Hot-Wire Plastic Cutter

A Hot-Wire Cutter for Plastic Sheets

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I was searching for a "living room friendly" and cheap method for cutting plastic sheets like 4mm polystyrene sheets from the hardware store and other thermoplastics.
So I modified an Ender 3 for using it as hot-wire cutter in combination with a modified microwave oven transformer and a variac.
I also added a ventilation to carry fumes from cutting away and blower fans to prevent the plastic from fusing back together after cutting.
I tested it out with 4mm polystyrene sheets and 0.9mm kanthal wire at 60mm/min and I think the quality is quite nice.
While it can not compete with the cutting quality of a good laser cutter, the machine should be cheaper than most laser cutters and there will be no need to wear eye protection or to build an enclosure. Just keep an eye on it, because if something goes wrong there is a chance of plastic catching fire.
With active ventilation the smell is comparable to SLA printing - not pleasant but bearable.

  • Turning a Bug into a Feature

    Dominik Meffert01/04/2023 at 06:04 0 comments

    While finding out a nice way for cutting plastic with a hot wire I faced the problem that if the temperature and cooling is too low, the wire can cross the plastic without actually cutting it.

    That happens, because with a low temperature setting the wire just melts the plastic without evaporating it, and without cooling, it just fuses back together after the wire moved far enough away from the molten plastic.

    The whole time, I was a bit unsatisfied with the machine, because while it can cut out simple shapes quite nicely, there was no way for starting a cut "inside" the later workpiece without cutting unwanted paths into it which weakened the part or made most cuts completely impossible.

    At least that's what I thought until now because I just realized that I actually can cross the part without cutting it and that I already did it before. 

    Doing that intentionally will leave a "scar" on the workpiece, so it may be not suitable for decorative parts, but for only functional parts, it will add a lot more functionality to the machine.

    To make this a reality the machine needs to be able to control heating power, fan cooling, and feedrate.

    I think using this technique could actually work and I will now start working on the implementation.

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Krzysztof wrote 01/02/2023 at 12:55 point

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.

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Dominik Meffert wrote 01/02/2023 at 20:29 point

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.

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Krzysztof wrote 01/03/2023 at 06:57 point

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

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Dominik Meffert wrote 01/03/2023 at 07:46 point

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

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Krzysztof wrote 01/03/2023 at 08:01 point

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.

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Dominik Meffert wrote 01/04/2023 at 11:38 point

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

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Florian Festi wrote 12/23/2022 at 12:07 point

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.

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Dominik Meffert wrote 12/23/2022 at 13:35 point

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

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Dominik Meffert wrote 12/24/2022 at 14:30 point

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.

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Dominik Meffert wrote 12/24/2022 at 15:02 point

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.

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Florian Festi wrote 12/23/2022 at 11:15 point

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.

  Are you sure? yes | no

Dominik Meffert wrote 12/23/2022 at 11:37 point

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.

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