Sanjiu / SANBrother Metal BMG extruder – Aero style

At the time I got my X5S, there were two extruders (cold ends / feeders) competing to be the best choice.
There was E3D’s excellent Titan Aero design (their blog describes it’s advantages in detail here).
And the Bondtech Mini Geared (commonly referred to as the BMG), which had finally overcome the disadvantages of the V2 (no filament quick relase) and the QR (expensive geared stepper motor). It now also took advantage of the same open (hand-turnable) gear reduction as the Titan.
You had to decide, if the Aero’s shorter filament path or the BMG’s dual, counter-rotating wheels were the killer feature for you. And I waited for one of the two innovators to finally come up with a combination of both. But now some chinese companies did just that.

To my surprise I did not only see a “Mellow” branded “Dual Gear NF All Metal Bmg Extruder”, but also a different “Sanjiu” / “SANBrother” branded “Dual Gear All Metal Bmg Extruder” appear on AliExpress – and both sported not only aluminium shells, but also heat break interfaces and cooling fins.

There was not much further info in the WWW about them. Jay’s Blog contained a post about his Sanjiu specimen and there was a reddit discussion linking to a picture of the Mellow version – where a certain “SanjayM”, who “contributed to pretty much every E3D product, many as design lead, some as sole designer”, doubted that the design would be really useable.

Sanjay also noted, that those vendors had “just cloned the work of the good folks at bondtech” – which is certainly true, when it comes to the implementation details of the filament advance mechanism. But Bondtech didn’t invent the dual drive extruder. There was a crowdfunding campaign in 2013 about such a “dual pinch wheel extruder” (3ders.org also reported on it). And Martin Bondéus published a YouTube video on his first batch of extruders more than a year after it.
Apart from this, Bondtech could not lower their prices into the tinkerer-region – this 3ders.org article from 2017 still shows the first BMGs  with parts produced by selective laser sintering (rather than injection moulding) and a set of gears was priced at a whopping 59 €. Until clones of that gears showed up (already blogged that here).

Sanjiu / SANBrother recently threw their “Metal BMG extruder” onto the market for 26.30 € including shipping – which is somehow exactly what customs just let pass into Germany…
…and even if it’s useless as an “Aero”, it could still be put to use as a “plain BMG”. So I ordered at the “SANJIUPrinter 3D Research Center Store”. And yesterday it arrived.

There was already a comment in the X5S FB group, that the gears look like they are for 2.85mm filament – but I don’t think the Chinese distinguish their „Cloned Btech Gears“. And neither does Bondtech. 5mm shaft versions are always 1.75mm filament versions. They are hobbed differently. The china clones have sharper, deeper teeth compared to the Bondtech parts, which might get clogged more easily.

So what we have here is a 1.75mm extruder. I can’t push a 3mm drill through the holes for the filament (but a 2mm one). The filament path is defined via a printed part – so it can be adjusted later, if anything needs modifications for flexibles. Which is a good thing. I’ve spent quite some time now to get PTFE tubes in Prusa extruders (Bondtech gears, but directly driven by the stepper) carved just right for Filaflex, RubberJet and so on.

As a precautionary measure, I’ve designed this piece in OpenSCAD. It can be found on Libre3D and YouMagine. The hole (filament path) is meant to be reamed out with a drill to get the proper diameter.

But what about the Aero feature? The Mellow BMG is depicted with “Pneumatic Connectors NF PC4-M7 Remote” – so they use E3D-style heat breaks.
The Sanjiu? 7mm smooth bore. *sigh* So it’s not the M7 E3D-type thread you want. And you can’t cut that M7x1 thread into it either.
Furthermore my XCR BP6 „Hexagon“ heat break is slightly too long. No Idea if Kraken/Chimera/Cyclops heat breaks would fit. But I won’t use it that way.

Grub screws are accessible only from the motor side. Those will make a lot of thermal cycles on a heat break – so I wouldn’t trust them to stay tightened…
And then there is the heat sink.

Roughly calculated those fins have less than 60% of the surface a Titan Aero, v5 or v6 ‘sink provides. And the Aero has an enormously loud 40mm, high static pressure fan where this seems to be for 30mm fans…
There’s no way I will test this in an Aero configuration. The risk of wasting my time designing a 5015 blower duct and then still having it fail to print PLA with an all-metal heatbreak is just too big.
…so I’ll try to adapt it to my carriage with the hotend keeping it’s own heatsink.

And maybe Sanjay Mortimer and Martin Bondéus can team up to finally deliver the proper geared dual pinch wheel extruder with integrated heat sink, that we all want. 😉

=> Edit: E3D did it! And they did even more than that. 🙂
=> https://e3d-online.com/blog/2019/11/29/e3d-hemera-a-next-generation-extrusion-system/

P.S.
Jay also commented about having to replace the stock pneumatic fitting for the reverse Bowden tube. The upper bore diameter is 8mm and the connector is held in place with another maggot screw.
So even if you don’t need an M7x1 thread-cutting tap, you might be better off having one fitting an appropriate replacement pneufit connector at hand…
And be aware, that a chinese “PC4-M10″ coupling might actually be G or R1/8”!

Update:
The filament guide I designed was still not tight enough for flexibles. Depicted below are “stock” (black), my 4th iteration (blue) and the 5th one (copper). Only with the last piece I was able to print flexible filaments (Filament PM RubberJet TPE 88 and Recreus FilaFlex 82A Original were the softest so far) without allowing it to kink or wrap around the gears.

YM and L3D are already updated.

You can already find my new carriage there (YM, L3D), but the blog post on that will still take some time. BTW: As I don’t use the upper bowden coupler, I chamfered the hole leading towards the gears to ease filament insertion.

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