Connect with us

Hot wire foam cutter

Discussion in 'Electronic Basics' started by JazzMan, Sep 10, 2005.

Scroll to continue with content
  1. JazzMan

    JazzMan Guest

    I was browsing through my junk collection and think I
    have the elements to make a hot-wire foam cutter, was
    wondering if anyone here had made one before? I've got
    a roll of small-guage NiChrome wire, a wall-switch style
    light dimmer, a large transformer that I think was 115V in
    and 24V out for an HVAC application, and the assorted bits
    of wood and metal to make the actual hot wire frame assembly.

    My thought was to run 115V into the dimmer, use the output
    through the transformer, and the transformer output to the
    wire. I wasn't too concerned with the voltages because I
    figure the dimmer will allow me to get voltage/currents to
    where they would work well. I'll have all high-voltage stuff
    in appropriate enclosures and will use a 5A breaker on the
    inbound circuit for safety.

    Does this sound like a plan? Or should I be updating my
    beneficiary information on my life insurance plan? :)

    JazzMan
    --
    **********************************************************
    Please reply to jsavage"at"airmail.net.
    Curse those darned bulk e-mailers!
    **********************************************************
    "Rats and roaches live by competition under the laws of
    supply and demand. It is the privilege of human beings to
    live under the laws of justice and mercy." - Wendell Berry
    **********************************************************
     
  2. Tom Biasi

    Tom Biasi Guest

    Sounds like you can make it work. Be cautious of the fumes coming from
    burning foam.
     
  3. JazzMan

    JazzMan Guest

    Yep, have an aggressive ventilation system already in place,
    plus if fumes still represent a problem I've got a respirator
    that I can use as well.

    JazzMan
    --
    **********************************************************
    Please reply to jsavage"at"airmail.net.
    Curse those darned bulk e-mailers!
    **********************************************************
    "Rats and roaches live by competition under the laws of
    supply and demand. It is the privilege of human beings to
    live under the laws of justice and mercy." - Wendell Berry
    **********************************************************
     
  4. Impmon

    Impmon Guest

    I remember seeing a hot wire foam cutter at craft shop and they used 2
    'D' batteries to run. So you might want to test your project with
    batteries first to see if it'll work or not.

    At best, you'll have a safer alternative to high voltage rig. At
    worst, you'd only waste some time.
     
  5. You have the right idea, except that some lamp dimmers do not work so
    well with transformers. If the positive and negative half cycles do
    not match, the net DC causes the transformer core to saturate and you
    get a big current spike at the end of the cycle (during whichever half
    is bigger.) But you can live with that if you also put a big light
    bulb in series with the primary to act as a current limit.

    Most people make the mistake of trying to get the wire bright red so
    they can cut fast. A lower wire temperature (that will not make
    nearly as much smoke and a patient cur will work better. Remember
    that the wire always cuts along a curved line, so if you want to
    change directions in the middle of a cut, you have to pause while a
    while for the wire to straighten under tension before you can turn a
    neat corner.
     
  6. JazzMan

    JazzMan Guest


    I'm shooting for a cutting speed of around 1/2"-1" inch per second.
    More important than speed for me is accuracy and smoothness
    of the cut. The smoother the cut, the less sanding and fill
    work I have to do, saving time and materials.

    I've got light bulbs from 5W to 300W, what would you recommend?

    Thanks!

    JazzMan
    --
    **********************************************************
    Please reply to jsavage"at"airmail.net.
    Curse those darned bulk e-mailers!
    **********************************************************
    "Rats and roaches live by competition under the laws of
    supply and demand. It is the privilege of human beings to
    live under the laws of justice and mercy." - Wendell Berry
    **********************************************************
     
  7. Pick one that is rated for about double the wattage of the
    transformer, so it won't too seriously degrade its output capability.
     
  8. spudnuty

    spudnuty Guest

    I've built these from scratch and used a 600W dimmer feeding a
    transformer salvaged from a audio amp.
    The best supply I had was a Lionel train transformer from the '50s.
    That thing kicked __! I also found that a thin piano wire worked better
    than the Nichrome wire. Less breakage. I cut all the blue board for my
    houses cathedral ceiling using one.
     
  9. Ken Moffett

    Ken Moffett Guest

    Been there..done that..works fine. I used the
    dimmer/transformer/nichrome setup with no problems. But, many factors to
    consider:

    1. NEVER NEVER NEVER hot-wire cut ureathane foam. It gives off cynide
    gas. Styrofoam stinks, but with a little ventilation is no problem.

    2. As someone said, you do not want a red hot wire. It melts stryofoam
    long before that temp.

    3. At the start of a cut the wire is hot, but cools as you continue the
    cut. You will need to adjust your speed to compensate as you go.

    4. If you stop part way through a cut, the wire will quickly heat back
    up. This will melt a hole around the wire.

    5. Someone also mentioned the curve of the wire as you cut. The wire at
    the middle of the material is cooler than the top and bottom, so it lags
    behind. I compensated for this by heavely spring loading the wire. Not
    perfect, but better. Slow down, but do not stop to let it straighten
    out.

    6. Cutting curves should be a continuous operation. But right angles or
    sharp corners should be done as a seperate pass for each side.

    7. Practice, practice, practice. Temperature...material
    thickness...speed...directional changes.

    The cutter I made looked like big jig saw. The top arm was cantilevered,
    so I could put an adjustable spring on the end opposite the upper
    nichrome attachment. The transformed and dimmer were mounted in the
    base. I made the lower wire attachment adjustable from front to back, so
    I could slant the wire for cone-shaped cuts. The top wire attachment was
    made easy to undo, so I could pierce the foam with the wire and reattach
    it for enclosed cuts. I also addad a small ammeter (uA meter, diode, low
    ohm resistor) in series with the wire. It gave me a better (more
    repeatable) setting of my initial temperature than the position of the
    dimmer knob.

    Sounds like you have all the stuff you need.
     
  10. David Harmon

    David Harmon Guest

    On Sat, 10 Sep 2005 08:11:46 -0500 in sci.electronics.basics,
    That will do fine. Hot wire foam cutters:
    http://wolfstone.halloweenhost.com/HalloweenTech/fotmak_MakingFoamTools.html
     
  11. Jasen Betts

    Jasen Betts Guest

    yes, earlier this year.
    use a light dimmer that's designed to dim transformers, a
    regular one can cause problems (mainly overheating)
    I used the transformer from an old microwave, which
    I brutally butchered and removed the secondary and
    replaced it with 5 turns of heavy electrical wire

    I used nichrome from a fan heater. (the elements were
    rated at 5A)

    I wasn't too concerned with the voltages because I
    first you need to find out if that transformer can produce
    enough current to get that nichrome hot enough to cut foam
    at a reasonable rate, about 15 years ago I destroyed one
    rated at 1.4A trying that trick.

    I think I'm feeding about 5A into mine at about 5V for 25W
    over about 4" of wire.

    looking at the voltages and current involved I see now I
    could have used a surplus computer powersupply as the power
    source...

    The dimmer is probably not needed: if your wire is getting
    too hot just make it longer

    Bye.
    Jasen
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-