Underextrusion BCN Sigma & Cura

[veedee 4]

Hi fellow makers,

I have a BCN3D Sigma for more than a month now and using Cura and S3D with it. But somehow I can't get a nice and smooth infill. The infill seems to have underextrusion at random places, but it also isn't random at the same time.

Every time I try to print a simple calibration cilinder with 100% infill, there are little open spaces between the infill (see picture). The weirdest thing about it is that the underextrusion happens on the same place when I print the same gcode multiple times, BUT I also get the same gcode to be printed out fine sometimes. I have tried every setting that possibly has to do with it in cura, but also in S3D. Sadly the problem has not been solved yet. I want to print colorfabb pla/pha with at least: 0.15 layers, 215C, 60mm/s, 50% fan speed. So these are my base settings.

I thought it has something to do with the hotend and cooling fan setup, maybe thermal interference between them (fan cooling the nozzle too much or whatever). When I crank up the temp to 250C, prints are printed better, but other temperature issues appeared. So maybe slowing down the layer time. At 20mm/s it looked better, but this is just terribly slow. Fan of also works (but not always), but I don't want to print without the fan because of sagging issues. Also I thought different layer heights may work, but for as well as 0.2 and 0.1 layers, the underextrusion happened in many cases.

I also tried different materials and different brands on both hotends. But it happens in every combination. Altough it looks like the left hotend is worse than the right hotend, but I'm not 100% sure about that.

So that's were I started looking at mechanical issues. Dirty drivegear maybe, or extruder skipping steps? No, sadly that was not the case. Maybe the wrong steps per E? Nope. When I installed a (slightly modificated) UMO geared extruder to see if that works, it initially looked like it worked. So I made two identical UMO geared extruders with a different mounting bracket and installed those (ofcourse calibrated the E-steps). After some testprints, the problem appeared to be still there. Still no grinding issues, skipping steps or wrong steps per E, so the amount of extruded material seems to be right. By the way, those extruders proved me to work very reliably, I have them on 6 UMO's. So I guess the extruder is ruled out at this point.

Other things I tried which all didn't work:

• Oiling the filament

• Cleaning the nozzles

• Thermal grease between the thread of the nozzle/heaterblock and heaterblock/heatbreak

• Hotend autotune (10x)

BCN3D is sending me new hotends to test, but I'm afraid this is not going to help since the construction of the hotend+carriage doesn't change.

Does someone have any ideas to solve this problem?

Also: I don't seem to be the only one having these issues, but many people don't even mention it since it's their first printer and have different expectations or no comparison.

Edit: Below you see exactly the same gcode printed at one of my UMOs. Did a 205ºC temperature and 300% speed override, still printed fine.

Edited May 12, 2017 by Guest

[burtoogle 508]

Hi, Sorry, I don't know anything about your make of printer but just looking at your images makes me think that the z-height is varying across the print because you have gradual changes from under to over-extrusion. So, can your z-height alter due to changes in x/y position?

[veedee 4]

Hi, Sorry, I don't know anything about your make of printer but just looking at your images makes me think that the z-height is varying across the print because you have gradual changes from under to over-extrusion. So, can your z-height alter due to changes in x/y position?

 

Thanks for your input, but I checked this already. The bed actually is very flat and the first layer always prints great. But the underextrusion problem keeps happening in the entire print after that. A varying Z-height can be visible in the first few layers but dampens out and disappears when you print taller parts.

[BIKBart 3]

Dear Veedee,

 

Did you ever solved this issue? I have a BCN3D sigma with similar underextrusion issues, and as far I can tell it has something to do with retraction. Because I noticed the underextrusion starts after a while (in the beginning its extruding fine) and increases as the details in a print increase or when the dual extrusion kicks in (thus the retraction increases). It's an old post but I hope you can tell me if and how you solved the issue. 

 

Kind regards,
Bart

[veedee 4]

Nope sadly not. I have heavily modified the machine to try and make it work reliable. I added UMO style extruders with hobb goblin drivegears, E3D hotends with silicone socks, better hotend carriages with improved airflow, but sadly nothing helps and I'm out of ideas.

[burtoogle 508]

I recently had some of this underextrusion on skins and the only way I could improve it was to print the skin slower. I am using an e3dv6 hotend I have come to the conclusion that it simply doesn't have the heat transfer capacity to continuously print large areas quickly. Setting top surface skin layers to a non-zero value and then using a much reduced speed for the top surface layers helps the speed/time trade off.

[veedee 4]

I actually do not think that the E3D hotend is the problem, because I use them on 10 other machine, where they work absolutely fine with higher extrusion rates. Also, printing PLA on an all metal hotend can be improved by seasoning the filament with a tiny wipe of vegetable oil.

 

I think it has something to do with the temperatures on the sigma, which probably are not displayed correctly. Higher temperatures print way better on my sigma.

[BIKBart 3]

That's sad to hear. All the modifications you describe where on my optional to-do list to improve the reliability of the machine but now I'm thinking to just give it back to the owner (I borrowed it with the option to buy). Probably better to invest my money in a new and more reliable dual-extrusion machine... I read somewhere on the internet that an owner of the Sigma thought the underextrusion had something to do with a bad stepper driver and that it misses steps as the driver gets warmer or something. Veedee, did you do the stepper driver upgrade on your machine or did you by the R17 model that has the improved stepper drives? I will try to google the post where I read this...

[veedee 4]

I have the R17 version. I really ran out of possible improvements to make the machine work. I think it's a temperature issue, but I don't have the right equipment to calibrate it.

[seuchato 0]

I had similar  issues on my sigma. It is an R17 with upgraded firmware and now bondtech extruders. I have e3d hot ends installed. I increased temperatures by about 10°C. Still had problems. In the R19 firmware, you can now control material flow. I set it to 115% and above described and shown problems are gone.

I'd like to set these 115% in cura 3.6.0 (running under opensuse leap 15.0). However, the flow setting and temperatures are not passed to the sigma. 

hth

chris

[gr5 2,004]

It is true that the flow value in cura does not "get passed to " the sigma.  But it doesn't need to as it affects the extruder values directly in the gcode.  For example if at normal/nominal/100% extrusion the extruder on the 50th move might move from extrusion of 3.5mm to 3.6mm instead (at 115% lfow) everything is 115% larger so it would move from 4.025 to 4.14 (15% more).

 

So it works just as one would want.  You can then increase the flow even more by messing with the flow parameter in the printer.