Not every metal cuts the same on a CNC plasma table. Mild steel, stainless steel, aluminum, and copper each have different cutting characteristics, gas requirements, speed settings, and edge quality challenges. This guide covers everything you need to know to cut each material cleanly and efficiently.
Plasma cutting works by forcing a superheated, electrically ionized gas stream through a constricted nozzle at high velocity. The arc melts the metal and the gas jet blows the molten material out of the kerf. Simple enough in principle, but the interaction between that plasma arc and the workpiece material changes dramatically depending on what you are cutting.
Each metal has different thermal conductivity, melting point, electrical resistivity, and oxide formation characteristics. These properties determine how fast you can cut, what gas produces the best edge quality, how much dross forms on the bottom, how wide the heat-affected zone extends, and how quickly your consumables wear. Running the same cut parameters on stainless steel that work perfectly on mild steel will produce a rough, discolored edge with excessive dross. Cutting copper at the same speed you cut aluminum will result in an incomplete cut or a destroyed nozzle.
This guide breaks down each of the four primary materials cut on CNC plasma tables. For each material, you will find recommended gas types, practical thickness ranges, common problems and how to solve them, and tips that experienced operators have learned through thousands of hours of arc-on time. Use the quick comparison table below to see all four materials side by side, then dive into each section for the full details.
| Property | Mild Steel | Stainless Steel | Aluminum | Copper & Brass |
|---|---|---|---|---|
| Max Thickness (65A) | 5/8" | 1/2" | 1/2" | 3/8" |
| Max Thickness (125A) | 1-1/2" | 1-1/4" | 1-1/4" | 3/4" |
| Recommended Gas | Air / O2 | N2 / H35 | N2 / Ar-H2 | N2 |
| Relative Cut Speed | Baseline | 20% slower | 20-30% faster | 30-40% slower |
| Material Cost | $ | $$$ | $$ | $$$$ |
| Cutting Difficulty | Easy | Moderate | Moderate | Difficult |
| Consumable Wear | Normal | Moderate | Moderate | High |
Thickness values represent clean, production-quality cuts. Severance cuts are possible at 30-50% greater thickness. Use our Amperage Calculator for specific settings.
Mild steel is the most commonly cut material on CNC plasma tables, and for good reason. It is affordable, widely available in every thickness from thin gauge sheet to heavy plate, and it cuts cleanly with the simplest and cheapest gas option available: compressed air. If you are setting up a new CNC plasma table and want to learn the machine before moving to more demanding materials, mild steel is where you start.
The plasma arc interacts with mild steel predictably. The iron content responds well to the ionized gas stream, producing a consistent kerf width and a relatively smooth cut edge across a wide range of speeds and amperages. This forgiveness is what makes mild steel the ideal material for dialing in your amperage settings, THC voltage, and cut speed before committing to more expensive metals.
For general cutting, compressed air is all you need. Air-plasma cutting on mild steel produces a clean edge with a thin oxide layer that is easily removed by grinding or wire brushing if cosmetic appearance matters. However, when you move into thicker material — 1/4 inch and above — switching to oxygen (O2) as the plasma gas makes a noticeable difference. Oxygen creates an exothermic reaction with the iron in the steel, meaning the oxidation process itself generates additional heat that assists the cut. This produces a smoother, squarer edge, narrower kerf, and less dross on the bottom of the workpiece. The trade-off is that oxygen consumables wear faster than air consumables, so reserve O2 cutting for jobs where edge quality justifies the extra consumable cost.
Stainless steel is the second most commonly cut material on CNC plasma tables, used heavily in food equipment fabrication, architectural metalwork, marine components, and any application where corrosion resistance matters. Cutting stainless requires more attention to gas selection and parameter tuning than mild steel, but the results are excellent when you get the settings right.
The key difference between cutting stainless and mild steel is the chromium content. Stainless steel contains at least 10.5% chromium, which forms a passive oxide layer that gives the material its corrosion resistance. During plasma cutting, this chromium reacts aggressively with oxygen. If you cut stainless with compressed air (which is 21% oxygen), you get a heavily oxidized, dark brown or black edge that compromises the corrosion resistance of the cut surface and looks terrible. The heat-affected zone is also wider with air, which can cause sensitization in some stainless grades — a metallurgical change that makes the material vulnerable to intergranular corrosion.
The solution is nitrogen (N2) gas. Nitrogen is inert with respect to chromium, so it produces a clean, bright edge with minimal oxide formation. For the absolute best results on stainless steel, use H35 gas — a mixture of 65% argon and 35% hydrogen. The hydrogen acts as a reducing agent that actively prevents oxide formation, and the argon provides a dense, stable gas column. H35 produces the brightest edges, the narrowest kerf, and the smallest heat-affected zone of any gas option on stainless steel. The downside is cost: H35 cylinders are significantly more expensive than straight nitrogen, so most shops reserve it for jobs where edge appearance and corrosion performance are critical.
Aluminum is a different beast from steel on a CNC plasma table. It cuts faster — significantly faster — because aluminum has a much lower melting point (1,220 degrees F versus 2,750 degrees F for steel) and about half the density. The plasma arc blasts through aluminum quickly and efficiently. But that speed comes with challenges: the molten aluminum re-solidifies rapidly and has a tendency to re-weld itself to the bottom edge of the cut, creating stubborn dross that is harder to remove than steel dross.
Aluminum is also highly reflective and has high thermal conductivity. The reflectivity can cause arc instability on very thin sheets (under 18 gauge) because the arc struggles to maintain consistent transfer to the shiny surface. The high thermal conductivity means heat spreads rapidly away from the cut zone, which is actually an advantage — it reduces the heat-affected zone and minimizes distortion compared to stainless steel. But it also means that the leading edge of the kerf cools quickly, which is what causes the molten material to re-weld as dross rather than falling away cleanly.
Nitrogen (N2) is the recommended plasma gas for aluminum. Air works in a pinch, but the oxygen component creates a rough, oxidized edge and accelerates nozzle wear. For the premium edge quality, an argon-hydrogen mix provides excellent results, though the cost is higher. Some high-definition plasma systems use an N2/N2 combination (nitrogen as both the plasma and shield gas) with great results on aluminum.
Copper and brass are the most challenging materials to cut on a CNC plasma table. The fundamental problem is thermal conductivity: copper conducts heat approximately six times faster than mild steel. This means the plasma arc's energy dissipates rapidly into the surrounding material rather than staying concentrated at the cut zone. The result is a wider kerf, a larger heat-affected zone, and the need for significantly more amperage to achieve a clean cut at any given thickness compared to steel.
Brass is somewhat easier than pure copper because its zinc content lowers the thermal conductivity and melting point, but it still requires more power and slower speeds than steel. Both materials share another challenge: rapid consumable wear. The high amperage required to cut copper and brass at production quality pushes the nozzle and electrode harder than steel cutting at the same thickness. Expect consumable life to be 30-50% shorter when cutting copper or brass compared to mild steel.
Nitrogen is the required plasma gas for copper and brass. Air introduces oxygen that reacts with the copper surface, creating a rough oxide layer that further degrades edge quality. Even with nitrogen, do not expect the same edge quality you get on steel. Copper and brass edges from plasma cutting are typically rougher, with more bevel and a wider kerf. For decorative or precision applications, plan on secondary finishing — deburring, filing, or light grinding — after cutting.
Compressed Air
Lowest Cost
Works on mild steel at all thicknesses. Produces an oxide layer on stainless and aluminum. Adequate for shops that primarily cut carbon steel and do not require cosmetic edges. Requires only a compressor and air dryer — no bottled gas.
Best for: Mild steel, general fabrication, budget-conscious shops
Oxygen (O2)
Best for Steel
Premium edge quality on mild steel 1/4 inch and thicker. The exothermic reaction produces smoother, squarer edges and narrower kerf than air. Do NOT use on stainless, aluminum, or copper. Requires O2 cylinders and oxygen-rated consumables.
Best for: Mild steel plate, production quality edges
Nitrogen (N2)
Most Versatile
The go-to gas for stainless steel, aluminum, copper, and brass. Produces clean, bright edges without oxidation. Also works on mild steel though edge quality is slightly below air on carbon steel. The single best choice if you cut multiple materials.
Best for: Stainless, aluminum, copper, multi-material shops
H35 / Ar-H2
Premium Edge
H35 (65% argon / 35% hydrogen) delivers the best possible edge quality on stainless steel and aluminum. Bright, oxide-free edges with the narrowest kerf and smallest HAZ. Higher gas cost limits it to critical applications. Requires dual-gas capable plasma systems.
Best for: Stainless steel (cosmetic), aluminum (cosmetic), HD plasma
Not sure which gas and amperage to run? Our calculators can help.
Plasma cutting only works on electrically conductive materials. The arc requires a continuous electrical circuit between the torch electrode, through the plasma gas, through the workpiece, and back through the work lead. This means you cannot plasma cut wood, plastic, glass, ceramic, or stone. For non-conductive materials, consider a CNC router, waterjet, or laser.
Within the conductive metals, a few other materials deserve mention:
Cuts like mild steel in terms of parameters, but the zinc coating vaporizes and produces toxic zinc oxide fumes (causes "metal fume fever" — flu-like symptoms). Always cut galvanized steel with adequate ventilation or a proper fume extraction system. A water table helps capture zinc fumes. The cut edge will not have the zinc coating and will need rust protection.
Plasma cuts titanium, but the edges are heavily oxidized and the heat-affected zone can embrittle the material. Argon shielding is essential. Most titanium fabrication shops prefer waterjet or laser for precision work. Plasma is used on titanium only for rough cuts or in applications where the HAZ will be machined away.
These high-carbon and alloy steels cut similarly to mild steel but the heat-affected zone can create a hard, brittle layer at the cut edge. If the parts will be used in fatigue-critical applications, the HAZ must be ground or machined away after cutting. Plasma is fine for rough blanking of tool steel that will be finish-machined.
Plasma can cut cast iron, but the high carbon content produces more smoke and spatter than steel. Cut speeds are similar to mild steel. The brittle nature of cast iron means thin sections can crack from thermal shock during cutting. Preheat thick cast iron pieces to 300-400 degrees F before cutting to reduce crack risk.
| Thickness | Mild Steel | Stainless Steel | Aluminum | Copper |
|---|---|---|---|---|
| 16 gauge (0.060") | 25-30A | 30-35A | 25-30A | 35-40A |
| 1/8" (0.125") | 30-40A | 40-45A | 30-40A | 45-55A |
| 1/4" (0.250") | 45-65A | 55-70A | 45-65A | 65-80A |
| 3/8" (0.375") | 55-80A | 70-85A | 55-80A | 85-105A |
| 1/2" (0.500") | 65-85A | 85-105A | 65-85A | 105-125A |
| 3/4" (0.750") | 80-105A | 105-125A | 85-105A | 125-200A |
| 1" (1.000") | 105-125A | 125-200A | 105-125A | 200A+ |
Values represent typical amperage ranges for production-quality cuts. Actual settings depend on your specific plasma system, gas type, and desired cut quality. Always consult your manufacturer's cut chart first.
Understanding material properties is what separates an operator who produces consistently clean parts from one who fights dross, discoloration, and poor edge quality on every job. The parameters that work perfectly on mild steel will produce terrible results on stainless or copper. Each material demands its own gas selection, speed adjustment, and amperage setting.
If you are just getting started with CNC plasma cutting, master mild steel first. It is the most forgiving material and lets you focus on learning your machine's motion, THC behavior, and software workflow without the added complexity of special gases and tricky cut parameters. Once you can consistently produce clean, dross-free cuts on mild steel at multiple thicknesses, move on to stainless and aluminum. Save copper for after you have experience with the other three.
For shops that cut multiple materials regularly, nitrogen is the most versatile gas investment — it works well on stainless, aluminum, and copper, and it is acceptable on mild steel when edge quality is not critical. Pair it with compressed air for everyday steel work, and you have a two-gas setup that handles everything a typical fabrication shop encounters.
Ready to find the right CNC plasma table for your material mix? Request free quotes from qualified dealers and tell them what materials and thicknesses you plan to cut — that information drives the plasma source and gas system recommendations. Or use our Amperage Calculator to check whether your current plasma cutter handles the materials you need.
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Mild steel (carbon steel) is by far the easiest material to cut with a CNC plasma table. It cuts cleanly with compressed air as the plasma gas, tolerates a wide range of cut speeds without excessive dross, and produces predictable results across all thickness ranges. Mild steel is also the most forgiving material for beginners learning to dial in cut parameters. If you are new to CNC plasma, start with mild steel and work your way up to stainless, aluminum, and copper as you gain experience.
Yes, CNC plasma tables cut aluminum well, but it requires different settings than steel. Use nitrogen (N2) as the plasma gas instead of air for the cleanest edge. Increase your cut speed by 20 to 30 percent compared to mild steel at the same thickness and amperage. Bottom dross is more common on aluminum because molten aluminum re-solidifies quickly. A water table helps cool the material and reduce dross, but be aware that moisture exposure can cause hydrogen porosity in some aluminum alloys if the parts will be welded later.
For mild steel, compressed air works for most applications and oxygen (O2) gives the best edge quality on thicker material. For stainless steel, nitrogen (N2) is the standard and H35 (65 percent argon, 35 percent hydrogen) gives the best results. For aluminum, nitrogen is recommended. For copper and brass, nitrogen is required. If you only cut mild steel, you can run on compressed air alone with no bottled gas. Shops that cut multiple materials typically keep both nitrogen and oxygen cylinders on hand.
Maximum cut thickness depends on your plasma amperage. With a 65-amp system, expect clean cuts up to 5/8 inch on mild steel, 1/2 inch on stainless, 1/2 inch on aluminum, and 3/8 inch on copper. With a 125-amp system, you can cleanly cut up to 1-1/2 inch mild steel, 1-1/4 inch stainless, 1-1/4 inch aluminum, and 3/4 inch copper. Severance cuts (rough edge, not production quality) are possible at 30 to 50 percent greater thickness. High-definition plasma systems at 200-plus amps push these limits further.
The dark discoloration on plasma-cut stainless steel is caused by oxidation of the chromium in the surface layer. When you cut stainless with compressed air, the oxygen in the air reacts with the hot chromium at the cut edge, creating a dark oxide layer. Switching to nitrogen (N2) as the plasma gas significantly reduces this discoloration. For the cleanest stainless edges with minimal heat-affected zone, use H35 gas (65 percent argon, 35 percent hydrogen). The oxide layer is cosmetic and can be removed with a stainless wire brush, pickling paste, or electrochemical cleaning if needed.
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