Different Types of Thread Mills – Thread Milling Principles and Advantages


The method of machining threads with a thread mill is called thread milling, speaking of the cutting tools, what are the different types of thread mills? In this article, we’ll get into the introduction of thread mills.

Types of Thread Mills

1. Straight flute thread mill

Straight flute thread mills can be divided into internal thread mills and external thread milling cutters. If the type can’t be distinguished from the appearance, check the parameter description on the cutter bar. The advantage of the straight flute thread mill is that it can process the required thread length as long as milling a circle. If the thread length exceeds the full length of the blade of the thread milling cutter, it needs to be raised or lowered by one length for milling. This length must be an integral multiple of the thread pitch, followed by grinding off part of the cutter bar. The disadvantage is that there are many cutting edges at the same time and the side pressure of cutting force is large, so the tool clamping should be as short as possible.


2. Single flute thread mill

The advantage of this kind of thread milling cutter is that it can mill both internal and external threads. It should be selected according to parameters such as thread profile. The cutting force and side pressure of the single flute milling cutter are small, the tool clamping can be very long, and the thread with a deep position and hard material can be processed. However, the processing efficiency is low, and the required thread length can only be obtained by milling many cycles.


3. TMLR (UN Long reach thread mills)

Long-reach thread mills, deep processing, spiral edge, taking into account the small cutting force and side pressure, and processing efficiency, are suitable for machining deep internal threads on hard materials.


4. Helical flute thread mill

A helically distributed thread mill can also be divided into an internal thread milling cutter and an external thread milling cutter. A helical distributed cutting edge is used to reduce cutting force and side pressure.


5. Pipe thread mill (NPT/NPTF)

The cutting edge of the pipe thread milling cutter can be straight, spiral, or staggered, and can also process internal and external threads. There are also UNC/UNF thread mills. If you want to machine UNC/UNF threads, you should select a UNC/UNF thread milling cutter with the same pitch. If NPT thread is to be machined, an NPT thread milling cutter with the same pitch should be selected.


6. Replaceable insert thread mill

When the thread is in a very deep position, the cutter bar is very long, and the replaceable blade must be ground to only one or two teeth to reduce the cutting force.

Machining Principle of Thread Milling

The cutting edges of the thread milling cutter are distributed in parallel according to the pitch, not like the spiral distribution of the tap, so the speed should be high while the feed speed should be low during processing. In addition, the milling degree can be run repeatedly, even when the milling cutter is replaced. G02/G03 is the thread processing code. When milling the thread with a thread milling cutter, it means moving a distance vertically along the arc, that is, moving the spiral.

Advantages of Thread Milling

– When machining titanium alloys, superalloys, and high-hardness materials, excessive cutting force twists or breaks the tap. If chip removal isn’t smooth in long chip materials, the chip will wind the tap or clog the orifice, cracking or breaking the tap. Broken tap removal can be time-consuming and damaging. The slow-cutting thread milling cutter rarely breaks. The broken milling cutter may be removed without damaging the part.

– Thread mill’s high-speed tool rotation and spindle interpolation. The cutting tool’s diameter is less than the thread’s, avoiding the tap’s revolving line. The original milling cutter lacks a turning line, requiring a tap. Chip-making is hard. Soft materials require low machine tool power due to chip stickiness. Thread milling involves chip-breaking cutting, thus the tool is in local contact and tap tool breakage is easy.

– Due to the tap’s slower cutting speed and reverse tool withdrawal after thread treatment, it’s difficult to increase thread processing efficiency in big quantities. High milling speed and a multi-cutter groove design optimize feed speed and processing efficiency. A longer blade can minimize the axial feed distance (equivalent to shortening the thread) to improve processing efficiency.

– Thread mills can save costs. The same cutter can mill the left-handed threads or right-handed threads and can machine both external and internal threads, which saves tooling costs and time for changing tools.