Hand held cutter head for the PWM hotwire controller

I have made a USD 2,- handheld cutter head for the PWM controller desribed in my previous blog post. The handheld cutter is nice for trimming off edges and so on. The spring keeps the wire tensioned. The final version don't need a series dropping resistor as the PWM driver stage uses two FETs.

The controller has also has been tested on a vertical setup for cutting spacers to my KFM3 depron wings (below):

The cutter gives nice clean cuts for vertical cutting operations (below). Please note the fan that sucks gases out from the workpiece. This is very important because blue and red foam gives off fumes that are very toxic when they are melted.

The PWM controller outputs pulses and is configurable both in duty cycle and several other parameters (below).

Based on interest, I may make a kit available.
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  • Well observed. It was just for illustration. The heat can be controlled from almost touchable with my finger to red hot and if you want so hot that the wire will snap off. Wide range is possible. I can also, with some software settings, reduce the gain of the potmeter input and limit the range of operation so that it will not be possible to set too cold or to hot.
  • First photo I saw wire is glowing red (probably in the 800 C range). It doesn't take this kind of heat to cut polystryrene or other foam types! But I am sure you will experiment and learn this yourself.
  • Sounds interesting. If you try it, please report back!

    By the way with a feedback loop controlled PWM cutter it should be easier to find the sweet spot.
  • No problem with power availability - just difficult to find a power between burn-and-melt, and bend-and-stick.
    the Vibration would move the wire longitudinally, so the cut would not be enlarged. I think I have seen such.
  • Hi. No that I haven't tried. However, wouldn't vibrating the wire give a cut that is not clean?

    If you feel that you struggle to cut thru the material, it might be that you run to little current with the voltage you have available from your voltage source.

    One test could be to shorten the heated part of the wire (put the electrodes that connect to the wire as close as possible to the piece that should be cut). Alternatively you could go to a thicker wire (less resistance). The best would be to try to increase the voltage with the setup you have. In case you have a PWM source, making the on time higher, would do the trick (provided the on time is not maxed out).
  • I got the impression my EPP cuts would be improved if I could vibrate the wire - anyone tried this?
  • Well, yes you can measure voltage over the wire. And if you multiply that with current (if pwm, peak current x duty cycle) you have calculated the power. Resistance changes allright, and that is excactly why you want to measure both voltage and current. You can determine wire resistance with R = U/I or R@peak = Upeak / Ipeak. The resitance of the wire changes as a function of temperature. It is power over time that determines the energy given off to the wire and then energy from the wire to the material you are trying to melt. However I am not sure sophisticated feedback controls are really necessary.
  • I'm not sure you can measure voltage over wire - because wire resistance changes under temperature - and temperature changes under use.
    You might should measure both current and voltage drop on wire, and try to stabilize the wire temp.
    - to be honest - I don't know ow to stabilize the wire - I use adjustable voltage power supply with current cut. Seems ok-ish - I still have trouble on EPP.
  • Excactly. You could also measure the voltage over the wire since U x I = P and the battery voltage may drop due to internal resistance and lower cell charge (if you use a battery). Alternatively you could also use a drop resistor of very low value and measure the voltage over that instead of the hall effect device. That would probably be cheaper. On the arduino, there are several A/D inputs you could use, just make sure to not exceed the max input voltage. A divider and a clamping diode could take care of that.
  • You can get a 90 A , ..5 mohm shunt from sparkfun with an amplifier, for 20 bucks+
    0-3.3 V output :) You could know the current & voltage on the wire. Set of an alarm if peak amps are to high.
    For a short wire you need to use less voltage to limit max amps. I think I will order some parts soon. I could use one of these things. look here
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