With my wife being a pre school teacher, I have often been called upon to cut styrene foam into various shapes and sizes.
I put this cutter together to make her, and my life easier.
Cutting wire: Nichrome wire, 0.8mm Guitar string or stainless fishing leader.
Voltage controller: Light Dimmer.
24 VAC Transformer.
I used guitar string, which requires higher current than the Nichrome or Stainless. My transformer is 24V 20VA, and can cut for ages without getting warm.
Wood scraps for the frame.
Bungee chord, spring or surgical rubber tube for tension
Click on the pictures to enlarge.
I wired the dimmer in series to the Line side (Primary) of the transformer. The cutting wire is connected across the Load (Secondary) of the transformer.
My dimmer has an "Off" position. Otherwise, I would recommend a switch to isolate the circuit.
I made hooks to fix the wire top and bottom.
The top support pivots on the vertical riser. Since the wire expands and contracts when heated, I fitted the surgical tubing to maintain tension to keep the wire straight.
Switch on, while holding some scrap styrofoam to the wire turn the voltage up using the dimmer. As soon as it starts cutting the foam, stop turning up the voltage and cut to your heart's content.
Warning: ALWAYS cut in a well ventilated area, and DO NOT breath in the fumes.
The foam vaporizes around the wire, it does not actually melt. The vapors are dangerous.