Laser Kerf Calculator and Test

Why kerf matters

A laser beam has width. Every cut removes a thin strip of material, so a 50 mm square comes out a fraction under 50 mm and a 50 mm hole a fraction over. On a sign you will never notice. On a finger joint, an inlay or a part that has to press onto a peg, that fraction decides whether it fits snugly, rattles or won’t go together at all.

Kerf compensation fixes it by moving each cut line outwards on parts and inwards on holes by half the kerf. To do that you need the real kerf of your laser in your material, and that is what this tool measures.

How the kerf test works

The Calibration Center makes its tests for your own machine and material from the details in My setup. Kerf is measured in the Size, square & kerf test, which includes a 20 mm coupon. You cut it, measure the coupon with calipers and type in what you measured. The app works out the kerf from the difference between the drawn size and the cut size and saves it to My setup, along with any scale or squareness correction the same test finds.

1. Open the Size, square & kerf test and choose the material and thickness you want to measure.
2. Cut the test with the settings you normally use for that material. Same focus, same air assist.
3. Measure the coupon with calipers, not a ruler.
4. Type the measurement into “Read my result”. The kerf is calculated and saved.

The quick bar method

If you prefer a manual check, the kerf gauge in Laser Test Cards cuts 10 bars side by side. Push the bars tightly together in their frame and measure the gap left at the end. Because the gap is made of 10 kerf widths, kerf = gap ÷ 10. The same card has a fit comb with slots at stepped offsets and peg holes at stepped sizes, so you can see directly which offset gives a press fit.

You measure	Kerf
Gap of 1.5 mm after 10 bars	0.15 mm
Gap of 2.0 mm after 10 bars	0.20 mm
Gap of 0.8 mm after 10 bars	0.08 mm

Using your kerf value

Enter the number in any studio that asks for it. In the box generator it makes finger joints snug. In Inlay & Kerf Offset it moves the pocket inward and the insert outward by half the kerf each, so the insert presses in without a gap. Fit is personal: if a joint is still too tight, reduce the value by 0.02 to 0.05 mm, and if it is loose, increase it.

More calibration tests

Kerf is one of several tests in the Calibration Center. Others check size and squareness, the offset between engrave and cut jobs (scan offset), the smallest readable text and holes, the useful power range for photos, depth per pass, cut-through, living hinges, alignment, corners, air assist and focus. Each test has a “Read my result” step, and the corrections are saved to My setup. The Calibration Center is free to use.

Living hinges are particularly sensitive to kerf and material, so if you plan to make bending panels, run the hinge test before using the living hinge generator.