Measuring instrument and measuring method for measuring internal thread position

Abstract

Provided are a measuring instrument and a measurement method that make it possible to improve measurement accuracy of the central axis position of an internal thread. Since the pitch p of an external thread 12 in a shaft portion 11 of a measuring instrument 10 is different from the pitch P of an internal thread 31 in a specific standard, when the shaft portion 11 is fitted into the internal thread 31 while rotating the measuring instrument 10, flanks 13, 33 of the external thread 12 and the internal thread 31 come into contact at two corresponding positions spaced apart in the axial direction, thereby stopping rotation of the measuring instrument 10. As a result, in a method for measuring the central axis C2 position of the internal thread 31 by, for example, applying a stylus 40 to a plug portion 15 of the measuring instrument 10 fitted into the internal thread 31, it is possible to improve the measurement accuracy.

Description

Measuring tool and method for measuring female screw position

[0001] The present invention relates to a measuring tool and a measuring method that can improve the accuracy of measuring the axial center position of a female screw.

[0002] Conventionally, a measuring tool such as that disclosed in Patent Document 1 is used to measure the axial center position of a female thread formed in a workpiece. The measuring tool in Patent Document 1 includes a shaft portion including a male thread that is fitted into the female thread, and a cylindrical plug portion that is arranged concentrically with the shaft portion. A tapered surface that decreases in diameter toward the male thread is formed around the entire circumference of the edge of the plug portion on the inner male thread side.

[0003] In the measurement described in Patent Document 1, first, the male thread of the measuring tool is fitted (threaded) into the female thread until the tapered surface of the measuring tool abuts against the tapered chamfer formed at the entrance of the female thread. Next, a stylus (probe) or vernier calipers of a three-dimensional measuring device is placed against the outer surface of the plug of the measuring tool, and the position of the axis of the measuring tool is measured (calculated) from the position of the outer surface and the radius of the plug. The position of the axis of this measuring tool is determined to be the axis of the female thread.

[0004] Japanese Patent Application Laid-Open No. 2005-61979

[0005] However, in Patent Document 1, even if the axis of the measuring tool is likely to align with the axis of the chamfered portion due to the abutment between the chamfered portion and the tapered surface, this does not necessarily mean that the chamfered portion and the internal thread are coaxial. Therefore, in Patent Document 1, the axis of the measuring tool and the axis of the internal thread may not align, which may prevent accurate measurement of the axis of the internal thread. Furthermore, if the workpiece surface on which the internal thread is formed is not perpendicular to the axis of the internal thread, the chamfered portion and the tapered surface may not align sufficiently. In this case, the axis of the measuring tool and the axis of the internal thread may not align, which may prevent accurate measurement of the axis of the internal thread.

[0006] The present invention has been made to solve the above-mentioned problems, and aims to provide a measuring tool and a measuring method that can improve the measurement accuracy of the axial center position of a female screw.

[0007] In order to achieve this object, the measuring tool of the present invention is used to measure the axial position of a female thread formed in accordance with a specific standard, and comprises a shank portion having a male thread formed on its outer surface to be fitted into the female thread, and a cylindrical plug portion arranged coaxially with and connected to the shank portion, wherein the flank angle of the male thread on the shank portion is the same as the flank angle of the female thread in the specific standard, and the pitch of the male thread on the shank portion is different from the pitch of the female thread in the specific standard.

[0008] According to the measuring tool described in claim 1, the pitch of the male thread on the shank is different from the pitch of the female thread in a specific standard. Therefore, when the male thread is fitted into the female thread while rotating the measuring tool, the flanks of the male thread and the female thread come into contact at two axially separated locations, causing the measuring tool to stop rotating. Furthermore, because the flank angles of the male thread and the female thread are the same, the contact between the flanks is surface contact, making it easier for the female thread and the measuring tool to be coaxial and less likely to wobble. As a result, the measurement accuracy can be improved in methods for measuring the axial center position of a female thread by, for example, applying a stylus or calipers to the plug of a measuring tool fitted into the female thread.

[0009] The measuring tool of claim 2 achieves the following effect in addition to the effect achieved by the measuring tool of claim 1. The flank angle of the male and female threads is represented as θ. In a specific standard, the minimum value of the pitch diameter of the female thread is represented as D2min, the tolerance of the pitch diameter of the female thread is represented as TD2, and the pitch of the female thread is represented as P. The pitch diameter of the male thread in the shank is represented as d2, and the pitch of the male thread is represented as p. When the formula using these is satisfied, "(TD2 + |D2min - d2|) / (|P - p| tan2θ) ≦ 4," the flanks of the male and female threads come into contact with each other at two axially separated locations within four rotations after the start of mating the male thread of the measuring tool with the female thread, and the rotation of the measuring tool stops. This improves the efficiency of attaching the measuring tool to the female thread.

[0010] The measuring tool of claim 3 achieves the following effect in addition to the effect achieved by the measuring tool of claim 1. The flank angle of the male thread and the female thread is represented as θ. The minimum value of the pitch diameter of the female thread in a specific standard is represented as D2min, and the pitch of the female thread is represented as P. The pitch diameter of the male thread in the shank is represented as d2, and the pitch of the male thread is represented as p. When the equation "|D2min - d2| / (|P - p| tan2θ) ≥ 2" using these is satisfied, at least two pitches of the male thread are engaged with the female thread before the rotation of the measuring tool stops. This further reduces rattling of the measuring tool relative to the female thread, further improving the measurement accuracy of the axial center position of the female thread.

[0011] The measuring tool of claim 4 achieves the following effect in addition to the effect achieved by the measuring tool of claim 1: Since the effective diameter of the male thread in the shank is smaller than the minimum value of the effective diameter of the female thread in a specific standard, it is possible to easily mate the male thread with the female thread.

[0012] The measuring tool of claim 5 achieves the following effect in addition to the effect achieved by the measuring tool of claim 1. Because the effective diameter of the male thread in the shank is equal to or greater than the minimum value of the minor diameter of the female thread in a specific standard, a sufficient contact area between the flanks of the male and female threads can be ensured. As a result, rattle between the female thread and the measuring tool can be further suppressed, and their coaxiality (amount of misalignment of the axial centers) can be easily reduced, thereby further improving the measurement accuracy of the axial center position of the female thread.

[0013] The measuring tool of claim 6 achieves the following effect in addition to the effect achieved by the measuring tool of claim 2. The axial length of the male thread in the shank is four or more times the pitch of the male thread. This allows the male thread to be fitted into the female thread until the flanks of the male thread and female thread come into contact with each other at two axially separated locations and the rotation of the measuring tool stops, under the condition of "(TD2 + |D2min - d2|) / (|P - p| tan2θ) ≦ 4." As a result, it is easier to suppress backlash between the female thread and the measuring tool and make them more coaxial, thereby further improving the measurement accuracy of the axial center position of the female thread.

[0014] The measuring method according to claim 7 is a method for measuring the axial center position of a female screw using the measuring tool according to any one of claims 1 to 6, and has the same effect as any one of claims 1 to 6.

[0015] The measuring tool may be configured by combining any two or more of claims 2 to 6. The method for measuring the axial center position of a female screw may be a method for measuring using a measuring tool that combines any two or more of claims 2 to 6.

[0016] 2 is a front view of a measuring tool according to an embodiment of the present invention; FIG. 3 is a schematic view showing a state in which the measuring tool is fitted into an internal thread of a workpiece; and FIG. 4 is a schematic view showing an enlarged view of part III of FIG. 2 , illustrating the measuring tool and the workpiece.

[0017] A preferred embodiment will now be described with reference to the accompanying drawings. Figure 1 is a front view of a measuring tool 10 according to one embodiment. For convenience, the upper and lower sides of each drawing will be referred to as the upper and lower sides of the measuring tool 10, respectively.

[0018] Measuring tool 10 is an auxiliary tool used to measure the axial center position of a female screw 31 (see FIG. 2) provided in workpiece 30 (see FIG. 2), and is made of metal, synthetic resin, or the like. Measuring tool 10 is a shaft-shaped member having a shaft portion 11, a plug portion 15, and a handle portion 17, which are coaxially aligned with a center line C1, and these portions are integrally molded. The upper end of shaft portion 11 is connected to the lower end of plug portion 15, and the upper end of plug portion 15 is connected to the lower end of handle portion 17.

[0019] The axis C1 of the shaft 11, the axis C1 of the plug 15, and the axis C1 of the handle 17 may differ slightly due to manufacturing errors, etc. The amount of deviation of these axes C1 is called concentricity. It is preferable that the concentricity of the shaft 11 and the plug 15 be 0.010 mm or less.

[0020] The shank 11 is a portion that constitutes one end of the shaft-shaped member. An external thread 12, with multiple threads continuing in the axial direction, is formed on the outer peripheral surface of the shank 11. The external thread 12 is provided from a position axially separated from the plug portion 15 to near the bottom end of the shank 11. The surface of the external thread 12 that connects the crest and root is the flank 13.

[0021] The stopper portion 15 is a portion that constitutes the middle portion of the shaft-shaped member. The stopper portion 15 is formed in a cylindrical shape having an axis C1, and the radius R from the axis C1 to the outer circumferential surface of the stopper portion 15 is configured to be approximately constant in the axial and circumferential directions. When measuring the axial center position of the internal thread 31, a stylus 40 (see FIG. 2) of a three-dimensional measuring device, a vernier caliper, or the like is placed against the outer circumferential surface of the stopper portion 15.

[0022] The handle 17 is a portion that constitutes the other end of the shaft-shaped member. When the measuring tool 10 is rotated to fit (screw) the shaft 11 into the internal thread 31, the handle 17 is grasped by the fingers of the measurer and a rotational force is applied to the handle 17.

[0023] The handle 17 is formed in a substantially cylindrical shape having an axis C1. A portion of the outer peripheral surface of the handle 17 is cut out to form a flat surface 18 that is substantially parallel to the axis C1. A plurality of grooves 19 are formed in a grid pattern on the outer peripheral surface of the handle 17 other than the flat surface 18. These flat surfaces 18 and the plurality of grooves 19 ensure a grip between the measurer's fingers and the handle 17, making it easier to rotate the measuring tool 10. At least one of the flat surfaces 18 and the grooves 19 may be omitted, or a known configuration for ensuring a grip may be applied to the handle 17.

[0024] The outer diameter 2R of plug 15 (twice the radius R) is larger than the outer diameter d of male thread 12 of shaft 11 and the outer diameter of handle 17. This makes it easier for a measurer or the like to distinguish between shaft 11, plug 15, and handle 17 from their appearance. In addition, because the outer peripheral surface of plug 15 protrudes radially from shaft 11 and handle 17, it is easier to apply a stylus 40 or the like to the outer peripheral surface of plug 15.

[0025] The diameter of the constricted portion between the male thread 12 and the plug portion 15 is reduced relative to them. This prevents the cutting process from affecting the plug portion 15 when the male thread 12 is formed by cutting or other processes, and prevents the cutting tool from interfering with the plug portion 15.

[0026] Next, the female thread 31 into which the male thread 12 (shank 11) is fitted will be described with reference to Figures 2 and 3. Figure 2 is a schematic diagram showing the state in which the measuring tool 10 is fitted into the female thread 31 of the workpiece 30. Figure 3 is a schematic diagram of the measuring tool 10 and the workpiece 30, showing an enlarged view of part III in Figure 2. Figures 2 and 3 show a schematic end view of a cut portion of the workpiece 30 taken along a cut plane including the axis C2 of the female thread 31, as well as a schematic front view of the measuring tool 10. Furthermore, in Figure 3, hatching indicating the cut plane of the workpiece 30 is omitted.

[0027] The internal thread 31 is a thread formed on the inner peripheral surface of a hole, and one or more internal threads 31 are provided in a workpiece 30 made of metal, synthetic resin, or the like. The internal thread 31 may or may not penetrate the workpiece 30. In the internal thread 31, the surface connecting the crest and the root is the flank 33.

[0028] The female thread 31 is formed in accordance with a specific standard. Examples of such specific standards include those established by ISO (International Organization for Standardization), JIS (Japanese Industrial Standards), and ANSI (American National Standards Institute). However, the specific standard is not limited to these exemplified standards and may be a standard established individually by various organizations or businesses. Furthermore, the male thread 12 of the measuring tool 10 is formed to fit into the female thread 31, and a portion of the male thread 12 may be formed in accordance with a specific standard.

[0029] For example, the standards for general-purpose metric threads shown in JIS B0205-1:2001 (ISO 68-1:1998), JIS B0205-2:2001 (ISO 261:1998), JIS B0205-3:2001 (ISO 262:1998), JIS B0205-4:2001 (ISO 724:1993), and JIS B0209-1:2001 (ISO 965-1:1998) are referred to as Standard S. Hereinafter, the present invention will be described assuming Standard S as a specific standard, but a standard other than Standard S may also be used as the specific standard.

[0030] According to this standard S, the flank angle θ of the internal thread 31 is 30 degrees. For any particular standard, the flank angle θ of the external thread 12 is made the same as the flank angle θ of the internal thread 31. This "same" means that the difference between the flank angles θ of the internal thread 31 and the external thread 12 is less than the tolerance of the flank angle θ.

[0031] The flank angle θ of the internal thread 31 is the angle between a line perpendicular to the axis C2 and the flank 33 in a cross section including the axis C2. The flank angle θ of the external thread 12 is the angle between a line perpendicular to the axis C1 and the flank 13 in a cross section including the axis C1.

[0032] Furthermore, according to Standard S, as shown in Table 1 below, for example, the pitch P of the internal thread 31, the maximum value D2max of the effective diameter D2 of the internal thread 31, the minimum value D2min of the effective diameter D2, the maximum value D1max of the internal diameter D1 of the internal thread 31, the minimum value D1min of the internal diameter D1, etc. are determined relative to the nominal diameter, which is the reference dimension of the root diameter D of the internal thread 31.

[0033] For example, a nominal diameter M6 means that the root diameter D of the internal thread 31 has a reference dimension of 6 mm. The effective diameter D2 of the internal thread 31 is the diameter of a virtual cylinder in which the width of the thread groove is equal to the width of the thread ridge. Similarly, the effective diameter d2 of the external thread 12 is the diameter of a virtual cylinder in which the width of the thread groove is equal to the width of the thread ridge.

[0034] The male thread 12 of the measuring tool 10 that is fitted into such a standard S female thread 31 may be one that can be fitted into the female thread 31 (having an equivalent nominal diameter), as long as the pitch p of the male thread 12 is different from the pitch P of the female thread 31. In other words, the effective diameter d2, outer diameter d, etc. of the male thread 12 may be different from those of standard S, or may conform to standard S. For example, for a female thread 31 with a nominal diameter of M10 and a pitch P of 1.5 mm, the male thread 12 may be one that conforms to standard S, with a nominal diameter of M10 and a pitch p of 1.25 mm.

[0035] Note that the pitch P of the internal thread 31 of standard S differs from the pitch p of the external thread 12 of the measuring tool 10 when the absolute value of the difference between them is 0.01 times or more the pitch P, that is, |P-p| ≧ 0.01P. However, if 0.01P is less than 0.01 mm, then |P-p| ≧ 0.01 mm is said to be the difference between the pitch P of standard S and the pitch p of the measuring tool 10. In these cases, it can be said that the pitch P of standard S differs from the pitch p of the measuring tool 10 by more than the general tolerance of pitches P and p.

[0036] The following describes a method for measuring the position of the axis C2 of the internal thread 31 using such a measuring tool 10. First, in a preparation step, the measuring tool 10 (external thread 12) is prepared as described above, which corresponds to the internal thread 31 of standard S that is the measurement target.

[0037] Next, in the installation process, the operator rotates the prepared measuring tool 10 while fitting the male thread 12 into the female thread 31 to be measured. In this initial stage, due to the difference between the pitches P and p, only one of the upper and lower surfaces of the flank 13 of the male thread 12 is in partial contact with the flank 33 of the female thread 31, so the operator feels almost no rotational resistance.

[0038] If the measuring tool 10 is continued to rotate in this state, for example, at position A shown in Fig. 2, the lower surface side of the flank 13 of the male thread 12 comes into contact with the upper surface side of the flank 33 of the female thread 31, and at position B shown in Fig. 2, the upper surface side of the flank 13 of the male thread 12 comes into contact with the lower surface side of the flank 33 of the female thread 31. This causes a sudden increase in rotational resistance, prompting the measurer to stop rotating the measuring tool 10.

[0039] When this rotation stops, the flanks 13, 33 of the male thread 12 and the female thread 31 are in contact with each other at two axially separated locations. Furthermore, because the flank angle θ of both the male thread 12 and the female thread 31 is the same, the flanks 13, 33 are in surface contact with each other. As a result, the female thread 31 and the measuring tool 10 are less likely to rattle, and the axis C2 of the female thread 31 and the axis C1 of the measuring tool 10 (shank 11, male thread 12) tend to be coaxial.

[0040] 2, the contact position is determined by moving the stylus 40 of the three-dimensional measuring device and contacting it with the outer peripheral surface of the plug portion 15. Furthermore, in the measurement process, the position of the axis C1 of the measuring tool 10 is measured (calculated) from the contact position and the radius R of the plug portion 15, and the position of the axis C1 is set as the position of the axis C2 of the internal thread 31.

[0041] The position of the axis C2 measured in this manner may be the position of the internal thread 31. Furthermore, for example, if the workpiece 30 is formed in an axial shape and the internal thread 31 is formed on the axial end surface of the workpiece 30, the coaxiality thereof may be measured from the measured position of the axis C2 and the axis of the workpiece 30. Furthermore, for example, the perpendicularity of the internal thread 31 with respect to the surface of the workpiece 30 on which the internal thread 31 is formed may be measured from the measured position of the axis C2.

[0042] Note that the method for measuring the position of the axis C2 of the internal thread 31 is not limited to the method using the stylus 40 of the three-dimensional measuring device. For example, the position of the axis C2 of the internal thread 31 may be measured as the distance between the two internal threads 31 by fitting a measuring tool 10 into each of the two internal threads 31 provided in the workpiece 30 and applying a vernier caliper to each of the outer peripheral surfaces of the plug portions 15 of the two measuring tools 10. Alternatively, the position of the axis C2 of the internal thread 31 may be measured by applying a laser beam emitted from a laser rangefinder to the outer peripheral surface of the plug portion 15.

[0043] In either measurement method, the position of the axis C2 of the female thread 31 can be easily measured by using a GO side thread plug gauge (GP) instead of the measuring tool 10. However, in this case, there is a risk that the position of the axis C2 of the female thread 31 cannot be accurately measured due to backlash during fitting, tilt when the end face of the plug portion of the gauge is placed against the surface of the workpiece 30 on which the female thread 31 is formed, etc. Also, while backlash can be suppressed by using a step gauge (with multiple effective diameters set in a stepped pattern) instead of a GO side thread plug gauge, it is necessary to test whether each of the many step gauges can be fitted into the female thread 31, and preparing a large number of such gauges poses a cost problem.

[0044] In contrast, when measurement is performed using the measuring tool 10, as described above, the female thread 31 and the measuring tool 10 are less likely to wobble and are more likely to be coaxial, thereby improving the measurement accuracy of the position of the axial center C2 of the female thread 31. Furthermore, unlike a step gauge, only one measuring tool is required, which makes it easier to reduce the cost of the measuring tool 10.

[0045] The measuring tool 10 includes the handle 17, which makes it difficult for the measurer to hold the stopper 15. As a result, it is difficult for oils and dust from the measurer's fingers to adhere to the outer circumferential surface of the stopper 15. As a result, it is possible to prevent a decrease in the measurement accuracy of the position of the axis C2 of the female thread 31 due to oils and dust on the outer circumferential surface of the stopper 15.

[0046] Furthermore, in measurements using the measuring tool 10, strictly speaking, the position of the axis C1 of the plug portion 15 is measured from the contact position of the stylus 40, so even if the axis C2 of the female thread 31 and the axis C1 of the shank 11 are approximately aligned, there is a risk that the measurement result of the position of the axis C2 of the female thread 31 will be deviated by the amount of coaxiality between the shank 11 and the plug portion 15. Therefore, as described above, if the coaxiality between the shank 11 and the plug portion 15 is 0.010 mm or less, the measurement accuracy of the position of the axis C2 of the female thread 31 can be ensured.

[0047] When the effective diameter D2 of the female thread 31 is a maximum value D2max during fitting in the installation process, the number of rotations Tmax from when the measuring tool 10 starts to rotate until it stops is given by the following formula 1. Formula 1: Tmax = |D2max - d2| / (|P - p| tan 2θ)

[0048] Using the tolerance TD2=D2max-D2min of the effective diameter D2 of the female thread 31, Equation 1 can be rewritten as Equation 2 below. Equation 2: Tmax=(TD2+|D2min-d2|) / (|P-p|·tan2θ)

[0049] It is preferable that Tmax is 4 or less, that is, that "(TD2 + |D2min - d2|) / (|P - p| tan2θ) ≦ 4" is satisfied. If this is satisfied, the flanks 13, 33 of the male thread 12 and the female thread 31 will come into contact with each other at two axially separated locations within four rotations from the start of fitting the shank 11 into the standard S female thread 31, and the rotation of the measuring tool 10 will stop. This improves the efficiency of the work of attaching the measuring tool 10 to the female thread 31.

[0050] Furthermore, it is more preferable that Tmax is 3.5 or less, and even more preferable that Tmax is 3 or less. In these cases, the efficiency of the work of attaching the measuring tool 10 to the internal thread 31 can be further improved.

[0051] When Tmax is 4 or less, the axial length L (see FIG. 1 ) of the male thread 12 of the shank 11 is preferably four times or more the pitch p of the male thread 12. Furthermore, the axial length of the female thread 31 is also preferably four times or more the pitch p of the male thread 12. In these cases, under the condition that Tmax is 4 or less, the shank 11 can be fitted into the female thread 31 until the flanks 13, 33 come into contact with each other at two axially separated locations and the rotation of the measuring tool 10 stops. In other words, it is possible to prevent the shank 11 from passing through the through-type female thread 31 without stopping the rotation of the measuring tool 10, or the shank 11 from hitting the bottom of the non-through-type female thread 31 and stopping the rotation of the measuring tool 10. As a result, it is easier to suppress play between the female thread 31 and the measuring tool 10 and make them more coaxial, thereby further improving the measurement accuracy of the axis C2 position of the female thread 31.

[0052] Similarly, when Tmax is 3.5 or less, it is preferable that the length L of the male thread 12 and the axial length of the female thread 31 are 3.5 times or more the pitch p, and when Tmax is 3 or less, it is preferable that the length L of the male thread 12 and the axial length of the female thread 31 are 3 times or more the pitch p.

[0053] The shank 11 has a narrowed portion between the male thread 12 and the plug portion 15, and the outer diameter of the narrowed portion is smaller than the root diameter d3 of the male thread 12. Therefore, even if the entire male thread 12 is fitted into the female thread 31, it is possible to prevent the narrowed portion of the shank 11 from interfering with the female thread 31 or the plug portion 15 from contacting the surface of the workpiece 30. Since it is possible to prevent the axis C1 of the shank 11 from tilting relative to the axis C2 of the female thread 31 due to this interference or contact, it is possible to further improve the measurement accuracy of the position of the axis C2 of the female thread 31.

[0054] Furthermore, when the effective diameter D2 of the internal thread 31 is the minimum value D2min, the number of rotations Tmin from when the measuring tool 10 starts to rotate until it stops is as shown in the following formula 3. Formula 3: Tmin = |D2min - d2| / (|P-p| tan 2θ)

[0055] It is preferable that Tmin is 2 or greater, that is, that "|D2min - d2| / (|P - p| tan2θ) ≥ 2" is satisfied. If this is satisfied, it is possible to mate a male thread 12 of 2 pitches p or more with a standard S female thread 31. As a result, rattle of the measuring tool 10 relative to the female thread 31 can be further suppressed, and the measurement accuracy of the position of the axis C2 of the female thread 31 can be further improved.

[0056] The effective diameter d2 of the male thread 12 in the shaft portion 11 is preferably smaller than the minimum value D2min of the effective diameter D2 of the female thread 31 in Standard S. This makes it easier to fit the male thread 12 into the female thread 31.

[0057] The effective diameter d2 of the male thread 12 in the shank 11 is preferably equal to or greater than the minimum value D1min of the inner diameter D1 of the female thread 31 in Standard S. In this case, the contact area between the flanks 13, 33 of the male thread 12 and the female thread 31 can be secured, which further reduces play between the female thread 31 and the measuring tool 10 and facilitates reducing their coaxiality. This further improves the measurement accuracy of the position of the axis C2 of the female thread 31.

[0058] Table 2 below shows examples of measuring tools 10 of samples 1 to 5 in which the dimensions of the male thread 12 are adjusted for the female thread 31 conforming to Standard S and having a nominal diameter of M10 and a pitch P of 1.25 in Table 1 above.

[0059] Table 2 further shows Tmax and Tmin for each of Samples 1 to 5. The "effective diameter condition" in Table 2 is marked "Good" when the effective diameter d2 is equal to or greater than the minimum value D1min = 8.647 of the inner diameter D1 of the internal thread 31 in Standard S, and marked "Poor" when it is less than the minimum value D1min. The "number of rotations condition" in Table 2 is marked "Good" when both Tmax is 4 or less and Tmin is 2 or more are satisfied, and marked "Poor" when at least one of the conditions is not satisfied.

[0060] In Samples 1 to 3, both the "effective diameter condition" and the "number of rotations condition" are "good," so the efficiency of attaching the measuring tool 10 to the female thread 31 can be improved, and the measurement accuracy of the position of the axis C2 of the female thread 31 can be further improved. In contrast to Samples 1 to 3, Sample 4 is "good" for the "effective diameter condition" but "bad" for the "number of rotations condition." Therefore, while Sample 4 is somewhat inferior to Samples 1 to 3, it is possible to improve the efficiency of attaching the measuring tool 10 to the female thread 31 and to improve to some extent the measurement accuracy of the position of the axis C2 of the female thread 31. Furthermore, Sample 5 is "bad" for the "effective diameter condition" but "good" for the "number of rotations condition," so it is somewhat inferior to Samples 1 to 3, but it is possible to improve to some extent the measurement accuracy of the position of the axis C2 of the female thread 31.

[0061] While the present invention has been described above based on the embodiments, it is not limited to the above embodiments, and various improvements and modifications are possible without departing from the spirit of the present invention. The shapes and dimensions of the components described in the above embodiments may be modified as appropriate. For example, the outer diameter 2R of the plug portion 15 may be smaller than or equal to the outer diameter d of the male thread 12 and the outer diameter of the shank portion 17.

[0062] In the above embodiment, the handle 17 may be omitted. The positions of the plug 15 and the handle 17 may also be reversed. The shank 11 or the plug 15 does not have to be coaxial with the handle 17. However, the smaller the degree of coaxiality between the shank 11 or the plug 15 and the handle 17, the easier it is to rotate the measuring tool 10 by holding the handle 17.

[0063] In the above embodiment, the shank 11, plug 15, and handle 17 are described as being integrally molded, but this is not necessarily limited to this. The shank 11, plug 15, and handle 17, each formed from separate members, may be connected by welding, adhesive, fastening members, or the like. However, it is preferable that the shank 11 and plug 15 are integrally molded from the same axial member by cutting or other processing. In this case, it is easier to reduce the coaxiality between the shank 11 and plug 15 compared to when the shank 11 and plug 15 are connected by post-processing.

[0064] 10 Measuring tool 11 Shank 12 Male thread 15 Plug 31 Female thread C1 Axial center (of plug and shank) C2 Axial center (of female thread)

Claims

1. A measuring tool for measuring the axial position of a female thread formed in accordance with a specific standard, comprising: a shank portion having a male thread formed on its outer surface to be fitted into the female thread; and a cylindrical plug portion arranged coaxially with and connected to the shank portion, wherein the flank angle of the male thread on the shank portion is the same as the flank angle of the female thread in the specific standard, and the pitch of the male thread on the shank portion is different from the pitch of the female thread in the specific standard.

2. The measuring tool according to claim 1, characterized in that the flank angles of the male thread and the female thread are represented as θ, the minimum value of the effective diameter of the female thread in the specific standard is represented as D2min, the tolerance of the effective diameter of the female thread is represented as TD2, and the pitch of the female thread is represented as P, and the effective diameter of the male thread in the shank is represented as d2 and the pitch of the male thread is represented as p, respectively, satisfies (TD2 + |D2min - d2|) / (|P - p| tan2θ) ≦ 4.

3. The measuring tool according to claim 1, characterized in that it satisfies |D2min-d2| / (|P-p|·tan2θ)≧2, where θ represents the flank angle of the male thread and the female thread, D2min represents the minimum effective diameter of the female thread in the specific standard, P represents the pitch of the female thread, and d2 represents the effective diameter of the male thread in the shank, and p represents the pitch of the male thread.

4. A measuring tool according to claim 1, characterized in that the effective diameter of the external thread in the shank is smaller than the minimum effective diameter of the internal thread in the specific standard.

5. A measuring tool according to claim 1, characterized in that the effective diameter of the male thread in the shank is equal to or greater than the minimum value of the inner diameter of the female thread in the specific standard.

6. A measuring tool according to claim 2, characterized in that the length of the shaft portion in the axial direction of the male thread is four times or more the pitch of the male thread.

7. A measuring method for measuring the axial center position of the female screw using a measuring tool according to any one of claims 1 to 6, comprising: an attachment step of screwing the corresponding male thread of the measuring tool into the female screw conforming to the specific standard until rotation stops; and a measurement step of measuring the axial center positions of the plug part and the shank part from the outer peripheral surface of the plug part after the attachment step, and setting the axial center position of the shank part as the axial center position of the female screw.

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