November 5, 2026 · Laser Cutting
Laser Cutting Tolerance: Kerf, ISO 2768 and Real Limits (2026)
A fiber laser holds about ±0.1 mm on 1-3 mm sheet and ±0.3 mm once you pass 12 mm plate. Kerf runs 0.15-0.3 mm on thin stock and widens to 0.4-0.5 mm on thick plate. Anything tighter than ±0.05 mm normally needs a second machining pass. Put those three numbers on your drawing before you ask anyone for a price.
What Tolerance Can a Laser Cutter Really Hold?
Machine accuracy and part tolerance are not the same thing. A 3kW fiber machine positions to about ±0.03 mm per metre and repeats within ±0.02 mm. Your finished part still lands at ±0.1 mm or wider.
The gap comes from the cut itself: kerf, heat, sheet flatness and how well the head tracks the surface. Anyone who quotes the positioning number as a part tolerance is selling, not engineering.
Here is what fabrication shops actually hold on mild steel, stainless and aluminum. These ranges come from shops that publish their own capability, checked against fiber laser cutting machine specs we quote in 2026.
| Material thickness | Mild steel | Stainless steel | Aluminum |
|---|---|---|---|
| 0.5-3 mm | ±0.10 mm | ±0.10 mm | ±0.13 mm |
| 3-6 mm | ±0.15 mm | ±0.15-0.20 mm | ±0.25 mm |
| 6-12 mm | ±0.25 mm | ±0.20 mm | ±0.40 mm |
| 12-25 mm | ±0.50 mm | ±0.30 mm | ±0.50 mm and up |
Thin stock is easy. Up to 3 mm, ±0.1 mm is normal and ±0.05 mm is possible on a machine with good optics and a clean lens.
Past 6 mm the beam has to work harder to keep the kerf clean. Above 12 mm, ±0.3 mm to ±0.5 mm is honest, and edge taper becomes visible around 10 mm. If your drawing asks ±0.1 mm on 20 mm plate, no laser will hold it cut after cut.
How Wide Is the Kerf, and Why It Moves Your Dimensions?
Kerf is the strip of metal the beam melts and blows away. Think of it like the blade thickness on a saw. It is not a line, and it does not disappear.
| Setup | Typical kerf | What it means for you |
|---|---|---|
| Fiber, 1 mm stainless | 0.15 mm | Fine detail work, tight slots |
| Fiber, 3 mm mild steel | 0.20 mm | Standard sheet metal range |
| Fiber, 6 mm mild steel | 0.25-0.30 mm | Structure parts, brackets |
| Fiber, 10 mm and above | 0.40 mm and up | Leave machining allowance |
| CO2, general metal | 0.20-0.50 mm | Wider and slower than fiber |
Good CAM software compensates automatically. The trouble starts when the DXF you sent is already compensated and the shop compensates again. Parts come out one kerf small and nobody notices until assembly day.
My habit is simple: send nominal geometry, and put a note on the drawing when the part has mating features. Something like "nominal kerf 0.20 mm, confirm compensation before cutting". Ten seconds of typing, one less rework.
ISO 2768: Pick a Class You Can Actually Hold
Most drawings we receive carry a title block note like "ISO 2768-m". That covers every dimension without its own tolerance, and the letter decides how tight the default is.
| Nominal size | f (fine) | m (medium) | c (coarse) |
|---|---|---|---|
| 0.5-3 mm | ±0.05 mm | ±0.10 mm | ±0.20 mm |
| 3-6 mm | ±0.05 mm | ±0.10 mm | ±0.30 mm |
| 6-30 mm | ±0.10 mm | ±0.20 mm | ±0.50 mm |
| 30-120 mm | ±0.15 mm | ±0.30 mm | ±0.80 mm |
| 120-400 mm | ±0.20 mm | ±0.50 mm | ±1.20 mm |
| 400-1000 mm | ±0.30 mm | ±0.80 mm | ±2.00 mm |
| 1000-2000 mm | ±0.50 mm | ±1.20 mm | ±3.00 mm |
The m class is the practical default for laser cut parts. It matches what a maintained fiber machine does on 6-30 mm features, and it does not force the shop to slow down and charge you for it.
The f class is where people get into trouble. On small features in thin sheet it is realistic. On a 1,500 mm long part in 10 mm plate, ±0.5 mm is a better promise than ±0.3 mm, because heat and residual stress do what they want.
For structural plate at the heavy end, c class is often the only honest note. Tighten the three or four dimensions that matter, and leave the rest alone.
ISO 9013: The Standard Nobody Puts on the Drawing
ISO 2768 controls size. ISO 9013:2017 controls the cut face itself, meaning squareness and roughness. Two numbers define each range: u for perpendicularity, taper included, and Rz5 for surface roughness.
| Range | Perpendicularity u | Roughness Rz5 | Where it lands |
|---|---|---|---|
| 1 | 0.05 + 0.003a mm | 10 + 0.6a µm | Fine cut, visible stainless edge |
| 2 | 0.15 + 0.007a mm | 40 + 0.8a µm | Normal production cut |
| 3 | 0.40 + 0.01a mm | 70 + 1.2a µm | Speed first, edge second |
| 4 | 0.80 + 0.02a mm | 110 + 1.8a µm | Rough separation cut |
Here a is the material thickness in millimetres. So on 6 mm plate, range 2 allows about 0.19 mm of perpendicularity deviation and roughly 45 µm Rz5.
Range 1 is slow and expensive. Range 2 is what most fiber machines deliver on 3-8 mm at normal speed. Range 3 and 4 are what you get when someone chases a price and pushes the feed.
If the part gets welded or powder coated, range 2 is plenty. If it is a visible edge on stainless, ask for range 1 and expect to pay for the extra time.
Where Laser Cutting Stops Being Accurate
Five things break tolerance faster than machine wear. I have seen every one of them blamed on the machine.
- Holes smaller than the material thickness. A 3 mm hole in 6 mm plate will not be round, and it will not hold ±0.1 mm. Rule of thumb: hole diameter at least 1:1 with thickness, 1.5:1 if you need a clean bore.
- Thick plate with a tight note. Heat builds, kerf widens, taper grows. Over 12 mm, plan a machining allowance instead of arguing later.
- Narrow slots. Below about 1.5 times kerf width the beam cannot clear dross, and the slot drifts off centre.
- Sharp internal corners. The beam has a radius. Add 0.3-0.5 mm corner radius or accept that the corner comes out rounded anyway.
- Bad nesting on stressed sheet. Cut a hot pattern into a stressed sheet and parts move after they drop free. Leave bridges or sequence the cut to balance heat.
How to Write a Drawing That Gets Quoted Right
- Title block: ISO 2768-m. Change it only if the part needs better.
- Tolerance the three to five critical dimensions individually. Leave the rest at the general note.
- Send nominal DXF and say that it is nominal.
- Write down the material grade and temper. 5052 H32 and 5052 O do not cut or move the same.
- Ask for a first-article inspection report with measured values, not a checkbox.
That last point matters more than the tolerance note. A supplier who measures and writes the numbers down will tell you when ±0.1 mm is not going to happen. One who stamps OK will ship it and let you find out at assembly.
Machine-side numbers such as positioning accuracy, repeatability and table size are on the laser cutting machine specification page.
When to Machine After Cutting
Laser cutting is fast and cheap per part down to about ±0.1 mm. Below that you are paying for a second operation whether you admit it or not.
Bearing seats, hydraulic mating faces, pin bores and anything with a press fit belong on a mill or a lathe. Common practice is to cut 0.3-0.5 mm oversize and machine to final size. Cheaper than fighting the laser.
If you are not sure which dimensions need it, send the drawing. We will mark the ones that will give you trouble and quote the machine side honestly. Start with the contact page.
Sources: HLH Sheet Metal, "Laser Cutting Tolerances: Drawing-Ready Rules for Designers" (August 2026); Kanyana Engineering, "A Practical Guide to Laser Cutting Tolerances" (May 2026); RivCut, "Laser Cutting Tolerances: Steel, Aluminum, Stainless" (March 2026); MNT Cutting, "Laser Cutting Tolerances: What You Can Actually Hold" (September 2026), citing ISO 9013:2017 and ISO 2768-1; TEPROSA, ISO 2768 tolerance tables. Ranges are typical shop capability, not a guarantee. Your material grade, machine condition and drawing geometry decide the final number, so confirm critical dimensions on a measured sample.
Frequently Asked Questions
What tolerance can a fiber laser cutting machine hold?
About ±0.1 mm on 0.5-3 mm sheet, ±0.15-0.25 mm at 3-12 mm, and ±0.3-0.5 mm above 12 mm. Those are part tolerances. The machine itself positions to roughly ±0.03 mm, but kerf, heat and sheet stress eat the difference. Current machine numbers are listed on the fiber laser cutting machine page.
How wide is the kerf on a fiber laser?
0.15 mm on 1 mm stainless, around 0.20 mm at 3 mm mild steel, 0.25-0.30 mm at 6 mm, and 0.40 mm or more on 10 mm plate and above. CO2 runs wider at 0.20-0.50 mm. If the shop compensates for kerf in CAM, your finished size comes out right. If nobody confirms the compensation, parts come out small by roughly one kerf.
Can laser cutting hold ±0.05 mm?
On thin sheet with small features, yes, and ISO 2768-f covers that case for dimensions under 30 mm. On thick plate or long parts, no, not repeatably. Below ±0.05 mm you are into machining. Plan a finishing pass rather than specifying a tolerance the process cannot deliver.
Which ISO 2768 class should I put on my drawing?
ISO 2768-m for most sheet metal work. Use f only where small thin features really need it, and c for thick structural plate where heat makes tight notes meaningless. Tolerance the critical dimensions individually and leave the general note at m. That keeps the quote realistic and the argument short.
Does thicker plate mean worse tolerance?
Yes. Kerf widens, taper becomes visible from about 10 mm, and the heat-affected zone grows. On fiber-cut mild steel the HAZ runs about 0.13-0.25 mm, on stainless 0.1-0.2 mm, on aluminum 0.2-0.4 mm. Above 12 mm, expect ±0.3 mm at best and plan machining for anything critical.
Related Articles
- Laser Cutting Defects: How to Fix Dross, Burrs and Taper
- Fiber Laser Cutting Speed and Thickness Chart by Power
- Assist Gas Guide: Nitrogen vs Oxygen vs Compressed Air
- How to Choose Laser Cutting Machine Power
- Stainless Steel Sheet Thickness Tolerance and Weight Verification
- Fiber Laser Cutting Machine ROI and Payback Period