LongLiveCHIEF/hemera_extruder_tips_and_gotchas.md

## hemera_extruder_tips_and_gotchas.md

      
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              hemera_extruder_tips_and_gotchas.md
            
          
    I got the E3D Hemera (formerly called the Hermes) a week ago, and at first glance was impressed by the amount of documentation/guides E3D worked with popular YouTubers to create.
However, as time went on with my install, I discovered each guide was missing critical information, had bits of information incorrect, or included firmware files in a old or flattened format, making it difficult to discern firmware changes required.
I'm very familiar with Marlin 2.x, and so I finally decided to just go straight to the Hemera Datasheet, and finally got things working.
I'm not going to do a full guide, since I'm hoping one of the popular YouTubers who is capable of a high production quality video will do a comprehensive guide, but I have put together the following tips and lessons learned that should help some of you who are struggling but can't figure out why things aren't working.
For reference: I have an Ender 3 with an SKR 1.3 using Marlin 2.x, equipped with TMC2208's in UART and a BLTouch. If you have an identical hardware configuration, you can download my firware from my fork of Marlin at https://github.com/HackerHappyHour/marlin
Verify and Calibrate Motor by doing a Cold Extrude before mounting

Do this step right out of the box, even before you thread in the heatbreak or heater block and nozzle. This will ensure you have a working motor before you mount everything, and be the easiest way to calibrate E axis steps per mm. Use Octoprint, pronterface, or similar software to send commands mentioned below.

Observe & confirm/fix polarity of stepper coil wiring harness.  If you're using a ramps compatible main board, you will find that the main board end of the stepper motor cable included in the kit is likely not wired correctly. For me, i found that it was easiest to reuse my existing ribbon cable for the old E stepper to ensure the correct coil wiring configuration. If you do the same, and it works, then you'll want to swap the position of the red and green wires (middle two wires) on the end of the cable that goes into your main board.  The stepper coil wiring is on page 6 of the hemera motor datasheet if you want to verify things against your own boards pinouts.
Set E axis steps per mm to 397.5  According to the datasheet, 409 steps/mm is the ideal value for 1/16th microstepping. I've found that that setting causes quite of a bit of over-extrusion, and after some fine tuning, I've settled on 397.5 steps/mm for E axis. If you have trinamic drivers, and aren't using interpolation for higher microstepping, than you'll need to multiply this value accordingly. If you're using Marlin and have trinamic drivers, you can to this by issuing gcode M92 E397.5. (Then M500 to save to EEPROM).
Set motor current. According to the datasheet the hemera motor runs at 1.33amp. (It's the only amperage given so I'm assuming that's the run current, not the max current or RMS current). If you're using Marlin and have trinamic drivers, you can do this by issuing gcode M906 E940(**). This should give you a Max current of ~1330 mA. If you don't have trinamic drivers, you'll need to do a potentiometer adjustment to reach the correct vref based on your driver and aim for 1200 mA (90% of 1.3 Amps).
Enable cold extrudes Send a M302 S0 command to enable cold extrudes. M302 reference
Test extrude 100mm Thread in filament until it is even with the bottom of the hole were the heat break is supposed to go. Send gcode G1 E100 F300 to tell the extruder to extrude 100mm of filament. Take a measurement from the bottom of extruder block to the tip of the extruded filament and verify it is 100mm.  If it's not, calibrate e steps per mm using the following formula until you consistently extrude 100mm of filament. (100/100 - mm of filament extruded)) × current steps/mm = new steps/mm value. Note, you'll want to do this after you've done final assembly using a hot extrude just make sure everything is calibrated properly under operating conditions

Attach Heat Break, Heater block, and Nozzle before mounting


For the back plate I had to mount against, I was unable to fully turn the heater block once I had mounted the motor assembly to the x axis mounting plate. Therefore, I recommend the cold mounting part be done prior to mounting the motor assembly to the mounting brackets
The heatbreak collet is extremely easy to break. Do NOT overtighten. Which brings me to the 3rd tip for mounting the heating components...
the nozzle is what is used to fully tighten the heat break inside the extruder.  This is a 3 component system that contributes to the angle of the fully tightened heater block assembly. The correct way to fully seat the heat break into the extruder housing, is to tightend the nozzle against the heatbreak inside heat block.  This took some getting used to on my part, because it means the heater block acts as a "floating lock" component and the heater block should be tightened last of the 3 pieces, ensuring the nozzle is fully tightened against the end of the heat break

STL Files for mounting hardware

I took this opportunity to upgrade my part cooling fan to a 5015 blower motor. The duct included by Joe Casha in the files for my particular hardware was too big for the 5015, and after a few searches, I found what I believe is the best duct for the 5015 on thingiverse. Thing 4042492 by user HangTight.
I did use the backplate designed by Joe, which includes a fixed mount for the BLTouch, and I've found it's dimensions to be perfect in every aspect. This part can be found here: https://www.myminifactory.com/object/3d-print-ender-3-e3d-hemera-mount-105802
Hotend Fan Mounting

This was a big gotcha. At first I thought I was missing the mounting screws for the fan, because none of them seemed to be long enough. But as it turns out, the fan is mounted so that the side of the fan that has the "blade guards" is mounted against the heat sink, and you use the two silver phillips head screws in the upper right and lower left corners of the fan case.
The receiving holes for these are soft aluminum, and are self-tapping.
Firmware changes & final fit calibrations


Update the thermistor settings in Marlin firmware, changing the value of TEMP_SENSOR_0 5 in Configuration.h
Update HEATER_0_MAXTEMP 285 in Configuration.h
PID Autotune.  Send gcode M303 C10 S<your most common printing temp> U  (the U will autosave the results to EEPROM
Hot Tighten nozzle Heat the nozzle to 285 C using gcode M104 S285 (Note, max temp settable via LCD is 15 degrees lower than configured firmware value, so this has to be done with gcode, or the firmware MAXTEMP needs to be set to 300 if you do this from LCD)
Final E step calibration Finally, do a hot calibration of e axis steps/mm by setting the extruder temp to whatever the norm is for the filament you are testing with, and extrude 100mm of filament, and verify 100mm of filament was fed through. You'll have to measure of the top of the extruder assembly this time around.

Permanent firmware changes

Once everything is running smoothly, set the values for the things you did above permanently in the firmware. Here's your checklist:

bed leveling probe geometry
trinamc driver current for E axis
X and E axis steps per mm (verify X doesn't change with the weight on your gantry. Shouldn't need to change it, but something to be mindful of)
PID settings