When should thread milling be used instead of tap cutting to create threads?

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With the development of CNC thread milling technology, particularly the advent of 3-axis machining centers, CNC thread milling has gradually gained widespread recognition in the machinery manufacturing industry. Furthermore, it is well known that threads can be obtained using the traditional thread machining methods we are familiar with, among which tapping is the most similar to thread milling. Because they both form threads through the relative rotational motion between the tool and the workpiece. So, when faced with different working conditions, how do we choose the appropriate approach? This article tells you their exact meaning. Conditions for CNC thread milling: 1. A machining center with 3-axis motion (or more). 2. The thread length should not exceed 3 times the length of the tool’s cutting edge. Advantages of CNC thread milling: 1. Thread mills can be used to create threads of different diameters while maintaining the same shape. For example, by using a threaded mill to change the interpolation radius to machine M15x1.0, M18x1.0, and M20x1.0 threads, it is possible to reduce the number of tools, save tool-changing time, improve efficiency, and simplify tool management. 2. It improves the accuracy and surface finish of the threads. Thread milling is accomplished through the high-speed rotation of the tool and spindle interpolation. The cutting method is milling; the cutting speed is high, and the resulting threads are aesthetically pleasing ； The tap has a low cutting speed and produces long chips, which can easily damage the inner hole surface. 3. The internal thread facilitates discharge. Thread milling involves chip breaking; the chips produced are short, and the diameter of the cutting tool is smaller than that of the threaded hole being machined. Therefore, chip removal occurs smoothly ； During continuous cutting with a tap, the chips are long, and since the diameter of the tap is the same as that of the hole being machined, it is difficult to remove the chips. 4. If a tap is used, it is certainly possible to use electric discharge to break off the broken part, but the process will be very complicated; if damage is caused to the part, there will be losses. If a threaded milling cutter is used, first of all, it is not easy to break due to the low force applied ； Even if it breaks, since the diameter of the machined hole is larger than that of the tool, the broken part can be easily removed. In terms of product output, thread milling is much higher than tap turning. 5. It is not easy to form viscous chips. For softer materials, sticky chips are prone to forming during machining; however, thread milling involves high-speed rotation that breaks up these chips. The tap’s cutting speed is low; the entire thread and the machined surface are involved, which makes it easy for debris to adhere. 6. Requires low machine power. 7. Due to chip breaking in thread milling, there is partial tool contact, resulting in low cutting forces; whereas with a tap, there is full thread contact, leading to high forces, thus requiring a machine with high power. 8. Broken tools are easy to handle. Firstly, thread mills are subjected to little force and rarely break. If this occurs, since the machining aperture is larger than the tool, the broken part can be easily removed ； The tap is subject to high stress, has poor chip removal, is prone to breaking, and results in a larger hole after breakage. It’s slightly easier to handle; however, small holes pose a problem. For instance, when machining ordinary threads, thread milling isn’t cost-effective, considering the cost per piece. Plain threads are classified as those with a general hardness of less than 50HRC and a diameter of less than 38 mm, although this is not a clear dividing line. Ordinary taps are generally made of high-speed steel, and their market price is several dozen dollars. However, the price of thread mills is more than 10 times that of taps; furthermore, the service life of thread mills cannot exceed 10 times that of taps. Secondly, the aspect ratio should not be too large; typically, an L/D ratio of 50 is required. This configuration is suitable for thread milling, as it facilitates chip breaking, results in less local contact with the tool, and the cutting inserts are made of cemented carbide, which reduces wear and extends their service life. Conventional high-speed steel taps are generally unsuitable for this purpose. For example, using solid cemented carbide taps is not inexpensive, with costs being similar to those of thread milling cutters. Based on our existing machining experience, the efficiency and cost-effectiveness of thread milling are definitely higher than those of taps. 2. Machining of composite holes (with chamfers) is also suitable for thread milling. Thread mills have many functions and can be integrated into threading and chamfering. 3. Suitable for processing thin-walled materials; ideal for thread milling. The cutting force exerted by thread mills is low, resulting in minimal deformation. Additionally, the bottom hole can be made flat, and the threads can be placed close to the bottom hole, thus requiring very little space. 4. For machining with high thread precision, thread milling offers a higher thread speed, good chip removal performance, higher thread precision, and better surface finish, making it more suitable for this type of work. 5. The material is soft and made of titanium alloy, making it suitable for thread milling, as thread mills do not tend to generate sticky debris. For unstable cutting conditions, thread mills are perfectly capable of handling such situations, as their cutting principle itself involves intermittent milling.