Not strictly 3D printing,

Not strictly 3D printing, but built with a 3D printer:

Never, ever, build a laser cutter/etcher that doesn’t have an enclosure + door kill switch. You may be wearing eye protection, but you never know who is going to enter the room unprotected.

@Shachar_Weis while I do agree with that, in this case other precautions have been taken. It is not In a shop where others would be around, it is in a locked room at my home. That said, I am working on a light guard that will be attached to the laser, as the construction of the 3d printer that was used as the base machine makes it infeasible to add an enclosure. Additionally, where it is very easy to stop the ir light from a co2 laser, using acrylic, the 445nm light emitted by this laser is much more difficult to stop with a material that is transparent to most optical wavelengths. And, not to downplay the danger of lasers, but we’re not dealing with a 40+ watt CO2 laser here, we’re dealing with a 2.5 watt commercially available HANDHELD laser. While its is true that there is still significant risk of dammage to eyes if you look directly at the beam, it is in a whole different ballpark than a proper laser cutter.