JPH0516062U - Tap for screw cutting - Google Patents

Abstract

(57) [Summary] [Purpose] To improve the accuracy of the internal thread so that a good guide action can be obtained from the beginning of biting. [Constitution] On the apex on the heel 28 side of the land 22a in the chamfered portion 18, the outer diameter is smoothed toward the heel 28 so that the outer diameter of the heel 28 is larger than the outer diameter of the cutting edge 24 of the land 22a. The rubbing portion 30 which becomes large is provided.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a tap for thread cutting, and particularly to a technique for preventing thinning of a thread of a female thread that has been cut.

[0002]

[Prior Art]

 Conventionally, taps have been frequently used as tools for cutting female threads. Such a screw cutting tap generally has a complete thread portion provided with a thread having a shape corresponding to the internal thread to be formed, and a tapered bite section in which the height of the thread gradually decreases, Grooves are provided in a direction that intersects with the threads of the complete threads and the chamfered portion, whereby the threads are divided into a plurality of lands, and a cutting edge is formed at the end on the screwing side of the lands. There is. Such a tap is rotated relative to the work piece, and is screwed from the side of the bite into the prepared hole that was previously provided in the work piece. A female screw is cut on the inner wall surface of the prepared hole. Further, the complete crest portion functions as a guide for screwing the tap into the prepared hole one lead by one rotation by being screwed with the formed female screw.

[0003]

[Problems to be solved by the device]

 However, with such taps for thread cutting, the tap is constrained in the radial and axial directions and guided in the proper screwing direction, especially before the initial biting, that is, before the complete ridge is screwed into the female thread. Since the force to move the tap is weak, the tap may sway or lead to an error due to the runout of the holder or machine holding the tap, or the component force of the cutting resistance caused by cutting. However, there was a problem that it was not possible to stably obtain high internal thread precision, for example, by cutting more than the regular cutting amount and causing thread thinning on the internal thread.

The present invention has been made in view of the above circumstances, and an object of the present invention is to improve the accuracy of the internal thread by obtaining a good guide action from the initial stage of biting.

[0005]

[Means for Solving the Problems]

 In order to achieve such an object, the present invention provides a complete thread portion provided with a thread having a shape corresponding to a female screw to be formed, and a tapered bite portion in which the height of the thread gradually decreases. By having a groove in the direction that intersects with the threads of the complete thread portion and the bite portion, the thread thread is divided into a plurality of lands, and a cutting edge is formed at the end of the land on the threading side. In the tap for thread cutting, the top of the land in the chamfer on the cutting edge side is provided with a flank with a positive clearance angle, while the top of the land on the heel side is provided. , The outer diameter of the heel is larger than the outer diameter of the cutting edge of the land, and a pressing portion whose outer diameter increases toward the heel is provided.

It is desirable that a positive relief is provided on the heel side of at least the flanks of the threads forming the land in the bite portion.

[0007]

[Action]

 In such a tap for thread cutting, a flank with a positive clearance angle is provided on the top of the land at the cutting edge side in the bite part, so that excellent sharpness is obtained and sufficient cutting durability is achieved. Of the female thread cut by the cutting edge is provided on the heel side of the land so that the outer diameter of the heel is larger than that of the cutting edge. Since it is designed to be rubbed while being pressed or bite into, it is possible to obtain a sufficient action to restrain the tap in the radial and axial directions from the initial stage of biting and guide it in the regular screwing direction. , It prevents thread thinning due to runout of tap and lead error. In particular, since the outer diameter of the scraping part is larger than the outer diameter of the preceding cutting edge, that is, the cutting edge of the same land, the scraping part can scrape the inner wall surface of the prepared hole even before the cutting of the internal thread is started. The tap is guided well from the beginning of cutting.

Further, when the female screw is cut into the blind hole, at the end of the cutting of the female screw, the chips cut by the cutting edge of the bite part remain attached to the workpiece, but the cutting of the female screw is completed. When the tap is later rotated in the reverse direction and pulled out from the female screw, the pressure scraping part breaks and removes chips from the work piece, so that chips enter between the flank of the cutting edge and the work piece, and the cutting edge There is no fear of losing.

Further, if a positive relief is provided at least on the heel side of the flank of the screw thread that constitutes the land in the bite portion, between the flank of the internal thread and the flank of the female screw in the portion where the pressure-rubbing portion is provided Since the space is formed, the plastic deformation of the work piece due to the biting of the rubbed portion is facilitated, and the welding and the increase in the cutting rotation resistance are favorably avoided.

[0010]

[Effect of the device]

 As described above, according to the thread cutting tap of the present invention, the thread thinness of the internal thread is prevented while maintaining sharpness and cutting durability, and high internal thread accuracy can be stably obtained. In machining the blind hole, it is possible to satisfactorily avoid the breakage of the cutting edge due to the biting of chips when the tap is rotated in the reverse direction to extract.

In addition, when a positive relief is provided at least on the heel side of the flanks of the screw threads forming the land in the bite portion, welding and cutting rotational resistance due to biting of the pressure rubbing portion increase. It has the advantage of being well prevented.

[0012]

【Example】

 An embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a front view of a thread cutting tap (hereinafter, simply referred to as a tap) 10 according to an embodiment of the present invention. The tap 10 is composed of a shank portion 12 that is gripped by a tapping machine or the like and is driven to rotate, and a screw portion 14 provided with a thread having a shape corresponding to the thread groove of the female screw to be cut. The threaded portion 14 is provided with a complete ridge portion 16 having a substantially constant diameter, and a chamfered portion 18 having a tapered top of the thread so that the diameter becomes smaller toward the tip side. .. The screw portion 14 is also provided with four straight grooves 20 in the axial direction. The screw thread is divided into a plurality of lands 22 having substantially the same width dimension, and the land 22 has a threading side end. A cutting edge 24 is formed at each of the portions, that is, the end portion in the counterclockwise direction in FIG. FIG. 2 is a view showing a II-II cross section in FIG.

A clearance surface 26 is provided on the apex of each land 22 on the cutting edge 24 side of the chamfered portion 18 so that the clearance angle is positive. The outer diameter of the ridge 28 is larger than the outer diameter of the cutting edge 24 of the same land 22 in a range smaller than the outer diameter of the cutting edge 24 of the succeeding land 22. A large friction portion 30 is provided. That is, the outer diameter of the heel 28 of the preceding land 22a in FIG. 2 is larger than the outer diameter of the cutting edge 24 of the land 22a and smaller than the outer diameter of the cutting edge 24 of the subsequent land 22b. The dashed-dotted line in FIG. 2 shows a concentric circle centered on the axis O of the tap 10, and the outermost dashed-dotted line represents the outer diameter of the complete mountain portion 16. The pressure rubbing portion 30 does not make the outer diameter of the heel 28 of each land 22 in the bite-in portion 18 larger than the outer diameter of the complete mountain portion 16.

A positive relief is provided on both side surfaces of the land 22, that is, on the flanks of the threads forming the land 22, and the thickness of the land 22 becomes thinner toward the heel 28 side. Is becoming The solid line in FIG. 3 shows the outer shape of the cutting edge 24 of one of the lands 22 in the bite part 18, and the dashed line in the figure shows the outer shape of the heel 28 of the same land 22. The width of the heel 28 is narrower than that of the cutting edge 24, but the height thereof is higher than that of the cutting edge 24. The broken line in the figure shows the outer shape of the cutting edge 24 in the complete mountain portion 16 for comparison.

The tap 10 as described above is attached to a tapping machine or the like and is driven to rotate about its axis while being screwed into the prepared hole of the workpiece 32, so that the tap 10 is lowered by the cutting edge 24 of the bite part 18. A female screw is cut on the inner wall surface of the hole. 4 and 5 are views showing a cutting state in the two lands 22a and 22b shown in FIG. 2. The cutting edges 24 of these lands 22 include the top and both side surfaces of the land 22. Since the positive relief is provided in the, excellent sharpness is obtained and sufficient cutting durability is secured.

Further, at the apex of the land 22, a pressing portion 30 is provided on the heel 28 side so that the outer diameter of the heel 28 is larger than the outer diameter of the cutting edge 24. The rubbing portion 30 bites into the trough portion 34 of the female screw cut by, and the trough portion 34 is rubbed while being plastically deformed. Therefore, the tap 10 is constrained in the radial and axial positions from the beginning of the biting of the biting portion 18 and is guided in the regular screwing direction. Mountain thinness is prevented. Since the outer diameter of the pressure rubbing portion 30 is larger than the outer diameter of the preceding cutting edge, that is, the cutting edge 24 of the same land 22, the pressure rubbing portion 30 can scrape the inner wall surface of the prepared hole before the cutting of the female screw is started. Thus, the tap 10 is guided well from the beginning of cutting.

Since both sides of the land 22 are provided with positive relief, as is clear from FIG. 5B, in the portion where the pressure rubbing portion 30 is provided, a female screw that has been machined A space is formed between the flank and the work piece 32 is easily plastically deformed due to the biting of the rubbing portion 30, so that welding and an increase in cutting rotation resistance are favorably avoided. Further, as shown in (c) of FIG. 5, the part where the pressure rubbing part 30 bites into the valley part 34 is cut and removed by the cutting edge 24 of the subsequent land 22 and the biting part 1 Since the outer diameter of the heel 28 of each land 22 in FIG. 8 is equal to or smaller than the outer diameter of the complete crest portion 16, the cut portion 34 of the internal thread does not leave a scratch due to the biting of the pressing portion 30.

When the land 22 of the complete mountain portion 16 is screwed into the female screw machined by the cutting edge 24 of the bite portion 18, the land 22 of the complete mountain portion 16 and the female screw are screwed together. According to the combination, the tap 10 is guided more satisfactorily and screwed into the prepared hole one lead at a time in one rotation, and the internal thread is cut with high accuracy.

On the other hand, when cutting the internal thread into the blind hole, at the end of cutting the internal thread, the chips 36 cut by the cutting edge 24 of the chamfered portion 18 are transferred to the workpiece 32 as shown in FIG. Although it remains attached, when the tap 10 is reversely rotated after the cutting of the female screw and the tap is pulled out from the female screw, the chips 36 are broken and removed from the workpiece 32 by the pressing portion 30. Therefore, there is no risk that the chips 36 will enter between the flank 26 of the cutting edge 24 and the work piece 32 and damage the cutting edge 24.

As described above, according to the tap 10 of the present embodiment, the thread ridge of the internal thread is prevented from being thin while maintaining the sharpness and the cutting durability, and a high internal thread precision can be stably obtained. In addition, when processing the internal thread of the blind hole, the chipping of the cutting edge 24 due to the biting of the chip 36 when the tap 10 is reversely rotated and withdrawn is favorably avoided. Further, the work piece 32 can be easily plastically deformed due to the biting of the pressure rubbing portion 30, and an increase in welding or cutting rotation resistance is favorably prevented, and the friction rubbing portion 30 bites into the valley portion 34. Since the part is cut and removed by the subsequent cutting edge 24, the scratch due to the biting of the pressing portion 30 does not remain.

Further, in this embodiment, since the four straight grooves 20 are formed to provide a plurality of lands 22 having substantially the same width dimension in a row in the axial direction, the land 22 of the bite part 18 is provided. In addition, there is an advantage that the processing for forming the flank 26 and the pressing portion 30 becomes easy.

Next, in order to clarify the effect of the present invention more specifically, the present invention products (Tool Nos. 1 to 6) in which the land of the bite portion is provided with the friction portion and the friction portion are not provided. The results of the performance test performed using the comparative products (tool Nos. 11 to 16) will be described. The tap and screw cutting conditions used are as follows. In the product of the present invention, the frictional part is provided on the land of the bite part so that the heel height is about 0.08 mm higher than the cutting edge. .. The tap 38 shown in FIG. 9 is a schematic view of the tap used in the performance test.

Tap type: Right 35 degree spiral tap Nominal: M10 × 1.5 Number of grooves: 3 grooves Material type: HSS Accuracy: Class 1 flank escape: 15 to 30 minutes from cutting edge Bit length: 3 pitch with bit Part escape (top): 2 to 50 minutes from the cutting edge

Cutting conditions Work material: SS41, HRB69 to 73 Prepared hole: φ8.5 × 25 mm Tapping length: 20 mm Cutting oil: Water insoluble JIS-C221 Rotation speed: 280 rpm (8.8 m / min) Feed: 1.5mm / rev Machine: Horizontal machining center Holder: Axial float type With tension / compression (brand B, N)

Then, using the holder brand: B for tool Nos. 1 to 3 and 11 to 13 and the holder brand: N for tool Nos. 4 to 6 and 14 to 16, respectively, 20 female screws for each tool are used. Table 1 shows the results of examining the number of ridges (pitch) in which the 6H NP (stop) gauge is cut by cutting. If the number of ridges is within 2 pitches, it passes. The cutting torque was about 816 to 940 N · cm, and almost no difference was recognized between the product of the present invention and the comparative product.

[0027]

[Table 1]

As is clear from Table 1, according to the product of the present invention, a high precision female screw can be stably obtained regardless of the brand of the holder, whereas in the comparative product not provided with the pressing portion, The accuracy of female thread varies greatly depending on the brand of holder.

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, the shape of the pressure rubbing portion 30 formed on the land 22 of the biting portion 18 can be appropriately changed, and a rounded heel 40 is formed as shown in FIG. Alternatively, as shown in FIG. 7, the groove 42 may be formed at the top of the pressing portion 30. When the concave groove 42 is provided, the workpiece 32 plastically flows in the concave groove 42, so that it is not always necessary to give positive relief to both side surfaces of the land 22.

Further, as shown in FIG. 8, it is also possible to form a crushing portion 44 having a sharp apex. In FIG. 8, the height of the heel is higher than that of the subsequent cutting edge 24, but if the height of the heel is at least equal to or less than the outer diameter of the cutting edge 24 in the complete mountain portion 16, the internal thread will not be damaged.

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 according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along line II-II in FIG.

3A and 3B are views showing the shapes of a cutting edge of a land and a heel in a chamfered portion of the tap shown in FIG.

FIG. 4 is a cross-sectional view showing a cutting state in a chamfered portion of the tap shown in FIG.

5 is a cross-sectional view illustrating the operation of each part in FIG.

FIG. 6 is a cross-sectional view showing another aspect of the pressing portion.

FIG. 7 is a cross-sectional view illustrating still another aspect of the pressing unit.

FIG. 8 is a cross-sectional view illustrating still another aspect of the pressing portion.

FIG. 9 is a front view of a tap used in a performance test.

[Explanation of symbols]

 10, 38: Tap for screw cutting 16: Complete mountain portion 18: Bited portion 20: Straight groove 22: Land 24: Cutting edge 26: Flank surface 28, 40: Heel 30, 44: Friction portion

Claims (2)

[Scope of utility model registration request] 1. A complete ridge portion provided with a thread having a shape corresponding to an internal thread to be formed, and a tapered bite portion in which the height of the thread gradually decreases. And a tap for thread cutting in which the thread is divided into a plurality of lands by providing a groove in a direction intersecting with the thread of the bite portion, and a cutting edge is formed at the threading side end of the land. The apex on the cutting edge side of the land in the bited portion,
While a clearance surface having a positive clearance angle is provided, the top of the land on the heel side has an outer diameter that increases toward the heel so that the outer diameter of the heel is larger than the outer diameter of the cutting edge of the land. A tap for thread cutting, which is provided with a friction portion having a large diameter. 2. The tap for thread cutting according to claim 1, wherein a positive relief is provided at least on a heel side of a flank of a screw thread forming a land in the bite portion.