How a 4th Axis Works in Multi-Axis Milling?
A 4th axis introduces rotation around a horizontal centerline. In a typical vertical machining center this is rotation around the X axis. The rotary axis can position the workpiece at a programmed angle and lock for machining, or it can rotate continuously for more advanced toolpaths. The rotary drive, bearings, brake, and encoder work together to deliver precise angular positioning.
In multi-axis milling the 4th axis is used in three distinct ways.
3+1 Machining
The rotary axis positions the part, locks, and stays fixed during machining. The machine uses standard three-axis linear motion to cut the part. The rotary axis provides access to different faces while maintaining strong clamping and rigidity. (Need illustrative image)
3+2 Machining
The 4th axis works together with a second rotary axis to tilt the part into compound angles. Both axes position, then lock, and standard three-axis cutting occurs. This allows angled holes, multi-plane surfaces, and better tool approach without requiring continuous five-axis motion. (Need illustrative image)
Simultaneous Five-Axis Milling
The 4th axis rotates in real time under CNC control and coordinates with a second rotary axis. All axes move together as the tool follows complex three-dimensional surfaces. This requires the highest level of stiffness, feedback resolution, braking power, and machine integration.
In all three cases the performance of the 4th axis determines the accuracy and efficiency of the machining system.