Hot-wire cutting foam for aero-mods

[bennelson]

Does anyone have experience with hot-wire cutting in terms of using it to cut foam for aerodynamic modifications to cars?

I have this idea about making a pickup truck cap out of a bunch of of sheets of 4" thick white styrofoam that I rescued from a dumpster.

I would stack them up, and then "sculpt" them into shape with a hot-wire cutter.

I had a dead toaster, so I took it aparts, ran a section of the heater wire between two screws on a non-conductive wood frame (sort of like a bow-saw), and put power to it through a lighting dimmer.

At about 250 watts, the wire glows a nice warm orange and slices fantastic through the foam.

The big drawback I have noticed, it that even though the wire is taut when cold, it droops and goes slack when warm. This makes it hard to cut a straight line! Perhaps I can add a small spring to keep the wire tight whether it's hot or cold?

Anyone have experience with a hotwire cutter and can give any advice?

(I am running this through a proper fuse-box, a GFI outlet, a dimmer switch to control current, and know better than to touch it!)

Ok, so, any advice other than "Please don't electricute yerself!"?

[Nevyn]

Perhaps some sort of tensioner like a guitar tuner? Turn a geared knob to tension the wire?

[BamZipPow]

You can put in a tensioner so you can tighten up the slack after the wire heats up. Keep in mind that you don't want to put too much tension on the wire as it will stretch and even break if under too much stress (pulling too fast).

Here's a good example on Instructables...
Hot wire foam cutter

[BamZipPow]

Good web page on hot wire cutting...
Hot Wire Foam Cutter Info.com

[bennelson]

I remember reading that Instructable a while back. I like the yard-stick-bow-saw design.

Maybe something like that with just a long, light spring on the bottom.
The spring on the bottom would force the top ends of the sticks apart, and the spring would be AWAY FROM the hot/electric components.

I don't think a guitar-tuner-type tensioner would work. The wire tightens and slacks very quickly when power is applied or turned-off.

I'm just playing around to learn right now, but when I am done, I might want something like a 5' long, hand-held cutter. That way, I could make a single cut all the way down one side at a time across the back of a pickup truck.

[thatguitarguy]

I think the problem with a guitar tuner is that after you tighten it up, when it's time to cool down the hot wire will want to contract, and might very likely break.
Maybe if the bow were made of something really like a bow - like maybe bamboo -then as the wire heats the bamboo bow will take up the extra slack.

Maybe?

[Varn]

I made one a year or two ago. I used some stainless wire safety wire that I had around and tensioned it with a door spring for the same reason as you mentioned. My spring is about 3/4" diameter and 6" long. I powered about 26-28" of wire.

I used a board with end boards to space the wire off the neck board.

I powered it with a 12v 6a battery charger after testing it on the 2a setting first.

Of course the wire stretches because it gets hot. If I went too fast it would still bow some.

[arcosine]

Yes, I used welding wire. Made a bow that kept hot wire tight.

[Varn]

I made mine like this to cut up a block of foam back into strips.


Good idea using mig wire arcosine. It wouldn't take much current.

[bennelson]

Hmmm....

I do now have a small wire-feed welder around. It would be easy to grab some wire off that.

As to using a battery charger to power it, I'm assuming an "old-school" charger - free of digital displays, etc, that usually have various fail-safes, etc.