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Hot wire foam cutter

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

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Reply to
JazzMan
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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

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Reply to
JazzMan

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

Reply to
Tom Biasi

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

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Reply to
JazzMan

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.

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Reply to
Impmon

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.

Reply to
John Popelish

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.

Reply to
spudnuty

Pick one that is rated for about double the wattage of the transformer, so it won't too seriously degrade its output capability.

Reply to
John Popelish

JazzMan wrote in news: snipped-for-privacy@airmail.net:

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.

Reply to
Ken Moffett

On Sat, 10 Sep 2005 08:11:46 -0500 in sci.electronics.basics, JazzMan wrote,

That will do fine. Hot wire foam cutters:

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Reply to
David Harmon

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

Reply to
Jasen Betts

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