Device and method for measuring coaxiality of fitting circle and outer circle of multiple small holes in inner cavity of shell

Abstract

The invention belongs to the technical field of precision measurement, and discloses a device and a method for measuring the coaxiality of a fitting circle and an outer circle of a plurality of small holes in an inner cavity of a shell. The device comprises a measuring base, a limiting block, a measuring core rod, a measuring meter frame and a measuring meter, the limiting block and the measuring meter frame are both arranged on the measuring base, the measuring core rod can be detachably connected with a shell to be measured, and the measuring meter is connected with the measuring meter frame. According to the measurement method, the coaxiality of the fitting circle of the four small holes of the inner cavity in the complex structure of the shell and the outer circle is precisely designed. Through the cooperation of the limiting block and the shell supporting frame, the stability and accuracy of the shell to be measured in the measurement process are ensured, through the measurement meter and the measurement core rod, the measurement process is simplified, and measurement data are accurate.

Description

Technical Field

[0001] The invention belongs to the field of precision measurement technology, and in particular to a device and method for measuring the coaxiality of a fitting circle of a plurality of small holes in an inner cavity of a shell and an outer circle. Background Art

[0002] The shell structure of a certain type of gyroscope is relatively complex, with many dimensions, shapes and positions, high precision requirements, great processing difficulty and long processing cycle. The structure of the shell can be as follows Figure 6 and Figure 7 As shown, when producing this part, due to the structural characteristics of the shell itself, many dimensions and shapes are difficult to be directly detected by conventional methods, especially the coaxiality between the fitting circles of the four small holes in the inner cavity and the outer circle. The accuracy of the detection results will directly affect the part and determine whether the part is qualified or not. Moreover, if the detection results are inaccurate, it will seriously affect the subsequent related operations.

[0003] Specifically, when testing the coaxiality between the four small holes in the inner cavity of the shell and the outer circle, it is difficult to accurately measure them because some of the measured elements, such as the diameter of the small hole, the cylindricality of the small hole, the depth of the small hole, etc., are located in a narrow inner cavity, have complex shapes, and the entities that can be extracted are small. In addition, the size and shape accuracy are high, especially the accuracy of the inner cavity boss reaches 0.002, which is difficult to process and has high requirements for personnel, machine tools, cutting tools, and alignment. The thinnest wall thickness after survival is only 0.2, which is a typical thin-walled part. Therefore, how to choose a suitable measurement method to accurately and efficiently measure these measured elements is a difficult problem for measurement personnel.

[0004] In the past, when measuring the coaxiality between the inner deep hole and the outer circle of the shell, a three-coordinate optical system was often used to measure the parts. This measurement method can only measure the diameter element of the hole mouth, but cannot measure the internal cross-section of the hole. The existence of positioning errors will cause uncertain distortion of the measurement data, affecting the efficiency and quality of the measurement.

[0005] Therefore, a new device and measurement method are urgently needed. Summary of the invention

[0006] The purpose of the present invention is to overcome the deficiencies in the prior art and to provide a device and method for measuring the coaxiality of a fitting circle of a plurality of small holes in an inner cavity of a shell and an outer circle.

[0007] The technical solution adopted by the present invention to solve its technical problem is:

[0008] A device for measuring the coaxiality of a fitting circle of a plurality of small holes in a shell cavity and an outer circle, the device comprising a measuring base, a stop block, a measuring mandrel, a measuring table frame and a measuring table, the stop block and the measuring table frame are both arranged on the measuring base, the measuring mandrel can be detachably connected to the shell to be measured, and the measuring table is connected to the measuring table frame;

[0009] The shell includes a shell body, a shell inner cavity hole and a shell inner cavity small hole. The shell body is arranged in a vertical direction, and the shell inner cavity hole is coaxially formed in the middle and lower parts of the shell body. There are a plurality of shell inner cavity small holes, and the plurality of shell inner cavity small holes are evenly spaced and arranged in a circumferential direction. The shell inner cavity small holes are arranged on the shell body above the shell inner cavity hole and are connected to the shell inner cavity.

[0010] Further, the measuring base includes a base body, a shell support frame and a measuring meter support frame, the base body is arranged in the horizontal direction, the measuring meter support frame and the shell support frame are both arranged in the vertical direction, a shell support frame is arranged on a horizontal side of the upper surface of the base body, the shell support frame is arranged to match the shape of the shell inner cavity hole of the shell to be measured, the shell to be measured can be coaxially slidably arranged on the shell support frame through the shell inner cavity hole, and the shell to be measured arranged on the shell support frame can rotate in a circumferential direction around its axis, a measuring meter support frame is arranged on the other horizontal side of the upper surface of the base body, and the measuring meter support frame and the shell support frame are arranged colinearly along the same horizontal line in the horizontal direction;

[0011] The limit block is provided in one or more than two and is provided in the vertical direction. The two or more limit blocks are evenly spaced and provided in the circumferential direction. The limit block is detachably connected to the upper part of the base body. The limit block can be matched with the outer circle of the shell to be tested, and the limit block is closely spaced and provided with the shell support frame.

[0012] The measuring meter frame is tilted in the horizontal direction, and one horizontal end of the measuring meter frame is detachably connected to the upper part of the measuring meter support frame;

[0013] The measuring meter is arranged in the vertical direction, and comprises a measuring meter fixing part, a measuring meter body and a measuring meter needle which are connected and arranged in sequence from top to bottom, the upper part of the measuring meter fixing part is detachably connected and arranged with the other horizontal end of the measuring meter frame, the lower part of the measuring meter fixing part is connected and arranged with the upper part of the measuring meter body, the measuring meter fixing part can fix the measuring meter body, and the measuring meter needle is connected and arranged with the lower part of the measuring meter body;

[0014] The measuring mandrels are provided in a plurality and can be coaxially and detachably connected to the shell inner cavity small hole of the shell to be measured. The bottom of the measuring mandrel provided on the shell inner cavity small hole can be detachably provided on the upper surface of the shell support frame.

[0015] Furthermore, the measuring meter is a lever meter.

[0016] The method for measuring the coaxiality between the fitting circles of multiple small holes in the inner cavity of a shell and the outer circle using the above-mentioned device is as follows:

[0017] (1) Device placement

[0018] Place the measuring base on the platform, align the measuring surface, and make the flatness less than 0.002m;

[0019] (2) Assembling the measuring device

[0020] According to the size of the shell to be measured, the limit block, the shell support frame, and the measuring meter support frame are installed on the base, and then the shell to be measured is coaxially placed on the shell support frame, and at the same time, it is necessary to ensure that the outer surface of the shell to be measured is set close to the inner surface of the limit block, and then the shell to be measured is slightly rotated and the limit block is adjusted until the shell to be measured is not displaced left and right on the shell support frame, and then the measuring mandrel is passed through the small hole in the shell cavity in the vertical direction. A measuring mandrel is set for each small hole in the shell cavity, and the lower end of the measuring mandrel is placed on the upper surface of the base body, and then the measuring meter, the measuring meter frame, and the measuring meter support frame are connected and installed, so that the measuring meter is naturally drooped in the vertical direction. After the setting, the measuring meter is fixed by the measuring meter fixing piece;

[0021] (3) Coaxiality measurement

[0022] Adjust the measuring stand so that the measuring needle is close to any measuring core rod. Then rotate the shell to evaluate the coaxiality error value according to the minimum area method. Measure and record the positions of the corresponding points of each core rod in several cross sections relative to the reference formed by the limit block and the outer circle. Take the maximum value of the reading difference of each corresponding point as the coaxiality error.

[0023] The advantages and positive effects achieved by the present invention are:

[0024] 1. The measuring device of the present invention is designed for measuring the coaxiality between the fitting circle of the four small holes in the inner cavity and the outer circle in the complex structure of the shell, and has good adaptability and versatility. It adopts a detachable connection method and modular design, and the measuring base, limit block, measuring mandrel and other components can be flexibly adjusted and configured according to different shell sizes and shapes. This design enables the measuring device of the present invention to be widely used in the measurement of shell parts of various types and specifications, improving the utilization rate and measurement efficiency of the equipment.

[0025] 2. The measuring method of the present invention is precisely designed for the coaxiality of the fitting circle of the four small holes in the inner cavity and the outer circle in the complex structure of the shell. The stability and accuracy of the shell to be measured during the measurement process are ensured by the cooperation between the limit block and the shell support frame. The measuring table and the measuring mandrel make the measuring process simple and the measuring data accurate. At the same time, the use of the detachable measuring mandrel and the measuring table frame can complete the measurement task quickly and easily. Compared with the traditional measurement method, the present invention significantly improves the measurement accuracy, reduces the measurement error, shortens the measurement cycle, and improves the work efficiency.

[0026] 3. The device of the present invention includes a measuring base, a limit block, a measuring core rod, a measuring table frame and a measuring table. The shell to be measured is placed on the measuring base, and the measuring position is fixed by the limit block. Multiple measuring core rods are passed through the small holes of the shell to be measured and placed at one end of the measuring base. The shell is rotated to measure the coaxiality between the outer circle and the measuring core rod to obtain the coaxiality between the fitting circles of multiple small holes in the inner cavity and the outer circle. The device of the present invention has a simple structure and is easy to manufacture. It can improve the measurement accuracy of the coaxiality between the fitting circles of the four small holes in the inner cavity of the shell and the outer circle, reduce the measurement error, shorten the measurement cycle, and improve the work efficiency. The measuring device has good adaptability and versatility. The device of the present invention can effectively solve the problem that the coaxiality between the fitting circles of the four small holes in the inner cavity of the shell and the outer circle is difficult to measure, and can accurately perform coaxiality measurement to improve measurement efficiency.

[0027] 4. When the device of the present invention is in use, the shell to be tested is mounted on the shell support frame, and then an appropriate limit block is selected to limit and fix the shell to be tested on the shell support frame so that it can rotate but cannot move horizontally. Then the measuring meter, the measuring meter frame and the measuring meter support frame are connected and assembled, and then the measuring meter is allowed to hang freely and placed in the vertical direction. Then the measuring mandrel is inserted into the small hole in the inner cavity of the shell to be tested in the vertical direction, and then the needle of the measuring meter is close to the measuring mandrel. At this point, the device is assembled. Adjust the measuring meter frame so that the measuring needle is close to any measuring mandrel, and then rotate the shell. The coaxiality error value is evaluated according to the minimum area method. The positions of the corresponding points of each mandrel in several cross sections relative to the reference formed by the limit block and the outer circle are measured and recorded in turn, and the maximum value of the reading difference of each corresponding point is taken as the coaxiality error. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A three-dimensional schematic diagram of a structural connection of the device of the present invention;

[0029] Figure 2 for Figure 1 A schematic diagram of a structural connection main view and section view;

[0030] Figure 3 for Figure 2 A top view schematic diagram of the structural connection;

[0031] Figure 4 A schematic diagram of a structural connection of a measuring mandrel in the device of the present invention;

[0032] Figure 5 for Figure 1 A schematic diagram of a structural connection of a middle limit block;

[0033] Figure 6 A schematic diagram of a structural connection of a housing in the prior art;

[0034] Figure 7The figure is a schematic top view of a structural connection of a shell in the prior art. DETAILED DESCRIPTION

[0035] The present invention will be further described in detail below in conjunction with specific examples. The following examples are only illustrative and not restrictive, and the protection scope of the present invention cannot be limited thereto.

[0036] The raw materials used in the present invention, unless otherwise specified, are conventional commercial products, the methods used in the present invention, unless otherwise specified, are conventional methods in the art, and the quality of each substance used in the present invention is conventional quality. The structures, connection relationships, etc. not described in detail in the present invention can be understood as conventional technical means in the art.

[0037] A device for measuring the coaxiality between a plurality of small holes in a shell cavity and an outer circle. Figures 1 to 7 As shown, the device includes a measuring base 1, a limit block 2, a measuring mandrel 3, a measuring meter frame 4 and a measuring meter 5, the limit block and the measuring meter frame are both arranged on the measuring base, the measuring mandrel can be detachably connected to the shell 6 to be measured, the measuring meter is connected to the measuring meter frame, and the measuring meter can perform coaxiality measurement on the shell to be measured;

[0038] The shell includes a shell body 60, a shell inner cavity hole 61 and a shell inner cavity small hole 62. The shell body is arranged in the vertical direction, and the shell inner cavity hole is coaxially formed in the middle and lower parts of the shell body. There are a plurality of shell inner cavity small holes, and the plurality of shell inner cavity small holes are evenly spaced and arranged in the circumferential direction. The shell inner cavity small holes are arranged on the shell body above the shell inner cavity hole and are connected with the shell inner cavity.

[0039] The device of the present invention comprises a measuring base, a limit block, a measuring mandrel, a measuring table frame and a measuring table. The shell to be measured is placed on the measuring base, the measuring position is fixed by the limit block, and multiple measuring mandrels are passed through the small holes of the shell to be measured and placed at one end of the measuring base. The shell is rotated to measure the coaxiality between the outer circle and the measuring mandrel to obtain the coaxiality between the fitting circles of multiple small holes in the inner cavity and the outer circle. The device of the present invention has a simple structure and is easy to manufacture. It can improve the measurement accuracy of the coaxiality between the fitting circles of the four small holes in the inner cavity of the shell and the outer circle, reduce the measurement error, shorten the measurement cycle, and improve the work efficiency. The measuring device has good adaptability and versatility. The device of the present invention can effectively solve the problem that the coaxiality between the fitting circles of the four small holes in the inner cavity of the shell and the outer circle is difficult to measure, and can accurately perform coaxiality measurement to improve measurement efficiency.

[0040] In this embodiment, the measuring base includes a base body 11, a shell support frame 12 and a measuring meter support frame 13. The base body is arranged in the horizontal direction, and the measuring meter support frame and the shell support frame are both arranged in the vertical direction. A shell support frame is arranged on the horizontal side of the upper surface of the base body, and the shell support frame is arranged to match the shape of the shell inner cavity hole of the shell to be measured. The shell to be measured can be coaxially slidably arranged on the shell support frame through the shell inner cavity hole, and the shell to be measured arranged on the shell support frame can rotate in a circumferential direction around its axis. This structure enables the shell to be measured to rotate during detection, so that the coaxiality of multiple shell inner cavity small holes and the outer circle of the shell to be measured can be detected, and then the coaxiality of the final shell inner cavity multiple small hole fitting circle and the outer circle is detected; a measuring meter support frame is arranged on the other horizontal side of the upper surface of the base body, and the measuring meter support frame and the shell support frame are collinearly arranged along the same horizontal line in the horizontal direction;

[0041] The limit block is provided as one or more than two and is provided in the vertical direction. The two or more limit blocks are evenly spaced and provided in the circumferential direction. The limit block is detachably connected to the upper part of the base body. The limit block can be matched with the outer circle of the shell to be tested. The limit block and the shell support frame are closely spaced. The limit block can perform a limit fixing operation on the shell to be tested set on the shell support frame, so as to avoid the change of position of the shell to be tested during the detection process, which affects the detection result and improves the accuracy of the detection.

[0042] The measuring meter frame is tilted in the horizontal direction, and one horizontal end of the measuring meter frame is detachably connected to the upper part of the measuring meter support frame;

[0043] The measuring meter is arranged in the vertical direction, and comprises a measuring meter fixing part 51, a measuring meter body 52 and a measuring meter needle 53 which are connected and arranged in sequence from top to bottom. The upper part of the measuring meter fixing part is detachably connected and arranged with the other horizontal end of the measuring meter frame, and the lower part of the measuring meter fixing part is connected and arranged with the upper part of the measuring meter body. The measuring meter fixing part can fix the measuring meter body, and the measuring meter needle is connected and arranged with the lower part of the measuring meter body. The measuring meter needle can measure the coaxiality of the outer circle of the measuring core rod arranged below it and the shell to be measured;

[0044] The measuring mandrels are provided in a plurality and can be coaxially and detachably connected to the shell inner cavity small hole of the shell to be measured. The bottom of the measuring mandrel provided on the shell inner cavity small hole can be detachably provided on the upper surface of the shell support frame.

[0045] When the device of the present invention is used, the shell to be tested is mounted on the shell support frame, and then an appropriate limit block is selected to limit and fix the shell to be tested on the shell support frame so that it can rotate but cannot move horizontally. Then the measuring meter, the measuring meter frame and the measuring meter support frame are connected and assembled, and then the measuring meter is allowed to hang freely and placed in the vertical direction, and then the measuring mandrel is inserted into the small hole in the inner cavity of the shell to be tested in the vertical direction, and then the needle of the measuring meter is close to the measuring mandrel, and the device is assembled. Adjust the measuring meter frame so that the measuring needle is close to any measuring mandrel, and then rotate the shell, measure the coaxiality of the outer circle of the measuring mandrel and the shell to be tested through the measuring meter, and detect the coaxiality of the outer circle of the remaining measuring mandrels and the shell to be tested in turn, and finally obtain the coaxiality of the fitting circle of the four small holes in the inner cavity and the outer circle.

[0046] In this embodiment, the measuring meter is a lever meter, which is a measuring instrument that uses a lever-gear transmission mechanism or a lever-screw transmission mechanism to convert dimension changes into pointer angular displacement and indicate the length dimension value. It is used to measure the geometric shape error and relative position correctness of workpieces, and can measure length by comparison method. The detection result is very accurate.

[0047] The method for measuring the coaxiality of the fitting circles of the four small holes in the inner cavity of the shell and the outer circle by using the coaxiality measuring device of the fitting circles of the multiple small holes in the inner cavity of the shell and the outer circle comprises the following steps:

[0048] (1) Device placement

[0049] Place the measuring base on the platform, align the measuring surface, and make the flatness less than 0.002m;

[0050] (2) Assembling the measuring device

[0051] According to the size of the shell to be measured, the limit block, the shell support frame, and the measuring meter support frame are installed on the base, and then the shell to be measured is coaxially placed on the shell support frame, and at the same time, it is necessary to ensure that the outer surface of the shell to be measured is set close to the inner surface of the limit block, and then the shell to be measured is slightly rotated and the limit block is adjusted until the shell to be measured is not displaced left and right on the shell support frame, and then the measuring mandrel is passed through the small hole in the shell cavity in the vertical direction. A measuring mandrel is set for each small hole in the shell cavity, and the lower end of the measuring mandrel is placed on the upper surface of the base body, and then the measuring meter, the measuring meter frame, and the measuring meter support frame are connected and installed, so that the measuring meter is naturally drooped in the vertical direction. After the setting, the measuring meter is fixed by the measuring meter fixing piece;

[0052] (3) Coaxiality measurement

[0053] Adjust the measuring stand so that the measuring needle is close to any measuring core rod, then rotate the shell, and evaluate the coaxiality error value according to the minimum area method. Measure and record the positions of corresponding points of each core rod in several cross sections relative to the reference formed by the limit block and the outer circle, and take the maximum value of the reading difference of each corresponding point as the coaxiality error.

[0054] The optical measurement and the present measurement method were used to experimentally measure eight shells, and the results are shown in Table 1.

[0055] Table 1 Experimental measurement of coaxiality values

[0056]

[0057] Optical measurement and this measurement method were used to experimentally measure 8 shells. The measurement values ​​of the original measurement method were generally smaller than those of this measurement method.

[0058] The measuring device and method of the present invention are precisely designed for the coaxiality of the fitting circle of the four small holes in the inner cavity and the outer circle in the complex structure of the shell. The stability and accuracy of the shell to be measured during the measurement process are ensured by the cooperation of the limit block and the shell support frame. At the same time, the measurement task can be completed quickly and easily by using the detachable measuring mandrel and the measuring table frame. Compared with the traditional measurement method, the present invention significantly improves the measurement accuracy, reduces the measurement error, shortens the measurement cycle, and improves the work efficiency. The measuring device has good adaptability and versatility. Due to the detachable connection method and modular design, the measuring base, the limit block, the measuring mandrel and other components can be flexibly adjusted and configured according to different shell sizes and shapes. This design enables the measuring device of the present invention to be widely used in the measurement of shell parts of various types and specifications, and improves the utilization rate and measurement efficiency of the equipment. The measuring method uses a mandrel to simulate the reference element, which can measure the effective size of the inner cavity hole, completely solves the measurement limitations caused by the original measurement method using optical measurement, greatly improves the measurement efficiency, and the stable measurement conditions ensure the reliability and accuracy of the coaxiality measurement. This measurement method more effectively shows the influence of the internal positioning error of the hole on the measurement result, making the measurement result more accurate.

[0059] Although the embodiments of the present invention are disclosed for illustrative purposes, those skilled in the art will appreciate that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments.

Claims

1. A device for measuring the coaxiality between a fitting circle of a plurality of small holes in a shell cavity and an outer circle, characterized in that: The device comprises a measuring base, a limit block, a measuring mandrel, a measuring meter frame and a measuring meter, wherein the limit block and the measuring meter frame are both arranged on the measuring base, the measuring mandrel can be detachably connected to the housing to be measured, and the measuring meter is connected to the measuring meter frame; The shell includes a shell body, a shell inner cavity hole and a shell inner cavity small hole. The shell body is arranged in a vertical direction, and the shell inner cavity hole is coaxially formed in the middle and lower parts of the shell body. There are a plurality of shell inner cavity small holes, and the plurality of shell inner cavity small holes are evenly spaced and arranged in a circumferential direction. The shell inner cavity small holes are arranged on the shell body above the shell inner cavity hole and are connected to the shell inner cavity.

2. The device for measuring the coaxiality between the fitting circles of the multiple small holes in the inner cavity of a shell and the outer circle according to claim 1, characterized in that: The measuring base comprises a base body, a shell support frame and a measuring meter support frame, the base body is arranged in the horizontal direction, the measuring meter support frame and the shell support frame are arranged in the vertical direction, a shell support frame is arranged on a horizontal side of the upper surface of the base body, the shell support frame is arranged to match the shape of the shell inner cavity hole of the shell to be measured, the shell to be measured can be coaxially slidably arranged on the shell support frame through the shell inner cavity hole, and the shell to be measured arranged on the shell support frame can rotate in a circumferential direction around its axis, a measuring meter support frame is arranged on the other horizontal side of the upper surface of the base body, and the measuring meter support frame and the shell support frame are arranged colinearly along the same horizontal line in the horizontal direction; The limit block is provided in one or more than two and is provided in the vertical direction. The two or more limit blocks are evenly spaced and provided in the circumferential direction. The limit block is detachably connected to the upper part of the base body. The limit block can be matched with the outer circle of the shell to be tested, and the limit block is closely spaced and provided with the shell support frame. The measuring meter frame is tilted in the horizontal direction, and one horizontal end of the measuring meter frame is detachably connected to the upper part of the measuring meter support frame; The measuring meter is arranged in the vertical direction, and comprises a measuring meter fixing part, a measuring meter body and a measuring meter needle which are connected and arranged in sequence from top to bottom, the upper part of the measuring meter fixing part is detachably connected and arranged with the other horizontal end of the measuring meter frame, the lower part of the measuring meter fixing part is connected and arranged with the upper part of the measuring meter body, the measuring meter fixing part can fix the measuring meter body, and the measuring meter needle is connected and arranged with the lower part of the measuring meter body; The measuring mandrels are provided in a plurality and can be coaxially and detachably connected to the shell inner cavity small hole of the shell to be measured. The bottom of the measuring mandrel provided on the shell inner cavity small hole can be detachably provided on the upper surface of the shell support frame.

3. The device for measuring the coaxiality between the fitting circles of the multiple small holes in the inner cavity of a shell and the outer circle according to claim 1, characterized in that: The measuring meter is a lever meter.

4. A method for measuring the coaxiality between the fitting circles of a plurality of small holes in the inner cavity of a shell and the outer circle using the device as claimed in any one of claims 1 to 3, characterized in that: Here are the steps: (1) Device placement Place the measuring base on the platform, align the measuring surface, and make the flatness less than 0.002m; (2) Assembling the measuring device According to the size of the shell to be measured, the limit block, the shell support frame, and the measuring meter support frame are installed on the base, and then the shell to be measured is coaxially placed on the shell support frame, and at the same time, it is necessary to ensure that the outer surface of the shell to be measured is set close to the inner surface of the limit block, and then the shell to be measured is slightly rotated and the limit block is adjusted until the shell to be measured is not displaced left and right on the shell support frame, and then the measuring mandrel is passed through the small hole in the shell cavity in the vertical direction. A measuring mandrel is set for each small hole in the shell cavity, and the lower end of the measuring mandrel is placed on the upper surface of the base body, and then the measuring meter, the measuring meter frame, and the measuring meter support frame are connected and installed, so that the measuring meter is naturally drooped in the vertical direction. After the setting, the measuring meter is fixed by the measuring meter fixing piece; (3) Coaxiality measurement Adjust the measuring stand so that the measuring needle is close to any measuring core rod, then rotate the shell, and evaluate the coaxiality error value according to the minimum area method. Measure and record the positions of corresponding points of each core rod in several cross sections relative to the reference formed by the limit block and the outer circle, and take the maximum value of the reading difference of each corresponding point as the coaxiality error.

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