Kerf: the millimetres that cost you parts
Kerf is the width of material a cut removes. In a cut list it is the gap you must leave between parts, and it adds up faster than most people expect.
One millimetre, one part per row
Take 606×300mm parts on a 2440×1220mm sheet. Across the 2440mm width, four parts need 4 × 606 = 2424mm plus three cuts between them:
| Kerf | Four across | Fits in 2440mm? | Parts per sheet |
|---|---|---|---|
| 5mm | 2424 + 3 × 5 = 2439mm | Yes, 1mm spare | 16 (4 across × 4 down) |
| 6mm | 2424 + 3 × 6 = 2442mm | No, 2mm over | 12 (3 across × 4 down) |
One extra millimetre of kerf loses a quarter of the sheet: 16 parts on one sheet becomes two sheets. That is why CutNest asks for your kerf before anything else, and why it keeps the exact figure (a 1/8″ blade stays 3.175mm, not “about 3”).
Typical kerf and spacing by process
These are typical figures to start from, not specifications. Measure your own blade or cutter, or ask whoever programs the machine what gap they leave between parts, and use that.
| Process | Typical gap to use | Notes |
|---|---|---|
| Panel saw / table saw | about 3–4.5mm | The blade’s tooth width. Scoring blades don’t add to it. |
| Track / plunge saw | about 2–3mm | Thinner blades; check the blade’s stated kerf. |
| Mitre saw (timber lengths) | about 2.5–3.5mm | Use as the saw kerf on a bar material. |
| Metal bandsaw | about 1.5–2mm | Common for box section and bar. |
| Cold saw | about 2–3mm | |
| CNC router | the cutter diameter, e.g. 6mm | Add any extra you leave for tabs or onion skin. |
| Fibre / CO₂ laser | a few mm between parts | The cut itself is well under 1mm; shops leave a gap for heat and a stable skeleton. |
| Plasma | about 5mm or more | Wider cut and more heat than a laser. |
| Waterjet | about 1–2mm plus spacing | |
| Turret punch | often 15–20mm | Clamp zones and tooling need space; ask your programmer. |
| Guillotine shear | 0mm | A shear removes no material. |
In CutNest the kerf is set once in Settings, and a bar material can have its own saw kerf, so the bandsaw for box section and the laser for plate can live in the same job.
Straight answers
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