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Jan 18, 2007, 10:03 PM
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Question

How do I build a hot wire foam cutter?


I want to be able to cut foam without the huge mess. Any suggestions welcome.

Sincerely

-Mr. Pimp
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Jan 18, 2007, 10:45 PM
3D wannabe
smokejohnson's Avatar
I found this today. I am looking for a better way too. I think I want a hot knife instead of a table set up. I do good with leaving the line and sanding to shape plus I don't have a lot of storage space for a table.foam cutter
Jan 18, 2007, 10:52 PM
3D wannabe
smokejohnson's Avatar
Another thing is I think you want a model train transformer to adjust the heat.
Jan 19, 2007, 12:11 AM
Registered User
BlazerB52's Avatar
Here is one that I built. Top is a 16" x 16" marble tile. Powered by a 12v battery charger that is plugged into a router speed controller to adjust heat. The bow is just metal rod bent bow shape with the ends heated and hammered flat. Drilled holes in end so a ceramic sandblaster nozzle fits half way in hole as wire insulator. Wing nut allows the bow to be adjusted to any angle you want.
Jan 19, 2007, 12:13 AM
Registered User
BlazerB52's Avatar
Newer train transformers won't work because of their protection circuits.
Ask me how I know. Just wanted to mention after I bought a couple.
Jan 19, 2007, 12:19 AM
Registered User
BlazerB52's Avatar
Here is another thread on the subject.

https://www.rcgroups.com/forums/showthread.php?t=561415
Jan 19, 2007, 12:25 AM
Soil Density Tester
TexasAce's Avatar
I read once where someone built one using a receiver and esc to power it and adjusted the heat with their Transmitter.
Jan 19, 2007, 05:35 AM
Time for another motto!
Just use a dimmer switch in series with a 12 volt transformer.
But I really like the idea with the adjustable angle. Gotta try that on my next one.
Jan 19, 2007, 02:07 PM
Registered User
Here is an inexpensive setup, with readily available parts.
12.6 Volt/3amp xfrmr from radio shack, Router speed control and multimeter from Harbor Freight, rectifier bridge, filter capacitors, fuse holder and line cord from Radio Shack.
Rectifying to DC is not absolutely necessary, but, I believe make heat control smoother and more repeatable.
After this picture was taken I added a 5amp auto fuse(ato) in the plus(+) DC line.
I have since built a slightly more expensive 24V/8amp supply, with variable voltage regulator, which will heat longer bows and I can use with other projects as well.
if there is interest I can post schematics.
BobK
Jan 19, 2007, 02:09 PM
Registered User
This is my version of a hotwire JigSaw.
Jan 19, 2007, 02:25 PM
The Junk Man
Nicely done Skinner.

Tom
Jan 19, 2007, 03:11 PM
JCL
JCL
Registered User
JCL's Avatar
I think people tend to make the power supply too complex. My system is very simple and works for me.

My power supply is a 6 volt car battery charger (actually, 6 or 12 volts via a switch, I use 6 for cutting).

I use some 24 guage (IIRC) stainless wire from a big box home store (home depot and lowes certainly both sell the stuff). I think people try to use too thin wire and this makes things much harder.

I suspect that people use thin wire, then need to very tightly control the current so it isn't way too hot (and then it breaks) or too cool to cut well.

I use a length of wire long enough to limit current to around 6 amps. I can fine tune the heat by using more or less wire. At a guess, I typically use around 3-4 ft of wire.

In order to limit the inrush current, I disconnect one of the battery clamps, then turn on the charger. I then tap one of the battery clamps to the wire several times to more slowly warm it, then clamp it to the wire. I think if it were connected right away, it could get too hot due to the low resistance at low temperature. Or maybe that isn't even necessary.

No soldering, no variacs or dimmers, no electronic parts to buy and put together. Why people try so hard to make this difficult I don't know. I think they assume it has to be complicated so they never try the simplest of solutions.

Just my 2c on wire cutters.

Joe
Jan 19, 2007, 05:53 PM
Registered User
Quote:
Originally Posted by JCL
I think people tend to make the power supply too complex. My system is very simple and works for me.

My power supply is a 6 volt car battery charger (actually, 6 or 12 volts via a switch, I use 6 for cutting).

I use some 24 guage (IIRC) stainless wire from a big box home store (home depot and lowes certainly both sell the stuff). I think people try to use too thin wire and this makes things much harder.

I suspect that people use thin wire, then need to very tightly control the current so it isn't way too hot (and then it breaks) or too cool to cut well.

I use a length of wire long enough to limit current to around 6 amps. I can fine tune the heat by using more or less wire. At a guess, I typically use around 3-4 ft of wire.

In order to limit the inrush current, I disconnect one of the battery clamps, then turn on the charger. I then tap one of the battery clamps to the wire several times to more slowly warm it, then clamp it to the wire. I think if it were connected right away, it could get too hot due to the low resistance at low temperature. Or maybe that isn't even necessary.

No soldering, no variacs or dimmers, no electronic parts to buy and put together. Why people try so hard to make this difficult I don't know. I think they assume it has to be complicated so they never try the simplest of solutions.

Just my 2c on wire cutters.

Joe
All this is great if you only need one setup. If you use many types of foam and several wire lengths you need more adjustments.
Also, if you need 8 amps from your supply you are using wire with a very low resistance. Smaller gauge SS wire only needs approximately 2.5 to 3amp to cut almost all types of foam.
BobK
Jan 19, 2007, 06:09 PM
e-flight in 24½th Century
Waldo Pepper's Avatar
Skinner,

Bring on the schematics! I'm never too old to learn

W
Jan 19, 2007, 07:26 PM
JCL
JCL
Registered User
JCL's Avatar
Skinner --

I agree that if you are working with several kinds of foam, you may need to have better control of heat.

As far as length goes, I think I could cut things up to 30" wide since I have at least that much wire hot.

I'm also just cutting FFF and occasionally blocks. If one were doing stuff like splitting thin sheets, it might be more critical as well.

I just think people should start simple and add complexity as needed. Many people seem to start complicated and add even more complexity to fix the problems that were cause by not starting simply.

Joe


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