Device and method for boring hole by radial drill

Abstract

Aiming at the problems in the prior art, the invention provides the device and the method for boring the radial drill, the device comprises a boring rod, a boring cutter, a shaft hub, a spline shaft, a shaft sleeve, a workbench and a bearing unit arranged on the vertical surface of the workbench, the position of the boring rod is adjusted through the radial drill, and the boring rod and the shaft hub are aligned and embedded, so that the boring cutter is arranged on the shaft hub; the bearing unit is fixed to the boring rod through the shaft hub, so that when the boring cutter cuts a workpiece, the shaft hub, the spline shaft, the shaft sleeve and the boring rod synchronously rotate, and the bearing unit is fixed to the vertical face of the workbench, so that vibration deviation of the boring rod is limited, the actual machining track of the boring cutter is matched with the preset machining track, and aperture size fluctuation is avoided; the actual dimension error of the aperture is far smaller than the standard dimension tolerance, and the machining precision is greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of boring, in particular to a device and method for boring with a radial drilling machine. BACKGROUND

[0002] In the prior art, the centering positioning method is commonly used, that is, the axis of the boring tool is adjusted to coincide with the theoretical center line of the hole to be machined in the workpiece. This method can meet the requirements in conventional tolerance machining, but in precision machining, the following defects exist due to dynamic deformation: during boring, the boring bar is subjected to periodic radial cutting force in a high-speed rotating state. When deep holes or hard materials are machined, the local rigidity barrier of the workpiece causes the boring bar to generate asymmetric load. This load causes the boring bar to vibrate, resulting in the actual rotation track of the boring tool deviating from the ideal circular motion and degenerating into a distorted elliptical track. The track distortion directly leads to hole size fluctuation, and the actual size error is much larger than the standard size tolerance.

[0003] The current measures taken and the corresponding problems are: 1. Increasing the diameter of the boring bar: the diameter of the boring bar is limited by the inner diameter of the hole to be machined in the workpiece; 2. Reducing the cutting parameters: sacrificing machining efficiency and unable to eliminate low-frequency vibration of the boring tool.

[0004] Therefore, there is an urgent need for a device and method for precision boring with a radial drilling machine to solve the above problems. SUMMARY

[0005] The present application aims to solve the problems in the prior art and provides a device and method for boring with a radial drilling machine. The position of the boring bar is adjusted by the radial drilling machine, the boring bar is embedded and fitted with the shaft hub, and then the bearing unit is fixed with the boring bar through the shaft hub. When the boring tool cuts the workpiece, the shaft hub, spline shaft and shaft sleeve rotate synchronously with the boring bar. Since the bearing unit is fixed on the vertical surface of the workbench, the vibration deviation of the boring bar is limited, the actual machining track of the boring tool matches the preset machining track, the hole size fluctuation is avoided, the actual size error of the hole diameter is much smaller than the standard size tolerance, and the machining precision is greatly improved.

[0006] To achieve the above-mentioned purpose, the technical solution adopted by the present application is:

[0007] A device for boring with a radial drilling machine, comprising a boring bar and a boring tool fixed on the boring bar, the boring tool being used to machine a workpiece located below it, the workpiece being clamped on a workbench by a clamping mechanism, a bearing unit being installed on the vertical surface of the workbench, the bearing unit being transversely displaced along the workbench, the rotational axis of the bearing unit coinciding with the straight line on which the central axis of the boring bar lies, an inner ring of the bearing unit being installed at the inner circle of the bearing unit, the inner ring and the shaft sleeve rotating synchronously, the shaft sleeve being slidingly connected with a spline shaft, one end of the spline shaft being fixedly connected with a shaft hub, and the bottom end of the boring bar being embedded with the top end of the shaft hub to achieve positioning.

[0008] Further, the boring bar is provided with a plurality of limiting holes one, the shaft hub is provided with a plurality of limiting holes two, the top of the shaft hub is provided with an inner cavity matched with the shape of the boring bar, the boring bar extends into the inner cavity and is detachably connected with the shaft hub through the limiting holes one and the limiting holes two.

[0009] Further, the shaft hub is provided with a plurality of limiting holes three, and the shaft hub and the spline shaft are detachably connected through the limiting holes three.

[0010] Further, a bushing is further included, the outer wall of the bushing is fixedly connected with the inner wall of the inner ring, the bushing is provided with a plurality of limiting holes four, and the bushing is detachably connected with the shaft sleeve through the limiting holes four, so that the inner ring and the shaft sleeve rotate synchronously.

[0011] Further, the top of the shaft hub is provided with a limiting groove matched with the boring cutter, and the shaft hub is provided with a through key groove matched with the spline shaft.

[0012] Further, the shaft sleeve is provided with a through inner spline pair, the inner spline pair is matched with the spline shaft, the shaft sleeve is matched with the spline shaft through the inner spline pair, and the spline shaft is longitudinally displaced along the shaft sleeve.

[0013] Further, the bearing unit is provided with two, and the two bearing units are detachably installed on the vertical surface of the workbench, the inner and outer diameters of the two bearing units are equal, the central axes of the inner rings of the two bearing units are located on the same straight line, the inner rings of the two bearing units are installed with the bushings, and the bushings are detachably fixed from top to bottom.

[0014] Further, the length of the spline shaft, the height of the workbench, the height of the bearing unit and the height of the hole to be machined of the workpiece are matched with each other.

[0015] Further, the workbench is provided with a transverse groove, the bearing unit further includes a support, the bearing unit is installed in the groove through the support, the support is provided with a hexagonal nut, the displacement of the bearing unit is limited through the hexagonal nut, and the bearing unit is fixed on the vertical surface of the workbench.

[0016] A method for rocker drilling and boring, the method adopts a device for rocker drilling and boring, the method comprises the following steps: feeding a workpiece with a rough hole to a workbench; polishing the edge burrs of the workpiece on the workbench; preliminarily centering the shaft hub below the workpiece with the rough hole of the workpiece; lifting the shaft hub, embedding the top end of the shaft hub at the bottom end of the boring bar, and fixing the boring bar, the boring cutter and the shaft hub; drawing a processing line on the upper end face of the workpiece with the boring cutter, judging the centering accuracy and performing precise centering; clamping the workpiece, opening the rocker drill to perform finish boring on the workpiece, and unloading after processing is completed.

[0017] Further, the preliminarily centering the shaft hub below the workpiece with the rough hole of the workpiece comprises the following steps: placing the scratch disc on the shaft hub, the axis of the scratch disc column and the axis of the shaft hub are located on the same straight line, judging the centering accuracy by the distance between the scratch needle and the hole wall of the rough hole, and adjusting the position of the workpiece, i.e. adjusting the relative position of the rough hole and the shaft hub.

[0018] Further, in the process of preliminarily centering the shaft hub below the workpiece with the rough hole of the workpiece, the shaft hub is below the workpiece, the bottom end of the shaft hub abuts against the top end of the shaft sleeve; the base of the scratch disc is installed on the shaft hub, and the column and the scratch needle of the scratch disc extend out of the rough hole from bottom to top, so that the scratch needle draws a line on the top end of the workpiece, thereby realizing distance measurement and judging the centering accuracy.

[0019] Further, the lifting of the shaft hub, the embedding of the top end of the shaft hub at the bottom end of the boring bar, and the fixing of the boring bar, the boring cutter and the shaft hub comprise the following steps: lifting the shaft hub, making the height of the shaft hub higher than the height of the workpiece, adjusting the position of the boring bar, so that the axis of the boring bar and the axis of the shaft hub are located on the same straight line, the position of the boring cutter matches the position of the limiting groove, lowering the boring bar, embedding the boring bar and the boring cutter in the inner cavity and the limiting groove of the shaft hub respectively, and detachably connecting the boring bar, the boring cutter and the shaft hub through the limiting hole one and the limiting hole two.

[0020] Further, the drawing of the processing line on the upper end face of the workpiece with the boring cutter, the judging of the centering accuracy and the performing of the precise centering comprise the following steps: rotating the boring bar, so that the cutting edge of the boring cutter draws a processing line on the upper end face of the workpiece, judging the centering accuracy by the distance between the processing line and the hole wall of the rough hole, and adjusting the position of the workpiece.

[0021] Compared with the prior art, the method has the following beneficial effects:

[0022] The application adjusts the position of the boring bar through the radial drilling machine, and then the boring bar is embedded and aligned with the shaft hub, and then the bearing unit is fixed through the shaft hub and the boring bar, so that the shaft hub, the spline shaft and the shaft sleeve rotate synchronously with the boring bar when the boring cutter cuts the workpiece, and the vibration deviation of the boring bar is limited due to the fact that the bearing unit is fixed on the vertical surface of the workbench, so that the actual machining track of the boring cutter matches the preset machining track, the hole diameter size fluctuation is avoided, the actual size error of the hole diameter is far less than the standard size tolerance, and the machining precision is greatly improved. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 It is a structure perspective view of the application;

[0024] Figure 2 It is a structure perspective view of the boring bar and the boring cutter of the application;

[0025] Figure 3 It is a structure perspective view of the workbench, the shaft hub, the spline shaft, the shaft sleeve and the bearing unit of the application;

[0026] Figure 4 It is a partial sectional view of the application;

[0027] Figure 5 It is a structure perspective view of the application; Figure 4 It is a local enlarged view of A in the application;

[0028] Figure 6 It is a local assembly exploded view of the application;

[0029] Figure 7 It is an assembly exploded view of the shaft hub and the spline shaft of the application;

[0030] Figure 8 It is a boring machining schematic view of the application;

[0031] Figure 9 It is a structure schematic view of the boring bar embedded and aligned with the shaft hub of the application;

[0032] Figure 10 It is a method flow chart of boring holes by the radial drilling machine in the application.

[0033] In the figure: 1, radial drilling machine; 2, boring bar; 21, limiting hole one; 3, boring cutter; 4, workbench; 5, shaft hub; 51, limiting groove; 52, limiting hole two; 53, limiting hole three; 54, key groove; 6, spline shaft; 7, shaft sleeve; 71, inner spline pair; 8, bushing; 81, limiting hole four; 9, bearing unit; 10, clamping mechanism; 101, workpiece. DETAILED DESCRIPTION

[0034] The technical solutions of the present application will be described clearly and completely below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0035] Embodiment 1

[0036] Please refer to Figures 1-9 A device for boring holes with a radial drilling machine, comprising a boring bar 2, and a boring tool 3 fixed on the boring bar 2, the boring tool 3 is used for machining a workpiece 101 located below, the workpiece 101 is clamped on a workbench 4 through a clamping mechanism 10, a bearing unit 9 is installed on the vertical surface of the workbench 4, the bearing unit 9 is displaced transversely along the workbench 4, the rotation axis of the bearing unit 9 coincides with the straight line where the central axis of the boring bar 2 is located, the inner ring of the bearing unit 9 is installed with a shaft sleeve 7, the inner ring of the bearing unit 9 rotates synchronously with the shaft sleeve 7, the shaft sleeve 7 is slidingly connected with a spline shaft 6, one end of the spline shaft 6 is fixedly connected with a shaft hub 5, the bottom end of the boring bar 2 is embedded with the top end of the shaft hub 5 to realize alignment.

[0037] When the device is used to bore holes, a rough machining hole is opened on the workpiece 101, the position of the boring bar 2 is adjusted through the radial drilling machine, the boring bar 2 is embedded and aligned with the shaft hub 5, then the shaft hub 5 is fixed with the boring bar 2, after the fixing is completed, the height of the boring bar 2 is adjusted, since the boring bar 2 is fixed with the shaft hub 5 at this time, the shaft hub 5 is fixed with the spline shaft 6, so that the spline shaft 6 is displaced longitudinally along the shaft sleeve 7, the height of the workpiece 101, the boring tool 3 and the shaft hub 5 are matched with each other, since the shaft sleeve 7 limits the displacement of the spline shaft 6 in the horizontal direction, the vibration deviation of the boring bar 2 in the machining process is limited, and the machining precision is greatly improved.

[0038] Four limiting holes one 21 are opened on the boring bar 2, four limiting holes two 52 are opened on the shaft hub 5, an inner cavity matching the shape of the boring bar 2 is opened on the top of the shaft hub 5, the boring bar 2 is inserted into the inner cavity and is detachably connected with the shaft hub 5 through the matched limiting holes one 21 and limiting holes two 52.

[0039] In this embodiment, the limiting holes two 52 are internally tapped, the matched limiting holes one 21 and limiting holes two 52 are fixed through hexagonal bolts, so that the boring bar 2 is tightly fixed on the shaft hub 5.

[0040] Three limiting holes three 53 are opened on the shaft hub 5, the shaft hub 5 and the spline shaft 6 are detachably connected through the limiting holes three 53.

[0041] In this embodiment, the limiting holes three 53 are internally tapped, the limiting holes three 53 and the spline shaft 6 are fixed through hexagonal bolts, so that the spline shaft 6 is tightly fixed on the shaft hub 5.

[0042] The device for boring holes by rocker drill further comprises a bushing 8, the outer wall of the bushing 8 is fixed to the inner wall of the inner ring of the bearing unit 9, three limiting holes four 81 are formed in the bushing 8, the bushing 8 is detachably connected to the shaft sleeve 7 through the limiting holes four 81, so that the inner ring of the bearing unit 9 rotates synchronously with the shaft sleeve 7.

[0043] In the embodiment, the limiting holes four 81 are tapped, the limiting holes four 81 are fixed to the shaft sleeve 7 through hex bolts, so that the shaft sleeve 7 is tightly connected to the bushing 8; when the shaft sleeve 7 rotates, the inner ring of the bearing unit 9 rotates synchronously through the bushing 8; the bushing 8 is a wear-resistant part, which protects the shaft sleeve 7.

[0044] The top of the shaft hub 5 is provided with a limiting groove 51, the shape of the limiting groove 51 matches the boring cutter 3; the shaft hub 5 is provided with a through key groove 54, the key groove 54 is embedded with the spline shaft 6.

[0045] In the embodiment, the boring cutter 3 is clamped with the limiting groove 51, and the boring bar 2 is embedded with the shaft hub 5, so that the boring cutter 3 is aligned with the rough machining hole of the workpiece 101; since the key groove 54 is embedded with the spline shaft 6, and the spline shaft 6 is fixed with the shaft hub 5, the freedom of the spline shaft 6 in each direction is limited, so that the spline shaft 6 rotates synchronously when the shaft hub 5 rotates.

[0046] The shaft sleeve 7 is provided with a through inner spline pair 71, the inner spline pair 71 is embedded with the spline shaft 6, the spline shaft 6 is longitudinally displaced along the shaft sleeve 7 through the inner spline pair 71 embedded with the spline shaft 6.

[0047] In the embodiment, when the boring bar 2 is lifted during the finishing process, since the bottom end of the boring bar 2 is fixed to the shaft hub 5, the shaft hub 5 is lifted with the boring bar 2, at this time, the spline shaft 6 is lifted along the shaft sleeve 7 to match the height of the hole to be machined.

[0048] Further, the bearing unit 9 is provided with two, which are detachably installed on the vertical surface of the workbench 4, the inner and outer diameters of the two bearing units 9 are equal, and the central axes of the inner rings of the two bearing units 9 are located on the same straight line, the inner rings of the two bearing units 9 are installed with the bushings 8, and the shaft sleeve 7 is detachably fixed with the two bushings 8 from top to bottom, so as to further limit the shock displacement of the boring cutter 3 when boring holes.

[0049] Further, the length of the spline shaft 6, the height of the workbench 4, the height of the bearing unit 9 and the height of the hole to be machined of the workpiece 101 are matched with each other; when the shaft hub 5 is in the lowest position, that is, the bottom end of the shaft hub 5 abuts against the top end of the shaft sleeve 7, the bottom end of the spline shaft 6 is kept at a safe height from the bottom surface of the workbench 4; when the boring cutter 3 is positioned at a safe distance above the hole to be machined, the spline shaft 6 is kept in the meshing state with the shaft sleeve 7.

[0050] Further, the workbench 4 is provided with a transverse groove, and the bearing unit 9 further comprises a support, the bearing unit 9 is transversely displaced by being mounted in the groove of the workbench 4, and the transverse displacement of the bearing unit 9 is limited by a hexagonal nut, so that the bearing unit 9 is fixed on the vertical surface of the workbench 4.

[0051] The device of the application fixes the boring bar 2 on the shaft hub 5 by aligning and fitting the boring bar 2 and the shaft hub 5, and then adjusts the height of the boring bar 2, since the boring bar 2 is fixed on the shaft hub 5, and the shaft hub 5 is fixed on the spline shaft 6, so that the spline shaft 6 is longitudinally displaced along the shaft sleeve 7, and since the shaft sleeve 7 limits the horizontal displacement of the spline shaft 6, the vibration deviation of the boring bar 2 during the machining process is limited without increasing the diameter of the boring bar 2 and reducing the cutting parameters, and the problem of deviation of the actual rotation track of the boring cutter from the expected track is solved.

[0052] Embodiment 2

[0053] Please refer to Figures 1-10 A method for boring holes by a radial drilling machine, comprising the following steps:

[0054] S1, loading a workpiece with a rough machining hole onto a workbench: placing the workpiece with the rough machining hole on the workbench, and initially aligning the axis of the rough machining hole of the workpiece with a straight line where the axis of the shaft hub is located.

[0055] S2, polishing the edge burrs of the workpiece on the workbench, i.e., edge burr polishing: polishing the edge burrs of the workpiece.

[0056] S3, initially aligning the shaft hub located below the workpiece with the rough machining hole of the workpiece, i.e., initially aligning the shaft hub and the rough machining hole: placing the scriber disc on the shaft hub, and aligning the axis where the column of the scriber disc is located with the axis of the shaft hub, judging the alignment accuracy by the distance between the scriber and the hole wall of the rough machining hole, and adjusting the relative position of the rough machining hole and the shaft hub.

[0057] The scriber disc is a prior art device, and will not be described here.

[0058] It should be noted that during the initial alignment of the shaft hub and the rough machining hole in S3, the shaft hub is located below the workpiece, as shown in Figure 4 The bottom end of the shaft hub abuts against the top end of the shaft sleeve; the base of the scriber disc is mounted on the shaft hub, and the column and the scriber of the scriber disc extend out of the rough machining hole from bottom to top, so that the scriber draws a line on the top end of the workpiece, thereby realizing distance measurement and judging the alignment accuracy.

[0059] S4, lift the shaft hub, embed the top end of the bottom end shaft hub of the boring bar, and fix the boring bar, boring cutter and shaft hub, that is, the boring bar, boring cutter and shaft hub are embedded and fixed: lift the shaft hub, make the height of the shaft hub slightly higher than the height of the workpiece, adjust the position of the boring bar through the radial drilling to make the boring bar axis and the shaft hub axis be in the same straight line, and the position of the boring cutter matches the position of the limiting groove, lower the boring bar, as shown in Figure 9 the boring bar, the boring cutter and the shaft hub are detachably connected through the limiting hole one and the limiting hole two.

[0060] Alternatively, the method of lifting the shaft hub provided in the embodiment can be selected, the spline shaft is manually lifted from the bottom end and padded into a pad with appropriate height, or a motor device is installed below the spline shaft to lift, after the boring bar and the shaft hub are fixed, the pad or the motor device is removed.

[0061] S5, draw a processing line on the upper end surface of the workpiece with the boring cutter, judge the centering accuracy and perform precise centering: make the boring bar rotate at a low speed through the radial drilling to make the cutting edge of the boring cutter draw a processing line on the upper end surface of the workpiece, judge the centering accuracy through the distance between the processing line and the wall of the rough machining hole, adjust the position of the workpiece to realize precise centering.

[0062] S6, clamp the workpiece: clamp the workpiece with precise centering completed on the workbench through the clamping mechanism.

[0063] S7, open the radial drilling to perform finish boring on the workpiece: open the radial drilling to make the boring bar rotate at a processing speed, and the boring cutter cuts the workpiece.

[0064] S8, unload after processing: record the hole diameter data with the vernier caliper, loosen the clamping device, and take the workpiece with finished finish boring from the workbench and put it into the warehouse.

[0065] The method provided by the application first centers the shaft hub and the rough machining hole for preliminary centering to realize embedding and fixing of the boring bar, boring cutter and shaft hub, and secondly centers the boring cutter and the axis of the hole to be processed. After ensuring the centering accuracy, the shaft hub, spline shaft and shaft sleeve rotate synchronously with the boring bar during finish boring, the boring bar vibration deviation is limited due to the fact that the bearing unit is fixed on the vertical surface of the workbench, the actual processing track of the boring cutter matches the preset processing track, the hole diameter size fluctuation is avoided, the actual size error of the hole diameter is much smaller than the standard size tolerance, and the processing accuracy is greatly improved.

Claims

1. An apparatus for drilling a bore with a rocker arm, characterized by: The application relates to a boring device, which comprises a boring rod and a boring cutter fixed on the boring rod, the boring cutter is used for machining a workpiece located below the boring cutter, the workpiece is clamped on a workbench through a clamping mechanism, a bearing unit is arranged on a vertical surface of the workbench, the bearing unit is transversely displaced along the workbench, the rotation axis of the bearing unit coincides with a straight line where the central axis of the boring rod is located, a sleeve is arranged on the inner ring of the bearing unit, the inner ring and the sleeve rotate synchronously, the sleeve is slidably connected with a spline shaft, one end of the spline shaft is fixedly connected with a hub, the bottom end of the boring rod is embedded into the top end of the hub to realize alignment.

2. A device for drilling holes with a radial drilling machine according to claim 1, characterized in that: A plurality of limiting holes one are formed in the boring rod, a plurality of limiting holes two are formed in the hub, an inner cavity matched with the shape of the boring rod is formed in the top of the hub, the boring rod extends into the inner cavity and is detachably connected with the hub through the limiting holes one and the limiting holes two.

3. A device for drilling a borehole with a swing arm according to claim 1, characterized in that: A plurality of limiting holes three are formed in the hub, and the hub and the spline shaft are detachably connected through the limiting holes three.

4. A device for drilling a borehole with a swing arm according to claim 1, characterized in that: The application further comprises a bushing, the outer wall of the bushing is fixedly connected with the inner wall of the inner ring, a plurality of limiting holes four are formed in the bushing, and the bushing is detachably connected with the sleeve through the limiting holes four, so that the inner ring and the sleeve rotate synchronously.

5. A device for drilling a borehole with a swing arm according to claim 1, characterized in that: The top of the hub is provided with a limiting groove matched with the shape of the boring cutter, and a through key groove is formed in the hub and embedded into the spline shaft.

6. A device for drilling a borehole with a swing arm according to claim 1, characterized in that: An inner spline pair is formed in the sleeve, the inner spline pair is embedded into the spline shaft, the sleeve is embedded into the spline shaft through the inner spline pair, and the spline shaft is longitudinally displaced along the sleeve.

7. A method for drilling a bore with a rocker arm, characterized in that: The method adopts the device for boring a hole in a rocker arm as claimed in any one of claims 1-6, and comprises the following steps: feeding a workpiece with a rough machining hole to a workbench; polishing the edge burrs of the workpiece on the workbench; preliminarily aligning the hub located below the workpiece with the rough machining hole of the workpiece; lifting the hub, embedding the bottom end of the boring rod into the top end of the hub, and fixing the boring rod, the boring cutter and the hub; drawing a machining line on the upper end surface of the workpiece by the boring cutter, judging the alignment accuracy and performing precise alignment; clamping the workpiece, precisely machining the boring hole of the workpiece by using the rocker arm, and discharging the workpiece after machining.

8. A method for drilling a bore with a radial arm according to claim 7, characterized in that: The preliminary alignment of the hub located below the workpiece with the rough machining hole of the workpiece comprises the following steps: placing a marking disc on the hub, arranging the axis of the marking disc column and the axis of the hub on the same straight line, judging the alignment accuracy by the distance between the marking needle and the hole wall of the rough machining hole, and adjusting the position of the workpiece.

9. A method for drilling a bore with a radial arm according to claim 7, characterized in that: The lifting of the hub, the embedding of the bottom end of the boring rod into the top end of the hub, and the fixing of the boring rod, the boring cutter and the hub comprise the following steps: lifting the hub, making the height of the hub higher than the height of the workpiece, adjusting the position of the boring rod, so that the axis of the boring rod and the axis of the hub are located on the same straight line, the position of the boring cutter matches the position of the limiting groove, lowering the boring rod, embedding the boring rod and the boring cutter into the inner cavity and the limiting groove of the hub respectively, and detachably connecting the boring rod, the boring cutter and the hub with the hub through the limiting holes one and the limiting holes two.

10. The method for boring a hole with a rocker drill according to claim 7, characterized in that: The method for drawing a machining line on the upper end face of a workpiece by a boring tool, judging the centering precision and performing precise centering, comprises the following steps: rotating a boring bar to draw a machining line on the upper end face of the workpiece by the cutting edge of the boring tool, judging the centering precision by the distance between the machining line and the rough machining hole wall, and adjusting the position of the workpiece.

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