What kerf does to a part
The beam follows the centre of the drawn line and removes half the kerf on each side. A part drawn 20 mm wide comes out one kerf narrower, and a hole drawn 20 mm wide comes out one kerf wider. See laser cutting on Wikipedia.
Measuring kerf with a test cut
- Draw a 20 × 20 mm square and cut it from the sheet you will use, at your usual power and speed.
- Measure the square with calipers. If it reads 19.85 mm, the kerf is 20 − 19.85 = 0.15 mm.
- Measure the sheet thickness too: nominal 3 mm sheet is often not 3.00 mm.
- Measure again when the material, lens, power or speed changes.
How the generator compensates
Every outline moves outwards by half the kerf on every cut side. Each tab is drawn one kerf wider and each slot one kerf narrower, so the cut part comes out at its nominal size. Type 0 for no compensation, or a little more than you measured for a tighter fit.
Worked example
Open tray, inner 100 × 60 × 40 mm, 3 mm sheet, target finger width 10 mm: 11 segments along the width.
| Kerf | Bottom drawn | Tab | Slot |
|---|---|---|---|
| 0 mm | 106 × 66 mm | 9.636 mm | 9.636 mm |
| 0.15 mm | 106.15 × 66.15 mm | 9.786 mm | 9.486 mm |
Inches are converted first: a closed 4 × 3 × 2 in box in 0.125 in sheet with 0.006 in kerf gets thickness 3.175 mm, kerf 0.1524 mm and an outer size of 107.95 × 82.55 × 57.15 mm. An automated script generates both boxes and measures these sizes on the outlines.
Why the files are in millimetres
An SVG without real-world units is read in pixels, and programs have not always agreed on pixels per inch, which rescales the drawing. The exported SVG gives its width and height in mm with a matching viewBox, so one user unit is one millimetre.
A DXF stores plain numbers. The export is ASCII DXF R12 with $INSUNITS set to 4, meaning millimetres. If your program asks for a unit on import, choose millimetres.
Free generators exist
Free and open-source box generators exist, and several compensate for kerf. 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.