Sharp internal corners may look clean on a CAD model, but they create significant challenges once tooling enters the picture. Unlike external corners, internal corners often require Electrical Discharge Machining (EDM) or specialized tooling to achieve precise geometry. These additional operations increase machining time, tooling cost, lead time, and long-term maintenance requirements.
Beyond manufacturing cost, sharp corners also create mechanical disadvantages. They concentrate stress, making both the production tooling and the finished component more susceptible to cracking, fatigue, and premature wear. Adding even a small internal radius helps distribute loads more evenly while simultaneously simplifying machining operations.
Toolmakers consistently recommend generous internal radii whenever functional requirements allow. Larger radii enable standard cutting tools to reach features more efficiently, reducing dependence on EDM and shortening machining cycles. They also improve cutter life, simplify polishing, and produce more durable tooling capable of supporting higher production volumes.
Design for Manufacturing is often about small decisions that generate large downstream savings. Replacing unnecessary sharp internal corners with appropriate radii reduces tooling costs, improves structural performance, shortens manufacturing lead times, and extends tool life. A simple geometry change during design can eliminate thousands of dollars in manufacturing expense while producing a stronger, more reliable part.