The formulas
- Outer size. You enter the inner width, depth and height. Width and depth grow by 2 × thickness. Height grows by 1 × thickness for an open tray and 2 × thickness for a closed box.
- Segment count. An edge of outer length L with target finger width f gets n = 2 × round((L / f − 1) / 2) + 1 segments, at least 3 and always odd. The target defaults to 3 × thickness.
- Minimum pitch. While L / n is under 1.5 × thickness and n is above 3, n drops by 2.
- Pitch. pitch = L / n, equal along the whole edge.
- Tabs. One panel keeps the even segments as tabs, corners included. Its neighbour keeps the odd ones.
- Kerf. The outline moves outwards by kerf / 2 on every cut side, so drawn tab = pitch + kerf and drawn slot = pitch − kerf. Slots stay one thickness deep.
Worked example: 100 × 60 × 40 mm tray
Open tray, inner 100 × 60 × 40 mm, 3 mm sheet, kerf 0.15 mm, target finger width 10 mm. The outer size is 106 × 66 × 43 mm. For the width, 106 / 10 = 10.6, (10.6 − 1) / 2 = 4.8, which rounds to 5, so n = 11.
| Edge | Length | Segments | Pitch | Drawn tab | Drawn slot |
|---|---|---|---|---|---|
| Width | 106 mm | 11 | 9.636 mm | 9.786 mm | 9.486 mm |
| Depth | 66 mm | 7 | 9.429 mm | 9.579 mm | 9.279 mm |
| Height | 43 mm | 5 | 8.600 mm | 8.750 mm | 8.450 mm |
A drawn tab plus the slot it enters is always two pitches: 9.786 + 9.486 = 19.272 mm. The tray has five parts and eight mating edges. The bottom is drawn 106.15 × 66.15 mm, the front and back walls 106.15 × 43.15 mm and the side walls 66.15 × 43.15 mm. An automated script generates this same tray and measures these values on the outlines.
Free generators exist
Free and open-source box generators exist, some with many more box styles than this one. This tool differs in one narrow way: a single form fits loose half-lap dividers to your inner dimensions and writes kerf-compensated SVG and DXF. If a free tool already does the job, use it.
Read this before you buy or cut
- Dimensions. You enter the inner width, depth and height. The outer size is the inner size plus two material thicknesses (an open tray has no lid panel, so its outer height is the inner height plus one thickness).
- Not test-cut. The geometry is computed and checked by a script (92 fixture assertions) but was never test-cut, so cut a test piece first and adjust kerf and material thickness.
- Made by AI agents. This tool and its code were generated by AI agents and no human maker has validated it.
- Price: $9 USD one-time.
- What the key unlocks: one licence key unlocks SVG and DXF download for any dimensions, in this browser tool.
- Refunds: Refund requests go through Gumroad, under Gumroad's refund policy.
- Free without a key. The form, the preview, the part list and the sheet size.