Learn/GcodePilot/Automation & safety
Arc Voltage THC (AVTHC)
Updated v2.3.4At a glance
- FluidNC plasma fork holds cut height by arc voltage — sampled, compared to target, Z nudged in firmware
- Live arc volts, arc-OK, and correcting state on the DRO; setpoint from the post via M103 Q
- Operator override: bump target volts from the pendant or run g-code controlled
- Armed/disarmed mid-program with M101/M102 — off during the probe, on after the pierce
- Arc-OK override: click (or hotkey) to confirm the arc and keep cutting when the sensor misses it
On the FluidNC plasma fork, torch height control runs in the firmware: it samples arc voltage, compares
it to a target, and nudges Z to hold standoff — no host round-trip in the loop. GcodePilot configures it
from the machine profile (the Torch Height Control node, plasma machines only), the post sets each
cut's target with M103 Q<volts>, and M101/M102 arm and disarm the loop mid-program — off through
the probe, on once the pierce is done and the torch is at cut height.
Reading the DRO
With AVTHC enabled the DRO gains an ARC row: the label is gray when the loop is off and orange when armed; the voltage readout is green while holding within tolerance, red while the loop is actively chasing the surface, and orange when armed but no arc has established yet. The arc-OK dot lights green when the arc has transferred — and it's clickable: if the arc is visibly cutting but a flaky or unwired sensor never asserts, a momentary click satisfies the pierce's arc-OK wait so the cut proceeds.
Operator override
The AVTHC pill on the bottom bar works in target volts and is safe to touch mid-cut — every action is
a realtime byte that never disturbs the running program. −/+ nudge the target 1 V (bindable hotkeys,
default − and =); clicking the value swaps in an inline input for an exact target. Gcode
Controlled hands the setpoint back to the program's M103, and Disable forces THC off for the rest
of the run. A separate Manual Comp toggle lets the Z jog keys hand-comp height mid-cut — pressing one
switches AVTHC to Disabled and drives Z directly; bring the loop back with +/− or a voltage entry.
Tuning without re-posting
Right-click a cut in the toolpath view → Change AVTHC… to retarget or disable THC for one segment, one cut, or the whole program — useful for skipping a lead-in ramp or dialing volts on the next pass. See Run From Here & Cut Tuning.