Best fiber laser settings for 20mm Mild Steel
These are conservative starting-point parameters for cutting 20mm mild steel on a fiber laser in roughly the 8 kW–15 kW class. Use them as the center of your first test, then dial in for your exact machine, optics, assist-gas purity, and material batch. They are not a guaranteed recipe — no published chart can be, because two same-wattage machines can differ 4–5x in real-world feed rate.
Recommended starting-point parameters
| Assist gas | Oxygen (O₂) |
|---|---|
| Gas pressure | 0.2–0.4 bar |
| Cutting speed | 350–600 mm/min Start here, then push faster only if edge stays clean. |
| Focus position | +3.5 to +5.0 mm (into material) |
| Nozzle | Single, Ø3.5 mm |
| Nozzle standoff | 1.5–2.5 mm |
| Pierce | 6–12 s, progressive pierce; pre-pierce strongly recommended |
| Power band assumed | 8 kW–15 kW |
Dialing it in
- ›Verify your assist-gas purity. With N₂, a drop from 99.999% to 99.5% can cost ~20–25% feed rate and leave an oxidized edge.
- ›Check focus on a stainless ramp test before trusting any number — focal shift from a hot or contaminated lens is the most common cause of sudden dross.
- ›If you see bottom-edge dross, drop speed ~10% or raise gas pressure ~1 bar before touching focus.
- ›Resonator hours and nozzle wear shift these numbers over time. Re-baseline after a nozzle change or a few hundred resonator hours.
The material-test workflow
The fastest way to a reliable cut is not a perfect chart — it's a tight test loop that you only run once per machine/material combination, then never repeat:
- 1Start from this baseline. Load the starting-point numbers above as the center of your test.
- 2Run a small array. Cut a grid that sweeps speed (and power, if cutting) ±20% around the baseline — typically 9–16 small squares.
- 3Judge the edge. Look for dross, burn-back, kerf width, and squareness. Pick the square that meets your part's requirement, not the prettiest one.
- 4Log it once. Save the winning parameters against this exact machine + material so the next job starts from your proven number — not a generic chart.
Stop re-running the same test square
CutLog gives you a starting point calibrated to your wattage and lens, then remembers every cut you log — so your machine builds its own proven library. Free to start.
Frequently asked questions
What speed should I cut 20mm mild steel at with a fiber laser?▾
A conservative starting point in the 8 kW–15 kW class is 350–600 mm/min. Treat this as the middle of your test range and adjust ±15–20% based on edge quality. Higher-wattage machines and clean optics will run faster; worn nozzles, low gas purity, or off-focus will run slower.
Which assist gas is best for 20mm mild steel?▾
This starting point uses Oxygen (O₂) at 0.2–0.4 bar. Gas choice trades cost, speed, and edge oxidation — confirm against the finish your parts require.
Why won't one settings chart work on every machine?▾
Beam quality, resonator hours, optics condition, nozzle wear, assist-gas purity, and material batch all move the numbers. Same-wattage machines from different brands routinely differ 4–5x in achievable feed rate. That is exactly why CutLog gives you a starting point and a fast test workflow instead of pretending there is one universal number.
Related settings
Last reviewed 2026-06-28. Values are conservative starting points generalized across brands and published cutting charts; always verify on your own machine.