Laser questions

[A_Camera]

Hi all,
I have a few questions regarding laser engraving. I intend to build a laser engraver using UCCNC but I am concerned about safety, so I will definitely make it safe or not at all. I am not very educated regarding the use of laser, so please excuse me if my questions sound simple and childish. I am only interested in diode laser, no CO2, so please don't waste time discussing that. I do not intend to use it for cutting, except some fairly thin plastic, I am mainly interested in engraving text in wood, paper, plastic and preferably aluminium. So, here are my questions:

1. I was thinking about 450nm blue laser. Is that usable for the purpose?
2. Would 2,5W be enough, or is it better with 5W? I know these are not very powerful, but as I said, it's about safety, and I was thinking that less power = safer.
3. I would like to box it in using green acrylic glass but will it block the light enough to keep it safe? Will I need some specific type or will any green acrylic sheet do?
4. Will it be possible to engrave text in aluminium? I have heard that 450nm wont work on any metal, but what does that mean? Since I don't want to cut, I don't care that it does not cut through metal, I just want to engrave.
5. Would it be possible to use it on glass? I mean real glass, not acrylic.

I hope some of the usual laser experts of this forum can give me some advice.
Thank you.

[spumco]

I am also not an expert, but I do have a "2.5w" cheap laser I've been playing with. Here are a some answers from another novice - perhaps to get the conversation going at least.

1. 450nm (in diode laser power levels) will generally not mark metal directly. It may mark a coating, anodizing, or other surface treatment depending on power and the substrate. The extremely high-power diodes (7+ real watts, not Aliexpress watts) may actually mark some metals. I've seen a video of a 10W cutting aluminum foil but it was not a clean cut.
2a. There is no 'safe' laser power level which will do anything to a material but not pose a risk to your eyesight. If it marks/cuts/burns a material, it will damage your eyes.
2b. My 2.5w(ish) laser will engrave/burn wood, paper, and cut mylar film. It's slow - painfully so. Higher power will permit faster engraving or processing, but it comes at a cost. My understanding is that higher power diodes have a larger minimum 'dot' size, and the 'dot' isn't actually a dot. It's more of a rectangle - and this is the reason I've given up on diode lasers for anything remotely serious.

The rectangle can be adjusted in size (focus), and shape (different lenses), but it's still going to be a rectangle. Meaning cuts/engraving will be different depending on the direction of motion. I found that my laser would cut fine in X, but not in Y. And if I slowed it down enough so Y cut properly, X would over-burn and I'd get comparatively ragged edges or darker lines. This was for cutting paper and mylar (polyester) film. Adjusting the 'dot' by fiddling the laser head and lens so that the rectangle was 45 degrees from X or Y helped a bit. A raster engraving with the scan lines at an angle to the regtangle also worked ok-ish. But the diodes are fundamentally non-circular beams.

3. No idea about the enclosure. I just bought safety glasses with the highest filtering value for the wavelength I'm using.

4. I seriously doubt it. Even the 10W laser I mentioned earlier just melted the aluminum foil - it wasn't pretty.
5. The 10W laser did it - actually etched/damaged the glass surface. I doubt anything less than a $200+ very high power diode will touch glass.

Regards,
Ralph

[dezsoe]

Hi Josef,

You should check the Hungarian forum and ask your questions there too. There are some members (especially PSoft) who could make these diode lasers work fine. Also, you can find some techniques to coat the aluminium and burn the paint onto it, so he made a well readable text or graphics.

[A_Camera]

Thank you for both of you.

I will post a question in Hungarian also, but I thought I'll start here.

Yes, I know there is no safe laser, if it burns through paper (and even before that) it will damage the eyes. What I meant by "safe" is that if it won't cut through a material (like thick acrylic glass) than it should be safe for what's on the other side of that plastic. Of course, sticking a hand in the light path would be pretty stupid, even dumber would be to look into the laser, which is why I want to box it so that I can be safe on the other side while the machine is working.

As I said, I don't intend to cut anything, only engrave. I'd still use my CNC, or all my other machines, to cut things.

[Battwell]

i have the 2.5 watt laser on my cnc router.
its good for wood engraving. maybe plastics but not much else!
i purchased a co2 laser for serious work.
its ok for marking joint numbers etc on my woodwork.