Hot Wire Cutters are used for cutting foam products into a variety of shapes and sizes for commercial and hobby applications.

General Information

There are a number of ways to create foam cutting devices, but all use the same basic principles.

You have a power supply which applies an electrical load across a metallic wire which has a defined resistance. When current then passes through this wire it generates heat proportional to the rate of that flowing current.

NiChrome Cutting Wire

The large majority of foam cutters use NiChrome Wire as their cutting element, which is a combination of Nickel and Chromium

Some cutting devices will use fuse wire, guitar strings, or even constantan wire (copper/nickel), but these either burn out too quickly or require too much power to heat up.

NiChrome Wire is the ideal wire candidate because it can easily be heated to desired temperatures using a much lower voltage and amperage, in comparison to the other available options.

Power Supply

When it comes to applying electrical energy across your circuit there are two options :

Alternating Current (AC)  or  Direct Current (DC)

Wall sockets (in the United States) supply 120 volts AC and in most homes can top out at 15-20 amps depending on your circuit breaker.  Not only will this level of electricity end up melting your nichrome wire, but it is VERY dangerous to have bare wires exposed at this electrical rating.

The risk of electrical shock can cause DEATH!

For Hot Wire Foam Cutters, a Direct Current is preferred because the output voltage is typically lower and safer for home use. You can still use Alternating Current but please only use power supplies that have less than 40 volts output to prevent electrical shock.

You may read elsewhere that you can use a doorbell transformer with a dimmer switch. Basically a doorbell transformer is a step-down AC transformer and you’re using the dimmer switch to alter the output electricity. While the theory is correct, the problem is that commercially available doorbell transformers cannot output the required amperage to heat nichrome wire. Many never achieve more than 1amp, and if you pull 2-4 amps like most circuits require, you’ll burn out your transformer. 

Jacobs-Online has custom manufactured high-end step-down transformers. If you are interested in building your own power supply, we have provided a tutorial video and page dedicated to the custom creation of your own AC step down transformer. Please go to this page if you are interested in creating your own power supply.

Determining the power supply your circuit requires is probably the most technical aspect of this entire process. It will likely be quite challenging for beginners, but carry on through the site and you will learn all that you need in making the appropriate selection!

Check out the power supply calculations page for a online flash calculator made by Jacobs Online!

Of course the next answer is, “well it depends on your cutter.”

“Plain and simple,

what do I need?”

Throughout this site you will find a plethora of information which will touch on practically every aspect of creating your own Hot Wire Foam Cutter.  Just consider this next little bit of information as a set of guidelines and abridged notes. For your specific application you may require different wires or power supplies, but the following recommendations should point you in the right direction for almost all hobby applications.

You will find more information under the Calculations Tab and ordering information under the Supplies Tab

NiChrome Cutting Wire

Straight Wire Cutters

24 or 26 Gauge NiChrome Wire Chromel C

May be used by all cutters...

Rigid Wire Cutters

18 or 20 Gauge NiChrome Wire Chromel C

Any small / medium sized hand cutter

26 gauge wire is the best all around candidate and is very versatile. It has a perfect balance of tensile strength and required energy.

Some users prefer stepping up to a bit larger wire at 24 gauge because it is a bit more stiff. When the wire is used over a longer span (over 2 feet) sometimes the extra rigidity is nice to prevent bowing while cutting. The trade off is by having a larger wire, you require more amperage to heat the wire which may mean a more expensive power supply.

For some, they require a wire that can be bent and shaped to make interesting designs, carve rivers, mountains, and more!

24 & 26 gauge wires are simply not stiff enough to hold any shape, but a well known online retailer of rigid wire foam cutters uses a wire close to 20 gauge. If it’s good enough for them, it’s good enough for us!

Remember that as you start to increase the overall diameter of the wire (meaning the gauge number decreases) your power supply requirements begin to increase. So exceeding anything larger than 18 gauge may require an expensive power supply to heat.

Power Supply

I absolutely insist, get rid of that old cell phone charger you want to use and go pick up a variable voltage power supply. Whether you make your own power supply or you purchase a manufactured power supply, You’ll save yourself a mountain of headaches..!

But don’t worry, a lot of the power supplies I’ve picked out are rather inexpensive and worth the investment. My favorite are Benchtop Power Supplies, but you can choose any others you’d like.

Rather than getting too technical right now, just know that your wire circuit has a measurable resistance, and the voltage from the power supply acts as an electrical pressure to push electrons through the wire and create an electrical current.

Water and plumbing is a great analogy. Think of the nichrome wire as the water pipe, and the voltage as the water pressure. With more water pressure you have, the faster the water will flow through the pipe. Electricity works virtually the same way.

On the power supply it will list an voltage and an amperage (current). The listed voltage is a constant output value. Whereas the listed amperage is the maximum output allowed by the power supply. The listed amperage is NOT the constant output rating, like it is with the voltage. So when you make your calculations, know that the power supply voltage will always be applied to your circuit, but the amperes should never exceed the listed rating on the power supply.

With lower resistance, if you apply a higher voltage (electrical pressure),

it will generate a greater current (electrical flow), and a hotter temperature.

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As you can see, ideally you would require a 2.1 amp power supply that can range between 0 and 10 volts.

Tattoo Power Supplies are generally 2 amps, 0-12 volts which should be about perfect because most foam will cut at 500°F so you can spare a little current and reduce amperage a little. But it will cut slower at lower temperatures. With the more sensitive tattoo power supplies, they might even clip out or shut off if you overload them too much.

Bench Top Power Supplies are probably my favorite type of power supply. For under $100USD you can get between 0-30v and between 3-5 amps an average. This will work for basically any cutter.

DIY Power Supply will vary depending on the step down transformer you select. But the XFR-1006D is capable of supplying between 0-6/0-12 volts and 0-8/0-16 amps depending on the setting.

Rigid Wire Cutters

20 Gauge NiChrome Wire Chromel C

10 - 12” Cutter

5 - 6” Cutter

18 - 20” Cutter

Medium Sized Vertical Cutter or

Horizontal Cutter

Small Table Cutter Small Hand Cutter

Large Hand Cutter Large Table Cutter

2.6 volts / 2.1 amps

600°F / 316°C

5.1 volts / 2.1 amps

9 volts / 2.1 amps

10 - 12” Cutter

5 - 6” Cutter

18 - 20” Cutter

Small Cutters

2 volt / 5.1 amps

600°F / 316°C

3.1 volts / 5.1 amps

5.3 volts / 5.1 amps

By comparison, you’ll notice that rigid wire cutters require more current (amps) to heat up, and less voltage. Just think... it is a larger pipe so it is easier to push electrons through it. You need less force to push the electrons, but you need more current flowing to heat the wire.

Tattoo Power Supplies will not work for this application, not enough output current / amperage

Bench Top Power Supplies are capable of powering rigid wire cutters, making them the best bang for your buck if you want both rigid and straight wire cutters at varying lengths.

DIY Power Supply will vary depending on the step down transformer you select. But the XFR-1006D is capable of supplying between 0-6/0-12 volts and 0-8/0-16 amps depending on the setting. This is the best power supply for this application, for the money.

Straight Wire Cutters

24 or 26 Gauge NiChrome Wire Chromel C

Connection Wire

You can essentially use any type of wire to connect your hot wire foam cutter to the power supply. You’ll see there are multiple ways to attach the wires together (snap connectors, ring terminals, etc.), but you can use anything from electrical housing wire, speaker cables, telephone cables, ethernet cords, or any other type of metal wire. Check out some easy connections in our video tutorials section.

One thing worth discussing is “Ampacity”, which is the amount of safe current (amperes) to pull through a copper cable. This safety rating is primarily used in home wiring becayse as electricity moves through a wire a small amount of heat is generated. So the ampacity rating is a way of keeping a home safe by reducing the heat generated. But for hot wire foam cutters, rarely is it necessary to even consider ampacity. But if you choose a very thin wire as your connection wire (telephone cables, ethernet cables, etc), you might end up inadvertently melting that wire if your current flow is high enough.

The listed ampacity is for soft or annealed copper wire. The resistance of hard-drawn copper is slightly greater by 2-3% and stranded wire is a bit higher as well.

The rated ampacity is at 20°C and there is about a 20% increase in resistance at 60°C

Click here for downloadable version

Here is a much larger chart that has a whole range of NiChrome Wire gauges as well as the amperage rating for desired temperatures and the associated voltage requirements for defined lengths of wire.

This should get you close, if you want a quick’n’dirty guide for choosing a power supply for a variety of gauges, lengths and temperatures.

Cheat Sheet

Lower resistance is achieved by having a shorter wire or a larger gauge wire.