Scavenging nichrome wire; makeshift hot wire cutter

[artfd]

I got a thin roll of Thermarest foam I needed to cut down to fit a narrow cot & got the bright idea of creating a DIY foam cutting tool. I was going to buy the $18 hot knife from HF, but the reviews were very poor - it tended to burn out.
Studied the internet for about 3 hours & learned about scavenging nichrome wire from a toaster. The same neighbor who gave me the foam had an old toaster she had just recently replaced. I got it and took it to pieces. I got about 20 feet of nichrome in about 6 segments. I don't know the gauge - the wire is serrated / zig-zag in cross-section unlike other nichrome toaster heating wire that is a flat ribbon in shape.
I took the wire from a single heating element - about 40" long, stretched it between 2 vertical supports, and connected alligator clips from a variable 1.5-12 VDC 2A voltage supply. Started with 1.5V, gradually worked up to 12V 2A - could feel minimal heat coming from the wire. At this point I switched to my 6-12VDC battery charger which supplies from 2 to 55 amps depending on its settings.
Cutting to the chase -- clipped the charger cables to the nichrome at a 13 inch gap. Set charger to 12 VDC, 10 A. Only about 2A registered on the charger's meter. The wire definitely felt hot at a distance, didn't visibly glow, cut my Thermarest easily,although the wire tended to cool if all the cutting action was confined to the same section. Moving the wire along the line in a sawing motion kept the cutting part of the wire from cooling off. The same setting cut through 3/4" thick styrofoam panelling more quickly than through the 1-1/2" thermarest.
I don't cut materials 13" thick. I found I could increase the nichrome's temp by decreasing the gap between the charger's clamps. In very dim light I can just barely see a dull red glow when the voltage is applied.
I have a 110VAC foot switch I sometimes use to control power tools. I used this to switch the charger off & on while manipulating the foam with both hands.
For what it's worth - hope it saves someone some time. Outside of scavenging the nichrome, everything I used, I already had in my shop.

[jstrubberg]

Just in case it's useful to someone, archers use nichrome wire to custom cut feathers on arrows. If you check out an archery supply place, you can buy a feather burner that ought to cut any foam you can fit through it. Three rivers archery online is the one I usually use.

[Kharn]

Hobby stores will have nichrome wire, it is used to cut foam boards for terrain in figurine war games.

[artfd]

Good point about the hobby stores. Obsolete toasters seem rather plentiful.