CN114964124A - Device and method for detecting symmetry degree of inner hole of small dovetail-shaped mortise - Google Patents

Abstract

A small dovetail type tongue and groove inner hole symmetry detection device, comprising: a gauge body, two side surfaces are respectively set as a first reference plane and a second reference plane; a dovetail head is arranged at the bottom of the gauge body; the first reference plane and the second reference plane The central axis of the two datum planes coincides with the central axis of the inclined surfaces on both sides of the dovetail head; the threaded ejector can be installed on the gauge body by sliding up and down, and the upper part of the threaded ejector is a threaded section and extends out of the gauge. There is a nut on it, 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 or retracts from the dovetail; The spring is in a compressed state, its upper end abuts on the gauge body, and its lower end abuts on the threaded ejector rod. The use of the small dovetail type tongue groove inner hole symmetry detection device solves the problem that the three-coordinate detection measuring instrument cannot measure the inclined surfaces on both sides of the dovetail type tongue groove because the width of the small dovetail type tongue groove is too narrow.

Description

A small dovetail type tongue and groove inner hole symmetry detection device and method

technical field

The invention relates to the technical field of aero-engine manufacturing, in particular to a tongue and groove detection technology, and in particular to a small dovetail type tongue and groove inner hole symmetry detection device and method.

Background technique

As shown in Figures 1 to 3, in aero-engines, the compressor disc parts are often evenly distributed with many dovetail grooves in the circumferential direction. The bottom of the groove needs to be drilled, and the design requires that the center of the hole is not more than 0.2mm symmetrical to the center of the inclined surfaces (E and F) on both sides of the tongue and groove. The small dovetail tongue and groove space is too narrow and the dovetail tongue groove has a fixed angle with the horizontal direction, so it is impossible to manufacture a special measuring tool to detect this size; , the measuring probe of the three-coordinate detection measuring instrument is still unable to take points on the inclined surfaces (E and F surfaces) on both sides of the dovetail groove, so the central axis of the inclined surfaces on both sides of the dovetail groove (E and F surfaces) cannot be obtained. face, resulting in the undetectable size of the symmetry of the hole relative to the dovetail groove.

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

For example, the patent with the application number CN201811024592.5 discloses a measuring device for the intersection of the arc dovetail type tongue and groove of the engine, which adopts a layered and split combination structure. The method of centering, punching the meter to read out the specific value, and finding the minimum size obtained by repeated points is the intersection point size of the measured part, which realizes the ease of processing and metrology of the arc-type axial dovetail groove intersection point measuring device.

For another example, the patent with the application number CN201020037750.3 discloses a comprehensive measuring instrument for the tenon and groove of the high-pressure compressor wheel disc. The dial indicator installed on the positioning device is checked, and then the measuring positioning device is placed on the wheel disc of the high-pressure compressor to be measured, and the measured part of the tongue and groove is transferred out through the adapter for measurement.

However, the above reference documents do not disclose the problem of detecting the symmetry of the inner hole at the bottom of the groove of the small dovetail groove of the compressor disc parts, which has always been a difficult problem in the machining industry. Solving this problem can fill the technical gap in the inspection of the symmetry of the inner hole of the small dovetail type tongue and groove in the industry and ensure the quality of the product, which is meaningful to the entire aero-engine manufacturing industry.

SUMMARY OF THE INVENTION

The main purpose of the present invention is to propose a small dovetail type tongue and groove inner hole symmetry detection device and method, aiming at solving the above technical problems.

In order to achieve the above purpose, on the one hand, the present invention proposes a small dovetail type tongue and groove inner hole symmetry detection device, comprising:

The two sides of the gauge body are respectively set as the first reference plane and the second reference plane; the bottom of the gauge body is provided with a dovetail head; the two sides of the dovetail head are provided with inclined surfaces for connecting with both sides of the small dovetail tenon groove on the workpiece to be detected The inclined surfaces are in contact with each other; the central axis surfaces of the first reference surface and the second reference surface coincide with the central axis surfaces of the inclined surfaces on both sides of the dovetail head;

The threaded mandrel can be installed on the gauge body by sliding up and down. The upper part of the threaded mandrel is a threaded section and extends out of the gauge. The threaded section is provided with a nut, which is used to adjust the longitudinal position of the threaded mandrel to make the thread The lower end of the ejector rod extends or retracts from the dovetail head;

The spring is arranged in the gauge body and is sleeved on the threaded ejector rod. The spring is in a compressed state, the upper end of the spring abuts on the gauge body, and the lower end abuts on the threaded ejector rod.

Preferably, a stepped hole is provided on the gauge body, and the diameter of the upper section of the stepped hole is larger than the diameter 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 between the upper section and the lower section of the stepped hole The middle part of the threaded ejector rod is a polished rod, and is slidably matched with the upper section of the stepped hole of the gauge body; an annular boss is arranged on the threaded ejector rod, and the lower end of the spring abuts on the annular boss.

Preferably, the fitting gap between the polished rod in the middle of the threaded ejector rod and the upper section of the stepped hole is 0.02-0.03 mm.

Preferably, the roughness of the bottom surface of the dovetail is not greater than Ra0.2.

Preferably, the verticality between the bottom surface of the dovetail head and the first reference plane or the second reference plane is 0.005; the verticality between the lower end surface of the threaded ejector and the first reference plane or the second reference plane is 0.005.

Preferably, the lower end of the threaded ejector is an ejector head, the shape of the ejector head is a dovetail structure, and the angle of the inclined surfaces on both sides of the ejector head is the same as the angle of the inclined surfaces on both sides of the dovetail head; There is a slot, the ejector head is located on the slot, and the matching gap between the ejector head and the two sides of the slot is 0.02-0.03mm.

Preferably, the roughness of the two sides of the slot is not greater than Ra0.8; the roughness of the surface where the ejector head matches the two sides of the slot is not greater than Ra0.8.

Preferably, the roughness of the lower end surface of the ejector head of the threaded ejector is not greater than Ra0.2, and the roughness of the inclined surfaces on both sides of the ejector head is not greater than Ra0.4.

Preferably, the length of the upper threaded section of the threaded ejector pin is greater than or equal to 3 times the maximum downward extension distance of the ejector pin head; an anti-skid structure is provided on the outer peripheral surface of the nut, and the anti-slip structure is knurled.

On the other hand, the present invention also proposes a small-scale dovetail type tongue-groove inner hole symmetry detection method, using the above-mentioned small-scale dovetail type tongue-and-groove inner hole symmetry detection device, comprising the following steps:

Step S1: place the workpiece to be tested with a small dovetail groove on a three-coordinate machine tool and fix it;

Step S2: putting the small-sized dovetail-shaped tongue-groove inner hole symmetry detection device into the small-sized dovetail-shaped tongue-groove of the workpiece to be detected, so that the dovetail head of the gauge body is inserted into the small-sized dovetail-shaped tongue-groove;

Step S3: Rotate the nut so that the threaded ejector rod moves downward, the lower end of the threaded ejector rod protrudes from the dovetail head, and the lower end surface of the threaded ejector rod is close to the groove bottom of the small dovetail groove, and the spring is used to align the gauge. The upward elastic force generated by the body makes the slopes on both sides of the dovetail head close to the slopes on both sides of the small dovetail tongue and groove on the workpiece to be tested;

Step S4: Use the three-coordinate device probe to take points on the first reference plane and the second reference plane of the gauge body respectively, and then use the three coordinates to generate the central axis plane of the first reference plane and the second reference plane, and the central axis plane is is the central axis surface of the inclined surfaces on both sides of the small dovetail groove under test;

Step S5: Loosen the nut 4, and remove the whole small dovetail-shaped tongue-groove inner hole symmetry detection device;

Step S6: using a 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;

Step S7: Evaluate the positional relationship between the central axis of the cylindrical hole and the central axis of the first reference plane and the second reference plane by using three coordinates, so as to obtain the symmetry of the small dovetail groove inner hole on the workpiece.

Owing to adopting the above-mentioned technical scheme, the beneficial effects of the present invention are as follows:

In the present invention, the detection device is put into the small dovetail tenon groove of the workpiece to be inspected, so that the dovetail head of the gauge body is inserted into the small dovetail tenon groove. The lower end of the mandrel protrudes from the dovetail head, and the lower end face of the threaded mandrel is close to the bottom of the small dovetail tenon groove, and the upward elastic force generated by the spring to the gauge body is used to make the inclined surfaces on both sides of the dovetail head close to the groove. On the slopes on both sides of the small dovetail groove on the workpiece to be inspected. Then use the three-coordinate equipment probe to take points on the first reference plane and the second reference plane of the gauge body respectively, and then use the three coordinates to generate the central axis plane of the first reference plane and the second reference plane. The central axis of the reference plane and the second reference plane coincide with the central axis of the inclined surfaces on both sides of the dovetail head, and during the inspection process, the inclined surfaces on both sides of the dovetail head are close to the two sides of the small dovetail groove on the workpiece to be inspected. superior. Therefore, the central axis planes of the first reference plane and the second reference plane can be the central axis planes of the inclined planes on both sides of the small dovetail groove. The invention utilizes the small dovetail type tongue groove inner hole symmetry detection device, and solves the problem that the three-coordinate detection measuring instrument cannot measure the inclined surfaces on both sides of the dovetail type tongue groove because the small dovetail type tongue groove closing groove width is too narrow. The invention can accurately measure the symmetry of the inner hole of the small dovetail type tongue groove without cutting parts, save a lot of cost, and ensure product quality.

Description of drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention, and for those of ordinary skill in the art, other drawings can also be obtained according to the structures shown in these drawings without creative efforts.

Figure 1 is a main cross-sectional view of a compressor disc type part provided with a dovetail tenon groove;

Figure 2 is a plan view of a compressor disc type part provided with a dovetail tenon groove;

Fig. 3 is the rear rotation view of the cross-sectional view of the dovetail type tongue groove along K-K in Fig. 2;

Figure 4 is a front view of a small dovetail type tongue and groove inner hole symmetry detection device provided by the present invention;

5 is a top view of a small-sized dovetail-shaped tongue-groove inner hole symmetry detection device provided by the present invention;

6 is a cross-sectional view along B-B of the small and medium-sized dovetail-shaped tongue-groove inner hole symmetry detection device in FIG. 4;

FIG. 7 is a view along the direction C of the small and medium-sized dovetail type tongue groove inner hole symmetry detection device in FIG. 4;

Fig. 8 is the front view of the regular body in the present invention;

Fig. 9 is the top view of the regular body in the present invention;

Figure 10 is a front view of a threaded ejector rod in the present invention;

Figure 11 is a left side view of a threaded ejector rod in the present invention;

Figure 12 is a front view of the nut in the present invention;

13 is a schematic structural diagram of the small-sized dovetail-shaped tongue-groove inner hole symmetry detection device provided by the present invention inserted into the dovetail-shaped tongue-groove of the workpiece to be tested.

Reference number description: 1-regular body; 101-dovetail head; 102-first reference plane; 103-second reference plane; 104-step hole; 105-slotting; 2-threaded ejector rod; 201-ring boss ; 3-spring; 4-nut.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relationship between various components under a certain posture (as shown in the accompanying drawings). The relative positional relationship, the movement situation, etc., if the specific posture changes, the directional indication also changes accordingly.

In addition, the descriptions involving "first", "second", etc. in the present invention are only for descriptive purposes, and should not be understood as indicating or implying their relative importance or implying the number of indicated technical features. Thus, a feature delimited with "first", "second" may expressly or implicitly include at least one of that feature. In addition, the technical solutions between the various embodiments can be combined with each other, but must be based on the realization by those of ordinary skill in the art. When the combination of technical solutions is contradictory or cannot be realized, it should be considered that the combination of such technical solutions does not exist. , is not within the scope of protection required by the present invention.

With reference to Figures 1 to 3, it is a schematic diagram of a compressor disc part with a dovetail tongue groove. The width of the tongue groove is D≤14mm. During processing, when the dovetail tongue groove is processed in place to meet the design shape requirements , it is necessary to drill holes at the bottom of the dovetail groove, and process a cylindrical hole M, and the symmetry of the center of the cylindrical hole M relative to the center of the inclined planes (E and F planes) on both sides of the tenon and groove does not exceed 0.2mm. In Figure 3, the groove bottom of the dovetail groove is denoted by U.

4 to 7, it is a small dovetail type tongue and groove inner hole symmetry detection device provided by the present invention, the detection device includes: a regular body 1, two sides are respectively set as a first reference plane 102 and a second Two reference planes 103; a dovetail head 101 is provided at the bottom of the body 1; the central axis planes of the first reference plane 102 and the second reference plane 103 coincide with the central axis planes of the inclined surfaces on both sides of the dovetail head 101; The side slopes are used to contact and cooperate with the slopes on both sides of the small dovetail groove on the workpiece to be inspected; the angle of the slopes on both sides of the dovetail head 101 is the same as the slope angle on both sides of the small dovetail groove on the workpiece to be inspected. The threaded mandrel 2 can be slid up and down and installed on the gauge body 1. The upper part of the threaded mandrel 2 is a threaded section and extends out of the gauge body 1. A nut 4 is provided on the threaded section, and the nut 4 is used to adjust the thread The longitudinal position of the ejector rod 2 causes the lower end of the threaded ejector rod 2 to extend or retract from the dovetail head 101; the spring 3 is arranged in the body 1 and is sleeved on the threaded ejector rod 2, and the spring 3 is in compression. In the state, its upper end abuts on the gauge body 1, and its lower end abuts on the threaded ejector rod 2.

6 and 8, 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 Abut on the stepped surface between the upper and lower sections of the stepped hole 104; the middle part of the threaded ejector rod 2 is a polished rod, and slidingly fits with the upper section of the stepped hole 104 of the gauge body 1; the threaded ejector rod 2 is provided with a ring The boss 201, the lower end of the spring 3 abuts on the annular boss 201.

Further, the fitting gap 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. On the basis of the assembly of the threaded mandrel 2 and the stepped hole 104, the assembly clearance between the polished rod in the middle of the threaded mandrel 2 and the upper section of the stepped hole 104 is checked to ensure the assembly clearance, so as to ensure that when the nut 4 is rotated, the The threaded ejector rod 2 can move up or down freely without jamming.

4, 8 and 9, the 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 tenon groove of the workpiece to be inspected, it is ensured that the dovetail head 101 is in the dovetail shape. Tongue and groove sliding in tongue and groove. The verticality between the bottom surface of the dovetail head 101 and the first reference surface 102 or the second reference surface 103 is 0.005, and the verticality 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, when the lower end face of the threaded ejector rod 2 is in contact with the groove bottom U of the dovetail groove, so as to ensure the accuracy of the measurement. During the manufacturing process, the lower end surface (G surface) of the threaded ejector rod 2 is ground on the basis of assembly, so that the perpendicularity between the G surface of the threaded ejector pin 2 and the first reference plane 102 or the second reference plane 103 is 0.005 requirement.

10, 11, 4 and 8, the lower end of the threaded mandrel 2 is a mandrel head, and the shape of the mandrel head is a dovetail structure, and the angle of the inclined surfaces on both sides of the mandrel head is the same as the dovetail head. The angles of the slopes on both sides of 101 are the same; a slot 105 is provided on the dovetail head 101, the ejector head is located on the slot 105, and the matching clearance between the ejector head and the two sides of the slot 105 is 0.02～ 0.03mm. Further, the roughness of the two sides of the slot 105 is not greater than Ra0.8; the roughness of the surface where the ejector head matches the two sides of the slot 105 is not greater than Ra0.8. During processing, according to the roughness requirements, it can be ensured that the threaded ejector rod 2 will not cause jamming when moving up and down. The roughness of the lower end surface of the ejector head of the threaded ejector rod 2 is not greater than Ra0.2, and the roughness of the inclined surfaces on both sides of the ejector head is not greater than Ra0.4, to ensure that the dovetail head 101 of the body 1 and the threaded ejector rod 2 are not more than Ra0.4. The ejector head slides tongue and groove in a dovetail type tongue and groove.

10 , the length L of the upper threaded section of the threaded ejector rod 2 is greater than or equal to 3 times the maximum downward extension distance of the ejector rod head, thereby ensuring the effective telescopic distance of the threaded ejector rod 2 .

6 and 12, an anti-skid structure is provided on the outer peripheral surface of the nut 4, and the anti-skid structure is knurled. The nut 4 is internally threaded, and by rotating the nut 4, the ejector head of the threaded ejector 2 can be moved upward or downward.

On the other hand, with reference to FIG. 3 , FIG. 4 and FIG. 13 , this embodiment also provides a method for detecting the symmetry of a small dovetail type tongue and groove inner hole, using the above-mentioned small dovetail type tongue and groove inner hole symmetry detection device, comprising: The following steps:

Step S1: place the workpiece to be tested with a small dovetail groove on a three-coordinate machine tool and fix it;

Step S2: putting the small-sized dovetail-shaped tongue-groove inner hole symmetry detection device into the small-sized dovetail-shaped tongue-groove of the workpiece to be detected, so that the dovetail head 101 of the gauge body 1 is inserted into the small-sized dovetail-shaped tongue-and-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 protrudes from the dovetail head 101, and the lower end surface (G surface) of the threaded ejector rod 2 is closely attached to the small dovetail tenon On the U surface of the groove bottom of the groove, the upward elastic force generated by the spring 3 to the gauge body 1 is used to make the inclined surfaces on both sides of the dovetail head 101 closely adhere to the two sides of the small dovetail groove on the workpiece to be tested. The E1 and F1 surfaces are respectively attached to the E and F surfaces of the small dovetail groove in the space to be tested;

Step S4: use the three-coordinate device probe to take points on the first reference plane 102 and the second reference plane 103 of the scale body 1 respectively, and then use the three coordinates to generate the central axis plane of the first reference plane 102 and the second reference plane 103, The central axis is the central axis of the inclined surfaces on both sides of the small dovetail groove to be measured;

Step S5: Loosen the nut 4, and remove the whole small dovetail-shaped tongue-groove inner hole symmetry detection device;

Step S6: using a 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;

Step S7: Use three coordinates to evaluate the positional relationship between the central axis of the cylindrical hole M and the central axis of the first reference plane 102 and the second reference plane 103, so as to obtain the small dovetail-shaped tongue groove inner hole (the cylindrical hole M) on the workpiece. ) symmetry.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the scope of the present invention. Under the inventive concept of the present invention, any equivalent structural transformations made by using the contents of the description and drawings of the present invention, or direct/indirect Applications in other related technical fields are included in the scope of patent protection of the present invention.

Claims (10)

1. The utility model provides a small-size dovetail tongue-and-groove hole symmetry detection device which characterized in that includes:

a gauge body (1) having a first reference surface (102) and a second reference surface (103) on both side surfaces thereof, respectively; a dovetail head (101) is arranged at the bottom of the gauge body (1); the middle shaft surfaces of the first reference surface (102) and the second reference surface (103) are overlapped with the middle shaft surfaces of the inclined surfaces at the two sides of the dovetail head (101);

the screw ejector rod (2) can be installed on the gauge body (1) in a vertically sliding mode, the upper portion of the screw ejector rod (2) is a screw thread section and extends out of the gauge body (1), a screw cap (4) is arranged on the screw thread section, and the screw cap (4) is used for adjusting the longitudinal position of the screw ejector rod (2) to enable the lower end of the screw ejector rod (2) to extend out of or retract into the dovetail head (101);

the spring (3) is arranged in the gauge body (1) and sleeved on the threaded ejector rod (2), the spring (3) is in a compressed state, the upper end of the spring abuts against the gauge body (1), and the lower end of the spring abuts against the threaded ejector rod (2).

2. The apparatus for detecting the symmetry of the inner hole of the small dovetail-shaped mortise as claimed in claim 1, wherein: a stepped hole (104) is arranged on the gauge body (1), and 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) is abutted against a step surface between the upper section and the lower section of the stepped hole (104);

the middle part of the threaded mandril (2) is a polished 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 arranged on the threaded mandril (2), and the lower end of the spring (3) is abutted against the annular boss (201).

3. The apparatus for detecting the symmetry of the inner hole of the small dovetail-shaped mortise as claimed in claim 2, wherein: and the fit 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.

4. The apparatus for detecting the symmetry of the inner hole of the small dovetail-shaped mortise as claimed in claim 1, wherein: the bottom surface roughness of the dovetail head (101) is not more than Ra0.2.

5. The apparatus for detecting the symmetry of the inner hole of the small dovetail-shaped mortise as claimed in 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 face of the threaded mandril (2) and the first reference surface (102) or the second reference surface (103) is 0.005.

6. The apparatus for detecting the symmetry of the inner hole of the small dovetail-shaped mortise as claimed in claim 1, wherein: the lower end of the threaded ejector rod (2) is provided with an ejector rod head, the ejector rod head is in a dovetail structure, and the angles of the inclined planes on the two sides of the ejector rod head are the same as those of the inclined planes on the two sides of the dovetail head (101); a slot (105) is formed in the dovetail (101), the ejector head is located on the slot (105), and the fit clearance between the ejector head and the two side faces of the slot (105) is 0.02-0.03 mm.

7. The apparatus for detecting the symmetry of the inner hole of the small dovetail-shaped mortise as claimed in claim 6, wherein: the roughness of two side surfaces of the slot (105) is not more than Ra0.8; the roughness of the surface of the ejector rod head matched with the two side surfaces of the groove (105) is not more than Ra0.8.

8. The apparatus for detecting the symmetry of the inner hole of the small dovetail-shaped mortise as claimed in claim 6, wherein: the roughness of the lower end face of the ejector rod head of the threaded ejector rod (2) is not more than Ra0.2, and the roughness of the inclined planes on the two sides of the ejector rod head is not more than Ra0.4.

9. The apparatus for detecting the symmetry of the inner hole of the small dovetail-shaped mortise as claimed in claim 6, wherein: the length of the thread section at the upper part of the thread ejector rod (2) is more than or equal to 3 times of the maximum downward extending distance of the ejector rod head; and an anti-slip structure is arranged on the peripheral surface of the nut (4), and the anti-slip structure is a knurl.

10. A method for detecting the symmetry of an inner hole of a small dovetail-shaped mortise, which is characterized in that the device for detecting the symmetry of the inner hole of the small dovetail-shaped mortise of any one of claims 1 to 9 is adopted, and comprises the following steps:

step S1: placing a workpiece to be detected with a small dovetail-shaped mortise on a three-coordinate machine tool and fixing;

step S2: placing the small dovetail type mortise inner hole symmetry degree detection device into a small dovetail type mortise of a workpiece to be detected, and enabling a dovetail head (101) of the gauge body (1) to be inserted into the small dovetail type mortise;

step S3: the screw cap (4) is rotated to enable the screw ejector rod (2) to move downwards, the lower end of the screw ejector rod (2) extends out of the dovetail head (101), the lower end face of the screw ejector rod (2) is attached to the bottom of the small dovetail type mortise, and the inclined planes on the two sides of the dovetail head (101) are attached to the inclined planes on the two sides of the small dovetail type mortise on the workpiece to be detected by utilizing the upward elasticity of the spring (3) on the gauge body (1);

step S4: respectively taking points of a first reference surface (102) and a second reference surface (103) of the gauge body (1) by using a probe of a three-coordinate device, and then generating a middle shaft surface of the first reference surface (102) and the second reference surface (103) by using three coordinates, wherein the middle shaft surface is the middle shaft surface of inclined surfaces on two sides of the measured small dovetail-shaped mortise;

step S5: loosening the screw cap 4, and taking down the whole small dovetail-shaped mortise inner hole symmetry degree detection device;

step S6: taking a point of a cylindrical hole at the bottom of the small dovetail-shaped mortise by adopting a three-coordinate measuring head, and generating a central axis of the cylindrical hole;

step S7: and evaluating the position relation between the central axis of the cylindrical hole and the central axis of the first datum plane (102) and the second datum plane (103) by using three coordinates, so as to obtain the symmetry of the inner hole of the small dovetail-shaped mortise on the workpiece.

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