Over extrusion as speed increases

  • Im having a weird problem that i cant seem to find when searching. Using a duet Ethernet on a good sized delta with a BMG set up as a flying extruder and about 120mm bowden between in and an e3dv6.

    The faster I print, the more I need to DECREASE the extrusion factor. example: using amazon basic black PLA I can print @ 50mm/s and 102% extruder flow and it prints perfect. If i increase to 80mm/s i need to DECREASE the extrusion rate to ~87% If I print @ 100mm/s i need to DECREASE extruder flow to ~70%. I thought maybe this was due to having non-linear extrusion enabled, its not enabled at all.

    This wouldnt be a problem if it didnt scale with speed... infill and supports get printed and higher speed than inner walls, and inner walls print faster than outer walls so if i make the outer walls look good, i get severe over extrusion on everything else.

    Any ideas?

  • This happens both if i increase/decrease the print speed in the slicer or if i do it via web control with leads me to believe that its a setting somewhere

  • @xsivspd It would be very unusual for the amount of filament extruded to vary in that way with print speed. I suspect that you have other problems which you may be interpreting as under or over extrusion.
    Here is a quick test. Print an object at say 50mm\sec and observe the value that DWC reports at the end of the print for filament used. Repeat at say 80 mm\sec and compare the two values. That will tell you if the amount of extrusion is indeed varying.

  • @deckingman I thought that it would be highly unusual also! I'll give that a try once my current print is finished. Where exactly should i look for that? "File Information" or the "filament Usage" over the progress bar in web control? I thought about that previously but just assumed that those numbers were generated by the slicer, not the boards' actual count.

    Ive just been making everything the same speed and then babysitting it for any layers under my minimum layer time. its a little more hands-on than i like sometimes.

  • @deckingman well, it seems like it's working properly now... i did power cycle it since the last print... maybe that was the issue? it usually stays on due to being plugged into a computer. maybe it needs occasional reboots?

    printed the same part that was at 50mm/s at 300% speed and the same extrusion factor and it still looks good. 🤔

  • @xsivspd That's weird. You don't normally have to power cycle the duet board. All I can suggest is that you monitor things. Maybe there is some sort of intermittent glitch such as bad crimp somewhere? These things are always a bugger when they happen intermittently.

    For info, DWC will give you a running total of filament used for each extruder drive (if you have more than one) in "real time" throughout a print - top left - machine status - under head position. I can't remember off hand if DWC separately reports filament used at the end of a print but if you look at that value for the extruder drive, it'll show you the total used.

  • @deckingman thanks for the heads up on real time output. i checked that versus the projected filament use based on the flow modifier that works at low speed and it was very close to dead on.

    Hopefully it was just a one time thing... I hate chasing intermittent problems, especially electrical ones.

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