Hot wire foam cutter

[JazzMan]

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
**********************************************************

 

[Tom Biasi]

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

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

 

[JazzMan]

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

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
**********************************************************

 

[Impmon]

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.

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.

 

[John Popelish]

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

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.

 

[JazzMan]

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.

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
**********************************************************

 

[John Popelish]

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

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

 

[spudnuty]

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.

 

[Ken Moffett]

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

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.

 

[David Harmon]

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

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.

That will do fine. Hot wire foam cutters:
http://wolfstone.halloweenhost.com/HalloweenTech/fotmak_MakingFoamTools.html

 

[Jasen Betts]

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?

yes, earlier this year.

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,

use a light dimmer that's designed to dim transformers, a
regular one can cause problems (mainly overheating)

and the transformer output to the wire.

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

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?

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