Making & Fabrication
Cut This Tiny Test Before You Waste Another Sheet
A ten-minute kerf and joint test can prevent a whole laser-cut project from becoming expensive wooden confetti. Here is what to measure.
Your “3 mm” plywood is probably lying
A beautiful laser-cut box can fail for a deeply boring reason: the material is not exactly the thickness printed on the label, and the laser removes a little material everywhere it travels.
That removed width is the kerf. It changes with material, thickness, focus, power and speed. A joint designed from a value you copied from somebody else’s machine may slide together, need a hammer or simply fall apart while looking disappointed.
Laser MTS can generate a free kerf strip or joint-fit comb. You can download an SVG or LightBurn file without an account; an account is only needed to save results to its material library.
Measure the sheet before measuring the laser
Use callipers to check the actual material in several places. Plywood and cardboard can vary across one sheet. Acrylic is usually more consistent, but “usually” is not a measurement.
Then run two small tests on an offcut from the same sheet:
- A kerf strip with multiple cuts, so the removed material can be measured over several lines rather than guessed from one tiny gap.
- A joint comb with slightly different slot widths, so you can physically choose tight, sliding and loose fits.
Laser MTS explains its own strip as ten pieces with a measured gap divided by eleven cuts. Follow the geometry of the file you actually use; do not blindly divide every test by eleven because you once saw the number online.
Save the boring information
Write down the machine, material supplier, measured thickness, lens, focus method, power, speed and date. “Birch ply — worked good” is not a material record. It is a message from a past version of you who has chosen violence.
Kerf compensation also depends on which side of the path must keep its size. The machine removes material centred on the cut line, so external parts and internal holes do not want the same offset direction.
Try this first
Generate one joint comb for the material on your bench. Cut it, label the best slot and use that value for a tiny corner joint before cutting the full project.
This is not glamorous. Neither is turning a $40 sheet into six panels that refuse to meet.