1. #1
    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?
    Last edited by Boyan Silyavski; 25-06-2017 at 02:37 PM.
    project 1 , 2, Dust Shoe ...

  2. #2
    At the moment i am looking to buy and try this one https://hotwirefoamfactory.com/CNC-Hot-Knife.html


    I was also thinking about sth like the mini induction heaters sold around in ebay for 10$ combined with 0.4mm disposable stainless steel rod or the 0.5mm TIG electrodes i found in aliexpress.

    I dont know anything about that induction heaters, maybe i will have to cool the coil or sth.
    Last edited by Boyan Silyavski; 02-07-2017 at 04:06 PM.
    project 1 , 2, Dust Shoe ...

  3. #3
    I had a quick look on Aliexpress and they have hot knives for $15 - $22, they seem to be 2mm dia and various lengths, up to 100mm. (for cutting styrofoam)

    My experience of goods from China is that they are slow to arrive, Aliexpress is slower than eBay. American goods are always saddled with customs charges and handling fees, which generally pisses me off, especially when you can't always find out the total cost in advance.
    Albert Einstein may have been a genius, but his brother Frank, was a monster

    Having just moved to Windows 10 (which is crap) My stress levels are through the roof !!!

  4. #4
    Forget rods, you will not get adequate conduction.
    Small stainless steel tube = medical needle.
    The steel is perfect for generating heat with a controlled current, enamelled (not lacquered-that's no good) copper wire through the middle and brazed at the bottom gives you a circuit with the greatest heat generation from the steel.
    The fan is to keep the connections, mounting block etc. at the top cool.
    Any good? :-)

    - Nick
    You think that's too expensive? You're not a Model Engineer are you? :D

  5. The Following User Says Thank You to magicniner For This Useful Post:


  6. #5
    Quote Originally Posted by magicniner View Post
    Forget rods, you will not get adequate conduction.
    Small stainless steel tube = medical needle.
    The steel is perfect for generating heat with a controlled current, enamelled (not lacquered-that's no good) copper wire through the middle and brazed at the bottom gives you a circuit with the greatest heat generation from the steel.
    The fan is to keep the connections, mounting block etc. at the top cool.
    Any good? :-)

    - Nick
    I was leaning that way. last night found some wires . The mechanical part as you say is buy the wire and make the tool. have absolutely no clue which of these wires will be any good, i assume any? As anyway i will be connecting this to a lab PSU so i will turn the knobs until it heats adequately

    I found 1mm diameter Hot Wire Foam Factory knife , but it becomes very expensive with shipping and tax and duty. I believe it will do the job way better than the Chinese foam knifes which all are 2mm thick.


    I think my next build will be foam cutter. They seem way under rated but from what i see for now, foam letters here is what people want most of all. As they are cheapest of all. But money are made.
    project 1 , 2, Dust Shoe ...

  7. #6
    Quote Originally Posted by magicniner View Post
    Forget rods, you will not get adequate conduction.
    Small stainless steel tube = medical needle.
    The steel is perfect for generating heat with a controlled current, enamelled (not lacquered-that's no good) copper wire through the middle and brazed at the bottom gives you a circuit with the greatest heat generation from the steel.
    The fan is to keep the connections, mounting block etc. at the top cool.
    Any good? :-)

    - Nick
    I believe you gave me the best idea till now. Just bought the needles from China.

    Inter Diameter(ID):0.232mm

    Outer Diameter(OD):0.5mm

    Tip Length:100mm,3.9"(needle length,not contain the base)



    I consulted with the guys from wire.co.uk and they said oxidized constantan wire will do the job and resist 400C, the temperature i need / 200-300C/. Was going to buy from them but quick check on ebay i found some military surplus from the cold war.

    So now soon i will have the needles and the wire. I hope there will be no problem inserting 0.16mm wire in 0.232mm needle. Whats left is the silver solder. I have some silver wire but i was going to figure the exact flux needed for that wire.



    The challenge as i see it is to terminate mechanically properly the whole contraption . may be solder the thick wire to needle body and other thick wire to the thin wire. Then fit this in needle with some teflon separator and pot it. solder then the tip side. cut off the extra wire and thats it. If i am lucky.
    project 1 , 2, Dust Shoe ...

  8. #7
    Boyan,
    Silver Solder a collar near to the top of the needle, use a fitting like a hollow brake pipe nut to clamp the collar into the mounting block whilst allowing the top of the needle and wire to show above the nut.
    Silver solder a small block to the top of the wire, power can then be connected quickly and the tips can be swapped out quickly and easily,
    Regards,
    Nick

    It's not an idea, more of a design description, with the right implementation it will definitely work ;-)
    You think that's too expensive? You're not a Model Engineer are you? :D

  9. #8
    Meanwhile here is a LOW FI/ i broke my edge 7/ video of my new contraption, while i am waiting for the needles and stuff. it could cut 1200x600mm foam sheets. ceramic contact block, isolated by silicone pad, 0.5?? mm mig wire , 2 old pc fans and 25x25mm steel profile . 700mm deep. Could cut 200mm thick foam
    300 mm/ min cut , radiation cutting, no pushing the wire

    Last edited by Boyan Silyavski; 07-07-2017 at 08:41 PM.
    project 1 , 2, Dust Shoe ...

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