Thread milling tool
Thread milling cuts internal and external threads with a rotating cutter that follows a helical path, so a worn or broken tool never gets stuck in the part the way a tap can. The STS ThreadMill® program covers solid carbide thread mills for small internal threads and indexable thread milling cutters for larger diameters, backed by more than 30 years of threading experience and used in over 40 countries.
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Why thread milling?
On a CNC machining centre with helical interpolation, one thread mill can produce many thread sizes with the same pitch. The final diameter is set with a radial offset in the control instead of a new tool. Compared with tapping, thread milling gives you:
- Lower risk of tool breakage, and a broken tool is easy to remove
- One tool for several diameters and pitches
- Better control over thread quality and tolerance
- Efficient chip evacuation in blind holes
- Reliable results in hard-to-machine materials such as titanium and Inconel
The STS ThreadMill® program
The ThreadMill® program is built in two families. Solid carbide thread mills are designed mainly for internal threads in small diameters. Indexable thread milling cutters cover larger diameters and can be used for both internal and external threads.
The program supports ISO Metric, UN/UNJ, Whitworth (BSP, BSPT), Trapezoidal, ACME, NPT/NPTF, API and STI threads. Inserts are available in the carbide grades STN20, STN50 and STN50X. Tool bodies are available with radial or axial coolant channels, and the same tool cuts right-hand and left-hand threads. Special tools are made on request.
See the full product range and download the catalogue on the ThreadMill® thread mills product page.
Key features and benefits
Multi-profile capability
One insert or cutter covers several diameters within the same pitch. That reduces tool inventory and changeover time in the machine.
Replaceable cutting edges
On indexable cutters only the insert is replaced when the edge is worn. The tool body stays in use, which lowers the cost per thread over time.
Grades and coatings for each material
Several carbide grades and coatings are available, so the tool can be matched to the workpiece material.
Support for multiple standards
The program follows ISO, ANSI, API and DIN thread standards, which makes it easy to use the same tooling across customers and markets.
Documentation and application support
Every ThreadMill® tool comes with cutting data, thread tables and programming strategies, and our application engineers help you with the first trial when needed.
Frequently asked questions about thread milling
What is thread milling?
Thread milling is a machining method where a rotating cutter follows a helical path to cut an internal or external thread. Unlike tapping, which cuts the full profile in one operation, the thread is built up as the cutter moves one pitch along its axis for every orbit around the hole or stud.
Is thread milling better than tapping?
For many jobs it is. A thread mill has a much lower risk of breaking, one tool can cut several diameters with the same pitch, and the chips are short and easy to evacuate from blind holes. Tapping can still be the faster choice for long series of small standard threads in easy-to-machine materials.
What materials is thread milling suitable for?
Thread milling works in most materials, from free-cutting steel and stainless steel to titanium and Inconel. The low cutting forces and short chips make it a safe choice in hard-to-machine materials where a tap risks breaking.
Do I need special CNC capability for thread milling?
Yes. The machine control must support helical interpolation, which means circular movement in X and Y (G02/G03) while Z moves at the same time. Most modern machining centres have this, and our thread milling guide shows a complete program example.
Should I choose a solid carbide or an indexable thread mill?
Solid carbide thread mills are mainly used for internal threads in small diameters. Indexable thread milling cutters cover larger diameters, work for both internal and external threads, and only the insert needs replacing when the edge is worn.
Can the same thread mill cut right-hand and left-hand threads?
Yes. The same ThreadMill® tool cuts both right-hand and left-hand threads. The direction is set by the toolpath in the CNC program, not by the tool.
How to choose the right thread milling tool
Five things decide which ThreadMill® tool fits your application:
- Thread profile and standard
- Thread size and pitch range
- Workpiece material
- Coolant supply in the machine
- Machine capability and spindle speed
Send us the thread specification and material, and we recommend a tool and starting values for your machine.
Programming and application tips
Use climb milling for better surface finish and tool life, and plan a smooth lead-in and lead-out so the cutter enters the material gradually. Start from the recommended cutting data and adjust speed and feed to the material and the cutter diameter. For internal threads, a tool with through coolant clears the chips from the hole.
Formulas, safe starting values, a worked M12×1.75 example and a troubleshooting table are collected in one place. Read our full thread milling guide with cutting data and G-code examples. Machining external threads? Then our guide to external thread milling covers setup and toolpaths for studs and shafts.
Tool life and productivity
Inserts can be indexed and replaced, which extends the life of the tool body. Fewer tool changes and less scrap give thread milling a lower total cost of ownership than tapping.
Ready to optimize your threading process?
Tell us the thread, the material and the machine, and our threading specialists in Insjön come back with a tool recommendation and cutting data. You can also buy STS tools through our distributors around the world.
