Master craftsmen generally say that the depth of thread screwing is generally 1.5 to 2 times the diameter of the thread. Is this sentence correct? Is there any reference? This value is of reference significance, but the specific situation needs to be analyzed collectively.
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Generally speaking, for the thread engagement length, the first three pitch lengths will carry more than 80% of the force. Therefore, the screw thread length should generally not be less than 5 times the pitch length.
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The empirical formula mentioned in the design manual mainly considers the performance of the material, that is, the thread damage of different materials is different, and the number of spare threads is different. Taking M16 screws as an example, the depth of the steel plate through hole is 20, and the blind hole is 16.
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When the thread is subjected to axial force, the strength it bears (that is, the pressure you are talking about) depends on the size and pitch of the thread, and the length is generally 8 to 10 pitches.
Because when the thread bears the axial force, the first thread pitch bears the largest force, and it decreases successively downwards, and there is almost no force at the 8th to 10th thread pitch, so no matter how long the thread is, it doesn't make sense.
This consideration ignores the influence of material properties and is only the force analysis of screws. Considering this way, the depth of the M16 screw plate is 16-20, which is basically consistent with the above analysis results.
To sum up the above two analysis methods, it is possible to screw in the steel plate connection M16 screw at a depth of 16-20mm, which is 1-1.25 times the diameter. If it is 1.5 times, there will be more margin. Generally, steel and cast iron can basically Satisfied, so generally speaking, the experience value of 1.5 times is very meaningful. Of course, special cases need special analysis.
