High-precision thread taps are divided into metric, inch, modulus and radial threads. High-precision thread taps can be used to produce high-precision internal threads and tight fit with common external threads (interference fit) The thread pair of the interference fit makes the ordinary thread pair obtain excellent self-locking anti-loose and anti-vibration performance. This type of thread pair is also referred to as a "full thread full tooth type full interference fit thread pair".
The method of making this tight fit thread pair is not complicated, so everyone can easily master it. The method is as follows:
First, the determination of the large diameter tolerance zone of the threaded tap
The tight fit of the ordinary thread pair described here is achieved by the interference (interference) fit of the large diameter of the thread.
The high-precision thread taps on the market have a large diameter tolerance of H4H5. To make a threaded pair that fits well with a common external thread, it is only necessary to grind the large diameter of the purchased tap.
A deviation and tolerance are now recommended. The selection and calculation are as follows:
1. Take the large diameter of the tap as the nominal size, check the "GB197 Ordinary Thread Tolerance", and record the lower deviation of the 6H internal thread diameter, which is intended to be A;
2. Take the large diameter of the tap as the nominal size, check the "GB1800 Tolerance and Coordination", and record the value of the IT10 standard tolerance, which is proposed as B;
3. "A+B" is used as the upper deviation of the large diameter of the common thread tap;
4. Check "GB1800 tolerance and cooperation", with the IT4 standard tolerance as the tolerance of the large diameter of the common thread tap;
5. Calculate the deviation of the large diameter of this series of common thread taps, the formula is:
Lower deviation = (upper deviation - IT4 level tolerance)
6. If the accuracy of the cylindrical grinder used does not reach IT4, the tap tolerance can be relaxed to IT5.
7. This is closely matched with the ordinary thread tap, and the size after the large diameter grinding is tested according to the routine inspection of the outer circle.
Second, tightly match the production of ordinary internal thread
This production process and procedure for tightly fitting ordinary internal threads is the same as the production of ordinary internal threads in the past: the internal threaded bottom hole (small diameter) is the same, and the tapping process is the same.
Third, the large diameter measuring tool tightly matched with the ordinary internal thread and the determination of its tolerance zone
For gauges with large diameters of ordinary threads, the gauges and gauges are made according to the single dimension of the large diameter. The determination and production of the tolerance zone are carried out according to the general smooth limit gauge.
Fourth, the inspection size and accuracy of ordinary external thread
Because the normal threading pair is made by the interference (interference) of the large diameter of the internal and external threads to achieve its self-locking anti-loose and anti-vibration performance, it is only required to be a standard ordinary external thread produced or purchased by itself. The diameter can reach 6H, but only the large diameter can be checked, and it is not necessary to check the diameter.
It should be noted that the accuracy of the 6H thread is only IT12-IT13 due to the internal thread produced by the tightening of the common thread tap. When measuring with a vernier caliper, there is a measurement error of 0.04 mm, and when using a swimming micrometer, there is a measurement error of 0.02 mm. Therefore, if the large diameter of the external thread is 0.02 to 0.04 mm below the lower deviation, the unqualified product will be judged as a qualified product due to the measurement error.
The self-locking anti-loose anti-vibration thread pair with large-diameter radial interference (interference) fit can be formed by matching the external thread which is qualified by the above-mentioned tap to the tightly matched ordinary internal thread which is processed by the above-mentioned tap.
5. High-precision external thread and high-precision tight-fitting production of thread pair
Using high-precision thread tools and corresponding production processes, it is economical to use a general machine tool to industrially mass-produce high-precision external threads with large diameter accuracy of IT6-IT8.
The process of producing a high-precision tight-fit internal thread is exactly the same as the production of a tight internal thread, but the tap used is different.
The parameter setting process is as follows :
1. Take the large diameter of the tap as the nominal size, check the "GB1800 Tolerance and Coordination", and record the deviation value under H6 or H8, which is intended to be A;
2. Take the large diameter of the tap as the nominal size, check the "GB1800 Tolerance and Coordination", and record the value of the IT10 standard tolerance, which is proposed as B;
3. "A+B" is used as the upper deviation of the large diameter of the high-precision thread tap;
4. Check "GB1800 Tolerance and Coordination", with the IT4 standard tolerance as the tolerance of the large diameter of the high-precision thread tap;
5. Calculate the deviation of the large diameter of this series of high-precision thread taps. The formula is:
Lower deviation = (upper deviation - IT4 level tolerance)
It can be seen that the tolerance of the high-precision tight-fit threaded tap is determined, except that the "A" value is different, and the other values ​​and calculations are the same as the tight-fit common thread tap.
Six, experience and recommendations
The high-precision tight-fit threaded tap produces the internal thread and the high-precision external thread to form a high-precision tight-fit thread pair. In essence, it embodies the connotation of the interference fit of GB1800 Tolerance and Coordination. Its cooperation and cooperation Performance reflects its inherent spiritual essence. Objectively speaking, the "discreteness" of the amount of interference (interference) is much smaller than that of the ordinary tight-fit thread.
Because of the production process and production cost of this high-precision tight-fit thread pair, it is the same as the production of ordinary thread. Therefore, for industries and products with higher reliability requirements such as aerospace, aviation, and military, this kind of cooperation should be preferred. Tolerance belt for the product.
For conventional high-precision tight-fitting thread by-products, the application manufacturer can directly order the corresponding products, directly use and assemble to high-precision thread tools and high-precision threaded parts manufacturers, eliminating all the troubles of self-production.
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