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Box & finger joint generator
Finger joints fail for one reason: the design was drawn at nominal size and the laser removed a strip of material nobody accounted for. Give this your measured kerf and it applies the compensation to every tab and slot, then hands you a cut-ready SVG.
Cut one corner first
This is the advice that saves sheets, and it is worth repeating even though nobody wants to hear it. Before you cut a whole box, cut two small pieces with three fingers each and check they press together properly. A joint that is one kerf too tight splits plywood along the tab; one kerf too loose and the box needs clamps and hope.
If the test corner is too tight, add 0.05 mm of clearance and try again. Too loose, take 0.05 mm off. Two iterations is normal and costs a scrap of offcut.
Getting the kerf number right
Everything here depends on your kerf, and your kerf is not the same as anyone else's — it changes with material, thickness, power, speed, focus and lens. Measure it rather than guessing: cut a 50 mm square, measure it, and the shortfall is your kerf. The kerf calculator does the arithmetic, and laser-cut joinery covers why it matters.
The compensation figure shown above is what gets applied to every tab and slot: tabs are drawn wider by that amount and slots narrower by the same, so both finish at nominal with your chosen clearance between them.
What this generates, and what it does not
- Four sides and a base, optionally a lid panel, finger-jointed at every corner and along the bottom.
- External dimensions. A 100 × 80 × 60 box measures that on the outside once assembled; internal volume is smaller by two thicknesses in each direction.
- Odd finger counts only. An even count puts a tab against a tab at one end of the edge. The field rounds up.
- No lid hinge, catch or handle — the lid is a plain panel that drops in. Add those yourself.
- Corners are left solid by one material thickness at each end of every jointed edge, so the vertical and base joints never fight over the same material.
Finger width sits best between 1.5 and 3 times material thickness. Narrower and tabs snap off in plywood; much wider and the joint looks coarse and loses glue area. The tool warns you when you drift outside that range.
Before you cut the sheet
Once the corner fits, check how many boxes actually fit on your stock — small panels waste sheet fast when placed by eye. Run the flat pattern through the nesting tool, and price the material with the sheet yield calculator before quoting.
FAQ
How much kerf compensation does a finger joint need?
Tabs should be drawn wider by roughly one kerf and slots narrower by the same amount, so both finish at nominal size after cutting. Applying it to only one of the two mating parts is the usual mistake, and it produces a joint that is out by a full kerf.
How wide should the fingers be?
Between 1.5 and 3 times material thickness. For 3 mm plywood that means roughly 6 to 9 mm. Narrower tabs snap off along the ply, wider ones look coarse and lose glue area. Always use an odd number per edge so both ends of the edge finish with a tab.
Are the dimensions internal or external?
External. A 100 by 80 by 60 box measures that on the outside once assembled. The internal volume is smaller by two material thicknesses in each direction, so subtract those if you are sizing the box around something specific.
Why should I cut one corner before the whole box?
Because a joint one kerf too tight splits plywood along the tab, and one kerf too loose needs clamps and glue to hold. Two small test pieces with three fingers each cost a scrap of offcut and take thirty seconds, and they tell you whether your kerf number is right before you commit a sheet.