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Home / All / Sheet Metal Fabrication / How accurate is laser cutting for custom sheet metal parts and what tolerances can I expect?
How accurate is laser cutting for custom sheet metal parts and what tolerances can I expect?
The short answer
Industrial fiber laser cutting holds about ±0.1 mm on sheet under 3 mm, ±0.15 to 0.2 mm on 3 to 10 mm plate and ±0.3 to 0.5 mm on plate over 10 mm, with repeatability near ±0.05 mm across a run. Kerf is 0.1 to 0.3 mm. Bending and welding then add their own error.
Accuracy and repeatability are two different numbers
Laser cutting tolerances get misquoted because two different measurements are both called accuracy. Positioning accuracy is how close the machine brings the head to where the program says the feature should be: a machine specification, usually quoted between about 0.03 and 0.05 mm on a well-built fiber machine. Repeatability is how closely the thousandth part matches the first: also typically 0.02 to 0.05 mm, and it is often the more useful figure for a production order, since a part that is consistently 0.04 mm off can be planned around while a part that wanders cannot.
Neither figure is the tolerance on your part, and that gap is where most disagreements start. The tolerance on a laser-cut part is the combined effect of positioning accuracy, repeatability, the kerf and the way the machine compensates for it, the material condition, and the thermal load the cut puts into the sheet. Machine specification is the floor, not the promise.
Tolerance by thickness
Thickness is the input that widens the band fastest, because a thicker section needs more energy, produces a wider kerf and loses rigidity as the cut progresses. Published practical figures for fiber laser cutting run at about plus or minus 0.1 mm on sheet under 3 mm, plus or minus 0.15 to 0.2 mm on 3 to 10 mm plate, and plus or minus 0.3 to 0.5 mm on plate from 10 to 25 mm. Those bands apply to flat parts measured in the plane of the sheet; they do not describe what happens after forming.
Kerf, and the parts of the drawing it constrains
Kerf is the width of material the beam removes, and it is a design input rather than a scrap figure. On fiber laser work it typically sits between 0.1 and 0.3 mm depending on thickness, lens and assist gas, and because the kerf is paid for on every contour it also drives how tightly parts can be nested on a sheet. Two consequences matter to a designer. First, an internal cut cannot be smaller than the kerf itself, and in practice a hole is usually specified at around one times the material thickness as a working minimum for a clean result. Second, a narrow kerf means tighter part-to-part spacing is possible, which changes the material yield on a high-volume nest rather than the accuracy of an individual part.
Cut edge quality
The cut edge is not uniform through the thickness: it usually shows a slightly rounded top edge, a smooth middle section, and a bottom edge that can carry dross on thicker material. Published figures put the cut edge between roughly Ra 3 and Ra 12 micrometres on thin sheet cut with nitrogen assist, rising toward Ra 25 micrometres on thick plate cut with oxygen, where the exothermic reaction speeds the cut but leaves a rougher face. Thermal cut quality is classified by ranges in ISO 9013, and a well-tuned fiber laser on thin carbon steel can reach the top range, which is why laser-cut edges frequently go straight to assembly without grinding or deburring.
The choice of assist gas is the practical lever here. Nitrogen produces a clean, oxide-free edge on stainless, which matters if the part will be welded or passivated; oxygen cuts faster on carbon steel and leaves an oxide edge that is usually acceptable for parts that will be painted or welded after cleaning. Asking which gas and which edge quality were used explains most of the price difference between two quotes for the same part.
What actually moves the tolerance
Six factors account for most of the variation between a good cut and a marginal one, and only the first is on the machine's specification sheet. Focus position and beam quality set the kerf width and the roughness of the edge. Assist gas choice and pressure change both cutting speed and edge chemistry. Material condition matters more than buyers expect: rust, mill scale, oil and coatings all change how the beam couples to the surface, and a change of supplier can move the result without anything else changing. Thermal load is the reason small, closely nested parts distort while large ones do not, because heat accumulates faster than the sheet can dissipate it. Machine rigidity is what holds the specification over time, since a light gantry will drift within months of production use even if its new-machine figure was good. And the condition of the support, slats or brush table, determines whether the sheet is flat at the moment of cutting.
The error added after cutting
The most expensive misunderstanding in laser-cut sheet metal is treating the laser tolerance as the tolerance of the finished part. Forming and joining add their own error on top. A typical press-brake operation holds the bend angle to about plus or minus 1 degree in air bending, which on a 100 mm flange is roughly 1.7 mm of movement at the far edge. A welded assembly conventionally holds plus or minus 0.5 to 1 mm on overall dimensions, because the heat that joins the parts also moves them. So a part specified as plus or minus 0.1 mm laser-cut can still finish at plus or minus 1 mm if two bends and a weld sit between the blank and the finished assembly.
The practical consequence is to place the tolerance where it is functional. Features that locate the part should be laser-cut and controlled at the cut; features that end up positioned by forming should carry a realistic formed tolerance rather than an inherited one. Where a bent or welded assembly genuinely needs a tighter final dimension than forming can hold, the honest route is a machining operation after forming, or a fixture that locates from a cut datum rather than from a formed edge.
How to specify a laser-cut part
Six items let a supplier quote and hold the right tolerance. State the material grade and the actual thickness. State which features are functional datums and which are cosmetic, because the two do not deserve the same tolerance. Give the tolerance on the cut profile separately from the tolerance on formed or assembled dimensions. Name the edge requirement, whether an as-cut edge is acceptable or whether the part will be welded or passivated and needs a nitrogen-cut edge. State the finish required after cutting, so deburring or tumbling is quoted rather than found later. And say what the parts are for, because a bracket and a visible cover panel justify very different amounts of inspection.
See sheet metal fabrication for how cutting sits in the process chain, laser cutting for the cutting service in detail, and CNC machining for the post-processing route when a feature needs to hold tighter than thermal cutting can promise.
Scope and sources. The distinction between positioning accuracy and repeatability, the machine-level figures of about 0.03 to 0.05 mm positioning and 0.02 to 0.05 mm repeatability, the kerf range of 0.1 to 0.3 mm, the surface finish of Ra 3.2 to 12.5 micrometres with ISO 9013 range classification, the minimum hole diameter of about one times material thickness, and the advice to judge a machine on frame and drive design rather than laser specification alone come from a fiber laser cutting reference and from a fiber laser machine overview (positioning accuracy around 0.05 mm, repeatability 0.02 to 0.03 mm depending on the drive system and machine bed, kerf typically 0.1 to 0.3 mm depending on thickness, focal lens and assist gas, and maximum cutting thickness around 25 mm on stainless and beyond 30 mm on carbon steel at higher power). The thickness-banded tolerance figures of about 0.1 mm below 3 mm, 0.15 to 0.2 mm on 3 to 10 mm, and 0.3 to 0.5 mm above 10 mm, the kerf bands, the three-zone description of the cut edge with a rounded top, smooth middle and possible bottom dross, the edge roughness bands of roughly Ra 6 to 12 micrometres on thin material cut with nitrogen and Ra 12 to 25 micrometres on thick material cut with oxygen, the note that bending adds about 0.5 degrees and welded assemblies about 0.5 to 1 mm, and the factors affecting accuracy including beam quality, focus position, assist gas, material condition, thermal effects and machine calibration come from a laser cutting accuracy reference. The comparison with plasma, waterjet and other cutting methods, and the note that a tight laser tolerance does not survive forming and joining unchanged, come from the same reference and from a cutting technology comparison. These figures are published practical ranges for fiber laser cutting rather than a specification for any particular machine; confirm them on your material, thickness and edge requirement.
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