JP2010228067A - Grinding of tapered hole - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To facilitate a centering for aligning a grinding tool with a cylindrical hole when a part of the cylindrical hole is ground to a tapered hole. <P>SOLUTION: A hone tool 14 enabling the grinding diameter of a grinding tool 34 therearound to be increased or decreased is attached to a spindle 11 which is rotatable and longitudinally movable in the axial direction through a joint 13 allowed to be eccentric while a drive shaft 16 and a driven shaft 17 are positioned parallel to each other. A workpiece 1 is affixed to the hone tool in the advancing direction, and the cylindrical hole 2 of the workpiece is disposed parallel to the hone tool. The hone tool is inserted into the cylindrical hole by moving forward, increased in diameter to bring the magnet into contact with the inner surface of the cylindrical hole, and centered. Next, the hone tool is moved backward while rotating in the cylindrical hole, gradually increased in grinding diameter while moving backward, and grinds the opening side portion of the cylindrical hole to a tapered hole 3. Also, the hone tool is increased in grinding diameter by an amount of removal in the next forward grinding step after the backward grinding step, moves forward while rotating, gradually reduced in grinding diameter while moving forward, and further grinds the tapered hole to a tapered shape. The backward grinding step and the forward grinding step of the hone tool are alternately performed repeatedly. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a technique for grinding a tapered hole into a part of a cylindrical hole.

  As shown in FIG. 1, the cylindrical hole 2 machined into the workpiece 1 may be ground into a concentric tapered hole 3 at the opening side portion at one end. The diameter of the tapered hole 3 gradually increases as it approaches the opening. The taper angle is small, and the conical inner surface is a gentle slope. For example, the taper hole 3 has a length of several tens of millimeters in the axial direction and a minimum diameter at the back end, that is, a diameter of the cylindrical hole 2 of several tens of millimeters. The small diameter difference is several tens of μm.

  A machine tool that grinds a tapered hole to an opening side portion of a cylindrical hole has a tapered grindstone mounted concentrically on the lower end of a main shaft that is provided vertically. A workpiece is fixed below the tapered grindstone, and a cylindrical hole of the workpiece is disposed concentrically with the tapered grindstone. The main shaft descends while rotating. The tapered tapered grindstone enters the cylindrical hole of the workpiece from the upper end opening while rotating. The cylindrical hole of the workpiece becomes a tapered hole by grinding the upper portion with a tapered grindstone.

  Patent Document 1 discloses a technique for concentrating a hole with a chamfered surface, that is, a conical surface of a steep slope, in a method for chamfering a start end of a hole. The conical whetstone has a guide pin concentrically connected to the tip. The guide pin has a groove for lubricating oil formed in the axial direction on the circumferential surface of the round bar. At the time of grinding, the rotating conical grindstone is pressed against the starting end of the hole with the rotating lubricating groove guide pin fitted in the hole.

Japanese Patent No. 2668213

[Task]
In the above case where the tapered hole is ground into a part of the cylindrical hole, the tapered hole and the conical inner surface are unlikely to be concentric with the cylindrical hole and the cylindrical inner surface.

  In a machine tool, it is difficult to align the center axis of the cylindrical hole of the workpiece with the center axis of the tapered grindstone. The operator recognizes the amount of eccentricity of the cylindrical hole of the workpiece and the tapered grindstone fixed to the lower side of the tapered grindstone, moves the workpiece, and adjusts the fixed position of the workpiece by a minute distance in units of μm. It takes a lot of work.

In the chamfering method of Patent Document 1, the conical inner surface of the chamfered surface may not be concentric with the cylindrical inner surface of the hole.
The hole and the guide pin fitted to the hole have a gap between them, and can be eccentric by the gap. Further, the guide pin connected to the conical whetstone may not be concentric with the conical whetstone due to manufacturing errors.

[Idea]
In grinding the tapered hole, it was decided to perform honing using a horn tool. The horn tool makes it possible to enlarge the diameter of the holder and holds the grindstone around the outer periphery of the holder. When the diameter of the holder is increased, the diameter of the grindstone around the outer periphery is increased and the grinding diameter is increased. When the diameter of the holder is reduced, the diameter of the grindstone around the outer periphery is reduced and the grinding diameter is reduced.

  This horn tool is arranged in parallel with the cylindrical hole of the workpiece and is moved in any direction in the radial direction. While maintaining this eccentric state, it is inserted into the cylindrical hole of the workpiece to increase the diameter. Then, the grindstone around the outer periphery of the horn tool hits the inner surface of the cylindrical hole and becomes concentric with the cylindrical hole. The grinding wheel of the rotating horn tool is concentric with the cylindrical hole or the taper hole while being ground in contact with the inner surface of the cylindrical hole or the taper hole. Automatic centering.

  Therefore, when the horn tool is mounted on the main shaft of the machine tool, the driving shaft and the driven shaft move in any radial direction while being parallel, that is, an eccentric joint is interposed. The joint connects the driving shaft to the main shaft of the machine tool and the driven shaft to the horn tool. Examples of the joint that can be eccentric while the driving shaft and the driven shaft are parallel include an Oldham joint that sandwiches a floating plate that moves in any radial direction between the driving shaft and the driven shaft.

  Then, the horn tool moves forward and is inserted into the cylindrical hole of the workpiece, the diameter is enlarged, and the grindstone is applied to the inner surface of the cylindrical hole so as to be concentric with the cylindrical hole. Next, the horn tool moves backward in the extraction direction while rotating in the cylindrical hole, and gradually increases the grinding diameter while moving backward. Then, the opening side portion of the cylindrical hole is ground into the tapered hole.

  When the taper hole does not reach the finished dimension in this backward grinding process, the horn tool increases the grinding diameter by the machining allowance of the next forward grinding process, reverses the moving direction, advances in the insertion direction while rotating, advances However, the grinding diameter is gradually reduced. Then, the tapered hole on the opening side of the cylindrical hole is further ground into a tapered shape.

The reverse grinding process and forward grinding process of the horn tool are alternately repeated until the tapered hole reaches the finished size.
The cylindrical hole of the workpiece and the horn tool in the cylindrical hole have a centering action, and the tapered hole on the opening side of the cylindrical hole tends to be concentric with the cylindrical hole.

1) A horn tool capable of increasing / decreasing the grinding diameter of the grinding wheel on the outer periphery is mounted on a main shaft that can rotate and move back and forth in the axial direction via a joint that can be eccentrically moved while the driving shaft and the driven shaft are parallel, Fix the workpiece in the forward direction of the horn tool, place the cylindrical hole of the workpiece parallel to the horn tool,
The horn tool is advanced and inserted into the cylindrical hole of the workpiece, the diameter is enlarged, the grindstone is applied to the inner surface of the cylindrical hole, centered, then moved backward while rotating in the cylindrical hole, while moving backward A method of grinding a tapered hole, characterized by gradually increasing a grinding diameter and grinding an opening side portion of the cylindrical hole into a tapered hole.
2) In the above taper hole grinding method,
After the reverse grinding process, the horn tool increases the grinding diameter by the allowance of the next forward grinding process, advances while rotating, gradually reduces the grinding diameter while moving forward, and forms a tapered hole on the opening side of the cylindrical hole. Further, it is characterized by grinding in a taper shape.
3) In the method for grinding a tapered hole of 2) above,
The reverse grinding process and the forward grinding process of the horn tool are alternately repeated.

4) A machine tool for grinding an opening side portion of a cylindrical hole of a workpiece into a tapered hole,
The main shaft is rotatable and can be moved back and forth in the axial direction, and a horn tool that can increase or decrease the grinding diameter of the grinding wheel on the outer circumference is mounted via a joint that can be eccentrically moved while the driving shaft and driven shaft are parallel,
A control device is provided to detect the front / rear position of the main shaft and stop the main shaft during forward or reverse movement at the set position,
In the forward direction of the horn tool, a workpiece attachment mechanism is provided that fixes the workpiece and arranges the cylindrical hole of the workpiece in parallel with the horn tool,
The horn tool moves forward and enters the cylindrical hole of the workpiece, expands the grinding diameter to center, and gradually increases the grinding diameter while moving backward to grind the opening side portion of the cylindrical hole into a tapered hole. A taper hole grinding apparatus characterized by the above.
5) In the taper hole grinding apparatus of 4) above,
After the reverse grinding process, the horn tool increases the grinding diameter by the allowance of the next forward grinding process, advances while rotating, gradually reduces the grinding diameter while moving forward, and forms a tapered hole on the opening side of the cylindrical hole. Further, it is characterized in that it is configured to be ground in a tapered shape.

  The cylindrical hole of the workpiece and the horn tool in the cylindrical hole have a centering action. The tapered hole on the opening side of the cylindrical hole tends to be concentric with the cylindrical hole. A lot of time and effort is not required for centering.

The workpiece which processed the cylindrical hole with a taper hole in the embodiment of the present invention is shown, the upper part is a top view and the lower part is a longitudinal side view. The partial longitudinal section side view of the taper hole grinding device in the embodiment of the present invention. The longitudinal side view of the eccentric joint of the grinding device. AA line sectional view of FIG. The side view of the horn tool of the grinding device. FIG. 6 is an enlarged cross-sectional view taken along line BB in FIG. 5. The partially vertical side view which shows the centering state of the horn tool of the grinding device and the cylindrical hole of a workpiece. The partially vertical side view which shows the completion | finish state of the reverse grinding process of the horn tool of the grinding device. The partial vertical side view which shows the next machining allowance increase state of the grinding diameter of the horn tool of the grinding device. The partially vertical side view which shows the completion | finish state of the forward grinding process of the horn tool of the grinding device.

  The workpiece 1 of the embodiment shows a form after the opening side portion of the cylindrical hole 2 is ground into the tapered hole 3, and the form before grinding is shown in FIG. The workpiece 1 before grinding passes through a cylindrical hole 2 having a uniform diameter in the vertical direction. The cylindrical hole 2 grinds the opening side portion at the upper end into a concentric tapered hole 3. The diameter of the tapered hole 3 gradually increases as it approaches the opening. The taper angle is small, and the conical inner surface is a gentle slope.

  In the embodiment, the taper hole 3 has a length in the axial direction of several tens of millimeters and a minimum diameter at the back end, that is, a diameter of the cylindrical hole 2 of several tens of millimeters. The difference in minimum diameter is several tens of μm.

  As shown in FIG. 2, the tapered hole grinding apparatus of the embodiment has a spindle body 7, a workpiece attachment mechanism 8, and a grinding diameter increasing / decreasing mechanism 9 attached to a vertical type body 6 in three stages.

  Although not shown, the upper spindle head 7 of the machine body 6 can be reciprocated in the vertical direction by a mechanism of a ball screw shaft and a nut, and the ball screw shaft is connected to an electric servo motor. The electric servo motor is connected to the control device. The spindle head 7 is lowered by the forward rotation drive of the electric servo motor, and is raised by the reverse rotation drive. Move forward and move backward. The forward speed and reverse speed of the spindle head 7 are set by adjusting the forward rotation speed and the reverse rotation speed of the electric servo motor, respectively. The vertical position of the spindle head 7 is detected, and the spindle head 7 moving forward or backward is stopped at the set position.

  The spindle head 7 is rotatably attached so as to penetrate the spindle 11 in the vertical direction. An electric motor 12 attached to the upper surface of the spindle head 7 is connected to the upper end of the spindle 11. The electric motor 12 is connected to the control device. The main shaft 11 is rotated by the rotational drive of the electric motor 12. A horn tool 14 is attached to the lower end of the main shaft 11 via a joint 13. The joint 13 is free to be eccentric while the driving shaft 16 and the driven shaft 19 are parallel. The upper driving shaft 16 of the joint 13 is connected to the main shaft 11 and the lower driven shaft 19 is connected to the horn tool 14 concentrically. The horn tool 14 can increase or decrease the grinding diameter of the grindstone around the outer periphery of the holder. The horn tool 14 has a central axis in the vertical direction and is parallel to the main shaft 11. Further, it is arranged concentrically with the main shaft 11.

  The eccentric joint 13 is shown in detail in FIGS. The driving shaft 16 is provided with an end plate portion 17 on the outer periphery of the front end of the cylindrical shaft portion, and a large-diameter cylindrical portion 18 is provided on the outer periphery of the end plate portion 17 so as to protrude forward. The driven shaft 19 is provided with an end plate portion 20 at the rear end of the cylindrical shaft portion. The rear end side of the driven shaft 19 is inserted into the large-diameter cylindrical portion 18 of the driving shaft 16. The end plate portion 17 of the driving shaft 16 and the end plate portion 20 of the driven shaft 19 face each other in parallel.

  A floating plate 21 is disposed between the both end plate portions 17 and 20. The disc-shaped floating plate 21 has a plurality of through holes 22 arranged at equal intervals around the center. In each through hole 22, a spacing ball 23 having a diameter larger than the thickness of the floating plate 21 is rotatably fitted. Each interval holding ball 23 has a rear end applied to the end plate portion 17 of the driving shaft and a front end applied to the end plate portion 20 of the driven shaft, and the interval between the both end plate portions 17 and 20 is maintained wider than the thickness of the floating plate 21. Yes. The floating plate 21 is allowed to float between both end plate portions 17 and 20.

  The floating plate 21 is provided with a pair of driven grooves 24 along the radial direction at opposing positions across the center. The end plate portion 17 of the driving shaft is provided with a pair of driving roller pins 25 projecting forward at opposing positions across the center. The pair of driving roller-equipped pins 25 is inserted into the pair of driven grooves 24. The floating plate 21 is movable in the radial direction along the pair of driven grooves 24 with respect to the end plate portion 17 of the driving shaft.

  Further, the floating plate 21 is provided with a pair of driving grooves 26 along the radial direction at opposing positions sandwiching the center. The end plate portion 20 of the driven shaft is provided with a pair of driven roller-attached pins 27 protruding rearward at opposing positions sandwiching the center. The pair of driven roller-equipped pins 27 are inserted into the pair of driving grooves 26. The floating plate 21 is movable in the radial direction along the pair of driving grooves 26 with respect to the end plate portion 20 of the driven shaft. The radial direction along the pair of driving grooves 26 is orthogonal to the radial direction along the pair of driven grooves 24.

  The large-diameter cylindrical portion 18 of the driving shaft is fixed by screwing a retaining ring 28 into the opening at the front end. An annular plate-shaped thrust bearing 29 is interposed between the retaining ring 28 and the end plate portion 20 of the driven shaft. The end plate portion 17 of the driving shaft, the floating plate 21 and the end plate portion 20 of the driven shaft are parallel to each other. The cylindrical shaft portion of the driving shaft 16 and the cylindrical shaft portion of the driven shaft 19 are parallel to the central axis. The driven shaft 19 can move in the radial direction while remaining parallel to the driving shaft 16. It can be translated. Although it can move in any direction in the radial direction, it cannot move in the central axis direction. When the driven shaft 19 receives a radial force, the driven shaft 19 translates in the radial direction and is eccentric while remaining parallel to the driving shaft 16.

  When the driving shaft 16 is rotated, the floating plate 21 rotates through a pair of driving roller pins 25 and a pair of driven grooves 24, and through a pair of driving grooves 26 and a pair of driven roller pins 27. The driven shaft 19 rotates. Even if the driven shaft 19 is eccentric from the driving shaft 16, the driving shaft 16 transmits rotation to the driven shaft 19 in an eccentric state.

  The cylindrical shaft portion of the driven shaft 19 is fixed by fitting the cover plate 30 around the outer periphery. The cover plate 30 closes the gap between the cylindrical shaft portion of the driven shaft 19 and the retaining ring 28.

  The details of the horn tool 14 are shown in FIGS. The holder 31 has a central hole 32 formed concentrically at the end portion of the round shaft. The center hole 32 opens at the end face of the holder 31 and gradually increases in diameter as it approaches the opening. Tapered hole. The central hole 32 forming portion and the cylindrical portion of the holder 31 are provided with a plurality of split grooves 33 on the peripheral wall along the central axis direction and arranged at equal intervals in the circumferential direction. The cylindrical portion of the holder 31 is equally divided into a plurality of rod-shaped pieces. A rod-shaped grindstone 34 is attached to the outer peripheral surface of each rod-shaped piece along the central axis direction. The plurality of grindstones 34 are arranged at equal intervals in the circumferential direction. Each bar-shaped piece with the grindstone 34 is a cantilever elastic beam. When it receives an outward force, it bends outward, and when the force is lost, it recovers. When the cylindrical portion with the grindstone 34 of the holder 31 receives an outward force, the outer diameter increases and the grinding diameter increases, and when the force disappears, the outer diameter decreases and the grinding diameter decreases.

  Moreover, the cylindrical part with the grindstone 34 of the holder 31 gradually decreases the outer diameter of the opening side portion as it approaches the opening. The opening side portion is tapered.

  The diameter increasing / decreasing rod 35 gradually decreases the diameter of the round shaft as it approaches the end. Tapered taper bar. When the diameter increasing / decreasing bar 35 is inserted into the cylindrical portion of the holder 31 with the grindstone 34, the grinding diameter increases. As the insertion distance of the diameter increasing / decreasing rod 35 increases, the grinding diameter gradually increases. As the insertion distance of the diameter increasing / decreasing rod 35 decreases, the grinding diameter gradually decreases.

  As shown in FIG. 2, the workpiece attachment mechanism 8 at the middle stage of the machine body 6 has a table-like attachment board 41 attached horizontally to the machine body 6. The mounting board 41 has a through hole 42 at a position directly below the main shaft 11. On the upper surface of the mounting plate 41, the workpiece 1 is fixed by a fixture 43, the cylindrical hole 2 of the workpiece 1 is communicated with the through hole 42, and the spindle 11 and the horn tool 14 are parallel to the position immediately below the spindle 11. To place.

  The grinding diameter increasing / decreasing mechanism 9 in the lower stage of the machine body 6 has a bearing body 46 attached to the machine body 6 as shown in FIG. Although not shown, the bearing body 46 can be reciprocated in the vertical direction by a mechanism of a ball screw shaft and a nut, and the ball screw shaft is connected to an electric servo motor. The electric servo motor is connected to the control device. The bearing body 46 is raised by the forward drive of the electric servo motor and lowered by the reverse drive. Move forward and move backward. The forward speed and the reverse speed of the bearing body 46 are respectively set by adjusting the forward rotation speed and the reverse rotation speed of the electric servo motor. The vertical position of the bearing body 46 is detected, and the bearing body 46 that is moving forward or backward is stopped at the set position.

  As shown in FIG. 2, a bearing shaft 47 is rotatably attached to the bearing body 46 so as to penetrate in the vertical direction. A diameter increasing / decreasing rod 35 is attached to the upper end of the receiving shaft 47 via a joint 48. The joint 48 can be eccentric while the upper and lower shafts 49 and 50 are parallel. The first shaft 49 on the upper side of the joint 48 is connected to the diameter increasing / decreasing rod 35 and the second shaft 50 on the lower side is connected to the receiving shaft 47 concentrically. The diameter increasing / decreasing bar 35 has a central axis in the vertical direction and parallel to the horn tool 14. Further, it is arranged concentrically with the main shaft 11.

  The eccentric joint 48 has the same structure as the eccentric joint 13 for the horn tool 14. The first shaft 49 corresponds to the driven shaft 19 of the joint 13 for the horn tool 14, and the second shaft 50 corresponds to the driving shaft 16 of the joint 13. When the first shaft 49 rotates, the second shaft 50 follows and rotates. Even if the first shaft 49 is eccentric from the second shaft 50, the rotation of the second shaft 50 continues in an eccentric state.

  When the tapered hole is ground by this grinding apparatus, as shown in FIG. 2, the workpiece 1 is fixed to the workpiece mounting mechanism 8, and the cylindrical hole 2 of the workpiece 1 is positioned directly below the spindle 11 with the horn tool 14 Placed in parallel.

  Operate the grinding machine and activate the controller. Then, the spindle head 7 moves downward to the set position. As shown in FIG. 7, the horn tool 14 enters the cylindrical hole 2 of the workpiece 1 and is fitted to the centering position in the cylindrical hole 2. On the other hand, the grinding diameter increasing / decreasing mechanism 9 advances and advances. As shown in FIG. 7, the diameter increasing / decreasing rod 35 enters the horn tool 14 in the cylindrical hole 2 and is fitted to the centering position in the horn tool 14. In the horn tool 14, the grinding diameter is increased by inserting the diameter increasing / decreasing rod 35, and the outer peripheral grinding stone 34 hits the inner surface of the cylindrical hole 2. Then, when the horn tool 14 is eccentric with the cylindrical hole 2, the horn tool 14 moves parallel to the radial direction and becomes concentric with the cylindrical hole 2. Centering is done.

  Next, the main shaft 11 rotates. The spindle head 7 reverses the direction of movement and moves backward to the set position. As shown in FIG. 8, the horn tool 14 moves backward while rotating. On the other hand, the grinding diameter increasing / decreasing mechanism 9 further advances and advances to the set position. As shown in FIG. 8, the diameter increasing / decreasing rod 35 advances while being driven and rotated in a state of being fitted to the horn tool 14. At this time, the ascending forward speed of the diameter increasing / decreasing rod 35 is set higher than the ascending backward speed of the horn tool 14. The forward / backward diameter increasing / decreasing rod 35 gradually increases the insertion distance to the backward traveling horn tool 14. The rotating horn tool 14 gradually increases the grinding diameter while moving backward. Then, the opening side portion of the cylindrical hole 2 is ground into the tapered hole 3. The horn tool 14 has a centering action even during grinding. The tapered hole 3 is concentric with the cylindrical hole 2.

  When the taper hole 3 does not reach the finished dimension in the reverse grinding process of the horn tool 14, the horn tool 14 stops reverse and the diameter increasing / decreasing rod 35 further advances as shown in FIG. The diameter increasing / decreasing rod 35 increases the insertion distance to the horn tool 14. The horn tool 14 increases the grinding diameter by the allowance for the next forward grinding process.

  Thereafter, as shown in FIG. 10, the horn tool 14 reverses the moving direction and advances while rotating in the cylindrical hole 2. On the other hand, the diameter increasing / decreasing rod 35 moves backward in a state of being fitted to the horn tool 14 in the cylindrical hole 2. At this time, the reverse speed of the diameter increasing / decreasing rod 35 is set higher than the forward speed of the horn tool 14. The reverse diameter increasing / decreasing rod 35 gradually reduces the insertion distance to the forwardly moving horn tool 14. The rotating horn tool 14 gradually decreases the grinding diameter while moving forward. Then, the tapered hole 3 on the opening side of the cylindrical hole 2 is further ground into a tapered shape.

  The reverse grinding process and the forward grinding process of the horn tool 14 are alternately repeated until the tapered hole 3 reaches the finished size.

[Modification]
1) In the above embodiment, the mechanism for increasing / decreasing the grinding diameter of the horn tool 14 is performed by inserting / removing the diameter increasing / decreasing rod 35. However, the mechanism is performed by air pressure, oil pressure or spring force.
2) In the above embodiment, the grinding device is a vertical type in which the horn tool 14 advances and moves backward in the vertical direction, but is a horizontal type in which the horn tool 14 advances and moves backward in the horizontal direction.

DESCRIPTION OF SYMBOLS 1 Workpiece 2 Cylindrical hole 3 Tapered hole 6 Machine body 7 Spindle head 8 Workpiece mounting mechanism 9 Grinding diameter increase / decrease mechanism 11 Spindle 12 Electric motor 13 Eccentric joint 14 for horn tool Horn tool 16 Driving shaft 17 for eccentric joint End plate 18 of shaft 18 Large-diameter cylindrical portion of drive shaft 19 Drive shaft 20 of eccentric joint End plate portion 21 of driven shaft Floating plate 22 of eccentric joint 25 Through hole 23 Spacing ball 24 A pair of driven grooves 25 A pair of driving roller pins 26 A pair of driving grooves 27 A pair of driven roller pins 28 A retaining ring 29 A thrust bearing 30 A cover plate 31 A horn tool holder 32 A central hole, a taper hole 33 A split groove 34 A rod-shaped grindstone 35 Diameter increase / decrease rod 41 Workpiece mounting mechanism mounting plate 42 Through hole 43 Mounting tool 46 Grinding diameter increasing / decreasing mechanism bearing body 47 Bearing shaft 48 Eccentric free joint 49 for grinding diameter increasing / decreasing mechanism First shaft 50 2-axis

Claims (5)

A horn tool that can be rotated and moved back and forth in the axial direction is mounted on a horn tool that can increase or decrease the grinding diameter of the grinding wheel on the outer periphery via a joint that can be eccentrically moved while the driving shaft and driven shaft are parallel. The work piece is fixed in the forward direction, and the cylindrical hole of the work piece is arranged parallel to the horn tool.
The horn tool is advanced and inserted into the cylindrical hole of the workpiece, the diameter is enlarged, the grindstone is applied to the inner surface of the cylindrical hole, centered, then moved backward while rotating in the cylindrical hole, while moving backward A method of grinding a tapered hole, characterized by gradually increasing a grinding diameter and grinding an opening side portion of the cylindrical hole into a tapered hole.   After the reverse grinding process, the horn tool increases the grinding diameter by the allowance of the next forward grinding process, advances while rotating, gradually reduces the grinding diameter while moving forward, and forms a tapered hole on the opening side of the cylindrical hole. 2. The method for grinding a tapered hole according to claim 1, further comprising grinding in a tapered shape.   The method of grinding a tapered hole according to claim 2, wherein the backward grinding step and the forward grinding step of the horn tool are alternately repeated. A machine tool that grinds an opening side portion of a cylindrical hole of a workpiece into a tapered hole,
The main shaft is rotatable and can be moved back and forth in the axial direction, and a horn tool that can increase or decrease the grinding diameter of the grinding wheel on the outer circumference is mounted via a joint that can be eccentrically moved while the driving shaft and driven shaft are parallel,
A control device is provided to detect the front / rear position of the main shaft and stop the main shaft during forward or reverse movement at the set position,
In the forward direction of the horn tool, a workpiece attachment mechanism is provided that fixes the workpiece and arranges the cylindrical hole of the workpiece in parallel with the horn tool,
The horn tool moves forward and enters the cylindrical hole of the workpiece, expands the grinding diameter to center, and gradually increases the grinding diameter while moving backward to grind the opening side portion of the cylindrical hole into a tapered hole. A taper hole grinding apparatus characterized by the above.   After the reverse grinding process, the horn tool increases the grinding diameter by the allowance of the next forward grinding process, advances while rotating, gradually reduces the grinding diameter while moving forward, and forms a tapered hole on the opening side of the cylindrical hole. 5. The taper hole grinding apparatus according to claim 4, wherein the taper hole is further ground.

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