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# Calibration Method of Cylindrical Thread Gauge 2019-03-09

Three-needle method can be used to detect the optimal diameter of the needle. The specific method is to determine the optimal diameter of the needle according to P (pitch) and thread angle (tooth shape angle alpha) of the thread gauge. The calculation formula is as follows:

Do= P/[2COS(a/2)]= 0.57735P (when a=60 degrees)= 0.5637P (when a=55 degrees);

Using the corresponding measuring instruments, such as length measuring machine, optical meter, external diameter micrometer, etc. (depending on the precision requirements of threads), the diameter of threads is measured together with three needles. The simplified calculation formula is as follows:

Thread angle (tooth shape angle alpha) is 60 degrees:

D2 = M-3d0 + 0.866P = M-A, A = 3do-0.866P;

Thread angle (tooth shape angle alpha) is 55 degrees:

D2 = M-3.1657d0 + 0.9605P = M-A, A = 3.1657d0-0.9605P.

In the upper formula M represents the numerical results obtained by the combination of measuring instruments/instruments and three needles.

2. Detection of threaded half angle (a/2):

Thread gauges can be placed between / large tool microscopes and measured by image or interferometry (recommended interferometry).

3. Measurement of pitch:

The threaded gauge is placed between the two parts of the large tool microscope for measurement.

4. The measurement of large diameter of thread can be carried out by instruments such as length measuring machine, optical meter, external diameter micrometer and lever external diameter micrometer.

5. The measurement of thread diameter can be carried out with a large tool microscope.

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