Wednesday, February 19, 2014

Very small cutter

This question came through YouTube, in response to my combination foam cutter

I am just curious, why aren't these cutters made to be a little smaller and more manageable...something like a little wire that is shaped like a U where the loop is like 1/32" so you can carve intricate stuff, or a cutter that is several inches long, shaped like an F with the wire going between the short lines of the F, where the wire itself is only 3" or so long??  For me, working at the end of that huge thing would be impossible;/

You can make cutters as small as you want, this is just an all-in-one prototype that I came up with. It is a work in progress, and I am moving forward with commercial fabrication. But more on that later.

Long story short, when it comes to a hot wire foam cutter, you're electrical requirements are a function of wire diameter/thickness and wire length. With a bendable wire, you cannot use smaller than 20 gauge wire. That size wire requires about 4-6 amps to become hot enough to cut foam. However, a large gauge wire has little resistance, and at 1/32" length, the maximum applied voltage would be incredibly low. In fact, you could not apply more than 0.007 volts to the circuit before overcoming 6 amps. There are virtually no commercially available power supplies that can micro-control voltage that low.

The solution would be to add a resistor to your circuit, to raise the overall circuit resistance. The best case scenario would be finding a variable voltage power supply, that can out put at least 10 amps. You'd have to find a 1 ohm / 50 watt resistor, and place it in-line with your 1/32" 20ga cutter. Your optimal cutting settings would be ~6 volts, drawing 6 amps from your power supply (36 watts), and not overloading the wattage of your resistor (50 watt max).

A very small cutter is definitely an option with the right tools and electrical supplies. But small resistors that can handle that level of heat dissipation (wattage) are hard to come by. In most circumstances you have to buy them in bulk. That said… I THINK I have 1ohm 50watt resistors in my shop.. I'd just have to look. how can something so simple be so complicated:)  Hey does cutting foam with a hot wire give off any fumes?

Thanks for your response, that was very thoughtful of you

I know!! It is both simple and complex at the same time!

Yes, cutting foam will emit fumes depending on the temperature of your wire. It is a bit of a trade off… A hot wire lets you cut faster but will emit more fumes but a cold wire will cut slower with less fumes. When you have a cold wire, you have to apply more pressure to cut the foam which will increase your chances of breaking the wire. A hot wire usually won't touch the foam because the radiant heat will melt the foam at a distance. Although, the hot wire will cut away more foam (a larger kerf) so sometimes your fine work is lost. Like I said… it's all a series of trade offs. It's a fine balance between temperature, cutting speed, fumes emitted and cutting kerf. 

I hope that doesn't overcomplicate!!

Wednesday, February 12, 2014

20" Cutter

I need is kind a large cutter which has the dimension more than 20", basically 0.3m or 0.45m would be the best. So would it be possible for you to make one and how much would it be

Check out this link, these cutters are really easy to make and all parts should be available at your local hardware store. 

That is going to be your best bet at a practical design for any cutter over 12"/30cm.

I would also suggest that you use 24 gauge nichrome wire, available through Jacobs online

You will need between 10-12 volts, and 3.5-4.5 amps. Here are a few options
- Option 1 - 30volt 5amp
- Option 2 - 30volt 5amp
- Option 3 - 30volt 5amp

If you're still interested in me making you a hot wire foam cutter, we can discuss cost of shipping and production. 

Monday, February 3, 2014

Beefy 16g Cutter with a battery?

I have a quick question for you, how long can I run 16 AWG nichrome wire for continuously off of a battery? The Nichrome wire is 8" each piece run in series. 

I was using a 18v drill battery and a 12v motorcycle battery and had horrible results. Both setups melted the wire I was using that was connected to the power source. Whenever I managed to power the nichrome wire I wasn't able to get a long run time before the battery would die, maximum run time was about 1 minute for the motorcycle battery and approximately 30 seconds with the 18v battery. 

Thanks for your response in advance.

I sure have been getting a ton of battery questions lately… weird!

Thank you for your praise of the site, and enjoying its content. It has grown quite vast over the last few years, and some of the information is hard to find. I'm not sure if you found this page, but I have a WHOLE page dedicated to battery power - Link ( )

There are a few problems with battery powered circuits…

Problem 1 - Fixed Voltage

First and foremost, they are a fixed voltage power supply. Obviously, meaning that they will always output their rated voltage - i.e. 12v, 18v, etc. What you've done with the 12v & 18v batteries is short circuited them both. It's probably good that the wire melted, if they'd have run for a longer duration of time, they'd probably have heated up and exploded.

16 gauge nichrome, at 8 inches, is approximately 0.173 ohms of resistance. Ohms law states that Amperage or Current is equal to Voltage divided by Resistance… A=V/R
A = 12v / 0.173o A = 18v / 0.173o
A = 69.3 amps A = 104.0 amps

That is some SERIOUS current pulled from those batteries. They'll die extremely quickly and/or heat up extremely quickly which is incredibly unsafe. 

Problem 2 - Available Amperage

Not every battery is designed to output amperages necessary to cut nichrome wire. There are internal resistances which restrict output amperage from a batter. Also, as a battery heats up, its internal resistance goes up, which also decreases output amperage. Ask any construction contractor who tries to use battery powered tools left in the sun on a HOT summer day. Their battery life is noticeably reduced. 

As a rough gauge, we say that you should not draw more than 1/10th of the Amp-hour (Ah) Rating of your battery. You'll notice the Ah or mAh listed somewhere on your battery.

So if you have a 20 amp-hour battery, it really should not output more than 2 amps for maximum efficiency.


Unfortunately there probably isn't an effective battery option for 16 gauge nichrome wire. It's liner foot resistance is far too low, and its current-to-heat demands are far too high. 

If you plan on using your 8" cutter to cut foam, I would recommend no less than 8-10 amps of current, which is about 1.4-1.8 amps. has a bunch of really effective and inexpensive AC step-down transformers that you can use to power your beefy 16g 8" cutter. Check them out, you'll be happy you did. 

I hope that answers your questions, but dive into the battery page for a lengthy explanation, and don't be afraid to ask more questions if you have them!