Materials you will need.
1 wire hanger
1 Propane torch
1 lighter or other ignition device
1 pair of vise grip pliers
3 pieces of scrap 2 x 4 lumber
Step 1: Making the Cutter
Bend the curved neck of the hanger straight then attach your vise grip pliers to the end. Lying the hanger on the ground while clamping the vise grips onto the end will help make your cutting tool more uniformed.
Alternatively you could create any shape with the wire hanger to fit your needs. Making a box shape would also work quite well.
Step 2: Make Your Cutting Table, Marking and Aligning.
In an open area of your garage place your 2x4 lumber in a reverse C shape or just a C shape for the lefties. Adjust the top and bottom 2x4's to accommodate your foam pieces. The top and bottom pieces are your adjustable pieces while the piece on the right or left is called your fence. The fence will guide your hot wire making cuts straight. Your fence will need to be long enough to accommodate the size of the styrofoam you plan to cut. I personally didn't use the C shape because I didn't have to cut large pieces.
Now mark or trace your foam where it needs to be cut and place it on your cutting table. Align the styrofoam flush to the bottom edge of the fence. Next align your cutting mark on the outer edge of the fence.
Step 3: Whoa There Pyro!
Now take your propane torch and lighter and embrace the pyromaniac inside... but before you do that make sure you are working in an area that is free of flammable items, fumes and is well ventilated.
Ignite your torch and place it within arms reach of your work area while pointing it away from yourself and your work pieces. Take your cutting tool and place it in the path of the flame. Aligning the wire parallel within the flame will help to heat a large area of the wire. Leave the cutting tool in the flame long enough for it to emit a red glow. Once the wire is glowing your ready to cut.
Take your cutting tool and run it along the ground and the outer edge of the fence. Be sure to guide the rear part of the hanger into the cutting line. If not it may snag on the outside of the foam and stop your progress. If all goes well you should have achieved a nice straight line. Now your free to make as many cuts as you like but make sure your Momma/Wife/Girl friend doesn't catch you burnin her clothes hangers!
Last but not least, recycle your scraps.