drill

Abstract

(Problem) To provide a sharp drill resistant to breakage. (Solution) A drill of the present invention is characterized by comprising: first and second cutting edges formed rotationally symmetrically; first and second flanks formed rotationally symmetrically on the rear surface of the first and second cutting edges, respectively; one chip discharge groove formed from one of the first and second cutting edges toward the outer peripheral side; and one or more arc-shaped grooves formed from the other one of the first and second cutting edges toward the outer peripheral side. (Selected drawing) FIG. 1

Description

[Technical Field]

[0001] The present invention relates to a drill, and more particularly to a drill that is not only used to drill holes in workpieces such as metal plates using hand drills or drill presses, etc., with excellent rotational torque resistance and cutting performance without breakage, but also to a drill that is used to directly drill holes in treatment areas during medical, particularly orthopedic, procedures. [Background technology]

[0002] Conventional two-flute drills are commonly used, which have two cutting edges at the tip of the drill body that rotates around the axis of the drill, with two chip discharge grooves formed in a spiral shape toward the rear end of the drill, point-symmetrical with respect to the center of rotation.

[0003] General industrial drills used in hand drills and drill presses use the arm strength of the operator to drill holes, so drilling is difficult if the cutting resistance is large. However, with regard to such drills, it was thought that the priority was to ensure the strength and rigidity of the drill itself, and in addition, due to the fact that workers who purchased the drills would polish them to their own liking before using them, drill manufacturers had hardly conducted any research into reducing cutting resistance.

[0004] The present applicant has proposed a general industrial drill that is suitable for use in peeling off spot welds on automobile bodies made of high-hardness steel plates (see Patent Document 1). This drill has two cutting edges symmetrical about the axis of rotation and has a thinning process applied to the tip.The chisel width is 0.05 mm to 0.3 mm, and the thinning is applied at an angle of 1° to 4° to the line connecting the cutting edges of the two cutting edges when viewed from the tip of the drill.

[0005] The applicant has also proposed a general industrial drill that can significantly reduce cutting resistance and makes it easy to perform manual drilling work using a hand drill, drill press, etc. (see Patent Document 2). This drill has two cutting edges symmetrical about the axis of rotation and has a thinning process applied to the tip, and the rake angle θ1 formed by the main cutting edge and the rake angle θ2 formed by the thinning cutting edge satisfy θ1>θ2>0° except directly below the chisel. As such, conventional two-flute drills have chip discharge grooves that run from the tip to the periphery, which makes the center thinner and increases the risk of breakage during drilling. To ensure the strength of the center, the center is formed to a certain thickness, and then the center of the tip is thinned by a thinning process.

[0006] Also known is a drill in which a thinning process is performed on the tip portion, and the second margin portion, when viewed from the tip side in the axial direction, is positioned so as to include the outer peripheral edge at the intersection ridge line between the tip relief face and the thinning portion, and further, the second margin portion is positioned so as to be spaced a predetermined distance forward in the direction of drill rotation from the heel portion of the cutting edge (see Patent Document 3).

[0007] The present applicant has proposed a drill with a shape that improves the sharpness of conventional drills, and has also proposed a medical drill for use in orthopedic surgery and other procedures (see Patent Document 4). Furthermore, the present applicant has also proposed a medical drill that does not have a chip discharge groove called a Kirschner wire, but has a shape in which a slope is provided from the round bar state to the tip, the tip is formed thin, and a drill-like tip is provided (see Patent Document 5). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-88267 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-192514 [Patent Document 3] Japanese Patent Application Laid-Open No. 2005-305610 [Patent Document 4] Japanese Patent Application Publication No. 2018-108223 [Patent Document 5] Japanese Patent Application Publication No. 2018-108224 Summary of the Invention [Problem to be solved by the invention]

[0009] There are two conflicting issues: forming the chip discharge flutes shallowly significantly dulls the cutting edge, and providing two chip discharge flutes on the outer periphery of the drill reduces its strength. These issues have not yet been resolved. In particular, for thin-diameter drills such as guide pins, conventional medical drills have a small diameter of approximately 2 mm and a long overall length. In addition, unlike industrial drills, they rarely drill perpendicular to the treatment site, and are often angled toward the horizontal. Because drilling is performed at an angle like this, there is a possibility that the portion where the chip discharge groove is provided may be more likely to break due to its strength, and since the rigidity is also poor as well as the strength, the tip is likely to slip when drilling at an angle, which may result in the possibility of not drilling accurately at the target location.To solve this problem, the aforementioned Patent Document 5 addresses this problem by using a Kirschner wire, which has a thin tip formed into a drill-like tip, but this shape is simply a rod with a sharp tip and has poor cutting properties, so there is a problem that it induces heat during bone drilling, which may lead to bone necrosis.

[0010] In the case of the drill of Patent Document 4 mentioned above, the chisel portion at the tip of the drill is thinned from both sides of the chip discharge flute to the center of the drill in order to reduce cutting resistance, which creates a problem in that the chip discharge flute cannot be formed up to near the center of the drill when it is formed. Patent Documents 4 and 5 disclose embodiments formed with arc-shaped grooves. However, the arc-shaped shape of these embodiments has problems such as chip evacuation and adhesion between the drilled hole and the outer periphery of the drill. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a drill that is hard to break and has a sharp cutting edge. [Means for solving the problem]

[0011] In order to achieve the above object, the invention according to claim 1 comprises first and second cutting edges formed symmetrically with respect to a rotation axis, first and second flanks formed on the back surfaces of the first and second cutting edges, respectively, symmetrically about the rotation axis; one chip discharge groove formed from one of the first and second cutting edges toward the outer periphery; one or more arcuate grooves formed from the other of the first and second cutting edges toward the outer periphery, Only one chip discharge groove is provided. And, Only one arcuate groove is formed, a third flank is formed between the one arcuate groove and the first flank, the one arcuate groove and the second flank are adjacent to each other, and the one arcuate groove and the first flank are partially adjacent to each other. The present invention relates to a drill characterized by the above.

[0013] Claim 2 The invention relates to: First and second cutting edges formed symmetrically about a rotation axis; first and second flanks formed on the back surfaces of the first and second cutting edges, respectively, symmetrically about the rotation axis; one chip discharge groove formed from one of the first and second cutting edges toward the outer periphery; one or more arcuate grooves formed from the other of the first and second cutting edges toward the outer periphery, Only one chip discharge groove is provided, Two or more of the arc-shaped grooves are formed adjacent to each other, and the two or more arc-shaped grooves all and the first flank face are partially adjacent to each other, and the two End Arc-shaped groove Our The first flank and the second flank are adjacent to each other. Characterized by Regarding drills.

[0014] Claim 3 The invention according to claim 1 is characterized in that first and second back grooves are provided on the first and second cutting edges from the rear of the outer peripheries of the first and second cutting edges to the first and second flanks, respectively, and first and second margin portions are provided on the first and second cutting edges. or 2 The present invention relates to a drill described in the above. [Effects of the Invention]

[0015] The invention of claim 1 comprises first and second cutting edges formed symmetrically about the rotational axis, first flank faces and second flank faces formed symmetrically about the rotational axis on the back surfaces of the first and second cutting edges, one chip discharge groove formed from one of the first and second cutting edges toward the outer periphery, and one or more arc-shaped grooves formed from the other of the first and second cutting edges toward the outer periphery, thereby ensuring strength while maintaining sharpness, thereby preventing breakage of the drill. Since the chip discharge flute can be formed close to the center of the drill without thinning, the chip discharge flute itself can achieve the same effect as thinning (i.e., good sharpness). Since the drill has a first flank and a second flank formed symmetrically about the axis of rotation, problems such as the center becoming unstable when drilling begins are suppressed. In addition, the drill has a configuration in which only one arc-shaped groove is formed, a third flank is formed between the one arc-shaped groove and the first flank, the one arc-shaped groove is adjacent to the second flank, and the one arc-shaped groove is partially adjacent to the first flank.In combination with the above configuration, the back surfaces of the first and second cutting edges form first and second flanks, as with conventional two-flute drills, and a third flank, which does not have a chip discharge groove, is provided on the rear heel side of the first flank, making it possible to avoid flank interference during drilling.

[0017] Claim 2 The invention according to the present invention is characterized in that two or more of the arc-shaped grooves are formed adjacent to each other, and the two or more arc-shaped grooves all and the first flank face are partially adjacent to each other, and the two or more arcuate grooves Our Since the first flank and the second flank are adjacent to each other, there is a risk that a small amount of chips generated by the second cutting edge may be trapped. Therefore, by providing an additional groove approximately parallel to the groove forming the second cutting edge, the problems of flank interference and chip trapping during drilling can be avoided.

[0018] Claim 3 The invention according to the present invention is configured such that each of the first and second cutting edges has a first and second back groove provided from the rear of the outer periphery of the first and second cutting edges to the first and second flank, respectively, and also has a first and second margin portion provided on the first and second cutting edges, so that even if the diameter of the drill becomes thicker, it is not affected by the frictional resistance of the outer periphery. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a front view showing the tip portion of a drill according to one embodiment of the present invention. [Figure 2] FIG. 2 is a bottom view of the tip portion of the drill in FIG. 1 as seen from the direction of arrow B. [Figure 3] FIG. 3 is a top view of the tip portion of the drill in FIG. 1 as viewed from the direction of arrow A. [Figure 4] FIG. 4 is a perspective view showing a first cutting edge of the drill of FIG. [Figure 5] FIG. 5 is a perspective view of the drill of FIG. 4 rotated about its axis by approximately 45°. [Figure 6] FIG. 6 is a perspective view of the drill of FIG. 4 rotated about half a turn. [Figure 7] FIG. 7 is a front view showing the tip portion of a drill according to another embodiment of the present invention. [Figure 8] FIG. 8 is a perspective view of the drill of FIG. [Figure 9] FIG. 9 is a front view showing the tip portion of a drill according to still another embodiment of the present invention. [Figure 10] 10 is a bottom view of the tip portion of the drill shown in FIG. 9 as seen from the direction of arrow B. FIG. [Figure 11] FIG. 11 is a top view of the tip portion of the drill shown in FIG. 9 as seen from the direction of arrow A. [Figure 12] FIG. 12 is a front view showing the tip portion of a drill according to still another embodiment of the present invention. [Figure 13] FIG. 13 is a perspective view of the drill of FIG. [Figure 14] FIG. 14 is an explanatory diagram of a conventional drill. DETAILED DESCRIPTION OF THE INVENTION

[0020] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A drill according to an embodiment of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a front view showing the tip portion of a drill according to one embodiment of the present invention. FIG. 2 is a bottom view of the tip portion of the drill of FIG. 1, as seen from the direction of arrow B. FIG. 3 is a top view of the tip portion of the drill of FIG. 1, as seen from the direction of arrow A. FIG. 4 is a perspective view showing a first cutting edge of the drill of FIG. 1. FIG. 5 is a perspective view of the drill of FIG. 4 rotated approximately 45° about its axis. FIG. 6 is a perspective view of the drill of FIG. 4 rotated approximately half a turn. FIG. 7 is a front view of the tip portion of a drill according to another embodiment of the present invention. FIG. 8 is a perspective view of the drill of FIG. 7. FIG. 9 is a front view of the tip portion of a drill according to yet another embodiment of the present invention. FIG. 10 is a bottom view of the tip portion of the drill of FIG. 9, as seen from the direction of arrow B. FIG. 11 is a top view of the tip portion of the drill of FIG. 9, as seen from the direction of arrow A. FIG. 12 is a front view of the tip portion of a drill according to yet another embodiment of the present invention. FIG. 13 is a perspective view of the drill of FIG. 12.

[0021] 1 to 4, the drill (D) of this embodiment includes a first cutting edge (1) and a second cutting edge (2) formed symmetrically about the rotation axis, a first flank surface (3) and a second flank surface (4) formed symmetrically about the rotation axis on the back surface of each of the first cutting edge (1) and the second cutting edge (2), a chip discharge groove (5) formed from one of the first cutting edge (1) and the second cutting edge (2) (for example, the first cutting edge (1)) toward the outer periphery, and an arc-shaped groove (6) formed from the other of the first cutting edge (1) and the second cutting edge (2) (for example, the second cutting edge (2)) toward the outer periphery.

[0022] Although only one arc-shaped groove (6) is shown in FIGS. 1 to 4, the number of arc-shaped grooves (6) is not limited to one, and may be, for example, two or three.

[0023] The second cutting edge (2) is formed by an arc-shaped groove (6), and for this arc-shaped groove (6), the rake angle (θ2) of the second cutting edge (2) is set to be greater than 0° and within 5° (i.e., 0°<θ2≦5°). The rake angle (θ1) of the first cutting edge (1) is formed by the twist angle of the chip flute (5), and since the rake angle (θ1) is different between the center and the outer periphery, it is not the same rake angle (θ1), but the rake angle (θ1) is always formed to have a positive rake angle (θ1) (i.e., θ1 > 0°). The reason why the rake angle (θ1) is made positive is because a negative rake angle (θ1) increases the cutting resistance of the drill (D) and dulls its sharpness.

[0024] The arc forming the arc-shaped groove (6), which is the scooping portion of the second cutting edge (2), may be formed with a single radius, or may be formed with two or more different radii, or may be formed as a groove that is part of an ellipse.

[0025] The drill D of this embodiment has the above-described configuration, which makes it possible to prevent breakage of the drill D. Furthermore, the drill D of this embodiment can form the chip discharge flutes 5 up to near the center of the drill D without thinning, thereby achieving the same effect (i.e., good sharpness) as when thinning the chip discharge flutes 5 themselves.

[0026] As described above, the drill (D) of this embodiment has a first flank (3) and a second flank (4) formed symmetrically about the rotation axis, thereby preventing problems such as the center becoming unstable when drilling begins.

[0027] <Modification of the First Embodiment> Referring to FIG. 1, the drill (D) according to a modified example of the first embodiment has only one arc-shaped groove (6) as described above, a third flank (4a) is formed between the single arc-shaped groove (6a) and the first flank (3), the single arc-shaped groove (6a) is adjacent to the second flank (4), and the single arc-shaped groove (6a) is partially adjacent to the first flank (3).

[0028] The drill (D) according to this modified example has such a configuration, and in combination with the configuration of the drill claim 1 according to the above-mentioned embodiment 1, the back surfaces of the first cutting edge (1) and the second cutting edge (2) form the first flank surface (3) and the second flank surface (4) in the same manner as in a conventional two-flute drill, and a third flank surface (4a) without a chip discharge groove is provided on the rear heel side of the first flank surface (3), making it possible to avoid flank surface interference during drilling.

[0029] 7 and 8, a drill (D) according to a further modification of the first embodiment has a first back groove (7) and a second back groove (8) respectively provided on each of the first cutting edge (1) and the second cutting edge (2) from the rear of the outer periphery of the first cutting edge (1) and the second cutting edge (2) to the first flank (3) and the second flank (4), and also has a first margin portion (M1) and a second margin portion (M2) provided on the first cutting edge (1) and the second cutting edge (2).

[0030] Therefore, the drill (D) according to this modification is not affected by the frictional resistance of the outer periphery even if the diameter of the drill (D) is increased. More specifically, the first back groove (7) and the second back groove (8) and the first margin portion (M1) and the second margin portion (M2) may be appropriately formed on the outer periphery depending on the drilling depth, and the portions where the first back groove (7) and the second back groove (8) are provided are narrower than the first margin portion (M1) and the second margin portion (M2), so that only the first margin portion (M1) and the second margin portion (M2) come into contact with the wall surface of the drilling portion, thereby reducing friction during drilling.

[0031] [Embodiment 2] 9 to 11, the drill D according to this embodiment has three adjacent arc-shaped flutes 6a of the drill D according to embodiment 1, the three arc-shaped flutes 6a, 6b, and 6c are partially adjacent to the first flank 3, and one of the three arc-shaped flutes 6a, 6b, and 6c (i.e., the arc-shaped flute 6a) is adjacent to the first flank 3. This configuration may result in the retention of a small amount of chips generated by the second cutting edge 2. Therefore, by providing additional flutes (i.e., the arc-shaped flutes 6b and 6c) approximately parallel to the flute (i.e., the arc-shaped flute 6a) that forms the second cutting edge 2, the problems of flank interference and chip retention during drilling can be avoided.

[0032] The number of grooves (i.e., arc-shaped grooves) may be one or more, but since too many will affect the strength problem mentioned above, it is desirable to provide at least one or two grooves other than the groove (i.e., arc-shaped groove 6a) that forms the second cutting edge 2. The depth of the grooves (i.e., arc-shaped grooves 6b, 6c) is set to be equal to or shallower than that of the arc-shaped groove 6a.

[0033] The number of grooves may be determined depending on the groove width, depth, etc., and the groove depth may also be set taking into consideration strength, etc. Also, by forming a substantially linear ridge where each of the three arc-shaped grooves (6a, 6b, 6c) meets, a gap is created from the cylindrical portion, which addresses the problem of chips, and the number of grooves may be determined depending on the depth of the drilling portion, which also addresses the problem of chip discharge on the side of the second cutting edge (2).

[0034] <Modification of the second embodiment> Referring to Figures 12 and 13, the first cutting edge (1) and the second cutting edge (2) are each provided with a first back groove (7) and a second back groove (8) extending from the rear of the outer periphery of the first cutting edge (1) and the second cutting edge (2) to the first flank (3) and the second flank (4), respectively, and the first cutting edge (1) and the second cutting edge (2) are each provided with a first margin portion (M1) and a second margin portion (M2).

[0035] The drill (D) of this modified example, like the drill (D) shown in Figures 7 and 8 above, has the first back groove (7) and second back groove (8) and the first margin portion (M1) and second margin portion (M2) that can be appropriately formed on the outer periphery depending on the drilling depth, and the portions where the first back groove (7) and second back groove (8) are provided are narrower than the first margin portion (M1) and second margin portion (M2), so that only the first margin portion (M1) and second margin portion (M2) come into contact with the wall surface of the drilling portion, thereby reducing friction during drilling.

[0036] The first back groove (7) and the second back groove (8) may be formed only on the outer periphery on the first cutting edge (1) side, which has a larger contact area, or only on the outer periphery on the first cutting edge (1) side, which has a double margin shape (not shown).

[0037] In forming the first back groove (7), since it is not necessary to form an accurate cylindrical surface by grinding with a grindstone, which is the forming means, a ridge line indicating the boundary of the grinding path of the grindstone may appear.

[0038] In the figures described above in the first and second embodiments, the length of the chip discharge groove is shown as going around the outer circumference of the drill, but it is not limited to this length and can be determined depending on the object of treatment (drilling).

[0039] Although not limited thereto, the specifications of the drill (D) according to the first and second embodiments are as follows. The drill diameter is approximately 2mm to 6mm, the point angle is 40° to 90°, the relief angle is 5° to 30°, the twist angle (chip discharge groove) is 15° to 20°, the length of the groove (chip discharge groove) is approximately 1 / 4 of the circumference (determined depending on the treatment object), and the total length of the drill is determined depending on the treatment object (100mm or more). [Example]

[0040] The drill of the present invention will be described in more detail based on examples, but the drill of the present invention is not limited to these examples.

[0041] In order to confirm the performance of the drill of the present invention, 1) a cutting resistance test, 2) an inclined surface cutting test, and 3) a bending test were carried out.

[0042] As a drill to be compared with the drill of the present invention, the drill (product name: "Medical Gekko Drill") described in the aforementioned Patent Document 4 (JP Patent Publication No. 2018-108223) was used. <Common specifications> Drill diameter: 2.4mm Total length: 200 mm (when used for cutting tests) 70mm (Bending test: cut) Groove length: 8 mm (fixing position of jig during bending test) Material: JIS SUS316L stainless steel

[0043] (1) Cutting resistance test (torque, thrust) Workpiece: Sawbone imitation bone, Material: Solid rigid polyurethane, Density 50pcf (product number: SAW1522-27) Width 6mm, thickness 6mm Cutting conditions Rotation speed: 1,000 RPM Feed speed: 120 mm / min (0.12 mm / rev) Distance from chuck to drill tip during cutting test: 150 mm (2) Inclined surface cutting test Cutting was performed on a surface inclined at 40 degrees from the horizontal, and the deviation of the hole position after cutting was measured. (1) A test piece made of the same material as in (1) was formed with a 40° inclined surface. The center position of the hole after drilling was measured to check for any deviation. The reference position of the hole is X=10, Y=7.5 (mm) from the reference point. Using this position as a reference, measure the hole position after drilling. L=√((X-10) 2 +(Y-7.5) 2 The amount of deviation L was calculated using the formula: (For example, if X=10.5 and Y=8.0, L=0.71) Cutting conditions Rotation speed: 300 RPM Feed rate: 43.26 mm / min The same material as in (1) was used. (3) Bending test (strength and rigidity test) The drill was cut to a total length of 70 mm. The chip discharge groove <1> So that it is pointing upward (0°), <2> To make it sideways (90°), The tip was fixed at a position 8 mm from the tip, and a load was applied at a position 50 mm from the fixed position at a rate of 10 mm per minute until the tip displaced 15.4 mm, and the load at that time was confirmed.

[0044] (3) Test results (3-1) Cutting resistance test The cutting resistance and rotational torque resistance of the simulated bone manufactured by Sawbone are measured and the maximum values ​​are compared. Through holes were drilled twice each using the drill of the present invention (Example) and the drill of the comparative example (Patent Document 4: JP 2018-108223 A).

[0045] The results are shown in the table below.

[0046] [Table 1]

[0047] As a result of the cutting test, it was confirmed that the present drill (the drill according to the embodiment) was superior in thrust resistance and torque resistance. That is, In terms of torque resistance, it was found that the drill of the present invention (the drill according to the embodiment) was 60% (first time) and 64% (second time) of the comparative drill (the drill according to the comparative example), in other words, it was 40% less (first time) and 36% less (second time) than the comparative drill (the drill according to the comparative example). on the other hand, It was found that the thrust load resistance ratio of the drill (the drill according to the embodiment) was 86% (first time) and 90% (second time) of that of the comparative drill (the drill according to the comparative example), in other words, 14% (first time) and 10% (second time) lower than that of the comparative drill (the drill according to the comparative example). From the above results, it was confirmed that the drills of the present invention (drills according to the examples) had excellent cutting performance that was equal to or better than that of the comparative drills (drills according to the comparative examples).

[0048] (3-2) Inclined surface cutting test Five drilling tests were carried out for each specimen, and the deviation of the drilled area on the inclined surface was confirmed.

[0049] [Table 2]

[0050] As described above, the average deviation amount was 0.302 mm for the drill of the present invention (Example), and 0.751 mm for the comparative drill (Comparative Example). In addition, the maximum deviation was 0.440 mm for the drill (Example) and 1.146 mm for the comparative drill (Comparative Example). The minimum deviation was 0.161 mm for the drill (Example) of the present invention, and 0.321 mm for the comparative drill (Comparative Example), demonstrating the superiority of the present drill (Example) on inclined surfaces. In particular, it was confirmed that more than half of the deviation in the X direction was on the positive side (upward), demonstrating the superiority of the present drill in drilling on inclined surfaces. (The comparative drill (Comparative Example) all deviated on the negative side (downward).)

[0051] (3-3) Bending test (strength test) The results are shown in the table below (Table 3).

[0052] [Table 3]

[0053] As shown in Table 3, it was confirmed that the drill (Example) had higher strength than the comparative drill. In particular, it was confirmed that the strength was superior in the direction (0°) where it is prone to breakage. From the above results, the drill (Example) 1) In cutting resistance tests, Compared to the drill in the comparative example (JP Patent Publication No. 2018-108223), this drill has higher cutting resistance in the straight line direction and rotational torque resistance in the rotational direction, and in particular, the rotational torque resistance is significantly higher. It has been confirmed that this drill has excellent cutting performance and can drill holes with less force. 2) In the inclined surface cutting test, Compared to the drill of the comparative example (JP 2018-108223 A), it shows superiority in drilling on inclined surfaces. This can be assumed to be due to the excellent rigidity of the drill itself, which makes it less likely to bend and reduces the risk of the tip slipping, and also because the cutting force at the tip (especially torque: cutting ability in the rotational direction) is excellent, which resulted in less misalignment. 3) In the bending test (strength test), The numerical values ​​clearly show that the drill has superior strength and rigidity compared to the drill of the comparative example (JP 2018-108223 A). [Industrial Applicability]

[0054] The drill of the present invention has first and second cutting edges formed symmetrically about the rotational axis, first and second flank faces formed symmetrically about the rotational axis on the back surfaces of the first and second cutting edges, one chip discharge groove formed from one of the first and second cutting edges toward the outer periphery, and one or more arc-shaped grooves formed from the other of the first and second cutting edges toward the outer periphery, thereby making it possible to prevent breakage of the drill. Furthermore, the drill of the present invention can form chip discharge flutes up to near the center of the drill without thinning, and therefore can achieve the same effect (i.e., sharpness) on the chip discharge flute itself as with thinning. Furthermore, the drill of the present invention has a first flank and a second flank formed symmetrically about the rotation axis, which prevents problems such as the center becoming unstable when drilling begins. Therefore, the drill of the present invention is not only used to drill holes in workpieces such as metal plates with excellent rotational torque resistance and cutting performance without breakage using a hand drill or drill press, but also to directly drill holes in the treatment area during medical, particularly orthopedic, procedures. Furthermore, in addition to being used as a drill to directly drill holes in the treatment area, the drill of the present invention is also used as a fixed rotation center for hollow drills (i.e., a through hole equivalent to a thin drill at the rotation center) that are small diameter drills known as guide pins, guide wires, eyelet pins, etc., after the drill is fixed in advance to a bone, joint, etc., of the treatment area. [Explanation of symbols]

[0055] 1 First cutting edge 2 Second cutting edge 3 First flank 4 Second relief face 4a Third flank 5 Chip discharge groove 6a, 6b, 6c Arc-shaped groove 7 First back groove 8 Second back groove D drill M1 First margin M2 Second margin θ1 Rake angle of the first cutting edge θ2 Rake angle of second cutting edge

Claims

1. First and second cutting edges formed symmetrically about a rotation axis; first and second flanks formed on the back surfaces of the first and second cutting edges, respectively, symmetrically about the rotation axis; one chip discharge groove formed from one of the first and second cutting edges toward an outer periphery; one or more arcuate grooves formed from the other of the first and second cutting edges toward the outer periphery, Only one chip discharge groove is provided, a drill characterized in that only one arc-shaped flute is formed, a third flank is formed between the one arc-shaped flute and the first flank, the one arc-shaped flute and the second flank are adjacent to each other, and the one arc-shaped flute and the first flank are partially adjacent to each other.

2. First and second cutting edges formed symmetrically about a rotation axis; first and second flanks formed on the back surfaces of the first and second cutting edges, respectively, symmetrically about the rotation axis; one chip discharge groove formed from one of the first and second cutting edges toward an outer periphery; one or more arcuate grooves formed from the other of the first and second cutting edges toward the outer periphery, Only one chip discharge groove is provided, a drill characterized in that two or more of the arc-shaped grooves are formed adjacent to each other, all of the two or more arc-shaped grooves are partially adjacent to the first flank surface, and one of the two or more arc-shaped grooves is adjacent to the second flank surface.

3. 3. The drill according to claim 1, wherein first and second back grooves are provided on the first and second cutting edges, respectively, from rear of the outer peripheries of the first and second cutting edges to the first and second flanks, and first and second margin portions are provided on the first and second cutting edges.

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