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Why Stainless Grating Is Hard on Plasma Cutters

Stainless steel grating looks like mild steel grating, but it cuts very differently. You are not making one long straight cut on flat plate. You are making dozens of interrupted cuts across bearing bars, cross rods, and open air gaps. Every time the arc crosses a gap, it has to re-establish. That punishes machines without a true pilot arc and eats consumables.

Stainless also needs more energy than mild steel for the same thickness. Thermal conductivity is lower, so heat stays in the cut, but chromium oxide raises the melting point and makes dross stickier. A cutter rated for 1/2-inch mild steel will often struggle to make a clean cut on 1/4-inch stainless grating, especially if your air is damp or your duty cycle is low. If you try to drag a weak arc slowly across grating, you will see heavy bottom dross that welds itself back on, angled kerf, and tips that foul after 20 to 30 pierces.

What to Look For in a Cutter for Grating

For grating, prioritize three things over raw amperage: pilot arc, duty cycle, and air management. Everything else is secondary.

Continuous pilot arc is non-negotiable for open grating. A non-pilot or scratch-start machine extinguishes every time you cross a void and has to re-fire with high-frequency. That slows you down and burns electrodes. A blowback pilot arc with non-HF start will maintain the arc across gaps and let you drag or hover without stopping. It also lets you cut expanded metal and grating without needing to keep the tip in constant contact with the workpiece.

Duty cycle determines whether you can finish a cut without waiting. Most small 40A inverters are rated 35-40% at 40A at 104F. That means 3.5 to 4 minutes of cutting in a 10-minute period before thermal shutdown. On a 2×4 foot section of 1-1/4″ x 3/16″ stainless grating, you will be on the trigger almost continuously. A low duty cycle machine will cut out mid-panel and leave a hard stop mark. Look for 60% duty cycle at max amps if you do more than occasional patch work.

Finally, consider consumable cost and availability. Grating is consumable-intensive. You will use more electrodes and nozzles than you would on plate because of all the restarts and pierces. Machines that use common IPT-40, IPT-60, or Trafimet-style torches are cheaper to feed long-term than proprietary torch designs.

How Much Amperage You Actually Need

Do not size by the machine’s “severance” rating. Use clean cut ratings on stainless.

For light stainless grating with 1″ x 1/8″ bearing bars and 3/16″ cross rods, a 40-amp machine on 240V will do the job if it has a real pilot arc and clean, dry air. Cut speed will be around 25-35 inches per minute with minimal dross if you keep the travel speed up.

For standard industrial grating with 1″ to 1-1/4″ x 3/16″ bars, or 1-1/2″ x 3/16″ heavy-duty grating, you want 50 to 60 amps. The extra amperage is not just for thickness. It lets you move faster, which reduces heat input and warping, and blows dross clear instead of letting it solidify on the bottom edge. Below about 30 IPM on 3/16″ stainless, the bottom edge will start to harden and the slots will need grinding.

If you are cutting 1/4″ bearing bars or doing repeated production cuts, a 60 amp plasma cutter for stainless steel on 240V is the sensible minimum. Anything larger than 65 amps is overkill for grating unless you are also cutting thick stainless plate in the same shop.

Input power matters. Most dual-voltage 120/240V machines only deliver their full rating on 240V. On 120V, a 50A machine might only give you 30-35 amps. That is not enough to keep a stable arc on stainless grating without severe slowdown. If you only have 120V access on site, size up one class or bring a generator with a clean 240V/30A outlet.

Comparison by Use Case

There is no single best cutter for everyone. This is how the trade-offs break down for stainless grating specifically:

For most fabricators who cut stainless grating a few times a month, a 50 amp plasma cutter with pilot arc hits the balance of price, portability, and clean cut quality. The cheaper 40A machines are fine if you accept that you will grind more and move slower, and you will stop to let the machine cool on larger panels. Do not buy a 30A hobby unit to save $150 if your main job is grating.

Pilot Arc and Torch Type Matter More Than Brand

Look for a blowback start, non-HF pilot arc. HF start works, but it interferes with CNC tables, nearby electronics, and will not re-fire as cleanly in the air gaps of grating. Blowback also reduces electrode wear.

For hand cutting grating, a drag-capable torch with a shield cup is useful. You can rest the shield on the top of the bearing bars and drag steadily. Without a drag shield, you have to hold a 1/16″ to 1/8″ standoff the entire time, which is tiring and causes arc wobble on uneven grating. If your torch is not drag-rated, do not drag it or you will double-arc and destroy the nozzle in minutes.

Cutting expanded stainless grating? Same rule. You need a machine explicitly rated for expanded metal. That rating means the pilot arc circuit is designed to stay lit without a workpiece under it. If the manual says “do not cut expanded metal,” your consumables will pay the price.

Air Supply, Consumables, and Cut Quality

Your air is half the cutter. Stainless is far less forgiving of moisture than mild steel. Wet air causes a sputtering arc, greenish oxidation on the cut face, and rapid electrode pitting. You need a real filter/dryer, not just the tiny disposable trap that comes in the box. A dedicated plasma cutter air dryer filter with a desiccant stage or Motorguard-style filter 25 feet from the compressor will double consumable life. Aim for air pressure set to the manufacturer’s spec at the back of the machine while flowing – typically 65-75 PSI for 40-50A torches, 70-85 PSI for 60A.

Air volume matters too. A 50A torch needs about 5 to 6 CFM at 75 PSI. A small pancake compressor rated at 2.6 CFM at 90 PSI will run constantly and still starve the arc. You will get an inconsistent kerf width of 0.06″ to 0.09″ instead of a tight 0.05″ kerf, and the arc will constrict poorly. Use at least a 20-gallon compressor with 5+ CFM at 90 PSI, or a larger shop compressor with a reserve tank.

On consumables, stainless will foul a tip faster if you pierce instead of starting from an edge. Whenever possible, start your cut off the end of a bearing bar or from an open space, not in the middle of a bar. Hold a slight 5 to 10-degree lead angle and move at a speed where sparks exit the bottom of the cut. If sparks are rolling off the top, you are too slow or too low on amps. If you have to grind heavy dross off every bar, you are going too slow – increase amps or increase travel speed, not the other way around.

Technique for Clean Grating Cuts

Clamp the grating solidly. Stainless grating vibrates when cut and will pinch the torch if not supported. Never cut on a steel table without a sacrificial grate or you will weld the grating to the table. Support it on steel horses with the cut line over an open gap.

Make relief cuts to control heat. Cutting all cross rods first and then the bearing bars lets the panel expand and can leave you with a parallelogram instead of a square. Work from the outside in and alternate sides to keep distortion down. Stainless moves more than mild steel when heated locally.

Expect to deburr. Even a good plasma cut on stainless leaves a sharp edge and a thin recast layer. For food-grade, marine, or architectural work, hit the cut edges with a flap wheel dedicated to stainless (never one that has touched carbon steel or you will embed iron and get rust staining) and passivate if corrosion resistance matters.

Finally, wear proper stainless fume protection. Hexavalent chromium in stainless plasma smoke is a real hazard. A P100 half-face respirator or powered air-purifying welding helmet is not optional in an enclosed space, and keep a fire watch – the molten spray falling through the grating will travel farther than you expect.