I’m interested in cutting foam for airplanes and I had read that I couldn’t cut “polystyrene”. However I have realized that something odd is going on: Both Depron and Gatorboard are polystyrene. The difference I can see if that they are extruded PS and instead of the common expanded PS (which I think is the material of takeout containers and premolded model airplanes).
So this leads to questions:
Can I safely cut Gatorboard-like coated extruded PS foams? I’m particularly thinking about Adam’s Readiboard (aka dollar tree foam board).
Is the main risk fire and melting? (Including the terrible molten bits dripping down and making hard lumps stuck to things) If so, would it be useful to do heat/flame testing to make sure the material behaves OK when it burns?
Now a few more thoughts that might be interesting/useful:
From basic research, I think expanded PS is an open cell foam making it brittle, whereas extruded PS is a closed cell foam and much more flexible and springy (Depron, some insolation foam, and I think readi-board as I mention above). I don’t understand laser cutting well enough yet to know how these properties would affect it.
I know there are a number people out there who cut a lot of readi-board on lasers, but I don’t know if they are taking risks that ASMBLY isn’t willing to take (very understandable).
I looked up cutting Readiboard and found someone who tested this on a Glowforge. The author found you can cut it but the results appear to show a bit of melting. In the comment section of that post someone contacted Readiboard about the safety of laser cutting their product and the response is yes but they do not expand very much on safely doing those cuts. LINK
All the examples I can find of cutting Readiboard shows someone using an Exacto knife. One thought is to get a drag knife set up for the CNC instead of the laser. A drag knife is essentially a blade that substitutes for the CNC bit that is pulled or dragged across the material. It is quieter than a regular CNC cut and produces no particulate waste.
There is a little melting when you cut it, but from everything I’ve seen (including what you link to) this shows up as a concave surface on the foam where it was cut, not as any kind of flow or dripping. This pocket isn’t an issue at all for my needs as I would often use hot glue and that melts the foam back from the paper a bit anyway. You can see this in the flitetest kits: FT Fun Pack MKR2 - Flite Test Retail Store.
Exacto is the way to go for hand cutting, absolutely. However, it’s slow and error prone to transfer complex plans onto the foam board so you can cut. You can print the plans and then stick them to the board, but that tends to leave gunk on the board or slip around while cutting. It’s also hard to accurately cut complex shapes, curves, inner corners (over cutting is really easy). It’s also pretty slow (especially when doing scoring since you need to avoid cutting throw the lower paper).
I have thought about a drag knife (though for some reason never though that you could attach one to a normal CNC machine). The lack of mess and vaporized plastic is really nice. I have assumed that a drag knife would not handle tight curves and inner corners well (same as hand cutting), but I could easily be wrong about this. I’m guessing it could do scoring as well by moving the Z-axis up. I’m signed up for the CNC class and I’ll keep this in mind. Maybe I can buy a drag knife attachment if we don’t have one and give it a try.
My end game plan is to build a reciprocating needle cutter with a pen plotter attachment to allow marking. This should have most of the ease of tool path planning of the laser cutter and still be relatively dust/gas free and do all the different operations I’m interested in (cutting, scoring, marking). I definitely have learning to do before I could successfully build a CNC machine myself though. (I have not really dug into the existing knowledge, but there are definitely resources out there. A quick search gets me: https://www.instructables.com/CNC-Needle-Cutter/, Mostly Printed CNC and cutting foam - RC Groups, and MPCNC Needle Cutter - YouTube)