Home-Made Hot Wire Foam Cutter

Discussion in 'FAQs' started by Doc Holliday, Jun 7, 2005.

  1. Doc Holliday

    Doc Holliday Member

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    Here's a pic of a hot-wire foam cutter I made from an old soldering gun I've had for about 25 years. It is 200watts. I took out and discarded the originag soldering tip. I used a piece of #10 copper wire to make two new tips. ONe is tunnel shaped and was used to cut the 18" raduiss tunnel through the foam block shown. The other tip is a long knife style. It can be bent into almost any configuration, as long as it doesn't touch itself anywhere. Cuts like a hot knife through butter. :thumb:
    Doc

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  2. Iron Goat

    Iron Goat Member

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    Great idea, Doc. In the attachment photo it looks like the "knife shaped" one, is twisted.

    Am I seeing it correctly ? (You cautioned that it shouldn't touch itself anywhere ?)

    Thanks, Bob
  3. Doc Holliday

    Doc Holliday Member

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    Bob,
    The pic isn't very clear, but the wire isn't twisted and doesn't touch itself for the entire length. Both sides are parallel and very close. That way the entire thing gets hot. When I first bent it, it touched about 2" from the gun connection. The current went through this "shortcut" and not through the entire length so the rest didn't get hot enough to melt the foam.
    Doc
  4. RailRon

    RailRon Active Member

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    Doc, did you do some calculations about wire thickness and length, or did you find the right wire just by trial and error?
    Isn't there a danger that you burn out the transformer of the soldering gun? :eek:

    I also have on old Weller gun and thought about making a foam cutter out of it - but so far I chickened out... :oops:

    Ron
  5. ezdays

    ezdays Out AZ way

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    This is a great use for one of these soldering guns. I haven't a clue what I did with my old one, probably sold it at a garage sale for a few bucks.:rolleyes: But, doing this does have its risks. The original tip on these irons have resistance. It is low, so the current running through it is actually high and so the power generated by this current and resistance is dissipated in heat. Get the resistance value too low and Like Ron says, you can burn out the transformer in the iron, or worse yet, start a fire. Get the value too high and you won't get enough heat to do any good. I don't know how critical this value is, but apparently you got the right combination since it does work.:thumb:

    Just remember that the thinner the wire (larger gage), the highert the resistance per length. Do you know what size wire you used, and how long it is? That would be good information for anyone else that would want to try this.

    That's also very clever making different shape tips for different cuts. :thumb::thumb:
  6. capt_turk

    capt_turk Member

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    I've used a soldering gun as a hot wire cutter for years. Use the largest diameter copper wire that fits easily in the tip holder. Try to make the wire at least as long as the original soldering tip, but it's not really critical. Electronic techs regularly twist the broken ends of burnt tips together to finish up a job when they don't have a replacement tip. As far as how long you can make it, if it doesn't get hot emough, just cut it shorter.
    I don't know about other brands, but the Weller soldering guns are almost indestructible. I've got a 125 watt Weller that I've been using for 35 years that's still going, and I've definitely "NOT" been gentle with it.
  7. ezdays

    ezdays Out AZ way

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    I don't know of anybody but Weller that made them. And yeah, 125 watts is a lot of power, 200 is even better, but unless there are some internal protections, you still have to be careful. There isn't much resistance in say one foot of #16 gage wire, but enough so it works, and that's just great. Now I wish I had kept that old solder gun, but who knew....
  8. capt_turk

    capt_turk Member

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    I can't remember for sure, it's been so many years since I had one apart, but as I recall, the secondary winding in the gun are "Very" heavy. My experience has been that the tips will burn into long before the gun is damaged. That's the built in protection. The tip holders will not accept a wire big enough to cause the windings to burn out. The windings are three or four times bigger than the tip wire.
  9. petepuma

    petepuma Member

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    Well, the resistance of #10 AWG copper wire is .00118 ohms per foot and can handel 30 amps at 120V. so the way I'm looking at it #10 is a great size wire for cutting foam! More power!!

    EZ is right in that you will burn out the transformer long before anything happens to that wire. :)
  10. petepuma

    petepuma Member

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    If anyone is interested to know exactly how much juice they have running through their new foam cutter then remember Mr. Ohm and his law: I=E/R. Amps=Volts/resistance.
    And when you have amps you can have watts! It's great!!

    Sorry. I get a little excited about electricity. I guess I am married to my job...
  11. Doc Holliday

    Doc Holliday Member

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    Thanks for the comments. I didn't over think it, I just did it. I said I'd had it for over 25 years. What I didn't say is that I've never used it in all that time. It was given to me, so if it burns out, I'm not really out anything. I don't know about the windings, but the gun itself is very heavy, almost too heavy to use one-handed. I cut lots of 2" thick foam just using the original soldering tip. I just needed something longer and also wanted something tunnel shaped. I first tried a piece of coat hanger, but it didn't get hot enough. I then used #10 copper wire, but a #8 would probably fit diameter-wise, but would be difficult to fit since the seated tips have to be bent at a right angle. The length of the tunnel shaped wire is based on the perimeter of the tunel shape. The length of the straight cutter is simply how much wire I had left over after cutting the tunnel wire off the piece I brought in from the garage. Really scientific, huh!
    Doc
  12. petepuma

    petepuma Member

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    Sometimes the best discoveries and inventions are just big accidents...you know, stuff like bubble gum and motor oil...:D :D :D
  13. ezdays

    ezdays Out AZ way

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    Science, we don't need no stinkin' science. Sucess is what counts.:thumb::thumb: When it doesn't work, that's when you turn to science.....
  14. RailRon

    RailRon Active Member

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    Doc wrote:
    Hey, and I always thought that Doc Holliday was really good at using guns! Is it REALLY heavier than a .45" Peacemaker? :D :D :D

    Thank you all for your hints - when I find the time, I'll try to modify my Weller and cut foam this way. (Frankly, I'm tired of the mess when you use knives and rasps for the job! The electrostatic charge of the slivers makes them cling to everything and drives you mad in no time! :mad: :mad: :mad: )

    However, one thing is for sure: Do it in a well ventilated place - melting foam STINKS! (And the fumes aren't healthy for your lungs either! :eek: )

    Ron
  15. Iron Goat

    Iron Goat Member

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    Thanks, Doc. Sorry for the late response to your answer, as I was on the road today.
    My ole Weller gun will be getting a "new job" very shortly... thanks again for your input.

    Bob
  16. Dave Farquhar

    Dave Farquhar Member

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    I wouldn't fret about selling your old gun at a garage sale. If you need one to turn into a hot wire cutter, it's easy enough to get one the same way you sold yours. Scan the classifieds in a Friday or Saturday paper, find a garage/yard/moving sale or two that advertise tools, and chances are you'll find one and probably won't pay much for it. You'll probably find lots of other stuff too. That's how I got my drill press.
  17. ezdays

    ezdays Out AZ way

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    Good thought Dave. There's a retirement community just north of us and instead of allowing individual yard sales, they have one big "swap meet" a couple of times a year. That would be a fine place to look.:thumb: