Designing Internal Radii for CNC Milling

Core Principle

CNC milling uses round cutting tools and therefore cannot create perfect 90-degree internal corners. All internal corners must have a radius, the size of which directly impacts cost.

Cost vs. Radius Guidelines

• Optimal Radius: R ≥ 1/2 the pocket depth
• For 10mm deep pocket: 5mm radius or larger is ideal
• Standard economical radii: 3mm or 6mm
• Radii under 1mm dramatically increase cost

Design Recommendations

• Standardize all internal radii to a single, large value
• Use largest possible radius for cost savings
• If sharp corner required, design corner relief or "dogbone" feature