Mild Steel Fiber Laser Cutting Settings — Speed, Power & Gas Pressure Chart

If you’ve ever tried to dial in mild steel cuts on a new fiber laser, you know the frustration: every machine has slightly different settings, every job shop manual gives slightly different numbers, and “trust the operator” is not a recipe for clean parts.

This is our reference chart based on cuts we’ve actually made at DXFForge across multiple machine classes. Settings work as a starting point — your machine’s beam diameter, nozzle wear, and lens condition will push numbers ±15%, but you’ll be in the right neighbourhood.

Quick context on assist gases

• Oxygen (O₂) — chemical-assist cutting, faster speeds, sooty edge that needs cleanup. Standard for ≥ 3 mm mild steel.
• Nitrogen (N₂) — clean inert-gas cutting, edge ready to paint/weld, slower speeds, higher gas cost. Use for thin material or premium-finish jobs.
• Compressed air — entry-level alternative, decent on ≤ 2 mm, leaves oxidation on the edge.

Cutting chart — 1 kW fiber laser

Thickness	Gas	Pressure (bar)	Speed (mm/min)	Power (%)	Focus (mm)
0.5 mm	N₂	12	12,000 – 15,000	70	0
1 mm	N₂	12	9,000 – 11,000	85	0
1 mm	O₂	0.6	6,000 – 7,500	90	-0.5
2 mm	O₂	0.5	3,500 – 4,500	95	-1
3 mm	O₂	0.4	2,200 – 2,800	100	-1.5
4 mm	O₂	0.3	1,400 – 1,800	100	-2
5 mm	O₂	0.3	900 – 1,100	100	-2.5
6 mm	O₂	0.25	600 – 750	100	-3

Notes for 1 kW: above 6 mm gets unreliable on hobby-class 1 kW machines. If you cut 8 mm+ regularly, upgrade to 1.5 kW minimum.

Cutting chart — 1.5 kW fiber laser

Thickness	Gas	Pressure (bar)	Speed (mm/min)	Power (%)	Focus (mm)
1 mm	N₂	14	13,000 – 15,000	80	0
2 mm	N₂	14	7,000 – 8,500	95	-0.5
2 mm	O₂	0.5	5,500 – 6,500	95	-1
3 mm	O₂	0.4	3,800 – 4,500	100	-1.5
4 mm	O₂	0.35	2,500 – 3,000	100	-2
5 mm	O₂	0.3	1,800 – 2,100	100	-2.5
6 mm	O₂	0.25	1,200 – 1,500	100	-3
8 mm	O₂	0.2	700 – 850	100	-4
10 mm	O₂	0.15	450 – 550	100	-5

Cutting chart — 3 kW fiber laser

Thickness	Gas	Pressure (bar)	Speed (mm/min)	Power (%)	Focus (mm)
1 mm	N₂	16	20,000 – 22,000	70	0
2 mm	N₂	16	12,000 – 14,000	85	-0.5
3 mm	N₂	18	7,500 – 8,500	95	-1
4 mm	N₂	18	5,000 – 6,000	100	-1.5
5 mm	N₂	20	3,500 – 4,200	100	-2
6 mm	O₂	0.3	2,800 – 3,300	100	-3
8 mm	O₂	0.25	1,800 – 2,200	100	-4
10 mm	O₂	0.2	1,200 – 1,500	100	-5
12 mm	O₂	0.15	800 – 1,000	100	-6
15 mm	O₂	0.15	500 – 650	100	-7

Cutting chart — 6 kW fiber laser

Thickness	Gas	Pressure (bar)	Speed (mm/min)	Power (%)	Focus (mm)
1 mm	N₂	18	30,000+	60	0
3 mm	N₂	20	15,000 – 17,000	85	-1
6 mm	N₂	24	6,000 – 7,500	100	-3
8 mm	N₂	26	4,000 – 5,000	100	-4
10 mm	N₂	28	2,800 – 3,500	100	-5
12 mm	O₂	0.2	1,800 – 2,200	100	-6
15 mm	O₂	0.15	1,200 – 1,500	100	-7
20 mm	O₂	0.1	700 – 900	100	-10

Choosing between oxygen and nitrogen

The decision is more nuanced than the charts let on. Here’s the practical version:

Use oxygen when:

• Material is ≥ 3 mm
• Customer is welding or painting the edge afterwards (a little oxide is fine)
• You’re priced competitively and gas cost matters
• You don’t have a high-pressure N₂ supply

Use nitrogen when:

• Final finish must be clean (no oxidation, no scaling)
• Stainless steel — N₂ is mandatory, don’t argue
• Customer is plating, anodising, or leaving the cut edge exposed
• Thickness ≤ 4 mm (N₂ at lower thicknesses is genuinely competitive on speed)

Use compressed air when:

• Material is ≤ 2 mm
• You’re prototyping (final part will be cut in production)
• Budget machine without bottled gas plumbing

Nozzle selection matters more than the chart

The settings above assume a clean, properly-sized nozzle. Wrong nozzle = wrong cut regardless of how perfect the speed/power numbers are.

Rough guide:

Thickness	Single nozzle Ø	Double nozzle Ø
≤ 1 mm	1.0 mm	1.0 / 1.2 mm
2 – 3 mm	1.5 mm	1.4 / 1.5 mm
4 – 6 mm	2.0 mm	—
8 – 10 mm	2.5 mm	—
12 – 15 mm	3.0 mm	—
20 mm	3.5 – 4.0 mm	—

Replace nozzles every 8 – 16 hours of cutting. Slag pickup on the tip distorts the gas column and your edge quality dies before your speed drops.

Common cutting problems & fixes on mild steel

Dross sticking under the cut

• Drop speed by 10 – 15%
• Increase O₂ pressure by 0.05 bar
• Re-focus 0.5 mm deeper into the material

Burn marks / heat damage on small features

• Add lead-in/lead-out on every internal cut
• Reduce power on detail pierces by 10%
• Slow pierce time by 0.2 seconds

Wide kerf / sloppy edge

• Re-focus the lens — most common cause
• Check nozzle concentricity
• Clean the focusing optic

Inconsistent cut quality across the sheet

• Re-level the cutting bed (especially after a crash)
• Re-zero the Z-axis via auto-focus probe
• Check sheet flatness — buy flatter material if you keep fighting this

Using DXFForge designs with these settings

Every design in our catalogue is drawn with 0.1 mm kerf compensation as default. That works for:

• Fiber laser on mild steel ≤ 6 mm with O₂
• Fiber laser on stainless ≤ 4 mm with N₂

For thicker mild steel (≥ 8 mm), increase kerf compensation to 0.3 – 0.5 mm in your CAM software before sending to the machine — otherwise the slots will be slightly tighter than designed.

If you want a quick test piece to dial in your settings, the ABS-01 design at 200 x 300 mm has internal cuts at multiple scales — perfect for verifying speed/power across feature sizes.

TL;DR

• Above tables = good starting point, ±15% for your machine
• O₂ for thick, N₂ for clean, air for ≤ 2 mm
• Nozzle wear ruins your cut faster than wrong settings
• Re-focus before blaming the design

Bookmark this page. Print the chart. Re-tune every 6 months as your machine ages.