5-Minute Foam Factory

Scrounge your workshop for scrap materials to build the cutter. None of the dimensions are critical, so feel free to adapt the sizes shown here to use what you’ve got.

When heated, EPS can produce benzene, and when burned, it gives off other noxious fumes. So always use your hot- wire cutter in a very well-ventilated area!

Use the train transformer’s speed control to set the wire temperature: just warm enough to cut the foam. Never cut with a red-hot, smoking wire!

Foam made by Woodland Scenics is specially manufactured so that it doesn’t give off harmful fumes when cut with a hot wire. Get it where model train supplies are sold or at woodlandscenics.com.

Measure and cut the pegboard to make a tabletop. Mine is 18″×18″. Then measure and cut 2 pieces of 2×4 to make leg rails.

Use screws to attach the top to the rails. Then place a ¼” drill bit through the outermost middle pegboard hole above one of the 2×4s and drill all the way through the rail. This will be the hole that the rod fits into.

Wear eye protection when using all tools, and to be extra safe, wear gloves when cutting with the hot wire. You don’t want to touch it — it’s over 200˚

Cut the aluminum rod to 21″ in length. Mark off 12″ and bend the rod about 90°. After bending the rod, insert the short leg into the hole you drilled in Step 1b and align as shown here. Mark the closest pegboard hole beneath a point 1″ or so from the tip of the rod. Then mark the top surface of the rod directly above the marked hole.

Use the hacksaw to make a shallow notch across the top of the rod where it’s marked.

Insert the rod and drill a small 5″ pilot hole through the rail and into and through the aluminum rod. Drive a nail into the hole and through the rod. This prevents the rod from swiveling in its hole as you cut in different directions.

Thread 2 nuts onto the bolt. Wrap, then tie the nichrome wire around the bolt, and add the remaining 2 nuts. Tighten the 2 nuts in the middle to pinch the wire.

Align the nuts so that they all lie flat. Put a drop of super glue on them to lock them tight.

Thread the nichrome wire through the marked hole in the pegboard (from Step 2a) and pull it up vertically. Press the tip of the rod down slightly and hold it there. (You want a little springy tension to keep the wire taut.) At the same time, make a loop in the wire so that the tip of the loop just reaches the deflected rod. Hold that loop and tie it off in a simple overhand knot.

As you press the rod down, slip the loop over the rod and into the notch. Let go. The gentle spring force of the rod should make the wire taut. If it’s too loose, shorten the wire by tying another knot. Trim any stray ends.

Remember your high school physics about electricity? Voltage equals current times resistance: V = I * R

You can measure the resistance of the wire with a voltmeter: set it to “ohms” and measure the wire by placing 1 probe at each end point. My wire measures 7Ω. My transformer puts out 12 volts DC. Plugging that into the formula gives:

12 = I * 7 or 12 / 7 = I. So I = 1.71.

So the current needed is just under 2 amps. My train transformer is rated at 2 amps, so that’s good, at least for short time periods. The resistance of the wire will change at various temperatures, so the current drawn will vary. Many train transformers have a built-in thermal breaker — if they get too warm, they’ll shut off. If that happens, unplug the transformer and let it cool down. It should work again later.

Use the alligator clip leads to attach the train transformer. First, unplug the transformer. Connect the first lead from one side of the regulated DC contacts to the bolt underneath the table. Connect 1 clip of the second lead to the remaining DC voltage contact on the transformer. Make sure the variable control is at its lowest setting, then plug in the transformer.

Ready to test it? Finally, connect the last alligator clip to the base of the rod. You’ve created a circuit that sends current through the wire. Adjust the transformer’s control so that the wire gets warm — not glowing red-hot. No heat? Check your connections and make sure the clips aren’t touching each other at the transformer.

Test your cutter with a scrap of foam. Place the foam on the table surface and gently slide it into the hot wire — it should cut easily with just the slightest pressure. Adjust the voltage if needed. Don’t press too hard, or you’ll pull the wire into an arc and your cuts will be curved instead of straight.

Use that last connection to the rod as your on/off switch. You can see when it’s connected and that the hot wire is “on.”

You can cut free-form shapes easily — just keep the foam moving at a smooth, constant speed. You’ll notice that the slightest wiggle in your movements will result in a wavy or ridged part! Here are a few tricks for easy cutting and perfect parts.

For straight cuts, make a guide from a piece of 1×2 lumber and some ¼” dowels. Drill 2 holes on 1″ centers and slip in pieces of dowel. Plug these dowel pins into the pegboard and you’ve got an adjustable fence for smooth, straight cuts.

Position the fence close to the wire to cut thin strips or position the fence farther away to make wide cuts and to square up blocks. For size adjustments of less than 1″, remove 1 of the dowel pins, and use just 1 pin as a pivot. Swivel the fence around the pin to adjust the angle until the distance between the wire and the fence is just right. Place a second long dowel pin behind the fence at the closest pegboard hole. Fast and easy!

For circles, make a circle cutter guide out of a dowel and a nail. Cut a dowel to a length so that when inserted into a pegboard hole, it’s flush with the tabletop. Drill a 5″ pilot hole into the end of the dowel and insert a small nail — head first. Tap it in with a hammer. Now you have a dowel with a pointy pin sticking out — be careful!

Place the dowel in any pegboard hole. The distance from the wire to the pin will be the radius of your circular cut. Energize the wire. Slide a piece of foam into the wire and impale the foam on the pin. As you spin the foam around on the pin, you’ll cut a perfect circle. Turn off the wire and remove your part.

You’re not limited to 90° cuts. For angled cuts build an elevated and angled wedge to make beveled cuts! Make a wedge of the desired angle and nail it to a block with dowels on the bottom.

Plug the wedge into the pegboard and slide the foam to make your angle cut!