· KAIPU Engineering · glossary · 2 min read
Kerf — Industry Glossary Entry
Definition of kerf in industrial cutting: the width of material removed by the cut, how it is measured, the substrate-by-substrate range, and how it relates to slitter-set-up and material yield.
Kerf is the width of material removed by a single cut, equal to the thickness of the knife at the cut plus any lateral spread of the cut into the substrate. Kerf is a critical parameter on slitting and cut-to-length lines because it directly determines material yield — every millimetre of kerf is a millimetre of substrate that becomes scrap instead of sellable product.
Units: millimetres (mm) on industrial blades, micrometres (µm) on thin-film / foil slitting.
How it is calculated:
- Slitting (top + bottom knife): kerf = knife thickness at cut + lateral spread. For a 1.5 mm top knife on a 0.1 mm film, the knife thickness dominates and the kerf is 1.5 mm.
- Shearing (single cut): kerf = clearance between upper and lower blades + lateral spread. For a 6 % gap on 1 mm sheet, the kerf is roughly 0.06 mm.
- Blanking (die cut): kerf = die clearance (typically 5–12 % of material thickness) + die wear.
Typical kerf by cut type:
| Cut type | Kerf | Yield impact |
|---|---|---|
| Industrial circular slitting (1–3 mm knives) | 1.0–3.0 mm | Low — the kerf is amortised over a wide web |
| Precision slitting (0.5–1.5 mm knives) | 0.5–1.5 mm | Moderate — multiple slits on a single web |
| Thin-film slitting (50–200 µm knives) | 0.05–0.20 mm | High — every 50 µm of kerf is yield lost |
| Plate shearing | 0.05–0.50 mm | Low — single cut on wide stock |
| Laser / waterjet cutting | 0.1–0.5 mm | Variable — depends on assist gas / nozzle |
Kerf and material yield on a slitting line: for a web of width W slit into N strips, the total kerf is (N-1) × kerf. The percentage of material lost to kerf is (N-1) × kerf / W. A 0.1 mm increase in kerf on a 1,000 mm wide web slit into 50 strips costs 0.5 % of yield. Over a year, that adds up.
How to minimise kerf:
- Use the thinnest knife that maintains the required strength and stiffness.
- For a given knife thickness, minimise the hone radius — a 5 µm hone cuts cleaner than a 15 µm hone.
- Ensure knife-to-anvil parallel within 0.01 mm to prevent the knife from tilting and widening the cut.
- Use the lowest knife grade that will survive the substrate (D2 instead of M2 if the wear life is acceptable — D2 is usually available in thinner stock).
See also: Hone (micro-hone), Clearance angle, The KAIPU 5-Factor Blade Selection Framework.