What is kerf in laser cutting, and how wide is it?
Updated:
Short answer
Kerf is the width of material the beam actually removes — narrower than a saw cut but not zero. On a 3–6 kW fiber it typically runs 0.1–0.3 mm on thin sheet and grows to 0.4–0.6 mm past 10 mm, driven mostly by nozzle diameter, focus and cutting gas.
What changes kerf width
| Symptom | Likely cause | First action |
|---|---|---|
| Parts come out slightly oversized or undersized versus the DXF. | Kerf not compensated in the nesting/CAM software. | Offset the toolpath by half the kerf width — inward for internal cuts, outward for the outer contour. |
| Kerf wider on one side of the contour than the other. | Nozzle not centred on the beam. | Re-centre the nozzle; a 0.1 mm offset already skews the jet and widens one side. |
| Kerf grows noticeably as thickness increases. | Normal — thicker material needs a wider jet to clear the melt. | Use the kerf value from the thickness table, not a flat number across all thicknesses. |
| Kerf wider than the table predicts on the same settings. | Larger nozzle diameter or higher gas pressure than needed. | Step down nozzle size or pressure until edge quality is still clean. |
Kerf width by material and thickness is in the cutting table — inside the app. Open SBM Laser Help →
Or take it with you:
How to measure kerf
- Cut a straight test line at production settings.
- Measure the slot width with calipers at the midpoint, not the top — the top of the kerf is always wider than mid-depth.
- Compare against the program’s expected line width; the difference is what to compensate in CAM.
Kerf width by thickness (6 kW fiber)
| Thickness | Nozzle | Stainless (N2) | Mild steel (O2) |
|---|---|---|---|
| 1 mm | 1.4–1.5 mm double | 0.12–0.18 mm | 0.15–0.20 mm |
| 3 mm | 2.0 mm double | 0.18–0.25 mm | 0.20–0.28 mm |
| 6 mm | 2.0–2.5 mm double | 0.25–0.35 mm | 0.30–0.40 mm |
| 10 mm | 2.5–3.0 mm double | 0.35–0.45 mm | 0.40–0.50 mm |
| 20 mm | — | — | 0.50–0.65 mm |
Measured at mid-thickness; kerf at the top surface runs 20–40% wider than these values.
Related questions
- Does kerf change if I run the machine faster?
- Slightly — kerf narrows a little at higher speed because less material has time to melt sideways, but the effect is small next to nozzle and gas changes.
- Do I need to compensate kerf for laser-cut DXF files?
- For interlocking or press-fit parts, yes. For most brackets and panels a millimetre either way does not matter and compensation is skipped.
- Is kerf the same as the heat-affected zone?
- No. Kerf is the material physically removed; the heat-affected zone is the narrow band next to it whose metallurgy changed from the heat, without being removed.