3+1, 3+2, and Simultaneous 5-Axis Machining
Expanding beyond standard three-axis machining introduces new ways to orient a part or tool relative to one another. The chosen configuration determines both the machine’s complexity and the type of work it can perform.
3+1 Machining
In 3+1 machining, a single rotary axis (typically the a 4th axis) is positioned and locked before each operation. The part is machined with standard three-axis motion while the rotary axis remains stationary. After one face is complete, the rotary axis re-indexes to a new angle. This method provides access to multiple sides of a workpiece in one setup, greatly reducing fixturing time without requiring multi-axis toolpaths.
3+2 Machining
3+2 machining adds a second rotary axis, allowing the workpiece or tool to tilt and rotate into virtually any orientation. Like 3+1, the rotary axes are held fixed during cutting, but their combined positioning enables compound angles and features that cannot be reached from orthogonal faces alone.
Because 3+2 requires the coordinated movement and locking of two rotary elements, the mechanical design is more complex. When implemented on a vertical or horizontal machining center using a tilting table, it often reduces the usable workspace and limits part size. As a result, multi-function machines, those combining turning and milling capabilities in a single lathe-like machine tool, have become increasingly popular for 3+2 work, offering greater travel and rigidity without the envelope constraints of a trunnion-mounted system.
Simultaneous 5-Axis Machining
In simultaneous 5-axis machining, all linear and rotary axes move together in real time under coordinated control. The cutting tool continuously re-orients toward the workpiece surface, producing smooth transitions, complex contours, and optimal cutting angles. This approach offers the highest flexibility and surface finish but demands advanced programming, control, and exceptional structural rigidity.
Simultaneous 5-axis machining places significantly higher demands on the mechanical stiffness of both the machine and its positioners. On a vertical machining center equipped with a trunnion table, 3+1 operations can be performed with relatively simple trunnion assemblies, sometimes using only an outboard brake to maintain stability under heavy cuts. True simultaneous 5-axis motion, however, almost always requires the trunnion or rotary assembly to be fully integrated into the machine casting. This integration provides the rigidity and geometric precision needed for continuous motion.
For more information on trunnion design, braking systems, and integration strategies, see the section on Trunnion Tables.
Choosing the Right Configuration
3+1 and 3+2 machining are ideal for prismatic parts requiring multiple orthogonal or angled features but not continuous tool-path blending. Simultaneous 5-axis machining is reserved for complex free-form surfaces or applications requiring uninterrupted multi-axis motion. In each case, the addition of rotary motion, whether by trunnion table, rotary indexer, or integrated 5-axis spindle, extends the capability of traditional machining centers for greater accuracy, flexibility, and throughput.