1. What is Laser Kerf?
Laser cutting is a thermal vaporization process. The focused laser beam does not cut like a razor blade; instead, it instantly boils and vaporizes a slit of material. The width of this vaporized channel is called the Kerf ($K$).
Because the laser beam travels along the centerline of your vector stroke, half the kerf width ($\frac{K}{2}$) is removed from both sides of the cut line. Without software compensation, male finger tabs end up slightly too small, and female slots end up too large — resulting in loose, wobbly box joints.
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Instant vector finger joint layout with automatic kerf compensation and live 2D unfolded panel previews.
2. The Optical Physics of Beam Spot Size
Kerf width is determined by three main variables:
- Focal Length of the Lens: A 1.5-inch lens produces a tiny 0.08mm spot (ideal for fine engraving), while a 2.5-inch lens produces a 0.20mm spot with a deeper waist for thick wood cutting.
- Material Density & Vaporization Point: Porous Baltic birch plywood chars slightly wider (0.15mm–0.18mm) than dense cast acrylic (0.12mm–0.14mm).
- Air Assist Pressure: High-pressure coaxial air assist (25–30 PSI) cools the cut zone and narrows the burn kerf.
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3. How to Measure Exact Kerf with a 10-Piece Gauge
To determine your laser's exact kerf:
- Draw a 100mm × 20mm rectangle in LightBurn and divide it into 10 equal vertical 10mm strips.
- Cut the file using your standard power and speed settings.
- Push the 10 cut strips tightly together against one side of the frame.
- Measure the remaining empty gap width with digital calipers.
Kerf (K) = Measured Gap Width / 10. If the gap is 1.50mm, your exact kerf is 0.15mm.
4. Recommended Kerf Benchmarks
| Laser Machine Type | Material & Thickness | Focal Lens | Recommended Kerf ($K$) | Joint Fit |
|---|---|---|---|---|
| 50W–100W CO2 Laser | 3mm (1/8") Baltic Birch Plywood | 2.0" Standard | 0.15 mm (0.006 in) | Airtight Friction Press (No Glue) |
| 50W–100W CO2 Laser | 6mm (1/4") MDF / Draftboard | 2.0" Standard | 0.18 mm (0.007 in) | Firm Mallet Press |
| 40W–55W RF Tube (Glowforge) | 1/8" Cast Acrylic | Internal Precision | 0.14 mm (0.0055 in) | Snap Fit |
| 10W–20W Diode (xTool D1 Pro) | 3mm Basswood Ply | 0.08mm Fine Spot | 0.09 mm (0.0035 in) | Smooth Press Fit |
5. Applying Kerf Compensation in Parametric CAD
When generating interlocking box finger joints:
- Extend the outer boundary of all male tab fingers outward by
+ K / 2. - Contract the inner boundary of all female slots inward by
- K / 2. - Our Parametric Laser Box Studio executes this mathematical offset automatically in pure client-side JavaScript.
⚡ Instant Interactive Calculation Engines
Launch Dedicated Calculators for this Guide:
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⚡ CO2 Laser Tube Wear / Hour Quoter →
⚡ xTool D1 / F1 / P2 Job Quoter →
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6. Frequently Asked Questions
Can I use kerf-compensated SVGs directly in LightBurn?
Yes. The SVG vector paths generated by our studio are already offset for your specified kerf value. Simply import the SVG into LightBurn, set layer mode to 'Line / Cut', and do not apply secondary kerf offset inside LightBurn.