Common 4-axis configurations
| Configuration | Rotary axis | Typical work |
|---|---|---|
| VMC with rotary table on the left/right | A (about X) | Shafts, multi-face parts, engraving |
| HMC with B-axis pallet | B (about Y) | Tombstones, housings, multi-part fixtures |
| Router with rotary attachment | A (about X) | Wood turning, cylindrical engraving |
Indexing vs continuous motion
- Indexing: rotate, clamp, cut in 3-axis, unclamp. Fast and rigid.
- Continuous: rotary moves with linear axes for cams, helical grooves, wrapped features.
Rotary feedrates
When the rotary axis moves with linear axes, the controller needs a feed it can interpret correctly. Options include inverse time (G93), degrees-per-minute calculation, or controller-specific modes. Wrong handling gives very slow or very fast actual cutting speeds.
G93
G01 X20. A45. F12.5 (complete move in 1/12.5 min)
G01 X25. A90. F10.0
G94Wrap-around and direction
The post decides whether A moves the short way, a fixed direction, or uses controller rollover, and keeps A values within safe ranges between operations.
Tombstone and multi-part work
On 4-axis HMCs, posts often output multiple work offsets per face and order operations to minimise indexing and tool changes.
4-axis posts are about control of one extra axis, and doing it without wasted motion.
4-axis post development
See our CNC post processor development service and inverse time feed explained.