Designing Undercuts in CNC Machined Components

In the world of precision CNC machining, designing for manufacturability (DFM) is paramount. One feature that often presents both a challenge and an opportunity is the undercut. An undercut is a recessed feature that is not directly accessible from the primary tool approach directions. While they add significant functional value, they require careful design consideration to ensure they are both machinable and costeffective.


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Undercuts are typically created using specialized tools like Tslot cutters or lollipop (undercut) end mills. These tools have cutting edges on their sides or ends, allowing them to reach beneath overhangs. The primary design rule is to ensure there is sufficient clearance for the tool shank, which is larger than the cutting diameter. Designing an undercut that is too deep or too narrow will make it impossible for a standard tool to reach without collision.

Key design parameters to consider include the internal corner radii, depth, and accessibility. For instance, the depth of a standard undercut should generally not exceed the diameter of the cutting portion of the tool. Furthermore, specifying a slightly larger radius than the tool's cutting radius can prevent stress concentrations and improve part strength. For external undercuts or more complex internal geometries, a multiaxis CNC machine becomes essential. 5axis machining provides the necessary tool angle flexibility to create these features in a single setup, enhancing accuracy and reducing production time.

Strategic use of undercuts can eliminate the need for secondary operations and multipart assemblies. They are invaluable for creating internal Oring grooves, snapfit connections, and threads that run to the edge of a shoulder. A welldesigned undercut simplifies the final product, reduces component count, and enhances reliability.

Partnering with a machining expert early in the design phase is crucial. We can advise on optimal undercut dimensions, suggest alternative designs that are easier to machine, and leverage our advanced multiaxis capabilities to produce complex parts efficiently. By mastering undercut design, you can unlock greater design freedom, create more sophisticated and functional components, and ultimately accelerate your product's time to market with a reliable manufacturing partner.