JPH0212021Y2 - - Google Patents

Description

[Detailed Description of the Invention] Technical Field The present invention relates to a tap, and more particularly to an improvement of a multi-screw tap in which an auxiliary thread groove for guiding the chamfer is provided at the top of the thread in the chamfer.

Prior Art Taps have traditionally been widely used as thread processing tools for forming internal threads. Generally, such taps are formed in a direction that intersects a thread consisting of a full thread and a chamfered part, dividing the thread into multiple parts, and using the thread to divide the thread into multiple parts. It is constructed with a groove section for discharging cut chips, and the chamfered section has the function of tapping the screw, while the fully threaded section has the function of ensuring the propelling action of the tap in the screwing direction. is fulfilled.

On the other hand, at the top of the thread of the chamfered part,
Furthermore, there are so-called multi-screw taps that are provided with an auxiliary thread groove for guiding the chamfer. This auxiliary thread groove serves to improve the chamfering property of the tap in the initial stage of machining, that is, the propulsion effect in the threading direction. Provided on the side part. For example, the tap described in Japanese Patent Publication No. 30-4650 is one example.

Problems to be Solved by the Invention However, since the auxiliary thread grooves in such conventional double screw taps were formed on the same helical winding of the same pitch as the screw thread, The chips cut out by the thread have a bent shape in the portion where the auxiliary thread groove is formed, and the width thereof becomes substantially wider and is deformed in a complicated manner during the cutting process. As a result, the flow of chips in the groove is obstructed, making chip clogging more likely to occur, increasing the cutting torque of the tap, making tapping impossible, and causing minute vibrations during machining, resulting in poor surface finish. There was a problem.

In addition, in such a double thread tap, the cutting action is also performed by the auxiliary thread groove formed at the top of the thread, and the actual cutting width, that is, the dimension of the part used for actual cutting, is As a result, the cutting torque is originally larger than that of a normal tap without an auxiliary thread groove, and the above-mentioned disadvantage becomes more noticeable.

Means for Solving the Problems The present invention has been made to solve the above problems, and its gist is that the present invention is provided with the threads and grooves, and at least on the distal end side of the chamfered portion. In a double screw tap in which an auxiliary thread groove for chamfering guidance is provided at the top of the thread, the auxiliary thread groove formed in the adjacent threads with the groove in between is cut by the auxiliary thread groove. This is because the remaining parts are placed at offset positions from each other so that they do not overlap.

Function and Effects of the Invention In such a multi-screw tap, an auxiliary thread groove is formed in the thread adjacent to each other across the groove, that is, the thread that performs cutting action back and forth when the tap is screwed into the pilot hole. However, since the parts left uncut by the auxiliary thread grooves are provided at positions shifted from each other so that they do not overlap, the part left uncut by the preceding thread is removed by the thread immediately after it, while The chips thus cut out are separated at the portion where the auxiliary thread groove is provided.

Therefore, the chips cut out by such a double screw tap have a small width and are not bent, although there are some uncut portions left by the preceding threads. Therefore, the deformation of chips during the cutting process is reduced, and the evacuation of chips from the groove is improved, the increase in cutting torque due to chip clogging is alleviated, and good tapping is performed.

In addition, since the cutting action is not performed near the bottom of the auxiliary thread groove, the actual cutting width is reduced compared to the conventional case where the cutting action is performed in all parts of the auxiliary thread groove. Cutting torque is also reduced regarding points. Note that this substantial cutting width can be made smaller than that of a normal tap without an auxiliary thread groove by widening the width of the auxiliary thread groove.

On the other hand, the inherent propulsion in the screwing direction of a double screw tap is due to the fact that the inner wall surface of the auxiliary thread groove formed on one thread is brought into sliding contact with the uncut portion due to the existence of the auxiliary thread groove. Therefore, even if the positions of the auxiliary thread grooves formed at the tops of individual threads are misaligned, the driving action in the threading direction is not impaired at all.

Embodiment Hereinafter, an embodiment of the present invention will be described in detail based on the drawings.

FIG. 1 is a front view showing a double screw tap 10 which is an embodiment of the present invention, and is composed of a shank portion 12 on the proximal end side and a threaded portion 16 on the distal side in which a thread 14 is formed. ing. The threaded portion 16 further includes:
Cylindrical complete thread portion 1 with threads 14 having the same height
8, and a chamfered portion 20 in which the thread 14 is cut into a tapered shape at the distal end side of the complete threaded portion 18. Further, the threaded portion 16 is provided with four grooves 22 in the axial direction, and the threaded thread 14 is divided into a plurality of parts, each of which has a cutting edge, and chips cut out by the cutting edge. It is designed to emit .

The top 24 of the thread 14 is provided with an auxiliary thread groove 26, as clearly shown in FIG. This auxiliary thread groove 26 is intended to improve the chamfering property at the initial stage of the tapping process, and is formed on the thread 14 on the tip side of the chamfered part 20, and its cross section has a substantially V-shape. ing.

Conventionally, the auxiliary thread groove 26 was formed on the same helical winding with the same pitch as the thread 14, but in this embodiment, the auxiliary thread groove 26 of the thread 14 adjacent to each other with the groove 22 in between is formed on the same helical winding. They are provided on different helical windings having the same pitch as the thread 14 but offset in the axial direction. That is, the auxiliary screw grooves 26 of the series of screw threads 14 located on both the left and right sides in FIG. The series of threads 14 and the auxiliary thread grooves 26 of the threads 14 (not shown) located on the opposite side of the threads 14 are located on a helical winding line different from the helical winding line shown by the dashed line above. It is formed in

Further, the depth of these auxiliary thread grooves 26 is greater than the cutting depth of the thread 14, and is formed at approximately the same depth relative to the top 24 of each thread 14. Theoretically, the cutting depth of the thread 14 is (thread height)/(number of chamfered threads x
The depth of the auxiliary thread groove 26 is determined by the number of grooves (number of grooves), but it actually varies depending on the material of the workpiece, cutting conditions, etc., so the depth of the auxiliary thread groove 26 must be set as necessary and sufficiently in consideration of these conditions, etc. There is.

On the other hand, the auxiliary thread grooves 26 provided in the individual threads 14 are each formed with a constant diameter centered on the axis of the multiple screw tap 10. Therefore, as the double screw tap 10 is screwed into the prepared hole, the inner wall surface of the auxiliary screw groove 26
Due to the existence of the auxiliary thread groove 26, it can be brought into sliding contact with the uncut portion. These sliding contacts improve the propulsion effect of the double screw tap 10 in the screwing direction.

Note that the thread 14 is a right-handed thread, and when viewed from the shank 12 side, a cutting edge is formed at the tip in the clockwise direction, and the height of the thread 14 gradually increases as it goes counterclockwise from the cutting edge. It's getting lower. Therefore, the apparent depth of the auxiliary thread groove 26 becomes gradually shallower as the height of the thread 14 becomes lower. Further, the thread 14 located on the left side in FIG. 2 shows the shape of its cutting edge side portion.

The multiple screw tap 10 configured as described above is
The auxiliary thread grooves 26 formed on the threads 14 that are adjacent to each other across the groove portion 22, that is, the threads 14 that perform a cutting action back and forth when the multiple thread tap 10 is screwed into the prepared hole, are arranged on different helical wires. Since the auxiliary thread grooves 26 are provided in the auxiliary screw grooves 26, the uncut portions thereof are shifted from each other. Therefore, the portion left uncut by the preceding thread 14 is scraped off by the immediately following thread 14, while the chips thus cut out are separated at the portion where the auxiliary thread groove 26 is provided. has been done.

FIG. 3 is a diagram showing the cross-sectional shape of chips cut out by such a multi-screw tap 10. In FIG. 3, reference numeral 28 represents the inner circumferential surface of the prepared hole in which the female thread is to be formed, and the shape shown by thin lines represents the cross-sectional shape of the chips. The chips shown in the lower part of the figure are those cut out by the thread 14 located on the tip side of the double screw tap 10, and the chips shown in the upper part are the chips shown in the chamfered part 20. This means a part cut out by the thread 14 located on the proximal end side. Multiple screw tap 1 of this example
0 forms a triangular thread, and the dimension of the top 24, that is, the cutting width, increases as the thread 14 is located on the tip side.
Since the auxiliary thread groove 26 is provided in the thread 14 on the distal end side where the dimension is large and the chips are divided, the width dimension of the chips becomes smaller as a whole. It should be noted that the number of threads 14 present in the chamfered portion 20 of the double screw tap 10 is greater than this, and FIG. 3 is a schematic illustration thereof. Further, in the figure, the left side corresponds to the tip end side of the multiple screw tap 10.

As described above, the width of the chips cut out by the double screw tap 10 of this embodiment is small;
Further, although there is a portion left uncut by the preceding thread 14, there is no bending. Since the width of the chips is narrow and there is no bending, the deformation of the chips during the cutting process is also reduced.
Therefore, the chips can be easily discharged from the groove 22, and the finished surface is not damaged due to the increase in cutting torque caused by chip clogging, which makes it impossible to tap or cause minute vibrations, resulting in a good surface finish. Thread processing can be performed.

On the other hand, the chips of a normal tap without an auxiliary thread groove have a shape as shown in Fig. 4,
The chips of a conventional double thread tap in which auxiliary thread grooves are formed on the same helical winding have a shape as shown in FIG. As is clear from these figures, the width of the chips of conventional taps, especially the width of the chips carved out by the threads on the tip end of the tap, is large, and in the case of double-threaded taps, the width of the chips removed by the auxiliary screw is large. There is a bend in the part corresponding to the groove. For this reason, the evacuation of chips in the groove was poor, leading to chip clogging and an increase in cutting torque.

On the other hand, the depth of the auxiliary thread groove 26 is greater than the depth of cut of the thread 14, and cutting action is not performed near the bottom of the auxiliary thread groove. The effective cutting width is reduced compared to the case where the cutting is done, and the cutting torque is also reduced in this regard. Since the groove width of the auxiliary thread groove 26 of this embodiment is relatively wide, there is almost no difference in the actual cutting width compared to a normal tap having no auxiliary thread groove.

Incidentally, an example of the results of measuring the cutting torque in relation to the progress of tapping when tapping is performed using the product of the present invention is shown by a solid line in FIG. The specifications of the taps, usage conditions, and cutting torque measuring device used are as follows. Furthermore, the one-dot chain line in FIG. 6 shows the case of a conventional double-screw tap, and the two-dot chain line shows the case of a normal tap without an auxiliary thread groove.

Standards of the taps used Type: Nut type Nominal dimensions: M20 x 2.5 Shape: Length of threaded part 70mm Length of chamfered part 50mm Length of auxiliary thread grooved part 25mm Number of grooves 3 pieces Threaded part accuracy JIS grade 2 Material: SKH58 Conditions of use Workpiece material: Austenitic stainless steel SUS304 HRB90 Cutting speed: 200 rpm Prepared hole: Diameter 17.5 mm, thickness 25 mm, through hole Cutting agent: Sulfurized tapping oil Machine: Radial drilling machine cutting torque measuring device Kistler, Switzerland Manufactured by Piezoelectric Cutting Torque Measuring Instrument Model 9271-A As is clear from FIG. . In addition, in the case of the conventional double screw tap shown by the dashed line, the cutting torque increases when the tap advance is in the range of 20 mm to 50 mm, but this is due to the cutting action of the auxiliary thread groove. This is thought to be because the cutting width became wider and bent chips were discharged into the groove. In addition, in the case of the normal tap shown by the two-dot chain line, the cutting torque is large at the initial stage of tapping, but this is because chips with a large width are discharged into the groove at the initial stage of tapping. This is thought to be due to vibration in the radial and axial directions.

Although one embodiment and an experimental example of the present invention have been described above, these are merely examples, and the present invention can be implemented in other embodiments.

For example, although the multi-screw tap 10 of the above embodiment forms a triangular thread, the present invention can be similarly applied to a multi-screw tap that forms threads of other shapes such as trapezoidal threads and square threads.

Further, in the embodiment described above, the auxiliary thread groove 26 is provided only on the tip side portion of the chamfered portion 20, but the auxiliary thread groove 26 is provided on all the threads 14 of the chamfered portion 20.
It is also possible to form

Further, the multiple screw tap 10 of the above embodiment is provided with four grooves 22 in the axial direction thereof.
Of course, the number and shape of the groove portions 22 can be changed as appropriate, and the same can be said of the cross-sectional shape of the auxiliary thread groove 26.

Further, the auxiliary thread grooves 26 do not necessarily need to be formed on the helical windings at the same pitch as the threads 14, and at least the auxiliary thread grooves 26 formed on the adjacent threads 14 with the groove portion 22 in between may be formed at positions shifted from each other. It would be good if it was provided.

Although no other examples are given, the present invention can be implemented with various modifications and improvements based on the knowledge of those skilled in the art without departing from the spirit thereof.

[Brief explanation of the drawing]

FIG. 1 is a front view of a double screw tap which is an embodiment of the present invention. FIG. 2 is a partially cutaway front view showing an enlarged chamfered portion of the double screw tap shown in FIG. 1. FIG. FIG. 3 is a diagram illustrating the shape of chips cut out by the double screw tap of FIG. 1. FIG. 4 is a diagram illustrating the shape of chips of a normal tap without an auxiliary thread groove. FIG. 5 is a diagram illustrating the shape of chips of a conventional double screw tap. 6th
The figure is a graph showing the cutting torque of the multi-screw tap according to the present invention in comparison with a conventional tap. 10: Double screw tap, 14: Thread, 18: Complete thread, 20: Chamfered part, 22: Groove, 24: Top, 26: Auxiliary thread groove.

Claims (1)

[Claims for Utility Model Registration] A screw thread consisting of a complete thread and a chamfer, and a thread formed in a direction intersecting the thread to divide the thread into a plurality of parts, and A double threaded tap is provided with a groove for discharging cut chips, and an auxiliary thread groove for guiding the chamfer is provided on the top of the thread at least on the distal end side of the chamfer. A multiple screw tap characterized in that the auxiliary thread grooves formed on the threads adjacent to each other are provided at positions shifted from each other so that the uncut portions of the auxiliary thread grooves do not overlap.