A CVD zinc selenide lens at the K40's standard 50.8mm focal length, but in an uncommon 14mm diameter. It suits heads bored for 14mm; most K40 heads are not.
Lens diameter is not a detail. It decides whether a lens fits your head at all. K40 heads are commonly made for 12, 15, 18 or 20mm lenses, and 14mm falls between the usual sizes.
| Head seat | This 14mm lens |
|---|---|
| 12mm (stock K40 head) | Too big, will not go in |
| 14mm | Correct fit |
| 15mm | Goes in with 1mm of play; needs a spacer |
| 18mm or 20mm | Far too loose without an adapter |
Look at the upgrade heads K40 owners buy most. The Lightobject head takes 12, 15, 18 and 20mm lenses. Cloudray, MCWlaser and FONLAND heads list 12mm and 18mm, with 15mm possible in some using an O-ring. None of them names 14mm.
The product name also mentions a 15mm size and some unrelated optical uses. Ignore the noise and order by the diameter your seat needs. If that number is 14mm, this lens is one of the few that match. If it is 12, 15, 18 or 20mm, buy that size instead.
Getting diameter wrong is the most common lens-ordering mistake on the K40. It costs a return, and worse, it tempts owners to wedge in a lens that does not fit. Five minutes with calipers prevents both.
| Spec | Value |
|---|---|
| Diameter | 14mm |
| Focal length | 50.8mm |
| Focal length in inches | 2 in |
| Material | CVD ZnSe |
| Material origin | Described as USA |
| Other diameter named | 15mm |
| Coating | Double-sided coating (maker) |
| Transmittance | High, no figure given |
| Finish | Precision sliced, polished and ground |
| Heat | Rated for higher operating temperatures (maker) |
| Laser type | CO2 engraving and cutting machines |
| Package size | 0.39 × 0.39 × 0.39 in |
| Shipping weight | 1.76 oz |
Diameter aside, the specification is sound. The lens is CVD zinc selenide, the grade used across industrial CO2 optics, and its focal length is the K40's standard 50.8mm. The material is described as US-made.
CVD, chemical vapour deposition, produces a dense, uniform crystal with low absorption at the CO2 wavelength. In practice CVD lenses have a reputation for running cooler and lasting longer than budget PVD lenses under the same load. That matters most on a machine that cuts at high current for long stretches.
The 50.8mm focal length means no bed changes if you are replacing a 2-inch lens. Your focus gauge, ramp-test notes and material settings stay valid.
No thickness figure is published. Lenses in this class are often around 2mm thick, but seats differ in depth, so measure your old lens and compare before fitting.
The K40 alignment guide covers focus height and ramp tests if you want to confirm the focal point after fitting.
If you have no 14mm seat but like the spec, CVD lenses at 50.8mm exist in every common diameter. That is usually the better route than adapting a head to fit an unusual lens. Common sizes are also easier to replace on short notice when a lens cracks mid-project.
Here is why a lens in the wrong seat is more than an annoyance. A focusing lens that sits off-centre from the beam bends the beam slightly sideways, like a weak prism. The focused spot shifts, and it can smear rather than stay round.
Worse, a loose lens can move. Head vibration during a job lets it creep in its seat, and the spot creeps with it. The symptom looks like bad alignment or a slipping belt, and it wastes hours of chasing.
Shimming with tape or foil is a bad fix. Adhesive and foil sit in the heat of the head, can outgas onto the lens and rarely centre it evenly. Use a machined ring or buy the right size.
Keep it clean once fitted: air first, then solvent on tissue, never the other way round and never dry. One stroke per clean face of the tissue.
A lens that clouds quickly is taking smoke. Air assist through the head keeps it clear, and the upgrade guide ranks it among the first improvements worth making.
The honest comparison is about fit. The same CVD material and 2-inch focus are available in the sizes K40 heads use. Unless your head needs 14mm, one of those will serve you better.
What sets the zwqpeic lens apart is the 14mm diameter and nothing else. For the few heads bored to that size, it gives you CVD grade at the standard focus in one step.
Run this check at the machine:
If you are unsure what head your K40 has, check the lens tube markings or measure the old lens. First-time owners will get more from the K40 setup and safety guide than from any lens swap.
Only if your head's lens seat is 14mm. The stock K40 head takes 12mm, and most upgrade heads take 12, 15, 18 or 20mm.
Only with a spacer that centres it. A loose lens sits off-centre, which shifts and smears the spot, and it can creep during a job.
CVD crystal absorbs less of the beam and tends to outlive PVD on a hard-worked machine. PVD is the budget option for spares and light duty.
Not if your current lens is also 50.8mm focal length. The focal point stays where it was.