Welcome to foamwire.com! Here you will find the best foam cutting method for your project. From homebuilt hotwires to custom cnc industrial cutters we can help. This site is still under construction, but feel free to look around.
The Wire
Most all hot wire foam cutters use nichrome or inconel wire for their strength and ability to resist oxidation under high temperature. This article mainly refers to nichrome wire since it is typically cheaper and more available to hobbyists. Either material will work very well for foam cutting. The key to success with nichrome/inconel wire is to use the proper electrical current. Too low of a current and the wire will not be hot enough resulting in a wavy cut. Too high of current and the wire may melt in two. The calculations page shows the resistances of different gauges of wire per foot and how to choose a power supply. If you are making one in your garage right now; increasing the current just till it just starts to glow red will be about right. Fortunately nichrome wire is cheap and allows for lots of experimenting. Once both your electric current setting and cutting method are perfected one strand will last through many hours of foam cutting.
The Frame
Purchasing the wire is the easy part; building the frame takes creativity. After the size of foam to be cut has been established, the biggest factor to consider in designing the frame is the method of tensioning. Some designs are simply a flexed bow in a "C" shape, some resemble a sling shot "Y", and others make a complex "H" spring/hinge configuration. First we must assess these key questions: What is maximum size of a needed cut? Will it be hand held or stationary? Does it need to be adjustable? Where will the electrical wire attached to the nichrome wire go? Once these questions are answered make sure to read down the list before beginning construction.
The Tensioner
In addition to selecting the proper current, the other trick to long wire life is to use keep it taught as it heats and cools. Not to mention this will make a nicer cut! This can be achieved by use of a spring, flexible pvc or even wood. It will take a few trials and errors to find the proper tension. Too tight will result in the wire snapping immediately or early in the cutting process. Too loose and it will sag during the cut resulting in a wavy cut and may even break when cutting is attempted. Tension must be balanced with current, since a cold wire will also cause a wavy cut; so pay attention to both factors when testing.
The Electrodes
Electrode in the world of foam cutting is a fancy name for a lump of metal that the nichrome hot wire attaches to. A simple set would consist of 2 eyebolts. As you may have already attempted, retaining the wire with wood, plastic or other flammable materials is not a good idea since the wire is equally hot everywhere along its length. Attaching to a larger portion of metal to the wire allows for easy connection to your power supply and a non-flammable attachment to the frame. The large portion of metal has low electrical resistance (so it doesnt create heat) and large surface area so it dissipates what heat it receives from conduction through the nichrome wire.
The Technique
Regardless of the quality of the cutter and the integrity of the wire the operator makes all the difference. When the wire is hot it must continue to move through the foam. If the wire hesitates it will melt a displeasing hole in the foam around it. If the wire is moved too fast it could break by the force of the foam against it. Anytime the wire breaks or the power supply is shut off during a cut the wire will cool and glue itself to the foam. Removing it, especially in large blocks of foam is not an enjoyable experience. I recommend hooking up a new wire and attempting the cut again; then removing the old wire after the cut is complete. Turning the power supply on and off during a cut will result in a jagged edge from the uneven melting. Basically, plan out how your are going to make the cut before you ever turn on the power. Remember too keep the wire at constant speed, and watch out for hang ups like your frame getting in the way or the wire being too short. Make sure to have good ventilation and to power off when not in use.

Slice away!