Key Takeaways

• Kerf is the width of material removed by the laser beam during cutting — typically 0.1mm to 0.3mm.
• Fibre lasers cutting thin steel have a kerf of around 0.1–0.15mm; thicker material and CO₂ lasers produce wider kerfs.
• For most parts, kerf is automatically compensated by the cutting software. For precision fit parts, design kerf into your DXF.
• Internal holes come out slightly larger than drawn; external profiles come out slightly smaller.

What is Kerf in Laser Cutting?

Kerf is the width of material that the laser beam removes as it cuts through a sheet. It is determined by the focused beam diameter, the assist gas pressure, and the cutting speed relative to the material being cut. Understanding kerf is essential for any application where parts must fit together precisely.

Typical Kerf Widths

Kerf width varies by laser type, material, and thickness:

• Mild steel 1–3mm (fibre laser): 0.1–0.15mm
• Mild steel 6–12mm (fibre laser): 0.2–0.3mm
• Stainless steel 1–3mm (fibre laser, nitrogen assist): 0.1–0.2mm
• Aluminium 1–3mm (fibre laser): 0.15–0.2mm

How Kerf Affects Your Parts

The laser cuts on a path, removing material centred on that line. This means:

• External profiles (the outline of your part) will be half the kerf width smaller on each edge than your drawn geometry.
• Internal holes and cutouts will be half the kerf width larger than your drawn geometry.

For a 100mm square part cut with a 0.2mm kerf, the actual part measures 99.9mm × 99.9mm. For most mechanical parts, this is within acceptable tolerance. For precision assemblies, you need to account for it.

Kerf Compensation for Press-Fit Assemblies

Laser-cut tabs and slots that must press-fit together require kerf compensation in the DXF:

• Draw tab widths 0.1mm wider than the target assembled gap
• Draw slot widths 0.1mm narrower than the target assembled gap

This produces an interference fit of ~0.05mm per side after cutting — enough for a firm press fit without deformation.

Always prototype a test piece when designing press-fit joints. Material hardness, surface finish, and exact kerf on the day of cutting all affect the result.

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