Cutting Guide
Kerf Width Explained
The cut itself removes material — kerf is how much, and why it needs allowing for when sizing parts and packing them onto a sheet.
Cutting a metal sheet doesn't leave a hairline gap — the plasma arc, laser beam or waterjet stream removes a strip of material as it passes through, and that strip is the kerf. Ignore it and a part drawn at exactly 100mm comes out slightly smaller, because both edges of that cut line lost material to the process.
See kerf's effect on nesting
The main calculator's gap setting between parts should account for your process's kerf.
Typical kerf by process
| Process | Typical kerf | Notes |
|---|---|---|
| Laser | 0.1 - 0.3 mm | Narrowest kerf, tightest tolerance |
| Waterjet | 0.8 - 1.2 mm | Widens slightly with nozzle wear |
| Plasma | 1.0 - 2.0 mm | Widest, increases with amperage and thickness |
These are guide figures — actual kerf varies with nozzle condition, cutting speed, gas pressure and material thickness, so measure a test cut on your own machine if a part needs to be precise.
Why it matters for part size
A cutting program follows a drawn line, but the process removes material centred on (or to one side of) that line. For an outer profile, cutting on the outside edge of the line keeps the part at full size; for a hole or inner cutout, cutting on the inside edge keeps the hole from coming out oversized. Most CAM software handles this automatically through a kerf compensation setting, offsetting the toolpath by half the kerf width in the correct direction.
Why it matters for nesting
When parts are packed tightly onto a sheet, the gap between them needs to be at least the kerf width — otherwise the cut removing material for one part's edge also eats into the neighbouring part. This is why the gap setting in a nesting calculation should never be smaller than your process's kerf, and in practice a small additional safety margin on top of kerf is common to avoid parts fusing or distorting from heat.
See the sheet nesting guide for how gap and edge margin combine to set parts per sheet.
Frequently asked questions
What is kerf in metal cutting?
Kerf is the width of material removed by the cutting process — the slot left as the torch, laser or jet passes through. A part cut exactly on a drawn line comes out slightly undersized unless compensated for.
How wide is laser cutting kerf?
Laser kerf is typically 0.1 to 0.3mm — much narrower than plasma or waterjet, which is one reason laser achieves tighter tolerances and finer detail.
Does kerf affect sheet nesting?
Yes. The gap between nested parts needs to be at least the kerf width, so it's normally built into the minimum part-to-part gap in a nesting layout.