JP2007098517A - Prepared hole machining method and boring tool - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a prepared hole machining method and a boring tool suitable for the machining method, securing the rigidity of a boring tool to prevent run-out when the boring tool is rotated at high speed and form a machined hole with good accuracy, and reducing cutting resistance to prevent breakage of the boring tool. <P>SOLUTION: In this machining method, the boring tool 21 is inserted in the prepared hole previously formed in a material W to be cut, thereby cutting the inner wall surface of the prepared hole to form a machined hole. The boring tool 21 includes a shank part 22 rotated round the axis O and a tip blade part 23 disposed at the tip of the shank part 22, and the tip blade part 23 is provided with a chip discharge groove 27 formed extending from the forward end side to the rear end side, and a cutting blade 30 is formed on an intersecting ridge line part of the wall surface pointing the front in the tool rotating direction T of the chip discharge groove 27 and the outer peripheral surface of the tip blade part 23. The method uses the boring tool 21 in which the length C of the cutting blade 30 is set smaller than the length H of the prepared hole. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for machining a pilot hole, in which a hole drilling tool is inserted into a pilot hole previously formed in a workpiece, the inner wall surface of the pilot hole is cut, and a drill hole having a predetermined inner diameter is formed. The invention relates to a drilling tool suitable for use in a method.

As this type of drilling tool, for example, a long cylindrical reamer as described in Patent Document 1 is known.
This reamer is used by being mounted on a cutting tool as disclosed in Patent Document 2, for example, and this cutting tool is mounted on a spindle end of a machine tool or the like and rotated around an axis. The material to be cut is inserted into a prepared hole, for example, a stem guide hole or a valve hole in a cylinder head of an engine, and an inner wall surface of the prepared hole is cut to form a processed hole having a predetermined inner diameter.

FIG. 9 shows an example of a pilot hole machining method using a conventional reamer. An example of a conventional reamer is shown in FIGS.
As shown in FIG. 11, the reamer 1 includes a shank portion 2 having a long cylindrical shape, and a tip blade portion 3 disposed on the tip side of the shank portion 2.
The shank portion 2 is made of steel and has a substantially multi-stage columnar shape, and a mounting portion 4 for mounting the reamer 1 on a cutting tool is provided on the rear end side. A V-shaped groove 5 having a central portion recessed toward the rear end side of the shank portion 2 is formed on the front end surface of the shank portion 2.
In addition, a coolant supply hole (not shown) is formed in the shank portion 2 so as to penetrate from the front end side to the rear end side of the shank portion 2 and is opened in the V-shaped groove 5.

The tip blade portion 3 is made of cemented carbide and has a substantially cylindrical shape, and a convex portion 6 that can be fitted into a V-shaped groove 5 formed on the tip surface of the shank portion 2 is formed on the rear end surface thereof. ing.
As shown in FIG. 10 and FIG. 11, six pieces of chips are discharged at the tip outer peripheral portion of the tip blade portion 3 and extend toward the rear end side in the axis O direction and twist at a predetermined angle toward the front side in the tool rotation direction T. The grooves 7 are arranged in 60-degree rotational symmetry with respect to the axis O at equal intervals in the circumferential direction. Here, the length S in the direction of the axis O of the chip discharge groove 7 is shorter than the length L in the direction of the axis O of the tip blade portion 3 made of cemented carbide as shown in FIG.

  A cutting edge 10 is formed at the intersecting ridge line portion between the wall surface 8 facing the tool rotation direction T front side of these chip discharge grooves 7 and the outer peripheral surface 9 connected to the tool rotation direction T rear side. By forming the cutting edge 10 in this manner, the wall surface 8 facing the front side in the tool rotation direction T of the chip discharge groove 7 is a rake face, and the outer peripheral surface 9 connected to the rear side in the tool rotation direction T is a flank face. .

  As shown in FIG. 10, the chip discharge groove 7 has a V-shaped cross section. The angle formed by the V-shape is approximately 80 °, and the wall surface 8 facing the front side in the tool rotation direction T, which is a rake face, is The outer end of the tip blade portion 3 is formed so as to extend along the radial direction of a circle formed by the outer cross section. Moreover, the front-end | tip blade part 3 is formed with the communicating hole (not shown) extended along the axis line O and opened by the rear-end side (convex-shaped part 6), Each chip discharge | emission from this communicating hole A discharge hole 11 extending in the groove 7 and opened at the bottom of the groove is provided.

  Further, the tip blade portion 3 is formed with a back taper portion 12 that gradually decreases in diameter from the tip side toward the rear end side. The length B of the back taper portion 12 in the direction of the axis O is as shown in FIG. 11, the chip discharge groove 7 is set to be shorter than the length S in the axis O direction. That is, the length B of the back taper portion 12 in the direction of the axis O, the length S of the chip discharge groove 7 in the direction of the axis O, and the length L of the tip blade portion 3 in the direction of the axis O are L> S> B. It has the relationship.

  The reamer 1 is mounted on a cutting tool, rotated around the axis O, and sent toward the tip side in the direction of the axis O, and inserted into a prepared hole formed in the workpiece W in advance. Cutting the inner wall surface. During the cutting, the chip discharge groove 7 is formed to be twisted forward in the tool rotation direction T, so that the chips generated by the cutting blade 11 are guided toward the tip of the reamer 1. Further, when the cutting fluid is discharged from the discharge hole 11 through the coolant supply hole and the communication hole, the chips are discharged toward the tip of the reamer 1 so as to be flowed by the cutting fluid flowing through the chip discharge groove 7. The

In the conventional pilot hole processing method, as shown in FIG. 9, the pilot hole is processed with the reamer 1 in which the length L of the tip blade portion 3 is longer than the length H of the pilot hole. The tip blade portion 3 of the reamer 1 is disposed so as to penetrate the processed hole formed by processing the inner wall surface of the hole.
JP 2000-263328 A JP 2002-59313 A

  By the way, when the reamer 1 in which the length L of the tip blade portion 3 is longer than the length H of the pilot hole is used in this way, a portion where the tip blade portion 3 and the inner wall surface of the machining hole are in sliding contact with each other becomes large. Therefore, cutting resistance will become large. Further, since the tip blade portion 3 is provided with a chip discharge groove 7 and a discharge hole 11 for cutting fluid, when the length L of the tip blade portion 3 is longer than necessary, the length of the chip discharge groove 7 is increased. Further, the rigidity of the reamer 1 is lowered and the reamer 1 may be broken by the cutting resistance. In addition, when the reamer 1 is rotated at a high speed, there is a problem that due to insufficient rigidity, vibration and chatter occur, and the processed hole cannot be accurately formed.

  The present invention has been made in view of the above-described circumstances, and by ensuring the rigidity of the hole machining tool, the machined hole can be formed with high accuracy by preventing runout when the hole machining tool is rotated at a high speed. Another object of the present invention is to provide a pilot hole machining method capable of reducing cutting resistance and preventing breakage of the drilling tool, and a drilling tool suitable for this machining method.

  In order to solve the above-described problems, the present invention provides a pilot hole for forming a drilled hole by inserting a drilling tool into a pilot hole previously formed in a workpiece and cutting the inner wall surface of the pilot hole. It is a processing method, Comprising: The said hole drilling tool has the shank part rotated by the periphery of an axis line, and the front-end | tip blade part arrange | positioned at the front-end | tip of this shank part. A chip discharge groove extending toward the side is formed, and a cutting blade is formed at a cross ridge line portion between a wall surface facing the front side in the tool rotation direction of the chip discharge groove and the outer peripheral surface of the tip blade portion, and the cutting blade The hole machining tool is used in which the length in the axial direction is shorter than the length of the pilot hole.

  According to this pilot hole machining method, cutting with a drilling tool having a cutting edge shorter than the length of the pilot hole formed in the workpiece, the cutting edge and the chip discharge groove become longer than necessary. Therefore, the rigidity of the drilling tool can be ensured, and the drilling of the drilling tool can be suppressed and the drilled hole can be accurately formed. Moreover, since there are few parts which are slidably contacted with a drilling hole, cutting resistance is reduced and it can prevent that a drilling tool breaks by cutting resistance.

  Further, a drilling tool is used in which the tip blade portion is made of a material having a higher hardness than the shank portion, and the length of the tip blade portion in the axial direction is shorter than the length of the pilot hole. As a result, the length of the cutting blade can be reliably shortened than the pilot hole, and the wear resistance of the cutting blade formed on the tip blade portion can be improved to extend the life.

As a hole drilling tool used for the above-mentioned pilot hole machining method, it has a shank part rotated around an axis and a tip blade part arranged at the tip of the shank part. A chip discharge groove extending toward the rear end side is formed, and a cutting blade is formed at a cross ridge line portion between the wall surface facing the front side in the tool rotation direction of the chip discharge groove and the outer peripheral surface of the tip blade part, A back taper portion is formed so that the outer diameter gradually decreases from the tip surface of the tip blade portion toward the rear end side, and the length of the back taper portion in the axial direction is the axis of the tip blade portion. The use of a tool that is shorter than the length in the direction is preferable because the outer diameter of the rear end side portion of the tip blade portion is not excessively reduced and the rigidity of the drilling tool can be secured.
In addition, since the back taper part is formed, the inner wall surface of the processing hole formed by the cutting edge provided on the outer periphery on the front end side of the front end blade part and the rear end side of the front end blade part are not in sliding contact with each other. Can be done smoothly.

  Furthermore, the length of the axial direction of the chip discharge groove formed in the drilling tool is made shorter than the length of the back taper portion in the axial direction, thereby reducing the portion where the tip blade portion is notched. And the rigidity of the drilling tool can be further improved.

  Further, by making the outer diameter on the front end side of the shank part 0.02 mm or more smaller than the outer diameter on the rear end side of the back taper part, the shank part is separated from the inner wall surface of the processing hole, thereby preventing contact. Therefore, there is no possibility that the inner wall surface of the processed hole is damaged, and an increase in the rotational torque of the reamer can be prevented. In addition, even if the tip blade portion is shorter than the pilot hole, the tip blade portion can be surely inserted into the pilot hole, so that the pilot hole can be reliably processed by this hole processing tool.

  Further, a cross section perpendicular to the axis of the chip discharge groove is U-shaped, that is, a wall surface facing the tool rotation direction front side and a wall surface facing the tool rotation direction rear side of the chip discharge groove are concave arcs in the cross section. For example, the radius of the concave arc formed by the groove bottom at the same groove depth as the above-described conventional reamer cross-section V-shaped chip discharge groove is formed. When the same is formed, the portion to be cut out is reduced, and the rigidity of the drilling tool can be ensured. Therefore, the machined hole can be formed with high accuracy by preventing runout during high-speed rotation, and the life can be extended by suppressing breakage due to cutting resistance.

  In addition, since the cross-sectional area of the chip discharge groove is reduced, when the cutting fluid is discharged from the discharge hole opened at the bottom of the chip discharge groove, the flow rate of the cutting oil passing through the chip discharge groove is increased, Chips generated by the cutting blade can be reliably discharged, for example, toward the tip of the hole machining tool. Therefore, even if the cross-sectional area of the chip discharge groove is reduced by discharging the chips in the tip direction in this way, the chips are not clogged in the chip discharge groove, and the machining with this drilling tool is performed smoothly. be able to.

  Further, a first land portion formed on the outer peripheral surface so as to be continuous with the cutting edge, a relief portion that is continuous with a rear side in the tool rotation direction of the first land and is retreated inward in the radial direction, and a tool of the relief portion By providing the second land portion formed so as to be continuous with the rear side in the rotation direction, the portion in sliding contact with the machining hole can be reduced, and the cutting resistance at the time of cutting with this drilling tool can be reduced. it can. In addition, since the first land portion and the second land portion are formed, the processing hole and the first and second land portions can be in sliding contact with each other to smoothly finish the inner wall surface of the processing hole. Moreover, these 1st, 2nd land parts play the role of a guide, rotation of this drilling tool is stabilized, and a process hole can be shape | molded accurately.

  As described above, according to the present invention, by ensuring the rigidity of the drilling tool, the drilling tool can be formed with high accuracy by preventing the deflection when the drilling tool is rotated at a high speed, and the cutting resistance is reduced. It is possible to provide a method for machining a pilot hole capable of preventing breakage of a hole machining tool and a hole machining tool suitable for this machining method.

  Hereinafter, a method for machining a pilot hole according to an embodiment of the present invention and a hole machining tool according to a first embodiment of the present invention used in the machining method will be described with reference to the accompanying drawings. FIG. 1 shows a prepared hole machining method according to an embodiment of the present invention, and FIGS. 2 and 3 show a reamer as a hole machining tool used in the prepared hole machining method. FIG. 4 shows a cutting tool to which this reamer is attached.

The reamer 21 includes a shank portion 22 having a long cylindrical shape and a tip blade portion 23 disposed on the tip side (lower side in FIG. 3) of the shank portion 22.
The shank portion 22 is made of a steel material or the like and has a substantially multi-stage columnar shape, and a mounting portion 24 for mounting the reamer 21 to the cutting tool 41 is provided on the rear end side (upper side in FIG. 3). ing. The mounting portion 24 is provided with a flat surface 24A that extends parallel to the axis O.

The outer diameter Ds on the front end side of the shank portion 22 is one step smaller than that on the rear end side where the mounting portion 24 is provided. A V-shaped groove 25 whose central portion is recessed toward the rear end side of the shank portion 22 is formed on the front end surface of the shank portion 22, and an angle formed by the V-shaped groove 25 is in a range of 60 ° to 120 °. In this embodiment, it is set to 90 °.
In addition, a coolant supply hole is formed in the shank portion 22 so as to penetrate from the front end side to the rear end side of the shank portion 22, and is opened at the center portion of the V-shaped groove 25.

The tip blade portion 23 is made of, for example, a cemented carbide having a hardness higher than that of the shank portion 22 and has a substantially cylindrical shape. The rear end face is fitted in a V-shaped groove 25 formed on the tip face of the shank portion 22. A convex portion 26 that can be mated is formed.
A plurality of chip discharge grooves 27 extending toward the rear end side in the axis O direction and twisted at a predetermined twist angle (10 ° in the present embodiment) toward the front side in the tool rotation direction T on the outer peripheral portion of the tip blade portion 23. Are arranged rotationally symmetrically with respect to the axis O by a predetermined angle at equal intervals in the circumferential direction. In the present embodiment, as shown in FIG. 2, six pieces of chip discharge grooves 27 are arranged rotationally symmetrically by 60 ° with respect to the axis O.

A cutting edge 30 is formed at the intersecting ridge line portion between the wall surface 28 of the chip discharge groove 27 facing the front side in the tool rotation direction T and the outer peripheral surface 29 connected to the rear side in the tool rotation direction T.
By forming the cutting edge 30 in this manner, the wall surface 28 facing the front side in the tool rotation direction T of the chip discharge groove 27 is a rake face, and the outer peripheral surface 29 connected to the rear side in the tool rotation direction T is a flank face. . The cutting blade 30 is spirally twisted at a predetermined twist angle (10 ° in the present embodiment) around the axis O in the tool rotation direction T as it goes to the rear end side in the same manner as the chip discharge groove 27. Is formed.

Here, the length S in the axis O direction of the chip discharge groove 27 is set shorter than the length L in the axis O direction of the tip blade portion 23 made of cemented carbide.
Further, as shown in FIG. 2, the chip discharge groove 27 has a V-shaped cross section. The angle formed by the V-shape is approximately 80 °, and the wall surface faces the front side in the tool rotation direction T, which is a rake face. 28 is formed so as to extend along the radial direction of the circle formed by the cross-section of the outline of the tip blade portion 23. Further, the tip blade portion 23 is formed with a communication hole (not shown) that extends along the axis O and is opened in the convex portion 26, and extends from the communication hole to each chip discharge groove 27. A discharge hole 31 opened at the bottom of the groove is provided.

  Further, the tip blade portion 23 is formed with a back taper portion 32 that gradually decreases in diameter from the front end side toward the rear end side. The length B of the back taper portion 32 in the direction of the axis O is defined as a chip. The length is set shorter than the length S of the discharge groove 27 in the axis O direction. In other words, the length B of the back taper portion 32, the length S of the chip discharge groove 27, and the length L of the tip blade portion 23 have a relationship of L> B> S. Further, the cutting edge 30 formed on the intersecting ridge line portion of the wall surface 28 facing the front side of the tool rotation direction T of the chip discharge groove 27 and the outer peripheral surface 29 is cut off on the rear end side of the chip discharge groove 27. In consideration, the length C in the direction of the axis O is shorter than the length S of the chip discharge groove 27.

  Further, the outer diameter Db at the rear end of the back taper portion 32 is set to be 0.02 mm or more larger than the outer diameter Ds at the front end side of the shank portion 22, and is increased by 0.02 mm in this embodiment. Yes. Here, in the present embodiment in which the length B of the back taper portion 32 is shorter than the length L of the tip blade portion 23, the tip blade portion 23 portion made of cemented carbide also on the rear end side from the back taper portion 32. This portion is reduced in diameter by one step from the rear end of the back taper portion 32 through a step so as to have the same diameter as the outer diameter Ds of the shank portion 22. The thickness is 0.01 mm or more (in this embodiment, 0.01 mm).

This reamer 21 is used by being mounted on a cutting tool 41 shown in FIG. The cutting tool 41 has a multi-stage cylindrical tool body 42 that rotates about the axis M.
A mounting hole 43 extending along the axis M is formed in the tip surface of the tool main body 42. A coolant hole 45 into which a position adjusting bolt 44 is inserted is provided so as to communicate with the rear end side of the mounting hole 43, and the coolant hole 45 is opened in a mounting portion 46 provided on the rear end side of the tool body 42. Has been.
In addition, a screw hole 47 is formed in the side surface of the tool body 42 and communicated with the mounting hole 43, and a clamp screw 48 is screwed into the screw hole 47.

  The reamer 21 is inserted into a mounting hole 43 formed in the front end surface of the tool body 42, the rear end surface of the shank portion 22 is brought into contact with the front end surface of the position adjusting bolt 44, and the flat surface 24A of the shank portion 22 is The tool body 42 is arranged so as to face the direction in which the screw hole 47 is provided, and the axis O of the reamer 21 and the axis M of the tool body 42 coincide with each other. Then, the reamer 21 is fixed to the tool body 42 by screwing a clamp screw 48 screwed into the screw hole 47 of the tool body 42 and pressing the flat surface 24A.

  The cutting tool 41 to which the reamer 21 is mounted in this way is attached to the spindle end of the machine tool via the attachment portion 46, and after adjusting the position of the reamer 21 in the axis M direction, the cutting tool 41 is rotated around the axis M (axis O). And the reamer 21 is inserted into a pilot hole (for example, a stem guide hole) formed in the workpiece W, and the inner wall surface of the pilot hole is rotated toward the tip of the axis M (axis O). Is cut to form a processed hole having a predetermined inner diameter.

  When cutting with the reamer 21, the cutting fluid is supplied from the machine tool to the coolant hole 45 of the tool body 42 through a pipe. The cutting fluid supplied to the coolant hole 45 is supplied to the tip blade portion 23 through the coolant supply hole formed in the shank portion 22 of the reamer 21, and the chips are passed through the communication hole and the discharge hole 31 formed in the tip blade portion 23. It is discharged from the groove bottom of the discharge groove 27 toward the inner wall surface of the prepared hole.

  Chips generated when the inner wall surface of the pilot hole is cut are formed so that the chip discharge grooves 27 are twisted forward in the tool rotation direction T, and therefore are guided toward the tip side of the reamer 21. become. Further, when the cutting fluid is discharged from the discharge hole 31 through the coolant supply hole and the communication hole, the chips are discharged toward the front end side of the reamer 21 so that the cutting fluid flows.

  Here, in the pilot hole processing method according to the present embodiment, a reamer 21 having a length L of the tip blade portion 23 that is shorter than the length H of the pilot hole is used, and accordingly, on the outer periphery of the tip blade portion 23. The reamer 21 whose length C in the direction of the axis O is shorter than the length H of the pilot hole is also used for the cutting blade 30 to be formed. As shown in FIG. 1, at the end of processing by the reamer 21, the tip blade portion 23 is positioned in the lower portion of the processing hole, and a part of the shank portion 22 is disposed in the upper portion.

  By using such a reamer 21, the sliding contact portion between the inner wall surface of the machining hole and the tip blade portion 23 is reduced, and the cutting resistance can be suppressed. Moreover, since the length L of the front-end | tip blade part 23 in which the chip discharge groove 27, the discharge hole 31, etc. were formed is short, the rigidity of this reamer 21 is ensured and the breakage by cutting resistance can be prevented. Furthermore, the machining hole can be formed with high accuracy by suppressing the shake and chatter during high-speed rotation by improving the rigidity.

In this reamer 21, since the back taper portion 32 is formed on the tip blade portion 23, the reamer 21 has the largest outer diameter and the rear end side has a smaller outer diameter, and the reamer 21 is placed inside the machining hole. It can be inserted reliably and cutting can be performed reliably.
Further, since the length B of the back taper portion 32 is smaller than the length L of the tip blade portion 23, the outer diameter on the rear end side of the tip blade portion 23 is not excessively reduced, and the rigidity of the reamer 21 is increased. Can be secured.

Further, since the length S of the chip discharge groove 27 in the axis O direction is shorter than the length B of the back taper portion 32 in the axis O direction, the portion that cuts out the tip edge portion 23 is reduced. The rigidity of the reamer 21 can be further improved.
Further, since the outer diameter Ds of the shank portion 22 is 0.02 mm smaller than the rear end side outer diameter Db of the back taper portion 32, the shank portion 22 is separated from the inner wall surface of the processing hole, The inner wall surface is not likely to be damaged, and an increase in the rotational torque of the reamer 21 can be prevented.

Next, a drilling tool according to a second embodiment of the present invention will be described with reference to the accompanying drawings. 5 and 6 show a reamer as a drilling tool according to the second embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the member same as 1st Embodiment, and description is abbreviate | omitted.
In this second embodiment, the chip discharge groove 27 has a U-shaped cross section as shown in FIG. 5, and the wall surface 28 facing the front side in the tool rotation direction T forming the rake face is substantially the tip edge portion 23. Are formed so as to extend along the radial direction of a circle formed by a cross-section of the outer shape. In the present embodiment, as shown in FIG. 5, the three chip discharge grooves 27 are arranged rotationally symmetrically by 120 ° with respect to the axis O.

  The outer peripheral surface 29 that is continuous with the cutting edge 30 and forms a flank face includes a first land portion 51 that is formed so as to be continuous with the cutting edge 30, and a radial direction that is continuous with the tool rotation direction T rear side of the first land portion 51. A relief portion 52 retracted inward and a second land portion 53 formed so as to continue to the rear side of the relief portion 52 in the tool rotation direction T are provided. The first land portion 51 and the second land portion 53 are formed in an arc shape having the same radius with the axis O as the center. In addition, the escape portion 52 protrudes radially inward with a radius larger than the radius of the groove bottom of the V-shaped cross section formed by the chip discharge groove 27 in a cross section perpendicular to the axis O, from the chip discharge groove 27. The relief portion 52 extends beyond the rear end of the back taper portion 32 and before the front end of the shank portion 22.

  In addition, a communication hole (not shown) that extends along the axis O and is opened in the convex portion 26 is formed in the tip blade portion 23, and from the communication hole toward each chip discharge groove 27. A discharge hole 31 that extends and opens at the bottom of the groove and a discharge hole 54 that extends toward each escape portion 52 and opens at the bottom of the R groove formed by the escape portion 52 are provided.

  Further, in the reamer 21 according to the second embodiment, the chip discharge groove 27 is formed in a U-shaped cross section, and is not greatly opened toward the outside in the radial direction. The rigidity of the reamer 21 is further improved. Accordingly, it is possible to prevent the shake when the reamer 21 is rotated at a high speed and form the processed hole with high accuracy. Moreover, it is possible to prevent the reamer 21 from being broken by cutting resistance and to extend the life of the reamer 21.

  Further, since the cross-sectional area of the chip discharge groove 27 is reduced, when the cutting fluid is discharged from the discharge hole 31 opened at the groove bottom portion of the chip discharge groove 27, the cutting oil passing through the chip discharge groove 27 is reduced. The flow velocity is increased, and the chips generated by the cutting blade 30 can be reliably discharged toward the tip of the reamer 21. Therefore, since the chips do not pass through the chip discharge groove 27, the chips can be reliably discharged even if the cross-sectional area of the chip discharge groove 27 is reduced, and the processing with the reamer 21 can be performed smoothly. it can.

In addition, since the relief portion 52 is formed on the outer peripheral surface 29 that forms the relief surface, the portion that is in sliding contact with the inner wall surface of the machining hole can be adjusted, and the cutting resistance of the reamer 21 can be reduced. In addition, since the first land portion 51 and the second land portion 53 are formed, the processing hole and the first and second land portions 51 and 53 are in sliding contact with each other to smoothly finish the inner wall surface of the processing hole. it can. Further, the first and second land portions 51 and 53 serve as a guide, and the rotation of the reamer 21 can be stabilized to form the machining hole with high accuracy.
Further, the cutting oil is supplied not only from the discharge hole 31 opened at the groove bottom of the chip discharge groove 27 but also from the discharge hole 54 opened at the groove bottom of the R groove formed by the escape portion 52. It is possible to reliably discharge chips.

As described above, the pilot hole processing method and the reamer 21 according to the embodiment of the present invention have been described. However, the present invention is not limited to this, and can be appropriately changed without departing from the technical idea of the present invention. .
For example, although the reamer 21 has been described as being used by being mounted on the cutting tool 41 shown in FIG. 3, it may be used by being mounted on another cutting tool or an adapter.

  Further, the chip discharge groove 27 is described as being formed to be twisted toward the front side of the tool rotation direction T as it goes toward the rear end side of the reamer 21, but the present invention is not limited to this. 7, the chip discharge groove 27 is formed to be twisted toward the rear side in the tool rotation direction T, and the chip discharge groove 27 is formed in a straight line without twist as shown in FIG. It may be.

  When the chip discharge groove 27 is formed as shown in FIGS. 7 and 8, the chip generated by the cutting blade 30 is not guided toward the distal end side of the reamer 21, but the cutting oil is removed from the chip discharge groove 27. The chip can be discharged to the tip side of the reamer 21 by flowing toward the tip side of the reamer 21 at a large flow rate.

It is explanatory drawing which shows the processing method of the prepared hole of this invention. It is a front view of the reamer which is the 1st Embodiment of this invention used for the processing method of FIG. FIG. 3 is a side view of the reamer shown in FIG. 2. It is a side surface fragmentary sectional view of the cutting tool with which the reamer shown in FIG. 2 is mounted | worn. It is a front view of the reamer which is the 2nd Embodiment of this invention used for the processing method of FIG. FIG. 6 is a side view of the reamer shown in FIG. 5. It is a side view of the reamer which is other embodiment of this invention. It is a side view of the reamer which is other embodiment of this invention. It is explanatory drawing which shows the processing method of the conventional prepared hole. It is a front view of the conventional reamer. It is a side view of the reamer shown in FIG.

Explanation of symbols

21 Reamer (Drilling tool)
22 Shank portion 23 Tip blade portion 27 Chip discharge groove 30 Cutting blade 32 Back taper portion 51 First land portion 52 Escape portion 53 Second land portion

Claims (7)

A method of machining a pilot hole, in which a hole machining tool is inserted into a pilot hole previously formed in a workpiece, and the inner wall surface of the pilot hole is cut to form a machining hole,
The hole drilling tool has a shank portion rotated about an axis and a tip blade portion disposed at the tip of the shank portion, and the tip blade portion has a chip extending from the tip side toward the rear end side. A discharge groove is formed, and a cutting blade is formed at the crossing ridge line part of the wall surface facing the front side in the tool rotation direction of the chip discharge groove and the outer peripheral surface of the tip blade part,
A drilling method for a prepared hole, wherein the drilling tool in which a length of the cutting edge in the axial direction is shorter than a length of the prepared hole is used.   The tip cutting edge portion is made of a material having a hardness higher than that of the shank portion, and the length of the tip cutting edge portion in the axial direction is shorter than the length of the pilot hole. The method for processing a pilot hole according to claim 1, wherein the method is used. A drilling tool used in the pilot hole machining method according to claim 2,
The tip blade portion is formed with a back taper portion so that the outer diameter gradually decreases from the tip surface toward the rear end side, and the length of the back taper portion in the axial direction is the tip blade portion. A drilling tool characterized by being shorter than the length in the axial direction.   The drilling tool according to claim 3, wherein a length of the chip discharge groove in the axial direction is shorter than a length of the back taper portion in the axial direction.   5. The drilling tool according to claim 3, wherein an outer diameter on the front end side of the shank portion is 0.02 mm or less smaller than an outer diameter on the rear end side of the back taper portion.   The hole cutting tool according to any one of claims 3 to 5, wherein the chip discharge groove has a U-shaped cross section perpendicular to the axis.   The outer peripheral surface includes a first land portion formed so as to be continuous with the cutting edge, a relief portion that is continuous with the rear side in the tool rotation direction of the first land and is retreated inward in the radial direction, and the tool rotation of the relief portion. The drilling tool according to any one of claims 3 to 6, further comprising a second land portion formed so as to be continuous to the rear side in the direction.

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