A three-axis mill can only ever see a part from one direction. Add two rotary axes and the cutter can approach from almost any vector in the hemisphere above the work. That does not simply add access. It changes the geometry of the cut itself. Five-axis work splits into two regimes: - 3+2, or indexed: the rotaries position, clamp, and the cut proceeds as ordinary three-axis motion. Rigid, easy to post-process, and responsible for most five-axis parts made today. - Simultaneous: all five axes interpolate at once. Necessary for impeller flanks, turbine aerofoils, and any surface where the tool vector must sweep continuously. The real prize is tool engagement. A ball nose cutter has zero surface speed at its exact centre. Hold the axis normal to the surface and that dead centre rubs rather than shears, burnishing the material and cooking the edge. Tilt ten to fifteen degrees of lead and contact shifts onto the flank, where effective diameter is genuine. Finish improves, tool life frequ...