Rotary broaching, sometimes called wobble broaching, is a machining method used to cut shapes like hexagons, squares, and splines into a workpiece. Unlike traditional push broaching, which requires long strokes and heavy forces, rotary broaching allows for these forms to be machined quickly and with impressive accuracy on CNC lathes, mills, and screw machines.

How Rotary Broaching Works

Rotary broaching uses a specially designed tool holder and broach to cut a form into the material. The broach is held at a slight angle, typically 1 degree, relative to the workpiece centerline. As the tool and workpiece rotate together, the angled broach wobbles in a controlled manner, gradually cutting the desired shape into the material.

This process creates the entire form in a single pass, often in less than 30 seconds, making it much faster than traditional methods.

Common Applications

Rotary broaching is widely used in industries where internal or external shapes are required for fasteners, fittings, or drive components. Some common applications include:

• Hexagon or square drive sockets
• Torx and spline forms
• Internal gear shapes
• External shaft features
• Aerospace and medical device components

It is especially popular for creating internal hex shapes in components such as fasteners, standoffs, and valve stems.

Advantages of Rotary Broaching

There are several reasons why manufacturers choose rotary broaching over other machining methods:

• Speed: Most shapes can be cut in under 30 seconds.
• No Secondary Operation: Forms are completed in a single pass.
• Versatility: Works on lathes, mills, and machining centers.
• Compact Setup: Does not require large or high-tonnage machines.
• Material Flexibility: Works on aluminum, brass, stainless steel, titanium, and more.
• Internal and External Forms: Can cut inside bores or on the outside of shafts.

Rotary Broach Tooling

A rotary broach setup includes two main components:

1. The Broach: A custom-shaped cutting tool that matches the desired profile (hex, square, etc.). It is often made from high-speed steel or carbide.
2. The Holder: A precision tool holder that allows the broach to tilt and rotate while maintaining alignment with the spindle.

Proper alignment, tool sharpness, and material selection are key to achieving the best results. Coolant usage also helps prolong tool life and improve surface finish.

Things to Consider

While rotary broaching is a powerful technique, there are some limitations:

• Depth Limits: Internal forms typically have a practical depth-to-diameter ratio of about 1.5:1.
• Shape Limitations: Complex or asymmetric profiles may not be feasible.
• Tool Wear: Broaches must be sharpened or replaced periodically.
• Material Hardness: Extremely hard materials may be difficult to broach without specialized tooling.

Understanding these limitations helps set realistic expectations for part design and tooling maintenance.

Conclusion

Rotary broaching is an efficient and effective machining process for creating internal and external shapes in a wide range of materials. Its ability to create precise forms in seconds, using standard machine tools, makes it a valuable technique in industries ranging from medical devices to aerospace. With the right setup and tooling, rotary broaching can significantly reduce cycle time and simplify part production.