The cost of sizing a plasma cutter wrongly is rarely the price of the machine itself. It shows up over years as lost cutting speed, wasted consumables and repeated thermal shutdowns. This guide gives you a thickness-driven sizing method: start from the relationship between output current and plate thickness, then work through duty cycle, air supply, torch configuration and CNC integration, and finish with a model-by-model recommendation from the Icyrobot range.
1. Three Different "Thickness" Numbers — Know Which One You Are Reading
Datasheets quote thickness in three different ways, and confusing them is the single most common sourcing mistake:
- Quality cut — a smooth, square edge with minimal dross that can go straight to welding or assembly.
- Production cut — the economical working range that balances acceptable edge quality with cutting speed. This is where the machine will spend most of its life.
- Severance cut — the absolute limit at which the machine can separate the plate, with slow speed, poor edge and heavy dross. Emergency use only.
A widely accepted rule of thumb: quality cut is roughly 50–60% of the severance figure, and production cut roughly 70–80%. Running continuously near the severance limit does not just ruin edge quality — it multiplies electrode and nozzle consumption.
2. Output Current vs. Plate Thickness
Rated output current is the first sizing parameter. The table below is a practical reference for carbon steel with an inverter source, standard torch and dry compressed air:
| Rated Current | Quality Cut | Production Cut | Severance | Typical Power Demand |
|---|---|---|---|---|
| 40 A | ≤ 6 mm | 8–10 mm | 12 mm | ≈ 6 kVA |
| 65 A | 8–10 mm | 12–16 mm | 20 mm | ≈ 10 kVA |
| 100 A | 12–15 mm | 18–22 mm | 30 mm | ≈ 16 kVA |
| 130 A | 16–20 mm | 25–30 mm | 40 mm | ≈ 22 kVA |
| 200 A | 22–28 mm | 35–40 mm | 55 mm | ≈ 35 kVA |
| 300 A | 30–38 mm | 45–55 mm | 70 mm | ≈ 55 kVA |
| 400 A | 40–50 mm | 60–70 mm | 85 mm | ≈ 75 kVA |
Stainless steel and aluminium behave differently because of their thermal conductivity and oxide behaviour. Expect 10–25% less thickness at the same current, and size one step up.
3. Size Against Your Actual Thickness Distribution
The right method is not to size for the thickest plate you have ever cut, but to review your plate consumption over the last twelve months:
- Common thickness ≤ 10 mm → LGK-65IGBT or LGK-100IGBT, balancing portability and capital cost.
- 10–20 mm → LGK-130IGBT, the workhorse for steel fabrication and construction machinery builders.
- 20–35 mm → LGK-200IGBT, with headroom reserved for peak jobs.
- 35–50 mm → LGK-300IGBT, preferably with a water-cooled or heavy-duty torch.
- Above 50 mm → LGK-400IGBT, or evaluate a high-precision plasma system if edge squareness is critical.
Practical rule: size the rated current at 1.3–1.5 times your most common plate thickness. That keeps everyday cutting efficient and prevents the machine from living at full load.
4. Duty Cycle — the Most Overlooked Specification
Duty cycle is the share of a ten-minute period during which the machine can run at rated current. "100 A at 60%" means six minutes of cutting followed by four minutes of cooling at idle.
Match it to your real working pattern:
- Manual cutting, intermittent work — a 40–60% duty cycle is sufficient.
- CNC cutting tables and automated lines — you need a 100% duty cycle rating, otherwise thermal protection will interrupt production repeatedly.
Icyrobot inverter models from 100 A upward are engineered for a 100% duty cycle at rated conditions, which supports full-shift continuous operation.
5. Air Supply and Electrical Requirements
Compressed air
Air plasma is highly sensitive to air quality. Water and oil in the line cause abnormal nozzle wear and visibly poorer edges. Baseline requirements:
- Pressure: 0.4–0.7 MPa (model and torch dependent)
- Flow: ≥ 0.3 m³/min at 100 A class; ≥ 0.6 m³/min at 200 A; ≥ 0.9 m³/min at 300 A
- Treatment: refrigerated dryer plus three-stage filtration (water, oil, particulate); pressure dew point ≤ 2 ℃ recommended; air quality classes are defined in the ISO 8573 series
If your plant air does not meet this standard, install a dedicated dryer and filter set at the cutting station. The payback from saved consumables is typically under one quarter.
Input power
- Confirm voltage and phase (commonly three-phase 380 V / 400 V / 415 V, 50/60 Hz; export machines must be built for the destination grid).
- Check that the upstream breaker and cable cross-section can handle the inrush current at arc initiation.
- Where the supply is unstable, add a voltage stabiliser.
6. Torch, Cable Length and CNC Integration
- Torch type — hand torches suit maintenance and site work; machine torches are designed for CNC tables, with better cooling and repeatable positioning.
- Cable length — longer leads drop arc voltage and cut capacity. Above roughly 7–10 m of extra length, move up one power rating or choose a model with voltage compensation.
- THC interface — CNC cutting requires torch height control for initial height sensing and arc-voltage tracking. It is essential for edge squareness and torch life.
- Arc starting method — non-HF starting, as used in the non-HF plasma cutting machines, avoids interference with CNC electronics and is the preferred choice for automated lines.
- Nesting and programming — StarCAM nesting software generates common-line cutting, bridges and lead-ins automatically, typically improving material yield by 5–15%.
7. Frequently Asked Questions
Can one machine cut both thin and thick plate?
Yes, within limits. Low current on thick plate is painfully slow, and high current on thin sheet burns the edge. Size for your dominant thickness and adapt current, speed and torch height for the extremes.
Why does my machine not reach the datasheet thickness?
In order of likelihood: insufficient air pressure or flow, water or oil in the supply, worn electrode and nozzle, low input voltage, or excessive torch cable length causing voltage drop. Work through that list first.
Air plasma or high-precision plasma?
For carbon steel plate cutting, air plasma gives the best value. For stainless and aluminium, or where edge quality is critical, specify a high-precision plasma system running nitrogen or an argon-hydrogen mix.
What generator size do I need for site work?
Size the generator at 1.5–2 times the machine's rated input power so it can absorb the arc-starting surge.
Final Word
Sizing a plasma cutter means translating four variables — thickness distribution, daily operating hours, material mix and automation level — into four specifications: rated current, duty cycle, air supply and torch type. Work through them in that order and the result is rarely far off.
For a sizing proposal and trial-cut report on your own material, contact the Icyrobot engineering team with your thickness distribution, material grades and monthly output. We will return a configuration and quotation.
