Selecting the Cutting Process Settings of the CNC Plasma Cutting Machine
This guide is for engineers and shop programmers who have to turn a cut chart into a real part. It covers the plasma cutting process settings that decide edge quality, the order to set them in, and the plate thickness ranges where plasma stops being the right call.
Key takeaways
What order to set the parameters in
Most cut charts are written for one gas, one nozzle, and one material condition. Your plate is never exactly that. So treat the chart as a starting point and work through the parameters in a fixed order: current, gas and flow, travel speed, then nozzle height. Changing two at once makes it impossible to tell which one fixed the edge.
Current comes first because it sets how much energy the arc carries. A 1.5 mm mild steel plate might run 30 A to 45 A, a 6 mm plate 80 A to 100 A, and a 12 mm plate 130 A to 200 A depending on the power supply. Push current above the nozzle rating and the orifice erodes within minutes; run well below it and the arc cannot punch through the plate cleanly.
Gas and flow come next. The plasma gas forms the jet, and the shield gas shapes it. On carbon steel, oxygen plasma gives a sharp, nearly dross-free edge. On stainless and aluminum, nitrogen is the usual choice because oxygen leaves an oxidized edge that has to be ground back before welding. Flow matters as much as type: too little gas and the arc wanders, too much and the jet cools before it exits the nozzle.
Travel speed is your trim. Start at the chart value and adjust in 10 percent steps. Nozzle height comes last, because arc voltage control will hold standoff automatically on most CNC tables, and the setpoint only needs a small correction once the other three are correct.
- 1CurrentSets capacity and kerf width. Stay inside the nozzle's rated window.
- 2Gas type and flowOxygen for carbon steel, nitrogen for stainless and aluminum.
- 3Travel speedTrim in 10 percent steps until dross just disappears.
- 4Nozzle heightHold 1.5 mm to 3 mm standoff with arc voltage control.
Matching current and speed to plate thickness
Current and speed are a pair. For a given plate thickness there is a band of current values that will cut through, and inside that band there is a narrow speed range that produces a square edge. If the arc does not fully penetrate, the bottom edge shows a heavy, bubbly dross bead. If speed is too slow, the kerf widens, the top edge rounds over, and low-melting dross sticks to the bottom.
A practical starting point on mild steel: 3 mm plate at 60 A and 2,000 mm/min to 2,600 mm/min, 6 mm plate at 100 A and 1,400 mm/min to 1,800 mm/min, 10 mm plate at 130 A and 900 mm/min to 1,200 mm/min. These are starting values, not fixed rules. Every power supply has its own arc characteristics, and a worn electrode shifts the arc voltage enough to change the optimum speed.
Watch the shape of the dross, not just its presence. A thin, easily brushed bead on the bottom usually means speed is slightly low. A hard, gray, tightly bonded bead means speed is too high or current is too low for the thickness. High-speed dross is the harder problem because it often requires grinding.
Above roughly 25 mm on carbon steel, plasma cutting starts to lose its edge on squareness and kerf control. That is usually the point to switch to oxy-fuel cutting or to a machining process. Plasma still cuts thicker plate, but the bevel and heat-affected zone grow, and downstream machining allowances have to be added.
- 1Penetration firstRaise current until the arc exits the bottom of the plate cleanly.
- 2Then trim speedAdjust in 10 percent steps and inspect the dross bead after each cut.
- 3Do not chase zero drossA thin, brushable bead is normal on many thicknesses.
- 4Know the ceilingPast about 25 mm on carbon steel, consider oxy-fuel or machining.
Gas selection and consumable wear
Gas selection is material-driven. Oxygen on carbon steel gives the best edge and the fastest cut because the oxygen reacts with the iron and adds chemical energy to the arc. Nitrogen on stainless steel and aluminum avoids the oxide layer that would otherwise form and interfere with later welding or anodizing. Argon alone gives a stable arc but low enthalpy, so it is rarely used for production cutting on thick plate.
Argon-hydrogen blends such as H35 raise cutting speed and edge quality on stainless steel, but hydrogen increases heat input. On thin material that shows up as warping and a wider heat-affected zone. Use these blends only where the cut chart or the material specification calls for them, and keep the ventilation and gas handling appropriate for hydrogen.
Consumables wear in a predictable way. The electrode tip erodes, the arc voltage drifts upward, and the cut quality falls off before the part is visibly bad. Log arc voltage at the start and end of each shift. A rise of more than about 10 V usually means the electrode or nozzle is due for replacement.
Nozzle orifice size must match the current. Running a 100 A nozzle at 130 A overheats the orifice and changes the arc shape. Running a 130 A nozzle at 80 A gives a soft, wide arc with poor kerf definition. When you change plate thickness by more than one step, change the nozzle with it.
- 1Carbon steelOxygen plasma, oxygen or air shield.
- 2Stainless and aluminumNitrogen plasma, nitrogen shield.
- 3Thick stainlessArgon-hydrogen blends only when specified.
- 4Consumable checkArc voltage drift over 10 V means replace the electrode.
Step by step: dialing in a new plate
Run this sequence on a test coupon before the first production part.
- 1Identify the material and thicknessConfirm alloy and actual thickness with a caliper. A 6 mm nominal plate is often 5.8 mm or 6.2 mm, and that changes the speed setting.
- 2Pick the nozzle and current from the chartChoose the nozzle whose rated current brackets your thickness. Set current to the middle of the chart range, not the top.
- 3Set gas type and flowOxygen for carbon steel, nitrogen for stainless or aluminum. Set flow to the torch manufacturer's value for that nozzle.
- 4Cut a 200 mm test line at chart speedUse the same plate and the same nesting orientation as production. Do not test on scrap of a different heat.
- 5Inspect the dross and kerfBrush the bottom edge. Thin, powdery dross means speed is close. Hard, bonded dross means reduce speed by 10 percent.
- 6Adjust speed in 10 percent stepsChange one variable per cut. Two or three iterations are usually enough on mild steel.
- 7Verify with arc voltageIf the arc voltage is drifting during the test cut, stop and replace the consumables before continuing.
- 8Record the final settingsWrite current, speed, gas, flow, nozzle, and standoff into the program setup sheet for that part.
Starting settings by material and thickness
Mild steel, oxygen plasma. Trim speed to the dross you see.
| Thickness | Current | Travel speed | Nozzle |
|---|---|---|---|
| 1.5 mm | 30–45 A | 3,000–4,000 mm/min | 0.9 mm orifice |
| 3 mm | 60 A | 2,000–2,600 mm/min | 1.0 mm orifice |
| 6 mm | 100 A | 1,400–1,800 mm/min | 1.2 mm orifice |
| 10 mm | 130 A | 900–1,200 mm/min | 1.4 mm orifice |
| 16 mm | 170 A | 600–800 mm/min | 1.6 mm orifice |
| 25 mm | 200 A | 350–500 mm/min | 1.8 mm orifice |
Set current, then trim speed
Pick the nozzle and current for the thickness, then move travel speed in 10 percent steps until the dross brushes off. If the drawing needs tighter than plasma can hold, cut oversize and finish on a CNC mill.
Common questions
Why does my cut have dross on one side only?
One-sided dross almost always points to a torch alignment or travel direction problem, not to the current or speed setting. Check that the torch is perpendicular to the plate and that the consumables are seated squarely.
It can also come from cutting too close to the edge of the plate, where the arc loses its shield gas on one side. Move the lead-in further from the edge and retest.
Can I use the same settings for stainless and mild steel?
No. The gas changes, and so does the speed. Nitrogen plasma on stainless steel cuts slower than oxygen plasma on the same thickness of mild steel, and the edge behaves differently.
Start from the stainless section of your cut chart and expect to trim speed by 10 to 20 percent from the mild steel value.
How do I know when to replace the electrode?
Track arc voltage. A steady rise of about 10 V above the value you recorded with new consumables means the electrode tip has eroded and the arc is getting longer.
Visually, a deep crater in the electrode tip or a rounded, enlarged nozzle orifice confirms it. Replace both together, not one at a time.
What causes a beveled or angled cut edge?
Some bevel is normal, especially on thick plate. Excess bevel usually comes from too much standoff, a worn nozzle, or cutting at the wrong speed for the thickness.
Check standoff first, then the nozzle, then the speed. On plate above 20 mm, expect more bevel and allow for it in the part tolerance.
When should I switch away from plasma cutting?
When the bevel, heat-affected zone, or kerf tolerance no longer fits the drawing. For tight tolerances such as ±0.005 mm, or for a fine surface finish, plasma is the wrong process.
In those cases the part should be cut oversize and finished by CNC milling, which is what we do for brackets, plates, and housings that need both a fast blank and a finished edge.
Does plate surface condition affect the settings?
Yes. Mill scale, rust, and oil change how the arc transfers and how the molten metal flows. Heavy mill scale on hot-rolled steel often needs slightly higher current or slower speed than the chart suggests.
Clean the plate, or expect to adjust from the recorded settings. Do not assume last month's program will run the same on a new heat of steel.
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