In short: A waterjet cutter is a CNC machine that cuts by forcing water through a tiny jewel orifice at very high pressure, usually with garnet grit fed into the stream so it can wear through metal, stone and glass. Since the material is eroded away rather than melted, the edge carries no heat-affected zone, and almost any flat stock can go on the table. Plain water with no grit is enough for soft materials such as foam, rubber, gasket sheet and food.
What you give up is time. A waterjet grinds its way through the part, so on the thin and medium steel sheet that most fabrication shops cut every day, it runs far slower than a fiber laser and costs more per hour to keep running. Knowing where each one earns its keep is most of the buying decision.
How a Waterjet Cutter Works
Everything starts at the pump. An intensifier pump, or on some machines a direct-drive pump, raises filtered tap water to a pressure commonly somewhere between 40,000 and 90,000 psi and sends it through thick-walled tubing to the cutting head.
Inside the head, the water passes through an orifice made of sapphire, ruby or diamond, a hole only a few tenths of a millimeter across. Pressure turns into speed there, and the stream leaves the orifice faster than sound. On an abrasive machine the jet then runs through a mixing chamber that draws in garnet, and on down a long carbide focusing tube that lines the particles up into a tight cutting stream.
The head rides on a CNC gantry above a tank of water. Once the jet is through the part, the tank catches what is left of it, slowing the stream and collecting spent garnet and cut material. The water also keeps the noise and the splash down.
Pure Water and Abrasive Cutting
Pure waterjet
Without abrasive, the stream is fine enough to slice soft, low-density materials: foam, rubber, gasket stock, paper, textiles, thin plastics and food. Parts come away with almost no force on them, which matters for soft goods that would tear or squash under a blade.
Abrasive waterjet
Feeding garnet into the jet turns it into a very fine saw made of moving grit, and this is what most metal shops mean when they talk about a waterjet. It cuts steel, stainless, aluminum, titanium, copper, stone, tile, glass and composites. The garnet is used once and ends up as sludge in the tank, so it is a running cost on every job, along with the wear parts in the head.
Most machines switch between the two simply by turning the abrasive feed on or off.
What a Waterjet Does Well
The cold cut is the headline. With no heat, there is no hardened edge, no discoloration and no change to the metal’s properties beside the cut, which is why waterjets turn up in aerospace work on titanium and heat-treated alloys, and in tool shops cutting hardened plate.
Range is the other reason. Stone and porcelain countertops, glass, thick laminates, carbon fiber and rubber can all go on the same table. A job shop that sees a little of everything often keeps a waterjet precisely so it never has to turn a material away.
Thickness can go well past what a laser of similar cost handles, provided you accept that the cut slows sharply as the part gets thicker. Several thin sheets can also be stacked and cut in one pass.
Where Waterjets Fall Short
Speed on sheet metal is the big one. On thin carbon steel or stainless, a fiber laser finishes a nest in a fraction of the time, and the gap widens as parts get smaller and more detailed.
Taper shows up on thicker work. The jet loses energy on its way down through the material, so the bottom of the cut lags behind the top and the kerf narrows or drifts toward the exit side. Turn a thick part over and you can see it on the face: a smooth band near the top and curved striation lines sweeping back toward the bottom. Tilting heads can compensate, but slowing down is still the main fix. A laser leaves a much narrower kerf, and the way that gap shifts finished part size has its own explainer on laser kerf.
Wet parts are an everyday detail people forget. Carbon steel blanks lifted out of the tank begin to flash rust within hours if nobody dries them, and small parts can drop between the slats into the sludge. Shops that run a lot of small parts leave tabs on them or fit a finer support grid.
Then there is upkeep. Orifices, focusing tubes and the high-pressure seals in the pump wear out and get changed on a schedule, and the tank has to be dug out of spent garnet every so often. None of it is hard, but none of it is cutting time either.
Waterjet or Fiber Laser for Sheet Metal
If most of your work is steel, stainless or aluminum sheet and plate, the choice usually comes down to part volume and thickness range. The side-by-side comparison of laser, waterjet and plasma in our resources covers how the three processes differ; in metal, the waterjet keeps its cold edge and material range, while the fiber laser takes speed and cost per part. Plasma sits at the heavy, low-cost end; our piece on plasma arc temperature explains what that arc does to an edge.
Check thickness first. On our 3015 sheet metal laser cutting machine with a 3,000 W source, the maximum single-pass cut is 18 mm in carbon steel and 10 mm in stainless. That covers the bulk of what passes through a typical fabrication shop; if your parts regularly sit above it, the question becomes a higher-power source or sending only the heavy end to a waterjet.
Speed comes next. Across our exchange-table series the head travels at up to 60 m/min between cuts, and one sheet is loaded while the other is being cut. What that means on the floor is a machine that spends its shift cutting rather than waiting on the crane, which is where a laser pulls furthest ahead of a waterjet on sheet work.
Capacity at each power level is listed on our metal laser cutting machines page. Send us your material list, the thickest part you run and a sample drawing, and we will mark which of those parts a fiber laser cuts and which would sit better on another process. Tell us what you cut
Common Questions
Is a waterjet the same as a water jet cutting machine?
Yes, both names describe the same machine, and waterjet is simply the more common spelling.
What abrasive does a waterjet use?
Almost always garnet, a hard natural mineral graded to a consistent mesh size. It is hard enough to cut steel and cheap enough to use once, which is why it ends up as sludge in the tank after a single pass.
Does a waterjet leave a heat-affected zone?
No. The cut is mechanical erosion, so the material beside the edge keeps its original hardness and structure.
Is a waterjet faster than a laser cutter?
On thin and medium sheet metal, no; a fiber laser is many times faster there. The gap narrows as material gets thicker, and on stone or glass a laser is not an option at all.
How do I reduce taper on waterjet-cut parts?
Slow the feed on thick sections, keep the nozzle at the correct standoff above the material and replace a worn focusing tube, since a worn tube widens the jet. If the machine has a tilting head, switch on its taper compensation for parts that need tight dimensions on both faces.
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- Tell us what you cut, the thickest part you run and a sample drawing.
