Plasma Cutter Guide: Types, Amperage, Settings & Safe Use

A plasma cutter is one of the most versatile and capable cutting tools available to Australian tradespeople, fabricators, and maintenance engineers. It will cut mild steel, stainless steel, aluminium, copper, and brass cleanly and quickly — and where mechanical cutting tools struggle with curves, profiles, and awkward positions in three-dimensional metalwork, a plasma cutter excels. Unlike angle grinders, it doesn't grind. Unlike oxy-acetylene, it doesn't oxidise. It melts the metal and blows it clear, leaving a narrow, clean kerf at speeds that mechanical methods simply cannot match.

This guide covers how plasma cutting works, the different types of plasma cutters available to Australian workshops, how to match amperage to material thickness, air compressor sizing, consumables maintenance, cut quality troubleshooting, and the WHS safety requirements that apply to plasma cutting in Australia. Whether you're buying your first plasma cutter or sharpening your technique, use this as your reference.

How Does a Plasma Cutter Work?

Plasma is the fourth state of matter — a gas that has been energised to the point where electrons separate from their atoms, creating an electrically conductive fluid. In a plasma cutter, this state is created by forcing compressed air through a narrow copper nozzle while simultaneously passing a powerful direct-current electrical arc through it. The arc ionises the gas into plasma, which reaches temperatures between 15,000°C and 25,000°C at the cutting point — hot enough to melt through virtually any electrically conductive metal in an instant.

The plasma jet does two things simultaneously: it melts the metal, and the high-velocity compressed gas stream blows the molten material clear of the cut zone, producing a narrow, clean kerf. This is the fundamental difference between plasma cutting and oxy-fuel cutting — there is no chemical reaction (oxidation) involved. The metal is melted thermally and evacuated mechanically. That is why plasma can cut metals like aluminium, stainless steel, and copper that oxy-fuel cannot: those metals don't oxidise readily, but they still melt.

The basic components of a plasma cutting system are:

• Power source — converts mains AC power to the high-voltage, high-amperage DC current required to sustain the arc
• Torch — houses the electrode and nozzle; channels the gas and the arc to the workpiece at the correct geometry
• Ground clamp — completes the electrical circuit through the workpiece back to the power source
• Air supply — provides the compressed air that forms the plasma jet and ejects molten material from the kerf

The ground clamp must be attached to clean, bare metal on the workpiece or a conductive metal table — not to paint, rust, or a non-conductive surface. A poor earth connection is one of the most common causes of arc instability and erratic cutting.

Types of Plasma Cutters

Plasma cutters vary by form factor, power delivery method, and arc-starting technology. Understanding these differences will help you select the right machine for your application.

Handheld (Manual) Plasma Cutters

Handheld plasma cutters are the most common type in Australian workshops, fabrication shops, and maintenance environments. The operator holds the torch and guides the cut by hand, or uses a guide rail for straight cuts. Most handheld units range from 20A to 80A and can cut mild steel up to 25mm clean — with severance capacity up to 35–40mm on the larger machines. These machines are the correct choice for workshop cutting, plate work, structural steel maintenance, and general fabrication. They require mains power (240V single-phase for machines up to approximately 60A; larger machines may require three-phase supply) and a properly sized air compressor.

CNC Plasma Cutters

CNC plasma cutters are table-mounted systems where the torch is guided by computer-controlled motion — a gantry or router-style machine moves the torch along programmed toolpaths. CNC plasma is used in fabrication shops, manufacturing, and sheet metal businesses for repeatable, precision cutting of parts. The plasma cutting head and consumables are the same technology as a handheld machine; what changes is the guidance system, the cutting speed, and the scale of production. CNC plasma cutting is not covered in detail in this guide, which focuses on handheld workshop use.

Inverter vs Transformer Power Sources

Modern plasma cutters almost universally use inverter technology — the same switch-mode power supply architecture used in modern MIG and TIG welders. Inverter machines are compact, lightweight, energy-efficient, and produce a stable arc at lower running costs than older transformer-based units. For any new purchase in a workshop or maintenance context, an inverter plasma cutter is the correct specification. Older transformer machines are heavy and inefficient by comparison, though they do tend to be more robust in harsh environments.

Pilot Arc vs High-Frequency Start — Why It Matters

Every plasma cutter must establish an initial arc to ionise the compressed air and begin cutting. There are two main methods for doing this, and the difference is practically important.

High-Frequency (HF) Start

High-frequency start generates a high-voltage, high-frequency spark inside the torch body to ionise the air and initiate the cutting arc. It works reliably on clean, bare metal. The problem is the high-frequency electrical interference it produces — this interference radiates outward and can disrupt nearby electronic equipment including CNC machine controllers, computers, PLCs, variable speed drives, and sensitive measuring instruments. For this reason, HF start plasma cutters are increasingly being phased out in electronics-rich workshop environments and are not recommended for use near CNC equipment.

Pilot Arc (Contact Start or Lift Arc)

Pilot arc plasma cutters create a low-energy arc within the torch head itself before the cutting arc is established on the workpiece. The pilot arc ionises the gas stream independently of the workpiece, which means the machine can start cutting on painted, rusty, scaled, galvanised, or coated surfaces without first making electrical contact with clean metal. Pilot arc also eliminates the HF interference issue entirely, making these machines fully compatible with CNC systems and electronics-heavy workshops.

The practical verdict: pilot arc machines cost more to purchase, but for most workshop applications the operational benefits — reliable starts on imperfect surfaces, compatibility with electronics, easier technique for operators — outweigh the price difference. If you are cutting exclusively in a bare workshop on clean, bare mild steel and budget is the primary constraint, HF start will cut adequately. For all other situations, pilot arc is the better investment.

Plasma Cutter Amperage vs Material Thickness

The most common question in plasma cutting is: what amperage do I need? The approximate rule of thumb is 1 amp per 0.025mm of mild steel for a clean cut — so cutting 6mm mild steel cleanly requires around 40A, and 12mm requires around 60A. Every plasma cutter manufacturer publishes two thickness ratings: clean cut capacity (quality cut suitable for further fabrication, welding, or presentation) and severance cut capacity (the maximum thickness the machine will penetrate, but with rough edges, heavy dross, and reduced quality).

Always size your machine against the clean cut rating for the material you'll regularly be working with. Severance capacity is only relevant when cut quality is not critical — rough demolition cutting, for example. Operating a machine at or near its severance limit also dramatically increases consumable wear.

Note: These figures are indicative. Actual performance depends on the specific machine, consumable condition, air supply quality, cutting speed, and standoff distance. Always refer to your machine's cut chart for exact settings — the manufacturer's data is the authoritative reference for your specific unit.

Standoff distance and effective capacity: The distance between the nozzle and the workpiece affects how much energy reaches the cut. When using a drag shield (the ceramic or plastic guide that rests directly on the workpiece surface), standoff is automatically controlled. Without a drag shield, maintain 3–6mm. Excessive standoff reduces penetration and cut quality; insufficient standoff risks nozzle damage from molten spatter.

Air Compressor Requirements for Plasma Cutting

The compressed air supply is not optional — it is integral to the cutting process. Without adequate airflow and pressure, a plasma cutter will not establish a stable arc, will cut poorly, and will destroy consumables rapidly. Air supply problems are the most commonly overlooked factor when setting up a plasma cutting station.

Three factors govern the air supply specification:

Pressure (PSI / bar): Most handheld plasma cutters require 60–90 PSI (4.1–6.2 bar) at the machine inlet, measured during cutting — not at the compressor tank. The compressor must maintain this pressure continuously during the cut, not just at idle. Check the compressor's rated delivery pressure at full airflow, not its maximum tank pressure, when sizing.

Airflow (L/min or CFM): This is where undersizing causes the most operational problems. A compressor's displacement rating (theoretical maximum output) is not the same as its real-world delivered airflow — the difference is typically 20–30%. Size the compressor at 30–50% above the plasma cutter's minimum airflow specification to maintain pressure through continuous cuts without the compressor cycling on and off mid-cut.

Moisture filtration — non-negotiable: Moisture in the air line is one of the most destructive forces in a plasma cutting setup. Even small amounts of water vapour degrade the arc, destroy consumables at a rate of two to three times normal, and cause arc instability and blow-out. A coalescing inline moisture filter and separator fitted as close as possible to the plasma cutter inlet is essential. Drain the compressor tank daily. In humid environments — coastal workshops, tropical climates — a refrigerant or desiccant air dryer is strongly recommended. For more on compressor selection and air treatment, see the AIMS Air Compressor Guide.

Always oversize your compressor by at least 30% above the plasma cutter's minimum specification. This ensures pressure is maintained during continuous cutting without the compressor cycling on and off mid-cut. A larger tank also reduces cycling frequency.

Understanding Duty Cycle

Duty cycle is the percentage of a 10-minute period that a plasma cutter can operate at its rated amperage before requiring a cooling period. A machine rated at 60% duty cycle at 45A can run for 6 continuous minutes, then must rest for 4 minutes before resuming at full amperage output. Attempting to run past the duty cycle limit triggers thermal cutout protection — the machine shuts down automatically.

Duty cycle is one of the most misread specifications when comparing plasma cutters. Budget and consumer-grade machines often quote duty cycle at a lower amperage than the machine's maximum — for example, 60% at 30A, but only 25% at the rated 45A. Always check the duty cycle specification at the amperage you actually intend to cut at, not the machine's peak amperage rating.

What duty cycle suits your application?

• Occasional workshop use, short cuts: 35–40% duty cycle at working amperage is adequate
• Regular workshop and trade use: 60% duty cycle at working amperage is the practical minimum
• Production or sustained cutting: 80–100% duty cycle; inverter machines at this level are built to a different standard and priced accordingly

Ambient temperature and duty cycle: Duty cycle ratings are tested at a specific ambient temperature — typically 25°C or 40°C. In hot Australian workshops, effective duty cycle is lower. A machine rated at 60% duty cycle at 40°C may only achieve 40–45% in a poorly ventilated workshop in summer. Check the manufacturer's ambient temperature specification, particularly if your workshop runs hot.

Plasma Cutter Consumables — What They Are and When to Replace Them

Plasma cutter consumables are the replaceable parts within the torch that wear through normal use. They are inexpensive relative to the machine cost — typically $5–$20 per part — but worn consumables are the single biggest cause of poor cut quality and the most common reason for premature machine damage. Inspect them regularly; don't wait until cut quality degrades to check.

Consumable maintenance rules:

• Inspect consumables before every session, not after cut quality problems appear. By the time quality degrades noticeably, the consumables are already causing excess wear on each other.
• Replace electrode and nozzle together — they wear as a matched pair. Installing a new electrode with a worn nozzle (or vice versa) negates the benefit and accelerates wear on the new part.
• Never touch the electrode hafnium insert or nozzle orifice with bare fingers. Skin oils contaminate the surface and accelerate erosion.
• Use consumables rated for your machine's amperage. Running a 40A nozzle in a 60A machine will destroy it almost immediately.
• Use genuine manufacturer-specified consumables. Generic consumables often physically fit but deliver significantly shorter service life and inconsistent cut quality, negating any apparent cost saving.

AIMS stocks plasma cutter consumables for a range of popular Australian machines. Browse plasma cutter consumables at AIMS Industrial.

What Can (and Can't) a Plasma Cutter Cut?

Plasma cutting works on any electrically conductive material. Non-conductive materials — wood, plastic, rubber, ceramic, glass — cannot be cut with plasma regardless of amperage.

Metals plasma cutting handles well:

• Mild steel — the primary application; fast, clean, highly controllable
• Stainless steel — cuts cleanly; see WHS note below
• Aluminium — cuts well; slightly more technique-sensitive than mild steel
• Copper and brass — cuts adequately at appropriate amperage; copper is highly conductive and dissipates heat quickly, so amperage and speed need adjustment
• Hardox, wear plate, and high-strength steel — cuts these materials that are difficult or impossible to cut mechanically

Special cases — with important WHS implications:

Galvanised steel: A plasma cutter will physically cut galvanised steel, but the process burns off the zinc coating and produces zinc oxide fume — a serious inhalation hazard that causes metal fume fever (chills, nausea, flu-like symptoms) and with repeated exposure can cause more serious respiratory effects. Cutting galvanised steel requires a P3 half-face or full-face respirator with an appropriate filter combination, forced mechanical ventilation or outdoor cutting, and ideally pre-stripping of the galvanising from the cut zone before cutting. Where possible, source uncoated steel and galvanise after cutting. See the AIMS Respirator and Dust Mask Guide for filter selection guidance.

Painted steel: Plasma cutting through paint produces toxic fumes, the nature of which depends on the paint formulation. Older industrial paints may contain lead or chromium compounds. Where the coating type is unknown, treat the fumes as hazardous — use a P3 respirator and ensure forced ventilation.

Stainless steel: Stainless steel produces hexavalent chromium (Cr(VI)) fume during cutting — one of the most hazardous industrial cutting and welding fumes, classified as a Group 1 carcinogen by IARC. A P3 particulate filter is mandatory for stainless cutting; P2 does not provide adequate protection. This is a regulatory obligation under the WHS Act, not a discretionary measure.

Rusty or scaled steel: Plasma cuts through rust and mill scale without difficulty — one of its key practical advantages over oxy-acetylene. Pilot arc machines handle severely corroded surfaces particularly well.

Cast iron: Plasma will cut cast iron, but the material's brittleness means cut edges are rough and thermal stress during cutting may cause cracking. It is not the preferred method for precision cast iron work.

Plasma Cutting Technique and Settings

Correct technique produces a clean, square cut with minimal dross and a narrow kerf. The most important variables to control are amperage, cutting speed, and standoff distance.

Setting amperage: Begin with the manufacturer's recommended cut chart setting for your material type and thickness. Do not guess — the cut chart is the starting point. Adjust from there based on results: too much dross at the bottom suggests speed is too slow or amperage too high; incomplete penetration means amperage is too low or speed is too fast.

Cutting speed — the key variable: The correct cutting speed produces a consistent stream of sparks trailing behind and below the cut path at approximately 5–10° from vertical (slightly backward). This is the most reliable visual indicator of correct speed. If sparks spray straight down, you are moving too slowly — increase speed or reduce amperage. If the arc struggles to penetrate and sparks spray forward, increase amperage or reduce speed.

Standoff distance: When using a drag shield (the plastic or ceramic guide that contacts the workpiece surface), standoff distance is controlled automatically — rest the shield on the metal and advance the cut. Without a drag shield, maintain 3–6mm between nozzle and workpiece. Inconsistent standoff is one of the most common causes of uneven cut quality on freehand work. A roller guide or straight-edge guide dramatically improves consistency on long straight cuts.

Pierce vs edge start:

• Edge start — begin the arc at the edge of the workpiece, then advance into the cut. This is the easiest method and produces the cleanest start. For most maintenance and fabrication cuts, start at an edge wherever possible.
• Pierce start — when beginning a cut in the middle of material, angle the torch 15–20° away from the direction of travel, fire the arc, then rotate to perpendicular and advance. The angled start deflects the initial molten blowback away from the nozzle. Never start a pierce directly vertical on material above 10mm — the blowback will hit the nozzle directly and destroy consumables.

Cutting straight lines: For long straight cuts, clamp a straight-edge guide to the workpiece and run the torch body or drag shield along it. This is far more consistent than freehand on anything longer than 200mm. For circles, plasma-cutting compass guides are available that pivot around a central point.

Cutting aluminium: Aluminium is highly thermally conductive, which means it dissipates heat quickly. Cut aluminium at a slightly faster speed than equivalent-thickness mild steel to prevent excess heat buildup. Aluminium also oxidises rapidly — the drag shield is particularly useful for aluminium cutting to maintain consistent standoff.

Troubleshooting Plasma Cutter Cut Quality

Most cut quality problems have a specific cause and a direct fix. Work through these systematically before blaming the machine.

Excessive bottom dross (slag on the underside of the cut): This is the most common complaint. Causes in order of frequency: cutting speed too slow; amperage too high; standoff too low; consumables worn; moisture in the air supply. Dross that looks like uneven, bubbly slag rather than a clean bead usually indicates moisture contamination — check the moisture filter and drain the compressor tank. Small amounts of bottom dross are normal on thicker material; it should knock off easily with a chipping hammer or angle grinder.

Top spatter (molten droplets on the top surface around the kerf): Usually caused by too-low pierce height on the start of the cut — the arc blows molten material back up rather than ejecting it downward. Increase pierce standoff at the start, or angle the torch on pierce starts as described above.

Bevel on the cut edge (cut is not square): One clean, square side and one angled side indicates the torch is not perpendicular to the workpiece, or the nozzle orifice has eroded unevenly. Check torch angle — it is very common to unconsciously hold the torch at a slight angle during freehand cutting. If angle is correct, replace consumables.

Arc blow-out or loss of arc mid-cut: Most common causes, in order: moisture in the air supply (the primary cause — check and replace the moisture filter, drain the tank); consumables worn past serviceable limits (electrode hafnium pit fully depleted); insufficient air pressure at the machine inlet (check for restrictions in the hose, compressor pressure drop during cutting); damaged shield cap causing arcing outside the nozzle.

Incomplete penetration: Amperage too low for the material thickness, cutting speed too fast, standoff too great, or consumables failing. Check the cut chart, reduce speed, and inspect consumables.

Excessive kerf width and rough cut: The nozzle orifice has eroded and widened with use. Replace nozzle and electrode together. Do not continue cutting on an oval nozzle — it accelerates electrode wear and produces unpredictable arc behaviour.

Machine cuts intermittently or arc keeps restarting: Usually an earth (ground) clamp problem. Check that the clamp is attached to clean, bare metal on the workpiece. An intermittent or high-resistance earth connection causes the arc to hunt and restrike.

Plasma Cutter vs Oxy-Acetylene vs Angle Grinder

These three cutting methods are the most common in Australian workshops, fabrication environments, and maintenance operations. Each has genuine strengths that make it the right choice in specific circumstances — none is universally superior.

Plasma cutter is the fastest method for cutting any conductive metal up to approximately 25mm clean, and the only practical method for cutting stainless steel, aluminium, copper, and brass with a portable tool. It requires mains power (240V single-phase for most workshop units) and a properly sized air compressor. Setup time is minimal — the machine is ready to cut within a minute. Operator learning curve is moderate; most operators are producing acceptable cuts within an hour of first use.

Oxy-acetylene cutting excels at very thick ferrous metal — above 25mm where plasma becomes expensive and impractical — and in field situations where neither mains power nor compressed air is available. The oxy-acetylene rig is a heating tool as well as a cutting tool: it heats seized fasteners, bends structural steel, and thaws hydraulic lines. Its critical limitation is that it only cuts ferrous metals through oxidation — it cannot cut aluminium, stainless, copper, or brass. It also demands significantly more operator skill than plasma (flame adjustment, preheat timing, torch manipulation), and it carries serious fire and explosion risks from the pressurised gas cylinders that require careful storage and handling.

Angle grinder with cutting disc is the correct choice for straight cuts on thin material when no air supply is available, for site work on small sections, and for cuts where a power tool is at hand and the plasma cutter is not. It is noisy, slow on anything above 6mm, and completely unsuitable for curves, internal profiles, or large sheet work. For a detailed overview of disc types and technique, see the AIMS Cutting Disc Guide.

For a full comparison of workshop cutting and grinding tools, see the AIMS Bench Grinder Guide, AIMS Angle Grinder Guide, and AIMS Belt Sander and Linisher Guide.

PPE and WHS Requirements for Plasma Cutting

Plasma cutting is a regulated hazardous activity. Under the Australian Work Health and Safety (WHS) Act 2011, a Person Conducting a Business or Undertaking (PCBU) must eliminate or minimise exposure to hazards so far as is reasonably practicable. For plasma cutting, the principal hazards are UV and infrared radiation, metal fume, electrical hazards, fire from sparks and molten metal, and noise.

Eye and face protection: Plasma cutting produces intense UV and infrared radiation capable of causing arc eye (photokeratitis) and retinal damage without adequate protection. The correct shade for handheld plasma cutting depends on amperage:

• Up to 25A — shade 5 or 6
• 25A to 80A — shade 6 or 7
• Above 80A — shade 7 or 8

An auto-darkening welding helmet set to the appropriate shade range is the preferred option for operators who are also welding — the lens adjusts between a light state (shade 3–4) for positioning and a dark state (shade 5–8) for cutting. A fixed-shade plasma cutting face shield is also acceptable. Standard safety glasses alone are insufficient — they do not block UV radiation. See the AIMS Welding Helmet Guide for shade selection and auto-darkening ratings, and the AIMS Safety Glasses Guide for eye protection standards.

Respiratory protection: All plasma cutting produces ozone, nitrogen dioxide (NOx), and metal particulate fume. The minimum respiratory protection for mild steel cutting in a ventilated space is a half-face respirator with a P2 particulate filter. For stainless steel (hexavalent chromium fume) and galvanised steel (zinc oxide fume), a P3 filter is mandatory — P2 provides insufficient protection for these materials and does not meet the regulatory standard. Always refer to the material Safety Data Sheet (SDS) and Safe Work Australia's welding fume guidance. See the AIMS Respirator and Dust Mask Guide for filter selection, half-face vs full-face options, and fit testing requirements.

Hands and body: Leather welding gloves are required — not cotton, not synthetic. Plasma spatter reaches temperatures that ignite cotton and melt synthetic fibres instantly on contact. A leather or flame-retardant (FR) apron, sleeves, or jacket is required for any cutting above the briefest touch-up work. Do not wear synthetic clothing when plasma cutting.

Footwear: Safety footwear compliant with AS/NZS 2210.3 with a steel or composite toecap. Molten droplets from plasma cutting fall and travel — open footwear is not acceptable. See the AIMS Safety Boots Guide for rating selection.

Electrical safety: The plasma cutter operates at high-voltage DC at the torch. Never touch the electrode, nozzle, or any live torch component while the machine is powered. Inspect the torch lead and power cable before each use for damage. Ensure the ground clamp connection is secure and to clean, bare metal. Do not cut in wet conditions or with wet hands.

Ventilation and fire prevention: Plasma cutting produces sparks and molten droplets that travel several metres from the cut zone. Clear all flammable materials — rags, cardboard, timber — from a minimum 2m radius before cutting. Mechanical extraction at the point of cut is the preferred ventilation control; natural ventilation through open doors and windows is the minimum. Never plasma cut in an enclosed space without mechanical ventilation. A dry powder or CO₂ fire extinguisher should be within reach whenever plasma cutting is in progress. See the AIMS Hi-Vis Vest Guide for site visibility requirements in busy workshop environments.

If you need PPE for plasma cutting, AIMS stocks safety glasses, respirators and dust masks, and safety footwear suited to Australian workshop conditions.

Frequently Asked Questions — Plasma Cutters

Have a question about plasma cutters or consumables? Contact the AIMS team — we stock plasma cutting equipment and consumables and can help you select the right setup for your application.