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 our team has a deep passion for thread cutting, exploring alternative methods can bring new insights and advantages. That’s why we’re taking a closer look at an often-overlooked technique: thread milling.

If you've ever worked with a thread cutting tool, many of the concepts in thread milling will feel familiar. Both are chip-removal processes, and the tools share some similarities. However, thread milling operates on a completely different set of principles. Let’s dive into what makes this method unique and how it works.

Key Features of Thread Milling

There are several characteristics that make thread milling stand out from other thread manufacturing techniques. Here are some of the most important ones.

Tool Design

At first glance, a thread mill might look similar to a thread cutter. Both have a shaft and a head with grooves. But upon closer inspection, you'll notice that the thread mill doesn't have a thread profile. Instead, it features profiled grooves spaced at the pitch distance. This design allows for more flexibility in the types of threads that can be produced.

Requires 3-Axis CNC Control

To create a thread using a thread mill, the machine must be involved. The tool follows a helical path inside the drilled hole, gradually removing material to form the thread. The final thread diameter is larger than the tool itself, which means precision is essential. The movement must match the pitch exactly to ensure a clean, accurate thread. This level of control is only possible with a 3-axis CNC machine.

High Versatility

One of the biggest advantages of thread milling is its versatility. Unlike traditional thread cutting tools, a thread mill can handle both left-hand and right-hand threads, as well as through-holes and blind holes. It can also produce external and internal threads. Depending on the type of tool, a single thread mill may even be able to cut different pitches and thread sizes. This reduces the number of tools needed for various applications.

Chip Formation

Another benefit of thread milling is the shape of the chips it produces. Instead of long, spiral-shaped chips that can cause issues, thread milling generates small, manageable fragments. This makes chip removal easier and reduces the risk of clogging or damage to the workpiece.

Handles Large Diameters

Thread mills are not limited by thread size, making them ideal for large-diameter applications. Traditional methods would require massive cutting tools for such tasks, but thread milling can handle them efficiently and effectively. This makes it a great choice for industrial and heavy-duty threading needs.

How Thread Milling Works

The thread milling process varies depending on the type of tool used. Some tools can streamline the process and save time. For simplicity, we’ll break down the process into two main categories: thread milling with and without pre-drilling.

Thread Milling with a Pre-Drilled Hole

Some thread mills require a pre-drilled hole. Unlike with thread cutting tools, there isn’t a strict formula for the core hole diameter—it can vary depending on the application. Once the hole is drilled and countersunk, the thread mill is inserted and starts with a 180° lead-in helix. The thread is then milled using a continuous helical motion, followed by a 180° lead-out helix before the tool exits the hole.

Another variation involves a thread chamfer mill with a chamfering stage. In this case, the chamfering step is performed during the milling process, eliminating the need for a separate operation.

Drill Thread Milling

A different type of thread mill can drill its own core hole. These drill thread mills feature a chamfering stage and a drilling tip, allowing them to both drill and mill in one pass. After creating the core hole, they proceed with the thread milling process just like other tools.

Important Considerations

Precision is key in thread milling. Even when pre-drilling is involved, the hole must be accurately positioned and sized. The workpiece should be securely mounted, as close as possible to the milling area, to reduce vibrations and improve accuracy. The machine itself must also have high rotational precision.

When setting up the cutting speed and feed rate, it’s important to adjust these values carefully. Since the cutting edge moves in a circular path relative to the axis, improper settings could lead to excessive stress on the tool, increasing the risk of breakage.

It's also worth noting that thread mills have limitations in terms of depth. Most tools can only mill threads up to about three times their diameter. Additionally, with smaller thread angles and coarser pitches, there may be slight deviations in the thread profile. This is especially true for non-standard thread forms like trapezoidal, buttress, or knuckle threads.

Is Thread Milling Right for You?

Thread milling offers many benefits under the right conditions. However, if you're working on small-scale projects or don’t have access to advanced machinery, simpler methods might be more practical. Many DIY enthusiasts lack the necessary equipment, and not everyone has a CNC machine at home. Plus, programming a CNC machine correctly can be challenging, even for experienced users.

If you occasionally need to produce threads or have a specific project in mind, traditional thread cutting tools might be a better choice. With BAER’s extensive range of screw taps, you're sure to find the right tool for your needs. And don’t forget—our expert customer service is always here to help!