Laser Cutting Parameters Explained

You send a DXF to the laser job shop, the parts come back, and the edges look like a serrated knife — or the holes are tapered, or the thin sheet warped into a potato chip. Laser cutting looks like magic until your parts come back wrong; then you learn it's a thermal process with parameters, and the parameters are knowable.

This guide explains the parameters that control cut quality on CO₂ and fiber lasers, how to design parts that cut cleanly, and what to specify when you hand a drawing to a job shop.

How laser cutting actually cuts

A focused laser beam (spot ~0.1–0.3mm) melts/vaporizes material while an assist gas blows the molten metal out of the kerf:

• Fusion cutting (nitrogen/argon): the laser does all the melting; inert gas just ejects melt. Clean, oxide-free edges — the choice for stainless, aluminium, and parts to be welded or powder-coated.
• Oxygen cutting (reactive): oxygen burns with the iron, adding exothermic heat — faster on mild steel, but leaves an oxide layer on the edge that must be removed before powder coating.
• Fiber vs CO₂: fiber lasers (1.06µm wavelength) couple far better into metals — faster on thin sheet, lower running cost. CO₂ (10.6µm) remains excellent on thick plate and non-metals (acrylic, wood). Most student sheet work (1–6mm MS/SS) is cut on fiber today.

The parameters that matter

The operator balances these per material and thickness — your job as the designer is to give them geometry that can be cut well, and to specify the edge quality you need.

Note: You don't need to memorize a parameter table for every thickness — job shops have cutting charts. What you must know: how parameters trade off (speed vs quality vs dross), so you can have an intelligent conversation when the shop says "this will cut, but the edge won't be pretty."

Reading cut quality: what the edge tells you

Kerf width (material removed by the beam, typically 0.1–0.3mm on thin sheet) must be compensated in your CAD: draw the part at nominal size and let the shop apply kerf compensation, or offset your profiles by half the kerf yourself — and confirm with the shop which one of you is doing it. Double compensation is a classic error.

Design rules for laser-cut parts

1. Minimum hole diameter ≥ material thickness. A 2mm hole in 5mm plate won't cut cleanly — the beam can't eject melt from a deep narrow hole. Rule of thumb: hole Ø ≥ 1× thickness (≥ 1.5× for thick plate).
2. Minimum feature/web width ≥ thickness. Thin webs between cutouts warp and burn away.
3. Corner radii ≥ 0.5× thickness on internal corners — sharp internal corners are stress risers and cut poorly (the beam must decelerate to a stop).
4. Lead-ins/lead-outs: the beam pierces inside the scrap or on the profile with a small lead-in — never specify a pierce point on a finished edge; the pierce leaves a blemish. On holes, pierce at the hole center where possible.
5. Nesting and common-cut lines: the shop nests your parts on the sheet; keep part spacing ≥ thickness, and supply the DXF clean (no duplicate lines, no splines exploded into a thousand segments, closed profiles only).
6. Etching/marking: part numbers, bend lines and logos can be laser-marked (low power) in the same setup — free and permanent. Mark bend lines on the inside of bends.
7. Flatness: thin large panels warp from heat — break them up, add stiffening bends, or accept post-cut flattening.

Tolerances: what laser cutting can hold

These are process-capability figures for a good shop on flat sheet — not guarantees on your warped 2mm panel. For press-fit or bearing features, laser-cut then ream/machine; don't expect H7 holes from a laser.

Warning: Laser cutting produces fumes (metal oxides, and toxic gases from coated/galvanized stock — never laser-cut galvanized or PVC without proper extraction and knowledge of the hazards), intense light, and hot parts. As the customer/designer your safety role is smaller, but in the college lab: laser safety glasses for the wavelength in use, interlocks respected, extraction on, and no watching the cut point directly. Follow the lab's laser safety induction — it overrides everything here.

What to send the job shop (the checklist)

• DXF/DWG, 1:1 scale, mm units, closed profiles, no duplicate geometry
• Material and grade specified (e.g. "MS CR sheet 3mm" / "SS304 2mm") — not just "steel"
• Thickness confirmed against the shop's stock (3.0mm vs 2.9mm matters for press fits)
• Quantity, including spares for the learning curve
• Edge requirement stated: as-cut / deburred / ready for powder coat (oxide-free → nitrogen cut)
• Kerf compensation: confirm who applies it
• Bend lines marked if the shop also bends (send the bending drawing too)
• Delivery: flat-packed with protective film kept on until assembly

Common mistakes

1. Holes smaller than thickness — then complaining about taper and dross.
2. Forgetting kerf compensation (or both sides applying it).
3. Sharp internal corners on load-bearing profiles.
4. Specifying laser-cut precision holes for bearings — laser, then ream.
5. Galvanized or coated sheet without telling the shop (fume hazard + ruined optics).
6. No deburr callout — as-cut edges are sharp; someone will bleed during assembly.

Where to go from here

• Engineering Tolerances & Fits Explained — what to tolerance on laser-cut drawings.
• Arc vs MIG vs TIG Welding — joining cut parts when fasteners won't do.
• More fabrication topics in the Mechanical branch hub.