[Additive] Severe under-extrusion with larger nozzles

Eric_Schubert · ‎05-11-2021

I have a Creality Ender 3 printer that I've modified a bit, swapping out the hot end and extruder to a Slice Engineering Mosquito and Bondtech BMG-M geared direct extruder. I've been utilizing Fusion 360 for my 3D printing needs for some time. I have run into an odd issue that I can't really explain away.

I've been tinkering with nozzle sizes other than 0.4mm. I've noticed I need to compensate for changes in flow rate. As nozzle sizes get larger or smaller, most of my flow rates have been somewhat predictable. For PLA, larger nozzles require lower flow rates to get proper wall thicknesses. But, not with PETG and a 0.8mm nozzle size. I'm getting severe under-extrusion and need massive flow rates to get solid lines down on the bed.

However, the fact that I have flow rates for PLA ranging from 95.7% with 0.4mm nozzles to 81.4% with 0.8mm nozzles tells me there's something off about how Fusion 360 is calculating the volume or linear distance that should exit the extruder. I've gotten comments elsewhere that flow rates should hover around 100% within a few percent, if settings are otherwise good.

Things I've verified are set properly:

Basic > Extrusion Width > 0.8mm
Extruder > Filament Diameter > 1.75mm
Layer > Perimeter Extrusion Width > 0.8mm
Layer > Layer 1 Extrusion Width > 0.8mm
Infill > Infill Extrusion Width > 0.8mm
Skirt-brim > Prime Extrusion Width > 2.0mm
Bridging > Bridge Extrusion Width > 0.9mm
Brim, Raft, and Support are unused. I do print a skirt with 2 passes, 1 layer.

So... why are my flow rates so varied? What's happening behind the scenes that could cause this issue? Why am I needing to crank up my flow rate with a 0.8mm nozzle to 160% just to get solid lines to lay down on the bed? Is this a bug in Fusion 360 or the Creality post-processor?

Smaller nozzles seem to print just fine, though again, I do need to adjust flow rates a noticeable amount to achieve good prints.

robert.bowerman · ‎05-14-2021

Hi @Eric_Schubert,

Thank you for your question. Are you able to provide a sample project where you are seeing under extrusion when printing? This will enable me to check if there is an issue with the extrusion value that is being output.

Thanks,

Rob

Eric_Schubert · ‎05-15-2021

Absolutely, @robert.bowerman. Here's the g-code for a simple 20mm calibration cube with 0.16mm walls meant for 0.8mm nozzles. The purpose is to print 2 perimeters thick and calibrate the flow rate based on the measured wall thickness to ensure accurate walls on prints.

I've provided the actual g-code file that is under-extruding. However, I had to recreate the F360 file's print settings, as I didn't save the original. The only things that I changed in there are flow rate and extrusion widths, so it should be identical to when I generated the g-code. I did not touch default settings in the Raft and Support tabs, as I had no need for those settings in this print, so they'll still be set as they would for 0.4mm nozzles.

See attachments for your review.

robert.bowerman · ‎05-17-2021

Hi @Eric_Schubert,

Thank you for providing these files. I've taken a few random points in the code and it appears that the extrusion values are as expected. As an example, I've attached an image of some quick calculations from the motion between line 660 and 661. You can see that the "travel volume" and "material volume" match for the given travelled distance and extruded distance. However, it is entirely possible that I'm missing something. I did notice that your travel speed in this region was lower than requested (887mm/min compared to 1500mm/min), might this be causing an issue?

Thanks,

Rob

Eric_Schubert · ‎05-17-2021

Travel speed should be right. I typically print first layers slower to ensure bed adhesion. In this case, it's likely a multiplier of 0.5 or 0.4. Layers 2 and up should print at full speed per the settings.

I don't believe this is an issue with my nozzle being clogged. When I manually feed the filament through the hot end, it comes out smoothly. When I increased the flow rate to 160%, I finally got full lines of plastic.

At this point, I'm not sure what else it could be, but I'm open to ideas.

Since I cannot be 100% sure the updated model matches the g-code provided, I can always try printing one more calibration cube to see how it looks. I don't think it'll make a difference, though.

robert.bowerman · ‎05-17-2021

Perhaps it's worth trying to print another.

The travel speed I was referring to was beyond the first layer (layer 9 in this instance), so shouldn't be affected by the multiplier. Also something you may or may not be aware of; the output print speeds and print volume are limited by the parameters set in the machine configuration, you can edit these by hitting the pencil button (edit) within the machine library and clicking on "Extruder Configuration".

Out of interest, have you tested the output with any other slicers to see if you have the same issue?

Eric_Schubert · ‎05-17-2021

I'm guessing I slowed it down quite a bit to see if the extruder just needed to keep up with the print head. It didn't help.