JP6581497B2 - Cutting tap - Google Patents

Description

  The present invention relates to a cutting tap for processing a female screw by cutting.

  In general, a cutting tap is used as a tap for processing a female screw in a pilot hole of a female screw formed on a workpiece such as a nut blank (for example, Patent Document 1). The cutting tap has a biting portion and a complete mountain portion that continues to the rear in the axial direction of the biting portion.

  A thread having a shape corresponding to the thread groove of the female thread to be processed is formed on the outer periphery of the bite portion and the complete thread portion. The thread on the outer periphery of the chamfered portion has an incomplete shape in which the top is obliquely removed so that the outer diameter gradually decreases toward the front in the axial direction. The outer diameter is a complete shape that is constant in the axial direction.

  By the way, when machining a female screw with a cutting tap into the pilot hole of the female screw formed on the workpiece, chips may be caught between the workpiece and the cutting tap, resulting in excessive cutting resistance of the cutting tap or on the surface of the female screw. Chips may be crimped to cause defective products.

JP 2010-221369 A

  The inventor of the present application investigated the cause of chip biting when machining a female screw with a cutting tap into the pilot hole of the female screw formed on the workpiece. In particular, the inlet of the pilot hole of the female screw formed on the workpiece was investigated. When the chamfered portion is provided in the chip, it has been found that chips are likely to bite. Furthermore, the inventor has found a mechanism in which chips are caught between the workpiece and the cutting tap by examining the biting portion when the chips are actually caught between the workpiece and the cutting tap.

  That is, as shown in FIG. 6, a chamfered portion 31 is provided in advance at the entrance of a pilot hole 30 formed in a work (for example, a nut blank) N, and a female screw 32 is machined with a cutting tap T on the inner periphery of the pilot hole 30. Usually, the inclination of the chamfered portion 31 is larger than the inclination of the flank surface 34 of the thread 33 on the outer periphery of the cutting tap T. Therefore, as shown in FIG. An axial gap 35 is formed between the thread 33 on the outer periphery of the cutting tap T. Here, the chamfered portion 31 at the entrance of the pilot hole 30 is a conical surface having no lead angle, whereas the flank surface 34 of the thread 33 on the outer periphery of the cutting tap T is a spiral shape having a lead angle. Surface. Therefore, as shown in FIG. 8, the axial gap 35 between the chamfered portion 31 and the screw thread 33 becomes a wedge-shaped gap that gradually narrows as it advances in the circumferential direction. When the internal thread 32 is machined with the cutting tap T, the moving direction of the cutting tap T with respect to the workpiece N is a direction from the wide side to the narrow side of the wedge-shaped axial gap 35 as shown by the arrows in FIG. Become.

  Therefore, as shown in FIG. 7, once the chip 36 enters the axial gap 35 between the chamfer 31 and the thread 33, the chip 36 is chamfered 31 and the thread 33 as illustrated in FIG. 8. The wedge-shaped axial gap 35 between them moves in the circumferential direction from the wide side to the narrow side, and bites between the chamfered portion 31 and the thread 33. FIG. 9 and FIG. 10 show photographs in which the chips 36 are actually caught between the chamfered portion 31 and the thread 33.

  The problem to be solved by the present invention is to provide a cutting tap that is less likely to cause chipping between the workpiece and the cutting tap when the female screw is machined into the pilot hole of the female screw formed on the workpiece. .

In order to solve the above problems, the present invention provides a cutting tap having the following configuration.
In a cutting tap having a plurality of threads on the outer periphery corresponding to the female thread to be processed,
The plurality of threads includes threads provided axially apart at an interval twice the pitch of the female thread;
Thread removal for chip relief having an outer diameter smaller than the root diameter of the reference thread shape of the thread between the threads provided apart in the axial direction at twice the pitch of the female thread The cutting tap characterized by the part being formed.

  When this cutting tap is used, when machining a female thread on a workpiece that has a chamfered portion provided in advance at the inlet of the pilot hole of the female screw, the workpiece is placed between the inner periphery of the workpiece and the thread removal portion on the outer periphery of the cutting tap. A space for chip relief that opens to an axial gap formed between the chamfered portion and the thread of the cutting tap is formed. Therefore, it is difficult for chips to be caught between the workpiece and the cutting tap.

  Preferably, the thread removal portion is formed to have a small diameter through a step with respect to a screw bottom adjacent to the thread provided apart in the axial direction at an interval twice the pitch of the female screw.

  In this way, when machining the female thread with the cutting tap, the screw bottom adjacent to the thread removal portion through the step can urge the top of the female thread, so that it is possible to prevent chips from adhering to the top of the female thread, It is possible to more effectively prevent chips from getting between the workpiece and the cutting tap.

The above-described cutting tap is preferably added with the following configuration.
The screw threads provided apart in the axial direction at intervals of twice the pitch of the female screw are formed so that the effective diameter relief gradually decreases from the front to the rear in the rotational direction and becomes zero or minute. And
The thread removal portion is provided with a relief whose outer diameter gradually decreases from the front to the rear in the rotation direction, and the relief is larger than the relief of the effective diameter.

  In this case, the chip relief formed between the inner periphery of the workpiece and the outer thread removal portion of the cutting tap is made smaller than when the escapement of the thread removal portion is made the same size as the relief of the effective diameter. Thus, it becomes possible to more effectively prevent chips from being caught between the workpiece and the cutting tap.

  In the cutting tap of the present invention, when a female screw is machined on a workpiece in which a chamfered portion is provided in advance at the entrance of a pilot hole of the female screw, the workpiece is placed between the inner periphery of the workpiece and the thread removal portion on the outer periphery of the cutting tap. A space for chip relief that opens to an axial gap formed between the chamfered portion and the thread of the cutting tap is formed. Therefore, it is difficult for chips to be caught between the workpiece and the cutting tap.

The side view which shows the cutting tap of embodiment of this invention Expanded sectional view along the line II-II in FIG. (A) is an enlarged sectional view in which the thread of the first land of the cutting tap shown in FIG. 1 is broken along a plane including the axis of the tap, and (b) is the second cutting tap shown in FIG. An enlarged cross-sectional view of the land thread cut along the plane containing the tap axis The expanded sectional view which shows the state which is cutting the inner periphery of the pilot hole of the internal thread of a nut blank with the cutting tap shown in FIG. Fig. 4 is an enlarged cross-sectional view of the vicinity of the inlet of the pilot hole of the nut blank shown in Fig. 4 An enlarged cross-sectional view showing a state in which the inner periphery of a pilot hole of a nut blank is cut with a conventional cutting tap FIG. 6 is an enlarged cross-sectional view of the vicinity of the inlet of the pilot hole of the female screw of the nut blank shown in FIG. FIG. 7 is an enlarged sectional view taken along line VIII-VIII in FIG. When the inner periphery of the pilot hole of the nut blank's internal thread is cut with a conventional cutting tap, the nut blank is cut while the chips are actually caught between the chamfered portion of the nut blank and the thread of the cutting tap. Taken from the inner diameter side Photograph taken by enlarging the bite portion of the chip shown in FIG.

  FIG. 1 shows a cutting tap T according to an embodiment of the present invention. The cutting tap T is a nut tap used for manufacturing a nut by a tapping machine, and includes a bite portion 1, a complete peak portion 2 provided continuously in the axial direction of the bite portion 1, and a complete peak. And a shank 3 provided continuously in the axially rear of the portion 2. The shank 3 is a cylindrical portion that is held by a tap holder (not shown) when the cutting tap T is used.

The outer circumference of the chamfer 1, threads 5 ₁ having a shape corresponding to the screw groove of the female screw 4 (see FIG. 4) to be processed is formed. A thread 52 having a shape corresponding to the thread groove of the female thread 4 to be processed is also formed on the outer periphery of the complete thread ₂ . Hereinafter, when collectively without distinction threads 5 ₂ thread 5 ₁ complete crest second chamfer 1, simply referred to as "screw thread 5". On the outer periphery of the cutting tap T, a groove 6 is formed from the front end in the axial direction of the cutting tap T to the shank 3 through the biting portion 1 and the complete peak portion 2 in order.

As shown in FIG. 2, the groove 6 is formed in plural at predetermined intervals in the circumferential direction, the outer periphery of the cutting tap T is divided into a plurality of lands 7 _{1-7 5} by the groove 6. The number of grooves 6 is an odd number (five in the figure). The number of lands ₇ 1-7 ₅ is equal to the number of grooves 6 (five in the figure). Blade 8 cut in a portion where the inner surface and the threads 5 ₁ of the surface of the groove 6 intersect is formed, chips generated in the cutting edge 8 is adapted to be discharged through the grooves 6. The top of each screw thread 5 ₁ of the chamfer 1, escape of gradually outer diameter smaller outside diameter toward the rear direction of rotation from the cutting edge 8 (counterclockwise direction in the drawing) (hereinafter, simply "outer Is called “radial escape”. Escape of the outer diameter of the thread 5 ₁ to ensure the sharpness of the cutting edge 8 is set to be larger than the escape of the effective diameter of the thread 5 ₁ (described later).

As shown in FIG. 3 (a), screw threads 5 ₁ of the outer circumference of the chamfer 1, is an incomplete shape in which the top portion is removed obliquely gradually outer diameter toward the axially forward decreases Yes. The effective diameter of the thread 5 ₁ is fixed in the axial direction. That is, the thread 51 on the outer periphery of the biting portion ₁ is a parallel screw.

Full crest threads 5 ₂ of the outer circumference of the 2 outer diameter of the thread 5 ₂ is a constant full shape in the axial direction. Full crest 2 of the effective diameter of the thread 5 ₂ are the same size as the effective diameter of the thread 5 ₁ of the chamfer 1, it is constant in the axial direction. That is, the thread 52 on the outer periphery of the complete thread ₂ is a parallel thread.

  The effective diameter of the thread 5 means that when the thread 5 is broken along a virtual cylinder (or cone), the axial width of the thread 5 is the pitch p of the internal thread 4 to be processed (see FIG. 4). This is the diameter of a virtual cylinder (or cone) that is half the size. Further, the fact that the effective diameter of the thread 5 is constant in the axial direction does not need to be constant in a strict sense, and the effective diameter of the thread 5 is reduced in order to reduce the cutting resistance when forming the female thread 4. Includes a back taper with a minute inclination (an inclination of about 1/1000 to 3/1000) that slightly decreases from the front to the rear in the axial direction.

Inclination angle of the flank 9 of each thread 5 _second chamfer flank 9 of each thread 5 ₁ of 1 and full crest 2 (i.e. flank angle) is a bevel angle of common screw pilot holes The size is smaller than 45 ° (usually 40 ° or less). In the figure, a triangular screw having a flank angle of 30 ° is shown as the thread 5 on the outer periphery of the cutting tap T. In addition, for example, a wit screw having a flank angle of 27.5 ° or a pipe screw, a trapezoidal screw having a flank angle of 15 ° or 14.5 °, a parallel screw for thin steel conduit having a flank angle of 40 ° (so-called CTC screw), etc. The present invention may be applied to the cutting tap T.

Each thread 5 ₂ of the threads 5 ₁ and full crest second chamfer 1, escape of effective diameter that gradually effective diameter from the rotation direction front toward the rear is small (hereinafter, simply "relief of the effective diameter ”) Is zero or minute. The reason why the effective diameter relief is zero or minute is to ensure the self-guiding property of the cutting tap T. That is, if the relief of the effective diameter is set to be large, when the internal thread 4 is processed by the cutting tap T, a deviation occurs between the advance amount of the cutting tap T and the lead of the internal thread 4, and the problem of the shape deformation of the internal thread 4 occurs. This is because. Further, the clearance of the outer diameter of the thread 52 on the outer periphery of the complete thread portion ₂ is also set to zero or very small in order to ensure the self-guiding property of the cutting tap T.

The thread 5 on the outer periphery of the cutting tap T is provided such that at least a part of the thread 5 is separated in the axial direction at an interval twice the pitch p (see FIG. 4) of the female thread 4 to be processed. In this embodiment, among the threads 5 _1, 5 ₂ of the outer circumference of the cutting tap T, a portion of the threads 5 ₁ continuous to the rear from the threads 5 ₁ in the axial forward end of the chamfered portion 1, the internal thread 4 provided at a pitch p identical axial spacing and the remaining threads 5 _1, 5 ₂ are provided spaced in the axial direction at twice the distance of the pitch p of the female thread 4.

As shown in FIG. 4, a screw thread removing portion 10 is formed between the screw threads 5 provided apart in the axial direction at an interval twice the pitch p of the female screw 4. The outer diameter d ₁ of the thread removal portion 10 is constant in the axial direction and is smaller than the root diameter d ₂ of the reference thread shape of the thread 5. Here, the root diameter d ₂ of the reference chevron thread 5, that intersects the flank surface 9 of the thread 5 ₁ arranged in the same pitch as the pitch p of the female thread 4 to be processed is extended to the side of the top and a, the height of the triangle (equilateral triangle in the figure) which is defined by the point B intersects extended flanks 9 of the thread 5 ₁ on the side of the valley when the H, from point B H / It is a diameter passing through a position shifted to the outer diameter side by 4. The reference thread shape of the thread 5 is a thread cross-sectional shape defined in Japanese Industrial Standards JIS B0205-1: 2001 “General Metric Screws—Part 1: Reference thread shape”. The outer diameter d ₁ of the thread removing unit 10 is more preferably set to a diameter smaller than a diameter passing through the position deviated from the point B on the outer diameter side by H / 6.

The screw thread removing portion 10 is formed to have a small diameter via a step 12 with respect to the screw bottom portion 11 adjacent to the screw thread 5 provided in the axial direction at an interval twice the pitch p of the female screw 4. ing. The inclination angle of the step 12 shown in FIG. 5 (inclination angle with respect to a virtual plane orthogonal to the axis of the cutting tap T) is the same as or smaller than the flank angle of the thread 5 (for example, an angle in the range of 10 to 20 °). ) Is set. Further, as shown in FIG. 5, the axial dimension f of the thread root 11 (the axial direction dimension of the boundary position of the thread root 11 and the step 12 to a boundary position of the thread root 11 and the screw thread 5 _2), thread removed It is preferable to form the thread removal portion 10 so as to be at least half of the axial dimension e of the screw bottom 11 when assuming a state in which the portion 10 is not present.

As shown in FIG. 4, the thread removal portion 10 is provided with a relief (hereinafter simply referred to as “relief of the thread removal portion 10”) in which the outer diameter gradually decreases from the front to the rear in the rotational direction. (See FIG. 2). Relief of the thread removing unit 10 is set to be larger than the escape of the effective diameter of the thread 5 ₁ and threads 5 _2.

  For example, the thread removing unit 10 firstly manufactures taps in which all the screw threads 5 are arranged at the same axial interval as the pitch p of the female thread 4 to be processed. It can be obtained by scraping every other mountain along the axial direction.

FIG. 3 (a), (b), the thread removing unit 10 of each land ₇ 1-7 _5, the thread 5 of the land ₇ 1-7 ₅ adjacent to the land ₇ 1-7 ₅ , So as to be adjacent to each other in the lead direction of the screw. For example, the thread removing unit 10 of the land ₇₁ shown in FIG. 3 (a), adjoin the lead direction of the land 7 ₂ thread 5 and the screw shown in FIG. 3 (b), shown in FIG. 3 (b) thread removing unit of the lands 7 ₂ 10 is adjacent to the lead direction of the land ₇₁ of the thread 5 and the screw shown in FIG. 3 (a). That is, the screw thread removing portion 10 and the screw thread 5 are alternately provided along the lead direction of the screw.

  Next, the example which processes the internal thread 4 in the nut blank N shown in FIG. 4 using this cutting tap T is demonstrated. Here, the example which manufactures a nut using the tapping machine of the type which rotates the nut blank N side among the cutting tap T and the nut blank N is demonstrated.

  The nut blank N has a pilot hole 20 formed in advance. The inner periphery of the pilot hole 20 is a cylindrical surface. The inner diameter of the pilot hole 20 is slightly larger than the outer diameter of the screw bottom 11 on the outer periphery of the cutting tap T. Further, a chamfered portion 21 is provided in advance at the entrance of the prepared hole 20. The chamfered portion 21 is a conical surface having an inclination angle of about 45 ° with respect to a direction perpendicular to the axis of the pilot hole 20.

And when processing the internal thread 4 to this nut blank N, it holds first in the state which stopped the cutting tap T, and bites it while rotating the nut blank N to the outer periphery of the cutting tap T. Then, the inner periphery of the prepared hole 20 is gradually cut in threads 5 ₁ of the chamfer 1, a screw groove of the female screw 4 is formed on the inner periphery of the prepared hole 20. Thereafter, the screw thread 52 of the complete thread part ₂ is fitted to the female screw 4 formed on the inner periphery of the pilot hole 20, and this fitting causes a gap between the advance amount of the cutting tap T and the lead of the female screw 4. Misalignment is prevented.

  Here, as shown in FIG. 5, the inclination angle of the chamfered portion 21 at the inlet of the pilot hole 20 of the nut blank N is larger than the inclination angle of the flank surface 9 of the thread 5 on the outer periphery of the cutting tap T. Therefore, when the internal thread 4 is processed on the inner periphery of the pilot hole 20 with the cutting tap T, an axial gap 22 is formed between the chamfered portion 21 and the thread 5. Further, a space 23 is formed between the inner periphery of the prepared hole 20 of the nut blank N and the thread removal portion 10 on the outer periphery of the cutting tap T. This space 23 is open to an axial gap 22 formed between the chamfered portion 21 and the screw thread 5, and when chips 24 generated by cutting of the inner periphery of the pilot hole 20 enter the axial gap 22. In addition, it has a function of receiving the chips 24 and escaping from the axial gap 22. Further, the screw bottom portion 11 adjacent to the screw thread removing portion 10 through the step 12 urges the top of the female screw 4 to prevent the chips 24 from adhering to the top of the female screw 4.

  When this cutting tap T is used, when the internal thread 4 is processed into a nut blank N in which a chamfered portion 21 is previously provided at the entrance of the pilot hole 20, a thread removal portion on the inner periphery of the nut blank N and the outer periphery of the cutting tap T is used. 10, a chip escape space 23 is formed that opens to an axial gap 22 formed between the chamfer 21 of the nut blank N and the thread 5 of the cutting tap T. Therefore, it is difficult for the chips 24 to be caught between the nut blank N and the cutting tap T.

  Further, in the cutting tap T, when machining the female screw 4, the screw bottom portion 11 adjacent to the screw thread removing portion 10 through the step 12 exposes the top of the female screw 4. Therefore, it is possible to prevent the chips 24 from adhering to the top of the female screw 4 and more effectively prevent the chips 24 from being caught between the nut blank N and the cutting tap T.

  Further, since the relief of the thread removal portion 10 is larger than the relief of the effective diameter, the cutting tap T has a nut blank N larger than the case of making the relief of the thread removal portion 10 the same as the relief of the effective diameter. A space 23 for chip relief formed between the inner circumference of the cutting tap T and the thread removal portion 10 on the outer circumference of the cutting tap T is wide. Therefore, it is possible to effectively prevent the chips 24 from being caught between the nut blank N and the cutting tap T.

In the above embodiment, provided in all of the threads 5 _1, 5 _2, identical axial spacing and the pitch p of the portion of threads 5 ₁ of chamfer 1 female thread 4 of the outer periphery of the cutting tap T, and all threads 5 ₂ remaining threads 5 ₁ complete crest 2 of the chamfer 1, an example provided axially away at twice the distance of the pitch p of the female thread 4, All the threads 5 ₁ and 5 ₂ on the outer periphery of the cutting tap T may be provided apart in the axial direction at intervals of twice the pitch p of the female screw 4. Also, among all the threads 5 _1, 5 ₂ of the outer circumference of the cutting tap T, full crest 2 thread 5 ₂ only, provided axially away at twice the distance of the pitch p of the female thread 4 It may be.

4 female thread _{5 1} thread _{5 2} thread 10 thread removing unit 11 thread root 12 step T cutting tap p pitch _{d 1} core diameter of the outer diameter _{d 2} standard chevron thread removing unit

Claims (4)

In the cutting tap having a plurality of threads (5) corresponding to the female thread (4) to be processed on the outer periphery,
The plurality of threads (5) includes threads (5) provided in the axial direction at intervals of twice the pitch (p) of the female threads (4);
Between the threads (5) provided apart in the axial direction at intervals of twice the pitch (p) of the female threads (4), the root diameter (d ₂ ) of the reference thread shape of the threads (5) The point A where the flank surface (9) of the thread (5) arranged at the same pitch as the pitch (p) of the female thread (4) to be machined is extended to the top side and is smaller than When the height of the triangle defined by the point B that intersects the flank surface (9) of the thread (5) extending to the bottom of the valley is H, only H / 6 from the point B A cutting tap, characterized in that a thread removal part (10) for chip relief having an outer diameter (d ₁ ) smaller than a diameter passing through a position shifted to the outer diameter side is formed.   The screw thread removal portion (10) is located on the screw bottom portion (11) adjacent to the screw thread (5) provided in the axial direction at an interval twice the pitch (p) of the female screw (4). The cutting tap according to claim 1, wherein the cutting tap is formed to have a small diameter through the step (12). Before Symbol thread removing unit (10) from the rotation direction front toward the rear is provided gradually escape to the outside diameter decreases, the relief, the threads (5), toward the rotation direction front to back The cutting tap according to claim 1 or 2, wherein the effective diameter gradually becomes larger than the relief of the effective diameter. In the cutting tap having a plurality of threads (5) corresponding to the female thread (4) to be processed on the outer periphery,
The plurality of threads (5) includes threads (5) provided in the axial direction at intervals of twice the pitch (p) of the female threads (4);
Between the threads (5) provided apart in the axial direction at intervals of twice the pitch (p) of the female threads (4), the root diameter (d ₂ ) of the reference thread shape of the threads (5) ) thread removing unit for relief chips having an outer diameter of the small diameter (d ₁₎ (10) is formed than,
Before Symbol thread removing unit (10) from the rotation direction front toward the rear is provided gradually escape to the outside diameter decreases, the relief, the threads (5), toward the rotation direction front to back A cutting tap characterized in that the effective diameter gradually becomes larger than the relief of the effective diameter.