Anyone who has ever opened a box knows how messy Styrofoam can get. Extruded polystyrene is a closed cell foam, which is why it feels like it’s made up of a bunch of small bead-like particles. Those make it difficult to cut with traditional tools, because the cells have a tendency to crumble apart. Fortunately, Styrofoam — and some other types of foam — can be cut very easily with a hot wire. You can even build a CNC hot wire cutting machine, as demonstrated on the How To Mechatronics YouTube channel.
Hot wire cutting is exactly what it sounds like; a thin strand of hot wire, often made of something like nichrome, is brought to a high temperature by passing electric current through it. The hot wire will almost instantly melt Styrofoam and cut through it like a warm knife through butter. The only downside to this cutting method is that your cuts will all have the profile of the wire itself. In this case, that’s just a straight line, which means it can be somewhat difficult to cut complex three-dimensional shapes. Luckily, this video guide will show you how to break a design up into multiple cuts to help overcome that limitation.
Building the machine itself is similar to how you would construct a 3D printer or CNC router. It’s made from a combination of 3D-printed parts and off-the-shelf hardware like aluminum extrusion. The controller is built around an Arduino Uno board. That will accept somewhat standard G-code commands, though you will need special software to generate the appropriate commands. You can use a special plugin for Inkscape to create G-code paths in two dimensions, and then combine multiple 2D profiles to get a 3D part. A bit of trial and error will help you determine the best settings for you, but you should be pleasantly surprised by how quickly you can cut out large Styrofoam parts with this machine.