Step 10: Wiring up the transformer and dimmer switch

This photo is your wiring diagram. The black two conductor wire on the left goes to the wall plug, and the brown one on the right goes to the hot wire.

This photo is just to show what connects where. You should of course use the wire nuts that came with the dimmer switch (esp on the 120V connections) and/or tape to ensure that no bare wires touch each other, or you, or your pet. Be careful not to electrocute yourself or start a fire.
<p>Here's my experience:</p><p>The idea of a dimmer and transformer didn't make sense to me and didn't work for a lot of people, so I went with a car battery charger with a 2A current limit setting. This worked, but the guitar string broke after about 30 seconds. I tried 3 different strings of different gauge and composition with the same result. I finally got some 22 gauge nichrome wire. At 15 inches it is 1.1 ohms cold. At 2A this would be around 4.4 watts (W=I^2*R), which doesn't seem like enough, but actually it gets plenty hot and works fine. I vaguely remember that light bulb resistance goes up by around a factor of 10 when it heats up. Maybe that's what's going on - a 44 watt light bulb would be plenty hot. Probably a much lighter gauge would work fine as well, but may not be as strong. The wire does get loose with heat. Instead of the ingenious tensioning method described, I used a guitar tuner, which I can tighten when the wire heats up and loosen after using. This thing cuts through styrofoam like butter.</p><p>I'm thinking about making a contraption that will run between the chuck and the base hole of my drill press (properly insulated!) so that I can get more accurate right angle cuts by guiding the styrofoam through it.</p>
<p>Hi! I just saw this video tutorial about how to make a simple and handy foam cutter, and they only use 2x AA 1,5V batteries. It seems a lot cheaper and easier, why? What is the difference if we are using a transformer or not? Is it due to the type of string they use (nichrome wire)? Thanks!<iframe allowfullscreen="" frameborder="0" height="281" src="//www.youtube.com/embed/FEMZZWjRDdw" width="500"></iframe></p>
<p>This is indeed a Very thorough instructable. Bonus points for production samples, and audience participation (users' comments). Thumbs Up! ;-)</p>
<p>Constantan... in my opinion bad idea, you want normal wire that has more resistance as it gets hotter, that way it helps keep temp more consistent.</p><p>Power source... old 12 volt lead acid battery with battery charger is often already available.</p><p>Ohm meter is your friend, measure resistance of wire, you take the voltage, divide by the resistance and you have the amps of power that will flow through wire. Make sure your power source/transformer (and fuse) is rated for higher than that to avoid wrecking transformers.</p>
<p>SO for example if your wire has 6 ohms of resistance, and you have 12 volt power source, you need about 2 amps of power. voltage may go a little higher, eg 14 volt in reality, so have safety margin.</p>
<p>Stringy or furry cuts are not hot enough that's all</p>
<p>hi,</p><p>i had a small comping saw and it was broken and i turned it into a hot knife cutter i put 2 machine screws and nuts to hold the hot wire, i used a 12v battary, it workd well</p>
<p>LA RUSTICA</p><p>polystyrene cutting machine</p><p>file:///D:/Hobby/Model%20hobby/Foam_Cutter_Cnc_Plans_Rusticaplan_v6.pdf</p>
<p>Instead of guitar string, use Constantan. https://en.wikipedia.org/wiki/Constantan</p>
<p>I want to cut a lead block by using the hot wire process. The melting point of lead is 330 degrees celcius. <br>Can this be attained by using this process.</p>
<p>Instead of guitar string, use Constantan. <a href="https://en.wikipedia.org/wiki/Constantan" rel="nofollow"> https://en.wikipedia.org/wiki/Constantan</a></p>
<p>No. Even if you could get the wire that would stay strong enough at the appropriate temperature, the lead would act as a big heat sink and wick heat away fromwhere you want your cut. Even if you could get the wire to cut, the lead would simply fuse together again once the wire had moved on. Foam cutting works because the foam shrinks where the wire cuts it (the bubbles in the foam collapse), so even though the melted foam re-hardens, a gap is left where the wire passed through.</p>
<p>this is an extremely smart idea good job!</p>
<p>I'm in the HVAC field and purchased a 50va 24v transformer for about 20 bucks, with the added bonus of a built in circuit breaker, this would be the best type to use if you can find one.</p>
<p>Another site suggested using a PC power supply instead of a dimmer switch, etc. I went that route and connected one of the 12V outputs of the power supply to a length of nichrome wire salvaged from an electric heater. It worked quite well. The wire did not turn red, but was quite hot enough to make a nice cut through 6 inch foam blocks.</p>
I use an old AAA battery charger, 120AC in -&gt; 12DC 1A out and nichrome wire (#30 AWG) over 12&quot; - no dimmers or pots, no probs,heat just right Han transformer doesn't even get warm. I also use same xformer and wire on a vertical machine and a horizontal machine and it works perfectly.<br><br>Tips - use nichrome wire, 26 - 30 gauge. Its heat tolerant properties are mentioned a lot but is not is its resistance qualities. On a machine where a guitar string would overheat, nichrome of similar gauge often barely gets warm. All around easier to work with and its dirt cheap in100ft spools at Amazon.<br><br>As already suggested, put a small lamp in series. Both a pwer indicator and (if you select a bulb rated between target output and transformer rating you've got a poor mans fuse as a bonus.<br><br>For power shoot for the 12 - 24 watt range (I have good luck at &gt;7VDC. A trickle/slow charger for 12Vcar batteries (cheap at WAlmart12VDC/6VDC at 2A is effective). You can also find the wall type cheap at goodwill.<br><br>Unless you require a lot of fast and heavy stock removal you'll get better results at just enough heat to cut and you'll generated much less nasty toxic smoke. The trick is to learn by doing what force and power yield what results in smoothest most accurate cutting.<br><br>To calculate the variables ref the Jacobs calculator already mentioned.<br><br>Good luck!
<p>Hi, I am from india. We have 240V AC powersupply here.</p><p>I am having a 240V AC to 24 V AC transformer. I have connected the Dimmer switch and also a 3A fuse. </p><p>My circuit is not working. Please help!!!</p>
I made a similar hot wire cutter, but I put mine in a Tupperware container. I also added a fuse for safety.
<p>Did your Tupperware box, hold up to the heat generated by the transformer? Did you put any holes in it for air exchange?</p>
<p>When I was younger I used to cut foam for model airplane wings. Used a bow just like this one, except I used nichrome wire. Tip for making templates, I used 1/8&quot; aircraft plywood, sanded edge and applied copper foil tape (the kind made for stained glass, to keep the wire from hanging up.</p>
<p>This instructable worked beautifully. When we first turned it on (with fingers crossed) we were careful to turn the dial up in very small increments, and discovered that you can feel the tool vibrate just ever so slightly when it becomes hot enough to slice. It also cools down pretty quickly. This will be used to carve up massive 8x4x2' blocks of EPS. Excellent!</p>
I did everything in your instructions except I made my frame out of 1/2 ' pvc but everything else I did as you instructed including the crappy plastic box. I couldn't&nbsp; find a 120v 25 with only 2 amps so I used a 120 24v 40 va transformer and put a 3 amp fuse on the hot side between the dimmer switch and the transformer. I tested it in my Garage and all worked well. I cut a test piece of foam cut like butter. Thanks you saved me about $ 140.00
<p>Actually, a 24volt 40VA is LESS than two amps. Glad it works. May I suggest you post it as an instructable?</p>
I'm surprised no one has suggested putting a small low-wattage light bulb in series with your hot-wire to act as a current-limiting device. That would sure save a lot of blown transformers and dimmers.
<p>That IS an excellent suggestion. Also, as another commenter suggested, a fuse for safety/protection of the transformer.</p>
There are several reasons that folk may be be burning out transformers. <br><br><br>The resistance of the cutting wire may be so low that the transformer is trying to supply more amps than it's own wire can carry, and so, just like the cutting wire the windings in the transformer heat up/melt.<br><br>Transformers are AC devices, they like a nice rounded (sinusoidal) waveform as input. Some cheap (expensive as well as cheap ones) dimmers can output a very square waveform and effectively put pulses of DC into the transformer's coil. <br><br>
Dimmers probably use a triac, which controls the conduction angle of the input sine wave. The output waveform is not sinusoidal, unless the dimmer is turned all the way up. The net effect is to produce high frequency components along with the low frequency line voltage. If the high frequency portion contributes to core heating, then this could have an effect on frying the transformer. But I think there is simply too much current. The only way to know for sure is to take some AC voltage and current measurements and find the power in and out.
<p>Would it be possible to use the dimmer on the OUTPUT of the transformer? It's still AC, and I can't imagine that the triac, etc. would care</p>
Great article! Can I use my soldering gun as the power source? I read of some people who use their soldering gun and use a dimmer to control the heat. Is this feasible?
<p>Actually, that should work fine.</p>
<p>I am sure I wired all things like on diagram but it is not working at all. There was no smoke, nothing. I have voltage before transformer but nothing after. Can it be because I am using electonic transformer.</p>
<p>By &quot;electronic transformer&quot; do you mean a &quot;wall wart&quot; power supply or &quot;brick&quot; power supply? If that's the case, you cannot use the dimmer. The dimmer requires an old school, iron transformer such as what is specified</p>
<p>my hot wire cutter is not working</p>
For a power supply, I just used an old ATX power supply from a dead Dell PC. Using NiChrome wire and this calculator : http://www.jacobs-online.biz/nichrome/NichromeCalc.html<br><br>I was able to get very close using the calculations alone and fine tuned it from there. I am using 10.4 inches of wire at 5vdc and it hits 620F along the length of the wire. Perfect cutting temp on everything from 1/8&quot; sheets to 8&quot; blocks. Consumes a touch over 2A, which is well within the 27A the PSU is rated for on the 5v rail.
<p>May be we can choose professional hot wire cutter from manufacturer .(robertlee@rongter.com)</p><p>Rongter company concentrates on developing and<br>producing the various<strong><br>Heat Cutter, Hot Wire Cutter, 3D Cutter</strong> for chemical,<br>textile, construction material. With 10 year experience, we can supply customer<br>with the various good quality heat cutter to meet indoor,<br>outdoor and in-plant cutting needs </p><p>Our<br>electric heat cutter including Hand-held tool, Bow cutting tool,<br>Table cutting tool, Hot wire cutting tool, 3Dcutting tool.</p><p>Applications</p><p>1.Expanded plastic: EPS,SIPs ICF,<br>EIFS, Sponge, Foam etc.</p><p>2.Wires cable, Rubber, PVC tube,<br>Nylon rope, Non-metallic belt, Aluminum foil, Metallized film, BOPP film etc.</p><p>3.Textile, Fabric, Leather, Carpet, </p><p>4.Packaging material, Thermal<br>insulation material, Inflating film, HDEP. Cushioning material etc. </p><p>In<br>order to expand our business line, we would like cooperate with you and supply<br>you hot cutter in best price and good quality. </p><p>Thanks &amp; best regards</p><p>Robert (<a href="mailto:robertlee@rongter.com" rel="nofollow">robertlee@rongter.com</a>)</p>
Hey. You're not kidding about turning that dimmer slowly. I found out that if you get impatient and crank that sucker quick, you hear a &quot;pop&quot;, then it no work no more. <br> <br>I friendly reminder from one of the foolish. :D
what if you wanted to cut a tree stump ? I want to build one that could burn though a tree stump in a hour . I am guessing I would need a full 110 volts and 10 Ohms resistance on the nichrome wire. I don't know ifs even possible but am looking forward to trying
here is my simple design: Was given 32 awg nichrome wire from a friend (cheap on ebay), wood (furring strip 8') fashioned into a &quot;C&quot; shape - I strung the wire at the end across the opening, hardware to attach the wire to the supply voltage (drilled through the wood and tightened the hardware to it), used the following power adapter from Lowes: <br>http://www.lowes.com/pd_168261-74985-57040_0__?productId=3354788&amp;Ntt=transformer&amp;pl=1&amp;currentURL=%3FNtt%3Dtransformer&amp;facetInfo= <br> <br>Which is essentially a step down transformer from 120VAC to 24VAC with a constant current output. Initially the wire secured across the opening was 2'8&quot; long. The wire did heat up and did cut foam but at a slow rate. I realized that the wire would get hotter if i shortened the wire. The opening was shortened to just under 2' which made the wire the shorter. Now the wire heats up to a hotter temp and cuts much easier and at a faster rate. The setup should only cost between 25 to 35 bucks considering that one has the hardware (nuts, bolts, washers, and lugs) instead of having to purchase large expensive packages of hardware that is generally sold today instead of individually. Built this for a friend. He says it works great.
I really like this simple cutter-tutorial. But is there a way to find a well working combination of wirelength, thickness and a not exploding transformer? ( try'n'error seems to be a little expenseive :D ) I want to build something like a cnc-foam-cutter for my 3D-Box and do not want to spent that much money on useless &quot;pooof&quot;s. If someone is interested in getting and sharing ideas about foam cutters he would be welcome on my Blog: <a href="http://3d-box.blogspot.de/" rel="nofollow">http://3d-box.blogspot.de/ </a>
I have a pair of 120/12V 4A transformers. 4A is not enough current. Does anyone know if they can be used together to get more amps through a single wire?
If they are identical, you can parallel them to increase the current output. (hook each of the two imputs to its companion, and likewise the outputs.) If they aren't identical, I wouldn't try it.
i've tried but my transformer blew up. i've founded that hot wire foam cutting technique is not safe anymore. if any one have suggestion here please feel free to comment. it will be much better if you give me the process how to hot wire not blowing anything.
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I made the hot wire foam cutter, it works great, for about a minute or 2, then there is a pop and a puff of smoke from the transformer. I've blown (2) Radio Shack 25 volt, 2 amp transformers. Dimmer switch is set to 1/3 or no more that 1/2 open. Does anyone have a solution? No more transformers left at Radio Shack.
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