The BCN3D Sigma R17 Review?

Dual extrusion has arrived, in a big way!

The fact that you need two filament paths is being solved creatively in a bunch of different ways: Either you’ve just got two fully featured hotends moving around at the same time, which does pose the issue of the inactive one oozing its filament onto your print. Then there’s the option of lifting one hotend, but unless you do that perfectly, it’s only going to cause more issues than it solves. Other setups use just one hotend and feed two or more filaments into it, one after another, but the BCN3D Sigma does things its own way – it just adds a second carriage and moves the idle hotend out of the way. Crutch or clutch? Let’s find out.

So this is BCN3D’s current version of the Sigma, commonly referred to as the R17. I’ve not used the previous version, so I can’t really tell you what’s changed, but I can tell you about how well this machine performs in absolute terms.

🛒 The Sigma R17 was provide through Matterhackers [🇺🇸] – buy one here!


Now, just to get it out of the way, yes, the most obvious machine to compare this to is the Ultimaker 3. And that has been my reference for all the testing I’ve done on the Sigma, but you have to realize that they are very different machines at their core and each one has its focus in a different area. Let’s leave all the direct comparisons to another video and just focus on the Sigma for now.

So the first thing that’s going to stand out is the machine’s looks – it’s aggressive, it’s mean, its frame is massive aluminum and with the linear motion components glowing in the purple LED lighting, there’s a distinct “modern” aura around the Sigma. It’s a very hefty machine, except for this wobbly plastic cover, and its large footprint comes with an equally large print volume of roughly 300x210x210mm or 12x8x8 inches, basically the size of an A4 sheet of paper as a build surface. There’s a lot of seemingly empty space to the left and right of the glass build plate, because that’s where the Sigma has its parking positions and waste buckets for the hotends. You get a fairly large touchscreen up front, flanked by an SD card slot, and a USB port on the back, which you can use to connect the Sigma to a computer for tethered printing. And yes, there’s no networking built in, neither through wired Ethernet nor through WiFi, which is a shame, considering the Sigma sells for almost 2655€ including tax or 27 hundred US dollars plus tax. But the thing is, the Sigma still runs the Marlin firmware on an 8-bit processor, which has plenty of horsepower for regular printing, but doesn’t exactly just let you plug in a WiFi dongle. Though adding OctoPrint with a separate Rapsberry Pi is trivial if you want networked printing.

The IDEX system

But the star, or stars of the show here are the dual independent extruders, dubbed IDEX. This really is the core of why the Sigma exists. The hotends in here are similar in concept to E3D’s, but not quite identical in all their dimensions. So this is a dual extruder setup, with two hotends, two bowden extruders, but also two X-axis-carriages. That means, that whenever it’s using one of the two hotends, it can park the other one off to the side. This reduces the moving weight on the X-axis, but most importantly, moves that second, idle hotend over a waste bucket with a wiper, where it can ooze as much filament as it want, and just before switching hotends, it primes the idle one into the bucket and wipes it clean with this flexible lip. This works great, and dual extrusion prints come out perfectly clean, without any extra oozy bits of the wrong filament stuck in the print. And there’s no priming tower that could get knocked over or otherwise ruin your print.

Having two independent X-carriages means aligning the two hotends is a bit trickier than if they were just next to each other, but BCN3D are including a powerful calibration routine on the Sigma. It feels a bit like the calibration you’d do on an a 2D inkjet machine to align the printhead, and at its core, it’s doing pretty much the same thing. The first time you start up the Sigma, it starts by adjusting the printbed, which uses an assisted manual leveling or, more precisely, tramming approach, with a microswitch on each carriage and the two adjustment knobs on the front. The rear mounting point of the bed is fixed, which gives the machine an absolute reference for height and it means you’ll never exceed the adjustment range on each of the thumbscrews, which is something that some other machines often struggle to work around. The microswitches measure the glass bed surface and the only thing left for you to do is to turn the left and right adjustment knob by the amount the machine tells you to. After that, the absolute nozzle height is calibrated, as usual, with a piece of paper with very specific instruction on how to hold it, and just to reconfirm everything, the machine then prints a test pattern and lets you pick which of the test strips looks best to you. And I think this last test is something that more machines should do, as it gives you that visual confirmation that your adjustment is correct. It does the same for the second hotend, and then a few more tests to align both hotends in X and Y direction. And the results of this process are really, really good. Though the process itself could use some tuning in my opinion, if you do the full run, it takes quite a while to complete, and the interface isn’t always totally logical if you’re not super concentrated. For example, not just in the calibration menus, but everywhere else, too, pressing “up” on the Z-axis screens moves the hotend closer to the bed, which would be the negative, down direction, in the printer’s own coordinates and in any host software, but in this case it refers the bed itself moving up and down. The menu structure in general could use a bit more work, too, just to get it closer in line with what we’re used to from smartphones these days. And to make the entire thing more stable, because right now there are still quite a few bugs in the interface. But in general, just having that large touchscreen instead of a clickwheel and a tiny display makes this printer not just easier, but also a lot faster to use.

So the rest of the hardware is mostly as expected – nice linear rails, 2GT belts, but for the Z-axis, they’re sticking to 12mm smooth rods and a trapezoid spindle. The spindle is fine, but the unsupported rods and the enormously long printbed do tend to visibly shake about as the rest of the printer moves. I’m not sure if this explains some of the inconsistencies I’m seeing in the prints, but it’s definitely not the greatest design choice using unsupported rods here. Print quality overall is ok, it’s not super-duper-awesome, but it’s very usable and most of the things I’m noticing can be worked around in software. For the most part, that would be some slight gaps in top layers and ringing. Quite a lot of ringing, actually. It can be dealt with by lowering the acceleration settings, and the underextrusion is just a slicer setting or firmware update away. Manually bumping the extrusion multiplier by about 10% fixed the gaps I was seeing with, basically, all materials.

Software options

Now, for the Sigma, slicer profiles are something that isn’t baked in anyways. BCN3D let you generate them through their Progen website for each material and nozzle size and quality setting. And this gives you print profiles both for Cura 15.04 or for Simplify 3D. Now, there is an 8-month-old build of a Cura BCN3D edition available, and I’ve been using that for the most part, but I didn’t find any differences to Ultimaker’s official Cura build, other than all references to Ultimaker being replaced by references to BCN3D. And not having any changes isn’t a good thing. If you look at even what for example Lulzbot are providing with material and quality selection in their custom version of Cura, or Prusa with the Slic3r build, BCN3D just having you manually load a new ini file for each new print setting or material choice feels utterly inappropriate. And on top of that, Cura 15.04 is complete garbage for dual extrusion. Yes, it does support multiple extruders, but it’s lacking so many essential features. You don’t see which parts of your models are going to use which extruder unless you memorize which color is which, so I took a shot in the dark and ended up with a false-color R2D2. Even for single extrusion where you just use one material, there’s no easy way to have your model printed with the second extruder instead, so if you have a different material or color loaded in the second slot, you can’t really print with it unless you’re also using the first one. And support material generation, particularly if you’re going to print with water-soluble PVA supports isn’t great, either. It uses a lot of the expensive PVA, there’s no option to use cheaper PLA for the inner parts of the support material that don’t need to be soluble, like with this battery holder that I could have easily printed with PVA supports, but it would have used a ton of PVA, so I decided to split it into two parts instead. I also ran into a configuration issue where the Cura profile was configured with quite a large gap between the support material and the actual build material, which is great if you’re using PLA for both the build and the support and don’t want it to stick too well, but in the case of PVA, the part I tried to print ended up detaching from the support material. Because BCN3D haven’t made Cura 2 work with the Sigma yet, and, in my opinion, Cura 2 overall has turned into the best slicer option out there right now and is pretty awesome for dual extrusion, because that option is not there yet, your only choices if you want to make use of the dual extrusion are to either configure the Sigma in Slic3r or Cura 2 yourself, which is non-trivial, or you can buy into Simplify 3D. I’ve asked BCN3D and their answer was basically yeah, just use Simplify 3D, if you’re seriously planning on using Cura 15.04, you are going to be crippling your shiny new 3D printer from the start.

I try to review commercial hardware as it is shipped, because there are infinite aftermarket options in how you can tweak the experience you have. As it stands, the Sigma only ships with Cura 15.04 and not with Simplify 3D.

And I’m not a huge fan of Simplify 3D aynways, both for it being overly complicated and for the fact that it’s closed-source, riddled with DRM, aka digital restrictions management, just maybe a bit overhyped, and of course, also a $149 purchase on top of your machine cost. Sure, in relation to what you’re paying for the Sigma, it’s not a huge deal, but just image if all those people buying Simplify 3D would have funded an open-source slicer instead. That would be an amazing piece of software! Instead, we have Simplify 3D. I tried the custom support material generation that Simplify 3D is often praised for and the supports just ended up fusing to the part instead of coming loose easily.

And I’m not quite sure why BCN3D are promoting Simplify 3D so much, because it does clash with their own open-source philosophy. BCN3D have done an awesome job on the Open-Source side of the Sigma. Not only are you getting all the CAD files, but also the bill of materials including suppliers, you’re getting manufacturing drawings, the full package. So if you ever want to modify or fix anything on the Sigma or even build a printer based on it, you’ve got everything you could ever want for that. And I don’t think anyone else, other than of course Lulzbot, are doing Open Source this thoroughly.

Details make the difference

And it does feel like BCN3D have put a lot of attention to detail into this machine. Starting with having Trinamic drivers right next the motors to reduce EMI and stray inductance, then the very usable spool mounts inside the printer frame, which allow you to take out each spool without having to touch the other one – yay – and lastly the magnetic quick-release glass bed, which relies on the included can of 3DLac to get adhesion, and that works great, but I’m sure you could also just print PLA onto the bare glass instead. However, things aren’t perfect, as those same spool mounts mean that the water-soluble PVA support material will be constantly exposed to ambient moisture, which could render it unprintable quite fast. The ESUN or Matterhackers PVA is a standard type, so it dissolves very easily, even in cold water without agitation, but it also sucks a lot more moisture out of the air than some of the custom types. Also, the heated bed PCB has a huge gap to the glass and takes forever to heat up even for PLA, and PETG and ABS are just a chore to print, the LCD menus feel undercooked and the firmware even freezes with non-Sigma gcode files on the SD card. And the noise level of the entire machine supposedly has been improved compared to the previous generation, but it’s still not exactly a quiet machine.

BCN3D have already addressed some of the software-fixable issues, like what we saw in the live unboxing, where the idle extruder head would constantly lose its positioning, that turned out to be a bad sample gcode file, if you freshly slice new designs, the motion system works perfectly. And I know the rest of the hiccups and especially the slicer situation will also be solved down the road, but it would have been nice to have all this stuff tested for and taken care of before releasing and shipping the machine. Again, I hate comparing the Sigma to the Ultimaker 3, but it was a very similar story there late last year, where the machine shipped with some issues that should have never made it out the door. Tough management and rigid deadlines in both cases? Sounds like it. But please, BCN3D, I know you’re working on Cura 2 support etc, don’t rush them out. Do it right. I know this might be a stereotypical clash between German and Spanish philosophies, but I’d much rather have a release a few weeks later if that means you’ve taken some extra time for testing and tweaking.

It doesn’t change the fact, though, that the dual-extrusion system itself in the Sigma works flawlessly and is probably the most universal and overall just the best system for dual-extrusion out there right now. Having two independent hotends, getting the idle one out of the way and priming it outside the build area is priceless, it just works really well. The calibrations wizards also do their job marvellously, but overall it feels like, right now, the software and firmware are really holding back what the machine is capable of.

Is it ready yet?

And because of that, I don’t think I can really come to a final verdict on the BCN3D Sigma R17 yet, there are still a few too many open questions that I have. Let’s just say, there’s going to be more content on the Sigma R17 vs. Ultimaker 3 maybe in, like two months, when everything should have settled in a bit? Because the thing is, when you’re buying a 3D printer for 27 hundred bucks, you’re probably going to keep it for a while and you’re going to see a few software and firmware iterations throughout its lifetime, even if that part not perfect right now. I know that is an unsatisfying conclusion, but I don’t think the current state of the Sigma lives up to what BCN3D had envisioned with it.

So I guess, yeah, I’m looking forward to what BCN3D do next with the Sigma, there’s a lot of potential there. If you agree, hit that like button and I’d love to know where you guy have your priorities – would you rather have a stripped-down machine with great software or a more complex package with everything being a bit unfinished?

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