JP2006346832A - Drill and drilling method of work by using drill - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily drill a work at low cost in drilling the work even when a surface of the work such as a forged part is a roughened surface. <P>SOLUTION: This drill 1 is furnished with a drill body 4 and a shank 6 arranged on a shaft center 5 of this drill body 4 and integrally formed with a base part of this drill body 4. A diameter D2 of the shank 6 is made larger than a diameter D1 of the drill body 4. The other helical flute 17 continued to a helical flute 9 of the drill body 4 is formed on the shank 6, and a bottom part of the other helical flute 17 is made almost in the same shape and in the same size as the helical flute 9. An outer edge 18 except for the other helical flute 17 on each part cross section in the axial direction of the shank 6 is positioned on a virtual circle with the shaft center 5 as its center. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a drill for processing a prepared hole prior to drilling a deep hole or the like, and a method for drilling a workpiece using the drill.

  When drilling a workpiece with a drill, generally, a machine tool such as a machining center is used to first process a prepared hole at a desired position on the surface of the workpiece with a short drill with little deflection. Next, the tip of a long drill is inserted into the prepared hole, and another hole continuous with the prepared hole is processed by the drill, thereby performing a desired hole processing.

  By the way, when the workpiece is a forged product or the like and the surface thereof is a rough surface having a large number of fine irregularities, the drill is rotated to try to process the pilot hole, and the drill is formed on the rough surface. When the tip of the drill is pressed, the tip of the drill tends to slide toward the concave portion of the rough surface. At this time, the drill receives a reaction force in the radial direction from the rough surface and is bent. Tend to be given. For this reason, it is not easy to accurately process the pilot hole at a desired position on the rough surface, and the drill may be easily broken due to bending in the rotating state of the drill.

  Therefore, when the surface of the workpiece is a rough surface, conventionally, as a first step, first, a shallow hole having a flat bottom surface is processed at a desired position of the rough surface by an end mill. This hole is accurately formed at the desired position in terms of the function of the end mill. Next, as a second step, a pilot hole is processed on the flat bottom surface of the hole with a short drill as described above. And as a 3rd process, another hole is processed with a long drill so that it may continue to the above-mentioned pilot hole, and, thereby, the target hole processing is made.

  However, the above-described hole drilling operation requires the first to third steps, and the number of steps is large. Therefore, the hole drilling operation is complicated.

  Then, when trying to process the above-mentioned prepared hole, even if the surface of the workpiece is rough, in order to prevent the drill from bending, it is necessary to use a stepped drill shown in Patent Document 1 below. It is conceivable (FIG. 1 (a) of the above publication and reference numeral 1 in FIG. 2).

  The stepped drill includes a small-diameter drill body, a large-diameter drill body that is disposed on the shaft center of the small-diameter drill body and is integrally formed on the base of the small-diameter drill body, and is disposed on the shaft center. A shank formed integrally with the base of the large-diameter drill body.

  And when processing the said pilot hole, although the said small diameter drill main body is used, this small diameter drill main body is reinforced with the large diameter drill main body, and sufficient rigidity is ensured. For this reason, even if the surface of the workpiece is a rough surface, when the tip of the small-diameter drill body is pressed against the rough surface, the small-diameter drill body resists the reaction force from the rough surface and is prevented from bending. The Therefore, this small-diameter drill body can accurately process the prepared hole at a desired position on the surface of the workpiece. As a result, it is considered that the first step by the above-described end mill is not necessary, and the hole processing can be made easier.

JP 2004-337997 A

  By the way, in the stepped drill, not only a small diameter drill body but also a large diameter drill body and a transition portion from the small diameter drill body to the large diameter drill body have cutting ability. However, the pilot hole can be processed only by the small-diameter drill body having cutting ability. For this reason, the stepped drill has an excessive capability as a drill for preparing a pilot hole, and its formation is complicated and expensive. As a result, there is a problem that the drilling using the step drill is complicated and expensive.

  The present invention has been made by paying attention to the above-described circumstances, and the object of the present invention is to form a hole when drilling a workpiece such as a forged product even if the surface of the workpiece is rough. It is to make processing easy and inexpensive.

The invention of claim 1 includes a drill body 4 and a shank 6 disposed on an axis 5 of the drill body 4 and integrally formed with a base portion of the drill body 4. In the drill in which the diameter D2 of the shank 6 is larger than D1,
Another twisted groove 17 continuous to the twisted groove 9 of the drill body 4 is formed in the shank 6, and the bottom of the other twisted groove 17 is substantially the same shape and size as the twisted groove 9,
The outer edge 18 excluding the other torsion grooves 17 in the cross section (FIG. 3) in the axial direction of the shank 6 is positioned on a virtual circle centered on the axis 5.

According to a second aspect of the present invention, in addition to the first aspect of the invention, the transition portion 20 from the drill body 4 to the shank 6 is formed so that its diameter gradually increases from the drill body 4 side toward the shank 6 side. ,
The outer edge 21 excluding the torsion grooves 9 and 17 in each cross section (two-dot chain line in FIG. 3) in the axial direction of the transition portion 20 is positioned on a virtual circle centered on the axis 5. .

The invention of claim 3 is a method of drilling a workpiece 2 using the drill 1 of claim 1,
Processing of the pilot hole 3 is started on the workpiece 2 by the drill body 4, and the processing of the pilot hole 3 is finished when the transition portion 20 contacts the workpiece 2 or before the contact. ,
Next, another drill 36 is inserted into the pilot hole 3, another hole 37 continuing to the pilot hole 3 is processed into the workpiece 2, and another drill 39 is inserted into the other hole 37. Thus, another hole 40 continuing to the other hole 37 is processed into the workpiece 2.

  According to a fourth aspect of the invention, in addition to the third aspect of the invention, the inner diameters of the pilot hole 3, the other hole 37, and the other hole 40 are made substantially the same.

  In this section, the reference numerals appended to the above terms are not to be construed as limiting the technical scope of the present invention to the section “Example” described later or the contents of the drawings.

  The effects of the present invention are as follows.

The invention of claim 1 comprises a drill body and a shank disposed on the axis of the drill body and integrally formed with the base of the drill body, the diameter of the shank being larger than the diameter of the drill body. In a drill with a larger
Forming another twisted groove continuous with the twisted groove of the drill body in the shank, and making the bottom of the other twisted groove substantially the same shape and size as the twisted groove;
The outer edge excluding the other torsion grooves in the cross section of each part in the axial direction of the shank is positioned on a virtual circle centered on the axis.

  Here, as described above, the drill main body and the shank are formed integrally with each other, and the drill main body is reinforced by the shank having a larger diameter than that to ensure sufficient rigidity.

  For this reason, at the time of drilling, even if the drill body of the drill pressed against the surface of the workpiece receives a reaction force directed in the radial direction from the surface, the drill body resists the reaction force and bends. It is prevented. Therefore, the drill body can accurately process the prepared hole at the desired position on the surface of the workpiece. As a result, the first step by the end mill shown in the conventional technique is not required at the time of drilling. Can be made easier.

  As described above, another torsion groove continuous with the torsion groove of the drill body is formed in the shank, and the bottom of the other torsion groove has substantially the same shape and size as the torsion groove.

  For this reason, firstly, the cutting waste of the workpiece at the time of drilling the prepared hole by the drill body passes through the torsion groove and the other torsion grooves in order without being disturbed by the shank, and moves outwardly from the surface of the workpiece. Can be discharged smoothly. Therefore, if the length of the drill body is shortened and this length is approximated to the target depth of the pilot hole, the shank approaches the surface of the workpiece immediately before completion of the processing of the pilot hole. Without being disturbed by the shank, the cutting waste is discharged smoothly, and the drilling of the prepared hole by the drill body can be performed smoothly. And as mentioned above, if the length of a drill main body is shortened, the rigidity of this drill main body can be improved more and the bending of the drill main body at the time of processing of a pilot hole can be prevented more. As a result, it is possible to process the prepared hole at a desired position on the surface of the workpiece with higher accuracy, and to improve the dimensional accuracy of the prepared hole.

  Second, when the tip of the drill body is consumed by repeating the processing of the pilot hole, it is regenerated by polishing the tip of the drill body. This grinding reduces the length of the drill body, but if the shank side is ground to create a new base in the drill body, a reduction in the length of the drill body is prevented. Then, the bottom of the other twisted groove appears at the new base of the drill body generated by the grinding on the shank side, and this bottom is almost the same shape and size as the twisted groove, so that Also in machining, the cutting waste is discharged smoothly.

  Further, as described above, the outer edge excluding the other torsion grooves in the cross section of each part in the axial direction of the shank is positioned on a virtual circle centered on the axis.

  For this reason, the shank of the drill does not have an outer peripheral cutting edge, a margin, and a flank as a drill structure. That is, the drill has a very simple structure as compared with a step drill. Therefore, since the drill can be easily formed and is inexpensive, drilling can be performed more easily and inexpensively.

  In the invention of claim 2, the transition portion from the drill body to the shank is formed so that its diameter gradually increases from the drill body side toward the shank side.

  For this reason, the diameter change of a drill toward the shank from the said drill main body can be made loose, the stress concentration in the said transition part can be suppressed small, and breakage of a drill can be prevented.

  Moreover, the outer edge except each said torsion groove in the cross section of each part of the axial direction of the said transition part is located on the virtual circle centering on the said axial center.

  For this reason, the transition part of the drill does not have an outer peripheral cutting edge, a margin, and a flank as a drill structure. In other words, the drill has a very simple structure as compared with a step drill. Therefore, since the drill can be easily formed and is inexpensive, drilling can be performed more easily and inexpensively.

The invention of claim 3 is a method of drilling a workpiece using the drill of claim 1 above.
For the workpiece, start drilling the pilot hole by the drill body, and when the transition portion contacts the workpiece, or before the contact, finish the pilot hole processing,
Next, another drill is inserted into the pilot hole, another hole continuous with the pilot hole is processed into the workpiece, and another drill is inserted into the other hole, and the other hole is inserted into the other hole. Another continuous hole is machined into the workpiece.

  For this reason, when deep holes are drilled using the above-mentioned various drills in sequence, as described above, the drilling of the prepared holes by the drill is easy and accurate, so that the deep holes are easy and accurate. I can do it well.

  According to a fourth aspect of the present invention, the inner diameters of the pilot hole, the other holes, and the other holes are substantially the same.

  For this reason, deep holes in which the inner diameters of the respective parts in the axial direction are substantially the same are processed. When the deep hole is processed, when another hole is processed by the other drill, the inner peripheral surface of the prepared hole prevents the other drill from bending. Further, when another hole is machined by the other drill, the inner hole of the other hole prevents the other drill from bending. Therefore, it is prevented that the other drills or other drills are easily broken by bending. As a result, the deep hole machining can be performed smoothly and easily.

  The inner diameter of the deep hole near the surface of the workpiece and the inner diameter of the deepest portion of the deep hole are substantially the same. For this reason, when the inner diameter of the deepest portion is to be set to a desired dimension, the area occupied on the surface of the workpiece for processing the deep hole is sufficient to be a circular area having the same diameter as the inner diameter of the deepest portion. In other words, the necessary area is sufficient for the above-mentioned occupied area for deep hole machining. Therefore, the deep hole having the above shape can be processed even in a narrow place on the surface of the workpiece.

  With regard to the drill of the present invention, even if the surface of a workpiece such as a forged product is rough, when drilling the workpiece, the purpose of enabling the drilling to be easily and inexpensively is realized. Therefore, the best mode for carrying out the present invention is as follows.

  That is, the drill includes a drill body and a shank disposed on the axis of the drill body and formed integrally with the base of the drill body, and the diameter of the shank is larger than the diameter of the drill body. Has been.

  Another twist groove continuous with the twist groove of the drill body is formed in the shank, and the bottom of the other twist groove is substantially the same shape and size as the twist groove. Moreover, the outer edge except each said torsion groove | channel in the axial direction part cross section of the said shank is located on the virtual circle centering on the said axial center.

  In order to explain the present invention in more detail, an embodiment thereof will be described with reference to the accompanying drawings.

  In FIG. 1-3, the code | symbol 1 is a drill for prepared holes.

  The drill 1 is arranged in a row on the drill main body 4 on the drill main body 4 capable of machining the pilot hole 3 of the work 2 and the axis 5 of the drill main body 4. And a shank 6 that is integrally formed. The diameter D2 of the shank 6 is larger than the diameter D1 of the drill body 4. In this case, (1.4−2.0) D1 = D2 is preferable, and (1.6−1.8) D1 = D2 is more preferable. The length L1 of the drill body 4 = the target depth L2 + of the pilot hole 3 + about 1 mm is preferable, and the target depth L2 of the pilot hole 3 = (0.8−2.5) D1 is preferable.

  1 and 2, two twisted grooves 9 are formed on the outer peripheral surface of the drill body 4. When the rotation direction R of the drill 1 is the front and the opposite direction is the rear, the rear edge of the end opening edges of the torsion grooves 9 on the tip surface 10 of the drill body 4 is the tip cutting edge 11. Has been. The rear edge of the pair of opening edges of each twisted groove 9 on the outer peripheral surface of the drill body 4 is an outer peripheral cutting edge 12.

  Further, the marginal portion 13 is an outer peripheral portion of the narrow drill body 4 which is located on a virtual circle passing through the outer peripheral cutting edge 12 with the axis 5 as a center and continues to the rear from the outer peripheral cutting edge 12. Further, the other outer peripheral portion of the drill body 4 between the margin 13 and the torsion groove 9 located behind the margin 13 is a relief located on another virtual circle having a slightly smaller diameter than the virtual circle. The surface 14 is used.

  1 and 3, the shank 6 is formed with two other twisted grooves 17 that are continuous with the twisted grooves 9 of the drill body 4, respectively. The bottoms of these other torsion grooves 17 are substantially the same shape and size as the torsion grooves 9. Specifically, when the cross-sectional shape of the drill body 4 and that of the shank 6 are superimposed, the torsional groove 9 and the bottom of the other torsional groove 17 are substantially matched (solid line in FIG. 3). And the pitch of twists in the axial direction of the drill 1 are substantially the same as each other.

  The outer edge 18 excluding the other torsional grooves 17 in the cross section of each part in the axial direction of the shank 6 in which the other torsional grooves 17 are formed is positioned on a virtual circle centered on the axis 5. . That is, none of the shanks 6 corresponds to the outer peripheral cutting edge 12, the margin 13, and the flank 14 of the drill body 4.

  The transition portion 20 from the drill body 4 to the shank 6 is formed so that its diameter gradually increases from the drill body 4 side toward the shank 6 side. The diameter of the transition portion 20 on the drill body 4 side is the same as the diameter D1 of the base portion of the drill body 4, and the diameter on the shank 6 side is the same as the diameter D2 of the shank 6. The transition portion 20 has a truncated cone shape as a whole, and the apex angle θ may be 60 ° -140 °. However, while the drill 1 is made compact in the axial direction, the stress concentration at the transition portion 20 is reduced. In order to prevent it, 80 ° -120 ° is more preferable. The apex angle θ may be approximately 180 °, that is, there may be a transition portion 20 with the axial dimension of approximately “zero”. In this case, the drill body 4 in the shank 6 is present. The side end face is substantially perpendicular to the axis 5.

  Outer edges 21 excluding the torsion grooves 9 and 17 in each cross section of the transition part 20 in the axial direction are positioned on a virtual circle centered on the axis 5 (two-dot chain line in FIG. 3).

  1 and 4, the work 2 is a crankshaft constituting an automobile or a motorcycle engine. The crankshaft is disposed on the crankshaft center 24 and is supported by a crankcase as a journal. A plurality of crank arms 26 projecting radially outward from the crank main shaft 25, and the crankshaft. A plurality of crankpins 27 are provided on the arm 26, and these 24-27 are integrally formed by forging.

  A bottomed hole 29 is formed which extends in a direction intersecting the crankshaft 24 and serves as an oil passage. This hole 29 is a so-called one-journal two-pin, and is formed so as to pass the crankpin 27, the crank main shaft 25, and the other crankpin 27 from the base portion of the crank arm 26. The opening end of the hole 29 is plugged with a metal ball 30. Further, a communication hole 31 is formed for communicating the hole 29 to the outer peripheral surface side of the crank main shaft 25 and each crankpin 27.

  In all the drawings, a hole machining method for machining a deep hole 29 in the workpiece 2 using the drill 1 will be described.

  First, the shank 6 of the drill 1 is fixed to an output part (chuck) of a machine tool 33 such as a machining center, and the drill 1 is driven to rotate in the rotational direction R around its axis 5. And the front-end | tip of the drill main body 4 of the said drill 1 is press-contacted to the desired position on the surface of the said workpiece | work 2, and the process of the said pilot hole 3 is started. When the machining of the pilot hole 3 has progressed and before the transition portion 20 abuts against the workpiece 2, when the length L1 of the drill body 4 = the target depth L2 + of the pilot hole 3 + about 1 mm, Processing of the pilot hole 3 is finished, and the drill 1 is extracted from the pilot hole 3. The processing of the pilot hole 3 may be advanced until the transition portion 20 contacts the workpiece 2.

  Next, another drill 36 that is rotationally driven by the machine tool 33 is inserted into the pilot hole 3, and another hole 37 that continues to the pilot hole 3 is processed into the workpiece 2. The other drill 36 is extracted from the other hole 37. Next, another drill 39 that is rotationally driven by the machine tool 33 is inserted into the prepared hole 3 and the other hole 37, and another hole 40 that continues to the other hole 37 is inserted into the workpiece 2. After this processing, another drill 39 is extracted from the other hole 40. Thereby, the hole 29 is processed.

  The other drill 36 is called a 20D drill and has a length 20 times the diameter thereof. The other drill 39 is called a 30D drill and has a length 30 times the diameter thereof. The diameters of the drill body 4, the other drill 36, and the further drill 39 of the drill 1 may be substantially the same as each other, but in this order, the diameter value is 0.5 to 1.0%. Is gradually reduced. For this reason, the inner diameters of the pilot hole 3, the other holes 37, and the other holes 40 are substantially the same as each other. Specifically, the inner diameters are 0.5 to 1.0% in this order. The value is gradually decreased.

  Here, as described above, the drill body 4 and the shank 6 are formed integrally with each other, and the drill body 4 is reinforced by the shank 6 having a diameter D2 larger than this, and sufficient rigidity is ensured. ing.

  For this reason, even if the drill body 4 of the drill 1 pressed against the surface of the workpiece 2 receives a reaction force in the radial direction from the surface during the drilling, the drill body 4 counters the reaction force. And it is prevented that it bends. Therefore, the drill body 4 can accurately process the pilot hole 3 at a desired position on the surface of the workpiece 2, and as a result, the first step by the end mill shown in the conventional technique is not required at the time of drilling. Hole processing can be made easier.

  Then, as described above, another torsion groove 17 continuing to the torsion groove 9 of the drill body 4 is formed in the shank 6, and the bottom of the other torsion groove 17 is substantially the same shape and size as the torsion groove 9. Yes.

  For this reason, firstly, the cutting waste of the workpiece 2 when the prepared hole 3 is processed by the drill body 4 passes through the torsion groove 9 and the other torsion grooves 17 without being interrupted by the shank 6. The workpiece 2 is smoothly discharged to the outside of the surface. Therefore, when the length L1 of the drill body 4 is shortened and this length L1 is approximated to the target hole 3 target depth L2, the shank 6 is formed on the surface of the workpiece 2 immediately before the completion of the processing of the pilot hole 3. Although it approaches, the cutting waste is smoothly discharged without being obstructed by the shank 6, and the processing of the prepared hole 3 by the drill body 4 can be performed smoothly. As described above, when the length L1 of the drill main body 4 is shortened, the rigidity of the drill main body 4 can be further improved and the bending of the drill main body 4 when the pilot hole 3 is processed is further prevented. it can. As a result, it is possible to process the prepared hole 3 at a desired position on the surface of the work 2 with higher accuracy.

  Moreover, the dimensional accuracy of the pilot hole 3 is also improved. For this reason, if the ball 30 is press-fitted into the prepared hole 3 left processed by the drill 1 in the hole 29 after the processing of the hole 29 is completed, a highly accurate press-fitting dimension can be obtained. As a result, the press-fit tightening margin is stabilized and the sealing performance of the plug is improved.

  Second, when the tip cutting edge 11 at the tip of the drill body 4 is consumed by repeating the processing of the pilot hole 3, it is regenerated by polishing the tip of the drill body 4. By this polishing, the length L1 of the drill body 4 is reduced, but if the shank 6 side is polished to produce a new base in the drill body 4, the reduction in the length L1 of the drill body 4 is prevented. . More specifically, the above-described shank 6 side corresponds to the end surface on the drill body 4 side in the transition portion 20, or the end surface on the drill body 4 side in the shank 6 when the transition portion 20 is zero. Then, the bottom of the other twisted groove 17 appears at the new base of the drill body 4 generated by the polishing on the shank 6 side, and since this bottom is approximately the same shape and size as the twisted groove 9, Also in the machining of the pilot hole 3, the cutting waste is discharged smoothly.

  Further, as described above, the outer edge 18 excluding the other torsion grooves 17 in the cross section of each part in the axial direction of the shank 6 (FIG. 3) is positioned on a virtual circle centered on the axis 5. .

  Therefore, the shank 6 of the drill 1 does not have the outer peripheral cutting edge 12, the margin 13, and the flank 14 as the drill structure. That is, the drill 1 has a very simple structure as compared with the step drill. It ’s enough. Therefore, the drill 1 can be formed easily and inexpensively, so that drilling can be performed more easily and inexpensively.

  Further, as described above, the transition portion 20 from the drill body 4 to the shank 6 is formed so that its diameter gradually increases from the drill body 4 side toward the shank 6 side.

  For this reason, the diameter change of the drill 1 from the said drill main body 4 toward the shank 6 can be made loose, the stress concentration in the said transition part 20 can be suppressed small, and breakage of the drill 1 can be prevented.

  Further, the outer edge 21 excluding the torsion grooves 9 and 17 in the cross sections (two-dot chain lines in FIG. 3) in the axial direction of the transition portion 20 is positioned on a virtual circle centered on the axis 5. .

  For this reason, the transition part 20 of the drill 1 does not have the outer peripheral cutting edge 12, the margin 13, and the flank 14 as a drill structure, that is, the drill 1 has a very simple structure as compared with the step drill. Is enough. Therefore, the drill 1 can be formed easily and inexpensively, so that drilling can be performed more easily and inexpensively.

In addition, as described above, a method for drilling a workpiece 2 using the drill 1 according to claim 1,
Processing of the pilot hole 3 is started on the workpiece 2 by the drill body 4, and the processing of the pilot hole 3 is finished when the transition portion 20 contacts the workpiece 2 or before the contact. ,
Next, another drill 36 longer than the drill body 4 is inserted into the pilot hole 3, and another hole 37 continuing to the pilot hole 3 is processed into the workpiece 2. A long other drill 39 is inserted into the other hole 37, and another hole 40 continuing to the other hole 37 is processed into the workpiece 2.

  Therefore, when deep holes are drilled using the various drills 1, 36, 39 in order, as described above, the deep holes 3 can be processed easily and accurately by the drill 1. Processing is easy and accurate.

  In addition, as described above, since the deep drilling is sequentially performed instead of the short drill, the drilling length of each drill can be kept short. Therefore, the cutting waste generated at the time of drilling each drill is smoothly discharged through the torsion groove of each drill. As a result, the occurrence of inconvenience such as breakage of each drill is prevented, and the deep hole can be processed smoothly and easily.

  Further, as described above, the inner diameters of the pilot hole 3, the other hole 37, and the other hole 40 are made substantially the same.

  For this reason, when the other hole 37 is machined by the other drill 36, it is prevented by the inner peripheral surface of the prepared hole 3 that the other drill 36 tries to bend. Further, when another hole 40 is machined by the other drill 39, the inner peripheral surface of the other hole 37 prevents the other drill 39 from bending. Therefore, it is prevented that the other drill 36 or the other drill 39 is easily broken by bending. As a result, the deep hole machining can be performed smoothly and easily.

  Although the above is based on the illustrated example, the hole 29 may be a through hole. The hole 29 may be a so-called one-journal one-pin formed so as to pass through the crank pin 27 and the crank main shaft 25 from the base of the crank arm 26. Further, in deep hole drilling, further drilling may be performed using one or more other drills.

It is the whole drill side view. It is the II-II sectional view taken on the line of FIG. FIG. 3 is a cross-sectional view taken along line III-III in FIG. 1. FIG. It is a figure explaining the hole processing method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Drill 2 Workpiece | work 3 Pilot hole 4 Drill main body 5 Axis center 6 Shank 9 Torsion groove 17 Other torsion groove 18 Outer edge 20 Transition part 21 Outer edge 29 Hole 36 Other drill 37 Other hole 39 Further other drill 40 Still other hole D1 diameter D2 diameter R rotational direction θ apex angle L1 length L2 target depth

Claims (4)

In a drill comprising a drill body and a shank disposed on the axis of the drill body and integrally formed with the base of the drill body, the diameter of the shank being larger than the diameter of the drill body,
Forming another twisted groove continuous with the twisted groove of the drill body in the shank, and making the bottom of the other twisted groove substantially the same shape and size as the twisted groove;
A drill characterized in that an outer edge excluding the other torsional grooves in a cross section of each part in the axial direction of the shank is positioned on a virtual circle centered on the axis. The transition part from the drill body to the shank is formed so that its diameter gradually increases from the drill body side toward the shank side,
2. The drill according to claim 1, wherein outer edges excluding the torsion grooves in the cross sections of the transition portions in the axial direction are positioned on a virtual circle centered on the axis. A hole drilling method for a workpiece using the drill according to claim 1,
For the workpiece, start drilling the pilot hole by the drill body, and when the transition portion contacts the workpiece, or before the contact, finish the pilot hole processing,
Next, another drill is inserted into the pilot hole, another hole continuous with the pilot hole is processed into the workpiece, and another drill is inserted into the other hole, and the other hole is inserted into the other hole. A hole drilling method for a workpiece, characterized in that further continuous holes are machined into the workpiece.   4. The method for drilling a workpiece according to claim 3, wherein the inner diameters of the pilot hole, the other holes, and the other holes are substantially the same.

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