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Review: The Prometheus all-metal hotend from Distech Automation

Every once in a while, in any field of endeavor, something comes along that really re-defines the paradigm. For reasons I won’t be going into here, I don’t like to use the term “Game Changer”, but that’s really what I’m talking about. The RepRap world in particular, and the 3D printing world in general, are not strangers to claims that use words like “Revolutionary”, “All-new design from the ground up”, and all sorts of other promises that our 3D printing lives are about to change forever.

At the very least, I have come to take these claims with a grain of salt. So it was with guarded optimism that I installed the new Prometheus all-metal hotend in my Makerfarm 8″ Prusa i3v, and set about seeing what all the fuss was about. Up until now, I thought I had a pretty good handle on what an all-metal hotend was all about, and I was pretty sure that the field was rapidly closing on a general configuration that was pretty close to as good as we could get it.

Then Prometheus brought the fire. Things will be different.

On the face of it, the Prometheus just looks good. It’s got a nice low profile, so it doesn’t eat up a bunch of your Z-axis, and the 25mm fan is bolted directly to the heat sink, which also saves space. Even more importantly, though, the solid connection dramatically reduces vibration, and therefore noise, when compared to something like the otherwise amazing E3D, which uses a printed ABS (or injection molded, as in the case of the V6) interface to attach the fan.

Working our way down the hotend, we see that the thermistor (A standard Marlin #5, or 100KOhm Semitec 104GT2 NTC to it’s friends) is held in place with a screw. This is another nice touch, as I personally have always found the traditional Kapton retention method to be awfully messy and subject to failure. The putty method is a little better, but the screw is the best of all worlds.

The last feature you can see just by looking is the heater resistor. Lately, I’ve been seeing cartridge heaters held in with grub screws. The resistor works just fine, of course, but requires a slightly more involved method of installation.

The major design elements of the Prometheus, though, are not necessarily apparent at the outset, and they are definitely worth investigating.

At the center of the Prometheus is a single piece of hollowed-out threaded rod with a 0.4mm orifice. In a traditional hotend design, the nozzle is two parts, which in the best case leaves a seam at the joint, and in the worst case, it’s a point of leakage. The single piece nozzle means that a leak is pretty much impossible except in the case of a completely catastrophic failure. It also makes in incredibly easy to clean out.

The second really interesting innovation is the ability of the user to determine the length of the transition zone as well as the melt zone.

At this point, a little bit of “hotend design 101” is in order.

  • The top part of a hot end is called the cold section, which is basically the part that is inside the heat sink. In this section of the hotend, the filiament should basically be at room temperature.
  • Just below the cold section is what’s called the transition zone. This is the part of the hotend where the filament is not being kept cool, but is not yet ready to be melted. This is where jams most often occur, especially in all-metal hotends. This generally happens when heat from the melt zone below propagates upward. PLA in particular tends to swell when it gets warm, and this can cause it to get stuck in the hotend. Conventional wisdom says to keep the transition zone as short as possible, to minimize the exposure of the filament to excessive temperature before it is ready to be melted.
  • After the transition zone, the filament then enters the melt zone, where it is actually melted and extruded. Here we encounter some more design choices: with all else being equal, a longer melt zone tends to allow for a faster rate of extrusion, but at the expense of additional “ooze” and a slightly lowered resolution and print accuracy. Conversely, a shorter melt zone generally allows for greater detail in the finished print, but at a cost of print speed.
  • The Prometheus kit (and it is available only in kit form at this time) comes with a number of hex nuts, which act as spacers to position the heater block and the heat sink on the central nozzle. This is how the user can define the length of the melt zone, as well as the transition zone.

    Want to print faster, and aren’t worried about getting a pretty print? Add another nut to the melt zone, and get printing! Or are you like me, and will wait patiently for an accurate and clean print? Leave some nuts off, settle in with a nice beverage, and wait for your artwork to appear. The choice is yours.

    The kit is quite complete, and goes together relatively easily. There is a little bit of soldering, but it requires no special tools. You’ll just need a few wrenches, shears and a few other things that are most likely already in your toolbox.

    DisTech Automation has also posted a very clear and thorough set of assembly instructions.

    I found the attachment point of the Prometheus was just a little bit loose in a standard J-head style aluminum mounting plate, but once it was installed, the Greg’s extruder in my i3v kept it solidly attached.

    The resistor and thermistor attached to the controller just like you’d expect them to. Also, as is standard practice, I attached the fan wires directly to the power supply leads, and I was off to the races.

    Right off the bat, I was impressed with the way the Prometheus extruded the glow-in-the-dark PLA that I loaded up. Just testing the extrusion, it flowed smoothly and cleanly, straight out of the extruder.

    I started off by using the same Slic3r settings that I had been using with the E3Dv5: 13mm/s and 1mm retraction, 210 °C. I found I had nothing to change.

    The first test prints I made (20mm cube, what else?) came out sharp and accurate.

    After I had a successful cube, I decided to move into some more advanced shapes, and also to see just how quickly I could get this hotend to print.

    My experience has generally been that shapes with long sides and gentle curves, with minimal retraction moves tend to be good candidates for printing at higher speeds. Just as an experiment, I loaded up a brain shape that I found on Thingiverse. This seemed to be a pretty good part to print as a test, since it had some long curves, but also some small squiggles. Just to add to the experiment, I also decided to print the shape at .01mm layer height which is half of the layer height that I generally use.

    I must say, I was duly impressed with the quality of the resulting parts. Next time I print a shape with a convoluted top and I’m printing with such a low layer height, I will think about printing with a higher number of solid top layers, as the part was a bit transparent in places, although the dome shapes at the top of the part were closed, and there were no strings, blobs, or other visible defects. Not bad for an early print!

    The Prometheus, at the time of this writing, is available for around $75.00US. At that price point, it is quite competitive compared to other all metal hotends, and will deliver performance that is way ahead of the field.

    The only real hesitation I have about this hotend is simply that it might not be for everyone. If you’re someone who likes to just open a box and pull out something that’s going to be put immediately into service, you might want to look at another hotend. The Prometheus does require some decisions be made before the kit can even be assembled, so it’s not really a plug-and-play solution. The reality, though, is that this is a piece of equipment that is intended for RepRap printers. I imagine most RepRappers are tinkering, tweaking, and fiddling types, and for those users, this is an amazing part.

    So if you enjoy working on your printer, you like exceptional performance, and you have seventy five bucks to spend on an awesome hot end, then head on over to the DisTech website and get yourself a Prometheus!

    2 comments to Review: The Prometheus all-metal hotend from Distech Automation

    • Dikkie

      I have just installed the prometheus on my 8 inch i3v.
      Installation went quite smooth and so far no jams or any other issues that i used to have with my e3d v6.

      Only problem im facing is that my hotend extrudes a little bit too much after retraction, leaving quite a thick blob on the starting point of each layer.

      Could you please share your slic3r(if that is what you use) configurations? I have calibrated everything firmware wise(e steps, level bed, etc) but am struggling to get my slicer settings up to speed.

      • I’m afraid I make it a policy not to share actual configuration files, but I can tell you that you are most likely experiencing a retraction issue. The settings that come from Makerfarm are way too high. In Slic3r, under Printer Settings -> Extruder 1, in the retraction setting, start with 1mm length, and 13mm/s. That should get you started.

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