Laser Engraving...resins with mica powders

[jrista]

I am working on a pen for a customer who wanted an engraving. This particular pen is using an acrylic blank with pebble shapes and mica powder pigments. So its slightly translucent, not a lot but a little. I've engraved resins before, although mostly solid color, and then mostly black. This particular resin scatters a lot of the laser light, and I am having some trouble getting all the details into the engraving. Thus far, I've only turned it just to round, and have been doing test engravings, as I was not 100% certain how it would take. Good thing...

I am wondering if anyone has engraved blanks like this before? If so, any tips or recommendations for how to engrave this kind of blank well? I originally tried with a thin masking tape. Tape I've used before, but for some reason the engraving did not actually fully penetrate the tape even after 25 passes at 100% power. I then took the tape off, and started test engraving, and while it is engraving the surface, its not going very deep (50 passes now so far), and I'm not sure its really a great quality engraving. I knew there would be some differences engraving this material, vs. the black or solid resins I've engraved in the past...however, it seems its a fair bit different than I originally expected.

Thanks!

 

[hokie]

I am working on a pen for a customer who wanted an engraving. This particular pen is using an acrylic blank with pebble shapes and mica powder pigments. So its slightly translucent, not a lot but a little. I've engraved resins before, although mostly solid color, and then mostly black. This particular resin scatters a lot of the laser light, and I am having some trouble getting all the details into the engraving. Thus far, I've only turned it just to round, and have been doing test engravings, as I was not 100% certain how it would take. Good thing...

I am wondering if anyone has engraved blanks like this before? If so, any tips or recommendations for how to engrave this kind of blank well? I originally tried with a thin masking tape. Tape I've used before, but for some reason the engraving did not actually fully penetrate the tape even after 25 passes at 100% power. I then took the tape off, and started test engraving, and while it is engraving the surface, its not going very deep (50 passes now so far), and I'm not sure its really a great quality engraving. I knew there would be some differences engraving this material, vs. the black or solid resins I've engraved in the past...however, it seems its a fair bit different than I originally expected.

Thanks!

Have you thought about applying a light coat of black spray paint? I've seen some marginal success with that approach on clear acrylic. For example:

A CO2 laser is required for proper etching/cutting, I believe. But if you're able to get away with a frosted look, the above method may work.

 

[jrista]

Have you thought about applying a light coat of black spray paint? I've seen some marginal success with that approach on clear acrylic. For example:

A CO2 laser is required for proper etching/cutting, I believe. But if you're able to get away with a frosted look, the above method may work.

I did eventually try that. Along with a bunch of other things. I think it is that my laser is a 5.5w (optical) diode, and it just doesn't have enough power to vaporize the material. Instead, it seems to diffuse, so the beam once it hits the resin, suddenly enlarges and the power drops significantly. So the resin melts, but it does not vaporize.

The frosted look was pretty bad, as the metallic particles cause hotspots, so some parts of the engraving were cavities, others were frosted goo.

It sounds like a CO2 laser engraver could do the job. They have much greater power and should be able to vaporize the material, although it seems you need an air assist to make sure that material is blown away before it resolidifies (lot of people talk about the issue of acrylic residue re-solidifying on their parts!) CO2 engraving system is well out of my budget right now, so I'll just shelve this idea.

Unless, I guess, the Ortur LM3-40A diode laser would work. They claim 40W output optical power, by using two sets of four 5W diode lasers internally and combining their power. I'm sure there are losses that limit the output power to some degree...but its significantly more powerful than my 5.5W. Dunno if its powerful enough to vaporize resins or not.

 

[jrista]

Well, did a few more experiments, and I think I've confirmed that if your laser is not high enough power, all it really does on most resins is melt it, and it will instantly resolidify. I am not quite sure of the exact nature of the issue, but once the resin has been melted like that, subsequent attempts to laser it away do not seem to do anything. So multiple passes, shallower but significantly more passes, don't help.

Another issue is that the pigments, can cause hot and cold spots. Where the pigment is denser, that often gets a lot hotter, and you can end up with pretty deep pitting. The pigments (this particular stuff is legit metallic, I think, not mica, but I could be wrong) can also scatter the beam a lot, and I don't know how dangerous that might be without an enclosure (I don't have a specialized enclosure for my Ortur LM2). My laser is a 5.5W optical power, but many are 20, 40 or even more powerful (and CO2 even more so).

I do not know if a 20W or 40W laser would do the trick for resins like this. That's 4-8x more powerful than my laser, so it may well be enough. Most people recommend a CO2 laser, though, and even at just 20% such a laser seems to be plenty powerful enough to properly engrave resins (or so I've read.)

 

[MRDucks2]

As I am looking at a potential second laser once the new shop is built, I have found there is more to lasers than power. The range they are firing in greatly affects how they perform on various materials. As a basic example, a fiber laser works on stainless and brass, but performs poorly on wood and doesn't touch clear acrylic or glass, a CO2 laser performs poorly on uncoated metal but does well on clear acrylic or glass. A diode laser, of which I own two different power laser heads, can do a lot of materials if you first apply the proper coating, does not cut well, and etch the bottom side of clear resin better than the top side (found that out by accident).

In all honesty, from my experiments with my diode lasers and my study of potential next level lasers, there is still a lot of "art" to the process when it comes to trying to find or develop methods to achieve what you want, with what you have, on various materials, for various effects.

With all that said… yeah, diode lasers melt resin.

 

[jrista]

As I am looking at a potential second laser once the new shop is built, I have found there is more to lasers than power. The range they are firing in greatly affects how they perform on various materials. As a basic example, a fiber laser works on stainless and brass, but performs poorly on wood and doesn't touch clear acrylic or glass, a CO2 laser performs poorly on uncoated metal but does well on clear acrylic or glass. A diode laser, of which I own two different power laser heads, can do a lot of materials if you first apply the proper coating, does not cut well, and etch the bottom side of clear resin better than the top side (found that out by accident).

In all honesty, from my experiments with my diode lasers and my study of potential next level lasers, there is still a lot of "art" to the process when it comes to trying to find or develop methods to achieve what you want, with what you have, on various materials, for various effects.

With all that said… yeah, diode lasers melt resin.

Thanks for the response.

I'm curious, what power have you used for Diode lasers? My 5.5W does not do a whole lot, I'm finding. I have done a little bit of experimentation with sprays for metals, and I have long had this idea of engraving all of my bushings with details of which kit and barrel part they are for. I haven't gotten around to doing that en-masse yet, as I'm not sure how well the spray will really hold up with just a 5.5W laser (I think they may even state that a 10W is required for best results.) In any case, when I bought my Orture (2021, IIRC), a 10W was as high as they went, although they were working on releasing a 20W. Today, there are 20W and even 40W (and this is the optical power, according to Ortur) laser modules, though they apparently only work with the Ortur LM3 (which is an even bigger investment than I've made in my LM2 so far.) Still, I really wonder if the 20W and 40W modules are really that much more powerful. I have some aspirations of doing cutting as well as engraving, mostly for custom wood pen boxes, and I don't think my 5.5W laser is up to the task even on thinner wood stock.

I have found, in my journey with my Ortur LM2 Pro, that once you REALLY find the focus point (which is not an easy task, and a factor of inconsistency between runs), you can get some INCREDIBLY FINE engraving. Its actually pretty amazing. Finding that perfect focus, though, is tough, and its a much narrower CFZ (at least with my laser) than indicated in the documentation. The trick I've come to use, is using one of those aluminum focusing cards, and when the beam reflects off the card and makes a tight reflection on the orange shroud, then I've reached optimal focus. There is a focusing block, but it does not seem to be accurate for my laser. So I always have to fiddle. I did pick up a manual z-index adjuster, which has GREATLY helped the process, but its still a bit of a chore, and sometimes if I don't totally nail that focus, the resulting engravings are not of the optimal quality (i.e. fatter engravings, like bolding a font...subtle, but still...annoying.)

Interesting about CO2 working on clear acrylic. That is what I've seen people do...I guess I haven't seen anyone engrave pigmented resins yet. I have done some engraving with BLACK acrylics and other resins, however the resins are opaque, dark, the engravings were shallow, and I am guessing that helped get the job done. Thinking back on it, though, I don't think I was entirely satisfied, even then, as I thought the edges were soft and the engravings did not look as good as I had imagined (my imagination was all sharp corners and angles and fine details, which was not the case.)