Finger-Joint Box Generator (laser & CNC)

What it is for

A finger-joint box (also called a box-joint box) is the classic laser-cut project: six flat panels whose edges interlock like the teeth of two combs. Drawing one by hand is fiddly, because every joint has to match its partner, the corners must not collide and the laser burns away a little material on every cut. This generator does that bookkeeping for you. You enter the size, the material thickness and a target finger width, choose a closed lid, an open tray or a sliding lid, and optionally a grid of dividers.

You get a layered SVG and DXF for LightBurn, Inkscape or your CAM program, a 1:1 PDF with a scale bar, a 3-D preview of the assembled box and, for CNC routers, G-code with dog-bone reliefs. It does not add captive nuts, hinges or engraving artwork, and it does not know your material: always check thickness and kerf first.

Worked example

The first example on the page is a box with a lid: inside 160 × 100 × 60 mm, 3 mm plywood, 10 mm target fingers and a kerf of 0.15 mm. The tool reports:

Finger-joint box with lid: outside 166 × 106 × 66 mm, inside 160 × 100 × 60 mm, 6 parts from 3 mm material with 12 finger joints.

The 160 mm edges get 17 fingers of 9.41 mm, the 100 mm edges 11 fingers of 9.09 mm and the 60 mm corners 7 fingers of 8.57 mm. Every count is odd, so both ends of a joint belong to the same panel and the corners stay solid. The parts table lists the bottom and lid at 166.15 × 106.15 mm: that is the outside size plus the 0.15 mm kerf, because the outline is moved out by half the kerf on every side.

For a 120 × 80 × 50 mm open tray in 3 mm material with 12 mm fingers, kerf 0.18 and two compartments, nested on a 300 × 200 mm bed, you get one divider of 79.98 × 50.18 mm and two compartments of 58.5 × 80 mm, all on one sheet with 62.5 % use.

How to read the result

• Outside and inside size show both sets of dimensions, whichever you entered.
• Finger width range is the real width after rounding to odd counts; it changes per edge.
• Parts gives the size of each panel as it will be cut, including kerf compensation.
• The cut file uses red for cuts and grey for labels; turn the label layer off before cutting.
• Sheets and Sheet use appear when you enter a laser bed or stock sheet size.
• With a sliding lid, the side walls get a slot that is open at the front, and the front and back stop below it.

Tips and common mistakes

• Measure the sheet with calipers. "3 mm" plywood is often 2.8–3.2 mm, and a wrong thickness spoils every joint.
• Cut the kerf test first and use the measured kerf. Too much compensation makes joints you cannot close.
• For routers set the kerf to 0, the part gap to at least the cutter diameter and the dog-bone diameter to the cutter.
• Fingers narrower than the material is thick break easily; the tool warns you.
• Dividers are loose and cross-halved, so you can glue them or leave them removable.

FAQ

Why is my finger width not exactly what I typed?

Each joint is split into an odd number of equal fingers, so the width is the edge length divided by the nearest odd count.

Do I need glue?

Tight joints hold without glue for light boxes, but wood glue makes them permanent. The sliding lid must stay dry.

Can I open the box in Kerfwise?

Yes. The Open in Kerfwise link opens the same settings in Maker boxes, where you can change them, nest the parts and export again.

Which software can read the files?

The SVG is in millimetres with one group per layer, and the DXF is R12 with CUT, SCORE, ENGRAVE and LABELS layers, which LightBurn, Inkscape and most CAM programs import.