How can a calibrated extrusion produce overextruion-ish prints?

  • Hello all! 🙂
    I wasn't satisfied with the print quality of my printer when it dawned on me that the artifacts I'm seeing are very much like these when over-extruding. The weird thing is that I calibrated my extrusion factor to produce walls with the exact thickness that is set in the slicer. I printed a 20x20 cube with two walls at a desired line width of 0.7 mm (with a 0.6 mm nozzle). The walls measure something around 1.4 mm and the calculated extrusion factor was conveniently exactly 100%. This led me to believe that my bondtech extruder is set up correctly.
    The problem now is that the walls and also the top surface don't look very smooth. The cube one the right is printed with 100% flow, the middle one with 90% and the left one with 85%:
    20191002_214028.jpg 20191002_214021.jpg

    The cube with 100% measures 20 mm quite exactly, the other ones come out 0.1 or 0.2 mm smaller but look way nicer (on the walls and on the top).

    Can someone tell me why that is the case? I would be very glad to resolve this issue! 🙂

  • The first thing you calibrate is the steps / mm for the extruder, then work on the extrusion factor in the slicer after that. None of my filaments are 1.0 extrusion factor, most are .88-.90 range after I calibrated the esteps.

    Another thing that can cause wall artifacts like that is a pcb heated bed that flexes as it turns on and off.

  • @Eumldeuml said in How can a calibrated extrusion produce overextruion-ish prints?:

    Can someone tell me why that is the case?

    Tricky, you'll probably get six different answers, all of them possibly correct. 😉

    I saw similar things om my machine as I explored 0.6 and 0.8 Nozzles, I solved some of them after reading this and spending a few hrs printing cats with different line widths and layer heights, I was surprised at how big a difference small changes made.

    The problem is that this combines with other stuff too; So; here is my 'hit list';

    • beds that move (even if not visible to you) with Z height or temperature cycles also wreck walls and layers like that.
    • overstuffed first layers; I dont think you have this; but it forces every subsequent layer to be a little bit overstuffed too, a bad first layer can ripple up through the rest of the print., especially if you are overextruding a bit anyway.
    • Slicing; You dont mention which slicer you use, but with so many parameters to tweak and forget it can be a good idea to start with a very plain 'vanilla' profile for your printer and re-do the slicer settings from scratch based on experience.
    • Filament; has bitten me hard. Very small filament diameter changes are over-represented in extrusion changes (it's that pesky πR squared business), without proper filament sensors (which do exist for the Duet) you have to trust suppliers to be consistent.

  • @JamesM I did calibrate the E-Steps quite a while ago and found no deviation from Bindtech's recommended 420 steps/mm. The problem I see there is the tension of the drive gears and the hardness of the filament since there's no way of adjusting it repeatably. More tension means more bite into the filament which reduces the effective diameter. As I print mostly PLA (which has a comparably high hardness), this isn't of much concern I think.
    Also the flow rate was calibrated so that the printer produces accurate line thicknesses and overall dimensions so I am very confused how that could result in those artifacts I mentioned...

    @EasyTarget Thank you for your detailed answer! 🙂
    I also think that those artifacts are in some way related to a bigger nozzle (I changed from 0.4 to 0.6 mm quite a while ago). Since I never cared really much about aesthetics so I considered the faster print time was worth more than the drop in optical quality. But now that my printer is getting better and better I start to dislike the uneven walls (which btw show up way more with 0.2 mm layer height than with 0.3 mm).

    For slicing I use the Prusa Slicer. I don't have a 'vanilla' profile for my printer since it's completely designed by myself 😅
    The filament I use most is PLA NX2 from extrudr which I print at 215/60°C. I measured the diameter at several points and it is quite consistent (1.75 +-0.01 mm).
    I also checked all the set screws on the pulleys and the belt tension, no problems there.

    My print bed does indeed move in Z (intentionally of course :P) but it also does wobble the slightest bit at certain print speeds. There might be some hysteresis in the wobbling so that could cause those artifacts on the walls which get amplified by lower layer heights (and presumably the flow rate). This might be the most likely cause but I don't know how to get rid of it since I already beefed up my Z-axis quite a bit (if you're interested check this thread.
    Could the problem be a result of interpolation or microsteps on the Z-axis? I'm thinking that the Z-axis might 'fall' to the next full step when commanded somewhere in between. Maybe even a similar effect on the other axes which could lead to lines being printed not exactly on top of each other?

Log in to reply