Use the machine's focus gauge as documented, then verify with a ramp test — two minutes, and it settles the question for good.
Prop a strip of scrap at a shallow angle, engrave one low-power line along it, and look for the thinnest darkest point. That's true focus. Compare with the gauge reading.
Common LP4 focus mistakes
- Focusing to the bed instead of the material surface. The gauge references the top face of what you're cutting.
- Forgetting to refocus after a thickness change. 3mm to 4mm ply is enough to soften an engrave visibly.
- Curved and cylindrical work. On a tumbler, focus to the highest point of the curve — the point nearest the lens — and keep the engrave band narrow. Wide bands on a curve go soft at the edges.
- Bowed material. Hold it flat with magnets or a honeycomb bed. Focus can't fix a moving surface.
If a good engrave has become a weak engrave with no settings change, check the protective lens before you re-examine focus.
LaserPecker publish their own documentation on this topic — worth reading alongside these community notes.
Official article