If you are sizing slots, holes, or mating features for a sheet metal part, you need two numbers from your fabricator before you finalize the drawing: the cutting tolerance they can hold, and the kerf width their laser removes. Most shops publish a single vague figure — or hide it behind a download. This page gives you the full breakdown by material and by thickness, so you can design with real numbers and know whether a shop can hold your spec before you send the file.
Tolerance vs. kerf: what each one means
These two terms get confused constantly, so let’s separate them clearly.
- Cutting tolerance is how far a finished dimension can deviate from your nominal drawing value. A tolerance of ±0.1mm on a 50mm edge means the part will measure between 49.9mm and 50.1mm.
- Kerf is the width of material the laser beam vaporizes as it cuts — the slot the beam leaves behind. On a fiber laser, kerf is typically 0.1–0.5mm depending on thickness and assist gas.
Why both matter for your design:
- Kerf affects internal vs. external features. A good shop offsets the toolpath to compensate for kerf, so your outside dimensions and hole diameters come out on-nominal. But on very small features — thin webs, narrow slots, sharp internal corners — kerf sets the hard minimum of what is physically cuttable.
- Tolerance affects fit. Press-fits, bearing bores, and parts that bolt to a mating assembly need a tolerance you can actually achieve. Asking for ±0.05mm on 16mm steel is not realistic on any laser — knowing the real number up front saves a failed first article.
Standard vs. tight tolerance
| Tolerance class | Value | When to use it |
|---|---|---|
| Standard (default) | ±0.15mm | General brackets, enclosures, weldments, most parts |
| Tight | ±0.1mm | Holes for fasteners, mating edges, parts that locate against each other |
| Fiber laser floor | ±0.05mm | Thin material (≤3mm), small precision parts — confirm per feature |
Anything tighter than the laser floor needs a secondary operation — reaming, machining, or grinding after cutting. Tell us up front and we’ll quote it.
Tolerance & kerf chart by material and thickness
This is the reference table. Values are for our 6kW fiber laser cutting flat parts; tolerance is the general cut tolerance on a single dimension. Our laser cuts mild steel to 25mm, stainless to 12mm, and aluminum to 10mm. Thicker material and oxygen-assist cutting widen both tolerance and kerf.
Mild steel (CT3 / SS400 / S235)
| Thickness | Cut tolerance | Typical kerf | Assist gas |
|---|---|---|---|
| 0.5 – 1mm | ±0.1mm | 0.10 – 0.15mm | N₂ / Air |
| 2 – 3mm | ±0.1mm | 0.15 – 0.20mm | N₂ / O₂ |
| 5mm | ±0.15mm | 0.20 – 0.30mm | O₂ |
| 8mm | ±0.15mm | 0.30 – 0.40mm | O₂ |
| 10 – 12mm | ±0.2mm | 0.40 – 0.50mm | O₂ |
| 16mm | ±0.3mm | 0.50 – 0.65mm | O₂ |
| 20mm | ±0.3mm | 0.65 – 0.80mm | O₂ |
| 25mm | ±0.5mm | 0.80 – 0.95mm | O₂ |
Stainless steel (304 / 316)
| Thickness | Cut tolerance | Typical kerf | Assist gas |
|---|---|---|---|
| 0.5 – 1mm | ±0.1mm | 0.10 – 0.15mm | N₂ |
| 2 – 3mm | ±0.1mm | 0.15 – 0.25mm | N₂ |
| 5 – 6mm | ±0.15mm | 0.25 – 0.35mm | N₂ |
| 8mm | ±0.2mm | 0.35 – 0.45mm | N₂ |
| 10 – 12mm | ±0.2mm | 0.45 – 0.55mm | N₂ |
Stainless is cut with nitrogen for a clean, oxide-free edge that needs no grinding before welding or finishing. Above ~12mm the edge quality drops — ask us before designing thick stainless parts.
Aluminum (5052 / 6061)
| Thickness | Cut tolerance | Typical kerf | Assist gas |
|---|---|---|---|
| 0.5 – 1mm | ±0.1mm | 0.10 – 0.15mm | N₂ |
| 2 – 3mm | ±0.15mm | 0.18 – 0.28mm | N₂ |
| 5 – 6mm | ±0.15mm | 0.28 – 0.40mm | N₂ |
| 8 – 10mm | ±0.2mm | 0.40 – 0.55mm | N₂ |
Aluminum is reflective and conducts heat fast, so kerf runs slightly wider than steel at the same thickness. Hold tight tolerances on aluminum ≤3mm only.
Quick rule: every time you double the thickness, expect tolerance and kerf to roughly double as well.
Minimum feature rules (so your part is actually cuttable)
Kerf and beam diameter set hard limits on small features. Keep your design above these and the laser will hold quality; go below them and edges round over, slots close up, or thin webs melt.
| Feature | Minimum rule |
|---|---|
| Hole diameter | ≥ material thickness (min 1mm) |
| Hole / slot to edge | ≥ 1.5× thickness (or ≥ 1× hole diameter, whichever is larger) |
| Hole to hole spacing | ≥ 2× thickness, center to center |
| Slot width | ≥ 1.5× the slot’s own width from any edge |
| Web / bridge between cuts | ≥ 50% of thickness (1–1.5× preferred) |
| Internal corner radius | ≥ 0.5mm (sharp internal corners are not cuttable) |
These come straight from the same physics as kerf — the beam needs room to turn and the material needs enough mass to stay flat and not overheat.
When the laser can’t hold your tolerance
Reach for a secondary process when:
- You need tighter than ±0.05mm, or a true bore/bearing fit → machining or reaming after cut.
- Thickness exceeds the clean-edge range (steel >20mm, stainless >12mm) → waterjet holds a squarer edge with no heat-affected zone.
- The edge must be square with zero taper on thick plate → waterjet or machining.
We run all of these in-house, so a part that mixes laser-cut features with one machined bore comes back as one job, not three suppliers.
How to specify tolerance on your drawing
To get an accurate quote on the first pass, send a 2D DXF with:
- A default tolerance in the title block (e.g. “General tol. ±0.15mm unless noted”).
- Tight features called out individually — only tolerance what truly needs it. Over-tolerancing every dimension inflates the price.
- Separate layers for CUT, BEND, and MARK.
- Material grade and thickness stated explicitly (material + thickness is the single most important input on any fab quote).
FAQ
What tolerance can a fiber laser hold? Standard is ±0.15mm; tight features down to ±0.1mm, and ±0.05mm on thin material. Below that you need a secondary machining step.
What is laser kerf width? The width of material the beam removes — roughly 0.1mm on thin sheet up to ~0.8–0.95mm on 25mm steel cut with oxygen. We offset the toolpath so your nominal dimensions come out correct.
Do I need to compensate for kerf in my DXF? No. Send nominal geometry and our CAM applies the kerf offset automatically. Just keep small features above the minimums in the table above.
Can you hold ±0.05mm? On thin material and specific features, yes — but call it out on the drawing so we can plan the process (and, if needed, a finishing pass) into the quote.
Get a quote with real tolerances
Upload your DXF and we’ll confirm the exact tolerance and kerf for your part and material — no guesswork. Request a quote or see transparent pricing.
