The primary relief angle in end mill geometry is the angle ground behind the cutting edge to reduce friction between the tool and the workpiece. It ensures that only the cutting edge engages with the material, preventing excessive rubbing that could generate heat and wear. A larger primary relief angle decreases contact and cutting forces, improving efficiency but potentially weakening the cutting edge. A smaller relief angle increases edge strength, making it better suited for harder materials. The proper balance of primary relief is crucial for optimizing tool life, surface finish, and cutting performance across different machining applications.
