Types of rotary limits
| Axis type | Example limit | Challenge |
|---|---|---|
| Tilt axis (A or B) | -120° to +30° | Some orientations only reachable with one solution |
| Limited rotary (C) | -360° to +360° | Long spiral toolpaths run out of travel |
| Continuous rotary (C) | Unlimited, with rollover | Shortest-path direction and position display |
Preventing limit problems
- Choose the starting solution that gives the most travel for the whole operation.
- Look ahead through the operation before committing to a solution.
- Prefer tilt directions that keep the part accessible.
Retract, rewind, re-engage
When a limit cannot be avoided, the post inserts a controlled sequence:
(Limit reached on C at +355 deg)
G01 Z.. F.. (retract along tool axis at feed or rapid)
G00 Z.. (move to safe height)
G00 C-5. (rewind C by 360 deg)
G00 X.. Y.. (reposition)
G01 Z.. F.. (re-engage at plunge feed)
(continue toolpath)The retract distance, re-engage feed and whether coolant stays on are all configurable in a well-designed post.
Rollover and continuous axes
With rollover enabled, the controller displays C between 0 and 360° and takes the shortest path. The post must know whether rollover is active; otherwise, it may command a 350° move when 10° was intended.
Between operations
Posts often "unwind" continuous axes to within 0–360° between operations, so the next operation starts from a known position and doesn't wind cables unnecessarily.
The best rewind is the one you avoid by choosing the right solution at the start.
5-axis limit handling
See our CNC post processor development service and rotary axis kinematics.