049] By using the second machining tool 20, the accuracy of the screw depth and screw diameter can be improved. The cutting edge of the tip of the first machining tool 10 is equipped with a cutting tap for rough machining, but the cutting edge at the very tip gradually wears down with use, so the accuracy of the screw groove (effective length, screw pitch diameter, screw thread shape, etc.) formed in the blind hole 2 of the pilot hole deteriorates with each use. By using the second machining tool 20, the screw groove whose accuracy has deteriorated can be adjusted to the target accuracy using the tap 40.

[0050] Tap 40 is a cutting tap, but this configuration can be used not only for cutting taps but also for rolling taps.

[0051] The tip of each tap has a tapered shape that narrows towards the end. Forming a female screw groove in a pilot hole means shaping it by cutting, and the cutting load is mainly applied to the tapered tip of the tap. Wear on the tip affects the machining accuracy and tool life. In this embodiment, the tapered portion of the tap of the first machining tool 10 (so-called rough tap) is short (about 3 pitches or less in screw pitch). This improves the machining accuracy of the tap of the second machining tool 20 (so-called finishing tap) and ensures the accuracy of the effective length L. As a result, a complete screw section is formed from the shoulder of the pilot hole 2 to 3 pitches or less in screw pitch. This configuration allows for the accurate formation of a screw groove of effective length L, thus shortening the pilot hole clearance. This configuration is particularly suitable when the pilot hole is very short, when the pilot hole clearance is short, or when the workpiece W is thin.

[0052] (Screw groove formation flow) The flow of forming screw grooves in a workpiece W using a machine tool 1 equipped with the second machining tool 20 configured as described above will be explained with reference to Figures 4 and 5.

[0053] First, in step S101, a pilot hole is drilled in the workpiece W as a pilot hole formation step. The workpiece W is fixed with the spindle rotation chuck 3, and a blind hole 2 is formed in the workpiece W as a pilot hole using a cutting tool (not shown).

[0054] Next, in step S102, the first machining tool 10 is set on the tool post 5 and positioned opposite the workpiece W. The control unit 7 is set to the feed rate and feed amount of the tool post drive unit 4, and the rotational speed of the spindle rotation drive unit 9, based on the required specifications. This determines the feed amount and feed rate of the first machining tool 10 and the second machining tool 20, and the rotational speed of the workpiece W.

[0055] Next, in step S103, a rough machining step is performed to form a screw groove in the workpiece W. Driven by the spindle rotation drive unit 9, the spindle 6 rotates, and the tool post 5, driven by the tool post drive unit 4, begins to move toward the rotating workpiece W, and a screw groove is formed in the blind hole 2 of the workpiece W by the first machining tool 10. At this time, the effective length L1 of the screw groove is shorter than the specified length RL (see Figures 5(B) and 5(C)).

[0056] Next, in step S104, the second machining tool 20 is positioned opposite the workpiece W. The tool post 5 moves left and right to position the second machining tool 20 opposite the workpiece W. Alternatively, the first machining tool 10 may be removed and the second machining tool 20 may be attached to position the second machining tool 20 opposite the workpiece W.

[0057] Next, in step S105, machining with the second machining tool 20 is started. The workpiece W fixed to the spindle 6 rotates due to the drive of the spindle rotation drive unit 9, the displacement sensor 50 starts measuring, and the tool post drive unit 4 is driven to start machining with the second machining tool 20.

[0058] Next, in step S106, alignment is performed. The tool post 5 moves forward toward the workpiece W, and the tap 40 comes into contact with the blind hole 2. The tool post 5 continues to move at a predetermined speed even after the tap 40 makes contact, and the tool holder 22, which supports the tip of the tap 40, retracts until the machining groove of the tap 40 aligns with the screw groove formed by the first machining tool 10. The displacement sensor 50 measures the amount of sliding of the tool holder 22 that fixes the tap 40 and constantly outputs the measured value to the control unit 7.

[0059] Next, in step S107, as a precision machining step, the second machining tool 20 forms a precise screw groove. When the tap 40 aligns with the screw groove formed by the first machining tool 10, and the tool holder 22 does not retract but begins to move forward together with the tool post 5, the sensor head 52 stops moving. The measurement value of the displacement sensor 50 at this time is fed back to the control unit 7 as the amount of sliding of the tool holder 22. The control unit 7 corrects the amount of movement of the tool post 5 based on the measurement value of the displacement sensor 50, and the second machining tool 20 moves forward to a predetermined depth. The second machining tool 20 performs additional machining on the screw groove of effective length L1 formed by the first machining tool 10, so that the screw groove becomes effective length L2 (see Figures 5(D) and 5(E)). The depth of the screw groove is corrected by the measurement value of the displacement sensor 50. The second machining tool 20 suppresses variations in the depth of the screw groove. This creates a precise female screw hole in the workpiece W, with reduced variation in the effective length L of the screw groove (precision machining step).

[0060] The embodiments described above are examples of the present invention, and these can be combined based on the knowledge of those skilled in the art; such combinations are also included within the scope of the present invention. [Explanation of Symbols]

[0061] 1: Machine tool 2: Blind hole (pilot hole) 5: Knife rest 7: Control Unit 10: 1st processing tool 20: 2nd processing tool 22: Tool holder 27: Return spring (biasing member) 30: Housing 40: Tap 50: Displacement sensor S101~S107: Step W: Work

Claims

1. A housing that is detachably attached to a device that can move forward and backward relative to the workpiece, A tool holder is slidably held within the housing in the direction of the forward and backward movement, A tap that is detachably attached to the tip of the tool holder, A biasing member that biases the tool holder in the direction in which the tap is attached, A displacement sensor that detects the amount of movement of the tool holder in the direction of forward and backward movement, Equipped with, When the machined groove of the tap and the screw groove formed in the workpiece become misaligned during tapping, the tool holder slides in the opposite direction to the movement of the device until the machined groove of the tap and the screw groove formed in the workpiece become aligned, and the displacement sensor detects the amount of sliding of the tool holder. A machining tool characterized by the following features.

2. A device capable of moving forward and backward relative to the workpiece, A control unit that controls the movement of the device, A first machining tool for forming screw grooves in a pilot hole provided in the workpiece, A housing detachably attached to the device; a tool holder slidably held within the housing in the direction of forward and backward movement; a tap detachably attached to the tip of the tool holder; a biasing member that biases the tool holder in the direction to which the tap is attached; and a displacement sensor that detects the amount of movement of the tool holder in the direction of forward and backward movement. A second machining tool having, Equipped with, When the second machining tool is attached to the apparatus and additional tapping is performed with the tap on the pilot hole in which the screw groove has been formed by the first machining tool, if the machining groove of the tap and the screw groove formed by the first machining tool do not match, the tool holder slides in the opposite direction to the movement of the apparatus until the machining groove of the tap and the screw groove match. The control unit corrects the amount of movement of the device based on the amount of sliding of the tool holder detected by the displacement sensor. A machine tool characterized by the following features.

3. A housing that is detachably attached to a device that can move forward and backward relative to the workpiece, The system comprises a tool holder slidably held within the housing in the direction of forward and backward movement, a tap detachably attached to the tip of the tool holder, a biasing member that biases the tool holder in the direction to which the tap is attached, and a displacement sensor that detects the amount of movement of the tool holder in the direction of forward and backward movement. A machining method for forming a female screw hole in a workpiece using a machining tool, wherein, when the machining groove of the tap attached to the tool holder becomes misaligned with the screw groove already formed in the workpiece during tapping, the tool holder slides in the opposite direction to the movement of the device until the machining groove of the tap and the screw groove align, and the displacement sensor detects the amount of sliding of the tool holder. A pilot hole forming step of forming a pilot hole in the workpiece, A rough machining step in which the screw groove is formed in the pilot hole provided in the workpiece, A precision machining step in which the screw groove is machined using the machining tool, with the machining length corrected by the amount of sliding of the tool holder obtained by the displacement sensor, A processing method characterized by comprising the following:

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