Laser kerf calculator and test strip
Kerf is the width of material your laser removes. It decides whether finger joints fall apart or need a mallet. Measure it on your own machine and your own material in two short cuts.
1. Make the test strip
Type the thickness of your material and the slot widths you want to try. You get a strip with a row of slots and a comb that fits them. The numbers already filled in are only an example — replace them with your own.
Colours: red lines are cuts, green text is the label for each slot width. Map the colours to layers in your laser software, cut the red layer, and mark the green text on a light engrave or skip it. File size is in millimetres.
64 x 56 mm
2. Work out your kerf
Kerf is the width of material your beam removes. Measure with calipers after cutting, then type the numbers here. Nothing on this page assumes a value for your machine.
- Kerf (total)
- Enter your measurements
- Kerf per side
- -
- Slot width to draw
- -
- Tab width to draw
- -
Outside cut: the part comes out smaller than drawn, so kerf = drawn size - measured size. Inside cut: the hole comes out larger, so kerf = measured size - drawn size. The cut edge sits half a kerf away from the drawn line on each side.
Snug slot method: a comb tooth drawn at thickness t comes out t - K wide; a slot drawn at w comes out w + K wide. They fit snugly when t - K = w + K, so K = (t - w) / 2.
What to draw: to get a slot as wide as the material is thick, draw it at thickness - K. To get a tab that ends up the material thickness, draw it at thickness + K. For a tighter press fit, go a little narrower on the slot and test again on an offcut.
How to use this
- Measure your material thickness with calipers and enter it above, with the slot widths you want to try.
- Download the SVG, import it into your laser software, and give the red lines a cut layer with your own tested settings.
- Cut the strip and the comb. Push the comb into each slot and note the narrowest slot where it still fits snugly.
- Enter that slot width in the calculator, or cut a square and measure it, to get your kerf.
Kerf changes with material, lens, focus and the settings you cut at, so measure again when any of them changes. The numbers on this page come only from what you type.
Where Vextrify uses your kerf
In Vextrify, Product Studio has a kerf field next to material thickness. For finger-jointed boxes it uses that value to size the tabs and slots, so the joints fit the way your laser actually cuts. Product Studio also checks that tabs fit their slots before anything is cut.
More free tools: material test grid, all tools.