Hemera Orthogonal Mount on MGN12 Rail for Grizzly Bear with Volcano & BL Touch

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UPDATE 20th July 2020 -Update of the 5015 Fan Duct with more holes for better air flow. Note that it is supposed to be plugged into the fan port from below, once the fan is already mounted. Can be printed without supports -Added fan duct design for the great Papst RLF35, probably the best miniature 24V blower fan of the market, and a real silver bullet for PLA cooling. I have redesigned the fan duct extensively to suite the different outlet size. Note that this duct is supposed to be mounted first, then the fan slides sideways into the mounting hooks. Needs to be printed with support for the 2 small attachment hooks at the top. Both duct designs have been tested extensively and work great. Considering the proximity with the hotend, CF PETG or better, ABS are the recommended print material. Or be ready to change the duct from time to time. Nothing terrible, but the back right corner section tends to deform a bit after several hours on my setup printing at 250°C. I'll try to add a layer of aluminium foil to solve this small issue. NB: The back mount part is designed to be directly used with European V-Slot 2020 extrusions such as the ones sold at RatRig. For T Slot or Misumi extrusions the back mount will need to me modified a little to file some material to accommodate the different groove profiles. The back mount should not touch the extrusion but just sit on it and glide freely, shy of a few tens of mm. The back mount is designed to align with the V Slot extrusion groove but without any significant friction to it. Following my build of a Grizzly Bear on a Bear V2.1 Frame and Enveloppe, thus with smaller print volumes, I was facing quite a challenge mounting the Hemera extruder in a way allowing the use of maximum X course. Please note that as my built is smaller than the recommended Grizzly, I have chosen to use an MGN12H caddy and MGN12R rail, not the recommended HGR15, which I bought anyway, but ended up being really too big for my smaller implementation. I have discovered in the process the many design issues of the Hemera, not to mention the general problems with quality control with cracked gears. Hopefully in the end I managed to get a stunning printer with super high quality prints at insane print speed for a cartesian (above 150mm/s), with a really maximized Z travel as a bonus. -First and foremost, almost all mounts designed for the Hemera put it along the X axis. But this extruder is highly asymmetrical, thus potentially losing precious real estate depending of the overall X course on your printer. -Added to this, the mount in such a standard configuration makes use of adapter parts, while the Hemera main advantage and innovation IMHO is that it can be used as a structural part by itself. It was designed this way and has the necessary mounting points to exploit this feature. So far I believe I have seen only one design taking advantage of this great feature. https://www.thingiverse.com/thing:4112731 -So in order to offer the Grizzly Bear a better solution, I started from scratch. I ended up with a quite compact (in the X direction) design, by making the mount at 90° compared to usual solutions. -As I wanted the Hemera body to be structural, I have minimized all interfaces with the printer structure, keeping only required parts which can thus be stiffer. I have printed the front part using carbon fiber PETG, and the 2 back parts using standard Dasfilament PETG. -While turning the extruder 90°, I wanted to place it ABOVE the MGN12 rail and supporting 2020 extrusion in order to maximize the Z travel. In such a configuration, the Hemara needs to be extremely close to the extrusion, and only a Volcano Hotend (or SuperVolcano) can be used in such a configuration. The nozzle protrudes by just a couple of millimetres from the MGN12H caddy lowest point, thus making the Z travel 100% available (minus these few mm). The result is quite impressive compared to usual solutions, as the use of a Volcano usually means you will lose some Z travel, but in such a design, it is not the case. Added benefit to this geometry, you get an extruder which center of gravity is very close to the supporting rail (it is balanced before adding the front heatbreak fan) thus minimizing print artifacts and ringing at high speed. Also the extruder is supported by the rail and not hanging from it. -As I use the BL Touch for Z probe, I have added the required mount with proper clearance for the Volcano. Note that the Volcano being a requirement of this design, it is a straight solution and I could adjust the BL Touch Z offset precisely inside the design. BL Touch Offsets are x_offset: -21 y_offset: -5 z_offset: 1.7 -I have faced many challenges in designing such a compact solution, one of the main being the belt locking path. I have spent several days scratching my head to find the best solution, as the rear mounting holes of the Hemera would interfere with the belt path. I wanted it to be easy to tension when mounting the extruder, and easy to maintain in case of extruder swap. I have ended up with an ultra compact locking path making use of the motor body (which happens to have angular corners at this location), to press against the belt, once it is passed through the tension slots. This adresses several problems at once. The solution is compact, can be printed stiff, it is easy to tension the belt when mounting, and the extra belt protruding is actually useful as a shock bumper when using TMC2130 or TMC2209 with sensorless homing. -Continuing in the same idea, I added a compact maintaining clip at the top of the extruder with a simple strain relief for cable management using a couple of zip ties to fix the wire harness into place. It also protects the motor connector. The overall result unfortunately has a few drawbacks that still need to be addressed in future revisions. -The nozzle being moved slightly more in front of the extrusion in this configuration, you will lose roughly 10mm in Y compared with a standard mount. I will be machining specific MK3s bed with included offset so that I can regain this without changing too many parts. I have the DXF if someone is interested. For this initial iteration, I have used a 220x220 mm precision machined bed + MK2 machined carriage that I had in stock. So this is certainly less of an issue with modern MK3s larger beds and carriages. -Another point to notice is that the X beam is close to the bed and this is quite impressive on first layers. So once the print is started, you won't have access to the nozzle if you are used to pick with tweezers for blobs or any annoyance of this kind during the first layers. The print head assembly really flies close to the bed. As a side note, an advantage of this configuration is that in case of a nozzle crash, the carriage will eventually make contact with the bed, sharing the load with the extruder, avoiding a catastrophic failure. This happened to me... -The nozzle change is quite annoying on my printer, but you may not have so many issues. I use a special insulation layer with aerogel wrapped in kapton around the hotend to basically keep it at room temperature on its external surface. This added to the insane E3D "twisting column" architecture, makes it difficult to lock the hotend in place when unscrewing the nozzle without damaging the insulation. It must be better when using a standard silicone sock. As an idea, it may be possible to modify the extruder to have a titanium screw coming down into the hotend to avoid it twisting when unscrewing the nozzle. This is another big drawback of the Hemera, compared to structurally better hotends (Mosquito, Dragon...), as this twisting issue, not only is annoying, but with the super thin new heatbreak of the Hemera, will certainly lead to many dramas when swapping nozzles. -Finally the top cable clip can easily be improved in order to offer a cable chain anchor. I have not decided if I want to go this direction as the chain makes my smaller printer quite bulky. I hope you will find this design interesting, I will post the F360 files if there is an interest for it by the community. Thanks to the great minds behind the Bear and Grizzly Bear designs !

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