Designing Undercuts and Other Challenging Features for CNC

CNC machining is renowned for its precision and versatility in creating complex parts from a block of solid material. However, certain geometries, like undercuts and other challenging features, push the boundaries of standard machining practices. Mastering their design is crucial for creating innovative, highperformance components while maintaining manufacturing efficiency and costeffectiveness.


cnc machining center
An undercut is a recessed feature that is not accessible from the main tool approach direction. Standard vertical tools cannot machine them, necessitating specialized equipment and strategies.

Key Types and Solutions:

1. Side Undercuts (Dovetails & Tslots): These require specialized cutters like Tslot or dovetail mills. The key is designing with the standard tool dimensions in mind, ensuring the neck width and depth are achievable with commercially available tools to avoid prohibitive custom tooling costs.

2. Internal Undercuts: For features like internal Oring grooves, the primary challenge is tool reach and deflection. Using a tool with a long, slender shank is common, but this can cause vibration and inaccuracies. Designers should specify the largest possible corner radius and minimize the depth of the undercut to enhance tool rigidity and surface finish.

cnc machining online

Design for Manufacturing (DFM) Guidelines for Challenging Features:

Avoid Unnecessary Undercuts: First, question if the undercut is essential. Often, a design modification can eliminate the need for one, drastically simplifying production.


Optimize Dimensions: Design undercuts to be machined with standard tool sizes. Provide clear, generous tolerances where possible.
Consider Alternative Methods: For complex internal undercuts or true 90degree internal corners, discuss with your manufacturing partner if EDM (Electrical Discharge Machining) might be a more economical solution, potentially as a secondary operation.
Access is Key: Ensure the tool has a clear, straight path to the undercut location. Obstructions can make a feature unmachinable.

Successfully integrating these features requires a collaborative partnership with your CNC provider. At our onestop CNC machining service, we combine expert DFM analysis with advanced machining capabilities, including a vast library of specialized tooling. We guide you through the intricacies of designing undercuts, deep cavities, and thin walls, transforming challenging designs into manufacturable, highquality reality. By designing smartly with manufacturing in mind, you can unlock greater part functionality without compromising on lead time or budget, driving your product's success and your company's growth.