ZNNRKMYO CO2 Laser Mirror

The flatness figure is quoted at 632.8nm, the red helium-neon wavelength optics are tested with. At the 10.6µm working wavelength, the same 158nm error is a far smaller fraction of a wave, roughly λ/67. In plain terms, flatness will not be what limits a K40.

• Clear aperture matters on a K40 because the beam rarely lands dead centre. Over 90% of a 25mm face leaves a wide usable zone.
• The negative-only diameter tolerance means the mirror drops into a 25mm seat without forcing.
• The bevel protects the edge when you pick it up with tweezers or gloved fingers.

No coating is mentioned, and none is needed. Molybdenum reflects the CO2 beam from its polished bare surface, which is why it survives cleaning that would strip a gold coat.

Everything above is ZNNRKMYO's stated specification. Treat it as what the part is made to, not a guarantee of how your beam will behave.

A single Mo mirror is a smart buy for one spot. The mirror in the head sits closest to the smoke and spatter rising off the work. It fouls first, gets cleaned most, and fails first. That is where a hard, uncoated surface pays back.

1. Keep gold silicon at positions one and two, where the air is cleaner and reflectivity counts.
2. Put the molybdenum mirror at position three, in the head.
3. Clean it as often as it needs without worrying about the coating.

What does that mix cost in power? Molybdenum reflects a little less than gold silicon, commonly quoted around 98% against 99% and up for gold silicon. With one Mo mirror in a three-mirror path, the difference at the lens is a percent or so on paper, less than a lightly dirty mirror costs.

This mirror needs a 25mm seat. Most stock K40s use 20mm mounts, so a 25mm Mo mirror belongs on a machine that has already moved to upgraded mounts and head. The K40 upgrade guide sets out that conversion.

If your machine runs clean with good extraction, the case for molybdenum weakens. It shines in shops where smoke is constant.

• Blow off loose dust with a hand bulb before any contact.
• Use isopropyl alcohol or acetone on a cotton swab or lens tissue.
• Wipe in one direction, turning to a clean face of the swab each pass.
• Moderate pressure is fine for baked-on smoke film; grit is the enemy, not pressure.
• Inspect under a torch for pits or burn marks in the centre.

Fitting follows the usual pattern. Wear clean gloves, hold the mirror by its bevelled edge, seat the polished face toward the incoming beam, and snug the retaining ring evenly. A ring bearing on one side tilts the mirror and walks the beam off target further down the path.

After fitting, realign. Even a like-for-like swap seats a fraction differently, and on a K40 small errors grow across the bed. The alignment guide has the tape-target method and the order to adjust each mount.

A target that clips onto the mount makes centring the beam on a fresh mirror far quicker.

Solvents are flammable. Clean with the machine off and let every trace evaporate before closing the lid and firing. Keep solvent bottles well away from the cutting area.

A Mo mirror that fouls every session is telling you something about airflow. Fix the exhaust and fit air assist, and every optic in the path will last longer.

• TEN-HIGH Mo: three molybdenum mirrors in 25mm or 30mm, for a full hard-surface path.
• Cloudray 25mm: gold silicon three-pack with a published reflectivity figure.
• OMTech 20mm set: Mo or gold silicon for stock 20mm mounts, not 25mm.

The ZNNRKMYO mirror's edge is the published optical specification. Few budget mirrors state scratch-dig, flatness and clear aperture, and those figures show the part was made to a known standard.

A mixed path is not a compromise if you plan it. Two gold silicon mirrors where the air is clean and one molybdenum mirror in the head give you high reflectivity and a tough surface exactly where each matters.

Run down these checks:

1. Your mount diameter: this mirror needs 25mm.
2. How many mirrors you need, since the count is not stated.
3. Which position the mirror will go in, and whether a mixed path suits you.
4. Your lens condition, because a burned lens hides any mirror gain.

For a machine you are still learning, start with how to use a K40. Optics upgrades make most sense once alignment, focus and airflow are sorted.