You already made cnc wire ecm machine, why not mashup these two? I've found one funny effect with plastic - you can cut thin plastic sheets just by dragging thin plastic or cotton thread perpendicular to sheet. It melts the plastic and it sticks to thread (so it removes material and plastic doesn't fuse back), it can easily cut a guitar pick out of cd case just using your hand and dragging strand from a synthetic rope back and forth. Melting is localised and results only from friction. What I've planned to do - buy some kevlar strand (easily available on internet, for use in sewing work clothes), do a machine which cuts anything by dragging a thread covered in diamond polishing paste. I wanted to do a cheap gear cutting machine, but I don't have enough free time currently. If you need any details, feel free to ask.

Hi Krzysztof,

nice to hear from you again.

Great idea, while building the hot wire cutter I also thought about building a diamond wire saw, but I couldn't find diamond wire for that and so I no longer thought about it.

Using a kevlar strand covered in diamond polishing paste could be an alternative for diamond wire.

I'm currently working on other projects, but I will try it out if I find the time for it.

For cutting plastic you don't even need paste, just any thread will do.

That's interesting. Would it be possible to use a closed nylon thread for cutting? 

Yeah, if it's long or thick. Short thin loop will probably disintegrate after 10 passes. Thicker one would survive much longer, but it should be long enough so that thread has enough time to cool. When you cut with just thread, melted plastic coats it, so after about two passes, it's mostly melting plastic in place and mixing with old plastic, leaving a burr near cut, but it should not solidify too much inside cut. Saws have advantage that they typically make flakes/dust which is constantly removed from cut and from saw. Here plastic is melted and stays on thread.

Ok, I will look into this when I have some time. Maybe the thread can be actively cooled to reduce wear.

That's annoying. The advantage of high temperature cutting is that the material evaporates and so can't fuse back together. But of course that's basically the same as laser cutting in that it requires fume extraction (and filters) which is what you wanted to avoid.

An alternative route could be using very strong air assist that is able to blow the molten material out of the slit before it solidifies again. But a lot of air is fighting your efforts to melt stuff in the first place. So I am not sure if that can be made work easily.

Good idea, maybe a coaxial high pressure air stream could do the trick.

Hi Florian, I thought about what you said in terms of using higher temperatures and thinner wire and I'm currently trying it out. It looks promising and I will tell you if I can get it working.

Ok, I'm cutting with a 0.5mm tungsten electrode and the cuts are looking better than ever before, but it will definitely need proper ventilation.

Maybe I can use the ventilation also for cooling the edges to prevent warping from the heat.

I only have experience with cutting foam and the method we used is not exactly smoke free. But we used much thinner wire and much higher temperatures. This allows to cut without touching and resulted in much smoother cuts. May be this is an option with exploring here, too. 1.8 mm feels awfully think to me.

Even with temperatures below the boiling point of polystyrene a thinner wire may result in better looking results.

Hi Florian,

I tried out 0.3mm kanthal wire and 0.9mm kanthal wire but had the problem that the wire can cross the plastic sheet without cutting it. It's fusing back together just after cutting. I just used the thicker wire because I couldn't cut with thinner wire and I would be very happy if I could get it to work with thinner wire.