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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Comments
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
\ \ \
Thanks
Sam
Nice cheap foam cutter, that works 100%
If you need any instructions, just send a msg or leave a comment
Gerrit
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.
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.
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