THIN FOAM HOT WIRE CUTTING PROGRESS REPORT, AKA, GOOD RIDDENCE TO SHIMS
Below you will find text explanation for the video. But first, notes and updates.
This video shows recycling seafood EPS containers into thin sheets for making gliders. I have good news and bad news.The good news is that I have found new recycled foam that is less than half the density of seafood packaging. This foam is used to cusion furniture imported from Asia. It is highly variable from on manufacturer to another, so you will have to experiment. I found that foam with smaller beads works better than bigger beads. The gliders made from the new foam are lighter weight, and they fly much more slowly. The slow gliders are much easier to learn to fly, and you can fly them in small rooms. They hotwire cut faster and easier than the old heavier foam. The bad news is that low-density foam releases more "aromatic hydrocarbons" when hotwire cutting. I am very careful to avoid the fumes. At the very least, you should cut in a large space with ventilation, such as a garage with the garage door open. Not in a kitchen. Also, the low-density foam does not work for the rotating tumblewing-type gliders.
Even if you plan to slice your own foam, you don't have to "re-invent the wheel". I suggest that you get a small package of gliders or foam and get a sense of what you are aiming for.
As my friend Phil Rossoni reminded me when he started cutting foam, if the hot wire hits even just a little drop of water on the foam, it will stop cutting. Make sure your foam is completely dry before cutting!
COUNTRY AND REGION SOURCES OF NI-CHROME WIRE
NORTH AMERICA http://jacobs-online.biz/nichrome_wire.htm
INDIA The video shows how to get ni-chrome heating wire from old soldering irons. Mr.Siddharth Erat reports. " Hello Mr Harrison. In India you will get 2 kinds of soldering iron.First,kind has a long tip.Second one has a short end as shown in your video.I have opened the second soldering wire and i found the 40 gauge nichrome wire. Regards,Siddharth" And he has informed me that he has also found nichrome wire inside "electric geysers" (tankless electric water heaters) in the immersion rods. However, he reports that the wire is more delicate than that found in soldering irons.
AUSTRALIA Darrell from Perth West Australia sent me two links for resistance wire as thin as 36 gage (.127 mm).
Thanks Darrel and Siddharth. Anybody else out there?
This text is illustrated by this video http://www.youtube.com/watch?v=fxbR2bwnjcw The numbers you see below correspond to the numbers in the in the video clips. How to make the gliders once you have the foam is here http://www.sciencetoymaker.org/airSurfKit/index.htm
The very best gliders that can be surfed on invisible waves of deflected air are made of thin slices of white foam. Mysteriously levitated “walkalong gliders” look like science fiction. They are not too difficult to make. My students like flying them, (I am a technology teacher). For a hand’s-on way to learn flight--and just for the sheer fun of it, too--more people ought to know about these.
That’s only going to happen if people have access to the thin foam. I think that having thin foam is as important—or more so--than the particular design of your glider. Thomas Buchwald in Germany and Chen Wenhwa in Taiwan have created whimsical birds, butterflies, sea creatures, even angels—all fly well as walkalong gliders, all made from thin foam.
If having a supply of thin foam is not too costly or too difficult to make, once you get a feel for the balance (center of gravity) and understand how the back flaps stabilize flight, soon you will be inventing your own designs.
Although I am selling thin-sliced foam, you can bypass me and do-it-yourself. The foam is right under our noses, being thrown away, available for free. It is not expensive to slice it into the thin sheets used for the gliders. Nor is it rocket science. The device to slice sheets is essentially a flat wooden board, some machine screws (costing a few pennies) from the hardware store, ni-chrome wire (available for a few dollars), and car battery charger (costing about $20 but somebody you know has one; most people who own a car have one already). All of these elements, and possible substitutes if you can’t find something, are covered in detail below.
I created two earlier (and now out-of-date) videos about cutting foam: Here, starting about a minute in http://www.youtube.com/watch?v=dXZ352ErX_s and here http://www.youtube.com/watch?v=Y-_f5qcLn5E
But it’s come a long way since those: simpler, more accurate. I think anybody who can use a recipe to make a basic food dish, or follow instructions to assemble a shelf or something…such a person will be able to slice their own foam.
Is foam cutting for you VS. buying pre-sliced foam?
There are advantages and disadvantages in all decisions. On the plus side:
My motivation and your responsibility
Even though I sell thin foam, don’t feel bad if you cut your own instead. I do not depend on selling foam to make a living. I direct the proceeds to work that I think is important (I am plenty well-enough paid as a teacher). Nevertheless, just because this information is given freely does not mean it is without value. I think the following applies:
USING THREADS FOR PERFECT FOAM SLICES
Start with two
When I started cutting thin sheets of foam, I used spacers called “shims” to lift the hot wire a precise distance off the table. The thicker the shim the thicker the foam is cut. Although it’s simple in theory, it was very time-consuming to get it working right and annoying variations creep in.
Now thin foam -cutting has entered the machine age. Now I wrap two (or more, see “ganging up”, below) hot wires partly around consecutive machine screw threads. That spaces it for perfect, uniform sheets every time (once you practice a bit). No micro setup adjustments.
1 Different screw pitches give different thicknesses of foam. For example, using common screws in North America, for the Mama Bug glider I use two 10-28 machine screws from the hardware store costing 11 cents each. The resulting cut is about .035” (thirty-five thousandths of an inch) which is about .9mm. ¼-20 screw thread gives slightly thicker foam for bigger gliders like the Papa Bug that need a little more rigidity. 8-32 gives slightly thinner foam, about .025” or .6mm for smaller gliders. These thicknesses assume you are using 40 gauge ni-chrome wire (see below) to make the cuts. Using thicker hot wire to cut would result in thinner slices.
Unfortunately, although I recognize the superiority of metric measurement in science and use it for some things, I have not worked very much with metric threads. I don’t know what the easy-to-find sizes are in metric countries. I am going to wait to add specific information about metric screws until someone more familiar can help me out. If you cut foam with metric screw threads, please send feedback.
Making a simple foam cutter with screws.
2,3 To make a foam cutter, drill two holes in a flat board, the centers about 11 centimeters or 4 ¼” apart. Use two 10-24 machine screws (if making the Mama Bug glider; use 8-32 for thinner slices if making smaller gliders).
4,5 The holes can be just big enough that the screws thread in if you prefer (the least work). The next two paragraphs about the size of hole to drill might be unnecessarily confusing—but it’s NOT important enough to worry about—something you can come back to later if you do a lot of foam cutting. If you find the next two paragraphs confusing, just drill holes a little smaller than the screw diameter, 11 centimeters apart. Screw them in so they are vertical, and move on to the next step.
6,7 Or the holes can be sized so the machine screws just slide right in. The later method will allow you to precisely adjust how far the wires are from the table. To most people, making just a few sheets, that adjusting won’t matter. But if you do a lot of cutting, it will cut down on waste (the bottom sheet is usually discarded).
8,9,10,11 If you drill so the holes slip through, you have to glue something (like a piece of plastic from a bottle) on the bottom so they don’t slip all the way through. As you will see later, turning the screws, one way or the other, lifts or lowers the wires a little (see clip 89 to understand how turning the screw raises or lowers the wire).
There are some details to consider when putting the wire on. 12 First, wire expands noticeably (and becomes very slack) when it heats up. So you have to have a spring—or in our case—a rubber band worked in that always pulls the slack out. If you keep breaking wires, try using a thinner rubber band with more stretch.
13,14 Second, I’m using a bright piece of twine (for visibility) to show the strange, zigzag way the wire routes on: like a “Z”. 15 And again for visibility, I’m making some fake screws with exaggerated pitch to show why. 16,17 If you push the string forward (as the foam will do to the wire), the left side tends to wrap up the screw thread. 18 However, the right side of the string wraps down. When the hot wire does that, it can make the sheets warp. It might seem like a small detail, but when your sheets are very thin to begin with it is noticeable. It’s easy just to wrap the wire like a Z ( 22) , creating a smoother, more uniform sheet.
19 I use very thin 40 gauge (about .08mm or .003”) nickel-chromium wires to hot-wire cut thin foam sheets (see below about nickel-chromium wire). Some people use wire that’s a little thicker (see Nyle Steiner’s feedback near the end). 20,21 The wires are inserted on consecutive (adjacent) threads, close to the board. It can be tricky to get them on the right thread. The distance between the wires is very accurate, determined by the machine screw threads.
22 Notice how the wire is rigged. It’s actually one wire, put through the rubber band loop, zigzagged around the screws, and the two ends are taped to the board (or wrapped around a nail, or whatever works to hold it there). It’s difficult to describe how much tension (how much to stretch the rubber band). Too much will break the wire. Too little tension will allow the wire to curve so much it might not cut as accurately.
23,25 The electric supply is hooked onto the two machine screws, so only the wire in-between the screws heats up (the rubber band will not get hot and break).
26,27,28 Expect to break a few wires before you figure out how hard to push the foam through. If you push too slowly, the foam overheats. You will be able to tell because instead of being smooth, the foam will look like it has some kind of skin disease and have holes. If you push too hard, the wire breaks.
29 The thin piece of foam cut between the wire and the board--the lowest piece of foam--is thrown away. 30 Only the slice cut between the two wires is accurate. If it drives you crazy to keep throwing away the lower piece, you might be able to adjust the distance between the table and lower wire. The holes that the machine screws go into need to be big enough that the threads to not grab. The holes must be big enough that the screws slip in the board without turning. The holes must have something on the bottom to keep the screws from protruding through the bottom (see clips 6 to ll). Now, when you turn the screws, they do not rise or fall. But the wire does go up or down, depending which way you turn them (see clip 89). You can preciously adjust the space between the board and the first wire, so you use the lower foam piece.
The electrical supply, ni-chrome wire, where to find free foam and how to rough-cut the blocks to the right size for slicing is all covered below.
31 to 34 Have you ever seen a hard-boiled egg slicer, with lots of thin wires? Yes it is possible to add more than two wires, to cut more than one sheet of foam at a time. That’s obviously more convenient—especially for teachers and other group leaders slicing out lots of sheets for many students-- but it gets more complicated. I am able to cut 6 sheets at a time with 7 wires. I have to use the thinnest wire I can buy: 40 gauge. If I use thicker wire it seems to overheat the foam. I am speculating that making wires too big (or putting too many wires in the parallel circuit) reduces the overall resistance enough to cause problems.
Furthermore I put a lot of care into making each wire the same length. I use high-quality rubber bands used to hold back long hair in “ponytails”.
Again, I broke some wires when I started trying to figure out how much pressure to push with. If you push too slowly the foam gets melted too much, blotchy. And since there are more wires to push against, you have push harder than if you are only pushing against 2 wires to get the same pressure against each individual wire (the force is divided by more wires. Figuring out exactly how much to push is definitely a learned skill but it’s worth it in the long run if you are doing a lot of cutting. I will likely (eventually) make another video devoted just to the challenges of mult-cutters.
Keeping the board from moving
This is not in the video, but I got tired of having to tape the board to keep it from sliding across the table as I push foam against the wires. I happened on a simple solution that works great. Just glue a strip of wood at the back, on the bottom, that gets caught on the edge of the table. In the picture, the table is black, the board light colored plywood. The strip glued to the underside of the board keeps it from moving when it is pushed to the left.
HOW ELECTICAL RESISTANCE HEATING WORKS (why it works)
This section is about some of the “whys” behind the mysteries of hot wire cutting. It‘s not exactly part of the instructions, but it’s helpful to understand how electrical resistance heating works. 37 to 39 (out of sequence) Toasters, electric ovens, hair dryers, soldering irons, and even the old kind of light bulb with a filament use the principle of electric resistance heating.
It’s actually a kind of friction. 36 If you push the palms of your hands together hard, and rub them back and forth, you very clearly feel heat. Heat is always a byproduct of friction. Electrical resistance heat cleverly uses electrical friction.
Usually you want good conductivity-- in transmission wires, in battery connections, in extension cords—so you use expensive metals like copper or sometimes aluminum and you make the wire as thick as possible.
But with electric resistance heating it’s topsy-turvy. Nickel-chromium wire is not nearly as good a conductor as the same diameter copper wire. Nickel-chromium wire has more resistance to electrical flow, and that’s good for hot-wire cutting. You don’t try to choke off the electrical flow altogether, but you design so it does not get an easy ride though, either
I used to wonder why heating up wire was different than a “short circuit”. Short circuits are dangerous (in house wiring can cause fires) and destructive (quickly ruin batteries). “Resistance” in Electric Resistance Heating is the key word. A short circuit lets the electricity run through unimpeded. Resistance heating does just that: there’s something in the circuit to resist the flow of electricity. Resistance is the opposite of conductivity, and it’s measured in “ohms”.
Of course, with higher resistance wire, the electricity does not “want” to go through. But crank up the electrical pressure and force it to go through! Electrical pressure is measured “volts” or “voltage”. Voltage and resistance fight against each other.
When we force electricity through high-resistance wire, it creates lots of electrical friction in the form of heat. Nickel-chromium wire can also get hot without losing much strength. 40 That said, I try to keep the wire below the temperature of glowing orange (except for a demonstration in the next section, where the orange glow provides a good way to see the effect of longer/shorter wire).
Way too much voltage (over 40 volts) will shock you, but we won’t go much over 12 volts with our power supply: a car battery charger or a car battery. By the way, amperage, or amps, are a measure of current : the amount of the flow of electricity. Although amps are important in very high temperature applications like welding, it’s not as important as voltage for what we’re doing. A car battery has much more amperage available than a cheap car battery trickle charger, but they have about the same amount of voltage, so they work about equally well to cut foam.
CONTROLLING WIRE HEAT
If your wire is too hot (I stop short of it glowing orange) it breaks more frequently. If the wire is not hot enough, it takes forever to push it through. There are lots of ways to adjust the heat, many of them involving controlling voltage. Because I stick with 12 volts, I use wire length to control heat. 42 Making the distance between electrical inputs shorter makes the wire hotter. Pulling back so the wire length between is longer cools it down.
CONTROLLING RESISTANCE and LONG/SHORT WIRE
There are three simple ways I use put resistance into a heating circuit. The first—as mentioned--is to use inexpensive (see below) nickel-chromium (ni-chrome) wire, sold under various brand names.
The second way to increase resistance is make the wire very thin. Wider wire makes it easier for electricity to get through—think of it as a wider road--less resistance and less friction. The math formula for area of a circle is π (about 3) times the radius, squared, so doubling the width of the wire increases the area (and therefore conductivity) 4 times! Later on I try (with limited success) to cut foam with a thin thin strand of copper wire removed from an old household lamp wire.
Third, unless you get to near “absolute zero” where there is a phenomenon known as “superconductivity”, there is some resistance even in good conductors like copper, so just making the wire longer will increase resistance.
44 So in practice this means that—with a constant 12 volt power supply--the thicker wire is best when the wire has to be long (cutting up big foam boxes). Thinner wire would not get hot enough (it would also not be strong enough). But if you use thick wire for a short length, it will get much too hot.
That’s bare bones. Any more electrical theory is beyond the scope of these building instructions. See below about getting resistance wire (ni-chrome).
WHENCE ELECTRICAL CURRENT ON THE CHEAP?
Automobile battery trickle charger
When I started cutting foam I used school power supply—not something everyone has. People who make model airplanes with foam wings have all kinds of clever devices to power hot wire cutting. They’ll just throw together an old microwave oven transformer with a lamp dimmer and—presto—a cheap power supply. I’m cheap, but I’m not that clever or daring. I was using 9 volt batteries for a while, but for a high-current application like this regular batteries are neither economical nor environmentally responsible (though car batteries work well in a pinch and they are rechargeable).
45 to 47 Mostly, I use the least expensive, common car battery trickle charger. It plugs into the wall but only puts out safe 12 volts. It even has a circuit breaker that turns it off rather than burn out the charger. I use it both for the long cuts (cutting up boxes) and the short, thin slicing cuts (but using different thicknesses of wire).
When you strike the two steel clamps together it sparks and looks scary, but you won’t get any shock from a 12 volt charger (unless you clamp it onto your tongue).
Do not use an “automatic” charger. It has fancy sensors and fuzzy logic circuits for charging car batteries, but it doesn’t work for hot wire cutting. Just the simple cheap, low-power charger works fine.
49 Behold, my 30 year old truck! 50 But no matter the age or kind, all gasoline-powered cars have 12 volt batteries—about the same as the battery charger. Some people will have easier access to a car battery than to a charger. I tried hooking directly to my hot wire cutter. 51 I was concerned that the much greater amperage available from a car battery—you can see it makes even more impressive sparks than a charger—would create too much heat and burn out the wire. However, I discovered that connecting to a car battery is about the same as connecting to a charger (thanks Diego Bellot Torres in Mexico for the tip).
Do not—as I foolishly did in the video—make sparks near the car battery. Sparks could ignite explosive gas bubbling from the battery.
Grocery store fresh seafood packaging
“I just want to say one word to you…Are you listening? Plastics!” Those are the famous words from a great, rebellious, funny movie from the 1960s called The Graduate. Well, I’ve got just one word for you: SEAFOOD! 53 to 56 Actually it’s the white foam packaging that fresh seafood comes from and it’s as close as your grocery store. I felt a little intimidated about asking at the seafood counter for their foam packaging, but they were very enthusiastic about finding a use for something that is just thrown out. It might have helped that I wowed them with some walkalong flying! I’ve stopped at other grocery stores and gotten the same helpful reaction. It’s free and they throw out more than I can possibly use. The rinsed-out boxes smell a little like fish, but the odor disappears when you dry them out.
Thanks Thomas Buchwald in Germany for the seafood packaging tip. As a rule-of-thumb I figure I’ll get at least 150 standard foam slices, each about .9mm thick, for making the Mama Bug gliders, more when I slice thinner. 57,58 I use two sheets per glider, so I get about 75 of the large gliders per box.
EPS strands for Expanded PolyStyrene. 59 It’s approved for food contact and the stuff they use to ship valuable seafood is high grade (except I don’t care for some foam packages of Tilapia). Of course you can find similar foam in electronics, furniture and appliance packaging. By all means, look around and see what works.
I used to buy my white EPS foam from a building supply store wall insulation), but it was terrible quality. Then I bought special high quality foam, but even that wasn’t as good as fish boxes. When cut thin it had lots of holes in it. I think the foam used for seafood packaging is so high quality because it has to be impermeable to liquid and the seafood is high-value: it’s worth it for them to protect their expensive product with good packaging.
Compared to white EPS I have not had good results with the closed-cell foam (blue, pink), depron, foam plates, etc.
When you watch the video of hot-wire cutting, you will see smoke—particularly after the cut is finished. Let’s be clear: no kind of smoke is good for you—not the sweet smell of leaves burning or a wood fire. Any kind of smoke is at least a respiratory irritant. But—although it stinks--white EPS foam does not give off the particularly toxic/ carcinogenic fumes that, say, burning PVC (polyvinyl chloride) or polyurethane put out.
You can minimize smoke exposure by having good ventilation or working outside. Also, the cutting operation keeps the wire cool enough during cutting so it does not make much smoke until after. If you put a foot pedal switch (see below for making a very crude one) you can reduce the amount of smoke generated considerably.
CUTTING UP FOAM FISH BOXES INTO BLANKS FOR THIN-SLICING
A crude but ok way to cut foam blocks to size
If you use a hacksaw blade to cut foam it is very messy—do it outside (the foam bits will still stick to your clothes)—but it works OK. 60,61 There is a pattern here (make sure there is no scaling or “fit to page” when you print)
that you can tape on to have a guide for what size to cut the blocks to. 63 Make sure you tape it at a place on the box where one of the big sides will be very flat, without bumps. 63 to 65 When you saw out the rectangles, the blocks don’t have to be exact, but if they are too wide the blocks might now fit in the foam slicer. You can also hot wire cut boxes…
Simple DIY horizontal cutter
Because of the longer span of wire required to cut boxes up, I use 30 gauge nichrome wire (see below for where to get ni-chrome wire or a substitute). The cutter is simplicity itself. First, a smooth board. 66 I had some plywood lying around that was too rough, so I glued on a smooth board that was too thin by itself.
67 I bought a couple of cheap, common threaded rods at the hardware store. In the U.S. they are 3 feet long (perhaps they are a meter long in metric countries?) and I got two. Any thickness works. I cut 4 pieces, each a foot (30cm) long. 68 For safety I put a blob of hot glue to blunt one end. 69 I drilled holes big enough that the threaded rods just slip in the holes.
70 Rubber bands keep the wire taut as it heats up and gets longer. 71 Because the electricity goes in at the two inner rods, only the wire in between those rods gets hot (so the rubber bands don’t get hot). The outside rods just hold the rubber bands. Adjusting the thickness of your cut is as easy as lifting the wire higher or lower.
Cutting foam box lids
72,73 I have a system for getting the maximum number of blocks from every fish container. Starting with some lids, I first cut a little from two adjacent sides 90 degrees to each other so have two good edges (the edges get banged up and dented). Running through several held together at once saves time. Use the standard size rectangle (make sure there is no scaling or “fit to page” when you print).
I glued it to some thin cardboard so it’s more rigid. I set the wire for the length and cut.
Next I decide which big side to cut smooth. 74 You can see in the video both concave depressions and convex bumps in the surface of the foam. 75 On the other side (inside of the lid) are the ridges along the edge that make the lid fit tight. 76 In this case I decide to cut off the ridges and set the wire height for that.
77 to 79 Finally, I set the width with the pattern and cut out blocks of foam ready for thin slicing. Only one of the big sides has to be smooth.
Cutting the boxes
I use the same cutter to cut the boxes that I used to cut the lids. 80 First I cut the sides off. The more I do it, the more I figure out faster, easier strategies. Ganging up pieces to be cut will save time.
81 You can also use a typical, commercially available vertical hot wire cutter for cutting blocks. My only caution is that frequently the wire is very thick, a guess to minimize breaking. The problem with very big wire is that the plastic that had been in the melted-out gap, called the kerf, has to go somewhere. Check to make sure the plastic did not form a shell that could impede slicing.
82 I don’t like to waste electricity. Attaching and removing an alligator clip is a hassle after a while. So I set to figuring how crude a foot pedal I could make, from a 2 liter plastic bottle, aluminum foil and tape. It’s ok for it to be crude because there is not shock hazard when using 12 volts. I cut out the middle of the plastic bottle, taped in aluminum foil, taped the striped lamp cord wire on. I step on and further crush the bottle, completing the circuit. Hey, I know it doesn’t get any points for style, but it works!
THE WEIRD WAY NI-CHROME WIRE IS SIZED AND WHAT IS THE BEST SIZE?
Apparently there wasn’t enough confusion in the world, so someone invented the counterintuitive gauge system for denoting wire diameter. Are you ready for this? 84 The higher the gauge number, the smaller the wire (as seen on this copper wire stripper). I just learned the origin for this counterintuitive system: The gauge number referred to how many times a wire was pulled through a die to make it smaller and smaller.
85 I usually use thick 30 gauge wire (.25mm, .01”)for cutting up foam boxes into blocks, then I use the much thinner 40 gauge wire (.08mm, .003”) for slicing out the thin sheets.
Some people think I’m crazy for using such the thin 40 gauge wire. It tangles and breaks so easily. But it is high-resistance (for gang cutting), it’s easy to pull out little bends, and the kerf (the part melted away by the wire) is very small. It took me some time to develop a sense of how much I could pull it before it breaks.
On the other hand, when cutting up big seafood boxes, you need a long wire. The bigger 30 gauge wire has enough conductivity to work with 12 volts, thinner wire does not get hot enough on long wires. And the long cuts create more tension in the wire, so it’s doubly good to use thicker wire.
I hear that there is a different gauge system for iron-containing wire (ferrous vs non-ferrous). I guess the rest of the world uses sensible metric measurement to denote wire size. Where’s the adventure in that?
FINDING WIRE, NI-CHROME OR A SUBSTITUTE FOR NI-CHROME
There is a terrific guy named Gary Jacobs who distributes small quantities of ni-chrome wire, reasonable priced, based in the United States (Washington State). For a couple of dollars—post already paid in the U.S. if it doesn’t require a spool. He’ll ship it anywhere, though it’s more involved to ship outside the country and you have to arrange that with him.
Ripping apart a soldering iron to get thin ni-chrome wire from it.
I knew that soldering irons use electric resistance heating and because my students use soldering irons a lot, I get broken ones from time to time. I don’t know if ALL soldering irons have good thin wire, but mine do. Counties that do not use 120 volt house current might have a different design.
88 The first wrapping of wire (I’m not sure what it’s for) is quite thick. It might be good for cutting blocks out of boxes. Then after a layer of mica is the thin stuff, about the same as 40 gauge wire.
Mr.Siddharth Erat reports. " Hello Mr Harrison. In India you will get 2 kinds of soldering iron.First,kind has a long tip.Second one has a short end as shown in your video.I have opened the second soldering wire and i found the 40 gauge nichrome wire. Regards,Siddharth" And he has informed me that he has also found nichrome wire inside "electric geysers" (tankless electric water heaters) in the immersion rods. However, he reports that the wire is more delicate than that found in soldering irons.
If you want a substitute for ni-chrome wire, here’s the science that will confront you
Let's be clear, wires made from different metals are NOT similar. There are good reasons why people use special wire for hot wire cutting. Nickel-chromium wire has high resistance (that's good for hot wire cutting) and stays strong even when heated. Substituting other wires, guitar strings etc. is better than nothing, but you'll face greater challenges and you might not be able to get as good quality foam slices. When using steel wire, guitar strings or copper strands I was frustrated by frequent breakage, tripping the circuit breaker on the (albeit crude)power supply and rougher texture on the foam sheets. Most of the alternative wire methods involve thicker wire that melts a wider "kerf". The kerf is the gap that forms in between the pieces you cut. That melted plastic has to go somewhere, so your slices might be slightly heavier.
I have not been able to make double cuts with the alternative wires, so you will have to make single cuts, which means you'll have to adjust the thickness. Even then, you have to push the foam through fairly fast or the foam will melt too much, but if you push it through too fast the wire will break.
Finally, remember that proper ni-chrome wire is cheap and can be shipped in an envelope. I'm sorry if I seem to be discouraging, but remember that I have spent many hours cutting wire many different ways. It's challenging enough even with nichrome wire; it would be irresponsible not to alert you to the extra time and work involved with substitutes. Some of this is outer fringes stuff.
Single cut system
When I used alternate wires, I could not use more than one wire to cut—my cheap car battery charger tripped its circuit breaker. With only one wire, I adjust the distance between that single wire and table to adjust the thickness of the foam cut. The holes are drilled big enough to slip right in without threading in. Glue something over the bottom of the hole so the screw does not protrude out the bottom.
89 Turning the screw should not now raise the screw up or down, but the wire partially wrapped around it does go up or down, depending which way you turn it. Unfortunately, even though the hole is too big for the screw threads to really engage, the screw often climbs up in the hole. So you have to push it doen as you make adjustments. You cut slices of foam, measure them (see directly below) and keep adjusting until you have the size you want.
As crude as the single-cut system seems to me now, I used it for years. And I used it with shims, which were much more difficult to adjust than this machine screw method.
Measuring foam thickness
Foam slices that are too thin become flimsy and floppy. Too thick and they become heavy, inefficient flyers. For Mama Bug gliders I use foam around .035” or .9mm. Foam for smaller gliders, like the Jagwing or Baby Bug, doesn’t need to be as stiff, so it can be thinner. The giant Papa Bug glider should be a bit thicker.
90 If you have 100 dollars to spend, a dial caliper is very fast and convenient. It should have a wide, soft foot for foam. But if not, there is a workaround.
91 Cut up and stack 10 pieces. Although you could not measure just one sheet with a ruler, 10 thicknesses is enough to get a measurement. Then just divide by 10 to get the thickness of one. This only works with a metric ruler. In the video, it looks like 10 pieces stacked is about 12mm. So each slice is about 1.2 mm—pretty thick, best for a big glider like the Papa Bug.
Using a guitar string
92 Steel guitar strings are actually alloys, a mix of steel and other metals. I gather that this method of hot wire cutting is quite well known among model airplane builders. Use the thinnest string. Some high e strings are a little thicker than others; I prefer the thinner ones because conductivity increases drastically as wire gets thicker.
Twisted steel cable strands
93 Starting with the thinnest braided steel cable I could find, I unwound it and found the strands to be too thick. But upon closer inspection I saw they in turn were made of still smaller strands.
The bends in the wire seemed impossible to straighten, but when I heated the wire it seemed to anneal or soften it enough. But the softening also made it quite prone to breaking in the middle of a cut. You can see a piece of foam cut with the cable strand. 94 It’s a little rough, but it will work.
Lamp cord strands
95 At first, a good conductor like copper would seem to be the worst thing to use for resistance heating, and it certainly does present challenges. But the stuff is ubiquitous. Everything that plugs in has it. And the thinness of the strands opens up some opportunity to counter the high conductivity. The very thin wires are used because thick wire fatigues and breaks when bent, but very thin wire is less prone to metal fatigue.
I tried cutting some foam and it worked. However, even with the thin wire I still had to run electricity through a much longer piece than I needed, to achieve enough resistance. I wrapped it around a glass bottle. Even then I tripped the breaker on the car battery charger after a minute of use. And yes, it is very easy to break a wire in the middle of a cut. Again, the cut is rough but better than nothing.
A British scout leader named Ralph Hughes who is getting his scouts involved in walkalong gliders told me that his uses “a single strand from a fishing trace” that he burned off the outer nylon with a match. In North America I asked my local store if they had any metal in fishing wire, but they didn’t know of any. Perhaps it’s for ocean fishing?
Nyle Steiner’s feedback
A very interesting person who created the Spark Bang Buzz website contacted me first to share a floating glider that used static electricity to levitate and has since become friend. http://www.sciencetoymaker.org/electrostaticLevitation/index.htm
He’s curious about everything, meticulous in his experiments, and happy to share his results. Below is an e-mail from Nyle about his hot wire experiments:
I noticed on your website that you are working on a section about foam cutting. This is not a suggestion about what to include but feel free to use the following if it seems to be interesting.
I have been using 40 gauge nichrome wire to slice styrofoam and I really like using it but there is always the curiosity for some, including myself, about what can be done using ordinary steel wire such as 28 gauge steel wire from the hardware store. The following are a few things that I have observed.
I have cut numerous batches of styrofoam sheets using both 40 gauge nichrome wire and ordinary 28 gauge galvanized steel wire from the hardware store. Foam sheets that have been cut using the thicker 28 gauge steel wire tend to be a bit heavier and stiffer for a given thickness, than foam sheets that have been cut using 40 gauge nichrome wire. Also, a foam sheet cut from the thicker 28 gauge steel wire will usually have many microscopic hairs on its surface due to the greater amount of plastic melted during the cut. A slight increase in stiffness can be a bonus and the microscopic hairs do not seem to cause much of a problem. When cutting with 28 gauge wire, it is easy to cut .015 inch thick sheets that fly as well as .020 inch thick sheets that have been cut using 40 gauge nichrome.
At this point, I have made many walkalong gliders from foam that has been cut both ways and I will say that it is very difficult to distinguish the difference. Gliders made of either type of foam slice will fly very well.
The temperature that allows a wire to cut well through styrofoam, is well below that of being red hot. Ordinary steel wire can work well at this temperature.
Here are a couple of hints that will help, when cutting with 28 gauge steel wire, to cut consistent foam slices that fly well.
When starting a slice, the wire is very hot and slices through the foam very fast for one or two inches. By this time the plastic has cooled the wire down considerably and the rest of the slice progresses much more slowly. This creates a surface that is inconsistent in smoothness and seems to have caused some gliders to have a strong turning tendency. After some frustration, I finally realized a simple solution. Simply turn off the current through the wire after every cut and let it cool. When starting a new cut, push the foam lightly against the cold wire before turning on the current. The wire will quickly reach cutting temperature and the foam can be pushed past the wire. The wire in this case never gets any hotter than just enough to make the cut. This produces a consistent surface and cut.
Another thing that helps to cut consistently is to reverse the direction of the foam block between each cut.
ABOUT THE MUSIC
I love the music of Martin Hayes and Dennis Cahill. Some movies/books/music entertains or informs—and then there’s the occasional work that sweeps you off to another dimension. That’s what the music in the video does to me. Martin Hayes and Dennis Cahill—and Irishman and American-- first met in Chicago in the 1980s and played jazz/rock/Irish fusion. When they returned to playing traditional Irish music of East County Clare, where Hayes grew up, they had something magical. As Colin Harper put it, "Sparsely accompanied fiddle music has rarely sounded so complete and so essential."
The piece of music is from here
The second is The Old Bush/The Reel with the Burl that I deliberately contaminated with noise in the middle. Buy it, we need to support great artists.
The third piece is from here
Here’s an interesting interview