JPH06304815A - Screw cutting tap - Google Patents

Abstract

PURPOSE:To machine a highly accurate female screw having excellent cutting surface roughness with high cutting performance by carrying out screw cutting work by accurate lead feed regardless of an inclination of cutting edges by twisted grooved. CONSTITUTION:Screw threads 14 corresponding to a female screw to be machined are divided into three lands 24 by twisted grooves 22, and in the end part on the cutting rotation direction side of the respective screw threads 14, cutting edge 26a and 26b are arranged alternately according to an advance of a screw. Since the cutting edge 26b is a normal cutting edge having high cutting performance, excellent cutting work is carried out, and on the other side, since the cutting edge 26a has a chamfer part 28 on the side where a side rake angle becomes positive, biting into a female screw flank is prevented, and screw cutting work is carried out by accurate lead feed. A dashed line shows a helix to connect between root parts of the screw threads 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tap for thread cutting, and more particularly to a technique for preventing the thinning of a female thread to be cut.

[0002]

2. Description of the Related Art Taps have been widely used as tools for cutting female threads. Such a tap for thread cutting generally includes a plurality of lands whose threads corresponding to the thread groove of the female screw to be machined are divided by the chip discharge groove, and the chip discharge at the end of the land of the thread in the cutting rotation direction. Cutting edges are provided along the groove. Then, the tapered biting portion where the height of the thread gradually becomes lower is screwed into the pilot hole provided in the workpiece in advance, and the inner wall surface of the pilot hole is formed by the cutting edge provided in the biting portion. The internal thread is cut. Further, the complete thread portion, which has a substantially constant height of the screw thread provided subsequent to the bite portion, is screwed into the internal thread machined by the bite portion, so that the tap is rotated once in one rotation. Acts as a guide to screw the leads into the prepared hole.

On the other hand, one of such taps for thread cutting is a twist groove tap in which the chip discharge groove is spirally twisted. With such a spiral groove tap, chips can be satisfactorily discharged in the axial direction of the tap as the tap rotates, but since the cutting edge is inclined along the spiral groove, the cutting resistance causes the chip to move in the axial direction of the tap. There is a problem that thrust is generated, and the tap advances too much or too much, so that the dimensional accuracy of the female screw is lowered, and a mountain thinning occurs. For example, right hand screw,
In the tap of the right-handed helical groove, a thrust force that is directed forward in the axial direction is generated, and the tap is more likely to advance with a larger lead than the regular lead. This also applies to a spiral point tap having a spiral point groove at the tip of the tap. In order to solve this, of the pair of cutting edges formed by the ridgeline of the pair of flanks and the above-mentioned twist groove, the side where the side rake angle with respect to the screwing direction is positive, that is, when the tap advances too much, the shaft If the tap is delayed with the front cutting edge in the axial direction, the rear cutting edge in the axial direction may be chamfered, or the flank following the cutting edge may be chamfered with a negative relief angle. It is suggested to do so. Mitsuko Sho 62-37
The tap described in Japanese Patent No. 615 is an example.

[0004]

However, when the cutting edge is chamfered or second-rounded as described above, the original cutting performance of the cutting edge is impaired, resulting in poor cutting performance and shortened tool life. At the same time, there is an inconvenience that the cutting surface roughness and the processing accuracy decrease.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a tap for thread cutting which can perform thread cutting with an accurate lead without impairing cutting performance. Especially.

[0006]

In order to achieve the above object, the present invention provides an odd land of 3 or more in which a thread corresponding to a thread groove of a female screw to be machined is divided by a thread groove for discharging chips. In the tap for thread cutting, which is provided with a cutting edge along the spiral groove at the end of the land in the direction of cutting rotation of the thread, in the cutting edge along the flanks on both sides of the thread. It is characterized in that the cutting edge on the side where the rake angle is positive is chamfered or rounded in steps of one land along the screw thread of the thread.

[0007]

In such a tap for thread cutting, the cutting edge on the side where the side rake angle is positive is chamfered or rounded (hereinafter referred to as chamfered edge).
, And a normal cutting edge with high cutting performance are provided alternately for every 1 land along the screw thread of the screw thread, so when cutting the internal thread, follow the tap screw The cutting edge allows highly accurate cutting, and the chamfering edge restricts the lead deviation of the tap, that is, the bite in the axial direction of the cut female screw. Sufficient cutting performance is not obtained at the chamfered or rounded portion of the chamfered blade, and the cutting surface roughness is poor, but that portion is cut and finished with high accuracy by the next normal cutting edge. Therefore, a highly accurate internal thread having excellent cutting surface roughness can be finally obtained. Also, since the threads are divided into odd lands of 3 or more, the chamfering edge and normal cutting edge are not biased to a certain land, and the chamfering edge and normal cutting edge are evenly distributed in each land. Therefore, the machining accuracy is not impaired due to the difference in cutting resistance between the two cutting edges.

As described above, according to the tap for thread cutting of the present invention, since the tap is accurately lead-fed by the presence of the chamfering edge, and the normal cutting edge provides excellent cutting performance with good sharpness, A highly accurate internal thread with excellent cutting surface roughness is cut. Further, since the uncut portion of the chamfering blade is immediately cut and finished by the next normal cutting edge, the burden on each chamfering blade is small, wear and welding are reduced, and the tool life is improved.

If the width dimension of the chamfering or rounding in the tap axis direction is smaller than 0.02 mm, the effect of chamfering or rounding cannot be sufficiently obtained and the cutting edge bites into the flank of the machined female thread. On the other hand, if it is larger than 0.20 mm, the cutting performance is remarkably deteriorated and wear or the like is promoted, while the width dimension varies depending on the material etc. of the workpiece. It is desirable to set in the range of 0.02 mm or more and 0.20 mm or less.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a front view showing a thread cutting tap 10 for a right-hand thread, which is an embodiment of the present invention. The shank 12 is rotatably driven by being held by a tapping machine or the like, and a thread groove of a female thread to be formed. And a threaded portion 16 provided with a thread 14 having a shape corresponding to. In the screw part 16,
A tapered chamfered portion 18 having a smaller diameter on the distal end side and a complete mountain portion 20 having a substantially constant diameter are provided.
Three twist grooves 22 twisted clockwise are formed for discharging chips. The screw thread 14 has the twist groove 22.
Is divided into three lands 24, and a cutting edge 26 is formed at one end thereof, that is, at the end in the clockwise direction when viewed from the shank 12 side in the cutting rotation direction.

FIG. 2 is a development view in which a part of the screw portion 16 is developed along the land 24, and the lower side of the drawing is the tip side of the tap 10. The alternate long and short dash line is a line connecting the troughs of the screw threads 14, and is a right-handed helical winding wire having the same lead L and lead angle α as the female screw to be formed. In FIG. 2, 28
Is a portion where the cutting edge 26 is chamfered, and the cutting edge 2
6 includes a chamfering blade 26a having the chamfered portion 28 and a normal cutting edge 26b having no chamfered portion 28. The chamfer 28 includes flanks on both sides of the thread 14 and the spiral groove 2.
Of the pair of cutting edge ridges where 2 intersects, the side on which the lateral rake angle with respect to the screwing direction is positive, in this embodiment, is provided on the cutting edge ridge on the advancing flank side, and the thread 14 The chamfering blades 26a and the normal cutting edges 26b, which are formed in every one land jump along the screw advancement and have such chamfered portions 28, are alternately present along the screw advancement. The width dimension of the chamfered portion 28 in the tap axis direction, that is, the dimension d in FIG. 3 showing the III-III cross section of FIG. 1 is set in the range of 0.02 mm or more and 0.20 mm or less. It should be noted that each thread 14 is provided with a relief as necessary to reduce friction with the cut female thread.

Such a tap 10 for screw cutting is screwed into the prepared hole previously provided in the workpiece from the side of the biting portion 18, and the cutting edge 26 provided in the biting portion 18 causes the internal wall surface of the prepared hole to be cut. Cutting the internal thread. The cut chips are discharged to the shank 12 side while being guided by the twist groove 22 as the tap 10 rotates. Further, in the complete mountain portion 20 provided subsequent to the bite portion 18, each thread ridge 14 is screwed into the thread groove of the female screw machined by the bite portion 18 to rotate the tap 10 once. Works as a guide to screw one lead into the pilot hole. Even in each thread 14 of the bite portion 18, the cutting action is the outer peripheral portion of the cutting edge 26, that is, the bite portion 18
Is performed only in the portion where the diameter dimension is increased due to the taper of No. 2, and the other portion is screwed into the thread groove machined by the cutting edge 26 of the preceding thread 14, so that the complete mountain portion 20 is formed.
Like the screw thread 14 in FIG.

Since each of the cutting edges 26 contributing to the cutting work is inclined along the spiral groove 22, the tap 10 of this embodiment having a right-handed thread and a right-handed groove,
Thrust is generated toward the tip side in the axial direction. However, in the present embodiment, the chamfered portion 28 is formed at the ridge of the leading flank.
Since the chamfering blades 26a provided with the and the normal cutting edges 26b are alternately present, the chamfering blades 26a can be used to tap 10
Is prevented from excessively advancing, and biting into the cut female screw is prevented. Sufficient cutting performance is not obtained at the chamfered portion 28 of the chamfered edge 26a, and the cutting surface roughness is poor, but since that portion is cut and finished with high accuracy by the next normal cutting edge 26b, it is finally cut. A highly accurate internal thread with excellent surface roughness can be obtained. Further, since the screw thread 14 is divided into three lands 24, the chamfering edge 26a and the normal cutting edge 26b are not biased toward the fixed land 24, and the chamfering edge 26a and the normal cutting edge 26b are attached to each land 24.
Are evenly distributed, and the machining accuracy is not impaired due to the difference in cutting resistance between the two cutting edges 26a and 26b.

As described above, according to the tap 10 for thread cutting of the present embodiment, the presence of the chamfering blade 26a causes the tap to be accurately lead-fed, and the normal cutting edge 26b.
As a result, excellent cutting performance with good sharpness is performed, so that a highly accurate internal thread with excellent cutting surface roughness is cut. Further, since the uncut portion of the chamfering blade 26a is immediately cut and finished by the next normal cutting edge 26b, the burden on each chamfering blade 26a is small, wear and welding are reduced, and the tool life is improved.

On the other hand, in the present embodiment, since the width dimension d of the chamfered portion 28 in the tap axis direction is 0.02 mm or more, the effect of the chamfered portion 28 is sufficiently obtained and the flank of the female screw machined is obtained. Biting of the cutting edge 26 is favorably avoided, and the width dimension d is 0.20 mm.
Since it is below, the cutting performance is not remarkably deteriorated and wear or the like is not promoted, and an excellent tool life can be obtained.

Although one embodiment of the present invention has been described in detail with reference to the drawings, the present invention can be implemented in other modes.

For example, although the chamfering blade 26a is provided in the entire area of the screw portion 16 in the above-described embodiment, the chamfering blade 26a is provided only in a part of the screw portion 16 including the chamfered portion 18, and the screw portion 16 is not always required. It is not necessary to distribute the chamfering blades 26a over the entire area.

Further, although the chamfered portion 28 is provided by chamfering in the above-mentioned embodiment, it does not matter if the chamfered portion 28 is rounded, and the width dimension d of the chamfered portion 28 does not necessarily have to be the same. Absent.

Further, the tap 10 for thread cutting of the above embodiment.
Was equipped with three twist grooves 22, but this twist groove 2
The number of 2 may be an odd number of 5 or more, and the present invention can be similarly applied to a spiral point tap having a spiral point groove at its tip.

Further, the tap 10 for thread cutting of the above embodiment.
Are right-handed threads and right-handed threads, but the present invention can be similarly applied to taps of right-handed threads, left-handed threads, left-handed threads, left-handed threads, and left-handed threads. It can be applied to left-hand spiral point taps as well.

Although not illustrated one by one, the present invention can be implemented in various modified and improved modes based on the knowledge of those skilled in the art.

[Brief description of drawings]

FIG. 1 is a front view of a tap for thread cutting which is an embodiment of the present invention.

FIG. 2 is a development view of a screw portion of the tap shown in FIG.

3 is a sectional view taken along line III-III in FIG.

[Explanation of symbols]

 10: Tap for thread cutting 14: Thread ridge 22: Twist groove 24: Land 26: Cutting edge 26a: Chamfering edge 26b: Normal cutting edge 28: Chamfering part

Claims (2)

[Claims] 1. A thread corresponding to the thread groove of a female screw to be machined is provided with an odd number of lands of 3 or more divided by a thread groove for discharging chips, and the land of the thread thread has a cutting rotation direction side end portion. In a tap for thread cutting provided with a cutting edge along the spiral groove, among the cutting edges along the flanks on both sides of the thread, the cutting edge on the side where the side rake angle is positive, of the thread A tap for thread cutting, which is chamfered or rounded in every 1 land along the screw progress. 2. The tap for thread cutting according to claim 1, wherein a width dimension of the chamfered or rounded portion in the tap axis direction is 0.02 mm or more and 0.20 mm or less.