So, the approved method of cutting styrofoam for model airplane wings is to get a nichrome wire (or stainless -- you pay extra if it's called "heater wire") hot, and run it through the styrofoam.
Many folks do this using a lamp dimmer connected straight (no isolation transformer!) to the wire that they're playing with just inches from their hands. For some _really odd_ reason I don't want to do this. (It can't have anything to do with not trusting that neutral is really neutral, of course).
As near as I can tell, the required current in the wire is on the order of a couple of amps. I know from extensive reading (but practically zero real experience) that having an adjustable supply to heat the wire is a good thing (hence the lamp dimmers -- egad!).
I'm thinking that, in this degenerate age, the best way to achieve this end would be to dig through the bucket-o-wall-warts and see if I have a laptop computer power supply, or some other supply capable of delivering a few amps at 12V, and chop the current with a sufficiently herky transistor, driven by a 555 for duty cycle control. _Real_ super-zoot systems would monitor the overall resistance of the wire and adjust the current to maintain constant resistance (hence constant temperature). I ain't gonna do that -- I'm too lazy, and I suspect that it's very much gilding the lily.
An alternative, depending on what I have in my junk box, would be to use a transformer from a quartz-halogen light. These have the right current rating, but they supply AC which is harder to switch. You really want to make the PWM reasonably fast -- the wire's thermal time constant is on the order of a half second or less. But fast PWM, without rectification and filtering, means that there's a very real danger of inducing some pretty significant DC in the transformer secondary. The notion of synchronizing the switch to the AC so that it starts and stops at the cycle boundaries is a tempting one, but then the controller complexity goes through the roof.
The easiest in principal would be a variac and a transformer -- but I don't have a variac.
So -- thoughts?