How to determine the connection length after threading pipe fittings are connected?

Thread measurement: The measurement of thread parameters in length measurement techniques. There are two methods for thread measurement: single-item measurement and comprehensive measurement. Single measurements are commonly used to determine parameters such as the pitch diameter of threads, the pitch, and the half-angle of the thread profile. Pitch diameter measurement: What are the common methods for measuring the pitch diameter of cylindrical threads? It can be measured using a thread micrometer. Place 3 cylinders with the same diameter – the three pins – in the thread flutes (Figure 1 shows the use of the three-pin method for measuring the pitch diameter). Then, depending on the required precision, use a micrometer, comparator, or length gauge (see length measuring machine) to obtain the relevant values; after calculation, the pitch diameter of the thread under inspection can be determined. Measurement by the imaging method under a stereomicroscope (Figure 2: Measurement of threads by the imaging method). Before measurement, tilt the column by an angle equal to the pitch angle of the thread being measured. Then, use the center line and midpoint of the crosshairs on the measuring microscope to align one side and the midpoint of the image of the thread’s profile, and take a reading. Move the transverse slide (or coordinate worktable) so that the center line and midpoint of the crosshairs align with the corresponding side and midpoint of the image of the opposite profile, and take a second reading. The difference between the two readings is the value of the pitch diameter of the thread being measured. To reduce measurement errors caused by tooth profile half-angle errors and installation errors, measurements are typically taken once along each of the left and right tooth profiles, and their arithmetic average is used as the value for the mean diameter. Measurement is carried out using the axial sectioning method under a stereomicroscope. This method uses a measuring tool to determine the pitch; the measurement of the pitch diameter for tapered threads is similar to that for circular threads, but adjustments must be made for the changes caused by the taper angle. The measurement of pitch and the half-angle of the thread profile is often carried out using a tool microscope; Figure 2 shows the measurement of threads by the imaging method. When measuring the half-angle of the thread profile using the imaging method, first align the angle-measuring eyepiece (not shown in the diagram for measuring threads by imaging method) with the thread profile, and ensure that the midpoint of the crosshairs coincides with the midpoint of one side of the image of the thread profile. Then rotate the handwheel of the angle-measuring eyepiece so that the center dashed line of the crosshairs aligns with this side; the value of the half-angle of the thread profile can then be read from the angle-measuring eyepiece. (Figure 2: Measuring threads by the image method) shows the measurement of pitch using the axial section method. In addition, the pitch can also be measured using a mechanical pitch gauge with percentages, or checked with a pitch gauge; the half-angle of the thread profile can be inspected using a thread template. The pitch and major diameter of internal threads are generally measured on a length measuring instrument. After creating a model of the thread profile using gypsum or some other setting material, the half-angle of that profile is measured under a tool microscope, and this value is then used as the measure for the half-angle of the thread in question. In the mid-1980s, a method was developed that used digital control technology based on computers to measure high-precision geometric parameters of internal threads on specially designed measuring instruments. The pitch diameter of the lead screw, as well as the half-angle and pitch errors, are also often measured using a tool microscope. Precision lead screws also require measurement of the helical error. Figure 3: Principle of the laser lead screw tester for measuring the helical error of precision lead screws. When the lead screw rotates by an angle, the circular grating that rotates in sync with the lead screw generates a number of Moiré fringes equivalent to the angle of rotation. The axial displacement of the helix is converted into the number of interference fringes by a laser-based length sensor, using a measuring head mounted on the floating support plate and a right-angled prism. These two optical signals are converted into electrical signals by their respective photoelectric conversion elements; after amplification, shaping, frequency division, and phase comparison, the error curve is recorded by a recorder, from which the pitch error can also be determined. It can measure lead screws with a precision of 1 meter class 5 and 2 meters class 6. Comprehensive measurement involves checking the actual mean diameter error and the equivalent mean diameter error of the thread, in order to control the quality of thread fitting. The converted mean diameter error is the error resulting from converting errors such as pitch and half-thread angle into an error in the mean diameter direction. Common thread gauges are inspected using the go/no-go method.