Kerf Width vs. Thickness & Nozzle
Practical reference tables for laser cutting kerf width. Understand how material thickness, nozzle diameter, and gas type affect kerf to optimize nesting compensation, dimensional accuracy, and part quality.
What is Kerf Width?
Kerf is the width of material removed during the laser cutting process. It consists of the actual laser beam spot size plus the molten material expelled by assist gas. Typical kerf ranges: 0.1-0.5mm depending on material, thickness, and nozzle.
Why It Matters: Kerf width directly affects part dimensions. Without proper compensation in your CAM software, parts will be oversized (external features) or undersized (holes/internal features) by half the kerf width on each side.
Factors Affecting Kerf Width
1. Material Thickness
Thicker materials require more energy to melt through, creating wider molten zones and larger kerf. Kerf increases approximately 0.02-0.05mm per mm of thickness.
Example: 1mm stainless = 0.15mm kerf; 10mm stainless = 0.30-0.40mm kerf
2. Nozzle Diameter
Larger nozzles allow wider beam focus and higher gas flow, increasing kerf width. Nozzle selection depends on material thickness and desired cut quality.
Typical range: 1.0mm nozzle → 0.10-0.15mm kerf; 3.0mm nozzle → 0.25-0.40mm kerf
3. Assist Gas Type & Pressure
Nitrogen (inert) produces cleaner, slightly narrower kerfs than oxygen (reactive). Higher gas pressure increases kerf slightly but improves material ejection.
Oxygen on mild steel: +10-20% kerf width vs nitrogen due to exothermic reaction
4. Laser Power & Focus Position
Higher power creates wider melted zones. Focus position (surface, middle, or below surface) affects beam diameter through the material thickness, influencing top/bottom kerf width.
Defocused cutting (thick material) can increase kerf by 20-40%
Kerf Width Reference Tables
Mild Steel (Oxygen Assist)
3-6kW fiber laser, standard cutting parameters. Kerf is typically 10-20% wider than nitrogen due to oxidation reaction.
| Thickness | Nozzle Ø | Focus Pos. | Kerf Width | Tolerance |
|---|---|---|---|---|
| 1mm | 1.0-1.5mm | On surface | 0.15-0.20mm | ±0.05mm |
| 3mm | 1.5-2.0mm | -1mm below | 0.20-0.25mm | ±0.05mm |
| 6mm | 2.0-2.5mm | -2mm below | 0.25-0.35mm | ±0.08mm |
| 10mm | 2.5-3.0mm | -3mm below | 0.35-0.45mm | ±0.10mm |
| 15mm | 3.0-3.5mm | -4mm below | 0.40-0.55mm | ±0.12mm |
| 20mm | 3.5-4.0mm | -5mm below | 0.50-0.65mm | ±0.15mm |
Stainless Steel 304 (Nitrogen Assist)
3-6kW fiber laser with high-pressure nitrogen. Produces clean, oxide-free edges with tighter kerf than oxygen cutting.
| Thickness | Nozzle Ø | Focus Pos. | Kerf Width | Tolerance |
|---|---|---|---|---|
| 0.5mm | 1.0mm | On surface | 0.10-0.14mm | ±0.03mm |
| 1mm | 1.0-1.5mm | On surface | 0.12-0.18mm | ±0.04mm |
| 3mm | 1.5-2.0mm | -1mm below | 0.18-0.25mm | ±0.05mm |
| 6mm | 2.0-2.5mm | -2mm below | 0.25-0.32mm | ±0.06mm |
| 8mm | 2.5mm | -2.5mm below | 0.28-0.38mm | ±0.08mm |
| 10mm | 2.5-3.0mm | -3mm below | 0.32-0.42mm | ±0.10mm |
| 12mm | 3.0mm | -3.5mm below | 0.35-0.48mm | ±0.12mm |
Aluminum 5052 (Nitrogen Assist)
High-power fiber laser (6-12kW) required for thick aluminum. Kerf tends to be wider due to high thermal conductivity and lower melting point.
| Thickness | Nozzle Ø | Focus Pos. | Kerf Width | Tolerance |
|---|---|---|---|---|
| 1mm | 1.5mm | On surface | 0.15-0.22mm | ±0.05mm |
| 3mm | 2.0mm | -1mm below | 0.22-0.30mm | ±0.06mm |
| 6mm | 2.5mm | -2mm below | 0.30-0.40mm | ±0.08mm |
| 10mm | 3.0mm | -3mm below | 0.38-0.50mm | ±0.10mm |
| 12mm | 3.0-3.5mm | -3.5mm below | 0.42-0.58mm | ±0.12mm |
| 15mm | 3.5mm | -4mm below | 0.48-0.65mm | ±0.15mm |
Important: These values are typical ranges. Actual kerf depends on specific machine configuration, focus quality, gas purity, and cutting parameters. Always verify with test cuts on your equipment before critical production runs.
Applying Kerf Compensation
CAM software compensates for kerf by offsetting the cutting path inward (for external features) or outward (for holes/internal features) by half the kerf width.
External Features (Perimeter Cuts)
Path is slightly larger; laser removes 0.10mm from each side, leaving exactly 100.00mm part.
Internal Features (Holes)
Path is slightly smaller; laser removes 0.10mm from each side, creating exactly 20.00mm hole.
Common CAM Software Settings
- SigmaNEST:Set "Kerf Width" in Material Database → Auto-compensates all features
- Lantek:Technology table → "Kerf compensation" → Inside/Outside/No compensation
- Radan:Material setup → "Beam offset" value → Automatically applied to paths
- SheetCAM:Tool definition → "Kerf width" → Specify compensation direction per cut
Common Mistakes
- • Forgetting to measure actual kerf: Using default values leads to dimensional errors
- • Wrong compensation direction: External features offset outward instead of inward
- • Ignoring tolerance variation: Kerf changes with worn nozzles, dirty optics, focus drift
- • Not updating for material changes: Switching from 3mm to 10mm requires different compensation
Kerf Width & Cut Quality
Dimensional Accuracy
Proper kerf compensation achieves ±0.05-0.15mm tolerance on thin materials (1-3mm) and ±0.10-0.25mm on thick materials (>6mm). Without compensation, errors are typically 2-5x the kerf width.
✓ With Compensation
100mm part measures 99.95-100.05mm
✗ Without Compensation
100mm part measures 100.20-100.40mm
Small Features & Thin Walls
Kerf width limits minimum feature size. A hole smaller than 1.5× the kerf width may not cut cleanly. Thin walls (bridges) should be at least 2× the kerf width to avoid burn-through.
Taper & Edge Quality
Kerf width at the top surface is typically 0.02-0.08mm narrower than at the bottom due to beam divergence. This creates slight taper (1-3° on thick materials). Tighter kerf generally correlates with better edge perpendicularity and less dross.
How to Measure Kerf Width
- 1.
Cut a test square with no kerf compensation
Program a 100.00mm × 100.00mm square in your CAM software with kerf comp disabled
- 2.
Measure the finished part with calipers or CMM
Record actual dimensions (e.g., 99.82mm × 99.80mm)
- 3.
Calculate kerf: Target - Actual = Total kerf removed
100.00mm - 99.82mm = 0.18mm total removed from both sides
- 4.
Verify with a test hole
Program 20.00mm hole, measure actual (e.g., 20.18mm). Kerf = 0.18mm confirms external cut result
- 5.
Enter kerf value into CAM software
Use the average measured value. Repeat for each material/thickness combination
Pro Tip: Perform kerf tests quarterly or after major maintenance (lens replacement, nozzle changes) to catch drift. Keep a logbook of kerf values by material/thickness for quick reference.