Boxes that close.
Finger joints with the odd-fingers rule, and two lid styles whose play has a source.
How many fingers? An odd number, chosen honestly.
The app picks the odd n ≥ 3 that brings edge/n closest to your target finger width — and on ties, more fingers win. Its own test example: a 100 mm edge at a 10 mm target gives 11 fingers of 9.09 mm. Why odd: both ends of the edge end on the same panel, which makes the corners unambiguous.
The app's default finger width is 10 mm, editable — boxes.py's default is 2× the thickness, for comparison.
Clearance and the kerf
| rule | value |
|---|---|
| clearance how it's applied | each finger boundary moves c/4, so a finger sits c narrower than its gap |
| outside vs inside | outside = inside + 2T on any axis with walls at both ends |
| baking the kerf in | every outline grows K/2, holes shrink K/2 |
| corners | front and back panels own the corners; left and right own the ends of their edges with bottom and top |
| dividers | cross-halved: slots T + c wide, half the strip deep |
| the sheet layout | parts 3 mm apart |
Lid play — sourced, not invented
A sliding or hinged lid needs play to move: the app uses your clearance, or 0.05 × T at minimum — the minimum is boxes.py's own default play for its slide-on lid, so the number has a source.
The sliding lid
The app's slide-on geometry is 3D-checked (its test slides the lid out clear, and holds it square, stopped and down): the walls rise by the slot (T + play) with a rail 2T tall; the notch opens at the left end; the lid's far end carries the tongue; the finger slot runs 2T wide, up to 30 mm long.
The hinged lid
A square pin turns on a circle — its corners swing at radius T√2/2, so the pin holes are T√2 + play wide. The pivot sits 1.5T from the back face (the hole stays inside the wall with about 0.8T of sheet around it); the end walls grow 2T cheeks above the body; the back wall lowers just enough for the lid's back corner to swing past, plus play — the app's test turns the lid to 90° without a touch. Dividers in a hinged box stop at the back wall's height, below the lid's swing.
The honest card: none of these lids has been cut on a real laser yet — the geometry is tested in 3D, so cut your first test box before you trust the fit with expensive sheet.