Hot-Wire Foamcutter (Battery Powered)




I have a hand-held battery powered foam cutter (these can be found at any hobby/craft shop). I find it quite useful, however I'm quite often frustrated by its inability to do detailed work. This instructable is simply a tabletop flat bed version of this handheld unit.


-Makes detailed work easy.
-Inexpensive (only a few dollars in parts)
-Small (easily storable)

Lets get started;

Step 1: Parts & Tools

Here is a list of the parts I used. Many of these can be replaced by easier to obtain equivalents, or cheaper options.

(also the metric components can be replaced with their nearest imperial counterpart if you are in Canada or America (M5 = 5mm ~= 1/4")

Parts: (Approximate cost $15)

-Bolt (M5 x 30mm) x 2
-Nut (M5) x 2
-Washer (M5) x 3
-Bolt (M3 x 15mm) x 2
-Nut (M3) x 2
-Washer (M3) x 3
-Nut (M20) x 4 (these are used as legs to lift the board off the table so 4 chunks of anything about 15mm tall will work)
-Nichrome Wire (can usually be found at hobby shops beside their foam cutters as a replacment part)
-Battery holder (2 x AA)
-Small Cutting board (mine was 16cm x 26cm)
-Wire (about 40 cm)
-~40cm of 4mm diameter metal rod


-Hot Glue Gun
-Soldering iron (I used a soldering iron to melt the holes into the cutting board this is because I did not have access to a drill)

Step 2: Hole Drilling

There are only three required holes.

I used a hot soldering iron to melt through my cutting board.

The middle hole has a 3mm hole drilled through and a 15 mm wide and 5mm deep depresion made around it. (this depression is to allow the bolt holding the bottom of the hotwire to rest flush with the cutting boards surface)

Below is a picture showing the hole layout.

Step 3: Bar Bending

Bend the bar so it has two loops large enough for a 5mm bolt to go through. One at the end and another 50mm in (these will line up with the holes you just drilled). Next bend the bar so it goes up for 10 cm, then over for 10 cm and then another loop bent onto the end. Precision is not particularily important as any small misalignments can be sorted out after assembly

If that writeup was a little vague (I certainly found it so) please find attached a drawing as well as a photo of the finished piece.

Step 4: Adding Feet

Glue the four large nuts to the bottom of the cutting board.

This provides clearance for the wire which runs beneath the board.

Step 5: Wiring

Two elements here.

Wiring the battery holder:

Attach a length of wire to each the positive and negative terminals of the battery holder. One length of wire needs to be long enough to reach the hole in the middle of the cutting board. The other needs to be long enough to reach the hole in the top corner of the board. (I attached washers to the end of these wires to make attaching them easier, I put a large washer on the shorter length and use it as a simple on off switch)

Wiring the hot-wire:

The required length of hot wire (nichrome) will vary depending on the type you have. Experiment with different lengths and 3 volts, use a length which produces a dull glow but does not cause the wire to melt. (takes a little trial and error)
Once you have the appropriate length figured out. Add a washer to both ends of it, twisting the wire to keep it connected (as in the photo)

Step 6: Assembling / Using

Time to put it all together.

1.I glued the battery holder close to the top corner (granted this did cut down on my cutting freedom so relocating this may be a good idea)

2.Attach the bent rod using the two 5mm x 30mm bolts to the two holes drilled into the top right of the board.

3.Run the long wire beneath the board to the hole in the middle of the board. Run one of the 3mm x 20mm bolts through one of the washers at the end of your hot wire length. Then feed this bolt through the hole, attaching the wire to the bottom and fixing it all in place with a nut.

4.Taking the free washer end of the hot wire, run the remaining 3mm x 20mm bolt through it. Next run this through the end loop in the bent rod, using the elasticity of the rod to pull it taught.

5.Use, attach the short length of wire to the 5mm x 30mm bolt and cut away.

Hoping that was helpful if anything is unclear (my wording can be rather cryptic at times) please feel free to ask any questions in the comments and I'll do my best to answer them.

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65 Discussions


10 years ago on Introduction

Excellent idea -- back in the 50s we used to use model train transformers to cut plastic, usually to "modify" plastic car or plane models. Our parents would have ****** if they'd seen us, of course, since the wire we put between the two screws would glow red-hot and could be really dangerous. It's amazing we ever survived childhood.

It took us some experimentation to find the right wire size to make the train transformer cut well without burning out the wire, though.

This is the same principle, and a great Instructable.

For larger work, like foam rubber, I used to use old electric carving knives I found at yard sales. It also worked great for fiberglass insulation batts when I built my first house.

12 replies

Reply 10 years ago on Introduction

They're taking all the fun out of childhood. What's the point of being a kid if you can't risk life and limb every day ... not to mention the fingers and eyes of your friends? Somehow we all got through our childhood in the 50s with monster firecrackers, firearms everywhere, helmetless bike-riding .... We might save a few kids from bad accidents with all these nanny-state laws, but I'm not sure it's worth the tradeoff. Perhaps Darwinism works better, where the unfit get weeded out early.


Reply 10 years ago on Introduction

Yeah, these new laws make life really dull for minors. You can't legally play with mercury or hydrochloric acid anymore, at least in the U.S. and U.K. I can't buy anything science-related without suspicion anymore. Ever since the terrorist attacks, I can't even take a soda on to a plane. It's ridiculous how paranoid people are about these things, especially chemistry. The problem seems to be human nature. Humans fear what they do not understand. In a panicked effort to evade any possible cause for injury, the government made everything deemed hazardous illegal. Despite the fact that millions of people grew up around these substances with no side effects. I like playing with mercury, and will continue to do so. I think it's ridiculous how paranoid everyone is, especially when it comes to chemicals. As soon as an average person hears the word "chemical" they think of poison. When they hear the word "radioactive", "Uranium", "Plutonium", "Radium", "radiation", or "nuclear", they think of bomb. It's because of all the crap the government has been spoonfeeding their people for years. It's the reason children no longer have the ability to experience high school chemistry class, or mix some acids and bases and watch the foam bubble up, or even something as simple as rolling a bead of mercury around a bowl and watching it all coalesce at the bottom. It all comes down to people's ignorance to the unknown.


Reply 10 years ago on Introduction

I concur, the fun in science is constantly being watered down by lawsuits. LEGAL PLEA "I didn't know the H2SO4 would burn my throat if I drank it!" Coming from a 13 year old, chemistry sets state that the "coolest" experiments are the ones that use only hot water and food coloring! Even then it requests that you have a parent around. My point is that black powder, sugar rockets (very fun), or making your own crystal iodine, may soon become tantamount to heresy. The only risk I see in this experiment when exercising common sense is benzene inhalation. Who knows? Maybe tomorrow we will need a license to own a screwdriver.


Reply 5 years ago on Introduction

I agree. It is moronic. Sugar rockets, yes, I remember mixing sugar with Potassiumperchlorate, stuffing it in a steel container, mounting it on a cart and ignite it. Sure, I had my feet burned by melted sugar shooting all over the place, so what, we had fun.
I made black powder basically on a daily basis, stuff it in a plastic pipe and light it with a fuse made of salpeter.

My kid of 13, never even climbed a tree, basically because the only trees around now are young trees without any low side branches + if a policeman would see him do it, he'd be cited for 'damaging a tree'.

What I hate most is those people who sadly had a child get brain damage coz he didn’t wear a bike helmet and got rear ended by a truck and then suddenly go on a crusade to make helmets mandatory by law. Mind yr own child, not mine


Huzzah! In my adulthood (well... while getting older anyway) I'm actually starting to recapture a lot of this. Now I can get or make the good stuff :)


Reply 10 years ago on Introduction

yah i know when i was little i would hide in my room making sparks for fun but coundnt make a wire hot it just goes click and you have to wait 10 minutes for it to reset itself


Reply 5 years ago on Introduction

"It's amazing we ever survived childhood."
I am with you. If I think at some of the dangerous things I have done, My god, I should have been dead a 100 times


Reply 5 years ago on Introduction


Somehow all of us survived stuff like skating and bicycle riding without helmets and tons of plastic armor all over us, and playing with fireworks you can't even buy anymore (quarter-sticks, half-sticks, M-80s, etc). We used to shoot .22 cartridges by putting them in eyebolts, mounted on a piece of 2 x 4, and shooting the end with a BB gun. Not very accurate, but lots of fun.

If you believed the nonsense put out by the safety Nazis, we all should have been maimed or dead fifty years ago.

Not to mention no seat belts (until the 60s) and certainly no child seats in cars. Nor air bags, obviously.

Of course, just having survived riding motorcycles for ten years, almost every day, should have killed me off long before Easy Rider was ever filmed.


Reply 5 years ago on Introduction

Man I have been ice shelf wiggling on the middle of deep lake, made gunpowder and managed to make nitoglycerine (it worked), filled the house with smoke from an experiment, tried to swing from tree to try on a rope that was too thin, made boxcars to go down a hill and of course i didn’t bother about brakes. Roller skating behind a truck.......
Safety helmets???

Souped up a scooter to run on a gasoline ether mixture and ad the motor litterally explode when I sat on it. wasnt even allowed to ride one. The railroad Shunting yard was my favorite playground. Explosive chemicals where freely available at the drugstore, a simple 'it is for my dad' was enough while now one would be put on the terrorist watchlist. The number of pipe bombs me and my friends made....
We would make bonfires outside at least once a week and none of the parents minded. Now they would call the police, the fire brigade and you'd get social workers on yr case just for being a kid.


8 years ago on Introduction

i have an idea..much easier. make a rig 2 hold the wire veridically. make it a few inches long for more flexibility. then take a torch and heat up the wire...problem...solved

1 reply

Reply 5 years ago on Introduction

umm a torch would melt the wire. not heat it up, a torch runs in the uot put range of 1,200 decrees faraneigh.


6 years ago on Step 6

and how to cut with it??? for what is using that other wire (yelow)? i dont knoow anything about this, but it looks seful for one project that i wanted to make


8 years ago on Introduction

Do you think a 15V DC phone charger would do a good job with sometihng like this?