What is kerf?

Kerf is the amount of material consumed (destroyed) by the cutting process itself. The word originally referred to the groove left by a saw blade, but it now applies to any cutting process that removes material:

Cutting process	Typical kerf width
Fiber laser (thin steel, under 3mm)	0.1–0.3 mm
CO₂ laser (wood, acrylic)	0.2–0.5 mm
Plasma cutter (steel 6–25mm)	1.5–4 mm
Waterjet	0.8–1.5 mm
CNC router (wood/MDF)	Equal to bit diameter (3–12mm)
Bandsaw	1–3 mm

Why kerf matters in nesting

If kerf is ignored in a nesting layout, the cut parts will be smaller than designed - by approximately half the kerf width on each edge (since the cut line removes material equally from both sides of the cut path).

For precision parts, even 0.2mm of unaccounted kerf can cause dimensional failures. For thicker plasma-cut parts with 3mm kerf, ignoring kerf can mean parts are 1.5mm undersized on every edge.

Kerf compensation in nesting software

Nesting software handles kerf in two ways:

Spacing compensation - The nesting tool adds a minimum gap between adjacent parts equal to the kerf width (or half kerf width if both parts are being cut). This prevents parts from being undersized due to shared cut lines.
Geometry offset (toolpath compensation) - More advanced CAM software offsets the entire cut path inward or outward by half the kerf width. This is typically done in CAM software after nesting rather than in the nesting step itself.

Lapas handles kerf via part spacing - you set the kerf width and minimum gap, and the optimizer ensures no two parts are placed closer than the specified distance. This is the correct approach for most nesting workflows where CAM handles final toolpath compensation.

Kerf and material utilization

Larger kerf widths reduce achievable material utilization because more space is required between parts. On a typical laser job with 0.2mm kerf, the impact is minimal. On a heavy plasma job with 3mm kerf and parts packed on a 2500×1250mm sheet, the kerf gaps can account for 3–5% of total sheet area.

Kerf and part-in-part nesting

Some nesting software supports common line cutting - where two adjacent parts share a single cut path, effectively halving the kerf loss between them. Lapas supports part spacing configuration; advanced common-line optimization is available in the Pro plan.

How to measure your kerf

Never assume the nominal kerf from your machine’s spec sheet. Measure it on your actual material:

Cut a known dimension (e.g., 100 × 100 mm square) at your standard settings
Measure the result with calipers
kerf = (programmed dimension − actual dimension) × 2

Example: programmed 100 mm, actual 98.2 mm → kerf = (100 − 98.2) × 2 = 3.6 mm

Repeat in both X and Y - kerf may not be symmetric. Create a reference table per material type and thickness.

Factors that change kerf

Factor	Effect on kerf
Thicker material	Wider kerf
Higher amperage (plasma)	Wider kerf
Faster feed rate	Narrower but rougher kerf
Worn nozzle or lens	Wider, less consistent kerf
Defocused beam (laser)	Wider kerf
Higher assist gas pressure	Narrower kerf (laser)

Kerf compensation vs. toolpath offset

These are often confused:

Nesting kerf - sets minimum spacing between adjacent parts on the sheet so they don’t share a cut path and come out undersized
CAM toolpath offset (G41/G42) - offsets the cut path inward or outward by half the kerf so the finished part matches its design dimension exactly

Both are needed for precision work. Nesting software handles the first; CAM software handles the second. They are complementary, not interchangeable.

Kerf in practice: laser vs. plasma vs. router

Laser cutting

Fiber laser kerf is typically 0.1–0.3 mm on thin steel, acrylic, and aluminium. This is small enough that for many jobs you can set it to 0.2 mm and get acceptable results without test cuts.

For precision work (tight tolerance parts, assemblies that press-fit together), measure kerf on every new material batch. Lens condition, gas pressure, and focal distance all affect it.

Plasma cutting

Plasma kerf varies more than laser kerf, typically 1.5–4 mm. It also varies with:

Cutting speed - faster cutting produces narrower (but rougher) kerf
Amperage - higher amperage produces wider kerf
Material thickness - thicker steel typically widens the kerf
Gas type - oxygen plasma produces different kerf than air plasma

For plasma nesting, use a kerf value from your machine’s cut charts (Hypertherm, ESAB, Lincoln publish these) or measure directly. Errors of 1–2 mm in kerf setting are common and will compound on jobs with many closely-packed parts.

CNC router

CNC router kerf is simply the diameter of the cutting bit. A 6 mm end mill has 6 mm kerf. A 3 mm spiral bit has 3 mm kerf.

For woodworking and MDF cutting, this is the most intuitive kerf setting. Note that for nested CNC routing, you often need larger part spacing than just the kerf, since the router path needs room to start and finish cuts without running into adjacent parts.

Common kerf mistakes

Setting kerf to zero - This tells the nesting software parts can touch. In practice, two adjacent parts with zero gap will share a cut path, making one or both undersized, and risks damaging the cutting head.

Using nominal kerf instead of measured kerf - Machine specs say 0.2 mm but your worn lens is actually cutting 0.35 mm. Always measure on your actual machine.

Using the same kerf for all materials - Steel, aluminium, acrylic, and wood all have different kerf on the same machine. Use material-specific values.

Confusing nesting kerf with CAM kerf compensation - These are different. Nesting software handles spacing between parts. CAM handles the toolpath offset so the cut lands on the right edge. Both are needed for precision work.

Kerf setting in Lapas

On the sheet configuration screen, set Kerf width to your measured value. Lapas enforces this as the minimum gap between all adjacent parts in the nested layout.

The Minimum part spacing field adds extra clearance on top of kerf - useful for plasma (HAZ clearance) or CNC routing (bit entry/exit room). For laser cutting thin materials, minimum spacing of 0 is usually correct.

FAQ

What happens if I set kerf to zero?

The nesting software will allow parts to touch. Adjacent parts will share a cut path - the beam or arc will cut material from both simultaneously, making one or both parts undersized. Always set kerf to at least your measured beam/arc width.

Do I need kerf compensation in both my nesting software and my CAM?

Yes - they solve different problems. Nesting kerf prevents parts from sharing cut paths on the sheet. CAM toolpath offset (G41/G42 or equivalent) ensures the cut path lands at the correct position so parts come out the right size. You need both for precision parts.

Why do my parts still come out undersized even after setting kerf?

Check that your CAM software is also applying toolpath compensation. Setting kerf in nesting software only controls spacing between parts, not the offset of the cut path relative to the part edge. Also verify you measured kerf on the same material and thickness as your current job.