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By the Arclight Dynamics team · Updated November 3, 2026 · 8 min read
Quick Answer: What Causes Bad Plasma Cuts?
Almost every bad plasma cut comes down to one of seven causes: worn consumables, wrong torch height, wrong cut speed or amperage, wet, oily or low-pressure air, a bad pierce, a poor ground or loose torch, and the material itself (rust, scale, warp or a dirty slat bed). The edge tells you which one: low-speed dross, top spatter, bevel, a wandering arc or a missed pierce each point to a short list of causes. Check the quick things first (consumables, air and ground) before you touch the cut chart. If you run an Arclight table and you’re still stuck, call support. It’s included for the life of the table.
In This Guide
How Do You Diagnose a Bad Plasma Cut From the Symptom?
A bad plasma cut tells you what went wrong. Find the symptom you’re seeing, then work the likely causes in order. The first one listed is the most common and the quickest to check.
| What you see | Most likely causes (check in this order) | Go to |
|---|---|---|
| Heavy, bubbly dross on the bottom edge that knocks off easily | Cutting too slow · torch too high · worn nozzle | Causes 3, 2, 1 |
| Small, hard dross bead that needs a grinder, often with bevel | Cutting too fast · amperage too low for the thickness | Cause 3 |
| Beveled or angled edge | Worn or damaged nozzle · torch height wrong · torch not square to the plate | Causes 1, 2, 6 |
| Rounded top edge or top spatter | Torch too low or diving · worn shield · speed too fast | Causes 2, 1, 3 |
| Wavy or wandering cut line | Worn electrode · moisture in the air · loose torch mount or gantry | Causes 1, 4, 6 |
| Arc won’t transfer, sputters or goes out mid-cut | Poor ground · low air pressure · consumables at end of life | Causes 6, 4, 1 |
| Pierce doesn’t go through, or blows back | Pierce delay or pierce height wrong · plate over the system’s pierce rating | Cause 5 |
| Cut quality changes across the sheet | Warped or dirty plate · slag on the slats · torch height control not tracking | Causes 7, 2 |
| Parts out of dimension or holes out of round | Kerf compensation wrong · speed through corners · mechanical slop | Causes 3, 6 and the software note below |
This page is for diagnosing bad cuts. For the habits that keep them from happening in the first place, see our CNC plasma cutting tips. Shopping for a table? Start with our complete buyer’s guide or compare Arclight CNC plasma tables.
Cause 1: Are Worn Plasma Consumables Causing Bad Cuts?
What it looks like: cuts that were fine last week and have slowly gotten worse. More bevel, more dross, a wider kerf, a cut line that starts to wander, or arc starts that take a second try.
Why it happens: the nozzle shapes the arc and the electrode carries it. As the nozzle orifice wears out of round and the electrode’s emitter pits, the arc loses its focus. Every pierce, every arc start and any moisture in the air speeds that up.
The fix: pull the consumables and look. If the orifice is out of round or the electrode is pitted, replace the nozzle and electrode as a pair, and check the shield and swirl ring while you’re in there. Match consumables to the amperage you run: a 45-amp nozzle won’t last on an 85-amp process. Keep a spare set at the table so a change is a two-minute job, not an excuse to keep cutting on worn parts.
Prevent it: inspect at every shift change and replace at the first sign of wear, not on a schedule. Arclight stocks Hypertherm® consumables and ships in-stock parts the same day.
Cause 2: Is the Torch Height Wrong on Your Plasma Table?
What it looks like: too high gives you bevel and heavy dross. Too low gives you a rounded top edge, top spatter and short consumable life, and at worst the torch drags or dives into the plate.
Why it happens: torch height control reads arc voltage to hold the torch at the right standoff. If the arc voltage setting doesn’t match your consumables and thickness, or the initial pierce height is off, the system holds the wrong height perfectly. Height control can also get fooled when it crosses a cut it already made or runs off the edge of the plate.
The fix: start from the cut chart for your system, amperage and thickness, and confirm the arc voltage and pierce height in the control software match it. Then watch a cut. The torch should ride steady over the plate, not hunt up and down. Every Arclight table ships with Advanced Digital Torch Height Control as standard, and tables running FlashCut CNC add kerf-crossing detection so the torch doesn’t dive over previous cuts.
Cause 3: Is Your Plasma Cut Speed or Amperage Wrong?
What it looks like: too slow leaves heavy, bubbly low-speed dross and a wide kerf. Too fast leaves a small, hard high-speed dross bead, bevel, and corners that don’t cut all the way through. Amperage too low for the thickness looks like cutting too fast, no matter how slow you go.
Why it happens: every material and thickness has a speed window at each amperage. Run a cut chart for the wrong consumables, a different material, or a thickness your system isn’t rated for, and you’re outside that window.
The fix: start from the cut chart, make a test cut on scrap, and adjust speed in small steps. Watch the arc as it leaves the bottom of the plate. A slight trailing angle is right. If no speed works at a given thickness, the cutter is undersized for that plate. Our guide to matching the plasma cutter to the table shows which system pierces what.
Corners and small holes: the torch has to slow down through tight corners and small holes. Lead-ins, hole settings and speed adjustments in your CAM software keep that change from showing up as dross or an out-of-round hole.
Cause 4: Is Wet or Dirty Air Ruining Your Plasma Cuts?
What it looks like: rough edges, a sputtering or wandering arc, and consumables that suddenly last a fraction as long, often right when the weather turns humid. A pop or hiss from the torch, or moisture you can see in the air line, gives it away.
Why it happens: water and oil in compressed air destabilize the arc and attack the electrode. Low pressure or flow starves the arc, especially on long cuts or at higher amperage, when the compressor can’t keep up.
The fix: drain the compressor tank and filters, then add or service filtration and an air dryer. Set pressure to your plasma cutter’s spec at the torch, not only at the tank, and check hoses and fittings for leaks. If the compressor runs flat out during a long cut, it’s undersized for the cutter. Arclight quotes compressors, filtration and dryers sized to your plasma system, and our air compressor sizing guide covers CFM, tank size and drying.
Cause 5: Why Is My Plasma Table Missing or Blowing Out Pierces?
What it looks like: the torch fires but starts moving before it gets through the plate, leaving a gouge instead of a cut. Or molten metal blows back onto the shield, or every part in the nest starts with an ugly crater.
Why it happens: the pierce delay (how long the torch waits before moving) is too short for the thickness, the pierce height is too low so spatter hits the torch, or the plate is thicker than the system’s rated pierce capacity.
The fix: set pierce height and pierce delay from the cut chart. Use proper lead-ins to keep pierce points off the finished edge; your CAM software handles this. If the plate is past the system’s pierce rating, start the cut from the plate edge or step up to a larger plasma system. Our thickness guide lists pierce and cut capacity by system. Sizing a new table? Get a quote built around the plate you cut.
Cause 6: Can a Bad Ground or Loose Torch Cause Bad Plasma Cuts?
What it looks like: arcs that won’t transfer, go out mid-cut, or behave differently from one side of the table to the other. Bevel on one side of a part but not the other. Wavy lines or out-of-round holes that settings don’t fix.
Why it happens: the plasma circuit runs through the work clamp. A corroded, loose or painted-over ground makes the arc inconsistent. On the mechanical side, a torch that isn’t square to the plate cuts a bevel on one side, and any slop in the torch mount, gantry or drive shows up directly in the part.
The fix: clean the work clamp and the surface it bites, and make sure it connects solidly to the table or the plate. Check that the torch is square to the plate and tight in its mount. Keep rails and bearings clean and stay on top of routine maintenance. Arclight sells maintenance kits for Arclight tables.
Cause 7: Is the Material or Table Setup Causing Bad Plasma Cuts?
What it looks like: cuts that are clean on one sheet and rough on the next, or clean in one area of the table and poor in another. Parts that tip up and catch the torch.
Why it happens: heavy rust, mill scale, paint and oil interfere with the arc and the ground. On aggressive settings, warped sheet changes torch height faster than height control can follow. Slag built up on the slats lifts the plate unevenly and grounds it poorly, and small parts that drop or tip as they’re cut can strike the torch.
The fix: clean heavy rust and scale off the cut area, keep the slats and water pan clear of slag, and support the plate flat. Use micro-joints or tabs on small parts so they stay put until the nest is done. When a part does tip, collision detection and a breakaway torch mount protect the torch. Both are standard on every Arclight table.
Don't forget the drawing and the software
When parts come off the table out of dimension, the problem is often in the software, not the cut. Check kerf compensation, lead-ins and lead-outs, and the original drawing for open contours or duplicate lines. Our guide to CNC plasma table software covers the CAD-to-cut workflow.
When Should You Call Arclight Support About Bad Plasma Cuts?
Work the quick checks first: fresh consumables, clean dry air at the right pressure, a solid ground, and the cut chart for your exact consumables and thickness. If the cut is still bad after that, call. You talk to someone who knows your table, and they can go through your settings with you and tell you whether it’s a process problem or a hardware problem.
Have this ready when you call: the plasma system and amperage, the material and thickness, the consumables in the torch, a photo of the cut edge (top and bottom), and the cut settings you’re running. Arclight’s tech support covers process, software and hardware for the life of the table, and it follows the table to the next owner. In-stock parts ship the same day, and the support video library walks through the common fixes.
Bad Plasma Cuts: Frequently Asked Questions
What causes bad plasma cuts?
Seven things cause almost all bad plasma cuts: worn consumables, wrong torch height, wrong cut speed or amperage, wet or low-pressure air, bad pierce settings, a poor ground or loose torch, and the material itself, such as rust, scale or warped sheet.
Why is my plasma cutter leaving so much dross?
Heavy, bubbly dross that knocks off easily means you’re cutting too slow or the torch is too high. A small, hard bead that needs a grinder means you’re cutting too fast or the amperage is too low. Worn consumables make either one worse.
Why are my plasma cut edges beveled?
Bevel usually comes from a worn nozzle, the wrong torch height, or a torch that isn’t square to the plate. Bevel on only one side of a part points to torch squareness or cut direction.
Why does my plasma arc keep going out?
An arc that won’t transfer or goes out mid-cut is most often a poor ground, low air pressure or flow, or consumables at the end of their life. Clean the work clamp connection and check air pressure at the torch first.
How do I know when to change plasma consumables?
Change the nozzle and electrode when cut quality drops, the nozzle orifice is out of round, or the electrode is pitted. Inspect them at every shift change instead of replacing them on a fixed schedule.
Can moisture in the air line cause bad plasma cuts?
Yes. Water and oil in compressed air destabilize the arc, roughen the edge and cut consumable life sharply. Drain the tank and filters, and run an air dryer and filtration sized to your plasma system.
Keep Researching
- Choosing a CNC Plasma Table: The Complete Buyer’s Guide: sizes, thickness, controllers, air and power in one reference
- CNC Plasma Cutting Tips: How to Get the Best Cut Quality: ten habits that prevent bad cuts
- What Can a CNC Plasma Table Cut?: pierce and cut capacity by material and system
- What Plasma Cutter Do You Need for a CNC Table?: match amperage to the plate you cut
- What Size Air Compressor Does a CNC Plasma Table Need?: CFM, tank size and clean, dry air
- What Software Does a CNC Plasma Table Need?: kerf, lead-ins and the CAD-to-cut workflow
- Arclight Support: lifetime tech support, videos and parts
- Hypertherm consumables: in-stock nozzles, electrodes, shields and kits
Get Help From Arclight, or Get a Quote on a Table
Arclight owners get lifetime support on process, software and hardware from someone who knows their table. Want a pro-grade table with that help behind it? We’ll quote one sized to your work.
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