Here I explain how they work, go to the foam-page to look at the results.
To make a hot-wire you need: Wire, Two sorts per tool, some conduit, pvc pipe or wood, energy source. that's all !
The main thing is to have the two sides of the cutting wire isolated from each other. And the part that has to get hot must be the thinnest wire of the whole wiring. Hence the two sorts of wire you need. Safety first. Look at the wiring diagram.
This is a schematic drawing how to make one.
Click it:
If you don't know how long the cutting-wire has to be, to get the right temperature for cutting, with a 12 volt charger: Take a few feet of wire, suspend it ISOLATED from your ceiling. Connect one wire of the charger to one side of the suspended wire. Switch the charger on. Connect the other wire of the charger SHORTLY to the other end of the suspended wire. You'll see sparks when doing this, it's supposed to do that. If the suspended wire gets red hot or a fuse popped, the wire is too short! Start over with a longer wire (and a new fuse). OK, it didn't glow red-hot, now you can move the connectors slowly bit by bit towards each other. Between these trails hold some foam against the wire till it cuts the foam nicely and you have the smoke and the fumes of "THIS WILL KILL ME". Take the size of the length of wire between the connecting points. This is the definite cutting length on your hot-wire-tool with this charger. The wire should not be red hot. And the cutting will not be fast.
.02" or .03" stainless steel will work fine, specially for bigger tools. Copper is not good (it will work, but you'll need a long wire and it gets soft after heating up and break easy) . Tungsten is the best, I bought it at a hobby shop.
Pic A is just under 10" tungsten 6 volts. Pics C,D and B-right have tungsten just under 2' wire with 12 volts. Pic B-left is S-Steel 24 volts, 5'3" long, 0,04" thick wire. And pic E is same as B but the arms are further apart. See thumbnail above.
A
This was my first one 10", used a battery charger set on 6 volts. The left connection runs inside the pvc pipe. Here you see the thick leads to the thin cutting wire . It works perfect.
B
The next generations, one with tungsten- and one with stainless steel-wire. But now with 12 and 24 volts. Stainless steel has les resistance, hence the higher voltage an longer wire.
C
Just make the cutting wire a bit long and use this fine adjustment for the right temperature.
D
If you make a setup like this, it's like a band-saw for foam. The string with weight is for perfect vertical adjustment of the wire.
This is the small charger for 6 and 12 volts. It says 8 amps but I'm lucky if it will do 6 amps.
The 24 V battery charger from a friend, it gives a bit more uhmpf and I can use a BIG wire now, for the "hood" and the front plough plane.
This is the BIG hotwire. (24 Volts) stainless steel 0,04"
E
And . . . . . there are also some hard points to make.
I used a stiff thin stainless steel wire/rod, in a piece of wood. I extended that with some stainless steel wire to create enough resitance to get all heated up enough and Voilá.
As you can see this is for the cleat hard point. On the right are the threads I used in the hard points
For the picture I arranged the lot to make a nice picture.