drill

Abstract

The present invention provides a drill capable of suppressing surface damage to the workpiece that can occur when drilling holes in a plate-shaped workpiece. [Solution] The drill 1 comprises a body 2, a target hole forming portion 4 provided approximately in the middle of the length of the body 2 and having a diameter D1 corresponding to the diameter of the target hole 31, a stopper portion 3 integrally formed on the body 2 at a position spaced apart from the base end of the target hole forming portion 4 and having a larger diameter than the target hole forming portion 4, and a chip discharge spiral groove 14 extending spirally and continuously from the tip surface 9 of the body 2 through the stopper portion 3 on the outer circumferential surface of the body 2. The portion of the body 2 closer to the tip of the target hole forming portion 4 is tapered. A small diameter column portion 11, having a smaller diameter than the target hole forming portion 4, is provided between the target hole forming portion 4 and the stopper portion 3 of the body 2.

Description

Technical Field

[0001] The present invention relates to a drill used for drilling a hole having a circular cross-section that penetrates from the surface of a plate-shaped workpiece in the thickness direction.

Background Art

[0002] In plate-shaped metal workpieces such as folded roof materials, holes having a circular cross-section such as bolt insertion holes are drilled so as to penetrate from the surface of the workpiece in the thickness direction. This hole drilling process is generally performed using a hand-held tool such as an electric driver. Conventionally, as this type of drill, a straight groove drill having a straight groove and an integral stopper portion formed at the base end of the body has been widely known (see Non-Patent Document 1).

[0003] In addition, for the purpose of reducing cutting resistance and improving propulsion force, a spiral groove drill that employs a spiral groove (twisted groove, spiral groove) and has a multi-step shape (bamboo shoot shape) from the tip to the target diameter has also been developed. In this type of drill, in order to regulate the drilling depth, there is also a drill in which a stopper portion of a separate member or a rotatable disk-shaped member (a thin plate having a washer shape called a so-called "scratch prevention ring", "rotating ring", etc.) is attached to the drill body later to reduce damage to the surface of the workpiece (see Non-Patent Document 2).

[0004] The reason why a stopper portion is essential in these drills is not only for simply regulating the drilling depth. At the roof construction site, if the drill accidentally falls off from the chuck portion of the tool after the hole drilling process is completed, without a stopper portion, the drill may pass through the drilled hole and fall to the back side of the workpiece. If the drill falls, it will also lead to an economic blow of losing an expensive drill for the operator. Therefore, due to strong demands from the work site, from the perspective of asset preservation (prevention of falling off), a stopper portion has become an indispensable configuration for this type of drill.

[0005] However, in both straight groove and spiral groove drills, the cylindrical part that forms the target hole (target diameter) and the stopper part (or scratch prevention ring) are joined at an angle that is approximately perpendicular to the axial direction of the body. Therefore, the current structure is such that the drill's progress is stopped by the stopper part or other component physically colliding with the surface of the workpiece immediately after the target hole is formed in the workpiece (collision stop type). [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Takashiba Gimune Manufacturing Co., Ltd. website, "Hexagonal Shank Roof Drill for Corrugated Sheet Metal Roofs," searched November 20, 2025, Internet.<https: / / www.dia-t.com / products / 4020 / > [Non-Patent Document 2] Top Kogyo Co., Ltd. website, "Roof drill for corrugated metal roofs ESD-125R for electric drills," searched on December 11, 2025, Internet.<https: / / www.toptools.co.jp / tools / hexagon_drill-0018_473 / > [Overview of the project] [Problems that the invention aims to solve]

[0007] The straight-groove drills described above have been valued for their low chip discharge onto the workpiece surface, but they have had a significant drawback: poor cleaning due to fine chips and the risk of rust galvanic damage. Straight-groove drills do not cut the workpiece sharply, but rather "pry" it apart as they cut. As a result, the generated chips tend to accumulate in the processed area without being discharged, and are subjected to a "mixer action (re-crushing)" where they are repeatedly churned between the blade and the workpiece by the rotation of the drill. Consequently, the chips tend to become a "fine powder" that is difficult to see. Even if the amount is small, this powdery chip easily gets into the fine irregularities and gaps in the workpiece, making it difficult for the operator to notice the chip residue. Furthermore, even if the chips are wiped away with a cloth, static electricity and oil cause them to spread, making it difficult to completely remove them. This "hard-to-see residual chip" has been the main cause of unexpected rust galvanic damage after work, especially when the workpiece is metal. In addition, because high-thrust cutting is required, the force of penetration could cause the stopper to collide with the surface of the workpiece, posing an unavoidable risk of physically destroying the decorative layer formed on the workpiece surface.

[0008] In the case of the spiral groove drill described above, the chips are discharged in a relatively large size, making them easy to visually inspect and encouraging cleaning (good cleanability). However, because the drill has a multi-step shape, a new problem arises: "large amounts of chips being kicked up." That is, the chips, which are broken up at the steps of the multi-step shape, are kicked up in large quantities onto the surface of the workpiece by the pumping action of the spiral groove. No matter how good the shape is, the amount of chips is too much, exceeding what the operator can realistically handle by cleaning.

[0009] Furthermore, this large amount of chips causes a "sandwich phenomenon" where accumulated chips become trapped. In other words, in a structure where the cylindrical part forming the target hole and the stopper part are joined at a right angle, the kicked-up chips inevitably get trapped between the stopper part (or scratch prevention ring) and the workpiece. As a result, the scratch prevention ring, which is supposed to prevent scratches, acts like an abrasive through the trapped chips, damaging the finishing layer—a contradiction indeed.

[0010] The present invention has been made in view of the above-mentioned technical background, and the object of the present invention is to provide a drill that can suppress surface damage to a workpiece that may occur when drilling holes in a plate-shaped workpiece. [Means for solving the problem]

[0011] The present invention provides the following means.

[0012] 1) A drill used to drill a target hole with a circular cross-section that penetrates through the surface in the thickness direction of a plate-shaped workpiece, The device comprises a body that rotates around an axis, a target hole forming portion provided approximately in the middle of the length of the body and having a diameter corresponding to the diameter of the target hole, a stopper portion integrally formed on the body at a position spaced apart from the target hole forming portion toward the base end and having a larger diameter than the target hole forming portion, and a spiral groove for chip discharge extending spirally and continuously from the front end of the body toward the base end, passing through the stopper portion, on the outer circumferential surface of the body. The portion of the body closer to the tip of the target hole forming portion is formed in a tapered shape towards the tip. A drill in which a small-diameter column portion, smaller in diameter than the target hole forming portion, is provided between the target hole forming portion and the stopper portion of the body.

[0013] 2) The drill according to item 1 above, wherein the distance between the target hole forming portion and the stopper portion is set to a length that can secure a braking distance from the completion of the formation of the target hole until the stopper portion contacts the surface of the workpiece.

[0014] 3) Between the tip surface of the body and the target hole forming portion, a tapered portion is provided that is continuously increasing in diameter toward the base end. The tapered portion and the target hole forming portion are adjacent to each other via a first stepped portion. The drill according to item 1 or 2 above, in which the rate of increase in diameter of the first stepped portion is set to be larger than the rate of increase in diameter of the tapered portion in the proximal direction of the body.

[0015] 4) A straight portion that extends parallel to the axis and has a diameter smaller than the diameter of the target hole forming portion is provided adjacent to the outer peripheral edge of the tip surface of the body. The straight portion and the tapered portion are adjacent to each other via a second stepped portion. The drill according to item 3 above, in which the rate of increase in diameter of the second stepped portion is set to be larger than the rate of increase in diameter of the tapered portion in the proximal direction of the body.

[0016] 5) A tapered portion with a continuously increasing diameter toward the proximal side is provided between the tip surface of the body and the target hole forming portion in the body. <ocke=" A straight portion that extends parallel to the axis and has a diameter smaller than the diameter of the target hole forming portion is provided adjacent to the outer peripheral edge of the tip surface of the body. The straight portion and the tapered portion are adjacent to each other via a second stepped portion. The drill according to item 1 or 2 above, in which the rate of increase in diameter of the second stepped portion is set to be larger than the rate of increase in diameter of the tapered portion in the proximal direction of the body.

[0017] 6) The drill according to any one of items 1 to 5 above, in which the diameter of the outer peripheral edge of the tip surface of the body is 3 mm to 7 mm.

[0018] 7) The drill according to any one of items 1 to 6 above, in which a countersink portion for removing the back burr of the target hole is formed at the adjacent portion of the small diameter column portion to the target hole forming portion.

Advantages of the Invention

[0019] The present invention has the following advantages.

[0020] · Realization of non-contact stop (position stopping) by a "torque dropout" signal In the drill of the present invention, a reduced-diameter column portion is provided between the target hole forming portion and the stopper portion in the body. As a result, a "torque dropout" phenomenon occurs in which the cutting resistance load suddenly disappears immediately after the target hole forming portion penetrates the workpiece. This physical load fluctuation acts as a clear tactile signal (feedback) to inform the operator that "drilling is completed". While a conventional drill could only be stopped by physically colliding the stopper portion with the surface of the workpiece, in the drill of the present invention, the operator can sense this signal and autonomously shift to the stop operation, so that it is possible to perform "inching stop" to stop immediately without causing the stopper portion to impact (contact) the workpiece. As a result, it is possible to solve the problem that was impossible to achieve in the prior art, that is, while maintaining the function of preventing the drill from falling off, which is the original role of the stopper portion, the surface of the workpiece is not damaged even though the drill has a stopper portion.

[0021] · Suppression of the risk of seizure rust due to "continuousization" of chips The drill of the present invention employs a tapered portion as a tapered shape without a stepped portion in the diameter-expanding portion for expanding the hole, instead of adopting the conventional multi-step shape. In the multi-step shape, the chips were forcibly divided at the stepped portion and scattered in a fine powder form, but in the shape of the drill of the present invention, the chips are not divided and are generated as "continuous long curl shapes". The chips having mass and intertwined with each other are difficult to be lifted up by the spiral groove and are mainly easily discharged to the back side of the workpiece by gravity or the like. As a result, "discharge of a large amount of chips onto the surface of the workpiece", which is a drawback of the spiral groove drill, is suppressed, and the amount of chips remaining on the surface of the workpiece is significantly reduced (for example, halved). When the workpiece is made of metal, the risk of seizure rust due to chips on the surface of the workpiece can be suppressed.

[0022] · Suppression of the sandwich phenomenon by "chip pocket" and "continuous spiral groove" In the drill of the present invention, a small diameter column provided between the target hole forming section and the stopper section functions as a "chip pocket (escape area)" that temporarily accommodates chips transported by the spiral groove. Furthermore, since the spiral groove extends continuously through the stopper section without interruption at the target hole forming section, the flow of chips is not hindered, and chip accumulation or clogging at the stopper section does not occur. As a result, the "sandwich phenomenon," in which wound-up chips are sandwiched between the stopper section and the workpiece, and the surface of the workpiece is damaged (including polishing) by the rotating stopper section (or scratch prevention ring), can be structurally suppressed.

[0023] • Improved construction quality due to low thrust and deburring function. The combination of a spiral groove and a tapered section enables drilling with extremely low thrust, resulting in less plastic deformation (extrusion deformation) of the workpiece and suppressing the generation of burrs during the drilling stage. In addition, when withdrawing the drill from the target hole, the countersink section provided adjacent to the target hole forming section on the small diameter column contacts the peripheral edge of the target hole opening on the back surface of the workpiece, removing any remaining burrs. Thus, the drill of the present invention can achieve both "suppression of burr generation" and "removal of burrs" in a single step. [Brief explanation of the drawing]

[0024] [Figure 1] Figure 1 is a perspective view of a drill according to one embodiment of the present invention. [Figure 2] Figure 2 is a front view of the drill. [Figure 3] Figure 3 is a front view of the outline of the tip of the drill body. [Figure 4] Figure 4 is an enlarged view of the body, from the tip surface to the second stepped section, as seen from the tip side. [Figure 5] Figure 5 is an enlarged view of section A in Figure 2. [Figure 6] Figure 6 is a front view showing the tapered portion of the body. [Figure 7] Figure 7 is an enlarged view of section B in Figure 2. [Figure 8] Figure 8 is an enlarged view of section C in Figure 2. [Modes for carrying out the invention]

[0025] One embodiment of the present invention is described below with reference to the drawings.

[0026] As shown in Figures 1 and 2, the drill 1 according to one embodiment of the present invention is used to drill a target hole 31 (i.e., a hole having a target diameter) in a plate-shaped workpiece 30 (shown by a dashed line in Figure 2), which is a through hole with a circular cross-section that penetrates from the surface 30a in the thickness direction.

[0027] The workpiece material 30 is a thin sheet of metal such as corrugated roofing material, deck plate, electrical panel cabinet material, siding material, thin sheet steel pipe material, panel material, and thin sheet metal component for automobiles. In particular, the drill 1 of this embodiment is suitable for drilling holes in building metal sheet components that have a decorative layer formed on their surface by rust-preventive coating or plating (galvalume, SGL, etc.).

[0028] In this embodiment, the workpiece 30 is, for example, a corrugated metal sheet used for roofing. The corrugated metal sheet is formed by bending a thin metal sheet into a roughly uneven shape. This workpiece 30 may be used as a single sheet at the construction site, or multiple sheets (usually two) may be stacked together to ensure waterproofing and strength. The drill 1 of this embodiment is configured to perform high-quality drilling on such "workpieces with a decorative layer" or "stacked workpieces" while suppressing damage to the surface 30a and preventing chips from entering between the workpieces.

[0029] The workpiece material (corrugated sheet) 30 is a thin sheet, and its thickness t as a single sheet is 0.3 mm to 1.2 mm. The drill 1 of this embodiment is configured to enable good drilling in both cases, whether the workpiece material 30 is a single sheet or two sheets overlapped, as can be seen at actual construction sites (up to two overlapping sections).

[0030] In other words, the actual thickness t of the workpiece 30 targeted by drill 1 ranges from the minimum thickness of a single sheet (0.3 mm) to the total thickness when two sheets are stacked together (maximum 2.4 mm).

[0031] As described above, the front surface 30a and back surface 30b of the workpiece 30 have decorative layers (paint films, plating layers, etc.) formed on them. Specifically, the workpiece 30 is made of SGL steel sheet, galvalume steel sheet (registered trademark), fluororesin coated steel sheet, galvanized steel sheet, etc., and the decorative layer is a thin, high-performance layer intended to maintain rust prevention, corrosion resistance, weather resistance, etc., on the workpiece 30 for a long period of time. Therefore, damage to the front surface 30a (damage to the decorative layer) during drilling significantly impairs the asset value and durability of the workpiece 30 and must be avoided as much as possible.

[0032] In the workpiece 30, the target hole 31 is used as a hole for inserting various fasteners (fastening members) such as roof bolts, self-drilling screws, and anchor bolts. In this case, the form of drilling the hole in the workpiece 30 is not limited; it may be drilled in a single sheet, or multiple sheets (mainly two) may be stacked on top of each other (overlap portion) to ensure waterproofing and strength. The drill 1 of this embodiment is configured to perform high-quality drilling while suppressing damage to the surface 30a and preventing chips from entering between the workpieces, regardless of whether it is a single sheet or stacked, and regardless of whether it is a corrugated sheet or a deck plate.

[0033] The drill 1 is made of a hard material such as cemented carbide or high-speed tool steel (e.g., high-speed steel) and comprises a rod-shaped body 2 and a shank 18.

[0034] The shank 18 is, in detail, a hexagonal shank, and this shank 18 is integrally formed with the base end of the body 2, coaxially with the body 2. Therefore, the drill 1 falls into the category of a so-called solid drill. When drilling a hole in the workpiece 30, the shank 18 is attached to the chuck of a handheld drilling tool such as an impact driver or drill driver (e.g., an electric screwdriver). Then, the rotational force of the tool causes the body 2 to rotate around the axis P of the body 2 (drill 1). Note that the arrow "Q" in Figure 2 indicates the direction of rotation of the body 2 (drill 1).

[0035] The body 2 includes a cylindrical target hole forming portion 4 located approximately in the middle of the length (i.e., axial direction) of the body 2, a stopper portion 3 integrally formed on the body 2 at a position spaced apart from the target hole forming portion 4 toward the base end, and two spiral grooves 14, 14 for chip discharge extending spirally and continuously from the front end surface 9 of the body 2 toward the base end, passing through the stopper portion 3.

[0036] The target hole forming section 4 is a part for forming a target hole 31 in the workpiece 30, and has a diameter D1 corresponding to the diameter of the target hole 31. The target hole forming section 4 is integrally formed coaxially with the body 2 in a cylindrical shape extending parallel to the axis P. The symbol "L2" in the figure represents the length of the target hole forming section 4 in the axial direction of the body 2.

[0037] The diameter of the target hole 31 (i.e., the diameter D1 of the target hole forming section 4) is not limited, but is specifically between 8mm and 25mm, and more specifically between 9mm and 23mm.

[0038] The stopper section 3 primarily functions as a "fall prevention mechanism (safety device)". In other words, the basic operation of the drill 1 in this embodiment is that the operator autonomously stops the progress of the drill 1 (stops just short of the target) when the operator senses a torque loss (sensing function) at the small diameter column section 11, which will be described later. However, as a "fail-safe (double safety measure)" in the event that the operator's reaction is delayed or excessive thrust is applied to the drill 1, the stopper section 3 physically restricts the progress of the drill 1 by contacting the surface 30a of the workpiece 30. This reliably prevents the drill 1 from falling out of the tool chuck or being lost.

[0039] In the figure, the symbol "L1" represents the distance between the target hole forming section 4 and the stopper section 3 in the axial direction of the body 2. In this embodiment, L1 is not merely a gap, but plays the role of a braking distance from the moment the operator senses the completion of the target hole 31 formation, i.e., the penetration (torque release) of the target hole 31, until the stopper section 3 contacts the surface 30a of the workpiece 30. Therefore, L1 is set to a sufficient length that takes into account the operator's reaction time.

[0040] The diameter of the stopper portion 3 is larger than the diameter D1 of the target hole forming portion 4, preferably set to be 2 mm to 10 mm larger than D1.

[0041] Furthermore, a smaller diameter columnar portion 11, smaller in diameter than the target hole forming portion 4, is coaxially and integrally formed on the body 2 between the target hole forming portion 4 and the stopper portion 3. This connects the target hole forming portion 4 and the stopper portion 3 via the smaller diameter columnar portion 11. Specifically, the target hole forming portion 4 is coaxially and integrally formed at the tip end of the smaller diameter columnar portion 11, and the stopper portion 3 is coaxially and integrally formed at the base end of the smaller diameter columnar portion 11.

[0042] The important point here is that the above-mentioned spiral groove 14 for chip discharge is continuously formed so as to pass through the stopper portion 3 via the small-diameter column portion 11 without interruption in the target hole forming portion 4. Further, the minimum diameter D3 of the small-diameter column portion 11 is intentionally set smaller than the diameter D1 of the target hole forming portion 4 (D3 < D1). Thereby, an annular space (chip pocket) 11a for accommodating the chips conveyed by the spiral groove 14 is formed between the target hole forming portion 4 and the stopper portion 3. The size of D3 relative to D1 is not limited, but preferably D3 is set to be 2 mm to 4 mm smaller than D1.

[0043] The entire portion on the tip side of the target hole forming portion 4 in the body 2 is formed to taper in the tip direction of the body 2. More specifically, this portion does not have a simple conical shape, but has a "composite tapered shape" in which a later-described "straight portion 8" located on the tip side and responsible for positioning performance and a later-described "taper portion 6" for reducing cutting resistance as the main cutting region are connected via later-described stepped portions 5 and 7.

[0044] The two spiral grooves 14, 14 are formed to extend spirally symmetrically about the axis P at portions on the outer peripheral surface 2a of the body 2 that are opposite to each other with respect to the axis P (see FIG. 4). Therefore, the drill 1 falls within the category of a so-called twist drill. The important point here is that the spiral groove 14 is continuously formed so as to sequentially pass through not only the target hole forming portion 4 but also the small-diameter column portion 11 (including a countersink portion 12 and an outer burr removal portion 13 described later) following the base end side thereof and the stopper portion 3. Thereby, "dead ends" are eliminated in the chip discharge path, and smooth discharge is possible at least until immediately before the stopper portion 3.

[0045] Incidentally, "θ1" in FIG. 2 is the twist angle of the spiral groove 14. This twist angle θ1 is preferably set to 20° to 40° in order to achieve both reduction of cutting resistance (thrust load) and chip dischargeability.

[0046] As shown in Figure 3, the tip surface 9 of the body 2 is formed in a conical shape that protrudes on the axis P in order to improve its grip on the workpiece 30. In Figure 3, "θ2" is the tip angle of the body 2.

[0047] The tip angle θ2 may be equivalent to the standard angle of a typical metalworking drill (approximately 118°), but it is preferable to set it to a smaller angle (i.e., less than 118°), and particularly preferably to 100° to 110°. By setting the tip angle θ2 within this preferred range, in combination with the effect of thinning (XR-type thinning) described later, the "walking phenomenon" in which the tip 9a of the body 2 slides on the surface 30a of the workpiece 30 at the start of drilling is suppressed, and reliable positioning is possible even without center punching.

[0048] As shown in Figure 4, a cutting edge 9b is formed along the ridge between the tip surface 9 of the body 2 and the inner surface 14a (see Figure 2) located on the rear side in the rotation direction Q of the drill 1 in the helical groove 14.

[0049] Here, because the helical groove 14 extends in a spiral shape (having a twist angle θ1), the angle between the inner surface 14a (rake face) and the tip surface 9 (relief face) of the helical groove 14, i.e., the "rake angle" of the cutting edge 9b, is set to a positive angle suitable for cutting. This sharp cutting edge shape significantly reduces the resistance to biting into the workpiece 30 (thrust load), ensuring that the aforementioned "low-thrust drilling" can be reliably performed.

[0050] Furthermore, as shown in Figure 2, the ridge between the outer surface 2a of the body 2 and the inner surface 14a of the helical groove 14 is defined as the leading edge portion 15. Therefore, the leading edge portion 15 is formed along this ridge portion from the outer surface end 9j of the cutting edge 9b (see Figure 4) toward the base end of the body 2.

[0051] The leading edge portion 15 functions as a "side cutting edge" that cuts and enlarges the inner wall of the hole 31 in the workpiece 30 at each part of the body 2 except for the stopper portion 3. Here, because the leading edge portion 15 is twisted in a spiral shape, "oblique cutting (shearing effect)" occurs, where the blade contacts the workpiece 30 at an angle. As a result, compared to a straight groove drill in which the blade strikes the workpiece at a right angle, the cutting resistance is dispersed and reduced, and the chips are more likely to be generated in a continuous curl shape without being broken up.

[0052] As shown in Figure 4, the tip surface 9 of the body 2 is thinned to reduce cutting resistance (thrust load) and improve bite. In this embodiment, the thinning is XR type thinning (a type of cross thinning). Therefore, the tip surface 9 of the body 2 has the aforementioned cutting edge 9b, chisel edge 9c, relief surface 9e, second relief surface 9f, thinning heel surface 9g, thinning blade 9h, thinning rake surface 9i, etc.

[0053] In conventional drills, the chisel edge (lateral blade) in the center of the tip surface has no cutting ability and crushes the workpiece 30 as it advances, requiring a large thrust and causing slippage (walking). In contrast, in the XR type thinning of this embodiment, the width of the chisel edge 9c is reduced to the absolute minimum, and a thinning blade 9h is formed as a sharp cutting edge all the way to the center of the tip surface 9. As a result, it becomes possible to "cut" into the workpiece 30 rather than "crush" it from the moment the drilling process begins, and even if a hard decorative layer (such as SGL) is formed on the surface 30a of the workpiece 30, the tip 9a of the body 2 can reliably bite into the surface 30a of the workpiece 30 without slipping on the surface 30a of the workpiece 30 with low thrust, without the need for center punching on the decorative layer.

[0054] As shown in Figure 2, a tapered portion 6 is provided between the front end surface 9 of the body 2 and the target hole forming portion 4, with the diameter gradually increasing continuously toward the base end. Furthermore, the tapered portion 6 and the target hole forming portion 4 are adjacent to each other via a first stepped portion 5. In the figure, the reference numeral "L3" represents the length of the first stepped portion 5 in the axial direction of the body 2. The reference numeral "L4" represents the length of the tapered portion 6 in the axial direction of the body 2.

[0055] The tapered section 6 functions as the "main cutting area" that bears the majority of the cutting resistance load during drilling the target hole 31. Importantly, the tapered section 6 is not a multi-step (bamboo shoot-shaped) structure like those found in conventional helical groove drills, but rather a "smooth inclined surface" without steps in the base direction. This configuration ensures that the chips generated during cutting are not forcibly broken up, but instead form a "continuous, long curl." This suppresses excessive chip entanglement and scattering by the helical groove 14, thereby reducing the risk of rust formation due to chip residue on the workpiece surface 30a.

[0056] The tapered portion 6 is formed in a substantially conical shape, with its diameter increasing at a substantially constant rate towards the base end. More specifically, the generatrix (contour) of this tapered portion 6 is set to have a gentle inclination angle with respect to the axis P. This inclination angle is preferably set to 2° to 20°, more preferably to 3° to 10°.

[0057] The gentle inclination angle of the tapered section 6 minimizes the cutting resistance load (depth of cut) per unit time as the drill 1 advances. As a result, the operator can use a light thrust as if using a straight drill, but in reality, the taper effect allows the hole 31 to gradually expand in diameter, enabling high-precision drilling while suppressing deformation (denting) of the workpiece 30.

[0058] Furthermore, a cylindrical straight section 8 is integrally formed adjacent to the outer peripheral edge 9k of the tip surface 9 of the body 2, extending parallel to the axis P and having a diameter smaller than the diameter D1 of the target hole forming section 4. The reference numeral "L6" represents the length of the straight section 8. Also, the reference numeral "D2" in Figure 3 represents the diameter of the outer peripheral edge 9k of the tip surface 9 of the body 2, which is the diameter of the straight section 8.

[0059] This straight section 8 forms a small-diameter through hole in the workpiece 30 as a pilot hole before the main diameter-expanding machining by the tapered section 6 begins. By aligning the outer circumference of the drill 1 with the inner wall of this hole, it acts as a "guide (runout stabilizer)" in the initial stages of machining. This guiding effect, combined with the cutting performance of the helical groove 14, suppresses runout and tilt of the drill 1, improving the cutting accuracy in the subsequent tapered section 6.

[0060] Furthermore, the straight section 8 and the tapered section 6 are adjacent to each other via the second stepped section 7. The reference numeral "L5" in the figure represents the length of the second stepped section 7 in the axial direction of the body 2.

[0061] In the base direction of body 2, the diameter expansion ratio α1 of the first stepped portion 5 is set to be greater than the diameter expansion ratio α2 of the tapered portion 6. Also, in the base direction of body 2, the diameter expansion ratio α3 of the second stepped portion 7 is set to be greater than the diameter expansion ratio α2 of the tapered portion 6. That is, α1 and α2 satisfy the relationship α1 > α2, and α3 and α2 satisfy the relationship α3 > α2.

[0062] Here, as shown in Figure 5, α1 represents the value obtained by dividing the radial increase ΔR1 of the first stepped section 5 over its entire length by the length L3 of the first stepped section 5, i.e., α1 = ΔR1 / L3. In other words, α1 is an index that represents the "average diameter increase rate (average gradient)" of the first stepped section 5 as a whole, regardless of minute shape changes within the first stepped section 5.

[0063] As shown in Figure 6, α2 represents the value obtained by dividing the radial increase ΔR2 of the tapered portion 6 over the entire length of the tapered portion 6 by the length L4 of the tapered portion 6, i.e., α2 = ΔR2 / L4.

[0064] As shown in Figure 7, α3 represents the value obtained by dividing the radial increase ΔR3 of the second stepped portion 7 over its entire length by the length L5 of the second stepped portion 7, i.e., α3 = ΔR3 / L5. Similar to α1 above, α3 is an index representing the "average diameter increase ratio" of the second stepped portion 7 as a whole.

[0065] As shown in Figure 5, the first stepped portion 5 is composed of either a single stepped portion 5a, or multiple stepped portions 5a (for example, two or three) arranged in a stepped manner towards the base end of the body 2 so as to connect the outer circumferential surface of the tapered portion 6 and the outer circumferential surface of the target hole forming portion 4.

[0066] In this embodiment, the first stepped portion 5 is composed of multiple stepped portions 5a. The stepped surface 5b of each stepped portion 5a is formed in a tapered shape with a gradually increasing diameter toward the base end, and the intermediate surfaces 5c between adjacent stepped portions 5a are formed parallel to the axis P. The stepped surface 5b enlarges the diameter of the hole 31 in the workpiece 30, while the intermediate surfaces 5c maintain and stabilize the diameter of the hole 31.

[0067] Thus, the first stepped section 5 is configured to alternately repeat stepped surfaces 5b (loaded section) and intermediate surfaces 5c (unloaded section) in the direction of the base end of the body 2. This suppresses an increase in the overall diameter ratio of the first stepped section 5, while clearly transmitting multiple consecutive pulse-like signals (click sensations) to the operator as the first stepped section 5 passes the position of the hole 31. This configuration disperses the impact caused by sudden changes in cutting resistance load, and more reliably and gently notifies the operator that the target hole forming section 4 is about to reach the position of the hole 31. In this embodiment, the first stepped section 5 is more specifically composed of two stepped sections 5a, 5a. Therefore, two consecutive pulse-like signals are transmitted to the operator.

[0068] As shown in Figure 7, the basic shape of the second stepped portion 7 is the same as the configuration of the first stepped portion 5 described above. Specifically, the second stepped portion 7 is composed of either a single stepped portion 7a, or multiple stepped portions 7a (for example, two or three) arranged in a stepped manner towards the base end of the body 2 so as to connect the outer circumferential surface of the straight portion 8 and the outer circumferential surface of the tapered portion 6.

[0069] In this embodiment, the second stepped portion 7 is composed of multiple stepped portions 7a. The stepped surface 7b of each stepped portion 7a is formed in a tapered shape with a gradually increasing diameter toward the base end, and the intermediate surface 7c between adjacent stepped portions 7a, 7a is formed parallel to the axis P. The stepped surface 7b enlarges the diameter of the hole 31 in the workpiece 30, while the intermediate surface 7c maintains and stabilizes the diameter of the hole 31.

[0070] Thus, the second stepped section 7 is configured to alternately repeat stepped surfaces 7b (loaded section) and intermediate surfaces 7c (unloaded section) in the direction of the base end of the body 2. This suppresses an increase in the overall diameter ratio of the second stepped section 7, while clearly transmitting multiple consecutive pulse-like signals (click sensations) to the operator as the second stepped section 7 passes the position of the hole 31. This configuration disperses the impact caused by sudden load fluctuations and more reliably and mildly notifies the operator that the tapered section 6 is about to reach the position of the hole 31. In this embodiment, the second stepped section 7 is more specifically composed of two stepped sections 7a, 7a. Therefore, two consecutive pulse-like signals are transmitted to the operator.

[0071] This configuration allows the operator to feel a light, pulsed signal, such as "thump-thump," immediately after the straight guide section 8 penetrates the workpiece 30. This makes it possible for the operator to clearly recognize the transition to the next phase—that positioning is complete and the main diameter-expanding process by the tapered section 6 is about to begin—solely through their sense of touch, without needing to look.

[0072] The diameter D2 (see Figure 3) of the outer edge 9k of the tip surface 9 of the body 2 is not limited, but is preferably between 3 mm and 7 mm. This numerical range is a suitable condition for achieving both the lifespan and machining performance of the drill 1.

[0073] If D2 is significantly smaller than 3mm, the effective length and area of ​​the cutting edge 9b become extremely small, resulting in insufficient heat capacity during cutting. This causes the tip surface 9 of the body 2 to overheat easily, and the cutting resistance load per unit area increases. As a result, wear and heat degradation of the tip surface 9 (cutting edge 9b, thinning edge 9h, etc.) are more likely to occur, and the lifespan of the drill 1 tends to be shortened. In contrast, by setting D2 to 3mm or more, wear and heat degradation of the tip surface 9 of the body 2 can be reliably suppressed, ensuring a longer lifespan for the drill 1. Furthermore, XR-shaped thinning can be reliably and easily formed on the tip surface 9 of the body 2.

[0074] The advantages of having a D2 of 7mm or less are as follows: Generally, when drilling a hole in a single step using a straight drill with the same diameter as the target hole 31 (e.g., 12.5mm), the cutting resistance is quite large. In the case of a drill with a hexagonal shank (e.g., 6.35mm across flats), the stress of the cutting resistance concentrates on the chuck-fixing neck portion 18a of the shank 18, which carries the risk of torsional fracture or deformation of the shank 18. Furthermore, because the entire tip surface 9 of the body 2 is subjected to a severe cutting resistance load, wear of the tip surface 9 (cutting edge 9b, thinning edge 9h, etc.) tends to progress rapidly, and the drill 1 tends to reach the end of its lifespan (loss of sharpness) in a short time. In contrast, by having a D2 of 7mm or less, the cutting resistance can be reliably reduced, the concentration of stress on the most vulnerable shank neck portion 18a can be reliably avoided, and furthermore, wear of the tip surface 9 of the body 2 can be reliably suppressed. This ensures that drill 1 can be used reliably for a long period of time, even if shank 18 is a hexagonal shank.

[0075] As shown in Figure 2, a countersink portion 12 is formed adjacent to the target hole forming portion 4 in the small diameter column portion 11 to remove the burr 32 on the back of the target hole 31.

[0076] Here, the burr 32 on the back of the target hole 31 refers to the burr 32 formed on the peripheral edge of the opening of the target hole 31 on the back surface 30b of the workpiece 30.

[0077] Similarly, the surface burr 33 of the target hole 31 refers to the burr 33 formed on the peripheral edge of the opening of the target hole 31 on the surface 30a of the workpiece 30. This surface burr 33 is formed when the cutting edge 9b bites into the surface 30a of the workpiece 30 at the start of drilling the workpiece 30 with the drill 1, or when the impact of penetration causes the material of the workpiece 30 to curl up towards the surface 30a side of the workpiece 30.

[0078] The greatest technical significance of the countersink section 12 lies in "improving work efficiency" and "stabilizing construction quality" in "subsequent processes (insertion and fastening of roof bolts, etc.)" that follow the completion of drilling.

[0079] Generally, if a large burr 32 remains on the periphery of the opening of the target hole 31 on the back surface 30b of the workpiece 30, it becomes a physical obstacle when inserting fasteners such as roof bolts into the target hole 31, preventing smooth insertion into the target hole 31. In addition, the burr 32 can get caught between the bolt and the workpiece 30, causing the bolt to not seat properly, resulting in unstable tightening torque or fastening at an angle, which is a risk of "bolt fastening failure." Such fastening failures can cause insufficient fixing strength and looseness of the roofing material.

[0080] In the drill 1 of this embodiment, the countersink portion 12 reliably removes the burr 32 when the drill 1 is withdrawn from the target hole 31, allowing fasteners such as bolts to be smoothly inserted into the target hole 31 in subsequent processes. This reduces the burden on the worker and enables the fasteners to be fastened to the workpiece 30 in the correct position and with secure contact, thereby reliably suppressing the occurrence of construction defects.

[0081] As shown in Figure 8, the countersink portion 12 has a basic configuration in which the first stepped portion 5 (see Figure 5) described above is inverted (mirror-image arrangement) on the base end side of the target hole forming portion 4.

[0082] In other words, the countersink portion 12 is composed of multiple (for example, two or three) stepped portions 12a arranged in a stepped manner toward the base end of the body 2 so as to connect the outer circumferential surface of the target hole forming portion 4 and the outer circumferential surface of the small diameter column portion 11.

[0083] In this embodiment, the countersink portion 12 is more specifically composed of two stepped portions 12a, 12a. The stepped surface 12b of each stepped portion 12a is formed in a tapered shape with a gradually decreasing diameter toward the base end, and the intermediate surface 12c between adjacent stepped portions 12a, 12a is formed parallel to the axis P.

[0084] In the stepped portion 12a, the stepped surface 12b adjacent to the target hole forming portion 4 is the area where the back burr 32 is first contacted and rough-cut. The intermediate surface 12c is the area where the penetration depth of the leading edge portion 15 is restricted and chatter vibration is suppressed. The stepped surface 12b adjacent to the small diameter column portion 11 is the area where the remaining back burr 32 is finished off.

[0085] The greatest advantages of this configuration are "suppression of chatter vibration" and "prevention of excessive biting (locking)." When withdrawing the drill 1, with a simple single leading edge, the leading edge comes into full contact with the burr 32, causing a sudden increase in cutting resistance, which tends to cause chatter vibration or lock the drill 1 and prevent it from being withdrawn. In contrast, as in this embodiment, by interposing an intermediate surface 12c parallel to the axis P on the leading edge 15 to distribute the cutting resistance load, the operator can remove the burr 32 smoothly and reliably with less chatter vibration using a light withdrawal force.

[0086] As shown in Figure 2, the portion of the small diameter column 11 adjacent to the stopper portion 3 is formed in a tapered shape (for example, a chamfered shape with a taper angle of 50° to 90°) that gradually increases in diameter towards the base end, thereby forming a surface burr removal portion 13 in the adjacent portion that removes the surface burr 33 of the target hole 31.

[0087] The purpose of this surface burr removal section 13 is to ensure watertightness (prevent leaks) during roof construction. If this surface burr 33 remains on the workpiece 30, when the roof bolts are tightened in a later step, the washers and waterproof gaskets on the bolt heads will lift up from the surface 30a of the workpiece, creating a gap through which rainwater can enter.

[0088] In the drill 1 of this embodiment, when the operator feels a loss of torque and stops the drill, or just before the stopper part 3 strikes the workpiece 30, the surface burr removal part 13 lightly contacts the opening periphery of the target hole 31 on the surface 30a of the workpiece 30, removing the raised surface burr 33 by chamfering. As a result, the opening periphery of the target hole 31 becomes smooth, and the waterproof packing adheres completely to the surface 30a of the workpiece 30 without any gaps, thereby achieving extremely high water-stopping performance.

[0089] The helical groove 14 extends continuously in a spiral shape from the tip surface 9 of the body 2 toward the base end, passing sequentially through the straight section 8, the second stepped section 7, the tapered section 6, the first stepped section 5, the small diameter column section 11 (including the countersink section 12 and the surface burr removal section 13), and the stopper section 3. The base end opening of the helical groove 14 is formed on the base end surface of the stopper section 3 (i.e., the surface of the stopper section 3 on the shank 18 side).

[0090] This configuration is extremely important. If the helical groove 14 were to stop just before the stopper portion 3 (for example, at the small diameter column portion 11) without passing through it, the moment the stopper portion 3 contacts the workpiece 30, the discharge port of the helical groove 14 would be "covered" by the stopper portion 3, causing the chips, having nowhere to go, to be compressed and accumulate inside. In contrast, as in this embodiment, by having the helical groove 14 completely pass through the stopper portion 3, a chip discharge path (air venting passage) is always ensured, even when the stopper portion 3 is in contact with the workpiece 30. This structurally makes it impossible for chips to clog and the resulting sandwich phenomenon (scratching of the workpiece surface 30a) to occur.

[0091] The drill 1 of this embodiment has the following advantages.

[0092] In this embodiment, the drilling process using the drill 1 proceeds in stages as follows, with each part of the body 2 playing its own role.

[0093] 1. Initial penetration and guiding (tip surface 9 to straight section 8): First, the small-diameter tip surface 9 bites into the workpiece 30, drilling a pilot hole through it. Subsequently, the straight section 8 enters the hole, suppressing the runout of the drill 1 and establishing a "guide" that serves as the basis for machining.

[0094] 2. Signal to begin diameter expansion (second stage section 7): Immediately after passing the straight section 8, the second stage section 7 comes into contact with the edge of the hole 31, transmitting a signal (click sensation) to the operator that "diameter expansion has begun".

[0095] 3. Low thrust, continuous cutting (tapered section 6): Next, the tapered section 6, which is the main cutting area, enters the hole 31. Here, the hole 31 is smoothly enlarged with extremely low cutting resistance due to the "oblique cutting (shearing effect)" by the spiral leading edge section 15 and the gentle inclination angle (diameter expansion ratio α2). At the same time, the chips are continuously curled without being broken and are stably discharged to the outside.

[0096] 4. Signal of final arrival (first stage 5): Just before the target hole forming section 4 reaches the position of hole 31, the first stage 5 (notification stage) passes the edge of hole 31. At this point, the operator feels a clear change in cutting resistance (a clicking sensation) and receives the final signal that "the target hole 31 will soon be formed (preparation for stopping just short)."

[0097] 5. Finishing and Completion (Target Hole Forming Unit 4): Finally, the target hole forming unit 4 reaches the position of the hole 31, and a target hole 31 with a circular cross-section having a target diameter D1 is formed in the workpiece 30.

[0098] As shown in Figure 2, in the drill 1 of this embodiment, a stopper portion 3 is provided at a position spaced apart from the base end of the target hole forming portion 4 in the body 2, and a small diameter column portion 11 is provided between the target hole forming portion 4 and the stopper portion 3 in the body 2.

[0099] The presence of this small diameter column 11 is key to achieving "non-contact stopping (stopping just short of the target)" in this embodiment. That is, immediately after the target hole forming section 4 completely penetrates the workpiece 30, the part of the drill 1 that was in contact with the inner wall of the hole 31 in the workpiece 30 shifts from the target hole forming section 4 (contact) to the small diameter column 11 (non-contact). At this time, a physical phenomenon called "torque release" occurs, in which the cutting resistance (including frictional resistance) disappears instantaneously.

[0100] The sudden disappearance of this cutting resistance load serves as a strong tactile signal to the operator indicating that "drilling is complete." Therefore, even without visually inspecting the stopper part 3, the operator can reflexively release the tool switch (or withdraw the drill 1) the moment they sense this signal, and as a result, the drill 1 can be stopped just before the stopper part 3 hits (comes into) the surface 30a of the workpiece.

[0101] Therefore, immediately after the target hole 31 is formed in the workpiece 30 by the target hole forming section 4 of the body 2, that is, immediately after the target hole forming section 4 completes the formation of the target hole 31, the drill 1 transitions to a "no-load idling state" due to the small diameter column section 11.

[0102] The section in which this small diameter column 11 exists (i.e., the distance L1 between the target hole forming section 4 and the stopper section 3) functions as a "braking distance (brake margin)" that absorbs the amount of inertia the drill 1 would have to move forward between the time the operator senses the torque release (drilling completion signal) and the time the operator releases the tool's rotation switch to release the thrust. Therefore, the operator can decelerate and stop the drill 1 with ample margin before the stopper section 3 reaches the surface 30a of the workpiece 30, and as a result, contact between the stopper section 3 and the surface 30a of the workpiece 30 is reliably avoided.

[0103] Furthermore, the fact that the chip evacuation groove is a helical groove 14 means not only an improvement in chip evacuation efficiency, but also a "fundamental transformation of the cutting mechanism."

[0104] Conventional straight groove drills, due to their structure, make it difficult to create a rake angle and cut by crushing the workpiece 30. As a result, the operator had to apply excessive thrust (pressing load) by putting their body weight onto the drill 1. In this state, immediately after penetration, the drill 1 and the operator's body would "lean forward," and the momentum (inertia) made it easy for the stopper part 3 to collide with the surface 30a of the workpiece 30.

[0105] In contrast, the helical groove 14 of this embodiment provides a sharp "positive rake angle" to the cutting edge 9b, allowing for smooth cutting of the workpiece 30 as if shearing (slicing). As a result, the operator can perform drilling with only a light thrust, just enough to support the drill 1, and no excessive forward inertial force acts immediately after penetration. Consequently, the operator can easily react immediately after penetration to stop and hold the drill 1, and the stopper portion 3 is more reliably prevented from hitting the surface 30a of the workpiece 30. This "improved controllability due to low inertia" reliably suppresses damage to the surface 30a of the workpiece 30 (e.g., damage to the cosmetic layer).

[0106] To ensure the above-mentioned effects are obtained, it is preferable that the distance L1 between the target hole forming portion 4 and the stopper portion 3 is greater than the thickness t of the workpiece 30 (i.e., L1 > t), more preferably that L1 is 7 times t or more (i.e., L1 ≥ 7 × t), and particularly preferably that L1 is 8 times t or more (i.e., L1 ≥ 8 × t). The preferred upper limit of L1 is 15 times t (i.e., L1 ≤ 15 × t).

[0107] Furthermore, it is preferable that L1 is 1.5 times or more the diameter D2 of the outer edge 9k of the tip surface 9 of the body 2 (i.e., L1 ≥ 1.5 × D2). This numerical specification is important to ensure the absolute length of L1 (braking distance). Even if D2 is 3 mm, with this magnification (1.5 times), L1 will be 4.5 mm or more. This ensures that a sufficient braking distance remains immediately after penetration, not only when drilling a target hole 31 in a single workpiece, but also when drilling target holes 31 in both workpieces stacked on top of each other, thus reliably obtaining the aforementioned "impact avoidance effect". The preferred upper limit of L1 is 5 times D2 (i.e., L1 ≤ 5 × D2).

[0108] The length L2 of the target hole forming section 4 is not limited, but it is preferable that L2 be at least three times the thickness t of the workpiece 30 (i.e., L2 ≥ 3 × t). This ensures high accuracy in the diameter and roundness of the target hole 31. The preferred upper limit of L2 is 50 times t (i.e., L2 ≤ 50 × t). Furthermore, in order to reliably obtain the above effects, it is preferable that L2 be at least 1.5 times D2 (i.e., L2 ≥ 1.5 × D2). The preferred upper limit of L2 is 5 times D2 (i.e., L2 ≤ 5 × D2).

[0109] Furthermore, a tapered portion 6 is provided between the tip surface 9 of body 2 and the target hole forming portion 4, and the tapered portion 6 and the target hole forming portion 4 are adjacent to each other via the first stepped portion 5.

[0110] An important configuration here is that the diameter expansion ratio α1 of the first stepped section 5 is set to be larger than the diameter expansion ratio α2 of the tapered section 6 (α1 > α2). This setting is essential for creating an "intentional step (contrast)" in the cutting resistance. In other words, by setting α2 of the tapered section 6, which performs the main cutting, to be as small as possible to maintain "low thrust and stable cutting," while setting only α1 of the first stepped section 5 to be relatively large, a clear change in cutting resistance (a click sensation) is generated that signals to the operator that they are "just before reaching the target hole."

[0111] Therefore, during drilling, when the tapered portion 6 of the body 2 is positioned in the hole 31 formed in the workpiece 30, the cutting resistance acting on the drill 1 and the cutting sound generated from the hole 31 in the workpiece 30 are approximately constant or continuously changing along the length of the tapered portion 6. When the drill 1 moves from the tapered portion 6 to the first stepped portion 5 relative to the position of the hole 31 in the workpiece 30, the cutting resistance increases sharply and the cutting sound changes (increases) sharply. Furthermore, when the drill 1 moves from the first stepped portion 5 to the target hole forming portion 4 relative to the position of the hole 31, the cutting resistance decreases sharply and the cutting sound changes (decreases) sharply. Furthermore, when the drill 1 moves from the target hole forming portion 4 to the small diameter column portion 11 relative to the position of the hole 31, the cutting resistance decreases sharply to no resistance and the cutting sound changes (decreases) sharply to silence.

[0112] Therefore, an operator performing drilling using a handheld drilling tool (such as an electric screwdriver) to which drill 1 is attached can clearly grasp the information transmitted in the following sequence (order) at the final stage of drilling through touch (cutting resistance) and hearing (cutting sound).

[0113] 1) Tapered section 6 (in diameter expansion): Low and stable cutting resistance and cutting noise. This indicates that "machining is proceeding smoothly."

[0114] 2) First stage 5 (warning signal): A "resistance pulse (click sensation)" just before reaching the target hole. The operator receives this as a warning signal that "penetration is imminent (prepare to stop)."

[0115] 3) Target hole forming section 4 (finishing): Stable cutting in an instant.

[0116] 4) Small diameter column section 11 (completion signal): Complete elimination of cutting resistance (torque release). The operator receives this as an execution signal for "completion and immediate stop".

[0117] Thus, the drill 1 is configured to send a gradual "countdown signal" to the operator, rather than an abrupt end. As a result, the operator can mentally prepare and stop the rotation of the drill 1 with ample time, and as a result, high-precision "stopping just short" can be achieved without the stopper part 3 hitting (contacting) the surface 30a of the workpiece 30.

[0118] Therefore, when the drill 1 moves from the tapered portion 6 to the first stepped portion 5 relative to the position of the hole 31 in the workpiece 30, the operator can know this by touch and hearing. In other words, the first stepped portion 5 functions as an "information step" that notifies the operator that the target hole forming portion 4 will soon reach the position of the hole 31 in the workpiece 30 and the target hole 31 will be formed. As a result, contact of the stopper portion 3 with the surface 30a of the workpiece 30 can be reliably suppressed, and damage to the surface 30a of the workpiece 30 can be reliably suppressed.

[0119] In this embodiment, the first stepped portion 5 is described as being composed of two stepped portions 5a, 5a, but the present invention is not limited thereto. Depending on the material of the workpiece 30 and the diameter size of the target hole 31, the α2 of the tapered portion 6 (main cutting area) may be set to be even gentler, and in that case, the increase in the diameter of the hole 31 that the first stepped portion 5 must bear may be larger. In such cases, in order to distribute the sudden increase in cutting resistance, the first stepped portion 5 may be composed of even more stepped portions (for example, three or four steps).

[0120] Specifically, the first stepped section 5 is shaped by repeatedly alternating between a "stepped surface 5b" and an "intermediate surface 5c," thereby transmitting an "intermittent pulse-like signal (multiple click sensations)" to the operator when passing over the first stepped section 5. This configuration makes it possible to maintain cutting with low thrust by reducing the radius difference between the entrance (tip end position) and exit (base end position) of the tapered section 6, which is the main cutting area, while reliably notifying the operator of the arrival of the target hole forming section 4 with a more emphasized signal pattern.

[0121] To ensure the above-mentioned effects are obtained, it is preferable that L3 is greater than the thickness t of the workpiece 30 (i.e., L3 > t), and particularly preferable that L3 is 1.2 times t or more (i.e., L3 ≥ 1.2 × t). The preferred upper limit for L3 is 5 times t (i.e., L3 ≤ 5 × t).

[0122] Furthermore, in order to reliably obtain the above-mentioned effects, it is preferable that the length L4 of the tapered portion 6 is greater than the length L3 of the first stepped portion 5 (i.e., L4 > L3), and in particular, L4 is preferably 8 to 40 times L3. Moreover, it is preferable that L4 is 20 times or more the thickness t of the workpiece 30 (i.e., L4 ≥ 20 × t). The preferred upper limit of L4 is 60 times t (i.e., L4 ≤ 60 × t).

[0123] Furthermore, in order to reliably obtain the above-mentioned effects, it is preferable that L4 be at least twice D2 (i.e., L4 ≥ 2 × D2). The preferred upper limit for L4 is 10 times D2 (i.e., L4 ≤ 10 × D2).

[0124] Furthermore, in order to reliably obtain the above-mentioned effects, α2 is preferably 0.035 to 0.40, and particularly preferably 0.05 to 0.15. Also, in order to reliably obtain the above-mentioned effects, α1 is preferably 2 to 10 times α2.

[0125] Furthermore, in this embodiment, the first stepped section 5 is composed of multiple stepped sections 5a, as described above. As a result, when the first stepped section 5 passes over the position of the hole 31, the cutting resistance does not increase monotonically, but changes with a unique modulation (rhythm) of "increase (stepped surface 5b) → stabilize (intermediate surface 5c)". This discontinuous change in cutting resistance is clearly transmitted to the operator's hand as a "pulsed signal (click sensation)". Therefore, the operator can distinguish it from a simple accumulation of cutting resistance load and reliably and intuitively recognize that "the target hole 31 will soon be formed", and the first stepped section 5 functions as a "high-precision notification step".

[0126] Furthermore, as mentioned above, the fact that the diameter increase ratio α1 of the first stepped portion 5 is set to be greater than the diameter increase ratio α2 of the tapered portion 6 has important technical significance in terms of "functional division of roles."

[0127] Firstly, the first stepped portion 5 (α1), which has a large diameter enlargement ratio, plays a role in efficiently expanding the diameter of the hole 31 toward the target hole forming portion 4. As a result, it becomes possible to set α2 of the tapered portion 6, which is the main cutting area, to be smaller (gentler). This minimizes the thrust burden on the operator in the tapered portion 6, where cutting is performed for the longest period, and ensures that chips are discharged in a continuous shape, thereby reliably suppressing the risk of chip residue on the surface (decorative surface) 30a of the workpiece 30 and the resulting galvanic corrosion.

[0128] Secondly, by setting a large difference between α2 and α1, the "signal-to-noise ratio (S / N ratio)" can be improved. In other words, by clearly defining the "difference (contrast)" when transitioning from the tapered section 6 (α2), where the cutting resistance is small, to the first stepped section 5 (α1), where the cutting resistance increases rapidly, the operator can more sensitively perceive the signal from the drill 1 (the signal just before reaching the target hole).

[0129] In other words, the setting α1 > α2 is not merely aimed at shortening the length, but is an optimal geometric distribution that achieves both "low thrust and high-quality machining" and "reliable sensing," while keeping the overall length of drill 1 within a practical range.

[0130] Furthermore, a straight section 8 is provided adjacent to the outer peripheral edge 9k of the front surface 9 of the body 2, and the straight section 8 and the tapered section 6 are adjacent to each other via a second stepped section 7.

[0131] As mentioned above, the diameter expansion ratio α3 of the second stepped section 7 is set to be greater than the diameter expansion ratio α2 of the tapered section 6 (α3 > α2). This relative size is a setting to communicate the transition of the machining phase to the operator. Specifically, the drill 1 first forms a stable pilot hole 31 in the workpiece 30 with the straight section 8 (diameter expansion ratio of zero). Immediately afterward, the second stepped section 7 (α3), which has a large diameter expansion ratio, contacts the edge of this hole 31, transmitting a "guide complete, diameter expansion start" signal (change in cutting resistance) to the operator, and then smoothly transitions to low-thrust machining with the tapered section 6 (α2), which has a small diameter expansion ratio.

[0132] Therefore, during drilling, the operator will perceive the following changes in "clear cutting resistance (tactile information)" and "cutting sound (auditory information)."

[0133] 1) First, the front surface 9 of the body 2 bites into the workpiece 30, generating initial cutting resistance and cutting noise (start of machining).

[0134] 2) Next, as the drill 1 moves and the straight section 8 enters the hole 31, the cutting resistance load decreases to almost no load, and a "silent state" is reached where the cutting noise is almost eliminated.

[0135] 3) Next, the moment the second stepped portion 7 (start signal) contacts the edge of the hole 31, the cutting resistance load temporarily increases sharply, and a "tap" contact sound is generated as a cutting sound, resulting in an "impact (pulse) state".

[0136] 4) Finally, when moving to the tapered section 6 (main cutting area), the cutting resistance load decreases again, and the machine transitions to a "stable diameter expansion state" accompanied by stable low cutting resistance and continuous cutting noise.

[0137] This series of dramatic changes—load (on) → no load (off) → impact (pulse) → stabilization (smooth)—allows the operator to be confident, without relying on visual inspection, that the tip of drill 1 is correctly guided and that the process has smoothly transitioned to the diameter expansion stage.

[0138] Therefore, the operator can intuitively and in real time determine which part of the drill body 2—the tip surface 9, the straight section 8, the second stepped section 7, and the tapered section 6—is currently acting on the hole 31 in the workpiece 30, through their sense of touch (changes in cutting resistance) and hearing (changes in cutting sound).

[0139] This "non-visual information transmission" is extremely important in the unique environment of roof construction. In many cases, the cutting point becomes a blind spot due to handheld tools or the worker's posture, making it difficult for the worker to visually confirm it. However, with the drill 1 of this embodiment, the worker can clearly visualize the situation inside the unseen hole as a "tactile sensation." Therefore, the worker can proceed with the work with confidence, accurately recognizing the progress of the drilling process (currently in the initial stage, expanding the diameter, etc.) without feeling anxious.

[0140] Therefore, the second stepped section 7 functions as a "start signal" to inform the operator that guiding (positioning) by the straight section 8 is complete and that the main diameter expansion process by the tapered section 6 will now begin.

[0141] In this specification, the term "notification step" mainly refers to the first step-shaped section 5 (completion notification) located immediately before the target hole forming section 4. However, in a broader sense, this second step-shaped section 7 is also a type of notification step that communicates the transition of the processing phase to the operator.

[0142] In this embodiment, the second stepped portion 7 is composed of multiple steps (more specifically, two steps) of stepped portion 7a, as shown in Figure 7. With this configuration, when the second stepped portion 7 passes over the hole 31, the operator will perceive a series of multiple (more specifically, two) fluctuations in cutting resistance load (pulse signals) in the order of "increased cutting resistance (stepped surface 7b) → stabilization (intermediate surface 7c)".

[0143] While a single load fluctuation might be mistaken for "noise" such as variations in the hardness of the workpiece 30, multiple consecutive signals intentionally generated in this way are extremely easy for the operator to distinguish. Therefore, the operator can be reliably informed that "guiding is complete and the full-scale diameter expansion by the tapered section 6 will now begin," and the second-stage section 7 functions as a "highly reliable signal to start machining (start signal)."

[0144] To ensure the above-mentioned effects are obtained, it is preferable that L5 is greater than the thickness t of the workpiece 30 (i.e., L5 > t), and particularly preferable that L5 is 1.2 times t or more (i.e., L5 ≥ 1.2 × t). The preferred upper limit for L5 is 5 times t (i.e., L5 ≤ 5 × t).

[0145] Furthermore, in order to reliably obtain the above-mentioned effects, it is preferable that the length L5 of the second stepped portion 7 is smaller than the length L4 of the tapered portion 6. In other words, it is preferable that L4 is larger than L5, and in particular, it is preferable that L4 be 8 to 40 times L5. This numerical range defines the functional division of roles between the "signal generation region (L5)" that sends the signal to start machining and the "main cutting region (L4)" that performs the actual diameter expansion machining, similar to the relationship between the first stepped portion 5 (L3) and the tapered portion 6 (L4) described above. Its significance is as follows.

[0146] 1. Significance of the lower limit (8 times): When the second stepped section 7 is composed of multiple stepped sections 7a (e.g., two, three, etc.), L5 needs to be of a certain length (e.g., 1.5 mm to 3 mm). In this case, if L4 is 8 times or more the length of L5, the "low thrust" effect of the tapered section 6 can be reliably obtained.

[0147] 2. Significance of the upper limit (40 times): By keeping L4 at 40 times or less of L5, it is possible to reliably maintain an appropriate ratio balance between L4 and L5, whether the second stepped section 7 is kept compact and only the tapered section 6 is lengthened, or whether the number of steps in the second stepped section 7 is increased and L5 becomes longer.

[0148] Furthermore, in order to reliably obtain the effects described above, it is preferable that α3 be 2 to 15 times greater than α2. The significance of this is as follows:

[0149] 1. Significance of the lower limit (2 times): When α3 is more than twice that of α2, the change in cutting resistance becomes clearly and reliably apparent. This allows the operator to reliably sense the timing of "guide completion and diameter expansion start" through touch.

[0150] 2. Significance of the upper limit (15 times): By keeping α3 at 15 times or less of α2, the resistance of the second stepped portion 7 to biting into the workpiece 30 can be reliably reduced. This reliably promotes a smooth start to diameter expansion.

[0151] Furthermore, in order to ensure that the above-mentioned effects are reliably obtained, it is preferable that the length L6 of the straight section 8 is greater than the thickness t of the workpiece 30 (i.e., L6 > t), and in particular, it is preferable that L6 be 1.1 times t or more (i.e., L6 ≥ 1.1 × t). This ensures that even when the thickness t of the workpiece 30 is a maximum of 1.2 mm, cutting by the second stepped section 7 and the tapered section 6 begins only after the straight section 8 has reliably penetrated the workpiece 30 and established a guide. The preferred upper limit of L6 is 10 times t (i.e., L6 ≤ 10 × t). The significance of this is as follows.

[0152] 1. Significance of the lower limit (1.1 times): When drilling holes in two stacked workpieces 30, if L6 is 1.1 times or more of t, when the straight section 8 penetrates the first workpiece 30 and enters the second workpiece 30, the second stepped section 7 reliably begins to act on the first workpiece 30, giving the operator a complex sensation. Through this complex sensation, the operator can reliably recognize that the drilling process has smoothly progressed to the second workpiece.

[0153] 2. Significance of the upper limit (10 times): By keeping L6 at 10 times or less of t, runout (wobble) when the drill tip bites into the workpiece 30 can be reliably suppressed.

[0154] Furthermore, it is preferable that L6 is 0.4 times or more D2 (i.e., L6 ≥ 0.4 × D2). This ensures that L6 is reliably larger than the thickness t of the workpiece 30, and the operator can reliably perceive by touch and hearing that the tip surface 9 of the body 2 has penetrated the workpiece 30 and the straight portion 8 has moved to the position of the hole 31 in the workpiece 30. In addition, by having L6 0.4 times or more D2, a clearance space for the grinding wheel can be reliably secured when grinding the tip surface 9 of the body 2 (e.g., thinning, cutting edge processing, tip angle processing), thereby making the grinding process easier. The preferred upper limit of L6 is 1.2 times D2 (i.e., L6 ≤ 1.2 × D2).

[0155] Furthermore, the twist angle θ1 of the helical groove 14 is not limited, but is preferably 22° to 26°. The tip angle θ2 of the body 2 is not limited, but as mentioned above, is preferably less than 118°, and is particularly preferably 100° to 110°.

[0156] Because θ1 and θ2 are within the above range, the tip 9a of the body 2 (cutting edge 9b, thinning edge 9h) reliably bites into the surface 30a of the workpiece 30, allowing drilling to begin with a small thrust to the drill 1. Furthermore, even without center punching the surface 30a of the workpiece 30 at the start of drilling, slippage of the tip 9a of the body 2 on the surface 30a of the workpiece 30 can be reliably suppressed.

[0157] Furthermore, in the drill 1 of this embodiment, a countersink portion 12 is formed on the part of the body 2 adjacent to the target hole forming portion 4 on the small diameter column portion 11. With this configuration, when the drill 1 is withdrawn from the target hole 31 of the workpiece 30 after drilling is complete, the countersink portion 12 contacts the opening edge of the target hole 31 on the back surface 30b of the workpiece 30, allowing the burr 32 to be sheared off (chamfered). As a result, the opening edge of the target hole 31 is finished smoothly, so when fastening roof bolts etc. in a subsequent process, washers and waterproof packings will adhere tightly to the back surface 30b of the workpiece 30 without any gaps, making it possible to reliably ensure "high watertightness," which is extremely important in roof construction.

[0158] Here, the countersink portion 12 may be composed of multiple stepped portions 12a (more specifically, two steps) as in this embodiment, or it may be composed of only a single tapered surface (not shown) that gradually decreases in diameter toward the base end. However, it is preferable that the countersink portion 12 is configured as in this embodiment. The reason is as follows.

[0159] If the countersink portion 12 consists only of a single tapered surface, when the drill 1 is withdrawn, the entire tapered surface will come into contact with the burr 32 on the back of the target hole 31 and the periphery of the opening at once. In this case, the cutting resistance will jump due to the sudden increase in the contact area, causing severe chattering vibrations and resulting in a rough surface finish. Alternatively, the leading edge portion 15 of the countersink portion 12 (single tapered surface) may bite excessively into the periphery of the opening of the target hole 31, causing the drill 1 to lock up and become unable to be removed from the target hole 31.

[0160] In contrast, by making the countersink portion 12 a multi-stage structure in which tapered stepped surfaces 12b and intermediate surfaces 12c parallel to the axis P are alternately arranged, as in this embodiment, the following advantages can be obtained.

[0161] Firstly, since the intermediate surface 12c functions as a "cutting depth regulating guide," excessive biting of the leading edge portion 15 is physically prevented, and the locking phenomenon of the drill 1 described above can be reliably suppressed.

[0162] Secondly, since the cutting resistance load during deburring is distributed across multiple stepped surfaces 12b, the cutting resistance applied at one time is reduced, ensuring an extremely smooth withdrawal operation with minimal chatter vibration and a smooth chamfered finish.

[0163] Furthermore, if the countersink section 12 has the latter configuration (a single tapered surface), the following problems may occur in actual operation.

[0164] In operations using handheld tools, it is unavoidable that the axis P of the body 2 will be slightly tilted relative to the axis of the hole 31 when the drill 1 is withdrawn from the target hole 31. In this tilted state, when a single tapered surface contacts the opening periphery of the target hole 31 on the back surface 30b of the workpiece 30, it becomes a geometrically "approximately elliptical line contact," and the contact length (the area subjected to cutting resistance) increases instantaneously.

[0165] This widespread contact creates a so-called "wedge effect," resulting in excessive cutting resistance and a tendency for "locking" to occur as the leading edge 15 of the tapered surface bites strongly into the edge of the hole 31. If this occurs, it becomes difficult to withdraw the drill 1 and can cause the deburring surface to become torn and rough.

[0166] In contrast, when the countersink section 12 is configured as in this embodiment (multi-stage structure), even if the axis P of the body 2 is pulled out while it is tilted, the intermediate surface 12c between the stepped sections functions as a "preventive guide for jamming" against the inner wall of the hole 31.

[0167] In other words, even if the leading edge portion 15 attempts to bite deeply due to the inclination of the axis P of the body 2, the intermediate surface 12c contacts the inner wall of the hole 31, physically preventing further excessive biting (wedge effect). In addition, since the contact between the opening periphery of the target hole 31 and the countersink portion 12 is divided into multiple sections, the cutting resistance required to remove the burr 32 is dispersed and reduced.

[0168] Therefore, it is preferable that the countersink portion 12 be configured as in this embodiment. With this configuration, even when the axis P of the body 2 is pulled out at an angle, locking (jamming) and chatter vibration of the drill 1 are reliably suppressed, and uniform and beautiful burr removal work can be reliably performed with light pulling force.

[0169] Furthermore, in the drill 1 of this embodiment, a surface burr removal section 13 is formed adjacent to the stopper section 3 on the small diameter column section 11. With this configuration, after the formation of the target hole 31 is complete, the surface burr removal section 13 can be lightly brought into contact with the surface burr 33 of the target hole 31 while the small diameter column section 11 is inside the hole 31, thereby removing it in a chamfered manner.

[0170] This smooths the periphery of the opening of the target hole 31 on the surface 30a of the workpiece 30. As a result, when roof bolts or the like are fastened in a later process, the waterproof packing and washers will adhere securely to the surface 30a of the workpiece 30, ensuring "watertightness (prevention of leaks)," which is considered important in the quality of roof construction.

[0171] Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and can be modified in various ways without departing from the spirit of the invention.

[0172] For example, in the drill of the present invention, it is preferable that the tapered portion 6 and the target hole forming portion 4 in the body 2 are adjacent to each other via the first stepped portion 5, as in the above embodiment. However, the tapered portion 6 and the target hole forming portion 4 may also be adjacent to each other without the first stepped portion 5.

[0173] Furthermore, in the drill of the present invention, it is preferable that the straight portion 8 and the tapered portion 6 in the body 2 are adjacent to each other via the second stepped portion 7, as in the above embodiment. However, the straight portion 8 and the tapered portion 6 may also be adjacent to each other without the second stepped portion 7.

[0174] Furthermore, the following modifications and applications are also included within the technical scope of the present invention.

[0175] (1) Changes to the shank shape and connection structure In the above embodiment, a hexagonal shank (6.35 mm across flats) compatible with electric screwdrivers and the like was exemplified, but the present invention is not limited thereto. For example, the configuration of the shank 18 can be appropriately changed according to the specifications of the drilling tool used, such as an SDS shank (SDS-plus, etc.) compatible with rotary hammer drills and hammer drills, a round shank compatible with electric drills and drill presses, or a square shank. Furthermore, the connection structure between the body 2 and the shank 18 is not limited to integral molding, but any joining means such as press-fitting, welding, or screw-in may be used.

[0176] (2) Diversification of materials and surface treatments In this invention, the material of the drill 1 is not limited to cemented carbide or high-speed tool steel (HSS, HSS-Co), but may also be powder high-speed steel or the like. Furthermore, various coatings (e.g., TiN, TiAlN, TiCN, DLC coating, etc.) may be applied to the surface of the drill 1 to improve wear resistance and anti-welding properties. In particular, by applying a treatment to the surface of the helical groove 14 to reduce the coefficient of friction, it is possible to further improve the "low thrust cutting" and "chip evacuation" characteristics of the drill of this invention.

[0177] (3) Independent setting of the number of tiers In this invention, the number of stages in the first stage section 5 (end notification) and the second stage section 7 (start signal) is not limited to two, but can be arbitrarily set according to the drill diameter and overall length. Furthermore, the number of stages in the first stage section 5 and the second stage section 7 do not necessarily have to be the same. For example, even if the number of stages in the first stage section 5 is three and the second stage section is two, an "asymmetrical configuration" combining different numbers of stages according to the importance of each signal and space constraints will be achieved without any impairment of the effects of this invention (situation recognition by signal).

[0178] (4) Expansion of scope of application In the above embodiment, the main purpose is to drill holes in thin metal sheets (single sheets and multiple sheets stacked) such as corrugated metal roofing materials, but the present invention is not limited to this. For example, it can be suitably applied to drilling holes in any workpiece material where impact suppression during penetration and burr removal are required, such as composite panels made by laminating metal plates and insulation materials, resin plates, FRP (fiber-reinforced plastic), or thin-walled pipe materials (drilling holes in curved surfaces). [Industrial applicability]

[0179] The present invention can be used in drills used to create through holes with a circular cross-section in plate-shaped workpieces. [Explanation of symbols]

[0180] 1: Drill 2: Body 3: Stopper section 4: Target hole forming section 5: First stepped section 6: Tapered section 7: Second stepped section 8: Straight section 9: Front end of the body 11: Small diameter column section 12: Countersink section 14: Spiral groove 30: Workpiece material 31: Hole (target hole) 32: Back burr P: Center of the body (drill)

Claims

1. A drill used to drill a target hole with a circular cross-section that penetrates through the surface in the thickness direction of a plate-shaped workpiece, The device comprises a body that rotates around an axis, a target hole forming portion provided approximately in the middle of the length of the body and having a diameter corresponding to the diameter of the target hole, a stopper portion integrally formed on the body at a position spaced apart from the target hole forming portion toward the base end and having a larger diameter than the target hole forming portion, and a spiral groove for chip discharge extending spirally and continuously from the front end of the body toward the base end, passing through the stopper portion, on the outer circumferential surface of the body. The portion of the body closer to the tip of the target hole forming portion is formed in a tapered shape towards the tip. Between the target hole forming portion and the stopper portion of the body, a smaller diameter column portion is provided, having a smaller diameter than the target hole forming portion. A cutting edge is formed on the ridge between the front surface of the body and the inner surface located on the rear side in the rotational direction of the body in the chip discharge spiral groove, and a lateral cutting edge is formed on the ridge between the outer surface of the body excluding the stopper portion and the inner surface of the chip discharge spiral groove. A drill in which the distance between the target hole forming portion and the stopper portion is set to be 1.5 times or more the diameter of the outer edge of the tip surface of the body, such that a braking distance can be secured from the completion of the formation of the target hole until the stopper portion contacts the surface of the workpiece.

2. Between the front surface of the body and the target hole forming portion, a tapered portion is provided that is continuously increasing in diameter toward the base end. The tapered portion and the target hole forming portion are adjacent to each other via a first stepped portion. The drill according to claim 1, wherein the diameter increase ratio of the first stepped portion is set to be greater than the diameter increase ratio of the tapered portion in the base end direction of the body.

3. A straight portion is provided adjacent to the outer peripheral edge of the front surface of the body, extending parallel to the axis and having a diameter smaller than the diameter of the target hole forming portion. The straight portion and the tapered portion are adjacent to each other via a second stepped portion. The drill according to claim 2, wherein the diameter increase ratio of the second stepped portion is set to be greater than the diameter increase ratio of the tapered portion in the base end direction of the body.

4. Between the front surface of the body and the target hole forming portion, a tapered portion is provided that is continuously increasing in diameter toward the base end. A straight portion is provided adjacent to the outer peripheral edge of the front surface of the body, extending parallel to the axis and having a diameter smaller than the diameter of the target hole forming portion. The straight portion and the tapered portion are adjacent to each other via a second stepped portion. The drill according to claim 1, wherein the diameter increase ratio of the second stepped portion is set to be greater than the diameter increase ratio of the tapered portion in the base end direction of the body.

5. The drill according to any one of claims 1 to 4, wherein the diameter of the outer edge of the tip surface of the body is 3 mm to 7 mm.

6. The drill according to any one of claims 1 to 4, wherein a countersink portion for removing burrs from the back of the target hole is formed adjacent to the target hole forming portion in the small diameter column portion.

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