A small dovetail type mortise internal hole symmetry detection device and method

Abstract

A small dovetail groove inner hole symmetry detection device, comprising: a gauge body, with its two side surfaces respectively set as a first reference surface and a second reference surface; a dovetail head is arranged at the bottom of the gauge body; the central axis plane of the first reference surface and the second reference surface coincides with the central axis plane of the two inclined surfaces of the dovetail head; a threaded ejector rod is slidably mounted on the gauge body up and down, the upper part of the threaded ejector rod is a threaded section and extends out of the gauge body, and a nut is arranged on this threaded section, and the nut is used to adjust the longitudinal position of the threaded ejector rod so that the lower end of the threaded ejector rod extends out or retracts from the dovetail head; a spring is arranged inside the gauge body and sleeved on the threaded ejector rod, the spring is in a compressed state, its upper end abuts against the gauge body, and its lower end abuts against the threaded ejector rod. By using this small dovetail groove inner hole symmetry detection device, the problem that the measuring probe of the three-coordinate measuring instrument cannot reach the two inclined surfaces of the dovetail groove due to the too narrow width of the closed mouth groove of the small dovetail groove is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of aero-engine manufacturing, specifically to tenon groove detection technology, and particularly to a device and method for detecting the symmetry of the inner hole of a small dovetail tenon groove. Background Art

[0002] As Figures 1 to 3 shown, in an aero-engine, there are often many dovetail tenon grooves evenly distributed circumferentially on compressor disk parts. After the dovetail tenon grooves are machined in place to meet the design shape requirements, holes need to be drilled at the bottom of the dovetail tenon grooves. The design requirement is that the symmetry of the center of the hole relative to the centers of the two inclined planes (plane E and plane F) of the tenon groove does not exceed 0.2 mm. When the width D of the small dovetail tenon groove at the closed end ≤ 14 mm, due to the too narrow space of the small dovetail tenon groove and the fixed angle between the dovetail tenon groove and the horizontal direction, it is impossible to manufacture a special measuring tool to detect this dimension; even if directly using a coordinate measuring machine for detection, due to the too narrow width of the dovetail tenon groove at the closed end, the probe of the coordinate measuring instrument still cannot take points on the two inclined planes (plane E and plane F) of the dovetail tenon groove, so it is impossible to obtain the central plane of the two inclined planes (plane E and plane F) of the dovetail tenon groove, resulting in the inability to detect the symmetry dimension of the hole relative to the dovetail tenon groove.

[0003] In the prior art, there are some detection methods or detection devices for dovetail tenon grooves.

[0004] For example, the patent with the application number CN201811024592.5 discloses a measuring device for the intersection point of an engine arc dovetail tenon groove, which adopts a layered and split combination structure. By rotating the measuring device, the measuring head is in direct contact with the part, and by means of automatic centering and reading the specific value by dial indicator, the minimum dimension obtained by finding the repeated points is the intersection point dimension of the measured part, realizing the easy machinability and metrology of the arc-shaped axial dovetail tenon groove intersection measuring device.

[0005] Another example is that the patent with the application number CN201020037750.3 discloses a comprehensive measuring instrument for the tenon groove of a high-pressure compressor disk. The adapter is inserted into the dovetail tenon groove of the measured high-pressure compressor disk, the dial indicator installed on the measuring and positioning device is calibrated by a standard part, and then the measuring and positioning device is placed on the measured high-pressure compressor disk, and the measured part of the tenon groove is transferred out through the adapter for measurement.

[0006] However, the above-mentioned comparative documents do not disclose the problem of detecting the symmetry of the inner hole at the bottom of the small dovetail tenon groove of compressor disk parts, and this problem has always been a difficult problem in the mechanical processing industry. Solving this problem can fill the technical gap in the detection of the symmetry of the inner hole of the small dovetail tenon groove in the industry and ensure product quality, which is meaningful for the entire aero-engine manufacturing industry. Summary of the Invention

[0007] The main object of the present invention is to propose a detection device and method for the symmetry of the inner hole of a small dovetail groove, aiming to solve the above technical problems.

[0008] To achieve the above object, on the one hand, the present invention proposes a detection device for the symmetry of the inner hole of a small dovetail groove, including:

[0009] A gauge body, with its two side surfaces respectively set as the first reference surface and the second reference surface; a dovetail head is provided at the bottom of the gauge body; inclined surfaces are provided on both sides of the dovetail head for contact and cooperation with the inclined surfaces on both sides of the small dovetail groove on the workpiece to be detected; the central axis plane of the first reference surface and the second reference surface coincides with the central axis plane of the inclined surfaces on both sides of the dovetail head;

[0010] A threaded ejector rod, which is slidably installed on the gauge body up and down. The upper part of the threaded ejector rod is a threaded section and extends out of the gauge body. A nut is provided on this threaded section, and the nut is used to adjust the longitudinal position of the threaded ejector rod so that the lower end of the threaded ejector rod extends out or retracts from the dovetail head;

[0011] A spring, which is arranged inside the gauge body and sleeved on the threaded ejector rod. The spring is in a compressed state, with its upper end abutted against the gauge body and its lower end abutted against the threaded ejector rod.

[0012] Preferably, a stepped hole is provided on the gauge body, and the diameter of the upper section of the stepped hole is larger than that of the lower section; the spring is arranged in the lower section of the stepped hole; the upper end of the spring abuts against the step surface between the upper section and the lower section of the stepped hole; the middle part of the threaded ejector rod is a smooth rod and is slidably matched with the upper section of the stepped hole of the gauge body; an annular boss is provided on the threaded ejector rod, and the lower end of the spring abuts against the annular boss.

[0013] Preferably, the clearance between the smooth rod in the middle of the threaded ejector rod and the upper section of the stepped hole is 0.02 - 0.03 mm.

[0014] Preferably, the surface roughness of the bottom surface of the dovetail head is not greater than Ra0.2.

[0015] Preferably, the perpendicularity between the bottom surface of the dovetail head and the first reference surface or the second reference surface is 0.005; the perpendicularity between the lower end surface of the threaded ejector rod and the first reference surface or the second reference surface is 0.005.

[0016] Preferably, at the lower end of the threaded ejector rod is an ejector head, and the shape of the ejector head is a dovetail structure. The angles of the inclined surfaces on both sides of the ejector head are the same as those of the inclined surfaces on both sides of the dovetail head; a slot is provided on the dovetail head, the ejector head is located on this slot, and the clearance between the ejector head and the two side surfaces of the slot is 0.02 - 0.03 mm.

[0017] Preferably, the roughness of both sides of the slot is not greater than Ra0.8; the roughness of the surface of the ejector rod head that mates with both sides of the slot is not greater than Ra0.8.

[0018] Preferably, the roughness of the lower end face of the ejector rod head of the threaded ejector rod is not greater than Ra0.2, and the roughness of the two inclined surfaces on both sides of the ejector rod head is not greater than Ra0.4.

[0019] Preferably, the length of the upper threaded section of the threaded ejector rod is greater than or equal to 3 times the maximum distance that the ejector rod head extends downward; an anti-slip structure is provided on the outer peripheral surface of the nut, and the anti-slip structure is knurling.

[0020] On the other hand, the present invention also provides a method for detecting the symmetry of the inner hole of a small dovetail groove, using the above-mentioned device for detecting the symmetry of the inner hole of a small dovetail groove, including the following steps:

[0021] Step S1: Place the workpiece with a small dovetail groove to be detected on a three-coordinate machine tool and fix it.

[0022] Step S2: Place the device for detecting the symmetry of the inner hole of the small dovetail groove into the small dovetail groove of the workpiece to be detected, so that the dovetail head of the gauge body is inserted into the small dovetail groove.

[0023] Step S3: Rotate the nut so that the threaded ejector rod moves downward, and the lower end of the threaded ejector rod extends out from the dovetail head, and the lower end face of the threaded ejector rod is tightly attached to the bottom of the small dovetail groove. Utilize the upward elastic force generated by the spring on the gauge body to make the two inclined surfaces on both sides of the dovetail head tightly attached to the two inclined surfaces of the small dovetail groove on the workpiece to be detected.

[0024] Step S4: Use the probe of the three-coordinate equipment to take points on the first reference plane and the second reference plane of the gauge body respectively, and then use the three-coordinate to generate the central plane of the first reference plane and the second reference plane. This central plane is the central plane of the two inclined surfaces of the measured small dovetail groove.

[0025] Step S5: Loosen the nut 4 and remove the entire device for detecting the symmetry of the inner hole of the small dovetail groove.

[0026] Step S6: Use the three-coordinate probe to take points on the cylindrical hole at the bottom of the upper groove of the small dovetail groove and generate the central axis of the cylindrical hole.

[0027] Step S7: Use the three-coordinate to evaluate the positional relationship between the central axis of the cylindrical hole and the central plane of the first reference plane and the second reference plane, and the symmetry of the inner hole of the small dovetail groove on the workpiece can be obtained.

[0028] Due to the adoption of the above technical solutions, the beneficial effects of the present invention are as follows:

[0029] In the present invention, by placing the detection device into the small dovetail groove of the workpiece to be detected, the dovetail head of the gauge body is inserted into the small dovetail groove. By rotating the nut, the threaded ejector rod moves downward, and the lower end of the threaded ejector rod extends from the dovetail head, and the lower end surface of the threaded ejector rod is tightly attached to the bottom of the small dovetail groove. Utilizing the upward elastic force generated by the spring on the gauge body, the inclined surfaces on both sides of the dovetail head are tightly attached to the inclined surfaces on both sides of the small dovetail groove on the workpiece to be detected. Then, using a three-coordinate device probe to take points on the first reference plane and the second reference plane of the gauge body respectively, and then using the three-coordinate to generate the central axis plane of the first reference plane and the second reference plane. Since the central axis plane of the first reference plane and the second reference plane on the gauge body coincides with the central axis plane of the inclined surfaces on both sides of the dovetail head, and during the detection process, the inclined surfaces on both sides of the dovetail head are tightly attached to the inclined surfaces on both sides of the small dovetail groove on the workpiece to be detected. Therefore, the central axis plane of the first reference plane and the second reference plane is the central axis plane of the inclined surfaces on both sides of the measured small dovetail groove. The present invention utilizes this small dovetail groove inner hole symmetry detection device to solve the problem that due to the too narrow width of the small dovetail groove closing groove, the probe of the three-coordinate measuring instrument cannot measure the inclined surfaces on both sides of the dovetail groove. Through the present invention, the inner hole symmetry of the small dovetail groove can be accurately measured without cutting the part, saving a large amount of cost and ensuring the product quality. Brief Description of the Drawings

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0031] Figure 1 It is the main sectional view of the compressor disc part provided with a dovetail groove;

[0032] Figure 2 It is the top view of the compressor disc part provided with a dovetail groove;

[0033] Figure 3 It is Figure 2 The rotated view after the dovetail groove in

[0034] Figure 4 It is the front view of the small dovetail groove inner hole symmetry detection device provided by the present invention;

[0035] Figure 5 It is the top view of the small dovetail groove inner hole symmetry detection device provided by the present invention;

[0036] Figure 6 It is Figure 4Cross-sectional view of the small and medium-sized dovetail groove inner hole symmetry detection device along B-B;

[0037] Figure 7 For Figure 4 View of the small and medium-sized dovetail groove inner hole symmetry detection device along the C direction;

[0038] Figure 8 Front view of the gauge body in the present invention;

[0039] Figure 9 Top view of the gauge body in the present invention;

[0040] Figure 10 Front view of the threaded ejector rod in the present invention;

[0041] Figure 11 Left view of the threaded ejector rod in the present invention;

[0042] Figure 12 Front view of the nut in the present invention;

[0043] Figure 13 Schematic structural diagram when the small dovetail groove inner hole symmetry detection device provided by the present invention is inserted into the dovetail groove of the workpiece to be inspected.

[0044] Explanation of the reference numerals in the attached drawings: 1 - gauge body; 101 - dovetail head; 102 - first reference plane; 103 - second reference plane; 104 - stepped hole; 105 - slot; 2 - threaded ejector rod; 201 - annular boss; 3 - spring; 4 - nut. Specific implementation manners

[0045] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0046] It should be noted that all the directional indications (such as up, down, left, right, front, back...) in the embodiments of the present invention are only used to explain the relative positional relationship and movement conditions between components in a specific posture (as shown in the drawings). If the specific posture changes, the directional indications will also change accordingly.

[0047] In addition, the descriptions of "first", "second", etc. in the present invention are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0048] Combination Figures 1 to 3 The figure shows a compressor disc-type part with a dovetail tenon groove. The closing width D of the tenon groove is ≤14mm. When the dovetail tenon groove is processed to meet the design shape requirements, it is necessary to drill a hole at the bottom of the dovetail tenon groove to form a cylindrical hole M. The symmetry of the center of the cylindrical hole M relative to the center of the inclined surfaces (E surface and F surface) on both sides of the tenon groove does not exceed 0.2mm. Figure 3 In the figure, the bottom of the dovetail groove is represented by U.

[0049] Combination Figures 4 to 7 As shown, a small dovetail mortise and tenon inner hole symmetry detection device provided by the present invention comprises: a gauge body 1, and two side surfaces are respectively set as a first reference plane 102 and a second reference plane 103; a dovetail head 101 is set at the bottom of the gauge body 1; the central axis surfaces of the first reference plane 102 and the second reference plane 103 coincide with the central axis surfaces of the inclined surfaces on both sides of the dovetail head 101; the inclined surfaces on both sides of the dovetail head 101 are used to contact and cooperate with the inclined surfaces on both sides of the small dovetail mortise and tenon on the workpiece to be detected; the angles of the inclined surfaces on both sides of the dovetail head 101 are the same as the angles of the inclined surfaces on both sides of the small dovetail mortise and tenon on the workpiece to be detected. A threaded push rod 2 can be slidably installed on the gauge body 1 up and down. The upper part of the threaded push rod 2 is a threaded section and extends out of the gauge body 1. A nut 4 is provided on the threaded section. The nut 4 is used to adjust the longitudinal position of the threaded push rod 2 so that the lower end of the threaded push rod 2 extends or retracts from the dovetail head 101; a spring 3 is provided in the gauge body 1 and is sleeved on the threaded push rod 2. The spring 3 is in a compressed state, with its upper end resting on the gauge body 1 and its lower end resting on the threaded push rod 2.

[0050] Combination Figure 6 and Figure 8 As shown, a stepped hole 104 is provided on the gauge body 1, and the diameter of the upper section of the stepped hole 104 is larger than the diameter of the lower section; the spring 3 is arranged in the lower section of the stepped hole 104; the upper end of the spring 3 abuts on the step surface between the upper section and the lower section of the stepped hole 104; the middle part of the threaded push rod 2 is a smooth rod, and is slidably matched with the upper section of the stepped hole 104 of the gauge body 1; an annular boss 201 is provided on the threaded push rod 2, and the lower end of the spring 3 abuts on the annular boss 201.

[0051] Furthermore, the fitting clearance between the polished rod in the middle of the threaded ejector rod 2 and the upper section of the stepped hole 104 is 0.02 - 0.03 mm. Based on the assembly of the threaded ejector rod 2 and the stepped hole 104, check the assembly clearance between the polished rod in the middle of the threaded ejector rod 2 and the upper section of the stepped hole 104 to ensure the assembly clearance, so as to ensure that when the nut 4 rotates, the threaded ejector rod 2 can move up or down freely without jamming.

[0052] Combined with Figure 4 、 Figure 8 、 Figure 9 As shown, the surface roughness of the bottom surface of the dovetail head 101 is not greater than Ra0.2. When the gauge body 1 is inserted into the dovetail groove of the workpiece to be inspected, ensure that the dovetail head 101 slides in the dovetail groove. The perpendicularity of the bottom surface of the dovetail head 101 to the first reference plane 102 or the second reference plane 103 is 0.005, and the perpendicularity of the lower end surface of the threaded ejector rod 2 to the first reference plane 102 or the second reference plane 103 is 0.005. When the lower end surface of the threaded ejector rod 2 contacts the bottom U of the dovetail groove, ensure the accuracy of measurement. During the manufacturing process, based on the assembly, grind the lower end surface (G surface) of the threaded ejector rod 2 to meet the requirement that the perpendicularity of the G surface of the threaded ejector rod 2 to the first reference plane 102 or the second reference plane 103 is 0.005.

[0053] Combined with Figure 10 、 Figure 11 、and Figure 4 、 Figure 8 As shown, at the lower end of the threaded ejector rod 2 is an ejector head, and the shape of the ejector head is a dovetail structure. The angles of the inclined surfaces on both sides of the ejector head are the same as those of the inclined surfaces on both sides of the dovetail head 101; there is a slot 105 on the dovetail head 101, the ejector head is located on the slot 105, and the fitting clearance between the ejector head and the two side surfaces of the slot 105 is 0.02 - 0.03 mm. Furthermore, the surface roughness of the two side surfaces of the slot 105 is not greater than Ra0.8; the surface roughness of the surfaces of the ejector head that cooperate with the two side surfaces of the slot 105 is not greater than Ra0.8. During processing, through the roughness requirements, it can be ensured that when the threaded ejector rod 2 moves up and down, it will not cause jamming. The surface roughness of the lower end surface of the ejector head of the threaded ejector rod 2 is not greater than Ra0.2, and the surface roughness of the inclined surfaces on both sides of the ejector head is not greater than Ra0.4, ensuring that the dovetail head 101 of the gauge body 1 and the ejector head of the threaded ejector rod 2 slide in the dovetail groove.

[0054] Combined with Figure 10 As shown, the length L of the threaded section at the upper part of the threaded ejector rod 2 is greater than or equal to 3 times the maximum downward extension distance of the ejector head, so as to ensure the effective telescopic distance of the threaded ejector rod 2.

[0055] Combined withFigure 6 , Figure 12 As shown, an anti-slip structure is provided on the outer peripheral surface of the nut 4, and the anti-slip structure is knurling. There is a thread inside the nut 4, and by rotating the nut 4, the ejector head of the threaded ejector rod 2 can move upward or downward.

[0056] On the other hand, in combination with Figure 3 , Figure 4 and Figure 13 shown, this embodiment also provides a method for detecting the symmetry of the inner hole of a small dovetail groove, using the above-mentioned device for detecting the symmetry of the inner hole of a small dovetail groove, including the following steps:

[0057] Step S1: Place the workpiece with a small dovetail groove to be detected on a three-coordinate machine tool and fix it;

[0058] Step S2: Place the device for detecting the symmetry of the inner hole of the small dovetail groove into the small dovetail groove of the workpiece to be detected, so that the dovetail head 101 of the gauge body 1 is inserted into the small dovetail groove;

[0059] Step S3: Rotate the nut 4 so that the threaded ejector rod 2 moves downward, and the lower end of the threaded ejector rod 2 extends from the dovetail head 101, and the lower end surface (G surface) of the threaded ejector rod 2 is tightly attached to the bottom surface U of the small dovetail groove. Using the upward elastic force generated by the spring 3 on the gauge body 1, make the inclined surfaces on both sides of the dovetail head 101 tightly attached to the inclined surfaces on both sides of the small dovetail groove on the workpiece to be detected, that is, the E1 surface and F1 surface of the dovetail head 101 are respectively attached to the E surface and F surface of the small dovetail groove in the space to be detected;

[0060] Step S4: Use the probe of the three-coordinate equipment to take points on the first reference plane 102 and the second reference plane 103 of the gauge body 1 respectively, and then use the three-coordinate to generate the central axis plane of the first reference plane 102 and the second reference plane 103, and this central axis plane is the central axis plane of the inclined surfaces on both sides of the measured small dovetail groove;

[0061] Step S5: Loosen the nut 4 and remove the whole device for detecting the symmetry of the inner hole of the small dovetail groove;

[0062] Step S6: Use the three-coordinate probe to take points on the cylindrical hole M at the bottom of the upper groove of the small dovetail groove and generate the central axis of the cylindrical hole M;

[0063] Step S7: Use the three-coordinate to evaluate the positional relationship between the central axis of the cylindrical hole M and the central axis plane of the first reference plane 102 and the second reference plane 103, and the symmetry of the inner hole (cylindrical hole M) of the small dovetail groove on the workpiece can be obtained.

[0064] The above are only the preferred embodiments of the present invention, and do not thereby limit the patent scope of the present invention. Any equivalent structural transformation made under the inventive concept of the present invention by using the content of the specification and drawings of the present invention, or any direct / indirect application in other related technical fields, is included in the patent protection scope of the present invention.

Claims

1. A small dovetail groove inner hole symmetry detection device, characterized in that, Comprising: A gauge body (1) with its two side surfaces respectively set as a first reference surface (102) and a second reference surface (103); a dovetail head (101) is provided at the bottom of the gauge body (1); the central axis plane of the first reference surface (102) and the second reference surface (103) coincides with the central axis plane of the two inclined surfaces of the dovetail head (101). A threaded ejector rod (2) is slidably mounted on the gauge body (1) up and down. The upper part of the threaded ejector rod (2) is a threaded section and extends outside the gauge body (1). A nut (4) is provided on this threaded section. The nut (4) is used to adjust the longitudinal position of the threaded ejector rod (2) so that the lower end of the threaded ejector rod (2) extends out or retracts from the dovetail head (101). A spring (3) is arranged inside the gauge body (1) and sleeved on the threaded ejector rod (2). The spring (3) is in a compressed state, with its upper end abutted against the gauge body (1) and its lower end abutted against the threaded ejector rod (2). A stepped hole (104) is provided on the gauge body (1). The diameter of the upper section of the stepped hole (104) is larger than that of the lower section; the spring (3) is arranged in the lower section of the stepped hole (104); the upper end of the spring (3) abuts against the step surface between the upper and lower sections of the stepped hole (104). The middle part of the threaded ejector rod (2) is a smooth rod and is in sliding fit with the upper section of the stepped hole (104) of the gauge body (1). An annular boss (201) is provided on the threaded ejector rod (2), and the lower end of the spring (3) abuts against the annular boss (201).

2. The small dovetail-shaped tenon groove inner hole symmetry detection device according to claim 1, wherein: The clearance between the smooth rod in the middle of the threaded ejector rod (2) and the upper section of the stepped hole (104) is 0.02 - 0.03 mm.

3. A small dovetail-shaped tenon groove inner hole symmetry detection device according to claim 1, characterized in that: The surface roughness of the bottom surface of the dovetail head (101) is not greater than Ra0.

2.

4. The small dovetail type tenon groove inner hole symmetry detection device according to claim 1, wherein: The perpendicularity between the bottom surface of the dovetail head (101) and the first reference surface (102) or the second reference surface (103) is 0.005; the perpendicularity between the lower end surface of the threaded ejector rod (2) and the first reference surface (102) or the second reference surface (103) is 0.

005.

5. A small dovetail-shaped mortise inner hole symmetry detection device according to claim 1, characterized in that: The lower end of the threaded ejector rod (2) is a ejector head, and the shape of this ejector head is a dovetail structure. The angles of the two inclined surfaces of the ejector head are the same as those of the two inclined surfaces of the dovetail head (101). A slot (105) is provided on the dovetail head (101). The ejector head is located on this slot (105), and the clearance between the ejector head and the two side surfaces of this slot (105) is 0.02 - 0.03 mm.

6. The small dovetail-shaped tenon groove inner hole symmetry detection device according to claim 5, characterized in that: The surface roughness of the two side surfaces of the slot (105) is not greater than Ra0.8; the surface roughness of the surfaces of the ejector head that cooperate with the two side surfaces of the slot (105) is not greater than Ra0.

8.

7. The small dovetail-shaped tenon groove inner hole symmetry detection device according to claim 5, characterized in that: The surface roughness of the lower end surface of the ejector head of the threaded ejector rod (2) is not greater than Ra0.2, and the surface roughness of the two inclined surfaces of the ejector head is not greater than Ra0.

4.

8. A small dovetail groove inner hole symmetry detection device according to claim 5, characterized in that: The length of the upper threaded section of the threaded ejector rod (2) is greater than or equal to 3 times the maximum distance that the ejector head extends downward; an anti-slip structure is provided on the outer peripheral surface of the nut (4), and this anti-slip structure is knurling.

9. A method for detecting the symmetry of the inner hole of a small dovetail groove, characterized in that Using the small dovetail type tenon groove inner hole symmetry detection device according to any one of claims 1 to 8, comprising the following steps: Step S1: Place the workpiece with a small dovetail groove to be detected on a three - coordinate machine tool and fix it. Step S2: Place the small dovetail groove inner - hole symmetry detection device into the small dovetail groove of the workpiece to be detected, so that the dovetail head (101) of the gauge body (1) is inserted into the small dovetail groove. Step S3: Rotate the nut (4) to make the threaded ejector rod (2) move downward. The lower end of the threaded ejector rod (2) extends from the dovetail head (101), and the lower end face of the threaded ejector rod (2) is tightly attached to the bottom of the small dovetail groove. Utilize the upward elastic force generated by the spring (3) on the gauge body (1) to make the inclined planes on both sides of the dovetail head (101) closely adhere to the inclined planes on both sides of the small dovetail groove on the workpiece to be detected. Step S4: Use the probe of the three - coordinate device to take points on the first reference plane (102) and the second reference plane (103) of the gauge body (1) respectively, and then use the three - coordinate to generate the central plane of the first reference plane (102) and the second reference plane (103). This central plane is the central plane of the inclined planes on both sides of the measured small dovetail groove. Step S5: Loosen the nut 4 and remove the whole small dovetail groove inner - hole symmetry detection device. Step S6: Use a three - coordinate probe to take points on the cylindrical hole at the bottom of the small dovetail groove and generate the central axis of this cylindrical hole. Step S7: Utilize the three - coordinate to evaluate the positional relationship between the central axis of the cylindrical hole and the central plane of the first reference plane (102) and the second reference plane (103), and then the symmetry of the inner hole of the small dovetail groove on the workpiece can be obtained.

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