Found this site that shows how to make a hotwire cutter. Thought you may find it helpful.
http://members.socket.net/~llile/LileEngineering/Hotwirev1_01.htm
Lile Engineering Hot Wire Foam Cutter Plans
V1.01
This is a simple, safe, and inexpensive hot wire foam cutter that is suitable for general tasks such as making train set scenery, cutting out forms for medium to large objects, making blanks for sculpting, making sign lettering, making foam models, and other tasks. It will cut foam from 4” thick or more down to wafer thin. It is not suitable for fine details less than 1/8” in diameter. Most shapes will need some touching up with sandpaper or a knife to achieve the net shape you desire. There are many other foam cutter plans available, but this is intended to be a basic, simple cutter that will get you cutting out shapes in less than an hour.
MATERIALS
12 inches #18 Gauge (0.437 Ohms/ft) Alloy Tophet C (www.lile.biz Stock #1028)
24 inches #28 Gauge (3.75 Ohms/ft) Alloy Tophet D (www.Lile.biz Stock #1027)
2 ceramic insulators (www.lile.biz Stock # 2001)
36" of 1/4" X 3/4" steel bar, galvanized or plain steel (size is not critical)
Two 1/4-20 X 1/2" steel bolts, hex nuts and four washers (size is not critical)
12 volt battery charger (the best kind has an ammeter on the front panel.)
Tools:
Pliers
Wire Cutters
Hacksaw
Drill and 1/8" drill bit (size is not critical)
Bench vise
Procedure:
Bend the steel bar into a “U” shape using the bench vise. The size can be anything that is handy, but mine is about 16" between the ends of the bar. Drill a 1/8" hole near each end of the bar. See the photo below.
Thread a piece of 18 gauge wire through two of the holes in a ceramic insulator. Be careful not to break the insulator by forcing the wire into the holes - use pliers to shape the wire so it fits naturally. Wind one end of the wire in a tight twist and thread it through the hole in the end of the bow. Do not tie the wire in a knot as this will weaken the wire. See pictures below:
Now thread the 28 gauge wire through the other two holes. Don’t twist it off just yet. You need to make two assemblies like this, and assemble them into the bow as shown in the pictures below.
You will need to twist the 18 gauge wire around the end of the bow, then pull the 28 gauge wire tight in the bow before twisting it off to fasten it. You can achieve more tension in the bow by having a friend compress it slightly while you pull the wire.
Keep part of the wire under tension straight. Use the loose end of the wire to wrap around the straight side 7 or 8 times. This will keep the wire from slipping through the ceramic insulator.
UNPLUG YOUR BATTERY CHARGER
Now you will need the two bolts. Capture several wraps of the 28 gauge wire between two steel washers. The bolts will help you make a good connection with your battery charger clamps. These clamps are too large to clamp onto a 28 gauge wire directly.
Now comes the tricky part. You must arrange the 28 gauge wire and the 18 gauge wire so they do not touch, even a little bit. You might try teasing the 28 gauge wire apart with a small nail until you are sure it is not shorted out by the other wire.
You are ready for a test run! Connect the negative battery charge clamp to one of the bolts. Connect the positive battery charger clamp to the other bolt. Plug in the battery charger BRIEFLY. One of two things will happen:
- About two amps will flow and the small 28 gauge wire will glow a dull red, which may not be visible in daylight. This is good OR 2. About 8 amps will flow and the bow will vibrate. The small 28 gauge wire will not glow at all. This is not good.
If # 2 occurs, your bow is shorting out the battery charger. Carefully check the ends of the ceramic insulator and you may find that the 18 gauge wire and the 28 gauge wire are touching at some point. Carefully tease them apart with a small screwdriver or a nail.
You are now ready to test your foam cutter for real! Please follow these safety rules:
SAFETY RULES 1. Never touch the cutting wire. It is hot, and has electricity flowing through it. 2. Always use your foam cutter outdoors with plenty of ventilation. Foam cutting generates toxic fumes. 3. Keep the hot wire away from your battery charger cables. The wire will cut the insulation instantly. 4. Never use your foam cutter with 120VAC mains current. This could result in a dangerous shock hazard. Also, the hot wire will melt instantly. 5. Keep plenty of tension on the hot wire by tightening the assembly under tension. This give you the most control over the foam cutting process. 6. Do not force the hot wire through the foam. Let it cut at its own speed to avoid breaking the hot wire. 7. If the hot wire breaks, disconnect the battery charger immediately before doing anything else. 8. Always wait 5 minutes after turning off your foam cutter for the hot wire to cool. Do not set the foam cutter down on any flammable surface. Bricks, metal or concrete are best. 9. Do not use the foam cutter near gasoline, or other flammable liquids. Stay well away from buildings. A concrete driveway is a great place to use the foam cutter, since there is very little that can catch on fire. 10. Always use leather gloves when operating your foam cutter to protect against accidental contact with the hot wire or hot plastic.