Cardboard laser kerf compensation
Compensate for laser kerf in cardboard by offsetting every cut line by half the measured kerf (k ÷ 2): outward on part outlines, inward on holes and slots. Kerf depends on the machine, lens, focus and speed, so measure it on your own CO2 laser with a test strip rather than using a published figure.
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| Step | Formula | Example |
|---|---|---|
| Cut a strip of squares sharing edges | n = 10, s = 10 mm | 100 mm drawn |
| Lay the pieces together and measure | L | 98.5 mm (example input) |
| Kerf | k = (n × s − L) ÷ n | (100 − 98.5) ÷ 10 = 0.15 mm |
| Offset per side | k ÷ 2 | 0.08 mm |
| Measured kerf k | Offset k/2 | Slot as drawn (cuts to) | Press fit: draw slot | Sliding fit: draw slot |
|---|---|---|---|---|
| 0.10 mm | 0.05 mm | 3 mm (3.10 mm) | 2.85 mm | 3.00 mm |
| 0.15 mm | 0.08 mm | 3 mm (3.15 mm) | 2.80 mm | 2.95 mm |
| 0.20 mm | 0.10 mm | 3 mm (3.20 mm) | 2.75 mm | 2.90 mm |
| 0.25 mm | 0.13 mm | 3 mm (3.25 mm) | 2.70 mm | 2.85 mm |
| 0.30 mm | 0.15 mm | 3 mm (3.30 mm) | 2.65 mm | 2.80 mm |
Practical notes
Kerf is the width of material the beam removes. Without compensation every outline comes out k/2 small on each side and every hole k/2 large, so a part drawn at 50.00 mm is cut at 50.00 − k and a hole drawn at 6.00 mm is cut at 6.00 + k.
The table assumes a press fit with 0.05 mm interference and a sliding fit with 0.10 mm clearance, as starting points only. Sheet thickness also varies (plywood and acrylic sold as 3 mm are often a few tenths off), so measure the actual sheet with calipers and cut a test joint before a full job.
Corrugated board crushes under calipers, so measure kerf on the test pieces with light pressure or against a square. Flutes run one way; cut test pieces in both directions.
Cardboard ignites easily. Use low power with more passes if needed and stay with the machine.
FAQ
How do I compensate for laser kerf in cardboard?
Measure the kerf k on your machine, then offset every cut line by k ÷ 2: outward on outlines and inward on holes and slots. Most CAM and laser software (LightBurn, RDWorks, Inkscape path offset) can apply the offset.
How do I measure laser kerf?
Cut a row of n squares of side s sharing their edges, lay the pieces together and measure the total length L. Kerf k = (n × s − L) ÷ n. Example input: 10 squares of 10 mm measuring 98.5 mm give k = 0.15 mm.
What size should I draw a slot for a 3 mm cardboard press fit?
Draw the slot at the tab thickness minus the kerf minus a little interference, e.g. 3 − k − 0.05 mm, then cut a test joint. With an example measured kerf of 0.15 mm that is 2.80 mm.
Is kerf the same on every laser?
No. It changes with laser type (CO2 or fibre), lens focal length, focus height, power, speed and material thickness, so a figure from someone else's machine is only a rough guide. Re-measure when any of these change.
Sources: Kerf compensation formulas (geometry: offset = k/2) · Laser safety: ANSI Z136.1 / IEC 60825-1; material fume guidance from laser manufacturers' material lists
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