Prometheus V2 Hot End - User Guide

Table of Contents

    1. User Guide
      1. Melt Zone Length Configuration
      2. Transition-Zone Length Configuration
      3. Bowden Users
      4. Cold-Zone Length Configuration
      5. Printing Temperatures
      6. Part Cooling
      7. Cleaning the 1-piece Nozzle
      8. V2 Nozzle Identification
      9. Troubleshooting
        1. Underextrusion
        2. Overextrusion
        3. Oozing
        4. Delamination
        5. Jamming
        6. CAD Drawings
          1. Prometheus V2 Hot End

        User Guide

        Here are some general tips for printing with Prometheus and customizing the thermal zones according to your specific needs. Enjoy!

        The image below illustrates the thermal zones of Prometheus V2:

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        Melt-Zone (MZ) Length Configuration

        This is the first thermal zone configured in the assembly. The Melt-Zone (MZ) length parameter has the most significant impact on the maximum feed rate (extrusion rate) of the hot end. In general, the max feed rate is proportional to the MZ length so a longer MZ means that the hot end can melt and extrude plastic faster. However, there are other tradeoffs involved in lengthening the MZ.

        These affects of MZ length on performance are outlined in the table below:

         Change in MZ Length Maximum Feed Rate "Ooze" (stringing) Extrusion/Retraction Responsiveness
        Longer Increased Increased Decreased
        Shorter Decreased Decreased Increased

        The primary advantage of a longer MZ is a higher maximum feed rate. If you want to print thicker layers at higher speeds then you should assemble your Prometheus with a longer MZ.

        The table below lists the recommended standard MZ length configurations for each nozzle size:

         Nozzle Orifice Size Recommended MZ Length # of Hex Nuts below the Heater Block
        0.3 mm 12 mm 1
        0.4 mm  16 mm 2
        0.6 mm 20 mm 3
        1.0 mm 24 mm 4
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        Transition-Zone (TZ) Length Configuration

        This is the next thermal zone that is assembled. The Transition-Zone (TZ) length parameter has the most significant impact on the reliability of the hot end. In general, the friction in the hot end is proportional to the length of the TZ so a short TZ will result in the lowest internal friction and therefore the most reliable "jam-free" printing. However, just like the MZ, there are tradeoffs involved here too.

        These affects of TZ length on performance are outlined in the table below:

         Change in TZ Length Friction Heat Loss to Cold-Zone Temperature Stability Maximum Retract Length Maximum Feed Rate
        Longer Increased Decreased Slightly Increased Increased Slightly Increased
        Shorter Decreased Increased Slightly Decreased Decreased Slightly Decreased

        The primary advantage of a shorter TZ is that it decreases the friction in the hot end, therefore reducing the extrusion force and increasing the reliability. A short TZ is especially important when printing PLA. However, a short TZ also means that more heat is lost to the Cold-Zone (CZ).

        Higher temperature plastics like ABS have a higher glass transition temperature (Tg), so you can get away with a longer TZ. This can be beneficial when printing at temperatures above 250C as it reduces the heat lost to the CZ and increases the stability of the temperature reading during extreme fluctuations in the feed rate.

        The table below lists the recommended TZ length configuration for printing various thermoplastics:

        Thermoplastic Recommended TZ Length
        PLA, Nylon 2mm
        ABS, PC, PET, etc... 2mm to 3mm
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        Bowden Users

        Keep in mind that the maximum retract length is proportional to the length of the transition-zone and the length of the bowden tube (BT).

        The max retract length can be approximated as follows:

        Max Retract Length = TZ length + (BT length / 250mm)

        (i.e. With a 2mm TZ and a 500mm bowden tube length, you should use a retraction length of 4mm)

        This is an important relation for bowden users to consider. If you retract longer than the TZ, molten plastic will be pulled into the Cold-Zone and will cool, fusing to the inside of the barrel and jamming the hot end.

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        Cold-Zone (CZ) Length Configuration

        The length of the CZ is not user configured as it does not affect performance. However, when you are assembling your hot end and configuring your MZ and TZ, please ensure that at least 10mm of the end of the nozzle is threaded into the bottom of the Alu Heat Sink. Therefore, when you are determining your MZ length, consider the following:

        Nozzle Length = Nozzle Tip (2 mm) + MZ Length + TZ Length + CZ Length,      MZ >= 8 mm,      TZ >= 2 mm,      CZ >= 10 mm

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        Printing Temperatures

        The printing temperature can have a significant impact on layer adhesion, bridging, overhangs, and "ooze" (stringing). Higher printing temperatures generally result in stronger layer adhesion, but at the expense of a loss of performance in other aspects of your print. 

        The effects of printing temperature are listed in the table below:

        Change in Printing Temperature Layer Adhesion Bridging/Overhangs "Ooze" (stringing) Maximum Feed Rate
        Increased Stronger Worse Increased Slightly Increased
        Decreased Weaker Better Decreased Slightly Decreased

        Since each user has different Slic3r settings, part cooling, etc, it is very difficult to recommend a specific printing temperature. Below are a range of recommended temperatures for printing various thermoplastics with Prometheus:

        Thermoplastic Recommended Printing Temperature
        PLA, PHA 180 C - 240 C
        ABS, PET (T-Glase) 220 C - 260 C
        Nylon (Taulman) 250 C - 280 C
        PC (Ultimachine) 270 C - 290 C
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        Part Cooling

        Enabling a part cooling fan can have a positive impact on the quality of bridges, overhangs, and corners of your print, especially when printing PLA. However, there are also some detrimental side effects of a part cooling fan, especially with regards to layer adhesion. 

        The below table lists the effects of part cooling on a print:

        Change in Part Cooling Layer Adhesion Bridges, Overhangs, and Corners
        Increased Weaker Better
        Decreased Stronger Worse

        In general, PLA prints benefit from increased part cooling with minor negative effects on layer adhesion. On the other hand, optimal ABS print results are achieved with minimal part cooling. Excessive part cooling on ABS prints can cause severe layer delamination. 

        *Important*: If using a part cooling fan you must ensure that the air flow is NOT blowing over the nozzle tip. Excessive cooling of the Stainless Steel Nozzle tip can result in inconsistent extrusion and increased extrusion pressure.

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        Cleaning the 1-Piece Nozzle

        The 1-Piece Nozzle can become clogged from foreign debris in your filament or from dust that has accumulated on the filament. The symptoms of a blocked nozzle are inconsistent extrusion and periodic clogging which can lead to "filament grinding" and "air printing".

        Please DO NOT:

        • Soak the nozzle in a solvent
        • Burn the nozzle with a torch
        • Hit the nozzle with a hammer (I am not sure why anyone would do this?? but just don't...)

        The solution is the "Cold-Pull" method! (AKA the PLA Pipe Cleaner method). This involves heating the hot end slightly above the Tg of the plastic and pulling the entire length of filament out of the Melt-Zone. This conveniently removes any debris in a non-destructive manner.

        The PLA Pipe Cleaner method is detailed here on NopHead's Blog.

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        V2 Nozzle Identification

        V2 nozzles are available in various sizes (0.3mm, 0.4mm, 0.6mm, and 1.0mm) and the nozzle length scales with orifice size so that the larger nozzles can be assembled with a longer melt-zone to allow for higher feed rates. This also makes nozzle identification much easier as you just have to measure the length of the nozzle.
        The table below shows the respective length of each nozzle size:
        Nozzle Orifice Size Nozzle Length
        0.3 mm 33 mm
        0.4 mm 34 mm
        0.6 mm 36 mm
        1.0 mm 40 mm
         
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        Troubleshooting

        NOTE: This Troubleshooting guide is a work-in-progress. Please check back regularly to see the most recent version.

        Underextrusion

        • Do you have the correct extruder steps/mm set for your extruder?
        • Have you measured the correct diameter of your filament using a caliper and entered that number into your slicer settings?
        • Do you have your extrusion multiplier calibrated correctly?
        • Have you ensured that your part cooling fans are NOT blowing air over the nozzle tip? This causes excessive cooling of the nozzle tip and is the most common cause of underextrusion and jamming.

        Overextrusion

        • Do you have the correct extruder steps/mm set for your extruder?
        • Have you measured the correct diameter of your filament using a caliper and entered that number into your slicer settings?
        • Do you have your extrusion multiplier calibrated correctly?
        • Do you have part cooling fans set up to cool the object as you print each layer? If layers are printed very quickly, heat buildup can cause deformation of the printed object and give the impression of overextrusion.

        Oozing

        • Have you properly set up your retraction? You should have the following settings configured for your extruder:
          • Retraction Jerk (Start Speed) = 15.0 mm/s
          • Retraction Speed = 80mm/s
          • Retraction Acceleration = 2000 mm/s^2
          • Retraction Length = 2mm (2mm for direct extruder, 3mm to 4mm for bowden extruders)

        Delamination

        • Are you printing hot enough? ABS suffers the most from poor layer adhesion. We have had good results printing ABS at 260C (no part cooling) with the Prometheus V2.

        Jamming

        • Are you using a 5:1 geared extruder? This is HIGHLY recommended for reliable extrusion.
        • Do you have your Prometheus V2 Hot End properly configured with a 2mm Transition-Zone as indicated in the assembly instructions?
        • Have you ensured that your part cooling fans are NOT blowing air over the nozzle tip?
        • Is the 25mm Heat Sink fan operating at full speed? Please ensure that this fan is always operating at 100% speed by wiring it directly to the 12V/24V output from your power supply.
        • Have you properly dried your filament overnight before printing with it? Extra moisture in the filament can lead to jamming.
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          CAD Drawings

          Prometheus V2 Hot End

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