Tap tool

Abstract

This tap tool (10) has a shank part (12) having a center axis Om, and a cutter body (14) connected to one end of the shank part. The cutter body has a screw part (16) that engages with a prepared hole (H) formed in a workpiece (W), and a non-engaging part (18) that does not engage with the prepared hole. The screw part includes a complete screw part (22) on the base end side and an incomplete screw part (20) continuously formed on the tip side of the complete screw part. The incomplete screw part includes a cutting edge (16a) for processing the prepared hole, and a guide pad part (16b) positioned behind the cutting edge in the rotation direction. The outer peripheral surface of the guide pad part is formed from a cylindrical surface having a radius of the cutting edge with respect to the central axis.

Description

tapping tool

[0001] The present invention relates to a tapping tool for machining a pilot hole provided in a workpiece into a threaded hole.

[0002] When tapping is performed using a machining center and a tap tool attached to it, so-called synchronous tapping is performed, in which rotation and linear feed are synchronized. In synchronous tapping, rotation and feed must also be synchronized when withdrawing the tap tool from the threaded hole. Therefore, the time required to withdraw the tap tool is approximately equal to the time required to advance the tap tool and drill the thread groove.

[0003] Patent document 1 describes a tapping tool that includes a threaded portion having a cutting edge for machining a thread groove in a screw hole, a pad portion that engages with the thread groove machined by the cutting edge, and a non-engaging portion that forms a space between the threaded hole and the pad portion when viewed in cross section with the rotation axis and the central axis of the screw hole aligned.

[0004] Japanese Patent Application Laid-Open No. 2020-168698

[0005] In the tapping tool of Patent Document 1, a space is formed between the non-engaging portion and the threaded hole, so that after the threading is completed, the tapping tool can be shifted in a direction perpendicular to the rotation axis within the threaded hole from a state in which the rotation axis and the central axis of the threaded hole are aligned, thereby simultaneously releasing the engagement between the threaded portion and the thread groove and the engagement between the pad portion and the thread groove, and then the tapping tool can be pulled out axially from the threaded hole.

[0006] In the tapping tool of Patent Document 1, when the cutting edge of the chamfer at the tip of the tapping tool first cuts in, the chamfer cannot be sufficiently supported at the entrance of the pilot hole, which can cause deformation of the tapping tool, such as bending or tilting. Furthermore, the tapping tool of Patent Document 1 has a relief angle on the cutting edge, which makes it prone to deformation, such as bending or tilting, particularly when the tapping tool first cuts in.

[0007] The present invention is an improved invention of Prior Art Document 1, an earlier application of the present applicant, and aims to solve the problems of the prior art. That is, the object is to provide a tapping tool that can be shifted in a direction perpendicular to the rotation axis within a screw hole after machining is completed, and then the tapping tool can be pulled out axially from the screw hole, and that does not cause deformation such as bending or tilting when the cutting edge of the chamfer at the tip of the tapping tool cuts into the workpiece.

[0008] In order to achieve the above-mentioned object, according to the present invention, there is provided a tapping tool for machining a pilot hole formed in a workpiece into a threaded hole, the tapping tool comprising a shank portion having a central axis and a cutter body connected to one end of the shank portion, the cutter body having a threaded portion that engages with the pilot hole formed in the workpiece and a non-engagement portion that does not engage with the pilot hole, the threaded portion having a complete thread portion on the base end side and an incomplete thread portion formed continuous with the complete thread portion on the tip side, the incomplete thread portion having a cutting edge that machines the pilot hole and a guide pad portion located rearward in the direction of rotation of the cutting edge, the outer peripheral surface of the guide pad portion being a cylindrical surface parallel to the central axis and having a radius equal to the distance from the central axis to the cutting edge.

[0009] According to the present invention, the outer peripheral surface of the guide pad portion of the incomplete thread portion is formed from a cylindrical surface that is parallel to the central axis and has a radius equal to the distance from the central axis to the cutting edge. Therefore, during machining, particularly when the incomplete thread portion of the tap tool begins to engage with the pilot hole in the workpiece (when the chamfering edge cuts in), the outer peripheral surface of the guide pad supports the cutting resistance, preventing the tap tool from bending.

[0010] 1 is a schematic diagram showing an example of a machine tool that performs tapping using the tap tool of the present invention. FIG. 2 is a front view of a tap tool according to an embodiment of the present invention. FIG. 3 is a side view of the tap tool of FIG. 2. FIG. 4 is an end view of the tip side of the tap tool of FIG. 2. FIG. 5 is a perspective view of the tap tool of FIG. 2. FIG. 6 is a partially enlarged sectional view showing an incomplete thread portion of the tap tool of FIG. 2. FIG. 7 is a partially enlarged sectional view showing an incomplete thread portion of a tap tool of the prior art. FIG. 8 is a cross-sectional view similar to FIG. 8, showing cutting resistance and its main component force and thrust component force. FIG. 9 is a cross-sectional view of the tap tool and the tap hole, showing a state in which the tap tool has shifted from the state of FIG. 8. FIG. 10 is a front view of a tap tool with grooves.

[0011] A preferred embodiment of the present invention will now be described with reference to the accompanying drawings. Referring to FIG. 1 , a machine tool 100 to which the tapping tool and tapping method of the present invention can be applied is illustrated. In FIG. 1 , the machine tool 100 includes a bed 102 as a base fixed to the factory floor. A Y-axis guide rail 118 is provided on the upper surface of the bed 102, extending in the horizontal front-rear direction or Y-axis direction (left-right direction in FIG. 1 ). A table 104 is provided so as to be able to reciprocate along the Y-axis guide rail 118. A workpiece W is clamped and fixed to the table 104. The machine tool 100 includes a Y-axis servo motor (not shown) as a Y-axis drive device that reciprocates the table 104 in the Y-axis direction. The machine tool 100 also includes a Y-axis digital scale (not shown) that detects the Y-axis coordinate of the table 104.

[0012] A column 108 is erected on the upper surface of the rear end side of bed 102. An X-axis guide rail 120 is installed on the front surface of column 108, extending in the horizontal left-right direction or in the X-axis direction (a direction perpendicular to the plane of the paper in FIG. 1 ), and an X-axis slider 110 is provided so as to be able to reciprocate along X-axis guide rail 120. Machine tool 100 is equipped with an X-axis servo motor (not shown) as an X-axis drive device that drives X-axis slider 110 reciprocally in the X-axis direction. Machine tool 100 also is equipped with an X-axis digital scale (not shown) that detects the X-axis coordinate of X-axis slider 110.

[0013] A Z-axis guide rail 122 extends vertically or in the Z-axis direction on the front surface of X-axis slider 110, and headstock 112 is provided so as to be able to reciprocate along Z-axis guide rail 122. Machine tool 100 is equipped with a Z-axis servo motor (not shown) as a Z-axis drive device that drives headstock 112 reciprocally in the Z-axis direction. Machine tool 100 also has a Z-axis digital scale (not shown) that detects the Z-axis coordinate of headstock 112.

[0014] A spindle head 116 is attached to the headstock 112, supporting the spindle 114 rotatably about a vertical rotation axis Om. A rotary tool T such as an end mill, face mill, or drill, particularly a tap tool 10 (described below), can be attached to the tip of the spindle 114. The spindle head 116 is equipped with a spindle servo motor 124 that drives the spindle 114 to rotate about the rotation axis Om. The machine tool 100 is equipped with a rotation position detection device that detects the rotational position of the spindle 114 about the rotation axis Om. The rotation position detection device can be, for example, a rotary encoder 126 attached to the spindle servo motor 124.

[0015] The machine tool 100 can further be a machining center equipped with a tool magazine (not shown) that stores multiple tools used in machining, an automatic tool changer (not shown) that changes tools between the tool magazine and the spindle 114, and a coolant supply device (not shown) that supplies coolant to the machining area of ​​the machine tool 100, and these peripheral devices are housed together with the machine tool 100 in a cover (not shown).

[0016] The machine tool 100 further includes a control device 130 that controls the machine tool 100. The control device 130 can be composed of a computer and associated software, including a CPU (Central Processing Unit), memory devices such as RAM (Random Access Memory) and ROM (Read Only Memory), storage devices such as HDD (Hard Disk Drive) and SSD (Solid State Drive), input / output ports, and a bidirectional bus interconnecting these. The control device 130 can be formed by an NC control device that controls, in particular, the X-axis servo motor, the Y-axis servo motor, the Z-axis servo motor, and the spindle servo motor 124.

[0017] The machine tool 100 controls the X-axis servo motor, Y-axis servo motor, Z-axis servo motor, and spindle servo motor 124 in accordance with a machining program supplied to the control device 130, and moves the rotary tool T attached to the tip of the spindle relative to the workpiece W fixed to the table 104 in three orthogonal axis directions of X, Y, and Z, thereby machining the workpiece W.

[0018] Machine tool 100 performs tapping by synchronizing the rotation of spindle 114 with the feed in the Z-axis direction. In this specification, the linear movement in the Z-axis direction by tap tool 10 to perform tapping is referred to as forward movement, and the linear movement in the Z-axis direction by which tap tool 10 is withdrawn from threaded hole 6 is referred to as retreat movement.

[0019] The tap tool 10 performs tapping, i.e., machining the pilot hole H into a threaded hole 6, with its central axis Ot aligned with the central axis Oh of the pilot hole H formed in the workpiece W. In Figures 8 to 10, reference numeral 8 indicates the inner periphery of the threaded hole 6, which coincides with the pilot hole H. Reference numeral 6 also indicates the root of the threaded hole 6, which corresponds to the nominal diameter of the tap tool 10. The tap tool 10 rotates in the direction of arrow A.

[0020] The tap tool 10 has a rod-shaped shank portion 12 extending along a central axis Ot and a cutter body 14 coupled to the tip end of the shank portion 12. The shank portion 12 is formed to be attached to the tip end of a spindle 114. The shank portion 12 can be formed to be attached directly to an attachment hole (not shown) formed in the tip end of the spindle 114. Alternatively, the tap tool 10 can be attached to the tip end of the spindle 114 via a tool holder (not shown) or a tool chuck (not shown) by attaching the shank portion 12 so that it can be attached to the tool holder or the tool chuck.

[0021] The cutter body 14 is formed asymmetrically with respect to the central axis Ot and has a male-threaded threaded portion 16 that engages with the inner peripheral surface of a pilot hole H pre-formed in the workpiece W to machine a thread groove, and a non-engagement portion 18 that does not engage with the inner peripheral surface of the pilot hole H. The threaded portion 16 has a plurality of threads 24, 26, 28, 30 (see FIGS. 6 and 7 ) that are spaced apart at a predetermined thread pitch in the longitudinal direction. In this embodiment, the tap tool 10 forms a triangular thread groove.

[0022] 8 and 9 , each thread of the threaded portion 16 has a cutting edge 16a formed at the tip in the rotational direction of the tap tool 10 and a guide pad portion 16b that extends rearward from the cutting edge 16a in the rotational direction. In FIGS. 8 to 10 , the guide pad portion 16b is the portion from the cutting edge 16a to the rear end 16d and has an outer peripheral surface 16c. In this embodiment, the outer peripheral surface 16c is formed from a part of a cylindrical surface having the same radius as the cutting edge 16a (the distance between the central axis Ot and the cutting edge 16a). In other words, in this embodiment, the cutting edge 16a of the threaded portion 16 does not have a relief angle, and in this embodiment, the tangent to the cutting edge 16a and the tangent to the circumference described by the cutting edge 16a coincide with each other.

[0023] The threaded portion 16 has an incomplete thread portion 20 that forms a chamfer formed at the tip portion, and a complete thread portion 22 on the base end side. In this embodiment, the incomplete thread portion 20 has three threads 24, 26, and 28. The complete thread portion 22 has a plurality of threads 30. Referring to FIG. 6 , the three threads 24, 26, and 28 of the incomplete thread portion 20 are spaced apart at a predetermined thread pitch in the axial direction of the tap tool 10 and have outer peripheral surfaces 24 a, 26 a, and 28 a and flank surfaces 24 b, 26 b, and 28 b. The flank surfaces 24 b, 26 b, and 28 b are arranged approximately symmetrically in the axial direction on both sides of the outer peripheral surfaces 24 a, 26 a, and 28 a.

[0024] In this embodiment, the outer peripheral surfaces 24a, 26a, and 28a are each formed from a portion of a cylindrical surface, and the outer peripheral surfaces 24a, 26a, and 28a are parallel to the central axis Ot. The outer peripheral surface 28a at the tip end of the tap tool 10 has the smallest radius and is therefore widest in the axial direction. In contrast, the outer peripheral surface 24a at the base end has the largest radius and is therefore narrowest in the axial direction. Thus, when viewed in a longitudinal cross section of the incomplete thread portion 20 or when viewed projected onto a plane, the outer peripheral surfaces 24a, 26a, and 28a are formed in a stepped pattern from the outer peripheral surface 24a at the tip end to the outer peripheral surface 28a at the base end.

[0025] In contrast, in a conventional tapping tool, as shown in Fig. 7, the incomplete thread portion 50 forming the chamfer has three threads 52, 54, and 56 spaced axially at a predetermined thread pitch, and includes outer peripheral surfaces 52a, 54a, and 56a and flank surfaces 52b, 52c; 54b, 54c; and 56b, 56c. The outer peripheral surfaces 52a, 54a, and 56a are arranged within a common conical surface, and therefore the incomplete thread portion 50 is tapered toward the tip. As a result, the base-end flank surfaces 52b, 54b, and 56b of each of the threads 52, 54, and 56 are wider than the tip-end flank surfaces 52c, 54c, and 56c, and during machining, the base-end flank surfaces 52b, 54b, and 56b are subjected to a greater machining load than the tip-end flank surfaces 52c, 54c, and 56c.

[0026] In conventional tapping tools, the difference in size between the flank surfaces on the base end and the tip end of the thread of the incomplete thread portion that forms the lead portion causes the tapping tool to tilt and deform during machining. In contrast, in this embodiment, the flank surfaces 24b, 26b, and 28b are arranged approximately symmetrically in the axial direction on both sides of the outer peripheral surfaces 24a, 26a, and 28a, so that the tapping tool 10 is prevented from tilting and deforming during machining, particularly when the incomplete thread portion 20 of the tapping tool 10 begins to engage with the pilot hole H of the workpiece W.

[0027] The fully threaded portion 22 has a plurality of threads 30, seven in this embodiment. The threads 30 have flank surfaces 30b and an outer peripheral surface 30a, and the flank surfaces 30b are arranged axially symmetrically on both sides of the outer peripheral surface 30a. The fully threaded portion 22 has a shape that matches the root shape of the internal thread to be machined.

[0028] The non-engagement portion 18 has a smooth curved surface and can be formed, for example, by a portion of a cylindrical surface having a smaller radius than the shank portion 12. A space 4 is formed between the non-engagement portion 18 and the inner surface 8 of the threaded hole 6 machined in the workpiece W. The space 4 is large enough to disengage the threaded portion 16 from the female thread machined in the workpiece W when the tap tool 10 moves (shifts) from a position coincident with the central axis Oh of the threaded hole 6 in the workpiece W in a direction perpendicular to the rotation axis Om, as shown by the arrow S in FIG. 10 , from a position coincident with the central axis Oh of the threaded hole 6 in the workpiece W, as shown in FIGS. 8 and 9 , the space 4 is large enough to disengage the threaded portion 16 from the female thread machined in the workpiece W; that is, to completely separate the threads 24, 26, 28, and 30 of the threaded portion 16 from the inner surface 8 of the female thread in the workpiece W. In FIG. 10 , the arrow S is a vector indicating the direction and amount of movement of the spindle 114.

[0029] It is desirable to form the size of the space 4 slightly larger to provide a safety margin. During cutting, the space 4 serves as a path for supplying cutting fluid to the cutting edge 16a and a path for discharging chips generated by cutting, which has the effect of improving the quality of the machined surface and extending the tool life.

[0030] 10, when the threaded portion 16 is disengaged from the thread groove of the workpiece W by shifting the spindle 114, the tap tool 10 can be withdrawn from the threaded hole 6 by moving backward along the rotation axis Om (moving upward along the Z-axis in FIG. 1). This withdrawal of the tap tool 10 can be performed at high speed because it does not involve a rotational motion as in the conventional method.

[0031] In the following description, the 3 o'clock direction in Figure 8 is the origin of the rotational position of the spindle 114 around the rotation axis Om (position where the rotation angle θ = 0°). In Figure 8, the rotational angle of the tap tool 10 (hereinafter referred to as the "phase angle") is illustrated as 180 degrees as the phase angle of the cutting edge 16a. The phase angle of the tap tool 10 that has stopped after machining differs for each threaded hole 6 because the number of rotations of the tap tool 10 required for machining differs depending on the depth of the threaded hole 6. Therefore, the direction of the shift S of the tap tool 10 also differs for each threaded hole 6.

[0032] In order to determine the direction in which to shift the spindle 114, in this embodiment, when the tap tool 10 is positioned at a machining start point (not shown), the spindle 114 is set to a predetermined phase angle. Then, when the tap tool 10 comes to a standstill after machining, the control device 130 calculates the phase angle of the tap tool 10 based on information from the rotary encoder 126 of the spindle servo motor 124. Based on the calculated phase angle of the tap tool 10, the control device 130 calculates the shift direction of the spindle 114 (angle θ in FIG. 0). Meanwhile, the required shift amount is determined by the cross-sectional shape of the tap tool 10, and can therefore be stored in advance in the control device 130.

[0033] An example of tapping performed using a tap tool 10 according to an embodiment of the present invention and a vertical machine tool 100 such as that shown in Fig. 1 will be described below. First, the tap tool 10 is attached to the spindle 114 and then positioned at the machining start point. That is, the rotation axis Om of the spindle 114 of the machine tool to which the tap tool 10 is attached is aligned with the central axis Oh of a pilot hole H drilled in a workpiece, and the tip of the tap tool 10 is positioned at the machining start point at a predetermined height in the Z-axis direction. At this time, the spindle 114 is rotated and fed at a predetermined phase angle so that the cutting edge 16a is positioned at a predetermined rotational position.

[0034] Next, the rotation speed of the spindle 114 and the feed rate in the Z-axis direction are synchronized according to the pitch of the thread to perform synchronous tapping. The tap tool 10 moves a predetermined distance in the Z-axis direction, and when it reaches the commanded thread depth, the rotation of the spindle 114 and the feed rate in the Z-axis direction are stopped. This completes the tapping of the pilot hole H in the workpiece into the threaded hole 6.

[0035] Next, the tap tool 10 is shifted in a direction perpendicular to the rotation axis Om. The shift direction of the tap tool 10 (the direction indicated by the arrow S in FIG. 10 ) is calculated based on the phase angle of the tap tool 10 (the rotational position of the cutting edge 16 a) calculated based on information from the rotary encoder 126 of the spindle servo motor 124. The shift amount is determined by a value previously registered in the control device 130. This process completely releases the engagement between the threaded portion 16 of the tap tool 10 and the thread groove of the tapped hole 6.

[0036] Next, the tap tool 10 is retracted upward to the starting point of tapping without rotating. The feed rate of the spindle 114 in the Z-axis direction at this time can be set to more than twice the feed rate during tapping, i.e., when moving forward. In this way, tapping of one screw hole 6 is completed.

[0037] According to this embodiment, a space 4 is formed between the non-engagement portion 18 of the tapping tool 10 and the inner diameter of the threaded hole 6, and the space 4 has a size that disengages the threaded portion 16 from the thread groove when the tapping tool 10 moves in a direction perpendicular to the rotation axis Om. Therefore, after machining, the tapping tool 10, which has been disengaged from the thread groove of the threaded hole 6, can be pulled out of the threaded hole 6 at high speed in the direction of the rotation axis without rotation.

[0038] 9, the cutting resistance Rc acting on the cutting edge 16a of the tap tool 10 as a reaction force to the cutting force while the tap tool 10 rotates to perform tapping, and its thrust force Rb and principal force Rp are shown as vectors. Because the principal force Rp is greater than the thrust force Rb, the resultant cutting resistance Rc acts toward the guide pad portion 16b behind the cutting edge 16a in the rotational direction. The outer peripheral surface of each thread of the guide pad portion 16b is a cylindrical surface parallel to the center line Ot and having a radius equal to the distance from the center line Ot to the cutting edge 16a. Therefore, the cutting resistance Rc is first supported by the outer cylindrical surface of the guide pad portion 16b being in contact with the workpiece W. As described above, according to this embodiment, the outer peripheral surface 16c of the guide pad portion 16b is formed from a part of a cylindrical surface having a radius equal to the radius of the cutting edge 16a. Therefore, the cutting resistance Rc is supported by the screw hole 6, particularly the surface of the thread groove (valley) formed in the workpiece W, via the outer peripheral surface 16c of the guide pad portion 16b. Therefore, the tap tool 10 does not tip or bend due to the cutting resistance Rc. As a result, the machining accuracy is equivalent to that when a conventional tap tool is used.

[0039] Although the radius of the outer peripheral surface 16c of the guide pad portion 16b is described as being equal to the radius of the cutting edge 16a, "equal" does not mean that they are completely the same in the strict sense. In the present invention, "equal radii" includes radii that are the same or smaller by several μm to several tens of μm. In other words, "equal radii" includes "approximately equal radii." For example, "equal radii" may include machining errors within a reasonable range.

[0040] Furthermore, in order to lubricate the area between the outer peripheral surface 16c of the guide pad portion 16b and the surface of the thread groove (valley) formed in the workpiece W with coolant or to prevent an excessive increase in cutting resistance Rc, the radius of the outer peripheral surface 16c of the guide pad portion 16b may be made smaller than the radius of the cutting edge 16a within a range in which the guide pad portion 16b can support the cutting resistance Rc and prevent deflection of the tap tool 10, thereby forming a gap between the outer peripheral surface 16c of the guide pad portion 16b and the workpiece W. This gap can be, for example, 100 μm or less, preferably several tens of μm or less, and more preferably 50 μm or less.

[0041] Alternatively, the radius of the outer peripheral surface 16c of the guide pad portion 16b may be gradually reduced in the circumferential direction from the cutting edge 16b toward the rear end 16d, so that a gap is formed between the outer peripheral surface 16c and the workpiece W. This gap can be set to, for example, 100 μm or less, preferably several tens of μm or less, and more preferably 50 μm or less at the rear end 16d of the guide pad portion 16b.

[0042] If the radius of the outer peripheral surface 16c of the guide pad portion 16b is smaller than the radius of the cutting edge 16a, a gap will be formed between the outer peripheral cylindrical surface 16c of the guide pad portion 16b and the workpiece W, which could cause the tap tool 10 to bend. However, the flank surfaces 24b, 26b, 28b of the threads 24, 26, 28 come into contact with the threads of the female screw formed in the workpiece W, thereby supporting the cutting resistance Rc, and if the difference in radius is in the range of several μm to several tens of μm, bending of the tap tool 10 can be prevented.

[0043] The widths GW1, GW2, and GW3 of the outer peripheral surface 16c of the guide pad portion 16b can be made constant in the circumferential direction, so that the cutting resistance Rc is supported not only by the outer peripheral surface 16c but also by the flank surfaces 24b, 26b, and 28b of the threads 24, 26, and 28 of the incomplete thread portion 20, further enhancing the effect of preventing the tap tool 10 from deflecting.

[0044] As a preferred embodiment of the present invention, the example in which the radius of the outer peripheral surface 16 c of the guide pad portion 16 b is equal to the radius of the cutting edge 16 a has been described. As another example, the widths GW1, GW2, GW3 of the outer peripheral surface 16 c of the guide pad portion 16 b may increase slightly in the circumferential direction, i.e., the cutting edge 16 a may have a slight clearance angle.

[0045] The threaded portion 16 may also have one or more axially extending grooves. Referring to FIG. 11 , the tap tool 60, like the tap tool 10, has a shank portion 62 and a cutter body 64 coupled to the distal end of the shank portion 62. The cutter body 64 is formed asymmetrically with respect to the central axis Ot and has a male-threaded threaded portion 66 that engages with the inner circumferential surface of a pilot hole H pre-formed in a workpiece W to form a thread groove, and a non-engaging portion (not shown) that does not engage with the inner circumferential surface of the pilot hole H. The threaded portion 66 has an incomplete threaded portion 68 that forms a chamfer formed at the distal end and a complete threaded portion 70 at the proximal end. In this embodiment, the tap tool 10 has two axially extending grooves 72 formed in the threaded portion 66. The grooves 72 improve lubrication by coolant and chip evacuation.

[0046] 6 Screw hole 8 Inner peripheral surface 10 Tapping tool 12 Shank portion 14 Cutter body 16 Thread portion 16a Cutting edge 16b Guide pad portion 16c Outer peripheral surface 18 Non-engaging portion 20 Incomplete thread portion 22 Complete thread portion 24, 26, 28, 30 Thread 24a, 26a, 28a, 30a Outer peripheral surface 24b, 26b, 28b, 30b Flank surface

Claims

1. In a tap tool for machining a drilled hole formed in a workpiece into a threaded hole, the tap tool comprises a shank portion having a central axis, and a cutter body coupled to one end of the shank portion. The cutter body has a threaded portion that engages with the drilled hole formed in the workpiece and a non-engaging portion that does not engage with the drilled hole. The threaded portion includes a complete thread portion on the base end side and an incomplete thread portion continuously formed on the tip end side of the complete thread portion. The incomplete thread portion includes a cutting edge for machining the drilled hole and a guide pad portion located rearward in the rotational direction of the cutting edge. The outer peripheral surface of the guide pad portion is a cylindrical surface parallel to the central axis and is formed from a cylindrical surface having a radius equal to the distance from the central axis to the cutting edge. A tap tool characterized by this.

2. The tap tool according to claim 1, wherein the outer peripheral surface of the incomplete thread portion is formed from a part of a cylindrical surface parallel to the central axis.

3. The tap tool according to claim 2, wherein the outer peripheral surfaces of the plurality of threads are formed in a stepped shape such that the radius gradually increases from the thread on the tip end side to the thread on the base end side.

4. The tap tool according to claim 2, wherein the axial width of the outer peripheral surface of the guide pad portion is constant in the circumferential direction.

5. The tap tool according to claim 1, wherein the threaded portion has a groove extending in the axial direction.

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