Most laser guidance starts with settings to try. The first-cut guide starts where the accidents start: the materials that never go under the beam, whatever the setting. The table is short enough to memorize and worth the memory work.
| never under the beam | why |
|---|---|
| PVC, vinyl, artificial leather | chlorine fumes — they eat the machine and the maker |
| Polycarbonate | fire, and it won't cut past about 1 mm |
| ABS, HDPE | melt, and ABS makes cyanide fumes |
| Polystyrene, polypropylene foam | fire |
| Fiberglass, coated carbon fiber, G10, FR4 | resin fumes |
Each line earns its place with chemistry: chlorine in PVC becomes hydrochloric acid in the air path; ABS carries nitrogen in its chain and releases it as hydrogen cyanide; the foams melt and burn in the same pass a veneer would sit still and edge-burn. The guide's closing rule covers everything the table cannot: a material not on this list isn't automatically safe — check its safety data sheet.
Watts, honestly stated
Start one step before the settings table, because the settings inherit a lie. Many diode modules are sold by their electrical wattage; the light reaching the work is several times lower. The app's converter makes you choose which kind you entered — in any energy math, the honest figure is the optical output. The makers' tables carry it properly: the first-cut guide stores starting rows for real machines (Creality's Falcon2 at 12–40 W, xTool's D1 at 5 and 10 W), read from each maker's own parameter pages, with the source named in every saved setting.
The rule that predicts fire
Every setting reduces to one number — the energy the beam deposits per millimetre of travel:
E = W · (p / 100) · N / v
watts × power fraction × passes ÷ speed, in joules per millimetre. Worked: 20 W at 80%, one pass, 10 mm/s = 1.6 J/mm. The app's fire caution shows at 1 J/mm or more in a single pass, and the two working regimes sit sensibly on either side: a 10 W diode cutting at 5 mm/s runs at 2 J/mm (the burn has time to carry), while engraving at 250 mm/s runs at 0.01. The 1 J/mm threshold is the app's own convention — no standards body publishes one — but the makers' tables agree on its direction: slow and powerful is where fires live.
Two more habits from the same guide: extra passes don't behave the same as one slow pass (the heat concentrates differently), and every inherited number is a starting point for a test grid on scrap of the same material — different altitude, different lens state, different day. The rule the app won't soften: it refuses to convert settings between laser types — clear acrylic that a CO₂ machine cuts passes diode light straight through, so a converted row would lie to you.
Read the sheet, test on scrap, and keep the table above the machine. — the bench crew
