3 axis machining implies that the work piece remains in the same position while the cutting tool operates along the XYZ plane to trim away material. 3 axis machining is most commonly used to produce mechanical components and is best suited for:
Automatic/interactive operation
Milling slots
Drilling holes
Cutting sharp edges
4 axis machining implies that a work piece is processed in the same way it would be with a 3 axis machine, but has an additional rotary movement around the X axis, which is named the A axis. 4 axis machining is multifunctional and can be used for:
Intermittent cutting
Continuous cutting
Engraving curved surfaces
5 axis machining implies that a work piece can be automatically manipulated from five sides at one time. In addition to automatic movements along the X, Y, and Z axes, 5 axis CNC machines can select two of the three rotational axes (A,B,C) to use. 5 axis machining is beneficial when components require a great deal of intricacy and quick precision. This includes:
Feature accuracy
Increased productivity
Higher quality finishes
Cutting intricate details
Machining complex shapes