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How modern CNC lathes can produce internal keyways and splines without dedicated broaching equipment
Many machine shops assume that producing internal keyways and splines requires a dedicated broaching machine, slotter, or secondary operation. While those methods are still used in some applications, modern CNC lathes are capable of performing many broaching operations directly in the machine.
A CNC lathe can perform internal broaching in the same setup used for turning. With the proper tooling, setup, and programming, shops can produce internal features without moving the part to a secondary machine.
Why Shops Are Bringing Broaching In-House
Traditional broaching often requires additional equipment, additional floor space, and additional handling. Parts may need to be removed from the lathe, transferred to another machine, and re-indicated before the broaching operation can begin.
Each of these steps adds time and introduces opportunities for error.
By broaching directly on the lathe, shops can machine the bore and cut the keyway or spline without moving the part. This reduces handling, simplifies scheduling, and helps maintain alignment between features.
For many applications, eliminating the secondary operation is one of the biggest advantages of CNC broaching.
How CNC Lathe Broaching Works
Unlike traditional broaches that use a series of progressively larger cutting teeth, CNC broaching uses a single insert mounted in a rigid holder.
The spindle remains stationary while the machine uses linear axis movement to drive the insert through the material. Each stroke removes a small amount of material until the final profile is achieved.
Because the process is controlled by the CNC program and machine axes, the same machine used for turning can also produce:
- Internal keyways
- Internal splines
- Custom internal forms
The result is a flexible process that can be integrated into existing machining operations.
The Importance of Toolholding and Alignment
A successful broaching setup begins with rigidity.
For lathe applications, CNC Broach Tools commonly recommends split sleeves because they provide strong support and allow accurate alignment of the broaching tool. Rigid support is especially important because broaching forces are applied through the tool as it moves linearly through the cut.
Centerline alignment should be maintained within 0.0005 inches whenever possible. Poor alignment can affect insert life, feature geometry, and overall process consistency.
Keeping tool overhang to a minimum also helps maintain stability throughout the operation.
Programming Considerations
Broaching programs are different from standard turning operations. Instead of continuous material removal, the insert advances through a series of controlled strokes.
Pass depths are typically programmed in small increments to maintain predictable cutting loads. Entry and exit clearance should also be included to allow the insert to engage and disengage the cut properly.
The insert should fully clear the feature before retracting. Maintaining straight-line loading throughout the stroke helps improve tool life and reduce unnecessary wear.
As with any machining operation, consistency in the program contributes directly to consistency in the finished part.
Expanding the Capability of Existing Equipment
One of the biggest advantages of CNC broaching is that it allows shops to add capability without adding another machine.
A properly equipped CNC lathe can perform operations that once required dedicated broaching equipment, helping reduce setup time, floor space requirements, and part handling.
For shops looking to produce keyways, splines, and other internal forms more efficiently, CNC broaching offers a practical way to expand capability using equipment already on the shop floor.
