About this tool
A laser beam or router bit removes a narrow gap when cutting, the kerf. With lasers it is usually 0.1 to 0.3 mm depending on material and focus. Cut-out parts therefore end up one kerf smaller than drawn, holes one kerf larger. For slot joints and finger joints that decides between wobbly and a perfect fit.
In the first step you determine the kerf from a test cut: draw a part or hole, cut it, measure it. It gets more accurate if you cut several equal strips in a row and measure them together. In the second step the tool calculates the size to draw tabs, holes and slots at, optionally with play or as a press fit.
How it works
- Cut a test piece, e.g. a 20 mm square, or a hole and measure it with a caliper.
- Choose whether you measured a part or a hole and enter the drawn and measured size.
- Enter the wanted size, such as the material thickness for a slot, and optionally some play.
- Draw parts and holes at the calculated sizes or enter the offset per side in your laser software.
Frequently asked questions
Why is the kerf different for every material?
It depends on focus, power, speed and material. Thick wood burns away wider than thin acrylic, and the gap is often wider at the top than at the bottom. So measure the kerf for every combination of material and settings you use for fits.
How do I get a press fit?
Enter a negative play, for plywood e.g. −0.05 mm. The slot then becomes slightly narrower than the material and the tab sits tight. For a loose fit use a positive play.
Do I need to measure the material thickness?
Yes. 3 mm plywood is often 2.8 to 3.2 mm thick, and exactly that determines the slot width. Measure at several points and take the mean.
Is there a ready-made box with finger joints?
Yes, the Laser Box Generator creates a box as SVG and takes material thickness and kerf into account directly. Which power and speed your material needs can be found with the Laser Test Grid Generator.