Laser-cut boxes tight one way, loose the other? Kerf on diode lasers

Updated 2026-10-23

Kerf is the width of material the beam burns away. Box generators add half the kerf to each edge so the joints fit. Most use one kerf value, which assumes a round spot.

Diode laser spots are usually rectangular or oval, so the cut is wider along one axis. With a single kerf, joints along one axis are tight and along the other loose.

Measure kerf per axis

1. Cut a row of 10 squares of 10 mm side by side, once along X and once along Y.
2. Push the pieces together and measure the total length with calipers.
3. Kerf = (100 mm − measured) ÷ 10, separately for X and Y.

Then compensate each axis separately, and measure material thickness with calipers rather than trusting the label. Kerf compensation won't fix loose belts or an out-of-square machine.

A tool that helps

Laser Box Generator: Finger-joint box generator with separate X and Y kerf for diode lasers. LightBurn-ready SVG, works offline. ($9). Free alternative: the steps above work by hand too.