JP2009285783A - Boring method of nc machine tool - Google Patents

Abstract

Disclosed is a drilling method for an NC machine tool that prevents a gap between a shaft center of a prepared hole and a shaft center of a finished hole and prevents the remaining of the prepared hole from being left behind.
A workpiece gripped by a chuck body is formed with a rotary cutter that is movable toward a target position corresponding to a machining position of the workpiece, and then a spindle is used as a rotation center. In the hole drilling method of the NC machine tool 1 that forms the finished hole H2 of a predetermined size by turning the lower hole with the turning tool 26 while rotating the chuck body, the rotary cutter moved to the first target position is used to A first step of calculating a misalignment amount L between an axis of a prepared hole formed in one workpiece W1 and an axis of a finish hole formed in the first workpiece; And a second step of forming a pilot hole in the second workpiece W by moving the amount of misalignment calculated in the first step to a second target position obtained by adding the amount to the first target position.
[Selection] Figure 2

Description

  The present invention relates to a drilling method for an NC machine tool in which a finished hole having a predetermined size is formed by a rotary blade and a turning tool.

  For example, Patent Document 1 discloses a case where a workpiece is machined from the center of the workpiece to an arbitrary position in the Y-axis direction by turning the turret to perform machining that does not face the axis center. A method for correcting misalignment in the Y-axis direction of the turret tool post that stabilizes machining accuracy is disclosed.

  The Y-axis misalignment correction method disclosed in Patent Document 1 includes a main shaft that can be rotated and indexed, a turret that can be moved in the X-axis and the Z-axis, and a rotary tool that is provided in parallel at an eccentric position with respect to the pivot axis of the turret An NC lathe capable of Y-axis function by means of the turret swivel index and the axis orthogonal to the axis of the rotary tool axis, and drilling a hole in the center of the workpiece end surface with the turret rotary tool, The position of both ends of the hole diameter in the X-axis direction is measured using a measuring instrument that rotates the Y-axis direction of the workpiece 90 ° in the X-axis direction and outputs a touch signal in the + -2 direction passing through the turning center provided on the tool post. A displacement amount with respect to the machining origin is obtained from the hole center position obtained from the measured value, and this value is used as the Y-axis origin displacement amount.

  According to the Y-axis direction misalignment correction method of Patent Document 1, instead of a Y-axis moving device having a headstock or a tool post that is movable in the Y-axis direction, a contact in the + -2 direction is provided on the tool post. A touch sensor or measuring instrument capable of outputting a signal is used.

Further, in the above correction method, even when machining is performed at an arbitrary position in the Y-axis direction from the center of the workpiece, a special measuring device is not required, and the touch sensor or measuring instrument and the NC lathe NC By using the function, there is no need to provide a large Y-axis moving means.
Furthermore, according to the correction method described above, it is possible to easily perform misalignment correction in the Y-axis direction while the workpiece is mounted on the NC lathe, while suppressing an increase in the price of the NC lathe and improving the machining accuracy of the workpiece. Stabilization can be achieved.
Japanese Patent Publication No. 6-92060

  By the way, when forming a small-diameter deep hole in a workpiece (workpiece) by an NC machine tool such as an NC lathe, the workpiece is gripped by a chuck body attached to the spindle of the NC machine tool. . Next, for example, a prepared hole is formed in the workpiece by a rotary blade such as a drill.

  Thereafter, the inner surface of the prepared hole is turned by a turning tool such as a finishing tool while rotating the workpiece by rotating the spindle. Thereby, a finishing hole of a predetermined dimension is formed in the workpiece.

However, in the NC machine tool described above, the chuck and the workpiece receive a centrifugal force by rotating the workpiece. For this reason, even when a balancer is provided in the chuck body, a shift occurs between the central axis of the main shaft and the rotational center of gravity of the workpiece due to the influence of centrifugal force.
Therefore, when turning with the above-mentioned finishing tool etc., even though a pilot hole is formed on the extension of the central axis of the main shaft, the center axis of the main shaft and the rotational center of gravity of the workpiece Due to the misalignment, the shaft center of the lower hole and the shaft center of the finishing hole may be displaced.
As a result, the machining position of the prepared hole in the workpiece and the machining position of the finishing hole do not coincide with each other, and the remaining of the prepared hole may occur.

  The present invention has been proposed in view of such a situation, and it is possible to prevent a deviation between the shaft center of the pilot hole and the shaft center of the finishing hole, resulting in a leftover of the pilot hole. An object of the present invention is to provide a drilling method for an NC machine tool that can prevent this.

According to a first aspect of the present invention, there is provided a drilling method for an NC machine tool in which a plurality of workpieces are sequentially exchanged and gripped by a chuck body attached to a spindle, and the workpieces gripped by the chuck body are gripped. On the other hand, after forming a pilot hole with a rotary blade that can move toward a target position corresponding to the processing position of the workpiece, the lower end is rotated by the turning tool while rotating the chuck body about the main shaft. In a drilling method for an NC machine tool that forms a finished hole of a predetermined size by turning a hole, the shaft of the pilot hole formed in the first workpiece by the rotary blade moved to the first target position A first step of calculating a misalignment amount between a center and an axis of the finishing hole formed in the first workpiece; and the misalignment calculated by the first step with respect to the rotary blade. Amount Serial moved to the second target position obtained by adding the first target position, characterized in that it comprises a second step of forming the lower hole in the second workpiece, the.
According to the hole drilling method of the NC machine tool according to the invention of claim 1, the axis of the pilot hole formed in the first workpiece by the rotary blade moved to the first target position by the second step; The rotary cutter is moved to a second target position obtained by adding an amount of misalignment between the center of the finishing hole formed in the first workpiece and the first target position. Therefore, in the first aspect of the invention, the second target position of the rotary blade can be changed in accordance with the amount of misalignment.
According to the first aspect of the present invention, in the second step, the pilot hole is formed in the second workpiece by the rotary blade moved to the second target position. Thereby, the said pilot hole can be formed in the process position of the 2nd to-be-processed object which reflected the amount of misalignment.
Therefore, when forming a finishing hole in the second workpiece with a turning tool, the turning process is performed on the lower hole reflecting the above-mentioned misalignment amount. It is possible to prevent a deviation from occurring between the shaft center.
Thereby, the machining position of the prepared hole and the machining position of the finishing hole can be matched. For this reason, when the finishing hole is formed, it is possible to prevent the remaining of the lower hole from occurring.

The invention of claim 2 is the workpiece according to claim 1, wherein the first workpiece is a misalignment measuring workpiece having the same shape as the first workpiece, wherein the first step comprises: After forming the prepared hole in the workpiece for measuring the amount of misalignment by the rotary blade that has been gripped by the chuck body and moved to the first target position, Based on the amount of deflection of the dial gauge pointer while rotating the chuck body in a state where the finishing hole is formed by the turning tool and the dial gauge contact is in contact with the inner surface of the finishing hole. And measuring the amount of eccentricity between the lower hole and the finishing hole as the amount of misalignment.
According to the invention of claim 2, while forming the prepared hole with the rotary blade moved to the first target position for the workpiece for measuring the amount of misalignment having the same shape as the first workpiece, A finishing hole is formed by turning the lower hole. Thereby, it is possible to reproduce the state in which the prepared hole and the finished hole are formed on the first workpiece, respectively, on the workpiece for measuring the amount of misalignment.
According to the second aspect of the present invention, the workpiece for measuring the amount of misalignment is formed on the workpiece for measuring the amount of misalignment, and the dial gauge contact is brought into contact with the inner surface of the finish hole. Rotate the chuck body that is gripped. Thereby, the contact of a dial gauge can be contact | abutted over the perimeter of the inner surface of said finishing hole.
Furthermore, according to the invention of claim 2, the eccentric amount of the finishing hole with respect to the lower hole is measured as the above-mentioned misalignment amount based on the deflection amount of the dial gauge pointer. Thereby, the amount of misalignment (the amount of eccentricity of the finishing hole with respect to the lower hole) can be easily measured based on the amount of deflection of the pointer caused by the movement of the contact that contacts the entire inner surface of the finishing hole. .

According to a third aspect of the present invention, in the first or second aspect, the second step rotates the main shaft to change the eccentric direction of the finishing hole with respect to the lower hole formed by the first step. It is characterized by the step of making it correspond to the direction which a cutter can move.
According to the invention of claim 3, the rotating blade moves in the direction of the amount of misalignment added to the first target position by matching the eccentric direction of the finishing hole with respect to the lower hole to the direction in which the rotating blade can move. Possible directions can be set. As a result, the second target position obtained by adding the first target position to the amount of misalignment can be set to a position where the rotary blade can move.

According to the hole machining method of the NC machine tool of the present invention, the shaft center of the prepared hole formed in the first workpiece by the rotary blade moved to the first target position and the first workpiece are formed. The second target position of the rotary cutter can be changed in accordance with the amount of misalignment with the axis of the finished hole.
Further, according to the above hole machining method of the NC machine tool, the above-described drilling method moves the second workpiece to the machining position of the second workpiece reflecting the amount of misalignment by the rotary blade moved to the second target position. A pilot hole can be formed.
Therefore, when forming a finishing hole in the second workpiece with a turning tool, the turning process is performed on the lower hole reflecting the above-mentioned misalignment amount. It is possible to prevent a deviation from occurring between the shaft center.
Thereby, the machining position of the prepared hole and the machining position of the finishing hole can be matched. For this reason, when the finishing hole is formed, it is possible to prevent the remaining of the lower hole from occurring.

<Embodiment>
An embodiment of the present invention will be described with reference to FIGS. 1 and 2 are main part configuration diagrams of the horizontal NC lathe 1. FIG. FIG. 1A and FIG. 2A are main part plan views of a horizontal NC lathe 1. FIGS. 1B and 2B are front views of the main part of the horizontal NC lathe 1. The horizontal NC lathe 1 is an example of the NC machine tool of the present invention. The horizontal NC lathe 1 includes a spindle stock 4 and a tool post 23.

  A spindle 5 is provided on the spindle stock 4. The hydraulic chuck 10 is attached to the main shaft 5 via the face plate 3 by screws 2. The main shaft 5 can be rotationally indexed by, for example, a servo motor (not shown).

  The hydraulic chuck 10 includes mounting claws (not shown). The hydraulic chuck 10 grips the workpiece W (see FIGS. 1 and 2) with the mounting claws. Reference numeral 11 in the figure indicates a balancer. The hydraulic chuck 10 is an example of a chuck body according to the present invention, and is constituted by, for example, a commercially available index chuck.

  The tool post 23 can be moved in the X direction and the Z direction. The X direction is a direction perpendicular to the central axis of the main shaft 5. The Z direction is a direction parallel to the central axis of the main shaft 5.

  As shown in FIG. 1, the turret 20 is provided on the tool post 23 so as to be able to rotate and index around an axis parallel to the Z direction. A rotating tool holder 21 is attached to the outer periphery of the turret 20. The drill 22 faces the Z direction and is mounted on the rotary tool holder 22 in a rotatable state. The drill 22 is rotated by a motor (not shown). The drill 22 is an example of the rotary blade of the present invention.

  As shown in FIG. 2, a turning tool holder 25 is attached to the outer periphery of the turret 20 at a position different from the attachment position of the rotary tool holder 21 described above. A finishing tool 26 is attached to the turning tool holder 25. The finishing bit 26 is fixed to the turning tool holder 25 by screws 27. Similar to the drill 22 described above, the finishing bit 26 is positioned perpendicular to the upper surface of the rotary tool holder 22. The finishing bit 26 is an example of the turning tool of the present invention.

  Next, a drilling method for the horizontal NC lathe 1 will be described. In the horizontal NC lathe 1, when the spindle 5 is rotated in the direction C1 (see FIG. 2B) with the workpiece W held by the hydraulic chuck 10, as described above, the workpiece W is subjected to centrifugal force F ( (See FIG. 2B). As a result, a deviation occurs between the central axis (rotation center) of the main shaft 5 and the rotational center of gravity of the workpiece W.

  The eccentric distance L in FIG. 2B shows the amount of deviation. The eccentric distance L is a distance between the central axis of the main shaft 5 and the rotational center of gravity of the workpiece W in the Y direction (see FIG. 2B). The Y direction is a direction orthogonal to the X direction. The eccentric distance L is an example of the amount of misalignment of the present invention.

  In the present embodiment, the eccentric distance L is measured in advance using the eccentric distance measuring workpiece W1 shown in FIG. Measuring the eccentric distance L in advance is an example of the first step of the present invention. The shape of the work W1 for measuring the eccentric distance is the same as the shape of the work W. The eccentric distance measurement workpiece W1 is an example of a workpiece for measuring an eccentricity amount (first workpiece) according to the present invention.

  When measuring the eccentric distance L, the work piece W1 for measuring the eccentric distance is gripped by the hydraulic chuck 10 by the mounting claw (see FIG. 1A). At this time, the center line CL of the eccentric distance measuring workpiece W1 is made to coincide with the center axis of the main shaft 5. Thereafter, the tool post 23 is moved in the X direction toward the workpiece W1 for measuring the eccentric distance by the numerical controller of the horizontal NC lathe 1. As a result, the center axis of the drill 22 is aligned with the center axis of the main shaft 5 and the center line CL described above.

  Further, the tool post 23 is moved in the Z direction while the drill 22 is rotated by the numerical control device. Thereby, the drill 22 is advanced toward the workpiece W1. Thereafter, the drill 22 abuts against the end surface of the workpiece W1, and then drills a pilot hole H1 (see FIG. 1A) having a predetermined depth in the workpiece W1. Here, a pilot hole H1 having a hole diameter of Φ8.5 mm was drilled. In the present embodiment, the position where the drill 22 reaches the bottom of the lower hole H1 is an example of the first target position of the present invention.

  When the lower hole H1 is drilled in the workpiece W1, the main shaft 5 is not rotated. For this reason, the centrifugal force F is not generated, and no deviation occurs between the center axis (rotation center) of the main shaft 5 and the center of gravity of the workpiece W1. In addition, after the drilling of the pilot hole H1 is completed, the tool post 20 is returned to the initial setting position by a command from the numerical control device.

Thereafter, the turret 20 is turned, and the turning tool holder 25 is indexed to the tool post 23 instead of the rotating tool holder 21 (see FIG. 2A). Similar to the movement of the finishing bit 26 described above, the cutting edge of the finishing bit 26 is adjusted to the inner diameter of the prepared hole H1 of the workpiece W1 by the numerical control device. Subsequently, the hydraulic chuck 10 and the workpiece W1 are rotated by rotating the main shaft 5 by the servo motor. In the present embodiment, the rotational speed of the servo motor is set to 2500 min ⁻¹ .

  In a state where the workpiece W1 is rotated, the finishing bit 26 is advanced toward the workpiece W1 according to a command from the numerical controller. The finishing bit 26 turns the workpiece W1 up to a predetermined turning depth. As a result, a finish hole H2 (see FIG. 2A) is formed in the workpiece W1. Here, the finishing hole H2 having a hole diameter of Φ8.65 mm was formed.

  When turning the finishing hole H2 with respect to the workpiece W1, the rotational center of gravity of the workpiece W1 is moved away from the central axis of the main shaft 5 by the centrifugal force F (here, the Y direction, see FIG. 2B). Sneak away. For this reason, the finishing hole H2 is formed in the workpiece W1 in a state where the axial center of the finishing hole H2 is located at a position separated from the axial center of the lower hole H1 in the Y direction.

  Next, as shown in FIG. 3, a contact 31 of a lever type dial gauge 30 is brought into contact with the inner surface of the finishing hole H2. In this embodiment, the dial gauge 30 is fixed to a tool holder (not shown) attached to the turret 20 by the fixed arm 40. In FIG. 3, the hydraulic chuck 10 is not shown.

  Thereafter, the main shaft 5 is brought into a free state, and the main shaft 5 is manually rotated at a rotational speed lower than the rotational speed of the servo motor that rotates the main shaft 5. Thereby, said contactor 31 is made to contact | abut to the perimeter of the inner surface of finishing hole H2. When the contact 31 is brought into contact with the entire inner surface, the amount of deflection of the pointer of the dial gauge 30 is measured.

  In the present embodiment, a value obtained by dividing the measured shake amount by 2 is set as the value of the eccentric distance L. Here, the value of the eccentric distance L is 0.05 mm. The value of the eccentric distance L is an example of the amount of eccentricity of the present invention. The pointer is provided on the scale plate 32 of the dial gauge 30.

  When measuring the amount of deflection, the rotation angle of the spindle 5 is displayed on the monitor of the horizontal NC lathe 1. In the present embodiment, the rotation angle of the spindle 5 displayed on the monitor is measured when the shake amount shows the maximum value. Based on the measured rotation angle, the eccentric direction (here, the Y direction) of the finishing hole H2 with respect to the pilot hole H1 can be specified.

  The operation when forming the prepared hole H1 and the finishing hole H2 in the workpiece W after reflecting the data of the eccentric distance L and the data of the rotation angle will be described below. When the lower hole H1 and the finishing hole H2 are formed, the numerical control device stores the data of the eccentric distance L and the data of the rotation angle. The hydraulic chuck 10 grips the workpiece W (see FIG. 1A) instead of the eccentric distance measuring workpiece W1. The workpiece W is an example of a second workpiece of the present invention.

  Thereafter, based on the rotation angle data, the spindle 5 is rotationally indexed in the C1 direction by a command from the numerical controller (see FIG. 4). Here, the workpiece W is rotated 90 degrees in the C1 direction by the rotation index of the main shaft 5. Thereby, the eccentric direction (Y direction) measured using said workpiece | work W1 is located in a X direction (refer FIG. 4). Rotating the spindle 5 to rotate the workpiece W by 90 degrees in the C1 direction is an example of the second step of the present invention.

  Next, the tool post 23 is moved in the X direction toward the workpiece W based on a command from the numerical controller based on the data of the eccentric distance L. Here, the center axis of the drill 22 is aligned with the position away from the center axis of the main shaft 5 by an eccentric distance L in the right direction in FIG.

  Further, the drill 22 is advanced toward the workpiece W according to a command from the numerical control device. Thereafter, the pilot hole H1 is drilled in the workpiece W in the same manner as the drilling process for the workpiece W1 described above. In the present embodiment, the position at which the drill 22 has reached the bottom of the pilot hole H1 by a command from the numerical controller based on the data on the eccentric distance L is an example of the second target position of the present invention.

  Subsequently, the hydraulic chuck 10 and the workpiece W are rotated as in the case where the finishing hole H2 is formed in the workpiece W1. At this time, the rotational center of gravity of the workpiece W coincides with the axis of the pilot hole H1 due to the centrifugal force applied to the workpiece W and the chuck body 10.

  In the state where the rotational center of gravity of the workpiece W coincides with the axis of the lower hole H1, the finishing bit 26 is advanced toward the workpiece W as in the case where the finishing hole H2 is formed in the workpiece W1 described above. As a result, the finishing hole H2 can be turned with respect to the workpiece W in a state where the axis of the lower hole H1 and the center axis of the finishing bit 26 coincide. Therefore, the axis of the lower hole H1 coincides with the axis of the finishing hole H2. For this reason, when turning with the finishing bit 26, the axis of the lower hole H1 and the axis of the finishing hole H2 are arranged on the same line.

  In the present embodiment, the finishing hole H2 is formed at a position away from the center line of the workpiece W by the eccentric distance L by the above-described hole machining method. The center line of the workpiece W is the same as the center line CL of the workpiece W1. In the present embodiment, the value of the eccentric distance L is 0.05 mm. Here, since the value of the eccentric distance L is relatively small, the position of the finishing hole H2 formed in the workpiece W is within the allowable range defined by the product standard.

<Operation and effect of this embodiment>
In the horizontal NC lathe 1 described above, the center axis of the drill 22 is aligned at a position separated from the center axis of the main shaft 5 by the eccentric distance L in accordance with a command from the numerical controller. For this reason, according to the value of the eccentric distance L, the movement destination of the center axis line of the drill 22 can be changed.

Further, in the horizontal NC lathe 1, after aligning the center axis of the drill 22 at a position separated from the center axis of the main shaft 5 by the eccentric distance L, the drill 22 drills a pilot hole H 1 in the work W. Thereby, the pilot hole H1 can be drilled at the machining position of the workpiece W reflecting the value of the eccentric distance L.
In the horizontal NC lathe 1, when the finishing hole H2 is formed by the finishing bit 26, the turning process is performed on the lower hole H1 drilled at the position reflecting the value of the eccentric distance L. It is possible to prevent a deviation from occurring between the shaft center and the shaft center of the finishing hole H2.
Thereby, the position where the lower hole H1 is drilled in the workpiece W can be matched with the position where the finishing hole H2 is turned in the workpiece W. For this reason, when forming the finishing hole H2 in the workpiece | work W, it can prevent that the lower hole H1 remains.

  In the horizontal NC lathe 1, the center axis of the drill 22 is aligned with the center axis of the main shaft 5 and the center line CL of the eccentric distance measuring work W 1, and then the drill 22 forms the prepared hole H 1 in the eccentric distance measuring work W 1. Perforate. In addition, the finishing hole H2 is formed by turning the lower hole H1 with the finishing bit 26. Thereby, also with respect to the workpiece W1 for measuring the eccentric distance having the same shape as the workpiece W, it is possible to reproduce the state of drilling the pilot hole H1 and the state of forming the finishing hole H2 respectively.

  Further, in the horizontal NC lathe 1, the value obtained by dividing the deflection amount of the pointer of the dial gauge 30 by 2 is set as the value of the eccentric distance L. Accordingly, the value of the eccentric distance L is easily calculated based on the amount of deflection of the pointer according to the movement of the contact 31 that is in contact with the inner peripheral surface of the finishing hole H2, regardless of the shape of the finishing hole H2. be able to.

  In the horizontal NC lathe 1, the eccentric direction (Y direction in FIG. 2) of the finishing hole H2 with respect to the lower hole H1 is made to coincide with the X direction (see FIG. 4) by rotational indexing of the main shaft 5. The X direction is a direction in which the tool post 23 to which the drill 22 is attached can move. In the horizontal NC lathe 1, the direction away from the center axis of the main shaft 5 by the eccentric distance L can be set to a direction in which the drill 22 can move by matching the eccentric direction (Y direction) with the X direction. it can.

  The present invention is not limited to the embodiment described above, and can be implemented by appropriately changing a part of the configuration without departing from the spirit of the invention. The eccentric distance measuring workpiece W1 is not limited to the shape illustrated in FIG. 3, and may have various shapes corresponding to the workpiece W.

  In the horizontal NC lathe 1 described above, the finishing bit 26 is used as a turning tool. However, other tools such as an end mill may be used instead of the finishing bit 26.

  Further, in the horizontal NC lathe 1 described above, the center axis of the drill 22 is aligned with the eccentric distance L from the center axis of the main shaft 5 in the X direction by the rotation index of the main shaft 5 described above. By moving the table 20 in the Y direction, the center axis of the drill 22 may be aligned with the position away from the center axis of the main shaft 5 by the eccentric distance L in the Y direction.

It is explanatory drawing of the operation | movement which forms a pilot hole with the horizontal NC lathe of embodiment of this invention. It is explanatory drawing of the operation | movement which forms a finishing hole with the horizontal NC lathe. It is explanatory drawing of the operation | movement which measures the deflection amount of the dial gauge pointer in the horizontal NC lathe. It is explanatory drawing of the operation | movement which carries out rotation indexing of the main axis | shaft in the horizontal NC lathe.

Explanation of symbols

  1 .... Horizontal NC lathe, 5 .... Spindle, 10 .... Hydraulic chuck, 22 .... Drill, 26 ... Finishing tool, 30 ... Dial gauge, 31 ... Contact, H1, ... Pre-hole, H2 .... Finishing hole, L · · Eccentric distance, W ··· Work, W1 ·· Eccentric distance measuring workpiece, Y ··· Eccentric direction

Claims (3)

A plurality of workpieces are sequentially exchanged and gripped by the chuck body attached to the spindle, and the workpieces gripped by the chuck body are brought into a target position corresponding to the machining position of the workpiece. An NC that forms a prepared hole with a predetermined dimension by turning the lower hole with a turning tool while rotating the chuck body about the main shaft as a rotation center after forming a prepared hole with a rotary cutter that can move toward the center. In the drilling method for machine tools,
A center between an axis of the lower hole formed in the first workpiece by the rotary blade moved to the first target position and an axis of the finishing hole formed in the first workpiece. A first step of calculating a deviation amount;
A second step of forming the prepared hole in a second workpiece by moving the rotary cutter to a second target position obtained by adding the amount of misalignment calculated in the first step to the first target position; When,
A drilling method for an NC machine tool, comprising: The first workpiece is a workpiece for measuring the amount of misalignment having the same shape as the first workpiece,
The first step includes
After forming the prepared hole in the workpiece for measuring the amount of misalignment by the rotary blade that has been gripped by the chuck body and moved to the first target position, Forming the finishing hole with the turning tool;
While rotating the chuck body with the dial gauge contact abutting against the inner surface of the finishing hole, based on the amount of deflection of the dial gauge pointer, as the amount of misalignment, the lower hole and the Measuring the amount of eccentricity between the finished holes;
The drilling method for an NC machine tool according to claim 1, comprising: The second step includes
2. The method according to claim 1, further comprising the step of causing the eccentric direction of the finishing hole with respect to the lower hole formed by the first step to coincide with a direction in which the rotary blade can move by rotating the main shaft. Or the drilling method of NC machine tool of 2 or 2.

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