By Pro Steel Solutions, plasma cutting in Ash, Kent. Updated
The short answer
Plasma is the most economical way to cut steel plate from about 3 mm upward, and the only one of the three that stays quick on thick plate. Laser is the choice for thin sheet and fine detail. Waterjet cuts almost any material without heat, but slowly and at a higher price.
For structural plates, brackets, gussets, flanges and most fabrication parts, plasma gives the best value. For cosmetic parts in thin sheet, or holes smaller than the plate thickness, laser is better. For materials that must not be heated, such as some composites, stone or glass, waterjet is the only one of the three that works.
How each process cuts
Plasma cutting forces an electric arc through a narrow nozzle with compressed gas. The arc melts the metal and the gas blows it away. It only cuts metals that conduct electricity.
Laser cutting focuses a high-power beam to a small spot that melts or vaporises the material. Fibre lasers are very fast on thin steel, stainless and aluminium, and slow down sharply as the plate gets thicker.
Waterjet cutting uses water at very high pressure, usually with an abrasive garnet, to erode the material. There is no heat, so there is no hardened or tinted edge.
Thickness
We plasma cut mild steel up to 50 mm thick, and stainless and aluminium are best up to about 25 mm. Laser cutting is most cost-effective up to about 10 to 20 mm, depending on the machine. Waterjet can cut very thick material, but the cutting speed drops as thickness rises.
Accuracy and edge finish
A typical plasma tolerance on a profile is about ±1 mm, with a slight bevel on the edge. Laser cutting typically holds about ±0.1 to 0.2 mm with a near-square edge. Waterjet is similar to laser on accuracy, with a fine sanded edge and a slight taper on thick material.
If a part needs a fitted bore, a machined face or a tolerance tighter than plasma gives, a common route is to plasma cut the blank and machine only the faces that matter.
Holes
On plasma, the smallest clean hole is about the plate thickness and never under 3 mm. Smaller holes come out tapered, so we mark them for drilling instead. Laser cuts smaller holes cleanly in thin material. Waterjet holes are limited by the jet and taper, not by heat.
Cost
Plasma machines are the cheapest of the three to buy and run, and the fastest on medium and thick plate, so it is usually the cheapest way to cut steel parts from 6 mm upward. Laser is often cheapest for thin sheet in large quantities. Waterjet is usually the most expensive per part because it cuts slowly.
Questions
Is plasma cutting accurate enough for base plates?
Yes. Base plates, fin plates and gussets are well within plasma tolerance; bolt holes from about the plate thickness upward are cut in place.
Do you offer laser or waterjet cutting?
No. We cut with plasma in our own workshop and will tell you if a part would be better laser cut or machined.
Related tools and guides
- Plasma tolerance guide What plasma holds, what needs drilling or machining, and a quick checker.
- Kerf and smallest hole Kerf width, cut speed, amperage and the smallest clean hole for any material and thickness.
- Material comparison Compare density, thickness range, cut speed and cost per square metre side by side.
- How to prepare drawings for plasma cutting
- Plasma cutting tolerances and minimum hole sizes
- How plasma cutting is priced, and how to pay less