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OT? Styrofoam cut by hot wire

Discussion in 'Electronic Basics' started by Rich Grise, Plainclothes Hippie, Oct 5, 2005.

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    Whoa, dude! I was interested in the thread about cutting styrofoam with a
    hot wire. Well, some months ago I saw a hank of nichrome wire on ebay, for
    a couple of bucks, which he said was #36, and just today I mic'd it [yes,
    that's proper use of the apostrophe - go look it up! - Rich the Pedagogue]
    at about .0047, maybe .0048. The thou on Joe's mic are like an eighth of
    an inch apart, so I had to interpolate the tenths.

    Anyway, in the ad that I bought it from, it said, "28 ohms per foot." I
    ohmed it out, and it was within as close as I could get the probes to a
    foot apart. :)

    BTW, the reason I bought it is because I was entertaining fantasies of
    building a THC evaporator. [still am, actually - Rich the proofreader]

    But that's a different story. %-) What prompted this post is that I have a
    "7.5VDC, 1A" wall wart that came with some kind of radio that somebody
    threw away, a set of Radio Shack clip leads, and this nichrome wire.
    "Hmm", I says to meself. Did I say I'm still stoned from that ONE HIT!??)

    But I remembered that "cut foam with a hot wire?" thread, and I thought,
    what's the worst that could happen? So I took a piece almost a foot long,
    clipped the clip leads to the ends - you can barely see the red-booted
    clip and red VOM lead, which for the pic have been disconnected. I just
    clipped the wall wart to a piece of this nichrome wire, on top of a couple
    of pieces of ceramic tile I'd scrounged, and it didn't get red, but it got
    uncomfortably warm to the touch, like, if I'd held it tightly between
    thumb and finger, it'd have left a mark in a few seconds. I don't know how
    to estimate temp, but I'd say more than 120 F, but decidedly less than
    450! :) So, anyways, this nichrome wire is lying there dissipating heat,
    and I grabbed this styrofoam block, and picked up the wire by the clips,
    and, well, I cut the styrofoam. :) It was kind of a weird feeling,
    actually - I felt almost no resistance (in the mechanical sense) as if I
    were cutting butter, please excuse the trite hackneyed cliche. ;-)

    Just for context, in the pic you can still see the nichrome wire, and it
    looks like it goes into the right-hnad corner of the small block and out
    of the top corner? Well, here's the thing. I was so freaking excited at my
    wonderful new discovery that I left the wire lying about where you see it
    in the picture, and by the time I got around to unclipping the leads from
    the wall wart plug, the wire had already melted itself into the botttom of
    the small block.

    The cavity that looks like a hole somebody tried to drill, who didn't know
    what an ordinary drill bit will do to that type/form of styrofoam, is a
    hole somebody (I) tried to drill, not knowing what an ordinary drill bit
    will do to that type/form of styrofoam. ;-)

    But the way the wire cut through it! I did feel the difference, but that
    cut is amazing! I did that by hand! Imagine if I put it in some kind of

    BWAHAHAHAHAAAA! Styrofoam cut to your spec - $0.12 per square inch of new
    surface!! ;-D ;-D ;-D

    BTW, if you get another server error, please, please let me know, because
    as I've said, I'm inside the firewall, and I have to trust my own
    blundering configurations to expose just the right stuff to the outside
    world. Damn, I'm still stoned, on that one hit, and it's been a couple
    hours! I might have another little hit soon though, since it _has_ been a
    couple hours. %-}

    Oh, yeah, before I hit "send" if you're wondering where that particular
    particularly nice block of styrofoam came from, it was in a box that
    somebody had shipped some big light bulbs that they've installed in the
    shop. Like the size of a 1,000 watt bulb, but halogen or mercury or
    something - anyway these big bulbs were packaged in these cool blocks of
    foam. :) (inside corrugated cardboard boxes, of course.)

  2. Jim Thompson

    Jim Thompson Guest

    Us "big boys" suspend the nichrome via a spring mount, so it stays
    straight as it heats and expands.

    I use that scheme to bend sharp edges on various types of plastics.

    ...Jim Thompson
  3. Shucks, there are thousands of homebuilt airplanes flying today that were
    cut out of styrofoam with a hot wire. It hasn't been rocket science for a
    few dozen years.

  4. You can get big CNC machines that hot-wire cut big chunks of styrofoam
    for POS (that's 'point of sale') displays, props and that sort of

    I'm not sure you should be inhaling the fumes from that, but maybe
    it's not so much worse than the other fumes you've been inhaling. ;-)

    Best regards,
    Spehro Pefhany
  5. Phil Allison

    Phil Allison Guest

    "RST Engineering (jw)"

    ** Nichrome wire is NOT the best stuff to use for this job - just the
    easiest due to its high resistance.

    Much better to use stainless steel and exploit its positive tempco of
    resistance to monitor and control the wire's temperature. If you can hold
    the voltage to current ratio in the wire constant - then the temp is held

    Scheme = low voltage switching regulator, wire in a bridge balance, op-amp
    feedback control of PWM etc.

    .......... Phil
  6. redbelly

    redbelly Guest

    How could we wonder about this BEFORE you hit "send"?

  7. blah

    blah Guest

    Does anyone here have a good idea for cutting foam blocks with embedded
    plastic? (Insulating Concrete Forms)

    These are blocks used for construction. Two pieces of foam are connected
    with plastic rebar and concrete gets poored in the middle.

    Currently, most people using these cut the blocks with a chain saw/table
    saw, resulting in poor cuts and major wear on the tools.

    Any thoughts appreciated...the plastic makes this a little tricky. Note the
    concrete only gets poored in later, so there is no need to cut through
    concrete :)

  8. Assuming the plastic is something like PE, a hot wire should cut them
    effectively. If it's rigid PVC rather than PE, it might kill the
    operator as a side effect.

    Best regards,
    Spehro Pefhany
  9. Phil Hobbs

    Phil Hobbs Guest

    Styrene monomer is massively carcinogenic, so you'll want to avoid
    breathing the vapour that comes off when you cut.


    Phil Hobbs
  10. Ken Muldrew

    Ken Muldrew Guest

    A small electric chainsaw works like a charm, and any flaws can be
    filled in with spray foam before the pour. There is absolutely no wear
    on the tool (even if it was useful for something else, which it
    isn't). If you really want an artistic cut, then one of those electric
    carving knives that you sometimes see at garage sales might do the

    Ken Muldrew

    (remove all letters after y in the alphabet)
  11. Ian Stirling

    Ian Stirling Guest

    Many sources disagree - for example

    If it was massively carcinogenic, I'd be looking for huge amounts
    of cancers from all the fiberglass boat-builders out there, often working
    in poorly ventilated spaces.
  12. John Ferrell

    John Ferrell Guest

    I believe the Polyurethane foam releases toxic gases when burnt or hot
    wire cut.
    Does anyone know for sure?
  13. The Australian government thinks so:

    "Recent testing has shown that when the polyurethane foam is heated or
    burned, toxic fumes are released which can pose a serious threat to
    the health of building workers. Fumes released contain nitrous oxides,
    carbon monoxide, hydrogen cyanide, isocyanates and chlorides."

    Best regards,
    Spehro Pefhany
  14. Phil Allison

    Phil Allison Guest

    "John Ferrell"

    ** The two part *polyurethane* foam used by boat builders is not easy to

    I bet it cannot be cut with a hot wire like *polystyrene* foam can.

    ............ Phil
  15. I read in alt.binaries.schematics.electronic that Spehro Pefhany
    There are nitrous oxide N2O and nitrogen oxides (mixed) NOx. 'Nitrous
    oxides' is not a term recognized in chemistry AFAIK.
    That's obviously about burning with an inadequate oxygen supply; you
    wouldn't get CO and 'nitrous oxides' from burning with adequate oxygen.

    Re the 'isocyanates and chlorides', it depends very much on what they
    are isocyanates and chlorides of! The whole statement reeks of 'press
    office' rather than 'toxicology lab'.
  16. Rich Grise

    Rich Grise Guest

    Well, (A) I don't believe in carciongens, that's just an excuse for people
    to find something to blame when they give themselves cancer, and (B) it
    never got hot enough to evaporate anything - I was kind of surprised that
    it cut through the plastic at all.

  17. If the Styrofoam wasn't such a good thermal insulator, the wire
    probably wouldn't have gotten nearly so hot.
  18. Chuck Harris

    Chuck Harris Guest

    Good for you Rich, unfortunately, cancer causing agents don't care what
    you believe in, or what you call them.

    When the wire is placed against the foam, it no longer loses its heat through
    conduction into the air (because foam is a great insulator), and it quickly
    heats up to the vaporizing temperature of the foam.... And fills the air with
    a cloud of plastic vapor, and partially combusted plastic gorp. All of which
    probably isn't good for you. It might not cause cancer, but it might plate
    your lungs with plastic, which could impair their ability to uptake oxygen.

    Oh yeah, that's right, you've already done that with your various vices.

    Don't forget, even though styrofoam fumes smell like PCP, it isn't really,
    so there is no point is whiffing the fumes.

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