WO2013065695A1

WO2013065695A1 - Small-diameter drill

Info

Publication number: WO2013065695A1
Application number: PCT/JP2012/078063
Authority: WO
Inventors: 崇香月; 恵大峯; 英児池上; 進一堀川
Original assignee: 株式会社タンガロイ
Priority date: 2011-10-31
Filing date: 2012-10-30
Publication date: 2013-05-10
Also published as: TW201338896A; CN103889623A; JPWO2013065695A1

Abstract

The objective of the present invention is to improve the flow of chips near the convergence point in a small-diameter drill for which grooves are made to converge, thereby improving the precision of the hole position, increasing the quality of the inner walls of the hole that is formed, and accommodating high-efficiency processing. This small-diameter drill is equipped with two or more grooves, a cutting edge arranged at the tip, at least two margins defining the outer circumferential surface of the small-diameter drill, and two or more outer-circumferential recesses that extend so as to make contact with the margins. In addition, this small-diameter drill has a point where two or more grooves converge. At least one of the two or more outer circumferential recesses has a connecting point for interconnecting the two or more grooves at a location closer to the tip than the convergence point.

Description

Small diameter drill

The present invention relates to a small-diameter drill, and particularly to a small-diameter drill that can be suitably used for making a hole in a printed wiring board.

The small diameter drill 1 generally has a shank having a diameter of 3.175 mm (1/8 inch). Therefore, the tool diameter is generally 3.175 mm or less. Patent document 1 discloses the drill used for the use including the drilling of a printed wiring board. The drill includes a cutting edge disposed at the tip and two grooves. The two grooves merge on the way to the rear end to form one groove. Two margins defining the outer peripheral surface of the drill are formed. The purpose of the drill of Patent Document 1 is to increase the rigidity and to improve the position accuracy of a hole to be processed (hereinafter referred to as hole position accuracy).

Patent Document 2 discloses a drill used for applications including drilling of printed wiring boards. The drill includes a cutting edge disposed at the tip and two grooves. The two grooves merge on the way to the rear end to form one groove. The purpose of the drill of Patent Document 2 is also to increase the rigidity and improve the hole position accuracy.

International publication WO2011 / 116540 pamphlet JP 2007-307642 A

The drills of

Patent Documents

1 and 2 have higher tool rigidity because the volume removed by the grooves is small compared to a drill in which the two grooves do not merge. For this reason, the hole position accuracy is improved to some extent. However, chips flowing toward the outside of the processing hole through the two grooves are concentrated at the junction of the two grooves. As a result of the concentration of chips at the junction, the chips may become clogged near the junction and damage the inner wall of the machined hole, and the drill is likely to break. Therefore, the drills of

Patent Documents

1 and 2 need to keep the feed rate during cutting low.

An object of the present invention is to improve chip flow in the vicinity of a merging point in a small diameter drill that merges a plurality of grooves.

The present invention includes at least two grooves, a cutting edge disposed at the tip, at least two margins defining a part of the outer peripheral surface of the small-diameter drill, and at least two outer peripheral recesses extending in contact with the margin. The at least two grooves have a confluence point, and of the at least two outer periphery recesses, at least one of the outer periphery recesses is on the tip side of the at least two grooves. It is a small diameter drill characterized by having a communication part for making mutually communicate.

FIG. 1 is an enlarged view of a portion A of a right side view of a small diameter drill in the first embodiment. FIG. 2 is a right side view of the small diameter drill of FIG. FIG. 3 is an enlarged view of the front view of the small diameter drill of FIG. FIG. 4 is a front view of the small diameter drill of FIG. FIG. 5 is an enlarged view of the left side view of the small diameter drill of FIG. FIG. 6 is an enlarged view of a plan view of the small diameter drill of FIG. FIG. 7 is an enlarged view of the bottom view of the small diameter drill of FIG. FIG. 8 is an enlarged view of a perspective view of the small diameter drill of FIG. FIG. 9 is an enlarged view of a perspective view of the small-diameter drill of FIG. 1 viewed from another direction. FIG. 10 is an explanatory diagram of the cross-sectional position of the XI-XI cross section in the small diameter drill of FIG. FIG. 11 is an enlarged cross-sectional view of the small diameter drill of FIG. FIG. 12 is an enlarged view of a right side view of the small-diameter drill according to the second embodiment. FIG. 13 is an enlarged view of the front view of the small diameter drill of FIG. 14 is an enlarged view of the left side view of the small diameter drill of FIG. FIG. 15 is an enlarged view of the right side view of the small diameter drill of the comparative product 1. FIG. 16 is an enlarged view of the front view of the small diameter drill of FIG. FIG. 17 is an enlarged view of the left side view of the small diameter drill of FIG. FIG. 18 is an enlarged view of the right side view of the small diameter drill of the comparative product 2. FIG. 19 is an enlarged view of a front view of the small diameter drill of FIG. 20 is an enlarged view of the left side view of the small diameter drill of FIG. FIG. 21 shows the first experimental result regarding the small diameter drill. FIG. 22 shows the second experimental result regarding the small diameter drill.

Embodiments of the present invention will be described with reference to the drawings.

As shown in FIGS. 1 to 9, the small-diameter drill 1 of the first embodiment includes two spiral grooves 2. The two grooves 2 are a first groove 2a that extends while twisting from the front end 3 side toward the rear end 8 side, and a second groove 2b that merges with the first groove 2a in the middle of the length of the small-diameter drill 1. including. The two grooves 2 are right-handed.

The length of the first groove 2 a is appropriately adjusted according to the tool diameter (diameter) φDmm corresponding to the hole diameter processed by the small diameter drill 1. In this embodiment, the length of the first groove 2a in the direction from the front end 3 to the rear end 8 of the small diameter drill 1 is about 3.5 mm. The second groove 2b passes through the junction 5 shown in FIG. 7 and terminates at a position that is substantially integrated with the first groove 2a. That is, the length of the second groove 2b is a length from the tip 3 to the end after passing the junction 5. As another configuration, the second groove 2b is adjusted so that the rear end 8 side extends in parallel with the first groove 2a and functions in the same manner as the single groove 2 after passing the junction 5. The Specifically, the twist angle of the first groove 2a and the twist angle of the second groove 2b are set to the same angle on the rear end 8 side from the merging point 5. Here, as shown in FIG. 7, the “merging point” is a point where two grooves 2 merge and function as if they were one groove on the rear end 8 side from that point.

The length Ld from the front end 3 to the joining point 5 in the direction from the front end 3 to the rear end 8 is appropriately adjusted so that the tool rigidity is increased and the chip discharging property is increased. In this embodiment, the two grooves 2 are merged as a result of giving a difference in their torsion angles, and the length Ld from the tip 3 to the merge point 5 is designated by the length and conforms to it. The twist angle is not determined to be. However, in order not to reduce the tool rigidity, the length Ld may be specified, and the twist angle of each groove 2 may be adjusted so as to match it.

The tip 3 is provided with two cutting edges 4. The cutting edge 4 is two main cutting edges, and is an intersecting ridge line between a rake face formed on the inner surface of the groove 2 and a main flank face formed on the end face of the tip 3. Two margins 11 are provided adjacent to the two grooves 2. The margin 11 defines a part of the outer peripheral surface of the small diameter drill 1 over its entire length. The “cutting edge” in the present embodiment also includes a secondary cutting edge that is a cross ridge line between the secondary flank and the rake face of the outer peripheral surface that is the margin 11. A chisel edge 10 is formed on the end surface of the tip 3. In general, the chisel edge 10 is not called a cutting edge. However, the chisel edge 10 has a function of generating chips such as small powder like a cutting edge.

A columnar or cylindrical shank 9 is formed on the rear end 8 side of the small diameter drill 1. In this embodiment, the tool diameter φDmm is about φ0.250 mm. The tool diameter can be arbitrarily set according to the size of the hole to be machined. The shank diameter (diameter) of the shank 9 is approximately φ3.175 mm.

The twist angle of the groove 2 is not particularly limited. In the case of a small-diameter drill for a printed wiring board, the twist angle of the first groove 2a of the small-diameter drill 1 of the present invention is preferably 20 ° or more and 70 ° or less. In particular, the twist angle of the first groove 2a from the tip 3 to the junction 5 is more preferably 30 ° or more and 55 ° or less. Although not shown, in this embodiment, the twist angle of the first groove 2a is about 45 °.

The twist angle of the second groove 2b is preferably the same as the twist angle of the first groove 2a in the vicinity of the tip 3 of the small diameter drill 1. If the twist angles of the first groove 2a and the second groove 2b are made the same in the vicinity of the tip 3, the cutting edge shape can be easily made the same surface shape, so that the balance during cutting is good. Furthermore, when the tip surface of the small diameter drill 1 is reground, the shape of the cutting edge 4 can be kept constant.

In order to join the two grooves 2, the twist angle of the second groove 2 b can be made different from the twist angle in the vicinity of the tip 3 at an arbitrary position. In this embodiment, the twist angle of the second groove 2b is changed at the position of the length Lc shown in FIG. The twist angle of the second groove 2b for joining the grooves 2 is preferably 30 ° or more and 80 ° or less, and more preferably 40 ° or more and 70 ° or less. Although not shown, in this embodiment, the twist angle of the second groove 2b from the change point (position of the length Lc) where the twist angle changes to the point of joining is about 60 °. In other words, in order to join the two grooves 2, the twist angle of the second groove 2 b is preferably larger than the twist angle of the first groove 2 a in the range of 10 ° to 30 °. If this angular difference is too small, a large axial length is required for the two grooves 2 to merge, and the tool rigidity is reduced. On the contrary, if this angle difference is too large, chips collide at the confluence 5 and a chip discharge is prevented.

The length Lc to the change point of the twist angle of the second groove 2b is preferably in the following range with respect to the tool diameter φD. The length Lc is preferably in the range of 0.1D ≦ Lc ≦ 4D. However, the preferable range of the length Lc is slightly different depending on the tool diameter φD. When φD is less than 0.1 mm, a range of 1.5D ≦ Lc ≦ 4D is preferable. When φD is 0.1 mm or more and less than 0.6 mm, a range of 0.5D ≦ Lc ≦ 3D is preferable. When φD is 0.6 or more and less than 1.0 mm, a range of 0.3D ≦ Lc ≦ 2D is preferable. When φD is 1.0 mm or more, a range of 0.1D ≦ Lc ≦ D is preferable. In this embodiment, the two grooves 2 are merged by making the twist angle of the second groove 2b larger than that of the first groove 2a. However, the method for merging is not limited to this. For example, the two grooves 2 can be merged by making the twist angle of the second groove 2b smaller than that of the first groove 2a.

In this embodiment, the twist angle of the groove 2 toward the rear end 8 after merging is the same angle as the twist angle of the first groove 2a, but is not limited thereto. The twist angle of the groove 2 toward the rear end 8 after merging may be matched with the twist angle of the second groove 2b having a larger angle than the first groove 2a. Moreover, you may set to an intermediate | middle angle or another angle, without matching with the twist angle of the 1st groove | channel 2a or the 2nd groove | channel 2b. This angle can be appropriately adjusted so that chips are smoothly discharged after the grooves 2 have joined. In this embodiment, the excellent chip evacuation property can be obtained by matching the twist angle of the groove 2 toward the rear end 8 after merging with the twist angle of the first groove 2a.

In general, in the case of the small diameter drill 1 having a tool diameter φDmm of φ1.500 mm or more, there is almost no problem with the hole position accuracy. That is, since the small diameter drill 1 having a tool diameter φDmm of φ1.500 mm or more has a sufficiently high rigidity, the problem of the hole position accuracy is small. The present invention is particularly effective in improving hole position accuracy in the case of the small diameter drill 1 having a tool diameter φDmm of less than φ1.500 mm. Especially, when the tool diameter φDmm is φ0.500 mm or less, the effect of improving the hole position accuracy is remarkable. The improvement in the hole position accuracy here means that the position accuracy at the hole entrance (positional deviation between the machine command position and the machined hole) is improved, and that the bending of the hole is improved and the hole exit is improved. This includes improving the positional accuracy.

The small diameter drill 1 has two outer peripheral recesses 6. Each outer peripheral recess 6 is parallel to each of the margins 11 and is adjacent to each of the two grooves 2. Each outer peripheral recess 6 extends in the direction toward the end 8 starting from the vicinity of the main cutting edge 4. The two outer peripheral recesses 6 include a first outer peripheral recess 6a and a second outer peripheral recess 6b. The first outer peripheral recess 6a is provided adjacent to the first groove 2a, and the second outer peripheral recess 6b is provided adjacent to the second groove 2b. Each outer peripheral recess 6 is connected to the groove 2 at one end in the width direction and to the margin 11 at the other end.

In the present embodiment, as shown in FIGS. 1 and 8, at least one outer peripheral recess 6 (that is, the first recess 6) is located on the tip 3 side of the junction 5 (shown in FIG. 7) of the two grooves 2. The two grooves 2 communicate with each other by one outer peripheral recess 6a). That is, the first outer peripheral recess 6 a is provided with a communication portion 7 that communicates between the two grooves 2 at the end on the rear end 8 side. For reference, the opposite side of the small diameter drill 1 is shown in FIGS. 5 and 9 in order to show the second outer peripheral recess 6b not provided with the communication portion 7. FIG. Similar to the second outer peripheral recess 6b, the conventional general outer peripheral recess is provided in parallel with the first groove 2a and the margin 11 while being connected to the first groove 2a and the margin 11. The end portion on the rear end 8 side does not reach the second groove 2b, and therefore the two grooves 2 do not communicate with each other. In contrast to this, in this embodiment, the outer peripheral recess 6 is provided with the communication portion 7 only in one, ie, the first outer peripheral recess 6a, so that the two grooves 2 communicate with each other, and the other, ie, the second outer peripheral recess. In 6b, the two grooves 2 are not communicated with each other.

When the communication portion 7 is viewed from the XI-XI cross-sectional position in FIG. 10 toward the rear end 8 side of the small-diameter drill 1, the communication portion 7 has an overall width direction that is larger than the outer peripheral surface as shown in FIG. Retreating inward, it provides a space for the chips to move between the two grooves 2. The depth of the communication portion 7 (that is, the distance from the outer peripheral surface) is substantially the same as the depth of the outer peripheral recess 6 and is smaller than the groove 2. When the two grooves 2 communicate with each other on the tip 3 side from the junction point 5, small powdery chips move between the two grooves 2 through the communication portion 7. For this reason, the chips flowing through the two grooves 2 are mixed in the region closer to the tip 3 than the junction 5. In addition, since the depth of the communication portion 7 is smaller than the groove 2, the small powdery chips that have passed through the communication portion 7 dig into the bottom of the large chips and play a role like a lubricant. It is thought that litter tends to rise. That is, it is considered that if a large chip rises even a little, the floating is further promoted on a small powdery chip. For this reason, the collision between the chips in the vicinity of the merging point 5 is alleviated, and the merging of the chips becomes smoother.

Therefore, the position at which the two grooves 2 are communicated with each other by the outer peripheral recess 6 is important, and the distance from the tip 3 to the communication portion 7 and the distance from the tip 3 to the junction 5 need to be adjusted appropriately. Even when two or more outer peripheral recesses 6 are provided, the length from the tip 3 of each outer peripheral recess 6 is appropriately adjusted. As a result, the two or more outer peripheral recesses 6 are formed so that the lengths from the tip 3 are different from each other. In the present embodiment, the second outer peripheral recess 6b is longer than the first outer peripheral recess 6a in the direction from the front end 3 to the rear end 8.

In addition, it is thought that a production | generation place differs mutually from a small powdery chip and a big chip. Small powder chips are considered to be generated mainly at the chisel edge 10. Small powdery chips are guided from the chisel edge 10 to the groove 2 through the gap formed by the main flank. Most of the large chips are considered to be generated by the cutting edge 4 which is the main cutting edge. That is, when a large chip is generated by the cutting edge 4 of the tip 3 of the small diameter drill 1, there is no room for the small chip to enter under the large chip. In order to lift a large chip by a small powdery chip, the two grooves 2 are connected so that the small chip can enter freely from under the large chip as in this embodiment. It is effective to do. In this embodiment, “communication” means that the two recesses 2 are connected by the outer peripheral recess 6. The communication part 7 means a part in the outer peripheral recess 6 where the two grooves 2 communicate with each other.

The margin 11 adjacent to the outer peripheral recess 6 is guided by the inner wall surface of the drilled hole and functions as a guide for maintaining the straightness of drilling. The outer peripheral recess 6 not only allows the groove 2 to communicate but also has a function of appropriately adjusting the width of the margin 11. By appropriately adjusting the width of the margin 11, the contact area is suppressed, the cutting resistance (rotational resistance and rotational axial thrust resistance) of the small diameter drill 1 is reduced, and the sharpness is improved.

The “length” of the outer circumferential recess 6 is the length in the direction from the front end 3 toward the rear end 8 as shown in FIGS. 1 and 5. The length Laa of the first outer peripheral recess 6a is shown in FIG. In this embodiment, the length Laa of the first outer peripheral recess 6a is 0.83 mm. The length Lba of the second outer peripheral recess 6b is shown in FIG. In this embodiment, the length Lba of the second outer peripheral recess 6b is 0.85 mm. If it is set as such length, the two outer periphery recessed parts 6 can be processed by the mutually similar grinding process. That is, since the NC program for grinding can be shared, it is easy to create and it is easy to form the outer peripheral recesses 6 having different lengths. Since the length Lba (FIG. 5) of the second outer peripheral recess 6b is longer than the length Laa (FIG. 1) of the first outer peripheral recess 6a, The cross-sectional area of the chip flow path constituted by the second groove 2b and the second outer peripheral recess 6b is expanded. For this reason, the chip | tip moved from the 1st groove | channel 2a to the 2nd groove | channel 2b through the communication part 7 can be received, and chip | tip discharge property can be improved.

The twist angle of the outer peripheral recess 6 is preferably the same as the twist angle of the first groove 2a. As described above, when the twist angle of the second groove 2b is the same as the twist angle of the first groove 2a in the vicinity of the tip 3 of the small diameter drill 1, the margin 11 adjacent to the two grooves 2 The width is constant near the tip 3. The twist angle of the outer peripheral recess 6 may be the same angle over the entire length of the outer peripheral recess 6. Such a shape is easy to process. Therefore, it is easy to adjust the length of each outer periphery recessed part 6 appropriately. However, the twist angle of the outer periphery recessed part 6 is not limited to this. Of course, the shape of the outer peripheral recess 6 is not limited to a shape parallel to the margin 11 in which the width of the margin 11 is constant. Any shape may be used as long as the width of the margin 11 can be appropriately adjusted and the two grooves 2 are communicated with each other.

Preferably, the small diameter drill 1 has an undercut portion 12 (see FIG. 1) having a smaller outer diameter compared to the tool diameter φDmm, which is the outer diameter at the tip 3. The undercut portion 12 generally has a function of reducing the frictional resistance with the machining hole and reducing the cutting resistance. The undercut portion 12 of the small-diameter drill 1 of the present invention enhances the effect of improving chip outflow near the junction 5 of the two grooves 2 in addition to the effect of reducing the cutting resistance. The degree of freedom in which chips can move is further expanded by the undercut portion 12. The undercut portion 12 suppresses the formation of chips in the vicinity of the junction 5 of the groove 2, and promotes the discharge of chips out of the processed hole along the groove 2. Regarding the direction from the front end 3 to the rear end 8 of the small-diameter drill 1, the lengths of the two outer peripheral recesses 6 may be formed to be longer than the end 3 side end of the undercut portion 12. As a result of this arrangement, the synergistic effect between the outer peripheral recessed portion 6 and the undercut portion 12 is enhanced, and the movement of fine chips closer to the tip 3 side than the junction 5 is performed more smoothly. It is preferable that the at least one outer peripheral recess 6 is formed to have a length that does not exceed the joining point 5, and the two grooves 2 are communicated with each other by the outer peripheral recess 6. After exceeding the merging point 5, it is preferable to increase the tool rigidity of the small diameter drill 1 by reducing the outer circumferential recess 6 from a short length. The tool diameter is the same as the outer diameter at the margin 11. A step portion is formed at the end portion of the undercut portion 12 on the front end 3 side. However, the vicinity of the tip 3 and the undercut portion 12 may be connected by a smooth curved surface, and the diameter of the follower heading toward the rear end 8 is reduced instead of or in addition to the undercut portion 12. A back taper portion may be provided.

The small-diameter drill 1 described above is detachably mounted on a machine tool dedicated to drilling, such as a printed wiring board, and is subjected to cutting (drilling) by giving a relative motion to the workpiece. For the machine tool, a drilling machine or a machining center may be used.

12 to 14 show a small diameter drill 101 of the second embodiment. 12 to 14, the same reference numerals are assigned to the same parts as those of the small diameter drill 1 of the first embodiment. The small diameter drill 101 of the second embodiment increases the length of the outer circumferential recess 6 as compared with the small diameter drill 1 of the first embodiment. That is, in FIG. 12, the length Lab of the first outer peripheral recess 6a is 0.93 mm. This length Lab is 0.10 mm longer than the length Laa (see FIG. 1) of the first outer peripheral recess 6a of the small-diameter drill 1 of the first embodiment. Thereby, the space for communicating between the two grooves 2 formed by the communication portion 7 becomes larger. The length Lbb of the second outer peripheral recess 6b is 1.10 mm.

As described in detail above, in the small-

diameter drills

1 and 101 of the first and second embodiments, the first outer peripheral recess 6a allows the two

grooves

2a and 2b to communicate with each other closer to the tip 3 side than the junction 5. The communication part 7 is provided. For this reason, chips move between the two

grooves

2a, 2b through the communication portion 7, and the collision between the chips near the junction 5 is alleviated.

Further, the length Lba (FIG. 5) of the second outer peripheral recess 6b is longer than the length Laa (FIG. 1) of the first outer peripheral recess 6a, so that the first outer peripheral recess 6a is provided. In a region downstream of the communication portion 7, the cross-sectional area of the flow path constituted by the second groove 2b and the second outer peripheral recess 6b is expanded. For this reason, the chip | tip moved from the 1st groove | channel 2a to the 2nd groove | channel 2b through the communication part 7 can be received, and chip | tip discharge property can be improved.

21 and 22 show the experimental results of a small diameter drill including the first and second embodiments of the present invention. The circles in FIG. 21 indicate feed rates that can ensure good chip dischargeability. The crosses in the figure indicate feed rates at which small-diameter drills break and stable drilling is not possible. The Δ mark in the figure indicates a feed speed that can be used without breaking, but has a slight problem in the quality of the hole to be machined due to the occurrence of flash or the like. The experimental conditions are as follows. The processed substrate was processed by stacking two FR-4s (a four-layer plate having a thickness of 1.6 mm). An aluminum plate was used as a backing plate. The spindle rotation speed was 160,000 min ⁻¹ (rotation per minute). The experiment was continued until the feed rate was gradually increased from the lower side and the small diameter drill broke. The comparative product 1 in the figure is a small diameter drill 201 as shown in FIGS. 15 to 17. That is, although the two grooves are merged in the same manner as in the first embodiment of the present invention, the outer peripheral recess is a small diameter drill that does not communicate the two grooves. The length Lac of the outer peripheral recess shown in FIG. 15 and the length Lbc of the outer peripheral recess shown in FIG. 17 were both set to 0.75 mm. The comparative product 2 is a small-diameter drill 301 as shown in FIGS. 18 to 20 in which the length of the outer peripheral recess is further longer than that of the second embodiment. The length Lbd of the outer circumferential recess shown in FIG. 20 was 1.54 mm, which was 0.44 mm longer than that of the second embodiment of the present invention. However, the length Lad of the outer periphery recessed part shown by FIG. 18 shall be 0.93 mm, and is the same as that of the 2nd Embodiment of this invention. That is, it was set as the length to the junction of two grooves. As a result of the experiment, as shown in FIG. 21, the small-

diameter drills

1 and 101 of the first and second embodiments are compared with the comparative product 1 in which the grooves 2 are joined and the outer peripheral recess is provided. The feed speed at which good chip dischargeability can be secured can be improved by about 33% from 3.6 m / min to 4.8 m / min. Moreover, the feed rate which can be used without breaking can be improved from 4.4 m / min to 5.2 m / min. Furthermore, as shown in FIG. 22, the small diameter drill 1 of the first embodiment has the same hole position accuracy at a feed rate of 3.6 m / min or less as compared with the comparative product 1, and the feed rate 4 Excellent at 0.0 m / min or more. Although the small diameter drill 101 of the second embodiment is slightly inferior to the small diameter drill 1 of the first embodiment, the hole position accuracy is superior to the comparative product 1 at a feed rate of 4.0 m / min or more. Yes. However, when the length of the outer peripheral concave portion is increased as in the comparative product 2, the chip discharging property shown in FIG. 21 is good, but the hole position accuracy shown in FIG. 22 is deteriorated. This is thought to be because the outer circumferential recess is too long and the tool rigidity is reduced.

The results of the experiment are summarized as follows. When the outer peripheral recess communicates with the two grooves, the chip discharging property is improved and the feeding speed can be improved. However, if the length of the outer peripheral recess is too long, the tool rigidity is lowered and the hole position accuracy is deteriorated. Therefore, the length of the outer peripheral recess is preferably as short as possible while communicating the two grooves. It is desirable that the length of at least one outer peripheral recess is formed so as not to exceed the junction 5. The numerical value of the hole position accuracy is a so-called average value + 3σ. The hole position accuracy of a printed wiring board is generally determined using a hole analyzer (hole position coordinate measuring machine) to determine how much the position is deviated from the original commanded position. Expressed as a distribution of values. For the hole position accuracy, there are two general methods: a method of representing the maximum value from the center, a method of representing the average value of dispersion plus a value obtained by adding three times the standard deviation σ (average value + 3σ), and two evaluation methods. . However, the method of evaluating with the maximum value may be affected by sudden problems such as surface scratches. Here, a method of evaluating the hole position accuracy with a numerical value of average value + 3σ was selected.

The present invention is not limited to the embodiment described above, and it goes without saying that the configuration can be changed, added and deleted as appropriate without departing from the gist of the invention. For example, a plurality of communication portions may be provided for a single outer peripheral recess. The communication portion may be provided in a plurality of outer peripheral recesses, or may be provided in all outer peripheral recesses. The outer circumferential recess does not need to extend continuously from the tip to the end, and may be intermittent. Three or more grooves, outer peripheral recesses, and margins may be provided. The margin may extend on both sides of a single outer peripheral recess so as to constitute a so-called double margin. In this case, the communication portion is particularly formed so as to cross the two margins. Is preferred. The present invention can be applied not only to a printed wiring board but also to other uses, for example, a drill for drilling metal.

DESCRIPTION OF SYMBOLS 1 Small diameter drill 2 Groove | channel 2a 1st groove | channel 2b 2nd groove | channel 3 Tip 4 Cutting edge 5 Joining point 6 Outer periphery recessed part 6a First outer periphery recessed part 6b Second outer periphery recessed part 7 Communication part 8 Rear end 9 Shank 10 Chisel edge 11 Margin 12 Undercut section

Claims

At least two grooves (2);
A cutting edge (4) arranged at the tip (3);
At least two margins (11) defining a part of the outer peripheral surface of the small diameter drill (1);
At least two peripheral recesses (6) extending in contact with the margin (11);
A small diameter drill (1) wherein the at least two grooves (2) have a confluence (5),
Of the at least two outer peripheral recesses (6), at least one outer peripheral recess (6) communicates the at least two grooves (2) with each other closer to the tip (3) side than the junction (5). A small diameter drill (1) having a communicating part (7).
The at least two outer peripheral recesses (6) include a first outer peripheral recess (6a) and a second outer peripheral recess (6b),
In the direction from the front end (3) to the rear end (8), the second outer peripheral recess (6b) is longer than the first outer peripheral recess (6a),
The small-diameter drill (1) according to claim 1, wherein the first outer peripheral recess (6a) has the communication portion (7).
The small diameter drill (1) according to claim 2, wherein the first outer peripheral recess (6a) has a length not exceeding the confluence (5).
The small diameter drill (1) according to any one of claims 1 to 3, further comprising an undercut portion (12) having a diameter smaller than a diameter at the tip (3).
All of the at least two outer peripheral recesses (6) are longer than the end of the undercut portion (12) on the front end (3) side in the direction from the front end (3) to the rear end (8). The small diameter drill according to claim 4 having a thickness.
Of the at least two grooves (2), the twist angle of the first groove (2a) is 20 ° or more and 60 ° or less near the tip (3),
The small diameter according to any one of claims 1 to 5, wherein the twist angle of the second groove (2b) is 20 ° or more and 60 ° or less near the tip (3), and changes from 30 ° to 80 ° from the middle. Drill (1).
The small-diameter drill (1) according to claim 6, wherein at least two of the grooves (2) have a twist angle of 20 ° or more and 80 ° or less in a region closer to the rear end (8) than the junction (5). .