Pulse width modulated (PWM) hotwire foam cutter prototype

Here are some photos of my new pulse width modulated (PWM) hotwire foam cutter prototype.


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I use it for cutting foam of all types. Instead of moving the wire, I move the object to be cut. In this way it is possible to make straight and 90 degree cuts referenced to the base plate. I have drilled a hole in the baseplate for the hot wire to run thru.

My new airframe that can contain a lot of electronics will be cut by this cutter.

Its not CNC controlled, however the PWM controller can be used for a CNC controlled unit (plans in progress).
I use a power fet and a Atmel controller do do the PWM control. It can accept PWM commands from a host PC or analog input via a A/D port.

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Comment by Wendi Smol on August 11, 2009 at 3:47pm
Hi, very nice control method. Do you have some feedback of the wire temperature (resistance)? What next? A nice table with automatic X/Y feed?

Regards

W.
Comment by UFO-MAN on August 12, 2009 at 12:26am
Hi, I use nichrome wire. IT has a low, sub 1 ohm, resistance on short lengths.
I do not have temp feedback at the moment, but that could be measured of course (voltage drop per current). I have found that the cutter works well without temp feedback as long as the movements of the object to be cut are slow and consistent. I have plans for a CNC wire cutter but that has low pri right now.
Comment by NingNong on August 13, 2009 at 6:11am
I used a 3A 12V battery charger and the 0.3mm Nichrome wire from (For the Aussies) Dick Smith (4m = $4 approx). Don't worry about calcs, just play with results.
1) less wire = more heat, more wire = less heat, start with about 30-50cm.
2) 2x battery chargers in series (or 24V charger) = double current/heat (yes I know resistance drops as it gets hotter so its less than double current/heat)
Use 70cm end cut off that old fishing rod stuck in a hole drilled in the shed wall as a bow to tension wire.
When you start off - don't get too fancy runt your tests first until you figure out the config you like best.

I originally bought a $20 radiator from the hardware and pulled out the wire but it was not strong enough.
Comment by NingNong on August 13, 2009 at 6:11am
I mean resistance increases current drops!
Comment by UFO-MAN on August 13, 2009 at 9:22am
Another tricks is to use croc-clips on the wire and move those to adjust the current.
Comment by Cronselaar on August 13, 2009 at 1:16pm
Guys, just use a normal downlight transformer(12v), a normal light dimmer, and stainless wire for the cutting wire.

Nice cheap foam cutter, that works 100%

If you need any instructions, just send a msg or leave a comment

Gerrit
Comment by UFO-MAN on August 13, 2009 at 1:25pm
Downlight trafo sounds good. My design may use almost all DC sources incl. car batteries, PSUs, PC power supplies (square bricks) etc. A rectified AC source may also be used. What is nice with a PWM controlled unit is that you can easily adjust to different wire sizes, different wire lenghts, different materials, different wire types. To have continuously adjustable current is very good. You also avoid the nasty smell that is given off if you overheat the foam.
Comment by Sam Harbold on December 10, 2009 at 7:32pm
I am very interested in your PWM hot wire. I am currently building a CNC hot wire foam cutter to cut wing cores for radio control airplanes as a hobby. I will be using Profili for my wing designs and MACH3 for my control software. I am looking for a means to control the wire heat via my control software which your PWM control sounds like it could be make to work with the MACH3 software. Any chance you would share the PWM circuit?
Thanks
Sam
Comment by UFO-MAN on December 17, 2009 at 10:57am
Hi Sam! Sorry for late answer.

I used my spare Arduino board connected to a FET transistor for the task.
The fet transistor is turned on and off by the PWM modulator output from the Arduino.

The code is posted here (very simple):

//
// Usage: foam wire cutter.
// Pulse width modulation of a cutting wire with PWM output
// Heat controlled by analog input (e.g. pot)
// Control the heat precisely with turning the pot
// Can be used by a car battery, NiCD battery or other power supply
// The lPin is the pin that is connected to the FET transistor
// Author: "UFO_MAN"
// Hardware: Arduino




int lPin = 9; // FET transistor (via driver) connected to digital pin 9
int analogPin = 0; // potentiometer connected to analog pin 3 (the pot meter need a voltage on the hot side and the cold side need to be connected to ground. a 5K pot will work fine.
int val = 0; // variable to store the read value

void setup()
{
pinMode(lPin, OUTPUT); // sets the pin as output
}

void loop()
{
val = analogRead(analogPin); // read the input pin
analogWrite(lPin, val / 4);
}


The nichrome wire is connected to the positive supply and to the FET drain. The FET source is connected to the negative supply (ground). The gate is driven by the arduino via a driver chip (not necessarily needed, depending on the gate capacitance and characteristics of the FET you use).

VCC
/
|
+-\-+
| |
| |
| |
| |NICHROME WIRE
| |OR OTHER SUITABLE
| |WIRE
| |
| |
+-/-+
|
,.-\,
PWM input / | `
`----\ \
-------------- | |
| | |FET
,----/ /
\ | `
`'-\`
|
|
|
|
|
|
/----/----/
| | |GND
\ \ \
Comment by UFO-MAN on December 17, 2009 at 10:58am
Ugh, the ASCII art turned out to be a bit crappy hehe .... Understandable heh?

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