How to avoid nozzle from hitting the model?

  • When printing objects higher than approximately 8-10 cm, sometimes nozzle hits the printed model and knocks over it. After 7-8 hours of printing that's really annoying. I'm using Creality Ender 3 Pro with Ultimaker Cura. How can I avoid this problem?



    As a note; it happens with thick, wide models without support structure too. I'm using Ender 3 Pro's stock magnetic bed.



    Here are some photos of printed model.



    Failed print - photo#1



    Failed print - photo#2



    Failed print - photo#3



    I use Esun PLA+, the part was on baseplate without any loss of contact. It was like one layer missed its coordinates and then all corrupted.



    I think it's not related with bed adhesion because for example for this model, it didn't knock over the model.



    There is no roof for the model, I think it doesn't need any support structure. Here you can see the expected finished one:



    Expected finished print


    Can you give examples of some models it happens with? You probably have both warping problems (bringing material above the nominal Z) and bed adhesion problems. Up to the point that printed, there should be no travel moves because the layers are simply connected. Is there a roof like the base that's getting started when it fails? If so the problem is likely failed bridging without support - the failed bridge creates string junk that curls randomly (sometimes up) for the print head (not just the nozzle) to catch on and drag.

    What material are you using? Often this "knock over" is due to warping or loss of contact with the baseplate, so that the nozzle isn't hitting the part but the filament itself is dragging the part along with the nozzle. Every photo there sure looks like the part moved, as you can see strings which should have been over the end-edge. As one layer was skipped then that suggests a possible skip in the X or Y-drive. Not to be a buzzkill, but Ender machines do seem to produce more 'failed print' questions here than any other brand.

    WIth a base like that, it should take some serious force to remove the part from the build plate, and I'd even worry about damaging the build surface if I didn't use a blade to separate it. I wonder if you have way too much distance between the nozzle at height 0 and the build surface resulting in poor adhesion. It's possible that you also have an issue like stepper skips/layer shift, as Carl suggested, but it's not clear which came first, the separation of the print from the build surface, or the misaligned attempted layers on top, and either could have caused the other.

    Folks voting to close this, **it's not a duplicate**; rather OP's question is misstated. The underlying problem here is not the nozzle hitting the model but something else (either breaking off the build plate, or a layer shift or other problem causing junk material that the print head can hit).

    If the Z axis is not level, it's likely that the screws holding the gantry to the roller structure on one or both sides are either loose or not square with the gantry. The ones on the right are easy to see and adjust, but the ones on the left are somewhat hidden between the gantry and the vertical rail, and only accessible after removing the whole assembly from the vertical rails, and only then with the short end of an allen wrench. Both sides have significant play if not tightened...

    For the ones on the right you can let them naturally align with the tension of the system, and tighten them down once it's aligned. But for the ones on the left, you have to just get them as square as you can with the X axis gantry removed, either eyeballing it or using some shims and straight reference to hold the bracket in place while you tighten it down.

    Unfortunately Ender 3's gantrys on Z axis are 3 wheeled gantry and it's almost impossible to level them with precision. There is always difference around 1mm

  • It seems the problem was because of Z-axis leveling (level of the X-axis), I found out that the right side was more than 3-4 mm below the left side when the Z-axis height exceeds around 8-10 cm. Below 8-10 cm, the two sides were even. I calibrated the X-axis by turning the eccentric nuts of the wheels and tighten them. I will try printing soon with some test objects.


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Content dated before 7/24/2021 11:53 AM