Point tap
Patent Information
- Application Number
- PCT/JP2024/008406
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-03-06
- Publication Date
- 2025-10-02
AI Technical Summary
Existing point taps experience premature wear and reduced tool life due to the reaction force generated when chips are ejected, causing the tap to be pushed back against the workpiece, leading to improper thread formation and uneven wear on the threads.
The point tap design incorporates a primary groove twisted in the same direction as the rotational direction and a secondary groove twisted in the opposite direction, offsetting the thrust forces and ensuring the tap advances along its intended lead, with balanced wear on the leading and trailing flank surfaces.
This design stabilizes the cutting process, reduces torque and thrust, and extends tool life by evenly distributing resistance and wear, resulting in more precise and durable thread formation.
Smart Images
Figure JP2024008406_02102025_PF_FP_ABST
Abstract
Description
Point Tap
[0001] The present invention relates to a point tap.
[0002] The thread portion of a point tap has a chamfer portion and a full thread portion (see, for example, Patent Document 1). The full thread portion has a linear primary flute. The chamfer portion has a secondary flute. The secondary flute twists in the opposite direction to the rotation of the thread portion. Therefore, the secondary flute pushes chips forward and discharges them.
[0003] U.S. Patent No. 7,144,208
[0004] The reaction force generated when chips are ejected acts on the point tap in the opposite direction to its forward movement. Because the point tap is pushed back against the workpiece, it creates a female thread with a delay compared to its original lead. This causes the slope of the point tap's threads on the base side to rub against the female thread in a stepped manner. This makes the threads of the point tap prone to wear, potentially affecting tool life.
[0005] An object of the present invention is to provide a point tap that can be expected to extend the tool life.
[0006] The point tap of the present invention comprises a threaded portion having a chamfer portion and a full thread portion, a primary groove provided in the full thread portion, and a secondary groove provided in the chamfer portion and twisted in a direction opposite to the rotational direction of the threaded portion, wherein the primary groove is twisted in the rotational direction or inclined toward the rotational direction with respect to the axial direction.
[0007] According to the present invention, the point tap has a driving force due to the twist in the rotational direction at the full thread portion. Therefore, a force acts on the point tap in the direction in which the point tap itself advances. The force acting on the point tap is offset by the return force generated by cutting in the secondary groove of the chamfer portion. This allows the point tap to achieve stable cutting. Furthermore, because the point tap advances along its original lead, the thread portion properly contacts the workpiece. This also reduces abnormal wear and chipping of the point tap. Furthermore, when the point tap rotates forward, there is a difference in the passage time between the leading end of the full thread portion and the trailing end of the full thread portion. The passage time is, for example, the time it takes to pass through an imaginary line drawn on the workpiece parallel to the axis of the point tap. This distributes the resistance received from the workpiece, allowing the point tap to achieve stable cutting.
[0008] The twist angle or inclination angle of the primary groove may be 1° or more and 7° or less. Therefore, the point tap can more effectively obtain the effect described in claim 1.
[0009] The connecting portion between the primary groove and the secondary groove may be located opposite the first complete crest at the most distal end of the complete crest portion. This allows the forward force generated by the primary groove and the return force generated by the secondary groove to be offset in a balanced manner, thereby enabling the point tap to achieve more stable cutting.
[0010] The point tap may be a right-hand cutting edge that rotates clockwise when viewed from the rear end in the axial direction, the secondary grooves may be left-handed, and the primary grooves may be right-hand helical or inclined in the direction of clockwise rotation relative to the axial direction. Therefore, the right-hand cutting edge point tap can achieve the effect described in claim 1.
[0011] The point tap may be a left-hand cutting edge that rotates leftward when viewed from the rear end in the axial direction, the secondary grooves may be right-handed, and the primary grooves may be left-hand twisted or inclined in the direction of left rotation relative to the axial direction. Therefore, the left-hand cutting edge point tap can achieve the effect described in claim 1.
[0012] 1 is a perspective view of the point tap 10; FIG. 2 is a side view of the point tap 10 (helix angle θ1 = 1°); FIG. 3 is a side view of the point tap 30 (helix angle θ2 = 5°); FIG. 4 is a diagram showing the principle of enlarging a female thread when cutting with a conventional point tap 100; FIG. 5 is a photograph of the workpiece surface after cutting with a conventional product; FIG. 6 is a photograph of the workpiece surface after cutting with a product of the invention; FIG. 7 is a graph showing test results comparing average torque; FIG. 8 is a graph showing test results comparing average thrust; FIG. 9 is a side view of the point tap 300 (helix angle θ1 = 1°).
[0013] An embodiment of the present invention will be described. In the following description, in the axial direction along the axis AX of the point tap 10 shown in Figure 1, the threaded portion 14 side is the leading end side of the point tap 10, and the shank portion 12 side is the rear end side of the point tap 10. To clarify the description of this embodiment, some parts in the drawings are shown with dimensional ratios that differ from the actual dimensional ratios. Therefore, the present invention should not be interpreted as being limited to the shapes in the drawings.
[0014] The configuration of a point tap 10 will be described with reference to Figures 1 and 2. The point tap 10 is a tool used to cut a female thread into a pilot hole pre-formed in a workpiece (shown). The pilot hole is a through hole. The point tap 10 comprises a shank portion 12 and a threaded portion 14. The shank portion 12 is attached to a machine spindle (not shown) or the like and is driven to rotate. A male thread is formed on the threaded portion 14. The male thread has a thread shape that corresponds to the thread groove of the female thread to be cut into the pilot hole (not shown) in the workpiece.
[0015] The thread portion 14 has a chamfering portion 16 and a full thread portion 18. The diameter of the chamfering portion 16 decreases toward the tip. The diameter of the full thread portion 18 is approximately constant. As shown in FIG. 2 , the slope on the leading side of the male thread 15 is a leading flank surface 151, and the slope on the following side is a following flank surface 152.
[0016] Five grooves 20 are provided in the threaded portion 14 in the axial direction. The axial direction is a direction parallel to the axis AX. The five grooves 20 extend from the tip of the threaded portion 14 to the tip side of the shank portion 12, dividing the male thread of the threaded portion 14 into five parts in the circumferential direction. A cutting edge 25 is formed at one end of the divided thread, i.e., the end in the counterclockwise direction as viewed from the tip side in Figure 2. The rotation direction R of the point tap 10 is right-handed (clockwise) when viewed from the rear end side of the point tap 10. Therefore, the point tap 10 is a right-hand cutting edge.
[0017] The groove 20 includes a primary groove 21 and a secondary groove 22. The primary groove 21 is formed in the complete thread portion 18 of the thread portion 14. The primary groove 21 supplies cutting oil to the tip side of the point tap 10. The secondary groove 22 is formed in the chamfer portion 16 of the thread portion 14. The secondary groove 22 is a helical groove that is twisted in the opposite direction to the rotation direction R (right rotation: clockwise) of the point tap 10, and in this embodiment, is a left-handed helix. The secondary groove 22 is formed by obliquely cutting away several threads from the groove 20 on the cutting edge 25 side of the chamfer portion 16. Therefore, during cutting with the point tap 10, chips are discharged in the direction of travel in the pilot hole. The junction Q between the primary groove 21 and the secondary groove 22 is located opposite the first complete thread 17, which is located at the tip end of the complete thread portion 18.
[0018] The primary grooves 21 are helical grooves that are twisted in the same direction as the rotational direction of the point tap 10, and in this embodiment are right-handed. For example, the helix angle θ1 of the primary grooves 21 of the point tap 10 shown in Figure 2 is 1°. The helix angle θ2 of the primary grooves 21 of the point tap 30 shown in Figure 3 is 5°. The helix angles θ1 and θ2 are the angles between the primary groove 21 and a line P that passes through a point on the primary groove 21 and is parallel to the axis AX. Note that although the primary grooves 21 in this embodiment are twisted in the same direction as the rotational direction, they may also be inclined toward the rotational direction with respect to the axis AX, for example.
[0019] The principle of female thread expansion using a conventional product will be described with reference to Figure 4. Point tap 100 is a conventional product. Point tap 100 includes a shank portion 12, a thread portion 14, and a groove 200. The primary groove 211 of groove 200 is a straight groove. The expansion of a female thread refers to a state in which, for example, after cutting a workpiece W with point tap 100, the quality of the female thread 60 is inspected using a thread plug gauge, and the no-thread side thread plug gauge is threaded in more than two turns.
[0020] The point tap 100 cuts a female thread 60 into a pilot hole 40 pre-drilled in a workpiece W. A thread 61 of the formed female thread 60 has an entry flank surface 62 and an exit flank surface 63 formed thereon.
[0021] During cutting, the point tap 100 must advance accurately along its intended lead. However, due to the reaction force generated when chips are discharged from the secondary groove 221, a strong thrust force acts on the point tap 100 in the direction opposite to its advance. This causes the point tap 100 to be pushed back in the opposite direction. Since the point tap 100 no longer advances along its intended lead, excessive cutting of the female thread 60 occurs.
[0022] Specifically, when the first cutting edge contacts and cuts the workpiece W, the next cutting edge overcuts the entry flank surface 62 of the workpiece W due to the opposite thrust force, later than the specified lead. Then, the next cutting edge overcuts the entry flank surface 62 of the workpiece W, later than the lead again. This is repeated, forming a step on the entry flank surface 62 of the thread 61. Therefore, collapse occurs on the mouth side of the female thread 60, causing the female thread to widen.
[0023] Furthermore, a strong thrust force acts in the direction opposite to the direction of advancement on the conventional point tap 100. Therefore, the point tap 100 performs machining in a state in which the trailing flank surface of the thread 14 (see trailing flank surface 152 shown in FIG. 2 ) rubs against the exit flank surface 63 of the female thread 60. This causes wear on the trailing flank surface of the thread 14 to progress faster than wear on the exit flank surface, resulting in a problem of shortened tool life.
[0024] Furthermore, because the conventional point tap 100 has a straight primary groove, when the point tap 100 rotates forward, the multiple threads that make up the full thread portion 18 begin to rotate in the same phase. In other words, if an imaginary line parallel to the axis AX (see imaginary line K in Figure 1) is drawn on the workpiece W, multiple threads will pass through that imaginary line at the same time. Therefore, the resistance received from the workpiece W tends to be concentrated when multiple threads come into contact with the workpiece W at the same time.
[0025] The effect of the point tap 10 of this embodiment will now be described. As described above, the primary groove 21 of the point tap 10 twists in the same direction as the rotational direction R. Therefore, the point tap 10 obtains a propulsive force with the same twist as the rotational direction R, and a thrust force acts on the point tap 10 in the forward direction. The thrust force in the forward direction generated in the primary groove 21 is offset by the opposite thrust force generated in the secondary groove 22. Therefore, the point tap 10 can accurately advance along its original lead during cutting, thereby suppressing the expansion of the female thread 60.
[0026] Furthermore, because a thrust force acts on the point tap 10 in the direction of advance, the leading flank surface 151 of the point tap 10 comes into contact with the entry flank surface 62 of the female thread 60, and the trailing flank surface 152 of the point tap 10 comes into contact with the exit flank surface 63 of the female thread 60 to the same extent. Therefore, the leading flank surface 151 and the trailing flank surface 152 of the point tap 10 wear to the same extent, which is expected to extend the tool life.
[0027] Furthermore, because the primary flutes 21 are twisted in the same direction as the rotation direction R, when the point tap 10 rotates forward, there is a difference in the time it takes for the imaginary line K (see FIG. 1) to pass through the complete thread portion 18 from the first complete thread 17 to the final complete thread 19. This distributes the resistance that the complete thread portion 18 receives from the workpiece, allowing the point tap 10 to achieve stable cutting of female threads.
[0028] Next, a comparative test was conducted on the workpiece surface after cutting using the point tap. In this test, a female thread was machined into each workpiece using the product of the present invention and a conventional product, and the state of the female thread surface after machining was compared. The product of the present invention is the point tap 10 of the present invention (see Figure 2) with a primary flute helix angle of 1°. The conventional product is the point tap 100 (see Figure 4) with a primary flute helix angle of 0°. The machining conditions were as follows: Point tap diameter = M14X1.5 Workpiece = S50C Cutting speed = 36 m / min Feed rate = 1.5 mm / rev
[0029] The results will be explained with reference to Figures 5 and 6. Figure 5 is a photograph of the surface of the female thread, viewed from the inlet side of the workpiece, after female thread machining using a conventional product. Looking at the surface of the female thread after machining, many thin, streaky chatter marks were observed. This is presumably because machining was performed in a state in which the follow-up flank surface of the point tap 100 was rubbing against the outlet flank surface 63 of the female thread 60, causing chatter in the point tap 100 and making the female thread machining unstable.
[0030] Figure 6 is a photograph of the surface of the female thread, viewed from the inlet side of the workpiece, after the female thread was machined using the product of the present invention. Looking at the surface of the female thread after machining, chatter marks were almost completely eliminated compared to the surface of the female thread of the conventional product. This is presumably because the point tap 10 advanced accurately along its original lead, and the leading flank surface 151 and the trailing flank surface 152 of the point tap 10 made equal contact with the inlet flank surface 62 and the outlet flank surface 63 of the female thread, suppressing chatter and stabilizing the cutting process. These results demonstrate that the product of the present invention can perform more stable machining than the conventional product.
[0031] Referring to Figure 7, a torque test of the point tap during cutting will be described. In this test, five types of point taps (product of the present invention) with primary flute helix angles of 1°, 3°, 5°, 7°, and 9° were prepared, along with a conventional product. In this test, the torque of the point tap was measured when cutting a female thread into a pilot hole (through hole) formed in the workpiece. The test was performed twice and the average values were compared. The conventional product was a point tap with a straight primary flute (helical angle = 0°). The cutting conditions were as follows: Point tap diameter = M14X1.5 Workpiece = S50C Cutting speed = 36 m / min Feed rate = 1.5 mm / rev
[0032] The results will be explained. As shown in Figure 7, the average torque of the conventional product was 1353 (Ncm). The average torque of the 1° twist point tap was 779 (Ncm). The average torque of the 3° twist point tap was 887 (Ncm). The average torque of the 5° twist point tap was 916 (Ncm). The average torque of the 7° twist point tap was 900 (Ncm). The average torque of the 9° twist point tap was 877 (Ncm). Among the products of the present invention, the 1° twist had the lowest average torque.
[0033] From these results, it is presumed that the torque increased with the conventional product because the cutting was performed with the trailing flank rubbing against the female thread slope. On the other hand, with the product of the present invention, the average torque during cutting was lower than with the conventional product for all five types of primary groove twist. This is presumed to be because the point tap advanced along its original lead, since a thrust force acted in the direction of advancement with all of the products of the present invention. Therefore, the product of the present invention was confirmed to have a torque reduction effect compared to the conventional product at all twist angles from 1° to 9°.
[0034] Referring to Figure 8, a thrust test of a point tap during cutting will be described. Five types of point taps (the present invention) with primary flute helix angles of 1°, 3°, 5°, 7°, and 9° were prepared for this test, along with a conventional point tap. In this test, the thrust of the point tap was measured when a female thread was drilled into a pilot hole (through hole) formed in a workpiece. The test was performed twice and the average values were compared. The conventional point tap had a straight primary flute (helical angle = 0°). The machining conditions were the same as those for the torque test. Note that the positive side of the average thrust (N) in the graph shown in Figure 8 represents the thrust in the direction opposite to the direction of advance, and the negative side represents the thrust in the direction of advance.
[0035] The results will be explained below. As shown in Figure 8, the average thrust of the conventional product was 187 (N). The average thrust of the 1° helix point tap was 148 (N). The average thrust of the 3° helix point tap was 103 (N). The average thrust of the 5° helix point tap was 68 (N). The average thrust of the 7° helix point tap was 32 (N). The average thrust of the 9° helix point tap was -15 (N).
[0036] These results show that the average thrust during cutting was lower than that of the conventional product in all cases where the twist angle was 1° to 9°. This is presumably due to the thrust force acting in the direction of advance.
[0037] However, at a 9° helix, the thrust reversed to the direction of advance. This is presumably because the twist of the primary groove was large, causing excessive thrust force in the direction of advance, causing the point tap to advance further in the direction of advance than its intended lead. Therefore, the product of the present invention was confirmed to have a reduced thrust effect compared to the conventional product at any helix between 1° and 9°, and it was also confirmed that a helix between 1° and 7° was more preferable.
[0038] As described above, the point tap 10 of this embodiment includes a threaded portion 14 and a groove 20. The threaded portion 14 includes a chamfer 16 and a full thread portion 18. The groove 20 includes a primary groove 21 and a secondary groove 22. The primary groove 21 is provided in the full thread portion 18. The secondary groove 22 is provided in the chamfer 16 and twists in the opposite direction to the rotational direction of the threaded portion 14. The primary groove 21 twists in the same direction as the rotational direction of the point tap 10. Therefore, the point tap 10 has a driving force due to the twist in the rotational direction at the full thread portion 18. A force acts on the point tap 10 in the direction in which the point tap 10 itself advances. The force acting on the point tap 10 is offset by a return force generated by cutting in the secondary groove 22 of the chamfer 16. Therefore, the point tap 10 can achieve stable cutting. Furthermore, because the point tap 10 advances along its original lead, the threaded portion 14 appropriately contacts the workpiece. This prevents abnormal wear and chipping of the point tap 10. Furthermore, when the point tap 10 rotates forward, there is a difference in the passage time between the first complete thread 17 on the leading edge side and the complete thread 19 on the trailing edge side of the full thread portion 18. This distributes the resistance received from the workpiece, allowing the point tap 10 to achieve stable cutting.
[0039] By setting the helix angle of the primary groove 21 to be between 1° and 7°, the point tap 10 can be prevented from lagging behind or overleading its original lead during cutting. Therefore, the point tap 10 can achieve stable cutting.
[0040] The connection portion Q between the primary groove 21 and the secondary groove 22 is located opposite the first complete crest 17 located at the most distal end of the complete crest portion 18. Therefore, the forward force of the primary groove 21 and the return force of the secondary groove 22 are offset in a balanced manner, allowing the point tap 10 to achieve more stable cutting.
[0041] The present invention is not limited to the above embodiment and various modifications are possible. The point tap 10 in this embodiment has a right-hand blade, the secondary flutes 22 are left-hand helix, and the primary flutes 21 are right-hand helix. For example, the present invention can be applied to a left-hand blade such as the point tap 300 shown in FIG. 9 . The rotation direction R of the point tap 300 is left-hand (counterclockwise) when viewed from the rear end of the point tap 300. In this configuration, the secondary flutes 122 are right-hand helix, and the primary flutes 121 are left-hand helix. The helix angle θ3 of the primary flutes 121 is 1°. The cutting edge 125 is formed at one end of the thread divided by the flutes 120, at the end in the clockwise direction when viewed from the front end. Even with this left-hand blade point tap 300, the same effects as those of the above embodiment can be achieved.
[0042] Although the primary grooves 21 of the point tap 10 are right-handed, the primary grooves may be inclined in a clockwise direction relative to the axial direction parallel to the axis AX. Also, if the point tap is a left-handed cutting edge and the secondary grooves are right-handed, the primary grooves may be inclined in a counterclockwise direction relative to the axial direction parallel to the axis AX.
[0043] Furthermore, the connection Q between the primary groove 21 and the secondary groove 22 is located opposite the first complete crest 17 , and specifically, it is desirable that the connection Q be within 0.5 crests of the first complete crest 17 .
[0044] Although the point tap 10 has five grooves 20, the number of grooves may be other than this, for example, two to four grooves, or six or more grooves.
Claims
1. A point tap comprising: a threaded portion having a chamfer and a full thread portion; a primary groove provided in the full thread portion; and a secondary groove provided in the chamfer and twisted in the opposite direction to the rotational direction of the threaded portion, wherein the primary groove is twisted in the rotational direction or is inclined toward the rotational direction with respect to the axial direction.
2. The point tap according to claim 1, characterized in that the twist angle or inclination angle of the primary groove is between 1° and 7°.
3. A point tap as claimed in claim 1 or 2, characterized in that the connection between the primary groove and the secondary groove is positioned opposite the first complete crest at the most distal end of the complete crest portion.
4. The point tap according to claim 1, wherein the point tap is a right-hand cutting edge that rotates right when viewed from the rear end in the axial direction, the secondary groove is left-handed, and the primary groove is right-handed or inclined in the direction of right rotation relative to the axial direction.
5. The point tap according to claim 1, wherein the point tap is a left-handed blade that rotates left when viewed from the rear end in the axial direction, the secondary groove is right-handed, and the primary groove is left-handed or inclined in the direction of left rotation relative to the axial direction.