What is Keyway Broaching?

Keyway broaching is a machining process used to cut a slot, called a keyway, inside a bore. A keyway is a groove that allows a key to fit between a shaft and a mating part such as a gear, pulley, or coupling. This slot-and-key connection locks components together, transmitting torque and maintaining alignment in mechanical systems.

How keyway broaching works

The process is performed with a broach tool that has a series of cutting teeth, each slightly larger than the last. As the broach is pushed or pulled across the bore, the teeth gradually remove material until the full depth and width of the keyway is achieved. Traditionally, this operation required a dedicated broaching machine or manual slotting tools, but today it can be done directly inside CNC mills and lathes using specialized tooling.

By integrating broaching into a CNC machine, machinists eliminate the need for secondary setups and outsourcing. The tool is held securely in the machine spindle or turret, and the CNC program controls the motion with precision. This makes it possible to cut accurate, repeatable keyways quickly, even in shops without traditional broaching equipment.

Carbide broaching tools for CNC machines

CNC Broach Tools uses carbide broaching inserts designed specifically for high-performance CNC applications. Rather than a series of teeth, CNC Broach Tools are programmed for multiple passes. Carbide is harder and more wear-resistant than high-speed steel, which allows it to maintain sharp cutting edges for longer tool life, even in tough materials like stainless steel, titanium, or Inconel. By using carbide tooling, machinists benefit from greater durability, reduced insert changes, and more consistent results across production runs.

These inserts, combined with rigid tool holders and proven programming strategies, give CNC machines the ability to produce clean and accurate keyways without the limitations of older broaching methods.

Blind keyway broaching

Not all bores go completely through a part. When a keyway must be cut in a blind hole, special clearance is required so the broach insert has space to exit. This is typically achieved by adding a relief groove, milling a slot with a Woodruff cutter, or drilling a cross hole that intersects the bore. Without this clearance, the tool has no place to retract, which can cause insert damage or poor-quality cuts.

By incorporating a proper relief, machinists can successfully broach blind keyways inside CNC machines with the same accuracy and reliability as standard through keyways. This capability expands the range of parts that can be produced in-house while maintaining efficiency and precision.

Have questions about keyway broaching or need help choosing the right tooling? Contact us today for expert support and guidance.