Key takeaways
- The smallest reliable waterjet hole is about 1.2–1.5 times the material thickness; below that the jet lag closes the hole and the taper dominates.
- Taper runs 0.025–0.1 mm per 10 mm of thickness per side, so a 20 mm part can be 0.1–0.4 mm narrower at the bottom than the top.
- A 1,200 mm contour through 20 mm stainless at 100 mm/min takes 12 minutes and consumes about 4.2 kg of garnet; the same contour on a 12 kW laser takes 1.3 minutes.
- ISO 9013 classifies thermal cuts, so a waterjet edge cannot be inspected against it unless the drawing names the process and the equivalent limits explicitly.
- Waterjet earns its cost on pre-hardened steel, titanium, composites and plate above 20 mm, not on 2 mm sheet with small holes.
Related reading: the Aluminium sheet laser cutting: process, gas and edge quality and the Deburring and edge quality after laser cutting take the same problem further. See the process and inspection scope on the capability pages, or send the drawing through the RFQ route.
A waterjet will cut a 1,200 mm contour through 20 mm stainless in twelve minutes. A 12 kW fibre laser does the same contour in about one and a third minutes. Neither number says the laser is better, because the waterjet leaves an edge that has never been above room temperature and the laser leaves one that has.
Waterjet cutting limits are worth knowing in both directions. The process is the only honest answer for pre-hardened tool steel, titanium, composites and plate past the laser envelope. It is the wrong answer for a 2 mm bracket with forty 4 mm holes, and the price of getting that wrong is paid in machine hours and abrasive.
The limits are geometric first, economic second and metallurgical never. Nothing about a waterjet damages the material; what it does is remove features it cannot hold and time it cannot recover.
What are the hard limits of a waterjet cut?
Three numbers decide most parts: the minimum hole at 1.2–1.5 times the thickness, the taper at 0.025–0.1 mm per 10 mm of depth per side, and the feed rate, which falls roughly with the square of thickness on stainless.
The mechanism behind all three is jet lag. The jet exits the nozzle at 3,000–4,000 bar carrying garnet at 0.2–0.5 kg/min, and as it travels through the kerf it slows, spreads and bends backwards. The cutting front at the bottom of the part therefore trails the nozzle position at the top. On a straight cut the result is taper. On a contour, the trailing front rounds the corner and lags the programmed path on the exit side.
That is why tolerance and speed are the same variable. Running at half the feed rate lets the front catch up, which halves the taper and doubles the cutting time. A waterjet job with a tight tolerance is a slow waterjet job, and the quotation should show which one it is priced as.
The taper, in millimetres
At 6 mm thickness and a normal feed rate, taper is 0.015–0.06 mm per side. At 20 mm it is 0.05–0.2 mm per side. At 50 mm it can reach 0.3–0.5 mm per side, which on a 100 mm bore is a full millimetre of difference between entry and exit.
Taper matters where the part has a press fit, a bore that carries a pin, or two parts that must sit flush. It does not matter on a cover plate, a gusset or a blank that will be machined afterwards. A drawing that calls a general ±0.1 mm on a 40 mm waterjet part is asking for a four-hour cut rather than a forty-minute one, and it is cheaper to tolerance the entry face and note the taper.
Holes, slots and corners
A hole smaller than about 1.2 times the thickness cannot be cut to size because the jet has to complete a circle inside a kerf that is already 0.8–1.5 mm wide. The practical result is an oversized, tapered, out-of-position hole that fails a go/no-go gauge.
Slots behave the same way. A slot narrower than the kerf plus 0.2 mm cannot be cut at all, and a slot of 1.5 times the kerf width will be tapered enough to close at depth. Internal corners are radiused to at least half the kerf, typically 0.5–0.8 mm, because the jet cannot turn a square corner without leaving a rounded witness.
Waterjet cutting limits by feature and thickness
The values below are for abrasive waterjet on stainless and mild steel at production feed rates. The Ganesh column says what our plant can do instead, because a limit only matters if the alternative is in the building.
| Limit | 6 mm | 20 mm | 50 mm | Ganesh limit or note |
|---|---|---|---|---|
| Minimum hole diameter | 8–9 mm | 24–30 mm | 60–75 mm | Laser holds about 1 × thickness to 20 mm |
| Kerf width | 0.8–1.0 mm | 1.0–1.3 mm | 1.2–1.5 mm | Laser kerf 0.2–1.2 mm over the same range |
| Taper per side | 0.015–0.06 mm | 0.05–0.2 mm | 0.3–0.5 mm | Not applicable to a laser cut |
| Achievable tolerance | ±0.15 mm | ±0.2 mm | ±0.5 mm | ±0.5 mm typical overall, tighter by agreement |
| Feed rate, stainless | 600–900 mm/min | 90–130 mm/min | 30–50 mm/min | 12 kW laser: about 900 mm/min at 20 mm |
| Abrasive use | 0.2–0.3 kg/min | 0.3–0.4 kg/min | 0.4–0.5 kg/min | No abrasive on the laser route |
| Heat-affected zone | None | None | None | Laser leaves 0.05–0.5 mm |
| Internal corner radius | 0.4–0.5 mm | 0.5–0.7 mm | 0.6–0.8 mm | Laser corner radius follows the kerf |
| Maximum practical thickness | — | — | 100 mm and beyond | Laser stops at 20 mm plate |
| Stack cutting | 5–10 sheets | Not practical | Not practical | Laser cuts one sheet at a time |
Two rows carry the decision. The minimum hole row ends most thin-sheet enquiries, because a 6 mm plate with a 5 mm hole is a drilling job whatever the cutting process. The maximum thickness row is the reason a waterjet exists at all in a fabrication shop: past 20 mm, the laser has nothing to offer and the choice becomes waterjet, plasma or oxy-fuel.
Where the cold edge pays for the taper
Waterjet earns its place on four material groups, and on each of them the taper is a price worth paying.
Pre-hardened tool steel. A die block at 45–60 HRC cannot be cut thermally without drawing the temper at the cut edge, and the edge is the working surface. Waterjet leaves it at the hardness it arrived with.
Titanium. The metal reacts with oxygen at cutting temperature, and a laser cut on thick titanium needs inert assistance and still leaves an alpha case that has to be removed. Waterjet leaves nothing to remove.
Composites and laminates. A thermal cut chars the matrix and delaminates the edge. There is no laser setting that avoids it, and no amount of clamping helps.
Plate past the laser envelope. Above 20 mm on steel, or above roughly 20 mm on aluminium where reflectivity and conduction defeat the beam, waterjet or plasma is the route. Between those two, waterjet wins where squareness and the absence of heat matter, and plasma wins on speed and cost per metre.
A fifth case is quieter: a part that will be machined immediately after cutting. A cold, unoxidised edge is a better starting surface for a mill than a laser edge with a 0.3 mm recast layer, particularly on a part where the first machining pass is only 0.2 mm deep.
Piercing and the lead-in
A waterjet cannot start a cut in mid-air. In thick material the pierce is a stationary jet that drills through, and on 20 mm stainless that takes 10–30 seconds, longer on ceramics or pre-hardened steel. On a part with twenty holes, piercing alone is 4–10 minutes before any contour is cut.
The pierce also leaves a small crater wider than the kerf, so it belongs on a scrap edge or in a slug that will be removed anyway. A drawing that places a hole 1 mm from a finished edge leaves no room to pierce without marking the face.
Lead-in length matters more than on a laser, because the jet needs 3–5 mm of travel to reach a stable kerf width. Starting a cosmetic contour directly at the part edge produces a notch, and the notch is visible after coating.
What a waterjet contour actually costs
A waterjet quotation is built from machine time, and machine time is built from feed rate. The consumables run underneath it, and the two largest are abrasive and pump maintenance.
Take a 1,200 mm contour through 20 mm 316L at 100 mm/min. The cut takes 12 minutes. Garnet runs at about 0.35 kg/min, so the contour consumes 4.2 kg of abrasive and roughly 40 litres of water at 3–5 L/min. Fifty of those contours is 600 machine minutes, ten hours, and 210 kg of garnet, before the pump seals and the nozzle are counted.
The same fifty contours on a 12 kW laser at 900 mm/min take 1.33 minutes each, about 67 minutes in total, with no abrasive and a nozzle and lens that are replaced on a schedule counted in hours rather than kilograms.
That ratio is the honest case against waterjet on steel that a laser can cut. The honest case for it is a material the laser cannot touch, and there the comparison stops: the alternative is not a faster cut, it is no part.
Abrasive disposal is the cost line that never appears on a quotation. Spent garnet, mixed with metal fines from the kerf, is a waste stream that has to be dewatered and disposed of under the plant's authorisation. The mass is close to the abrasive purchased, so 210 kg of garnet becomes a similar mass of sludge, plus the water it holds.
What Ganesh runs instead
We do not operate an abrasive waterjet, and we say so rather than subcontract one quietly. Our cutting envelope is a 12 kW fibre laser on a 40 ft × 16 ft bed, with two 6 kW and two 3 kW support machines, cutting mild steel, CRCA, stainless, aluminium, brass and copper to 20 mm plate.
Above that, the iron worker shears and punches plate to 30–40 mm, which covers straight cuts and holes in thick material but not profiles. Between the two, the 12 kW laser holds hole position to about ±0.1–0.2 mm on thin sheet and ±0.5 mm on 10 mm plate, which is tighter than a waterjet holds on the same thickness at production speed.
The practical consequence is simple. A 30 mm stainless flange with a profiled outline is not a part we quote; a 30 mm bracket with straight edges, sheared and punched, is. The laser cutting capability page lists the envelope and the thickness bands, and custom parts shows the work that comes off the cut blanks.
Where a customer's design needs the cold edge, we will say so at review and point at the material rather than the machine. That is a shorter conversation than discovering it after the first article.
What to put on the drawing
- Material grade and thickness, with the standard it is bought to.
- The smallest hole and its position tolerance, because that decides whether the process can hold it at all.
- Whether a heat-affected zone is permitted, stated as yes or no rather than left to inference.
- Taper allowance on bores and mating faces: which faces are functional and which are not.
- The edge requirement as a roughness value plus a perpendicularity limit, not as a class from a thermal cutting standard.
- Whether the part may be stack cut, if the quantity is high and the thickness is under 3 mm.
Line three is the one that selects waterjet. Line five is the one that stops an inspection argument, because it gives the inspector a measurement rather than an adjective.
When waterjet is the wrong answer
Waterjet is slow, abrasive-hungry and geometrically limited, and on some parts that is disqualifying regardless of edge quality.
Thin sheet at volume. Below 3 mm, the laser is five to ten times faster and holds tighter features. A waterjet on 1.6 mm CRCA with fifty holes per part spends its advantage on traverse time.
Small holes and fine slots. Under 1.2 times the thickness, the hole will not hold size. Drilling after cutting is usually cheaper than cutting a hole the jet cannot make.
Parts that need a sharp internal corner. A waterjet corner is radiused to at least half the kerf. If the design needs a square corner for a bearing block, the corner is machined, and the cutting process does not matter.
High-tolerance fits on thick plate. At 50 mm, ±0.5 mm is the realistic limit and taper is 0.3–0.5 mm per side. A bearing bore at that thickness is bored after cutting, not cut to size.
None of this makes waterjet a poor process. It makes it a process with a narrow, well-defined job: cold, thick, hard or non-metallic. Send the drawing with the material, thickness and smallest hole to request a quote, and we will confirm whether it fits our envelope or needs a route we do not run. The laser cutting and fabrication hub covers the thickness, tolerance and nesting side of that envelope.
Frequently asked questions
What is the minimum hole size a waterjet can cut?
About 1.2–1.5 times the material thickness for a hole that holds its size and position. In 20 mm plate that means a 24–30 mm hole; a 5 mm hole will be cut, but it will be tapered, oversized at entry and often out of position. Drill holes below that ratio instead.
How accurate is abrasive waterjet cutting?
Typically ±0.2 mm on a production part, improving to ±0.1 mm on thinner sections at reduced speed. The limit is not the machine resolution but jet lag: the cutting front trails the nozzle, so the bottom of the kerf lags the top on every contour and the error grows with thickness and feed rate.
Does waterjet leave a heat-affected zone?
No. The cut is mechanical, so there is no oxide, no martensitic layer and no change in hardness at the edge. That is the reason to specify it on pre-hardened tool steel, titanium and parts that will be machined immediately after cutting.
Why is waterjet slow on thick plate?
Because the jet loses coherence as it travels through the material. A 20 mm stainless contour runs at about 100 mm/min and a 50 mm contour at 30–50 mm/min, against roughly 900 mm/min for a 12 kW laser on 20 mm. Slower passes also consume abrasive for longer, so time and consumables rise together.
Can waterjet cut stacked sheets?
Yes, and this is one of its real advantages on thin material. Several sheets can be clamped and cut as one stack, which amortises the slow traverse across the batch. The limit is stack height: above about 50 mm the taper and the clamping error show on the bottom sheet.
Sources and further reading
- ISO 9013:2017 — Thermal cutting: classification of thermal cuts, covering oxy-fuel, plasma and laser rather than abrasive waterjet · reviewed 3 Nov 2026
- ISO 2768-1 — General tolerances for linear and angular dimensions without individual tolerance indications · reviewed 3 Nov 2026
- Bureau of Indian Standards — IS 513 cold reduced carbon steel sheet, the substrate most sheet metal nests are cut from · reviewed 3 Nov 2026
Not sure whether your part needs a waterjet?
Send the drawing with material, thickness and the smallest hole. We will confirm whether the laser can hold it or whether the part belongs on a route we do not run.
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