Diode Laser Engraving: Power, Speed, and Material Settings That Actually Work

Diode laser settings are frustrating because no two machines are the same — even the same model will vary based on lens condition, air assist pressure, and ambient temperature. This guide gives you a systematic approach to dialing in settings for any material, plus a starting-point table for common ones tested on a 20W diode laser.

How Diode Lasers Cut and Engrave

A diode laser (like the Longer Ray5 20W or xTool D1 Pro) works by concentrating light into a tiny spot. The laser doesn't "cut" — it vaporizes and oxidizes material. The two variables you control are:

Power (%) — How much of the laser's rated wattage is being used. At 100% you get maximum output; most engraving is done at 30–80%.
Speed (mm/min) — How fast the head moves. Slower = more energy per mm of travel = deeper/darker marks.

These two interact multiplicatively. Halving speed has roughly the same effect as doubling power — but they're not perfectly interchangeable, because material response is nonlinear at extremes.

Air Assist: Don't Skip It

Air assist blows a stream of air across the cut line, ejecting smoke from the beam path and suppressing flare-ups. Without it, smoke deposits on the lens (kills power output fast), materials char rather than cut cleanly, and fire risk increases significantly. Run it for all cutting jobs. For engraving, light air assist reduces char on edges without blowing away fine engraving residue.

Focus: Get It Right First

A defocused laser spreads power over a larger area — result: less depth, wider kerf, worse edge quality. Most diode lasers ship with a fixed-focus lens and a focus block or card. Use it every time you change material thickness:

Home the Z axis or set Z to zero
Place material on the bed
Use the focus spacer to set the correct nozzle-to-material distance
Lock the Z and remove the spacer before running

If your machine has autofocus, still verify it on thick or irregular materials — it can misread dark or shiny surfaces.

Starting Point Settings (20W Diode Laser)

These are starting points for a 20W optical output diode laser with air assist at ~15 PSI. Run a test grid on scrap before committing to a full job.

MaterialOperationPower %Speed (mm/min)PassesNotes 3mm Baltic birchCut1006002–3Grain direction affects clean-through consistency 3mm Baltic birchEngrave (fill)4540001Line interval 0.1mm for fine detail 6mm pineCut1003003–4Resinous knots won't cut cleanly — avoid or plan for it 3mm acrylic (cast)Cut1004002Cast only — extruded acrylic doesn't cut well with diode Leather (veg-tan, 3mm)Engrave3530001Lower power for lighter burn; high power chars deep Leather (veg-tan, 3mm)Cut855002Chrome-tan leather releases toxic Cr(VI) — don't cut it Anodized aluminumEngrave8015001Ablates anodize layer; bare aluminum underneath CardboardCut708001Watch for fire — always supervise Slate tileEngrave9010001High contrast; no air assist needed Cork (3mm)Cut607001Very clean cuts; great for gaskets and stamps

Materials to Never Laser

Some materials produce toxic or corrosive fumes that will harm you and destroy your machine:

PVC / vinyl — releases chlorine gas. Damages lungs and corrodes the machine's metal parts.
Chrome-tanned leather — produces carcinogenic Cr(VI) fumes. Veg-tan only.
ABS plastic — releases cyanide-containing compounds. Use acrylic instead.
Fiberglass / FR4 (PCB material) — glass fiber and resin fumes are severely hazardous.
Carbon fiber — fine carbon particulate is a serious respiratory hazard and electrically conductive dust.
Polycarbonate — cuts very poorly and produces thick yellow smoke.
Mirrors / reflective metals (bare) — will reflect the beam unpredictably and potentially back into the laser module.

How to Dial In Your Own Settings

LightBurn has a built-in Material Test generator (Edit → Material Test). It creates a grid varying power on one axis and speed on the other. Run it on a piece of scrap, pick the cell that looks best, and log the values. Key things to record:

Material, thickness, and source (same nominal spec from different suppliers can vary)
Power, speed, interval, passes
Air assist pressure
Ambient temperature (laser diode output drops in heat)

Keep a log — either a spreadsheet or a text file. After a few months you'll have a reference library that saves hours of test time.

Maintaining Output Power

Laser power degrades over time and faster if the lens is dirty. Symptoms: jobs that used to cut clean are now barely scoring. Check and clean the lens first before increasing power. Use a cotton swab with IPA (isopropyl alcohol) — drag, don't scrub. Inspect the protective window if your module has one. Also check that the laser module cooling is working; thermal throttling silently reduces output.

🔧 Related tool: Material Settings Lookup

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