In metalworking, ultra-light cuts push the process out of stable cutting and into a messy regime of friction, elastic deformation, and vibration. When the uncut chip thickness drops below a critical value (often on the order of the tool’s edge radius), the material no longer shears cleanly. Instead of forming a chip, the tool begins to plow and rub the surface. At this scale, the cutting edge isn’t sharp relative to the material—it behaves like a rounded wedge. The metal elastically deflects ahead of the tool, springs back after the pass, and resists being separated. Cutting forces become inconsistent, dominated by friction rather than shear, which dramatically increases tool wear and heat while producing poor surface finish. This is why you often see chatter, squealing, work hardening, and dimensional inaccuracy on tiny finishing passes. Add in machine compliance, backlash, and micro-vibrations, and that “easy” last cut suddenly becomes the hardest one to control. Paradoxically, inc...