A measuring tool for three-point closed-end thread minor diameter and a measuring method thereof

Abstract

This application relates to the field of fastener measurement technology, specifically disclosing a measuring fixture and method for measuring the minor diameter of a three-point tapered self-locking nut. The fixture includes a threaded sleeve and a tapered bolt that can be threadedly connected to the inner wall of the sleeve. The tapered bolt includes a threaded section and a pointed cone section that can extend into the nut to be measured. This solution can solve the problem that two-point measuring tools cannot directly measure the minor diameter of a three-point tapered self-locking nut after the inner diameter of the self-locking nut has deformed.

Description

Technical Field

[0001] This invention relates to the field of fastener measurement technology, specifically to a measuring fixture and method for measuring the minor diameter of a thread after three-point closing. Background Technology

[0002] Self-locking nuts, widely used in aerospace, shipbuilding, and other industries, are processed in various specifications, in large quantities, and with high requirements. The accuracy of the measurement of their closing dimensions directly affects the locking performance and the quality of product delivery. Closing is achieved by first manufacturing the nut using conventional processes, then using a pressing method to compress the closing portion of the nut. This causes radial plastic deformation of the threaded hole in the closing portion, making its radial dimension smaller than that of the connected screw. When the screw enters the deformed threaded hole of the nut, the radial pressure generated by the elastic deformation of the threaded hole ensures a tight connection between the nut and the screw, thus preventing loosening.

[0003] The extrusion deformation methods used in the closing of self-locking nuts generally fall into two main categories: surface contact closing and point contact closing. Surface contact closing includes elliptical and rectangular closing, achieved by using a tool to extrude the outer wall of the nut's threaded section into an elliptical or rectangular shape. Point contact closing includes two-point and three-point closing, achieved by using a pressure head to deform the nut's threaded end. Our company processes three-point closing self-locking nuts... Figure 1 Similar to the nut shown, it has three closing points on the threaded section at the end. The position of the closing points is set at the end or middle of the threaded section according to actual needs. When testing the closing size, it is necessary to measure the inner diameter (minor diameter of the thread) of the concentric circle formed by the three points. This dimension cannot be measured using existing two-point measuring tools such as vernier calipers and micrometers. It is also impractical to use a large precision measuring system to measure it on the processing site, as it is costly and inefficient. Therefore, a method for measuring the minor diameter of the thread after three-point closing is proposed. Summary of the Invention

[0004] The present invention provides a measuring fixture and method for measuring the minor diameter of a thread after three-point closing, in order to solve the problem that a two-point measuring tool cannot directly measure the minor diameter of a three-point closing self-locking nut after the inner diameter of the self-locking nut has been deformed.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a measuring fixture for measuring the minor diameter of a thread after three-point closing, comprising a threaded sleeve and a tapered bolt that can be threadedly connected to the inner wall of the threaded sleeve, wherein the tapered bolt comprises a threaded section and a pointed cone section.

[0006] The basic principle of this scheme is as follows: Since the conical surface of the pointed section is composed of continuous circular rings, the diameter of the rings is different at different lengths of the pointed section. The three-point closing is formed by pressing the same feed amount at three equidistant points on the outer circumference of the nut. Therefore, the inner wall of the nut at the closing point is inscribed with the same circular ring. By using the contact between the conical surface and the circular ring, the value of the minor diameter of the thread at the closing point can be obtained by measuring the outer diameter of the conical surface.

[0007] In addition, a method for measuring the minor diameter of threads based on this auxiliary tooling is proposed.

[0008] S1: Fully screw the tapered bolt inside the measuring fixture into the threaded sleeve;

[0009] S2: Align the concave end of the nut to be tested with the pointed tip of the tapered bolt and place it against the end face of the threaded sleeve;

[0010] S3: Tighten the tapered bolt and screw the pointed tip of the tapered bolt into the nut to be tested until the pointed tip is completely in contact with the inner wall of the constriction.

[0011] S4: Move the entire measuring fixture horizontally out of the nut's closing point;

[0012] S5: Use an external diameter measuring tool to contact the intersection of the threaded sleeve and the tapered bolt, and use the external diameter measuring tool to obtain the external diameter value at that point. This external diameter value is the minor diameter of the thread of the nut to be measured after the three-point closing.

[0013] The beneficial effects of this solution are as follows: After the nut to be tested completes the three-point closing process, it is necessary to measure the minor diameter of the thread. Since the value of the minor diameter of the thread is the diameter of the inscribed circle formed by the three points, and the distance between any two of the three points is only the straight-line distance between the two ends of the 1 / 3 arc of the inscribed circle, it is impossible to directly measure the diameter of the inscribed circle using commonly used two-point measuring instruments such as vernier calipers and micrometers, making measurement difficult. The fixture designed in this solution uses a conical surface with adjustable insertion depth to convert the inner diameter of the three-point inscribed circle into the outer diameter of the conical surface, making it convenient to obtain the measurement value of the minor diameter of the thread using commonly used vernier calipers and micrometers. The fixture has a simple structure and is convenient for measurement.

[0014] Furthermore, the threaded sleeve is provided with at least three safety mechanisms spaced apart circumferentially. Each safety mechanism includes a telescopic bar 8 that can extend and retract axially along the threaded sleeve, and a telescopic pin perpendicular to the telescopic bar 8 and slidably connected to the inner wall of the threaded sleeve. A limiting hole is opened at the end of the telescopic bar 8 near the telescopic pin. The telescopic pin includes a pin sleeve and a pin head, with a first spring connecting the pin sleeve and the pin head. Several axially spaced grooves are spaced apart circumferentially on the tapered bolt. When the nut is not in contact with the end wall of the threaded sleeve, the telescopic pin is engaged in the groove, preventing the tapered bolt from rotating. When the nut is in contact with the end wall of the threaded sleeve, the telescopic bar is compressed and retracts into the threaded sleeve. The limiting hole on the telescopic bar aligns with the telescopic pin, and the telescopic pin slides upward into the limiting hole, disengaging from the groove. At this time, the tapered bolt can be rotated, and the pin head retracts towards the pin sleeve, contacting the external thread of the tapered bolt.

[0015] The purpose of setting up a safety mechanism is to ensure that the sleeve is fully pressed against the surface of the nut so that measurements can be taken; at least three control points of the telescopic strip are set on the sleeve to prevent the sleeve from being tilted or offset relative to the nut, which would lead to inaccurate measurement results.

[0016] Furthermore, a handle is attached to the end of the tapered bolt away from the pointed tip. Holding the handle allows for easy rotation of the entire tapered bolt.

[0017] Furthermore, the handle, threaded section, and tapered section are all coaxially arranged.

[0018] Furthermore, the handle is equipped with a rubber sleeve to increase friction, improving the comfort of the operator when holding the handle.

[0019] Furthermore, the rubber sleeve has a textured surface. This textured surface increases the friction between the palm and the auxiliary tool, making it easier to twist.

[0020] Furthermore, before S1, steps S2 to S5 are repeated before the nut is finished to obtain the minor diameter of the thread before finishing; after S5, the difference between the minor diameter of the thread before finishing and the minor diameter of the thread after finishing is calculated to obtain the finishing amount. The deformation of the nut finishing is obtained. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of a three-point self-locking nut.

[0022] Figure 2 This is a schematic diagram of the measuring fixture in this embodiment;

[0023] Figure 3 This is a schematic diagram illustrating the use of the measuring fixture in this embodiment;

[0024] Figure 4 This is a partial cross-sectional view of the measuring fixture in this embodiment;

[0025] Figure 5for Figure 4 An enlarged schematic diagram of part A in the middle. Detailed Implementation

[0026] The following detailed description illustrates the specific implementation method:

[0027] The reference numerals in the accompanying drawings include: 1. Screw sleeve; 2. Tapered bolt; 3. Handle; 4. Internal thread; 5. External thread; 6. Tapered section; 7. Groove; 8. Telescopic strip; 81. Limiting hole; 82. Magnet; 82. Second spring; 9. Telescopic ejector pin; 91. Ejector pin head; 92. Ejector pin sleeve; 93. Snap ring; 94. First spring.

[0028] The basic implementation examples are as follows: Figure 1 To be continued Figure 3 As shown:

[0029] The measuring fixture consists of two components: a cylindrical threaded sleeve 1 and a tapered bolt 2. The inner wall of the threaded sleeve 1 is machined with an internal thread 4. The tapered bolt 2, from left to right, consists of a one-piece handle 3, a threaded section, and a conical section 6, all three sections coaxially arranged. The external thread 5 machined on the outside of the threaded section can be threadedly matched with the internal thread 4 on the threaded sleeve 1. The diameter of the conical surface of the conical section 6 gradually decreases from left to right, and the entire conical section 6 can be completely retracted into the threaded sleeve 1. A rubber sleeve with a spiral pattern is wrapped around the handle 3 to increase friction with the hand, facilitating the tightening of the tapered bolt 2.

[0030] To prevent the tapered bolt 2 from rotating before the nut to be tested has fully contacted the threaded sleeve 1, a safety mechanism with equal intervals is installed circumferentially on the threaded sleeve 1. In this embodiment, there are three safety mechanisms. Figure 4 , 5As shown, taking a single safety mechanism as an example, a blind hole with its opening facing the nut is machined into the inner wall of the threaded sleeve 1. A telescopic bar 8 is connected to the blind hole via a second spring 82. The telescopic bar 8 can extend and retract axially. A limiting hole 81 with a conical inner wall is opened on the outer wall of the telescopic bar 8. A magnet 82 is installed at the bottom of the limiting hole 81, allowing the telescopic pin 9 to be drawn into the limiting hole 81. A through hole communicating with the blind hole is vertically machined into the inner wall of the threaded sleeve 1. The telescopic pin 9 is slidably connected within the through hole. Both ends of the through hole are sealed with annular components. A retaining ring 93 is fitted around the upper end of the telescopic pin 9. The retaining ring 93, blocked by the annular component, can only move up and down in the middle section of the through hole, thus preventing the telescopic pin 9 from dislodging from the through hole. The telescopic pin 9 includes a pin sleeve 92 and a pin head 91. The pin sleeve 92 is located at the end closest to the telescopic bar 8. The ejector sleeve 92 and ejector head 91 are cylindrical shells with opposite openings, and the ejector head 91 can slide along the outer wall of the ejector sleeve 92. The two are connected as one unit by an internal first spring 94. The opening of the ejector sleeve 92 is constricted, while the opening of the ejector head 91 is a protruding limiting ridge. The engagement of the constricted opening and the limiting ridge prevents the ejector sleeve and ejector head from separating. On the outer wall of the tapered bolt 2, there is an axially extending groove 7, and the end of the ejector head 91 near the groove 7 is an arc surface.

[0031] The working process of the safety device is as follows: When the nut to be tested is not in contact with the threaded sleeve 1, the second spring 82 is in its natural state, the telescopic bar 8 extends out of the threaded sleeve 1, and the telescopic pin 9 is inserted into the groove 7 (if the telescopic pin 9 is not inserted into the groove 7, the tapered screw 2 is slightly rotated, and under the action of the first spring 94, the telescopic pin 9 will enter the groove 7), and the tapered bolt 2 cannot be rotated; when the nut to be tested is in contact with the threaded sleeve 1, the telescopic bar 8 squeezes the second spring 82 and retracts into the threaded sleeve 1, the limiting hole 81 on the telescopic bar 8 aligns with the telescopic pin 9, the telescopic pin 9 slides upward, and its end disengages from the groove 7, allowing the tapered bolt 2 to rotate smoothly. After measurement, the tapered bolt 2 needs to be rotated in the reverse direction to retract into the sleeve 1. Only when the telescopic bar 8 is fully pressed into the blind hole can the tapered bolt 2 be rotated in the reverse direction. At this time, the telescopic ejector pin 9 is still inserted into the limiting hole 81. The external thread 5 of the tapered bolt 2 pushes the ejector pin head 91 towards the ejector pin sleeve 92, so that the ejector pin head 91 is also in the state of being disengaged from the groove 7, until the tapered bolt 2 is fully retracted into the sleeve 1, the nut leaves the surface of the sleeve 1, the telescopic bar 8 extends out of the blind hole under the action of the second spring 82, the telescopic ejector pin 9 is pushed out of the limiting hole 81, and the ejector pin head 91 extends into the groove 7 under the action of the first spring 94. When using this tool to measure the deformation of the nut, first use this tool or a micrometer to measure the minor diameter of the thread before the nut is closed. After the closure is processed, use this tool to measure the closure dimension.

[0032] Specifically, S1: Fully screw the tapered bolt 2 inside the measuring fixture into the threaded sleeve 1;

[0033] S2: Align the closed end of the nut to be tested with the pointed cone section 6 of the tapered bolt 2, press the nut against the end face of the threaded sleeve 1 and fully press the telescopic strip 8 into the blind hole;

[0034] S3: Tighten the tapered bolt 2 to screw the pointed section 6 of the tapered bolt 2 into the nut to be tested until the pointed section 6 is completely in contact with the inner wall of the constriction.

[0035] S4: Move the entire measuring fixture horizontally out of the nut's closing point;

[0036] S5: Use a vernier caliper or micrometer to measure the outer diameter of the conical surface at the intersection of the threaded sleeve 1 and the tapered bolt 2. This outer diameter is the minor diameter of the thread of the nut to be measured after the three-point taper.

[0037] S6: Calculate the difference between the minor diameter of the thread before and after the closing to obtain the closing amount.

[0038] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific structures and characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A measuring tool for three-point back-tight minor diameter, characterized in that: The device includes a threaded sleeve and a tapered bolt that can be threaded to the inner wall of the sleeve. The tapered bolt includes a threaded section and a pointed cone section that can extend into the nut to be tested. The threaded sleeve has several safety mechanisms spaced apart circumferentially. Each safety mechanism includes a telescopic bar that can extend and retract axially along the threaded sleeve, and a telescopic pin perpendicular to the telescopic bar and slidably connected to the inner wall of the threaded sleeve. A limit hole is opened at the end of the telescopic bar near the telescopic pin, and a magnet is provided in the limit hole to attract the telescopic pin. The telescopic pin includes a pin sleeve and a pin head, and a first spring connects the pin sleeve and the pin head. The tapered bolt has several axially spaced grooves spaced apart circumferentially. A blind hole facing the nut is opened in the inner wall of the threaded sleeve, and a telescopic bolt is connected to the blind hole by a second spring. The sleeve has a through hole with a blind hole on its inner wall. A telescopic ejector pin is slidably connected in the through hole, and the two ends of the through hole are sealed with an annular part. A retaining ring is fitted on the upper end of the telescopic ejector pin. The retaining ring can only move up and down in the middle of the through hole due to the obstruction of the annular part, so that the telescopic ejector pin is prevented from coming out of the through hole by the retaining ring. The ejector pin sleeve is at the end near the telescopic strip. The ejector pin sleeve and the ejector pin head are cylindrical shells with opposite openings. The ejector pin head can slide along the outer wall of the ejector pin sleeve. The two are connected as one piece by the first spring inside. The opening of the ejector pin sleeve is narrowed, and the opening of the ejector pin head is a limiting ridge that protrudes outward. The narrowing and the limiting ridge prevent the ejector pin sleeve and the ejector pin head from separating. The end of the ejector pin head near the groove is an arc surface.

2. The auxiliary tooling for measuring the minor diameter of a thread after three-point tapping, as described in claim 1, is characterized in that: A handle is connected to the end of the tapered bolt away from the pointed tip.

3. The auxiliary tooling for measuring the minor diameter of a thread after three-point tapping, as described in claim 2, is characterized in that: The handle, threaded section, and tapered section are all coaxially arranged.

4. The auxiliary tooling for measuring the minor diameter of a thread after three-point closing, as described in claim 3, is characterized in that: The handle is equipped with a rubber sleeve that increases friction.

5. The auxiliary tooling for measuring the minor diameter of a thread after three-point tapping, as described in claim 4, is characterized in that: The rubber sleeve has a pattern.

6. A method for measuring the minor diameter of a thread after three-point tapping using any of the measuring fixtures claimed in claims 1 to 5, characterized in that: S1: Fully screw the tapered bolt inside the measuring fixture into the threaded sleeve; S2: Align the concave end of the nut to be tested with the pointed tip of the tapered bolt and place it against the end face of the threaded sleeve; S3: Tighten the tapered bolt and screw the pointed tip of the tapered bolt into the nut to be tested until the pointed tip is completely in contact with the inner wall of the constriction. S4: Move the entire measuring fixture horizontally out of the nut's closing point; S5: Use an external diameter measuring tool to contact the intersection of the threaded sleeve and the tapered bolt, and use the external diameter measuring tool to obtain the external diameter value at that point. This external diameter value is the minor diameter of the thread of the nut to be measured after the three-point closing.

7. The method according to claim 6, characterized in that: Before S1, steps S2 to S5 are repeated before the nut is closed to obtain the minor diameter of the thread before closing; after S5, the difference between the minor diameter of the thread before closing and the minor diameter of the thread after closing is calculated to obtain the closing amount.

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