What is Keyway Broaching? | The Ultimate Guide

Introduction

Keyway broaching is a precise machining process used to create keyways—slots that accommodate keys in mechanical power transmission components like gears, pulleys, and shafts. This technique ensures secure mechanical connections and prevents slippage between components.

At CNC Broach Tools, we specialize in carbide broaching tools that allow machinists to cut keyways, splines, and other custom profiles directly on CNC lathes and mills, eliminating the need for secondary operations. In this guide, we’ll explore how keyway broaching works, the benefits of CNC broaching, and how our industry-leading tooling solutions can improve your manufacturing efficiency.

What is Keyway Broaching?

Keyway broaching involves using a cutting tool (broach) to create a precise, repeatable slot inside a bore or along the surface of a part. Traditional broaching operations require a dedicated broaching machine, but CNC broaching allows machinists to broach keyways directly in a CNC lathe or mill, saving time and improving accuracy.

How CNC Keyway Broaching Works

1. Secure Workpiece & Tool Setup – The broach tool is rigidly mounted in a CNC lathe or mill. Proper clamping and a stop behind the tool prevent movement during cutting.
2. Toolpath Programming – The CNC machine is programmed to move the broach tool in a linear motion, cutting the keyway in multiple passes. CNC Broach Tools offers a free G-code generator to simplify programming.
3. Multiple Passes for Precision – Unlike a single-pass push broach, CNC broaching gradually removes material in small depths per pass, ensuring tight tolerances and improved tool life.
4. Chip Evacuation – Chips are pushed into a relief area to prevent tool damage and improve cutting efficiency. For blind keyways, proper undercuts or cross-holes are required for chip clearance.

Benefits of CNC Keyway Broaching

Eliminate Secondary Operations

Traditionally, keyways were cut using keyway slotters, broaching presses, or EDM, requiring separate setups. CNC broaching allows you to cut keyways in-cycle without moving the part to another machine.

More Cost-Effective Than EDM

EDM (Electrical Discharge Machining) is commonly used for internal keyways but is slow and expensive. CNC broaching is faster and more cost-effective, making it ideal for high-production machining.

High Precision and Repeatability

CNC-controlled tool paths provide consistent slot width, depth, and finish, ensuring parts meet engineering tolerances without the variability of manual setups.

Increased Tool Life with Carbide Inserts

CNC Broach Tools exclusively uses carbide inserts, offering superior wear resistance compared to high-speed steel (HSS) broaches. This results in longer tool life, faster cutting speeds, and reduced downtime.

Can You Broach Blind Keyways?

Yes! Blind hole keyway broaching is possible with CNC machines if the correct relief is in place. Unlike through-hole broaching, where chips exit out the back, blind broaching requires:

A proper relief groove or cross-hole to accommodate chip evacuation
Programming adjustments to ensure the insert passes completely through the material before retracting
Correct feed rates and depth of cut based on material hardness

Check out our Blind Keyway Broaching Guide for best practices: Blind Keyway Broaching

Broaching More Than Just Keyways

While CNC broaching is most commonly used for keyways, our carbide inserts can be custom-ground for:

Splines – Internal and external spline profiles for shafts
Hexagonal & Square Features – Ideal for specialized drive components
Full Radius Forms – Smooth curves and blended transitions
90° & 120° Corners – Clean, sharp internal features
Custom Profiles – We can grind any special shape based on your specifications

Learn more about custom broaching solutions here: Custom Spline Broaching

Choosing the Right CNC Broach Tool

To achieve the best results when CNC broaching keyways, consider:

Bore Diameter & Keyway Width – Ensure the insert width matches the desired keyway size.
Material & Hardness – Different materials require adjusted feed rates and depth of cut.
Tool Clamping Method – Use hydraulic holders or split sleeves for maximum rigidity.
Programmed Feed & Depth – Recommended feed rates vary from 550 IPM in aluminum to 200 IPM in hardened steels.

For more guidance, check out our feed and speed recommendations: Keyway Cutting Speeds & Feeds

Get the Best Keyway Broaching Tools for Your CNC Machine

CNC Broach Tools provides industry-leading carbide broach inserts designed for high-performance, long tool life, and precise machining. Whether you need standard keyway tools or custom spline and form inserts, we can help.

Explore our full selection of CNC broaching tools: CNC Broach Tools

Got questions? Contact us today! (877) 248-1631