A thread milling cutter is a tool that processes threads by rotating the cutting tool and moving it relative to the workpiece in a cutting manner. The principle is to use the cutting edge of the tool to come into contact with the surface of the workpiece, and through the cutting force, remove the material of the workpiece to form a threaded structure.
I. The Historical Evolution of Thread Processing
The main application of the screw principle can be traced back to the spiral water-lifting tool created by the Greek scholar Archimedes in 220 BC. In the 4th century AD, countries along the Mediterranean coast began to apply the principle of bolts and nuts to pressure machines used for winemaking. At that time, the external threads were made by winding a rope around a cylindrical rod and then marking and engraving according to this pattern. While the internal threads were often formed by wrapping a softer material around the external threads and then hammering it into shape.
Around 1500, in the sketch of the processing device for creating spiral threads drawn by the Italian Leonardo da Vinci, there was already an idea of using a master screw and exchange gears to process threads of different pitches.
In the 1820s, Mozley produced the first sets of taps and die sets for processing threads. At the beginning of the 20th century, the development of the automotive industry promoted the standardization of threads and the development of various precise and efficient methods for thread processing. Various automatic opening die heads and automatic retracting taps were invented successively, and thread milling began to be applied.
II. The significant advantages of thread milling cutter
1.Economy:
A thread milling cutter can machine any thread diameter with the same pitch, eliminating the need to use a large number of different types of taps. It can operate in blind holes and through holes and can machine any thread with any fit, tolerance or position requirements. Compared with traditional high-speed steel (HSS) tapping, using carbide thread milling can significantly increase productivity: achieving higher cutting speeds, more cutting edges and higher feed rates.
2. Technical and Quality Advantages:
The thread milling cutter actually does not have a "guiding cone". This enables the thread to be machined all the way to the bottom of the hole while ensuring that the processing requirements are met. It can easily machine threads in almost any type of material, including those that cannot be processed using traditional methods. The machining accuracy is high and the surface quality is good: since thread milling is completed through the high-speed rotation of the tool and the interpolation of the spindle, the cutting method is milling, and the cutting speed is high. While tap cutting has a low cutting speed and long chips, which are prone to damaging the inner hole surface. By changing the program, different diameters of threads, left and right threads, and internal and external threads can be machined, and its flexibility is very ideal.
3. Safety and operational advantages:
Internal thread chip removal is convenient: Thread milling is a type of chip-breaking cutting, with short chips. Additionally, the diameter of the processing tool is smaller than that of the thread hole, so chip removal is smooth. While a tap belongs to continuous forming cutting, with long chips. Moreover, the diameter of the tap is the same as that of the processing hole, making chip removal difficult. This can prevent the formation of a rotational line when the tap is reversed (which is not allowed in situations with high sealing requirements). Handling of tool damage is easier: Firstly, the force of a thread milling cutter is small, and damage rarely occurs. If it does happen, since the processing hole diameter is larger than the tool diameter, the broken part can be easily removed. However, a tap is subjected to high force, has poor chip removal, and is prone to breakage. After breaking, larger holes are slightly easier to handle, while smaller holes are very troublesome.
To more vividly demonstrate the advantages of thread milling, we have summarized the following table:
| Product feature | thread milling |
| Operating principle | Using CNC three-axis linkage for spiral interpolation, a thread is 'milled' out. |
| Versatility of cutting tools | High: With one tool, you can machine both left-handed and right-handed internal and external threads of different diameters and the same pitch. |
| Chip removal situation | Good: Chip-free cutting, with short chips and smooth chip removal. |
| Accuracy of thread | High: This can be compensated as long as the interpolation accuracy of the machine tool is guaranteed. |
| Blind hole processing | Advantage: It can be processed into flat-bottomed threads, and the cutting tool can be easily withdrawn. |
| Material availability | Wang: It can process high-strength and high-hardness materials. |
| Cost of cutting tools | The unit price is high, but the cost per hole may be lower (due to its versatility and long lifespan). |
| Safety | High: The cutting force is low, and the damage to the tool is easy to handle. The workpiece is less likely to be scrapped. |
III. Application Scenarios of Thread Milling Cutte
Thread milling cutters are widely used in precision processing in various fields, especially playing a crucial role in thread processing in industries such as automobiles, aerospace, and mechanical manufacturing. They can be used for both internal and external thread machining and are suitable for processing various materials, including steel, aluminum, and copper. The application scope of thread milling cutters covers various processing requirements ranging from small parts to large workpieces.
The following situations are particularly suitable for using thread milling:
Processing of large-diameter threads (typically > M12 or 1/2").
Difficult-to-machine materials, such as high-strength steel, hardened steel, titanium alloys, etc.
High-precision thread requirements, situations where precise control of dimensions is necessary.
Blind hole thread processing, with difficult chip removal in deep holes.
Single-piece and small-batch production, where a single tool is required to cover various thread sizes.
When the torque of the machine tool is insufficient and traditional tapping cannot be carried out.
IV. Main Types of Thread Milling Cutters
1. Classified by tooth shape structure:
Single-tooth thread milling cutter: Suitable for processing small-diameter threads, with high processing accuracy. The thread processing principle of the single-tooth thread milling cutter is: The tool rotates fixedly for one full turn, and then descends by one pitch in the negative Z-axis direction.
Multi-tooth thread milling cutter (threading cutter): Suitable for processing large-diameter threads, with high processing efficiency. For example, when using a 9-tooth thread milling cutter to machine threads, this processing efficiency is extremely high, significantly reducing the processing time. In large-scale thread processing, it has a significant advantage.
Full tooth thread milling cutter: It is designed with a complete tooth profile, and the entire thread shape can usually be machined in one pass.
2. Classification by tool structure:
Overall hard alloy thread milling cutter: Covers a smaller diameter range and is typically used for thread processing below M12. The overall hard alloy milling cutter is faster and more productive than tools using interchangeable inserts.
Swappable thread milling cutter: Equipped with swappable blades, it is suitable for processing larger diameter threads (usually > M12 or 1/2"). The milling cutter with interchangeable blades is more versatile (can process any thread pitch and type), and is very cost-effective for users who have small processing batches and need to frequently switch from one thread type to another.
Swappable head thread milling cutter: The shank and the cutter head are separated. It has good economy and high flexibility. When the cutter head is worn or damaged, only the cutter head needs to be replaced, thus saving costs.
V. Processing Steps for Thread Milling
Thread milling is a process where a helical interpolation milling operation is carried out using a thread milling cutter through the three-axis linkage of a CNC machine. The tool makes a complete circular motion on the horizontal plane and moves linearly by one pitch in the vertical plane each time.
Processing Preparation:
According to the general processing method, determine the milling methods for both internal and external threads, and prepare the measuring tools and jigs based on the processing method, and then compile the program.
Internal thread milling procedure:
1. Processing of thread bottom hole: Before using a thread milling cutter to mill the thread, the processing of the thread bottom hole must be completed first. Calculating the diameter of the thread bottom hole: Nominal diameter - 1.08P (P is the pitch).
For example, for a thread with M30×1.5: Nominal diameter - 1.08P = 30 - 1.62 = 28.38mm, so the diameter of the thread bottom hole is a through hole of 28.38mm."
2. Selecting tools and parameters: Choose a suitable size of end mill or thread milling cutter. For example, a⌀12mm two-tooth end mill can be selected, with the spindle speed S set at 700 r/min, the tool material being high-speed steel, and the feed rate F at 120 mm/min.
3. Writing processing program: Thread milling requires the use of CNC program to control the three-axis linkage of the machine tool to achieve helical interpolation motion. The program usually includes:
Approach section: The milling cutter moves from the outside of the thread until it reaches the full depth of the thread. The tool path should be set so that it enters the cutting direction.
Thread processing section: The tool rotates around the circumference for 360° while moving a pitch in the Z direction.
Retract tool section: The tool withdraws from the material. Usually, it also adopts the tangential withdrawal method.
4. Actual milling process: After confirming that the bottom hole has been processed and using a chamfering drill to chamfer the edges, select a single-edge thread milling cutter or a thread comb tool for milling.
Steps for external thread milling
The milling of external threads is similar to that of internal threads, but the tool path is different. For the same thread milling cutter, it can be used to machine both internal threads of the same pitch and external threads. When programming, attention should be paid to the tool radius compensation and the direction of helical interpolation.
VI. How to Select the Appropriate Thread Milling Cutter
1. Material hardness: The boundary for high-hardness materials is around HRC 40. For materials with a hardness exceeding this level, a high-hardness thread milling cutter needs to be selected.
2. Thread Type (Internal or External): For some specifications, the internal and external threads of the thread milling cutter are not compatible (such as M and UN). However, for all other thread specifications, the thread milling cutter is compatible for both internal and external use.
3. Thread length: The basic principle to follow is that the thread length should not exceed three times the diameter of the cutting tool. When the thread length is long, it is recommended to choose a solid carbide thread milling cutter. If the length exceeds three times the diameter (D), a thread milling cutter with a shock-absorbing device can be customized.
4. Thread size: Generally, for thread milling cutters with a diameter of M12 or smaller, a solid carbide thread milling cutter should be selected. For sizes larger than this, a replaceable thread milling cutter should be chosen. Also, the requirements of the customer and the processing environment should be considered. For example, if the required surface finish is high, a solid thread milling cutter should be used.
5. Workpiece batch size: There are many samples and a large number of individual orders, with various thread specifications. In such cases, a single-tooth range thread milling cutter with adjustable pitch should be selected. This type of thread milling cutter has adjustable pitch. For large batches of workpieces, a convertible thread milling cutter should be used; for medium-sized batches, a complete thread milling cutter should be chosen.
6. Cooling method consideration: Unless it is for high-hardness materials, particularly difficult-to-machine materials, deep-hole threads, or threads requiring high finish, an external cooling thread milling cutter can be selected. Internal cooling thread milling cutters are more expensive.
7. Machine conditions: Factors to consider include the power, rigidity of the machine, and whether it supports three-axis linkage functionality, etc.
VII. To sum up, as mentioned above
The thread milling technology, by replacing the traditional thread cutting and forming processing, provides modern manufacturing with an efficient, precise and flexible solution. With the popularization of numerical control technology and the advancement of tool technology, the application scope of thread milling cutters will further expand, and it is expected to replace the traditional thread processing methods in more fields and become the mainstream choice for thread processing.
Post time: Sep-06-2025
