Traditional methods for thread machining primarily involve using single-point turning tools to cut threads on a lathe or employing taps and dies for manual threading and die-cutting. With the advancement of CNC machining technology, particularly the advent of three-axis simultaneous control CNC machining systems, a more advanced thread machining method—CNC thread milling—has been realized. Compared to traditional thread machining methods, thread milling offers significant advantages in terms of machining accuracy and efficiency. Furthermore, it is not constrained by thread structure or thread handedness during the machining process. For instance, a single thread milling cutter can machine both internal and external threads with various different handednesses. For threads that do not permit a thread run-out or a relief groove structure, traditional turning methods or taps and dies struggle considerably, yet CNC milling accomplishes this with ease. Additionally, the tool life of a thread milling cutter is ten times, or even several tens of times, greater than that of a tap. Moreover, during the CNC thread milling process, adjusting the thread diameter size is extremely convenient, a feat difficult to achieve with taps and dies. Due to the numerous advantages of thread milling, high-volume thread production in developed countries has adopted milling processes quite extensively.

Advantages:

 Lower Overall Cost: Although a single thread milling cutter is more expensive than a single tap, the cost per threaded hole is often lower when calculated comprehensively. This is due to the vastly superior tool life of the milling cutter, reducing the frequency of tool changes and associated costs, and its ability to replace multiple dedicated taps.

 Higher Precision: Thread milling cutters achieve precision through tool radius compensation (cutter comp) within the CNC program. This allows customers to flexibly select the specific thread fit and tolerance class they require simply by adjusting the tool path offset, rather than being locked into the precision of a specific tap.

 Superior Surface Finish: Threads produced by thread milling cutters generally exhibit a better surface finish and appearance compared to those made with taps. The milling process typically results in a cleaner, more well-defined thread form with fewer imperfections.

 Longer Tool Life: The lifespan of a thread milling cutter is tenfold or even several tens of times greater than that of a tap. This dramatically reduces tooling costs over long production runs and minimizes machine downtime for tool changes and subsequent adjustments, thereby increasing overall equipment effectiveness (OEE).

 Elimination of Tap Breakage Risks: A broken tap inside a workpiece often leads to significant rework efforts, potential damage to the part beyond repair, and consequently, scrap. In contrast, if a thread milling cutter breaks (often due to severe user error), the remaining fragments are typically much easier to extract from the hole without necessarily causing the workpiece to be scrapped, as the solid portion of the tool is not fully engaged like a tap.

 Higher Machining Efficiency: The processing speed and material removal rates of thread milling are generally far superior to those of tapping, especially for larger diameter threads or in challenging materials, leading to reduced cycle times.

 Capability for Blind Holes: Thread milling cutters can machine threads effectively all the way to the bottom of a blind hole. Taps, due to their design and the need for a chamfer, cannot thread completely to the bottom without a specific undersized pre-drill, which thread milling avoids.

 Multi-Functionality for Certain Materials: For some materials, specific types of thread milling cutters can perform drilling, threading, and chamfering operations in a single tool path and with one tool, a process known as multi-functional machining. Taps are incapable of this combined operation.

 Versatility in Thread Handedness and Type: A single thread milling cutter can be used to machine both internal and external threads, as well as both left-hand and right-hand threads. A tap, being a dedicated tool, can only produce one specific type (e.g., internal, right-hand).

 Interchangeability for Same Pitch, Different Sizes: For threaded holes sharing the same pitch but differing in major or minor diameters, multiple specific taps would be required. A single thread milling cutter, however, can often be programmed to machine all of them by simply adjusting the tool path and diameter compensation, offering great flexibility.

 Correctability for Inspection Failures: If the first inspection of a threaded hole indicates it is out of tolerance (e.g., slightly undersized), a thread milling cutter can frequently correct the error by adjusting the tool radius compensation and re-running the milling cycle. If a tapped hole is out of spec, correction is usually impossible, and the workpiece often must be scrapped or undergo complex, time-consuming repair procedures.

 Efficiency in Large Diameter Threads: When machining large diameter threaded holes, tapping becomes highly inefficient, requiring immense torque and potentially multiple tools. Thread milling can accomplish this much faster and with significantly lower cutting forces.

 Favorable Chip Formation: Thread milling produces small, fragmented, powder-like chips (in many materials) that are easily evacuated. Tapping, conversely, generates long, continuous, spiral-shaped chips which are prone to wrapping around the tool ("bird's nesting"), potentially causing tool breakage and damaging the thread surface.

 Reduced Cutting Forces and Machine Load: The thread milling process involves intermittent, multi-tooth engagement rather than full-profile, continuous contact like tapping. This results in significantly lower radial and axial cutting forces, reduced stress on the machine tool spindle, and lower power consumption. It is particularly beneficial for machining centers with limited torque capacity or when working with thin-walled or delicate components.

 Simplified Tool Holding: Tapping often requires specialized, more expensive tension-compression ("floating") tap holders to accommodate slight synchronization errors between the spindle rotation and Z-axis feed. Thread milling cutters, however, can be held in standard, rigid tool holders such as ER collet chucks, HSK shanks, hydraulic chucks, or heat-shrink holders, simplifying tooling inventory.

 Economic Benefits of Indexable Tooling: For indexable (insert-type) thread milling systems, a single cutter body can accommodate a variety of interchangeable carbide inserts designed for different thread forms (e.g., Metric, UN, Whitworth). This offers excellent economic efficiency and tool management simplicity compared to stocking numerous solid taps.

 Capability for Hard Materials: When machining threads in high-hardness materials, taps wear out extremely rapidly and may even fail to cut altogether. Thread milling cutters, particularly those with advanced carbide grades and coatings, can handle these hard materials effectively and efficiently.

Applications:

1. Mold and Die Manufacturing: Molds and dies are precision components with high production costs. Precisely for this reason, threads within large molds—where accurate hole center-to-center distances and full, well-formed thread profiles are critical—are often machined using thread milling cutters to guarantee the final quality and integrity of the expensive workpiece.

2. Non-Rotational or Asymmetrical Parts: For parts that are not rotationally symmetric or have irregular shapes, the primary challenge with thread turning on a lathe is workholding and achieving balanced rotation. Thread milling on a CNC machining center circumvents this issue entirely, as the part can be securely fixtured once, and the thread is generated by the precise movement of the cutter. This also ensures high machining accuracy for the threads.

3. Large Bore Diameters and Interrupted Cuts: Thread milling is exceptionally well-suited for machining threads in large diameters where taps would be impractical due to size and torque requirements. It is also highly effective in situations involving interrupted cuts, such as threads crossing keyways or oil grooves, where a tap would be prone to chipping, breaking, or producing imperfect threads. The milling cutter's intermittent engagement handles these interruptions more robustly.

Thread milling technology is finding increasingly widespread application within the mechanical manufacturing industry, actively driving progress and efficiency gains in the sector. The successful application of thread milling necessitates careful attention to suitable workpiece geometries, the development of advantageous machining strategies and CNC programs, and the selection of high-quality, reliable thread milling tools. Only through the comprehensive and thoughtful application of thread milling technology can its full range of advantages be leveraged to achieve tangible results and productivity enhancements. Simultaneously, this advanced process allows the capabilities of modern CNC machine tools—their precision, flexibility, and power—to be fully utilized and showcased, which in turn stimulates further advancements and refinements in the production capabilities and designs of the thread milling cutters themselves, creating a positive feedback loop of technological improvement.