What Is Broaching? Process, Types & Applications

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What Is Broaching?

Broaching is a machining process that uses a multi-tooth cutting tool called a broach to progressively remove material and form a precise internal or external profile. In conventional linear broaching, the broach can produce the final profile in a single stroke, making the process well suited to repeated production of defined features.

The main tradeoff is tooling flexibility. A broach is designed for a specific profile, so it can provide consistent results once the tooling is established, but CNC milling is usually more practical when part geometry or production requirements change.

How Does a Broach Remove Material?

A broach contains multiple cutting teeth arranged progressively along its length.

The first cutting teeth remove a small amount of material. Each successive cutting tooth removes a controlled increment of stock, known as the rise per tooth, until the roughing teeth have removed most of the material and the finishing teeth establish the final profile and dimensions. This continues through the roughing and finishing teeth until the final tooth reaches the required profile.

A simplified sequence looks like this:

Workpiece → roughing teeth → intermediate teeth → finishing teeth → finished profile

The important point is that the entire machining allowance is divided among many teeth rather than removed by one cutting edge.

The vertical or radial increase between successive cutting teeth is the rise per tooth. This value controls how much stock each tooth removes and is selected based on the workpiece material, profile, and required cutting load.

For a simple internal keyway, for example, the first teeth may barely enter the material. Teeth farther along the broach progressively deepen the keyway until the finishing teeth establish the final width and depth.

This incremental cutting action is the foundation of the broaching process.

It also explains why a broach is generally designed for a particular geometry. The tooth progression itself contains much of the information needed to generate the final feature.

What Are the Main Types of Broaching?

Broaching is commonly described by where the feature is cut, how the tool is loaded, and how the tool moves. These categories can overlap. An internal spline may be produced by pull broaching, while a small hexagonal socket may use rotary broaching.

Internal and External Broaching

Internal broaching cuts a profile inside an existing opening, such as a keyway, spline, square hole, or hexagonal hole. The starting hole must be large enough for the broach to pass through.

External broaching removes material from the outside of a part to produce features such as flats, slots, serrations, or external profiles. The key distinction is simply whether the broach works through an opening or across an exterior surface.

Pull and Push Broaching

Pull broaching draws the tool through the workpiece. Because the broach is loaded in tension, it can be relatively long and carry a large number of progressively larger teeth. This makes pull broaching common in production work.

Push broaching forces the tool through the part in compression. Push broaches are generally shorter because compressive loading increases the risk of tool buckling, especially with long, slender tools.

Rotary Broaching

Rotary broaching uses a specialized holder that offsets the broach axis to create a controlled wobbling motion. This allows the tool to form polygonal profiles such as hexagonal and square holes on CNC lathes and machining centers.

It is often used for small polygonal features such as hexagonal or square sockets and can be performed on CNC lathes without a dedicated linear broaching machine.

What Is Broaching Used For?

Broached precision metal component

Broaching is used primarily to produce defined internal and external profiles that need to be repeated accurately across multiple parts.

The process is especially effective when the geometry is difficult or inefficient to produce through conventional drilling or milling but can be represented directly by the broach profile.

Internal Keyways, Splines, and Polygonal Holes

Internal keyways are one of the classic applications of broaching.

A keyway must have controlled width, depth, and location relative to the surrounding bore. Broaching allows these dimensions to be established with a dedicated tool containing the required tooth progression.

If you're comparing broaching with milling for a keyway or precision slot, here's a guide to CNC slot milling and the tooling, methods, and tolerances involved.

Splines are another important application. Internal spline profiles can contain many teeth around the circumference, making them difficult to generate efficiently with conventional machining methods.

Broaching can produce the complete spline profile through a controlled sequence of cutting teeth.

Polygonal holes are also common. Square, hexagonal, and other non-round internal profiles can be produced when the broach geometry is designed around the required shape.

These applications share one characteristic: the desired profile is clearly defined and needs to be reproduced consistently.

External Profiles and Surfaces

External broaching is used when a defined shape must be produced across the outside of a component.

Examples include:

• External flats
• Serrations
• External splines
• Slots
• Contoured surfaces

Instead of programming multiple milling passes to generate the same profile, a dedicated broach can contain the geometry directly in its cutting teeth.

That can make the operation highly repeatable once the tooling and setup have been established.

What Are the Advantages and Limitations of Broaching?

Broaching works best when the same profile has to be produced repeatedly. The cutting teeth increase in size along the tool, so material is removed in controlled increments and the final profile is largely determined by the broach itself. This makes the process predictable for production features such as keyways and internal splines.

Advantages of Broaching

High repeatability. Once the broach, workholding, and machine are set correctly, the same feature can be reproduced with little toolpath-related variation. This is useful for keyways or splines that must maintain a consistent fit across a production run.

Efficient cutting. Several teeth share the cutting load, with each tooth removing only part of the stock. A conventional push or pull broach can therefore finish the feature in a single stroke rather than building the profile through multiple milling passes.

The process is also relatively insensitive to operator-dependent tool positioning because the broach physically contains the required profile. For high-volume parts, that can reduce cycle time and simplify process control.

Limitations of Broaching

If the keyway width, spline form, or finished bore changes between revisions, the dedicated broach may need to be replaced rather than simply reprogrammed. The tool is dedicated to a specific profile, and a new feature may require a different broach. For a short production run, the tooling cost can outweigh the machining-time savings.

Part geometry can also limit its use. Internal broaching normally requires a hole large enough for the broach to enter, and the workpiece must be rigid enough to resist the cutting force without distortion. Blind internal features are generally unsuitable for conventional through-broaching, although rotary broaching can produce certain blind polygonal features.

Conventional linear broaching works best when the feature is accessible along the direction of the broach stroke and the surfaces being cut do not interrupt tool travel. Geometry that prevents the broach from passing through the feature may require another process.

For example, a production keyway repeated on thousands of shafts can justify a dedicated broach, while a small batch with several different keyway sizes is often easier to produce by CNC milling.

Broaching isn't the right fit for every project, especially when you're working with prototypes, low volumes, changing designs, or geometries that are easier to produce with CNC machining. JLCCNC provides CNC milling and turning for parts where dedicated broaching tooling is not economical.

Upload your CAD file for an engineering review of the geometry, tolerances, and production requirements.

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What Materials Can Be Broached?

A wide range of metals can be broached, including carbon steels, alloy steels, stainless steels, aluminum alloys, brass, bronze, and cast iron.

Material selection matters because hardness, ductility, machinability, and work-hardening behavior influence cutting forces and tool life.

Material condition matters as much as alloy designation. Heat-treated steels, work-hardening stainless grades, and abrasive cast irons can require different broach geometry, cutting conditions, and tooling materials.

Broaching vs. Milling: Which Process Should You Choose?

Broaching is generally the better choice when the same defined profile must be produced repeatedly, while CNC milling is usually the better choice for prototypes, low-volume production, complex geometries, and designs that may change.

Broaching is optimized for repeatedly producing a defined profile with dedicated tooling, while CNC milling is optimized for flexibility and programmable geometry.

Neither process is universally better though.

The right choice depends on the geometry, quantity, tooling requirements, cycle time, and likelihood of design changes.

Choose broaching when the profile is fixed and repeated production justifies dedicated tooling. Choose CNC milling when flexibility, low-volume production, complex geometry, or frequent design changes matter more.

For a broader overview of milling methods, see the guide to types of milling operations.

FAQs About Broaching

Conclusion: When Is Broaching the Right Choice?

Broaching is most effective when a fixed profile needs to be produced repeatedly and consistently. Because the broach contains the required geometry, the feature can often be completed in a single stroke once the tooling and setup are established.

For production parts with the same keyway, spline, or polygonal profile, broaching can offer faster and more consistent results than milling. When volumes are low or the design is likely to change, CNC milling is usually more practical because the geometry can be changed through the toolpath rather than by replacing dedicated tooling.

The choice therefore depends largely on how stable the design is and how much production volume can justify the broach. A fixed profile in a repeat production run may favor broaching, while a more flexible machining route is often better for prototypes and shorter runs.

JLCCNC provides CNC milling for precision machined parts where dedicated broaching tooling is not the most practical option. The engineering team can review the part geometry and drawing requirements to determine a suitable machining approach.

Upload Your CAD File for Engineering Review & Quote

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