JP2555470B2 - Twist groove tap - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a spiral groove tap for cutting an internal thread, and more particularly to a technique for preventing thread thinning in a thread of the internal thread that has been cut.

Conventional technology As a type of tap for thread cutting, a screw thread that forms a perfect shape from an incomplete shape with the top cut away from the tip of the tapered chamfer to the complete thread forms in a spiral shape. Is divided in the circumferential direction by the twisted groove, one end of the divided thread, that is, a spiral cutting edge along the above-mentioned twisted groove on the ridgeline of one end face and the thread flank formed by the division There is a twist groove tap that is constructed.

In such a spiral groove tap, the cut chips are discharged through the spiral groove to the rear side or the front side with respect to the advance direction of the tap, but the cutting edge inclined with respect to the central axis is used for cutting. Based on the axial component force of the cutting resistance generated by performing, the forward or backward thrust force acts on the spiral groove tap, and the actual lead of the spiral groove tap is too advanced than the correct lead equal to the pitch of the screw. It may be delayed. For this reason,
One of the factors that reduces the accuracy of the internal thread may be that the cutting edge bites into the thread of the internal thread that has already been partially cut, cutting more than the normal amount of cutting and causing the thread to be thinned. Has become.

In the twist groove tap previously filed by the present applicant for the purpose of preventing such thread thinning of the female screw, in the one disclosed in Japanese Utility Model Publication No. 62-37615, there is a cut along the flanks on both sides of the thread. Side of the blade where the side rake angle is positive,
That is, by chamfering the cutting edge on the side that is pressed by the female screw by the thrust force or by negatively chamfering the flank following the cutting edge, the bite to the female screw is restricted and the progression of the twist groove tap is advanced. It is designed to prevent the passage and the delay and prevent the thinning of the formed internal thread.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the above-described conventional spiral groove tap, the chamfering or the negative second chamfering is performed, so that the cutting edge is originally cut in the cutting edge along one flank of the thread. Performance is sacrificed.In particular, the cutting edge of the chamfered part, which is mainly used for cutting, has a large cutting resistance, which deteriorates sharpness and makes the cutting surface rough, which inevitably reduces the tap life. Along with this, there is an inconvenience that the processing accuracy of the formed female screw is adversely affected.

The present invention has been made against the background of the above circumstances, and an object thereof is to provide a spiral groove tap capable of thread cutting with an accurate lead without impairing the original machinability of the cutting edge. To provide.

Means for Solving the Problem The gist of the present invention for achieving such an object is that a thread from an incomplete shape to a complete shape is twisted from the tip of the bite part toward the complete thread part. In a spiral groove tap that is divided in the circumferential direction by a groove, and a cutting edge is configured along the spiral groove at one end of the divided screw thread, along flanks on both sides of the screw thread in the bite portion. Of the cutting edges, the cutting edge on the side where the side rake angle is positive is chamfered on the base end side part located on the inner peripheral side of the tip side part of the screw thread involved in cutting, or its side rake This is because the flank following the base end side portion located on the inner peripheral side of the tip side portion of the screw thread involved in the cutting among the cutting edges on the positive side has a negative second chamfer.

Action and Effect of the Invention In the above-mentioned spiral groove tap, for the cutting edge on the side where the side rake angle is positive in the chamfered portion that mainly performs cutting, the tip side portion of the screw thread involved in cutting has the necessary cutting ability. While it has a shape similar to that of a normal cutting edge for obtaining, it is chamfered on the inner peripheral side, that is, the base end side part that does not participate in cutting except the tip side part, or its base end. The flank following the side cutting edge has a negative second cut. For this reason, during the internal thread cutting process, good sharpness is maintained in the tip side portion, and high-precision cutting with little cutting resistance is performed,
In the base end side portion, the chamfering or the negative second chamfering restricts the biting into the internal thread, and the self-guided action of the spiral groove tap by the accurate lead is sufficiently obtained to reliably prevent the internal thread from becoming thin. . Therefore, accurate lead can be achieved without sacrificing the original cutting ability of the cutting edge as in the conventional spiral groove tap that prevents thinning and without shortening the life of the tap or adversely affecting the machining accuracy of the internal thread. It is possible to perform highly accurate and highly accurate thread cutting.

Embodiment Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a spiral groove tap 10 which is an embodiment of the present invention.
FIG. 1 is a front view showing a thread groove tap 10 including a male thread portion 12 on the tip side for thread cutting and a shank portion 14 on the side held by a tool such as a tap holder (not shown). The male screw portion 12 is provided with screw threads 16 corresponding to the female screw to be formed, which is wound around the axial center so as to have a predetermined screw pitch. This spiral groove tap 10 is for cutting a right-handed female thread, and
The threads 16 of 12 are formed on the right-hand thread. This male thread
12 is a complete ridge portion 18 with a constant outer diameter in which the heights of the screw threads 16 are substantially equal.
The taper shape is formed on the tip side of the complete ridge portion 18 to form a complete shape from an incomplete shape in which the top of the screw thread 16 is cut away from the tip toward the complete ridge portion 18. It is composed of an attachment part 20.

Further, the male screw portion 12 is provided with three spiral twisted grooves 22 having a twist angle α around the axis of the twisted groove tap 10, and the screw threads 16 are equally spaced in the circumferential direction by the twisted grooves 22. It is divided into three land parts 24, 26, 28. The spiral winding direction is right-handed, and the spiral groove tap 10 of the present embodiment is of the so-called right-handed right-handed type. Then, on each of the end portions of the land portions 24, 26, 28 on the front side in the right-hand screw rotation direction, that is, on the ridge line between the end face on the front side in the rotation direction formed by division and the flank surface of the thread 16, the twist A cutting edge 30 along the groove 22 is formed in a spiral shape. The chips cut by the cutting edge 30 are discharged through the spiral groove 22 to the shank 14 side, that is, to the rear side of the spiral groove tap 10.

The land portions 24, 26, 28 of the bited portion 20 are sectional views of each cutting edge 30 during the cutting of the female screw on the member to be processed. The cross-sectional views are shown in the upper, middle and lower stages of FIG. Show. One blade of each cutting edge 30 of the chamfered portion 20 is incomplete as a screw thread, but the cutting edges 30 share the same cutting depth to perform cutting, and the chamfered portion 20
A complete female thread is cut and formed by the whole and the first complete mountain 18a of the complete mountain portion 18. The meshed portion in FIG. 2 indicates the cutting amount of each cutting edge 30.

An enlarged portion of the cutting edge 30 corresponding to one thread is shown in FIG. Cutting is mainly on the top of the cutting edge 30,
That is, it is performed in the outer peripheral portion 31 along the tapered surface of the chamfered portion 20, but the cutting edge 30 along the leading flank 32 and the trailing flank 34 of the spiral groove tap 10 and the outer peripheral portion
Each tip 36,38 corresponding to a depth of cut of 31
But it is done. Further, by the sliding between the both flanks 32, 34 and the flanks 40, 42 of the partially formed internal threads which have already been cut and formed, the self-guiding action of advancing and guiding the spiral groove tap 10 with a lead equal to the pitch of the thread 16 is provided. Is caused.

A top view of one imperfect pile 44 including the cutting edge 30 of FIG. 3,
That is, a view as seen from the outer peripheral side of the spiral groove tap 10 is shown in FIG. Here, the side rake angle of each of the cutting edge 30 of the leading side flank 32 and the cutting edge 30 of the trailing side flank 34 is a positive value α on the leading side flank 32 side with respect to a straight line parallel to the axis.
(The same as the twist angle α of the twist groove 22) and the negative value −α on the trailing flank 34 side. Therefore,
In the spiral groove tap 10, a thrust force toward the advance side is generated in association with the cutting action of the spiral cutting edge 30 corresponding to the spiral groove 22, so that the cutting edge 30 of the advance side flank 32 is generated.
However, it tends to easily bite into the flank 40 of the female screw which has already been partially cut.

The rear side of the outer peripheral portion 31 of the cutting edge 30 in the right-hand screw rotating direction,
That is, on the outer peripheral surface facing the heel 46, a flank 48 is provided for the purpose of giving a clearance angle in the tangential direction to reduce friction and suppress heat generation and improve sharpness to improve finish surface accuracy. The clearance angle is generally 3 ° to 12 °. Incidentally, 56 in FIGS. 3 and 4 is the root of the screw thread 16.

Leading flank 32 with positive side rake angle as described above
Although the cutting edge 30 has a tendency to relatively easily bite into the flank 40 of the internal thread, in the spiral groove tap 10 of the present embodiment, among the cutting edges 30 of the advance flank 32 in which the lateral rake angle is positive, A base end side portion 50 that is located on the inner peripheral side of the tip end side portion of the screw thread 16 that performs a cutting action and hardly participates in cutting
A chamfer 52 is applied at. This chamfer 52 is formed on the tip side portion 36 as shown in FIGS. 3 and 4, respectively.
The cutting edge 30 is linearly dropped from the boundary point between and, and has a function of limiting the biting of the internal thread to the flank 40 during cutting. That is, although the base end side portion 50 is slid while being pressed by the thrust force, the chamfer 52 is applied to the female screw flank 40 that has already been partially formed. The biting of the end portion 50 is unlikely to occur.

Further, in FIG. 5 which is a cross section within the cutting depth range including the tip side portions 36, 38 of the cutting edge 30, in FIG. 5, the clearance angle θ of the clearance provided on the flank 32 and the flank 34
₁ is normally set to 0.5 ° or less, but in this embodiment, 1
The cutting resistance at the tip side portions 36, 38 can be greatly reduced, which can be a large value from 0 to 2 °. In this portion, female thread cutting is performed with high surface accuracy and good sharpness. In FIG. 5, the lateral rake angles α ′, −α ′ of the flanks 32, 34 with respect to the respective cutting directions are shown.
Is a lateral rake angle α, −α with respect to a straight line parallel to the axis.
The lead angle of the thread 16 is offset from the above.

On the other hand, in FIG. 6 which is a cross-section outside the cutting depth range including the base end side portions 50 and 54 of the cutting edge 30, both flanks are shown.
The clearance angle θ _{2 of} 32 and 34 is the clearance angle θ _{1 in} FIG.
It is almost the same size as.

Female threaded flank 40 by chamfer 52 as described above.
By preventing the bite into the spiral groove tap 10
Is accurately guided by the flanks 40, 42 of the female thread to ensure the self-guided action of advancing with the correct lead, so that the distal end portion 36 and the proximal end portion 50 on the flank 32 side are respectively Clearance angles θ ₁ and θ ₂ are 1 ° ~
It is possible to set a large value up to about 2 °.

Further, in the complete ridge portion 18, the cutting edge 30 and the flanks 32, 34 are provided in the same manner as the thread 16 (incomplete ridge 44) in the bite-in portion 20 so that each of the land portions 24, 26, 28 is completely formed. Many mountains 58 are continuous. And these full mountains
As for 58, the cutting edge 30 on the flank 32 side where the side rake angle is positive is chamfered 60 in a state in which the cutting edge 30 is dropped from the tip to the root without cutting. The clearance angle between the top of the complete mountain portion 18 and both flanks 32, 34 is 0.5 ° or less. In addition, only the first complete mountain 18a has an incomplete mountain 4 in the bite part 20.
Since it has a tip side portion 36 that performs cutting similarly to 4 etc., a chamfer 52 is applied in a state where the cutting edge 30 is dropped at the base end side portion 50 on the inner peripheral side of the tip side portion 36. In addition, the flanks having the clearance angles θ ₁ and θ ₂ are similarly provided.

The thread groove tap 10 configured in this manner is attached to a tap holder or the like, and is screwed into the prepared hole previously formed in the member to be processed from the tip end side thereof, so that the bite part 20
The cutting process is performed by the imperfect crests at and the cutting edge 30 at the first complete crest 18a. At this time, thrust force toward the tap tip side is generated in association with the cutting of the spiral cutting edge 30 corresponding to the spiral groove 30, but a chamfer 52 is formed on the proximal end side portion 50 of the advance flank 32 of the cutting edge 30. Since the internal thread is restricted from biting into the flank 40, the self-guiding action in which the spiral groove tap advances with an accurate lead equal to the pitch of the thread 16 is accurately obtained, and the thread of the internal thread becomes thin. Is reliably prevented.

Further, in the spiral groove tap 10 of the present embodiment, the chamfer 52 is not provided on the tip side portion 36 on the flank 32 side, and a relief having a clearance angle θ ₁ larger than usual is formed, so that a good sharpness is obtained. Is obtained and high-precision screw cutting is performed, and the surface precision and tap life of the internal thread are improved.

Although one embodiment of the present invention has been described in detail above, the present invention can be implemented in other modes.

For example, in the above-described embodiment, the cutting edge 30 in the base end side portion 50 on the flank 32 side was chamfered 52, but the cutting edge 30 in the base end side portion 50.
May be held down to the position of 30 '(see FIG. 6) on the inner side of the flank 32, and the flank 32 may be provided with a negative second pick following the cutting edge 30'. In this case,
Since the negative second chamfering following the cutting edge 30 'produces the same action as the chamfer 52, it is possible to obtain the same effect as that of the above-mentioned embodiment. The chamfer 52 is a cutting edge.
There is no problem even if the edge of 30 has a rounded corner.

Further, in the above-described embodiment, the chamfer 52 is applied over the entire base end side portion 50 on the flank 32 side for all the cutting edges 30 of the thread 16 in the bite portion 20, but it is not always necessary. Not some thread 16 for example
The cutting edge 30 may be chamfered 52, or any part of the base end portion 50 may be chamfered. In short, it suffices that chamfering or negative second chamfering is performed to the extent that the biting of the internal thread to the flank 40 is limited.

Also, in the above embodiment, the flanks 32,3 on both sides
4 of distal portion 36,38 and a proximal portion 50,54 relief angle theta ₁ substantially of the same size, although relief of theta ₂ are provided respectively, these relief angle theta _1, theta ₂ is appropriately The size may be changed, and the sizes may be different from each other, or the leading side flank 32 side and the trailing side flank 34 side may be different. Further, the relief may be provided only on the flank 34 side where the side rake angle is negative, or both flanks 32, 34 may not be provided with the relief.

In addition, in the above-described embodiment, the three right-hand spiral grooves 22
Although the spiral groove tap 10 having the above has been described, the number of the spiral grooves can be appropriately changed, and the present invention is similarly applied to the spiral groove tap having the left spiral groove and the spiral groove tap for cutting the female screw of the left screw. Can be done. That is, in the right-handed thread groove tap having a left-hand thread groove, chamfering is applied to the base end side portion except the tip end side portion for cutting the cutting edge along the tracking flank,
The flank following the cutting edge of the base end side may be negatively numbered, and in the case of a left-handed threaded groove tap, if there is a left-handed groove, the base of the leading side flank should be used. In the case where the end side portion has a right-handed groove, the base end side portion of the trailing side flank may be chamfered or negatively chamfered.

Further, in the above-described embodiment, for the thread 16 in the complete thread portion 18, except for the first complete thread 18a, the entire chamfer 60 from the tip to the root of the cutting edge 30 of the flank 32 is performed.
However, the chamfering 60 is not always an essential requirement.

Further, in the above-described embodiment, the spiral groove tap 10 for cutting an internal thread having a trapezoidal thread trough has been described, but a thread of a female thread to be formed, such as a thread trough having an arc shape. The crest shape can be changed as appropriate, and the present invention can be similarly applied to the thread cross-sectional shape of the spiral groove tap determined accordingly.

Although not exemplified one by one, the present invention can be carried out in variously modified and improved modes based on the knowledge of those skilled in the art without departing from the spirit thereof.

[Brief description of drawings]

FIG. 1 is a front view of a spiral groove tap which is an embodiment of the present invention. FIG. 2 is a diagram for explaining a cutting edge shape in a chamfered portion of the spiral groove tap of FIG. 1, and is a diagram showing a cutting state by each land in a cutting progress order. FIG. 3 is a diagram for explaining in detail one cutting edge in the chamfered portion of the spiral groove tap of FIG. 1. FIG. 4 is a plan view of the imperfect ridge having the cutting edge of FIG. 3 as seen from the outer peripheral side. FIG. 5 is a cross-sectional view taken along line VV of FIG. 3, and is a view for explaining the cutting edge shape and the like of the tip side portion for cutting. FIG. 6 is a sectional view taken along line VI-VI in FIG. 3, and is a view for explaining the cutting edge shape and the like of the base end side portion that is not involved in cutting. 10: Twisted groove tap 16: Thread, 16: Complete thread 20: Bited portion, 22: Twisted groove 30: Cutting edge, 32, 34: Frank 36: Tip side part, 50: Base side part 52: Chamfer

Claims (1)

(57) [Claims] 1. A thread from an incomplete shape to a complete shape is divided in the circumferential direction by a helical groove from the tip of the chamfered portion toward the complete thread, and at one end of the divided thread. In a spiral groove tap in which a cutting edge is configured along the spiral groove, among the cutting edges along the flanks on both sides of the screw thread in the bite part, the cutting edge on the side where the side rake angle is positive is The chamfering is performed on the base end side portion located on the inner peripheral side of the tip side portion of the screw thread involved in cutting, or the screw thread involved in cutting of the cutting edges on the side where the side rake angle is positive. A twist groove tap, characterized in that the flank following the base end side portion located on the inner peripheral side of the tip end side portion is provided with a negative second cut.