Plasma Cutting
Plasma cutting blows an ionised gas jet through conductive metal, melting and ejecting a kerf far faster than a laser on thick plate.
- Part
- Cutting
- Revised
- 2026-08-11
At a glance
- Family
- Thermal
- Typical tolerances
- Conventional plasma ±0.030–0.060 in (±0.75–1.5 mm); high-definition plasma ±0.010–0.020 in (±0.25–0.5 mm); 1–3° of bevel on the cut face
- Surface finish
- Cut faces carry visible drag lines, 1–3° of bevel and some dross; edge quality is classified to ISO 9013 rather than by Ra
- Typical volumes
- 1–5,000 parts; no tooling required
- Lead time
- 1–5 business days; same-day for simple plate profiles
- Materials
- Metal
What it is
Plasma cutting forces gas through a constricted nozzle and an electric arc, ionizing it into a plasma jet hot enough to melt the workpiece while the gas velocity blows the molten metal out of the kerf. The workpiece must be electrically conductive, which limits it to metals — mild steel, stainless and aluminum in practice.
Its territory is thick conductive plate. Quality cuts run from about 0.030 in to 2 in (0.8–50 mm), with severance cuts on high-current systems beyond that, and above roughly 0.75 in (19 mm) plasma is generally faster and cheaper per foot than a laser.
The tradeoffs are dimensional. Kerf is 0.06–0.15 in (1.5–4 mm), the cut face carries 1–3° of bevel, and conventional plasma holds only ±0.030–0.060 in (±0.75–1.5 mm), tightening to ±0.010–0.020 in (±0.25–0.5 mm) on high-definition systems.
How it works
- Arc initiation. A pilot arc is struck between electrode and nozzle, then transferred to the workpiece once contact is established. The work must be grounded, which is why the process is limited to conductive material.
- Gas selection. Compressed air is the general-purpose choice and is standard for mild steel. Oxygen gives the squarest edge and least dross on mild steel; nitrogen, or nitrogen with hydrogen or argon mixtures, is used on stainless and aluminum to avoid oxidation and improve edge color.
- Constriction and swirl. The nozzle orifice constricts the arc into a high-velocity column, and a swirl ring spins the gas so the jet stays coherent. That swirl direction is why one side of the kerf comes out squarer than the other.
- Piercing. The torch pierces from above with the head raised, then drops to cutting height. Piercing is hard on consumables and pierce count is a real driver of nozzle and electrode life.
- Cutting. The torch follows the profile at a height held by arc-voltage or capacitive control. Speed is high — far faster than water jet, and faster than laser on thick plate — but the kerf is wide and the tolerance loose by comparison.
- Dross and bevel. Too fast leaves high-speed dross on the bottom edge; too slow leaves low-speed dross that is harder to remove. The cut face carries 1–3° of bevel and a heat affected zone of roughly 0.010–0.050 in (0.25–1.3 mm).
- Post-processing. Dross is ground or chipped off. Air plasma cutting of mild steel leaves a nitrogen-enriched cut face that can cause weld porosity, so critical weld preps are ground back to clean metal.
Design guidelines
Do not use plasma for holes
Round holes are plasma's weakest feature. Keep any plasma-cut hole at least 1.5–2× material thickness in diameter, and expect taper and a rough entry. Bolt holes, dowel holes and anything with a fit requirement should be drilled or punched afterward — call them out that way on the drawing.
Budget the kerf
At 0.06–0.15 in (1.5–4 mm), plasma kerf is one to two orders of magnitude wider than an EDM kerf and several times a laser's. It matters for nesting, for narrow webs, and for any feature dimensioned to a cut edge.
Allow for bevel and specify the good side
The swirling gas makes one side of the kerf squarer than the other. On a typical torch with clockwise swirl, the squarer face is on the right of the direction of travel, so outside profiles are cut clockwise and internal holes counterclockwise to keep the good side on the part. If one face of the part must be square, say which one.
Leave grind stock on weld preps
Air plasma cutting of mild steel leaves a nitrogen-enriched surface on the cut face that can produce porosity in a subsequent weld. Specify that weld-prep faces be ground back to clean metal, or use an oxygen or nitrogen-based process gas.
Choose high-definition plasma when tolerance matters
Conventional plasma holds ±0.030–0.060 in (±0.75–1.5 mm); high-definition systems with finer nozzles and better gas control reach ±0.010–0.020 in (±0.25–0.5 mm) with less bevel. If the drawing needs better than that, the part belongs on a laser or water jet.
Mind distortion on thin and long parts
Plasma puts more heat into the work than laser does. Long thin parts and thin sheet can bow. Below about 0.1 in (2.5 mm), laser cutting is generally both more accurate and less distorting. Cutting speed also tracks the material's melting point and thermal conductivity, which is why copper and brass cut slowly despite being perfectly conductive — see metal melting points.
| Material | Plasma suitability | Notes |
|---|---|---|
| Mild steel / carbon steel plate | Excellent | The core application; oxygen gives the squarest edge |
| Stainless steel | Good | Nitrogen or nitrogen mixes; edge discolors, needs cleanup before polish |
| Aluminum | Good | Nitrogen or air; dross removal is harder than on steel |
| Copper, brass | Marginal | High conductivity and heat capacity; slow and rough |
| Thin sheet under 0.1 in (2.5 mm) | Marginal | Heat distortion; laser is better |
| Non-conductive materials | Not possible | The arc requires a conductive path to the work |
| Feature | Recommended | Limit | Why |
|---|---|---|---|
| Plate thickness | 0.25–1.5 in (6–38 mm) | ~2 in (50 mm) quality cut | The range where plasma beats laser on cost |
| Hole diameter | ≥ 2× thickness | 1.5× thickness | Small holes come out tapered and rough |
| Kerf allowance | 0.06–0.15 in (1.5–4 mm) | — | Wide kerf affects nesting and webs |
| Web between features | ≥ 2× thickness | 1× thickness | Heat input distorts narrow webs |
| Tolerance expectation | ±0.030 in (±0.75 mm) | ±0.010 in (±0.25 mm) high-definition | Arc wander and bevel |
| Weld prep faces | Grind after cutting | — | Nitrogen-enriched face causes weld porosity |
Cost drivers
Plasma is the low cost per foot option on thick conductive plate, and its economics are driven by consumables and speed rather than by tooling.
Thickness and current. Higher amperage cuts thicker and faster but consumes more power and consumables. Within its range, plasma cutting speed on plate is high enough that machine time is rarely the dominant cost.
Consumables. Nozzles and electrodes are wear items with a finite number of pierces and arc-on hours. A nest full of small internal cutouts consumes consumables far faster than the same cut length as open profiles.
Pierce count. Piercing is the hardest thing a torch does. Fewer, larger internal features means longer consumable life.
Secondary operations. Dross grinding, weld-prep grinding and any drilling of holes that plasma cannot hold to tolerance all add labor after the cut.
High-definition versus conventional. A high-definition system costs more per hour but can eliminate a downstream machining operation by holding ±0.010–0.020 in (±0.25–0.5 mm).
Four ways to take cost out:
- Use plasma for outlines and drill the holes that carry a fit; do not ask the torch for precision it does not have.
- Consolidate small internal cutouts to reduce pierce count and consumable wear.
- Reserve stainless and aluminum for laser or water jet where edge appearance matters; plasma edges on those materials need cleanup.
- Below about 0.25 in (6 mm), price it against laser cutting before committing — plasma's advantage appears in thick plate.
Questions
6 questionsHow thick can plasma cut?
Quality cuts run from about 0.030 in to 2 in (0.8–50 mm) depending on system current, with severance cuts possible beyond that on high-amperage systems. Above roughly 0.75 in (19 mm), plasma is generally faster and cheaper per foot of cut than a fiber laser, which is where it earns its place in a fabrication shop.
What tolerance can plasma cutting hold?
Conventional plasma holds ±0.030–0.060 in (±0.75–1.5 mm). High-definition systems with finer nozzles and tighter gas control reach ±0.010–0.020 in (±0.25–0.5 mm) with less bevel. Anything tighter than that should go to laser or water jet cutting rather than to a plasma table.
Why are plasma-cut holes poor quality?
The kerf is wide at 0.06–0.15 in (1.5–4 mm), the arc has to pierce and then immediately turn a tight radius, and the cut face carries 1–3° of bevel. Keep plasma-cut holes at least 1.5–2× material thickness in diameter, and drill or ream any hole that carries a fit.
Can plasma cut aluminum and stainless steel?
Yes — both are conductive, which is the only hard requirement. Nitrogen or nitrogen-based mixtures are used instead of oxygen to limit oxidation. Edges discolor and dross removal is harder than on mild steel, so where edge appearance matters, laser or water jet cutting is usually the better choice.
Do I need to grind a plasma cut before welding?
For critical welds, yes. Air plasma cutting of mild steel leaves a nitrogen-enriched layer on the cut face that can cause porosity in a subsequent weld. Either specify that weld-prep faces be ground back to clean metal, or have the cut made with an oxygen or nitrogen process gas rather than shop air.
Plasma or laser — which should I use?
Thickness and tolerance decide. Below about 0.25 in (6 mm), laser is more accurate, cleaner and usually cheaper. Above roughly 0.75 in (19 mm) in mild steel, plasma cuts faster and at lower cost per foot. In between, the choice comes down to whether the part needs the laser's ±0.005 in (±0.13 mm) and square edge.