While thread cutting is a widely used method in thread production, it's not the only option available. Threads can also be created through processes like turning, whirling, shaping, rolling, or even erosion. Although we have a deep appreciation for thread cutting, expanding our knowledge beyond familiar techniques often leads to better solutions. That’s why today, we’re taking a closer look at an alternative method that isn’t always discussed: thread milling.

If you’ve ever used a thread cutting tool, many of the concepts behind thread milling will feel familiar. Both methods involve removing material from the workpiece, and the tools share some similarities. However, thread milling operates on a different set of principles. Let’s explore what makes this technique unique and how it works.

Key Features of Thread Milling

Thread milling stands out from other thread manufacturing techniques due to several distinct characteristics. Here are some of the most important ones.

Design of a Thread Mill

At first glance, a thread mill might look similar to a thread cutter. Both have a shaft and a head with grooves. But there's a key difference: a thread mill doesn't have a pre-formed thread. Instead, it features profiled grooves spaced at the pitch distance, allowing it to cut threads during operation.

Thread Milling Requires 3-Axis CNC Control

To create a thread using a thread mill, the machine must move the tool in a precise helical motion within the drilled hole. This motion allows the tool to carve the thread into the material. The resulting thread diameter is slightly larger than the tool itself. Achieving this requires a high level of precision—especially in matching the movement to the pitch. This is only possible with a 3-axis CNC machine capable of following complex paths.

Thread Milling Offers Greater Flexibility

One of the major advantages of thread milling is its versatility. Unlike traditional thread cutting tools, a thread mill can handle a wide range of applications. It can produce both left-hand and right-hand threads, as well as through-holes and blind holes. In addition, it can create internal and external threads. Some advanced thread mills can even produce multiple pitches and sizes with a single tool, reducing the number of tools required for the job.

Thread Milling Produces Small, Manageable Chips

A significant benefit of thread milling is the chip shape. Instead of long, spiral-shaped chips that can be difficult to manage, thread milling produces small, fragmented chips. This helps prevent chip clogging and makes cleanup much easier, especially in tight or deep holes.

Thread Milling Can Handle Large Diameters

Another advantage of thread milling is its ability to handle large-diameter threads. Traditional cutting tools would require massive setups for such tasks, but a thread mill can easily accommodate them. This makes it ideal for applications where size is a limiting factor.

How to Use a Thread Mill

The thread milling process varies depending on the type of tool being used. Some tools streamline the process by eliminating multiple steps. For clarity, we’ll break down the process into two main scenarios: thread milling with and without pre-drilling.

Thread Milling with a Pre-Drilled Hole

Some thread mills require a pre-drilled hole. Unlike thread cutting, where the core hole size is typically determined by a formula, the diameter here can vary. Once the hole is drilled, it’s countersunk, and the thread mill is inserted to the desired depth. The process begins with a 180° lead-in helix, followed by a continuous helical motion to cut the thread. A final 180° lead-out helix ensures the tool exits cleanly.

There's also a variation known as the thread chamfer mill with chamfering stage. This type of tool performs the chamfering step automatically, eliminating the need for a separate countersinking operation.

Drill Thread Milling

Another type of thread mill, called a drill thread mill, can operate without pre-drilling. These tools feature a drilling tip and a chamfering stage, allowing them to drill their own core hole and chamfer it simultaneously. Afterward, the threading process proceeds in the same way as with other types of thread mills.

Important Considerations for Thread Milling

Precision is essential in thread milling. Even when pre-drilling is involved, the hole must be accurately positioned and sized. The workpiece should be securely and stably mounted close to the milling area to minimize vibrations. The machine itself must also have high rotational accuracy to ensure consistent results.

When it comes to cutting speed and feed rate, these can be adjusted independently. However, because of the circular motion between the tool’s edge and its axis, the feed rate needs careful adjustment. Otherwise, the machine may misinterpret the speed, leading to potential tool damage.

Another limitation of thread milling is the maximum thread depth achievable. Most tools can only reach about three times the tool diameter. Additionally, with smaller thread angles and coarser pitches, there may be slight deviations in the thread profile. This is particularly noticeable in specialized thread forms like trapezoidal, buttress, or knuckle threads.

Is Thread Milling Right for You?

Thread milling offers many benefits when the right conditions are met. However, if you're not working in mass production or don't have access to a well-equipped workshop, simpler methods may be more practical. Many hobbyists lack the necessary CNC machines for thread milling, and even professionals can find programming challenging.

If you occasionally need to produce threads or require them for a specific project, traditional thread cutting tools might still be the best choice. With a wide selection from screw tap manufacturer BAER, you're sure to find the right tool for your needs. Plus, our expert customer service is always here to help!