1. Poor tap quality: main materials, tool design, heat treatment, machining accuracy, coating quality, etc.  For example, the size difference at the transition of tap section is too large or the transition fillet is not designed, resulting in stress concentration, which is easy to fracture at the stress concentration when in use.  The section transition at the junction of the shank and the blade is too close to the weld joint, resulting in the superposition of complex welding stress and stress concentration at the section transition, resulting in larger stress concentration, leading to the tap fracture in use.  For example, the heat treatment process is improper.  During heat treatment of taps, cracks may occur if the taps are not preheated before quenching and heating, if quenching is overheated or burnt, if tempering is not carried out in time, and if cleaning is carried out too early.  This is also an important reason why the overall performance of domestic taps is inferior to that of imported taps.  2. Improper tap selection: For tapping parts with too high hardness, high-quality taps should be selected, such as cobalt-containing high-speed steel taps, hard alloy taps, coated taps, etc.  In addition, different tap designs are applied in different working situations.  For example, the number, size and angle of the flutes of the tap have an impact on the chip removal performance.  3. Taps do not match with processed materials: This problem has been paid more and more attention in recent years. In the past, domestic manufacturers always thought that imported taps were good, expensive taps were good, but they were actually suitable ones.  With the increasing number of new materials and the difficulty of machining, the variety of cutting tool materials is also increasing in order to meet this need.  This requires selecting a suitable tap product before tapping.  4. The hole diameter of the bottom hole is relatively small: for example, when processing m5×0.5 threads of ferrous metal material, a 4.5mm diameter drill bit should be selected as the backing hole for the cutting tap. If the 4.2mm drill bit is misused to back the hole, the part of the tap that needs to be cut during tapping will inevitably increase, thus causing the tap to break.  It is suggested to choose the correct diameter of bottom hole according to the type of tap and the material of tapping piece. If there is no completely matching drill bit, the larger one can be selected.  5. Tapping material problem: The tapping material is impure, and there are some hard points or pores in some parts, causing the tap to lose balance and break off instantly.  6. The machine tool did not meet the precision requirements of the tap: the machine tool and the clamping body are also very important, especially for high-quality taps, only the machine tool and the clamping body with a certain precision can give full play to the performance of the tap.  Common is not enough concentricity.  At the beginning of tapping, the starting and positioning of the tap is not correct, i.e. the spindle axis is different from the center line of the bottom hole, and the torque is too large during tapping, which is the main reason for the tap to break.  7. The quality of cutting fluid and lubricating oil is not good: many domestic enterprises have begun to pay attention to this point. Many companies that have purchased foreign cutting tools and machine tools have very profound experience. The quality of cutting fluid and lubricating oil has problems. The quality of processed products is prone to burrs and other undesirable conditions, while the service life will be greatly reduced.  8. Irrational cutting speed and feed rate: when problems occur in processing, most domestic users reduce cutting speed and feed rate, thus reducing the driving force of the tap and greatly reducing the thread precision produced. This increases the roughness of the thread surface, and the thread diameter and thread precision are beyond control. Burrs and other problems are of course even more inevitable.  However, if the feed speed is too high, the screw tap will easily break if the torque is too high.  The cutting speed during machine tapping is generally 6-15m/min for steel.  Quenched and tempered steel or harder steel is 5-10m/min;  Stainless steel is 2-7m/min;  Cast iron is 8-10m/min.  For the same material, the smaller the tap diameter, the higher the value, and the larger the tap diameter, the lower the value.  9. The technology and skills of the operators do not meet the requirements: the above problems require the operators to make judgments or feedback to the technicians, but most of the domestic operators do not pay enough attention at present.  For example, when processing blind hole threads, when the tap is about to contact the bottom of the hole, the operator does not realize that the tap is still fed at the tapping speed before reaching the bottom of the hole, or the tap is broken due to forced feeding when chip removal is not smooth.  It is suggested that operators should strengthen their sense of responsibility.  From the above, it can be seen that the causes of tap fracture are various. Machine tools, jigs, workpieces, techniques, chucks and tools are all possible. The real causes may never be found by mere theory.  As a qualified and responsible tool application engineer, the most important thing is to go deep into the site, not just imagine.  Let's take the simplest example. If the length of the tap cutting cone is too long, the tap will break when hitting the bottom of the bottom hole. If you don't go deep into the site, how can you know by guessing the tap performance, workpiece material, processing technology, etc?  I couldn't even dream about it at the beginning, but there were customers who had such problems that you might think were extremely low-level, but you had to face them.  In fact, neither traditional tapping equipment nor expensive cnc equipment can solve the above problems in principle.  Because the machine cannot recognize the working condition of the tap and the most appropriate torque required, it will only repeat the machining according to the preset parameters.  Only when the machined parts are finally inspected with the thread gauge can the unqualified parts be found, but it is too late to find out at this moment.  Even if it is found, it is useless. The expensive parts that should be scrapped will have to be scrapped, and the unqualified products will have to be thrown away as inferior products.  Therefore, for large, expensive and precise workpiece processing in large enterprises, even imported taps that cost a high price need not be made in China, because once the taps break and the workpiece is scrapped, the cost is quite high.  Foreigners are taking advantage of their skills and the price of tap is very high. It is not painful to see that a considerable part of the profits of enterprises are taken by foreigners.  Alas, the Chinese still need to work hard!