Assorted hot-wire tools we have built

General Theory

All of our home-made foam tools are based on a simple principle: take a piece of thin wire; run low voltage high current electricity through it; and it gets hot.

We created several different cutting and shaping tools, for use in specific areas. In all cases, the cutting tool was just a way of holding a piece of stainless-steel wire, which was heated up by the power from the auto battery charger.

This is a block diagram of our setup.

This is a picture of the main components, as demonstrated at CalHaunts [September 2005].

A creative builder can make substitutions for just about everything here:

• plug - We get our power from the wall outlet. We don't have to worry about running out of batteries.
• foot switch - When the wire is hot, it is a fine cutting tool, but you don't want to leave the wire hot all the time. By using a foot switch, the wire is hot only as long as we need it. And if we get und walk away, the wire cools to safe temperature in seconds. [I can't count the numerous times I have left a soldering iron on overnight!]
• heat control - Different types, lengths, and thicknesses of wire all need different power in order to get just hot enough. By using a control, we can fine-tune the performance.
• transformer - The transformer does two things: it isolates us from the main power lines (a safety feature) and steps the voltage down to a convenient level
• working tool - We have serveral kinds.

Safety

• Electrical issues
  • line isolation - It is dangerous to hook anything directly ("DC path") to the main power lines. In our setup, we use a transformer to provide "line isolation" (as well as a lower working voltage).
  • high voltages - All of the electrical connections up until you hit the high side of the transformer are at line voltage, which is dangerous. In our case, everything on the high voltage side are comercial components that simply plug toether.
• toxic fumes - Melting or burning plastic can produce toxic fumes. Always work outdoors, preferably when there is a breeze blowing away from your work. Our setup tends to minimize this problem by using a heat control. We use as lttle heat as posible.
• burning and fire danger - The hot wire gets hot!
  • don't burn youself
  • don't cause a fire

Note: Many of our tools have handles of wood or plastic. Since plastic can melt and wood can char and burn, you have to be very careful about this! We used wood because it cheap, easy to find, and can easily be modified - by backing out the screws and putting them in another place. The places where screws hold the hot wire to the wood seem to be OK, because we put a ring terminal (crimped to the incoming power wire) next to the wood, the wire on tho of that, and then the screw. So the resistance heating wire never directly contacts the wood. If you use similar materials, you must constantly watch out for unwanted heat!

Foot Switch

We decided on a foot switch, normally open, momentary contact

This is the foot switch we used.

Heat Control

• temperature of the cutting blade can be varied
• the power level can be adjusted for different thicknesses of wire
• the power level can be adjusted for different lengths of wire
• the power level can be adjusted for wire made of different materials

Transformer

In one neat package, this provided us with:

• a safe low voltage
• a nice high current
• a circuit breaker
• an amp-meter to measure how much current is being used
• line isolation

The amp meter is particularly handy - it provides a relative indication of how hot the wire is. If the wire is just a little cool at 3 amps, you can turn it up to 3.5 amps and see how that works.

Instead of a battery charger, you could simply use a 12 Volt AC transformer. With the various cutting tools we use, the current has never gone above 10 Amps, and we usually run at just a couple of Amps.

Assorted Tool Tips

Knife Blade Tool

We use a thicker wire that is stiff enough to hold the shape of a simple loop.

Coping Saw Tool

The outer frame is made from a "pendaflex" file-folder support.

We use a thin wire for a crisp, clean cut. Tension on the wire keeps it straight.

This close-up shows the handle of the "coping saw" arrangement.

Hocky Puck Engraving Tool

From the bottom of the puck, a V-shaped wire blade protrudes.

The hot wire "V" does a nice job of cutting "engraved" words and art in foam plastic. The smooth plastic bottom slides cleanly over the foam. The clear plastic of the puck allows you to see through, into the area being cut.

Edge Routing Tool

This picture looks down on two tombstones from the top.

• The tombstone on the right shows the sharp edge.
• The stone on the left shows a rounded edge made with David's edger.

Attached to one end of the frame is the hot-wire. For this application, you want to use a thick, stiff wire that can be bent into a custom shape and hold it.

The edger is placed on the end of a piece of foam. When power is applied, the wire will cut through the foam, sculpting a three-dimensional groove in the material.

With the wire hot, you slide the frame along the edge of the foam. It carves as it goes.

Here, the cutter sits in a groove it has cut.

Note that this cutter is not a simple rounded edge: It combines a rounded edge on the outside, with a groove on the inside. This allows the simple carving of elaborate decorative patterns.

When you are done, you wind up with the desired groove in the big piece of foam, and a "negative" loose piece.

You could use this technique to create custom "moulding" to add to other decorations.

What Kind Of Wire?

Getting the proper sort of wire is important. Many kinds will work, but a few won't.

Selection criteria include:

Gun Engraving Tool

Pencil Engraving Tool

In this case, it is vital to control the power to the iron, because it is designed to run much hotter than is practical for foam cutting.

Related Pages