A three-pack of 25mm gold-plated silicon mirrors, 3mm thick and precision polished flat. They suit K40s that have moved to 25mm mounts, and they come with a firm warning to keep solvents off the coating.
The Qding set is sized for upgraded machines. Most K40s leave the factory with 20mm mirror mounts, and a 25mm mirror will not go into a 20mm seat. If you are still on stock mounts, this pack is the second half of a conversion, not a drop-in swap.
Why convert at all? A 25mm mirror presents a wider target. On a K40 the beam rarely hits dead centre on every mirror at every corner of the bed, and a bigger mirror keeps an off-centre beam on the reflective face instead of clipping the edge. Owners who fight alignment every week often find the extra margin worth the work.
Qding rates the mirrors for 60W to 400W. Do not read the lower figure as a minimum. A mirror has no lower power limit in practice; the range just tells you the coating tolerates far more heat than a K40 tube produces.
The mirrors are 3mm thick, the usual depth for CO2 mirror mounts, and precision polished flat. Qding does not publish a reflectivity figure for this set. Gold-plated silicon in general reflects well over 99% at 10,600nm, but that is the material class, not a Qding measurement.
The size change also affects spares. Once you convert, every future mirror order is 25mm, and the 20mm spares in your drawer become useless for this machine.
Three mirrors cover the whole beam path: one by the tube, one on the gantry, one in the head. Replace them together so every surface starts equal.
| Spec | Value |
|---|---|
| Diameter | 25mm (0.98 in) |
| Thickness | 3mm (0.12 in) |
| Shape | Plane, optically flat |
| Substrate | Silicon |
| Coating | Gold plated |
| Mirrors per pack | 3 |
| Wavelength | 10,600nm CO2 |
| Power range | 60–400W |
| Finish | Precision polished and ground |
| Cleaning | Avoid alcohol and other solvents |
| Storage | Keep away from water vapour and humidity |
| Mirror dimensions | 0.12 × 1.05 × 0.98 in |
| Weight | 1.12 oz |
A mirror conversion goes smoothly when the mounts, head and mirrors are all on the bench at once. Half a conversion leaves the machine down while you wait for parts. Work out the full list first, then order it together.
Expect alignment to take longer than a straight mirror swap. New mounts sit at new heights, and the tube may need shimming so the beam enters mirror one level. The K40 alignment guide covers the tape-target routine and how to square each mount.
A beam alignment tool makes the job quicker.
The K40 upgrade guide puts mounts and optics in context with air assist and the bed, so you can batch jobs that need the machine opened up.
Qding is unusually direct about the coating. It describes it as silicon-based and relatively fragile, and says not to wipe it with alcohol or other solvents. That runs against the routine many owners use on gold silicon mirrors, so follow the maker's word on these.
That makes prevention the whole game. A mirror you are not allowed to clean with solvent has to stay clean in the first place.
Qding also warns about water vapour. Residual moisture in a humid room can lift the coating. Store spares sealed with a desiccant, and do not run cooling water so cold that the machine sweats inside.
Condensation is a warning sign for the whole machine. If water forms on the optics, it may also form on the tube and high-voltage lead, which is dangerous. Keep coolant near room temperature, and let a cold machine warm up before firing.
Check the mirrors on a schedule rather than when cuts go weak. A quick look with a torch every few sessions catches a film while it is still loose enough to blow away.
This coating suits a clean, dry, well-ventilated shop. If your K40 lives in a damp garage with a stock exhaust fan, a molybdenum mirror that tolerates scrubbing will serve you better.
At 25mm the choices are close. Several makers sell three gold silicon mirrors, 3mm thick, rated well past K40 power. The differences sit in published figures, packing and care instructions.
| Set | Material | Stated reflectivity | Notable |
|---|---|---|---|
| Qding 25mm | Gold silicon | Not stated | No solvents on coating |
| Cloudray 25mm | Gold silicon | Over 99.2% | Rated to 300W |
| CNCOLETECH 25mm | Gold silicon | Up to 99.8% | Vacuum packed, single pieces |
| TEN-HIGH 25mm | Molybdenum | Lower, as bare Mo | Uncoated, scrub tolerant |
The Cloudray set and the CNCOLETECH set both publish reflectivity, which makes them easier to judge. TEN-HIGH's molybdenum option gives up some reflectivity for a surface you can clean hard.
Pack size is identical across the four, so compare on care and conditions, not on count. Three mirrors in each case means one full beam path with no spare.
Whatever you choose, pull the lens for inspection in the same session. A cloudy lens wastes more beam than any mirror difference in this comparison. The K40 setup guide lists the checks worth doing before the first cut on new optics.
Usually not. Most stock K40 mounts take 20mm mirrors, so 25mm mirrors need upgraded mounts and a head with a 25mm mirror seat.
Qding says to avoid alcohol and other solvents. Blow dust off with a hand bulb, handle only by the edge, and replace a mirror that has baked-on residue.
No. Mirrors have no lower power limit in practice; the rating shows how much heat the coating tolerates.
A wider mirror keeps a slightly off-centre beam on the reflective face, which makes alignment more forgiving across the whole bed.