What is kerf, and how do I measure mine?
Kerf is the width of material the beam removes, so a cut piece comes out smaller than it was drawn and a cut hole comes out larger. To measure it, cut one square of a known size, measure the piece with callipers, and subtract: a 20 mm square that measures 19.85 mm has a kerf of 0.15 mm. It changes with material, thickness and speed.
What the number then tells you
The offset per edge is half the kerf, because the beam sits on the line and eats half of it from each side. That is what you move a line by when you offset it yourself.
Type the whole kerf, not the half, into laser software that compensates for you. xTool Studio calls the switch Kerf offset and the box under it Compensated width, and asks for the actual cut width; it works out the per-edge half itself and which way to move each line, because it can tell an inner contour from an outer one.
Measure the piece, not the hole it came out of, and measure both directions and average them.
| Measured on a drawn 20 mm square | Kerf | Offset per edge | Slot for a 3 mm sheet |
|---|---|---|---|
| 19.90 mm | 0.10 mm | 0.05 mm | 2.90 mm |
| 19.85 mm | 0.15 mm | 0.075 mm | 2.85 mm |
| 19.80 mm | 0.20 mm | 0.10 mm | 2.80 mm |
Do it again when anything changes
- A different material or a different thickness.
- A different speed or power, or another pass.
- A new lens, or a lens that has been cleaned after a while.
- A sheet from another supplier, even at the same nominal thickness.
A number to start from
Hobby diode and CO2 lasers cutting 3 mm plywood usually land between 0.15 and 0.20 mm. MakerWizard starts there when you have not measured, and says so; your own measurement always replaces it.