DIY Plunge Foam heat wire cutting

[Boyan Silyavski]

Hi,

As recently i dived into sign making, one of the most cheap and most demanded jobs is cut XPS polystyrene foam letters. The hard insulation closed cell foam 20-30 kg per M3. While i try to show the light to customers and teach them Polyurethane foam , there is no denial cheap letters could do the job in many occasions.

So its wire cutting or CNC bit cutting. I cut them on the CNC using 6mm tools and speeds no more than 1500mm/min and the result is great. Work holding is the key, so i made a fixture for cutting them better, typically i cut 30-40mm thickness. But after all they need carefull sanding with 180 fine sponge.

While sanding all day with 3M mask on my face, i thought about the better way. If attaching a hot foam knife will do the job. Problem is its 2mm in diameter and only sb in USA sells 1mm diameter heaters.

But somebody in Argentina have made a cool 0.4mm needle. Which does exactly what i want. Cuts up to 50mm. See video below. So i contacted them but, price they want for the system is according to me ridiculously high. 3 needles plus thermo controller whopping 450$ which will come to 500 euros and more brought here in Europe.

I am still speaking with them trying to convince them to price it right, boy i could even resell them here in Spain or EU. But no result for the moment.




So i am thinking, why not do a DIY one so anyone could make it, as after all i dont see it so complicated.

What i figured from video, they use some kind of micro coil that is controlled by resistance?? and not thermo couple. So coil heats the needle as they call it. There seems to be a bigger tube that envelopes the needle at the upper part where no cutting hapens, may be for better heat transfer. A ventilator cools the thing from upside, for reason the if needle is hotter at that part, polystyrene cut will be wider.



Now some brainstorming and some help is needed.

What would be the best material for the needle? i figured it could be tungsten carbide bar 0.4mm. Looking at the table of heat transmission. Or some kind of silver maybe? The trick here is not to rust and more or less to be strong to stay straight, though when it burns the material slowly there will be almost no force.

I think also that temperature for at the needle to be 200-300C?? that means the heater should heat it much more, at least 600C

The controller?? now thats sth i have no idea. How is called that one which can see temperature by coil resistance? Or am i wrong

I am thinking of forming a tip for my soldering iron which goes up to 400C and is digitally controlled. I tried yesterday heating some Mig wire to no avail, obviously it must be one piece or micro welded or silver brazed?? so heat transmits better.


So why all that? because if made, no sanding will be necessary as the hot wire will seal the cut. I see this a very useful contraption for anyone that has CNC


Any ideas folks about it all or any detail of it?