Troubleshooting guide › Cutting problems › Plasma cutting problems
Air plasma cutting has only four variables: current, speed, torch height and the air. The consumables wear in a predictable way and tell you what went wrong. Most bad cuts come from speed and height, most short consumable life comes from wet air and bad piercing, and most “the machine will not cut” calls are an air supply or a worn electrode. This page covers hand torches and machine torches on inverter air plasma cutters from 40 A to 200 A.
Reviewed by the Cruxweld technical team, October 2026. Settings are starting points to confirm on a test piece; acceptance is decided by the code or drawing the job is built to. Checks marked “call” are for our technical team.
| What you see | What it means | Change |
|---|---|---|
| Fine, easily removed dross on the bottom edge; smooth face; drag lines slightly trailing | Correct | Nothing |
| Heavy, bubbly, globular dross on the bottom edge that chips or flakes off easily; wide kerf; top edge rounded | Low-speed dross: speed too low or current too high for the thickness | Speed up; or lower the current |
| Thin, hard, linear dross welded to the bottom edge that needs grinding to remove; drag lines curve strongly backwards; corners not cut through | High-speed dross: speed too high | Slow down, or raise current, or reduce torch height slightly |
| Spatter and dross on the top surface | Torch too high, or nozzle worn | Lower the torch to 3-5 mm (hand) or the set cut height (CNC); check the nozzle |
| Edge bevelled on one side of the cut, square on the other | Normal plasma swirl: one side is always slightly better. Cut so the good side is on the part (clockwise on outside contours for most torches) | Choose the cut direction; measure both edges |
| Both edges bevelled, kerf V-shaped | Torch too high, worn nozzle or electrode, or current too low for the thickness | Lower the torch; replace consumables as a pair; raise current |
| Edge concave or wavy, kerf wide | Nozzle orifice enlarged or oval, or double arcing | Replace the nozzle; check the shield cup and stand-off |
| Cut does not go through; arc blows back up | Speed too high, current too low, plate too thick for the current, worn electrode | Slow down; raise current; check the thickness limit; replace consumables |
| Edge rough with gouges, intermittent | Wet or oily air; air pressure fluctuating; worn swirl ring | Drain the filter, fit a dryer; check the compressor; replace the swirl ring |
| Hole in a nut-plate not round, lead-in gouge | Pierce height wrong; arc trailing on small holes; no lead-in | Pierce at 1.5-2 times cut height; slow down on holes; use a lead-in |
The machine will not fire the pilot arc without the set air pressure. Compressor too small, hose too long or too thin, water in the filter, regulator set low.
The pilot arc jumps inside the torch and does not transfer.
The arc pilots but cannot transfer to the plate.
Pilot arc cannot reach the plate.
Air flow too small so pressure drops, or poor work cable contact.
Duty cycle exceeded; mains sagging on a long thin cable.
Trigger switch, torch lead, or the safety interlock (shield cup not fitted or not fully tightened).
Spark gap dirty, torch consumables wet from a humid night, or the machine is on a supply with a missing phase.
Double arcing is a second arc from the nozzle to the plate (instead of only from the electrode through the nozzle). It eats the nozzle orifice in seconds and gives a wide, ragged kerf.
Consumable life has no fixed figure: it depends on the number of arc starts (each pilot start costs more than a metre of cutting), arc hours, current, how the pierces are done and how dry the air is. Learn the usual life on your own jobs and treat a sudden drop as a fault signal. Inspect every hour on production work. Replace the electrode when the hafnium insert is pitted more than about 1.5 mm deep, and the nozzle when the orifice is enlarged, oval or has a build-up; replace both together. The signs that it is time: speed drops, kerf widens, bevel grows, the arc is hard to start.
| Wear pattern | Cause |
|---|---|
| Electrode pit deep and central, nozzle fine | Normal wear; too many starts (each pilot start costs more than a metre of cutting) |
| Electrode pit off-centre | Swirl ring damaged or wrong; air flow wrong |
| Nozzle orifice oval, gouged on one side | Double arcing; piercing too low; dragging |
| Nozzle and electrode black and wet | Water or oil in the air |
| Shield cup burnt | Stand-off too low; spatter not cleaned off |
| Everything worn fast, cut poor from the start | Non-genuine consumables that do not match the torch; current too high for the parts |
| Thickness | Current | Speed (hand or machine) | Note |
|---|---|---|---|
| 1-2 mm | 20-40 A | 3000-5000 mm/min | Drag cut at low current for sheet |
| 3 mm | 40-60 A | 2500-3500 mm/min | |
| 6 mm | 60-80 A | 1500-2200 mm/min | |
| 10 mm | 100-120 A | 900-1300 mm/min | |
| 16 mm | 130-160 A | 600-900 mm/min | |
| 20 mm | 160 A | 450-650 mm/min | |
| 25 mm | 160 A | 300-450 mm/min | Quality cut limit for 160 A |
| 32 mm | 160 A | 200-300 mm/min | Edge start recommended |
| 45 mm | 160 A | 100-150 mm/min | Edge start only |
Starting values at 3-5 mm stand-off. Stainless: reduce speed about 20 %. Aluminium: raise current one step and expect more dross. Each machine has its own quality-cut and severance limits; stay inside the quality-cut figure for parts that matter.
Wet air, piercing too low, and too many pilot starts, in that order. Fit a dryer, raise the pierce height, and avoid starting the arc in the air.
Yes. The edge on stainless is darker and slightly rougher, aluminium gives more dross and the edge may need dressing. Nitrogen gives a cleaner stainless edge but is not needed for general fabrication.
Two figures: the quality-cut thickness, where the edge needs no dressing, and the severance thickness, where it just gets through. Buy for the quality-cut figure of the plate you cut most, and let the severance figure cover the occasional thick job.
Almost always torch height: the CNC holds a height set once, while the hand follows the plate. Set the cut height correctly, use the arc-voltage height control, and square the torch to the table after any collision. See the CNC cutting page.
Lamps, fault codes and the checks an operator can do outside the cabinet, for the machines this page applies to.
Cut quality on plasma is mainly the consumables and the operator. The machine decides the thickness you can cut cleanly (as a rule, about 1 mm per 6-7 A for a quality cut on mild steel), the duty cycle on long cuts, and whether it can be driven by a CNC (arc transfer signal, arc voltage output for height control, pilot arc control). An inverter with pre-flow, up-slope and down-slope settings extends consumable life noticeably.
Send a photo of the weld or cut, your machine model, consumable and plate thickness. Our technical team replies on WhatsApp with the likely causes and the next checks to make.
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