Wide Hot Wire Foam Cutter

Here is another question I received today from user just like you!

"Looking for best benchtop variabe powersupply to cut 2lb eps foam into surfboard blanks. The 26 g nicrome in bowcutter is 5ft in length. Thank you"

Anyone people use cutters longer than 2 feet, I typically recommend stepping it up to 24 gauge NiCr wire. You'll get better tension and less sag using 24 over 26.

If you're truly going to work with 5 feet of cutting wire, you're going to need to have a power supply with a bit of a higher voltage output. Five feet of 24 gauge will need at least 30-40 volts if you want to get up to about 5 amps. Now… five amps is just a relative value. Most foam will cut at about 2.5 amps (when using 24 gauge). But at such a long wire, you're probably going to have to go with a hotter wire to make sure your cuts are nice and fast. A wire of that length will definitely lose some heat to the environment and take a while to replenish heat when consumed by cutting the substrate.

You probably won't be able to find a cheap DC power supply that can output 40v5a. But some of the AC step down transformers are really nice, they're called "Variacs"

Circuit Specialists have a few that they stock ( http://www.circuitspecialists.com/variacs ). Honestly, if you don't mind spending the 100 bucks, I'd go with the 20amp model ( http://goo.gl/9o5ho ). That thing is a BEAST. And because it can go well beyond 5 amps, you'll be able to fiddle with your cutter until you get a nice and fast cut. 

But be cautious, any voltage setting above 45 volts has the ability to penetrate dry human skin. They do have an in-line fuse which will help prevent against short circuits and electrocution. But just be really careful that no one touches any of the metal components on your cutter. Also, be careful when you set the cutter down that it doesn't touch a metal bench or a puddle on the ground, or that kinda thing. I know what some people have done is spray the metal brackets/bolts with GrillPaint. Its a high temperature and nonconductive paint, available at most hardware stores. Just a thought. 

One other thing you might consider is using stainless steel leader wire, used in deep sea fishing. A lot of the model RC wing builders will use stainless steel wire because they can put it under higher tension. Now, I haven't tested it myself for the electrical requirements, but apparently it is similar to nichrome wire.

Check these guys out - http://www.terminaltackleco.com/prod_detail_list/144

For leader wire gauge, I think the 80-100lb test is typically used, but maybe thinner. The stuff is pretty cheap, so you can experiment too. 

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If you guys have any questions, get a hold of me!

-carlo

AC v DC

Another question emailed by a user, with my reply...

I found your video and info on NiChrome wire interesting.  I am working on a much longer run of NiChrome wire to burn through some tough fabric.  Are you available to discuss AC vs DC voltages?

No problem at all.

Long story short, when it comes to a resistance wire application (nichrome wire) it really doesn't matter. The fact of the matter is, NiChrome wire only requires an applied electrical pressure (voltage) and a current running through the circuit. Whether its a constant flow from direct current, or an alternating flow from alternating current it doesn't make any difference.

But as far as what your specific project requires, it really depends on the length of wire and the diameter you'll require - as you may be aware, both will impact the electrical requirements. 

AC power supplies are usually cheaper and have a higher voltage capability. Whereas DC power supplies are sometimes easier to come by.  I always warn users to be cautious of any power supply that outputs more than 45 volts, which is the threshold for penetrating dry human skin. Not many circuits require voltages this high, so why run the risk with a high output AC transformer? But both are perfectly acceptable options.

Jacob's Online has some good solid state step down AC transformers that are beefy and can handle quite the load. So if you intend on making your own supply, check out what he has stocked. I've personally made a power supply from his units, and it works great!

Otherwise check out the Benchtop Power Supply Section of the website which lists a few vendors that have great customer service and a variety of power supplies. I've referenced MastechPowerSupplies.com a few times, they have a great section on AC transformers. 

Hope that helps!

-carlo

Power Supplies & Wire

Here is another emailed question from a user regarding power supplies and type of wire. 

Hello, 

I was looking at your webpage regarding hot wire foam cutters. I tried making a cutter but it seems that I may have bought the wrong wire. I have a toy train transformer that cuts of in about 15 seconds after it heats the wire to cut. I bought fishing wire (stainless steel)... I am very frustrated with this and really want to make this work. I'm not interested in cutting foam but as I am in cutting PVC boards. 

Hello!

I would recommend spending a little time and cruise through my website, it has all the information you desire. But I think the Introduction Page may answer alot of your questions.

There are a few things, stainless steel wire does not have published heating/electrical requirements so a lot of it's use is experimentation. NiChrome wire is preferred because we know how much electricity it takes to heat different lengths and gauges. That information is located here. 

It is unlikely that the train power supply will be effective for long term use. It wasn't designed to output the wattage (amperage (x) voltage) required to heat nichrome wire (or stainless steel wire) for extended periods of time or even short periods of time. Check out the power supply calculations page which will help explain why, and also provide you with ways of estimating your power supply requirements. 

The Introduction Page does have some general power supply information, but on the Materials Page there is a link to recommended power supplies for general small scale use. You may end up spending a bit to get a decent power supply, but it is worth alleviating the headache! On the Materials Page you'll also find a link to purchase NiChrome Wire, but I have always had superior customer service and recommend Jacobs-Online for nichrome wire. 

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I know there wasn't a lot of content in this FAQ, but I just wanted to post so you can see the types of questions we receive. Also, I wanted to post the links to the website in case you too have similar questions. I always recommend people start out by reading through the introduction page for abridged notes to foam cutters. 

-Carlo

Adding Resistance

Here is another email from a user that has a perfect question regarding power supply voltage... check it out!! This is the exact question (in blue) and my reply (in black)

Question ::

I want to make a hot wire cutter to cut rabbets in the edges of rigid styrofoam insulation. I have calculated my voltage and current requirements with the calculator on this site.

To heat my 1" 18ga Nichrome wire to 300F/600C, I need ~6.5A at 0.25V.

My variable power supply won't go that low, and because this is a one-time project, I don't want to spend $30-40 on batteries and another $30-40 on an appropriate charger.

I'm looking for suggestions for a voltage divider that would allow me to use an existing [variable voltage] 12VDC 10A power supply to power the cutter.

No problem at all, and great research! I always love when people like you utilize the website and have almost all your own answers!

You're close :) All you have to do is increase the resistance of your circuit to account for the lowest power supply voltage. 

Just play with ohms law to see how much you need to add, but here is the link to the main page for resistance modification

http://hotwirefoamcutterinfo.com/Hot_Wire_Foam_Cutter_Info/_ResistanceCalc.html

You'll be adding resistance in series with your nichrome wire circuit. 

Here is a quick series of calculations you can do, figuring the lowest voltage your power supply can output. Lets just use 2 volts (just guessing) as the lowest voltage your supply can provide. 

Resistance = Voltage / Current

Resistance = 2/6.5

Necessary Circuit Resistance = 0.307 ohms

Resistance of 1 inch 18 gauge wire = 0.035ohms

Unaccounted Resistance = 0.307 - 0.035ohms

Unaccounted Resistance = 0.272 ohms

So basically, all you have to do is add about 0.3 ohms and you can use a power supply that can only go as low as 2 volts (theoretical).

A REALLY cheap way to make a resistor is like this

http://www.youtube.com/watch?v=P92V6jBYCA0

I've never tried to pull more than a few amps through that wire, but theoretically it could handle quite a lot. I get a little wordy in the video, so I apologize, i haven't updated that video yet. But you should get the idea. I had also considered using a frayed telephone cable (which has 4x small cables in it) but you might melt that small of a cable. Anyway, a little playing around might save you some money.

Otherwise check out Digi-Key, this link goes straight to their resistor search page

http://search.digikey.com/us/en/cat/resistors/through-hole-resistors/66690

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On hand, I have 1ohm5Watt resistors. So placing a handful in series or combined series / parallel will provide a lot of circuits with the resistance and wattage they'd require.

I hope that wasn't too confusing!!

-carlo

2011, 1202 - YouTube Update

Hello Everyone,
Thank you for visiting our blog and here are some brief links for the most recent YouTube Update (2011, 1202)

Main Link to JacobsOnline - http://jacobs-online.biz/
Step Down Transformers - http://jacobs-online.biz/transformers.htm


I have selected the XFR-1006D as my primary power supply. As a sneak preview, here is the diagram I showed in the video but will be creating a custom power supply within the next month or so.

This electrical arrangement will allow for three power states from this supply - 6v8.3a, 6v16.7a, 12v8.3a - when the DPDT switch toggles the circuit to series (double voltage), parallel (double amperage), & off (single voltage, single amperage.

All that for a transformer under 30 bucks!! (yes yes... there are other costs in the switches, etc, but c'mon 30bucks!)

Stay tuned for more videos!

Large Scale Cutting

Hello everyone,

Just another question on cutting foam..! I've gotten this one a few times before, not necessarily for surf boards, but just larger hand held projects. The questions are in blue, take a look!

I am a surfboard builder and am interested in cutting blanks out of EPS foam -I know nothing about electrical systems but would like to build my own cutting tool- 

what do you recomend for this type  of project?

I'd certainly recommend a large scale hand held cutter

http://hotwirefoamcutterinfo.com/Hot_Wire_Foam_Cutter_Info/_LargeHandDesign.html

the bow needs to be aproximately 32" inches wide. 

You should easily be able to make this cutter at any length you desire. 

You could even use 3/4" PVC rather than 1/2". The 3/4" will be a bit heavier, but will be more rigid and strong for larger cuts. 

If you want me to make you the electrical end caps, just let me know and I can send them to you. But I will be uploading some new videos tonight, so you may be able to follow along in those and make them yourself. 

what should I use as my power source? ( I have been looking at variacs on ebay)

The variac series are nice. They are an AC power supply rather than the typical DC power, which works well at a wide range of voltages and amperes.

mastechpowersupply.com has the greatest selection of variacs available online, and they are very reasonably priced. Check out what they have for AC transformers, and you can always get model numbers to see what you can find online. 

http://www.mastechpowersupply.com/variac/cat_3.html

Be VERY VERY careful when using AC transformers. Typically any voltage above 45 volts can penetrate human skin and cause electrocution. While you'll probably need less than 20 volts, ever, this wont be a problem. But just be careful!

Here are two power supplies I'd choose for your project

http://www.mastechpowersupply.com/variac-auto-transformer/0-5k-va-variable-transformer-variac-500va-0-150v-110v-input/prod_52.html

http://www.mastechpowersupply.com/variac-auto-transformer/mastech-2kva-variable-transformer-variac-2000va-0-150v-110v-input/prod_51.html

The first one SHOULD be enough power for you. It says it can only put out 3.3 amps at 150 volts, but its rated as a 500VA (or watt) transformer. So at lower voltages you should be able to safely obtain a higher amperage.  I'd guess the first one will be more than enough for your project, but the second one will DEFINATELY work!

I  can build the cutting bow but dont know what gauge on nichrome wire to use or if it would be best to use stainless steel.

I would recommend NiChrome, only because it is most reliable and there are known electrical values. (Meaning, we know how much amperes/voltage it requires to heat up.)

I'd recommend either 24 gauge or 22 gauge wire. 20-22 gauge are pretty stiff, so might not be ideal. I've personally used 26 gauge at lengths under two feet, but you should probably use 24 gauge.

the good news is, Nichrome is CHEAP. so you can always buy 24 and 22 and see which you like better.

On the other hand, with the variac transformer you will be able to test out 22 gauge, 24 gauge nichrome, as well as stainless steel if you wanted. The power supplies are hearty enough that they will heat up a lot of different wires. 

Check out this fishing line retailer, they have stainless steel fishing line, that I had a customer use for making RC plane wings. He said he liked it better than nichrome at longer lengths and is pretty cheap too. 

http://www.terminaltackleco.com/

here is the link to their stainless steel leader wire page

http://www.terminaltackleco.com/prod_detail_list/144

I don't remember the recommend lb test wire, but I THINK it was between 30-60lb test stainless steel wire that worked the best. But at a few dollars per pack, it's still pretty cheap to buy a variety of wires, and see what you like!






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That's it guys! I hope it was some what informative. And remember, all those links are already on the website!


-carlo

Calculator Question

Happy Halloween!

I just wanted to post a quick question I had from a user that used the Jacob's Online Calculator, found on the website. This is a copy/pasted message from the email I sent back. His questions are in blue, my responses in black.

Question

Please help me to understand your calculator.

Here is a link to the main help page, which may answer some of your questions. 

http://hotwirefoamcutterinfo.com/Hot_Wire_Foam_Cutter_Info/JacobsHelp.html

I need the tempereture to be 160 degree celsius.
The length should be around 60cm.
The gage should be 32 because i am using it as a heater.
The diameter is 0.203 mm the volts would be 12 volts .
if I punch this on your calculator 

the result show that I need a power that is =+/- 7 Watt with the current of +/- 0.5 amps . Is this correct ?

So if I go to a shop for my particular application I need to buy a power supply that has 7 watt ,12 volts,0.5 amp.
Is this correct?

You're pretty much correct, yes.

Check out the electrical theory page to reference what I am about to discuss. 

http://hotwirefoamcutterinfo.com/Hot_Wire_Foam_Cutter_Info/__ETheory.html

Just remember that the VOLTAGE needs to be similar between what you calculated and what is on the power supply. From the power supply, the output voltage is always constant. But the amperage or current flow is a function of the resistance of your circuit. (See Ohms law).  The listed amperage on the power supply is the maximum safe output amperage for that power supply. 

Think of it this way. You need to find a power supply that is 12 volts, but has an amperage rating HIGHER than 0.5 amps. A 12v 2a power supply would work great, because you're always putting out 12 volts, but your circuit will only draw 0.5 amps and it's rated for a maximum of 2 amps.

If you reduce the length of your wire, or increase the gauge, you will reduce the resistance of your circuit. Lower resistance, when you apply the 12v from your power supply, will draw a greater current from the power supply. 

But a long-story-short, find a 12v power supply, and an amperage rating of anything higher than 0.5 amps, id probably say 1 amp or more. 

As for wattage, it is similar. The listed wattage is the maximum safe wattage output from the power supply. 

Also,

Watts = Volts * Current

...

Current = Watts / Volts

If you find a power supply that has just voltage and wattage, just divide the wattage by the voltage and you'll see the maximum safe output current. 


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Okay everyone, as promised just a quick note. Take care and don't eat all your candy at once!


-carlo