Let’s make a foam cutter! First you need to understand that Styrofoam (polystyrene) vaporizes at certain temperature. A foam cutter, is nothing but a hot wire that pass through foam like a hot knife through butter. How to heat a wire?

Simplest way: connect a wire to the positive of a battery and the other end to the negative of a battery.
This is extremely dangerous. The wire will become so hot that the wire itself might melt! You will be burnt if you hold it! Its insulation will melt! Depending on what is around, you can start a fire. Safer method is to use nichrome wire - or high resistance wire as some colloquially call it. Now to understand why it is safer, you need to understand why a wire heats up. A wire has resistance. And resistance’s job is to convert electrical energy to heat energy. Nichrome wire has a lot of resistance compared to copper wire. So if you connect your battery using low resistance wire (e.g. copper wire you find in almost all wires around the house) to a nichrome wire - since the nichrome wire has more resistance, all the heat conversion happens there and your low resistance copper wire does not heat up.

However this is not a working solution, because the wire can get so hot too much foam will be vaporized. So you need to control how much electricity is going to this wire to be converted to heat.

So let’s build! To get the wire, I use a wire wound resistor I bought from your local electronic store - radio shack, conrad, amazon etc.

A 10 ohm or 100 ohm works great! They are in cuboid "square" block shapes.
You gently break one with a hammer and remove the wire. This wire is your nichrome wire...looks like ordinary wire but it has high resistance. It is wrapped on a soft spool.

You now need a circuit to control the current going through your wire. You cannot use a variable resistance because they usually have more resistance than the nichrome wire. So you would not get the heat conversion you need at the nichrome wire.
Instead you can use a pulse modulated circuit. Such a circuit turns on the power for a brief while, then turns it off and does this over and over many times per second.

The ratio of how long the current is on to how long it’s off is called the Duty Cycle. We can now control how hot the wire becomes.
This circuit is easy to build and all of the parts you can get from a local electronic store. Connect the circuit and now you can control the electricity going through the wire. (NOTE: the terminals in this circuit labled Motor + and Motor - connect to your hot wire) Mount your wire and your circuit – I suspended my nichrome wire on two paint paddles and secured it with screws washers and nuts. And that’s it! Turn on and voila! Foam Cutter!
The fully assembled foam cutter!

Here is a fully assembled foam cutter. On the left is a switch, and the pulse modulating circuit, and on the right is the hot wire jig.

Here is the foam cutter at work. It is fitted onto my computer controlled CNC router.

In an other article I will talk about a program I built that converts 3D .obj files into slices. These slices are fed to my computer controlled CNC router and sliced out of styrofoam plates.

3D Printer Style! The result are slices cut that I fit together by hand like lego with no glue needed to hold in place. A 3D form is born. Very interesting side note - the neck of this head - quite strong if you try to squeeze it.

Here is another view of the head from the top. Again, being able to control the heat allows you to make very thin cuts in the styrofoam - which is what made this head possible.

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