Hot end progress halted by breaking Power Resistor lead! Doh!

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I have made good progress on my dual hot end extruder design and despite breaking the thermistor, then snapping a lead off the resistor when dismantling the existing hot end, I managed to get the test done. Further progress is now on hold until replacement components are delivered :(

The first problem I had to overcome when testing my design was no voltage at D10! So no voltage or power to the power resistor. After checking it was not switched off in software I asked Richard if he could help and eventually the solution was found. Because of the damage to the thermistor (it wasn't there!) this meant that no power was available. Following an article on the RepRap site I had to wire a 10k resistor between the 2 ends of the thermistor wires. This proved to be the solution and as soon as the components arrive I am sure I can get it to print in 3d!

For a more detailed explanation I wired the ends of the resistor (before I snapped one of the resistors leads) to the 12v ramps fan output and was pleased to see the temperature rise, and rise and rise!

Using my new temperature meter  I removed the leads when it got to 220 degree and fed some filament through and there was little resistance with good filament flow,  so I am happy that the stepper/extruder motor will work fine feeding it.

This was with a nozzle with a 0.7mm hole so I made up another with 0.4mm to see if the size would be a restricter and that's when I snapped the resistors lead!! So I had my wife feeding filament by hand whilst I held on end of the resistors lead against the minute metal snub still left on the resistor. Real Fred Carney stuff but I wanted to know if it would work with the 0.4mm nozzle before continuing development. I was really pleased to see the filament again flow out. It did need more pressure but I am sure it will be ok. The results are encouraging enough to continue.

My reasons for developing my own hot end rather than using the official one is to allow me to experiment with different nozzle sizes and also different filament sizes. One of the extruders is to be 3mm filament and the other the original 1.7mm and since my design has screw in nozzles, it allows easy change in sizes.

Because I could not do anymore on the electronics side I thought Iwould make use of the time by redesigning the MDF dual holder in light of experience and milling out a new one. After I had redrawn the part in Alibre 3D CAD and exported the file to stl, then Skienforge, and finally ReplicatorG there was no drama as I set up the SumPod, loaded in the code and away it went.

I am really gaining confidence in its milling abilities and the Z handle I made really did make a big difference. Its now so easy to use and get the Z position correct. Overall a good result.


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  1. Highcooley says:

    Hi Mike

    Wow, this hot-end looks great…slim and light for a dual extruder setup. So, is this a passive cooling aproach or is it more of a test version before you add a heatsink?

    Although never having built a hot-end before, I am already thinking about the dual version. One thing, which I don’t get out of my mind is the problem with the inactive nozzle smearing over the freshly printed area (as seen many times, even on the latest prints of the new Makerbot Replicator). I was thinking about some kind of double solenoid construction which lifts the inactive hot-end up about 1mm (or better pushes the active hot end down with a spring release). Probably this would need some guiding rods and adjustable end-stops. Another version could be built with only one solenoid and some kind of a seesaw, but in the end, I guess it would be too complicated to adjust and to get it stiff enough. So far, I haven’t found any aproach like these on the net. Maybe it is worth thinking about it.

    Another thought concerning smearing…maybe you should think about tapering the nozzle a little bit to prevent it from accumulating filament and smearing.

    Hey, great work in the Sumpod community… I am so much looking forward to get mine.


    • admin says:

      It is still experimental but I get good temperature (measured by a meter) and extrusion by hand seems good. The PTFE rod is cold so I do not anticipate any cooling needed but as I say its experimental.

      I do need to sort out a lower mounting position as the nozzle is not low enough below the top axis. Thanks for the interest and come back for information. Mike

  2. Fixer says:

    Hi Mike,
    Nice article. I like the idea of changeable nozzles, making it easy to change emphasis (when using only a single extruder) between detail and volume between prints.

    I’m also interested that your extruder doesn’t require active cooling, since it seems to be the current flavour to fan/heatsink the ‘cold’ portion of extruder.

    Lastly if your design is indicative of what we can expect in the future, the narrow extruder profile may allow for more than dual extruder operation.

    • admin says:

      Printed with the new nozzle today similar to the above which consists of only 3 parts now (push fitting, Peek body, and nozzle/heater block ) and it does perform better I think. In all I printed 3 items, 2 at just over 1 hour each and the 3rd for over 6 hours, yes…..6… hours!!!! So its looking good. No fan anymore.

  3. Ben Whykes says:

    What was the name and address of the document you found to fix the issue of no power coming out of D10? I’m sadly having the same issue.


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