It’s a large-ish remnant of clear plastic, ~6mm thickness. It might be cast acrylic… but I was struck that it just sort of “feels” wrong. It seems relatively heavy/dense, as well as possibly harder. The laser-cut edges also look “meltier” than I usually see in cut acrylic.
I’ll admit that I might be imagining mysteries where there are none, but also thinking of this as a chance to learn. If it is some acrylic-adjacent polymer that has different properties while still being laserable, that is nice to know.
Hmm, could be. I have very little experience with extruded acrylic, aside from a general impression that cast acrylic has a better reputation (i.e. more consistent / less brittle) — honestly I’m not sure how true that really is.
It did occur to me later that the “extra melty” edge texture might be a side effect of leaving the soft protective film on it — that looks like a stretchy poly film that quite possibly leaves more residue. I didn’t make those cuts though so I don’t know.
Just playing armchair detective here, but if I were to hazard a guess I would say low power, low speed? Or maybe artwork with an outer edge that cut multiple times? You can kind of see points on the left side where the beam may have lingered for longer where the artwork met the edge.
But in my experience this just results in vaporized material rather than “melty” looking edges.
2nd guess would be possibly Lexan? (polycarbonate)
This is a wild guess because I steer clear of the stuff since it’s on the PLZ NO CUT list.
But a quick googling says that: “Laser-cutting polycarbonate can sometimes result in rough or melted edges”
So if the material seems “off” compared to what you’re used to seeing from acrylic that would be a good candidate given that it’s stocked at Home Depot right next to the acrylic.
EDIT: the more I think about it the more I’m leaning towards Lexan. Esp since James said it felt “relatively heavy/dense” That and the fact that it was 6x thicker than what the wiki warns against makes me think that all the pieces fit.
I’ve found sources saying that laser cutting polycarbonate is totally fine, but I’ve also seen sources that say it gives off toxic fumes.
I think this warrants some attention since I don’t know if it’s common knowledge among asmbly members that Lexan is not allowed on the lasers. I’m too lazy to find any citations on the Lexan=Toxic point, but I’d prefer to err on the safe side naturally.
It’s not polycarbonate (Lexan). That stuff isn’t toxic but on a laser it just cracks, chars, and smokes without any usable cut.
I’d suspect it’s acrylic, probably extruded. Cast acrylic is literally poured into forms of a particular size and allowed to harden. Extruded is made in a continuous sheet as a viscous, near-molten state extruded much like 3D printing but a huge ribbon instead of circular nozzle orifice. Then it passes through rollers to flatten it while still soft.
The extrusion process creates internal stresses as the polymer chains are stretched out and frozen into place. When lasered, the heat-affected zone around the cut softens or liquifies and the stretched polymer chains contract again, pull away from their cooler neighbors, creating cracks.
