Building a Balsa Violin, pt 2; a.k.a. The Ballad of the Vaporized Wire

The first step to building a violin out of balsa wood and foam is cutting the basic shape out using a hot wire foam cutter. A quick google search shows that a) they’re easy to build and perhaps more importantly b) very cheap to construct; mine cost me about $11 to build including tax and some scrap wood I had laying around in the garage.

First off; don’t try this at home. Don’t try it period. Don’t even think about trying it. You will die, and it will cause a fire, burning the house down while you’re stunned/dead. If you google around you’ll find lots of people showing you how they built their own hot wire foam cutter, and you’ll note that they haven’t updated their site in a long time. This is because they died using their stupid-dangerous device. So don’t do it.

That said, they’re pretty simple to construct. Like I said, mine cost me $11 in parts and some scrap wood out of the garage. It’s not rocket science. You quite literally wire a guitar string in to the wall, regulated by a dimmer switch. My parts list looked like this: 6′ two prong extension cord: $1.15. Electrical outlet box: $1.21. Dimmer switch: $7.98. Wood and screws for the frame came from the garage; wires came from old sets of guitar strings I’d put aside for this purpose. As it turns out, guitar strings are roughly the same chemical composition as the wires in your space heater or toaster… just thinner.

So right, most people build this H-shaped thing out of rulers or what have you with some sort of elaborate spring loaded tensioning system. Mine looks like this, and uses three screws to hold the thing together.

death trap hot wire foam cutterThis is two long, thin pieces of wood screwed in to a heavy block of wood. The bottom piece (boom) uses two screws to keep it from rotating; the top piece (mast) is mounted with one screw loose enough that it can rotate on it’s axis. The guitar wire runs through small holes at the end of the mast and boom. At the other end of the mast is another hole to which a weight is attached. I started off with 30oz (850g), but later switched to 12oz (340g). This weight raises the business end of the mast and tensions the wire. The weight is lifted about 1″ off the ground so that if (When!) the wire breaks, it isn’t flailing about wildly. A wire leads out from the dimmer switch box to the end of the boom and attaches to the guitar string, the other end goes to a wire that plugs back in to the wall. All of this is run through a surge protector on the floor that acts as sort of a backup safety switch I can activate with my foot. The last thing you want to be doing when a live 36″ wire is flopping about at waist level is waving your hands around in that general vicinity.

Someone else had tried running this sort of setup using a 9v AC/DC adapter. I tried that. Didn’t work.  Read up some more, found out dimmer switches are a popular method. Went out the next day, bought a dimmer switch, attached everything, not expecting it to work. Doesn’t work. Twist the knob back and forth, nothing. Push the knob however and… ZAP!!! flash of white light, a loud POP, house lights dim for a quarter second, and there is some slag on the floor and a puff of smoke where the guitar string once existed in the space between two wires. Holy hell! I could have died just then. Neat.

Clearly I had the dial set too high. I rotated the dimmer switch dial fully in the clockwise direction, reloaded the mechanism with a new wire and… ZAP!!! Hum. Clearly I am not doing something right. Finally loaded it up with an D or A wire (.032-.042 gauge), rotated the dial back to the far counter-clockwise position, and gave it another shot:

Neat. As it turns out, modern dimmer switches don’t just work as a traditional voltage regulator, burning up extra electricity at the switch before it reaches the bulb (wire). Instead, after an initial burst of energy, modern dimmer switches rapidly fluctuate the power on and off. You end up with some interesting behavior, where you need to rotate the dimmer switch enough to get it to kick back in, and then dial it back where the wire is still hot and dimmer switch is still working. This is an art and I’m still working on this; and also why I switched to a lighter counterweight; as the wire heats up it stretches, eventually breaking (always at the lower attach point).

Anyways, in the mean time I managed to cut 95% of my foam block out. Crudely. But it’s a start, there’s always time and room for version 2.0.

Last shot shows a closeup of the unaltered, cut product. Wires leave a smooth cut. The thing everyone else says is “cool and slow is best”; I have to agree with them. The wire can get so hot that it will vaporize the foam when it gets within half a millimeter. A hot wire cuts a line as wide as a table saw does. Last shot also shows the end of the bottom attach point where the wire just vanished. Be careful.

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4 Responses to Building a Balsa Violin, pt 2; a.k.a. The Ballad of the Vaporized Wire

  1. asgar says:

    hi. thanks for youre useful information
    can you please send me Dimensions and details of violin too

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