Symptom table
| Symptom | What it means | How to check | What to do |
|---|---|---|---|
| Cut quality degrades over several days | Dust and metal fume build-up | Inspect under raking light — an even haze | Clean with proper solution and lens tissue |
| Cut quality drops suddenly within one shift | It has burn spots | Look for black dots or pitting | Replace, do not clean |
| Cutting head temperature alarm | Lens absorbing energy because it is dirty or burned | Check the controller alarm | Stop the machine and inspect immediately |
| Newly fitted lens gets dirty fast | Contaminated assist gas, or insufficient purge | Check the gas filter and moisture | Replace filters; drain water from the line |
| Dirties very fast on film-coated sheet | Normal — coating produces adherent fume | Compare against bare sheet | Inspect more often; consider removing the film first |
Telling dirty from burned
Hold the lens at an angle under a strong light and look both through it and at its reflection:
- Even haze, no darker spot anywhere → dirty. Cleanable.
- Black dots, small rings, or pitting → burned. Must be replaced.
- Cracks or chips at the edge → replace immediately, even if it still cuts.
A burned lens absorbs energy instead of passing it. It heats up fast, and that heat travels up into the focusing lens. This is how a cheap part destroys an expensive one.
Changing it correctly
- Power down the laser source completely — not just the program
- Let the head cool
- Clean your hands and the surrounding area before opening — dust that falls in at that moment is a common reason a new lens is dirty immediately
- Lint-free gloves, handle by the edge only
- Correct orientation, correct seal, hand-tight
- Run a test part and compare the edge against a reference part
The most commonly misjudged point
Many shops replace the lens only when the machine stops cutting. By then it is usually too late.
Cut quality declines well before the machine stops cutting — and during that period, a dirty lens is pushing heat into the optics upstream of it. The real cost is not the lens; it is what the lens takes with it.
The right practice: inspect on a schedule, not on symptoms. Once per shift under heavy load, once per week under light load. Log the replacement date.
How many to stock
Keep at least two on the shelf at all times. It is the cheapest part in the head and the one that causes the longest downtime when you do not have it. We supply protective lenses and nozzles for the machines we sell — tell us your cutting head model and we will quote the right part, even if the machine did not come from us.