4-axis CNC milling integrates a precision rotary table (A-axis or B-axis) into a standard 3-axis platform, allowing continuous cylindrical machining and multi-angle indexing in a single setup.
4-axis machining features linear X, Y, Z motion plus rotational motion around the X-axis (A-axis) or Y-axis (B-axis).
Operating Modes
Positional 4th-Axis (Indexing / Tombstone): The rotary table rotates the workpiece to a specific angle (e.g. 0, 90, 180, 270 degrees) and clamps rigidly for 3-axis milling on each face.
Continuous 4-Axis Simultaneous Contouring: All four axes move in synchronized interpolation to machine complex continuous helical grooves, cylindrical cams, and turbine augers.
Toolpath Programming Considerations
CAM systems output inverse time feed rate mode (G93) during continuous 4-axis rotation to maintain constant surface chip load across varying part radii.
Frequently Asked Questions
What is the difference between 4-axis indexing and continuous 4-axis?
Indexing locks the rotary axis at fixed angles before cutting; continuous rotates the table dynamically while the cutting tool is in full cut.
Why is a tailstock used in 4-axis setups?
A tailstock or pneumatic trunnion outboard support supports the free end of long parts, eliminating deflection and chatter.
