What is Broaching? The Process, Uses, and Products

Broaching is a machining process that uses a specific tool called a broach. The broach is a custom tool with teeth that removes material to shape a part. It’s often used for components requiring specific internal features—like keyways, splines, or uniquely shaped holes.

Broaching has been used since the 1850s, but it became more precise and useful around 100 years ago with better tool steel, more powerful machines, and the demands of the automotive industry. 

This is a unique type of machining because each broach is made to cut a uniquely shaped part. In the broaching process, the cuts are made in a single pass of the broach tool which makes this machining process efficient for high volumes of identical parts. 

In this post, we’ll explain how broaching works and what it’s used for today. 

Overview of the broaching process

At the heart of the process is the broach itself—a custom-made cutting tool engineered for one specific job. Think of it less like a simple saw blade and more like a series of blades combined into a single, highly efficient tool. Each broach has distinct sections that work sequentially in a single pass:

• Roughing Teeth: These do the heavy lifting, removing the bulk of the material.
• Semi-Finishing Teeth: These begin to refine the surface and bring the feature closer to its final dimension.
• Finishing Teeth: These perform the final cut, delivering a smooth surface and ensuring the part meets exact specifications.

The process is simple: the broach is moved against the stationary part to remove material and form the part features, or the part is moved against the broach.

Moving Broach, Stationary Part: This is the most common setup. In push or pull broaching, the workpiece is secured in a fixture, and the broach is driven through it or across its surface.

Moving Part, Stationary Broach: This configuration is often used in high-volume, continuous broaching machines. Parts are loaded onto a conveyor-like chain or a rotating table that moves them past a stationary broaching tool.

This single-pass operation is the key to its efficiency, delivering exceptional repeatability and consistent quality across an entire production run.

A strategic investment for high-volume production

A custom broach is a significant investment (sometimes up to $30,000 each). But for high-volume projects, it’s an investment that strategically drives down the per-piece cost and streamlines your supply chain. One tool can machine thousands of identical parts with speed and consistency. Once the run is complete, the tool can often be resharpened, extending its life and maximizing the return.

This makes broaching the ideal solution when you need to optimize costs without sacrificing the quality of high-volume components.

Here’s an example of what a broaching tool might look like:

What is broaching used for?

Broaching was first developed for cutting simple keyways and rifling gun barrels. Today it’s a go-to solution for manufacturing a variety of metal and plastic parts. 

It provides the perfect balance of speed and precision for high-volume production runs. While a process like CNC milling may achieve tighter tolerances on a single part , broaching delivers exceptional repeatability for thousands of parts, holding tolerances of up to ±0.005 inches.

Because a single broach can machine thousands of parts, it's the ideal method for creating components with internal features like:

• Internal gear teeth
• Keyways and slots
• Splines
• Uniquely shaped holes (e.g., square, hexagonal, or double-D)

Here are some examples of common features created with broaching, including an external gear, an internal square hole, a keyway, internal splines, and a double-D hole.

Broaching works best when a part is parallel to the broach tool. When there are multiple surfaces, angles, or curves on the part, the broach can’t perform cuts in a single pass, and usually isn’t the best machining option. 

Broaching can be used for any type of metal or plastic, but softer metals like brass and aluminum are usually ideal. Hard stainless steel, Titanium, and superalloys like Monel or Hastelloy can be broached, but the broach wears out quickly so it’s less efficient. 

At Spex, we have experience machining broached components for leaders in these key sectors:

• Power & Electrical: Broaching is essential for cutting precise keyways into motor shafts and creating the square or double-D shaped holes common in electrical housings, switchgear, and connectors.
• Measurement & Instrumentation: For mechanical instruments that rely on precise movement, broaching creates the clean, highly consistent internal gears and splines needed for valve stems and control knobs, ensuring reliability and accuracy.
• HVAC & Heat Exchange: In HVAC systems, broaching is used to efficiently machine internal splines on compressor shafts and create hexagonal or square fittings for high-pressure valves and connectors.
• Precision Hardware: From custom locking mechanisms to drivetrain components, broaching is used to create a huge range of parts with complex internal forms that must be perfectly identical across multi-million piece orders.

Different types of broaching

Broaching processes can be defined in two main ways: by where the cutting action takes place and by how the machine applies force to the tool.

Based on Cut Location:

• Internal Broaching: This is used to machine features on the inside of a workpiece. A pilot hole must be present in the part first. The broach is then passed through the hole to create features like internal gear teeth, splines, keyways, or to change a round hole into a square, hexagonal, or other unique shape.
• Surface Broaching: As the name suggests, this process machines features on the external surface of a part. It's commonly used to create flat surfaces, external slots, or other contours.

Based on Machine Action:

• Pull Broaching: In this setup, the machine pulls the broach through or across the workpiece. Pull broaches can be longer, which allows for more cutting teeth and a greater amount of material to be removed in a single, efficient pass. This makes it well-suited for larger parts or deeper cuts.
• Push Broaching: Here, the broaching tool is pushed through the workpiece under compression. Push broaches are typically shorter and thicker to withstand the compressive force and prevent breakage.

If you have more questions about broaching machining, don’t hesitate to reach out to our team. We have worked on thousands of custom projects in a range of industries. We are happy to help you pick the most efficient machining process for your next project.