A 3-axis mill moves the tool in X, Y and Z. 5-axis adds two rotary axes so the tool or part can tilt and rotate while cutting. The extra motion changes what geometry you can reach and how well you can cut it.
3-Axis
Simple, affordable, and plenty for flat and prismatic parts. Complex parts need re-fixturing to reach multiple faces, which adds setups and stack-up error.
5-Axis
Reaches five faces in one setup and keeps the cutter at the ideal angle to contoured surfaces — impellers, blades, molds, aerospace. Also allows shorter, more rigid tools and better finish. '3+2' orients a face then locks; full simultaneous 5-axis moves all five at once for true contouring. Costs more and needs more skill/CAM.
Bottom line
3-axis for straightforward parts and budget; 5-axis for complex geometry, fewer setups and better accuracy on contoured work. '3+2' is the practical middle ground many shops start with.
