How does amperage affect cut speed?

Higher amperage delivers more energy to the arc, so it can melt and blow away metal faster, allowing higher travel speeds at a given thickness. It also raises the maximum thickness the torch can sever. Too little amperage for the thickness leaves dross or fails to cut through.

What is dross and how does speed control it?

Dross is re-solidified metal stuck to the cut edge. Going too slow lets molten metal pool and form low-speed dross on top; going too fast leaves high-speed dross on the bottom and an angled, lagging cut. The right speed produces a clean, near-vertical edge with minimal dross.

Why is aluminum cut differently from steel?

Aluminum conducts heat away from the cut zone much faster than steel, so it generally needs higher current or slower speed for the same thickness. Stainless behaves between the two and benefits from higher current and sometimes specialty gases for clean edges.

What happens if I cut too fast?

Too fast and the arc lags behind, leaving an incomplete cut or a V-shaped bevel that does not penetrate the bottom. You will see sparks blowing back up toward the torch instead of out the bottom, a sign to slow down or raise amperage.

Are these speeds exact for my machine?

They are manufacturer-style estimates and a strong starting point. Exact speeds depend on your torch, consumables, gas, voltage, and pierce height. Always run a test cut and fine-tune for a square edge and clean bottom before production.

Plasma Cut Speed Calculator

Plasma cut speed is the single biggest lever on edge quality. Run too slow and you build top dross and a wide kerf; run too fast and the arc lags, leaving an incomplete, beveled cut. This calculator estimates a target inches-per-minute speed for mild steel, stainless, and aluminum from thickness and amperage using manufacturer-style cut-speed curves, and warns when the amperage is simply too low for the plate.

How it works

Cut speed falls steeply as thickness rises and climbs with amperage. The tool models speed as a base capacity for the selected amperage, divided by a thickness factor and scaled by a material conductivity factor:

capacity     = k × amperage            (energy available)
speed (IPM)  = capacity / (thickness^p × materialFactor)

where the exponent p is greater than 1 because thicker plate needs disproportionately more dwell, and materialFactor is 1.0 for mild steel, higher for stainless, and higher still for aluminum, which sheds heat fastest. A minimum amperage is required to pierce a given thickness; below it the tool flags an incomplete cut.

Example and notes

At 45 A on 1/4 in mild steel the tool suggests roughly 40 to 60 IPM, a typical hand or CNC range for that combination. The same 45 A on 1/2 in plate drops to a slow, marginal speed and the tool warns you are near the torch’s limit, where edge quality suffers. Aluminum of the same thickness returns a lower speed because it pulls heat away from the cut. Treat the number as a starting point: run a test coupon, watch where the sparks exit, and adjust for a square top edge and a clean, dross-free bottom.