SOLVED Printing artifact

  • This happens on only one of 4 sides:

    printing crap.jpeg

    There is obviously a big ringing problem but I am not worried about that for the time being. I am worried about these divots that show up. They are all the way through to the other side.
    Material is PLA, 215C, Volcano hot end, 0.8 mm nozzle, 50 mm/sec speed
    Hot end is a two nozzle setup and the nozzles are 20 mm apart in the y direction. The artifacts are at about 22 mm apart when they appear on the same print level. The artifacts only appear on the y moves.

    I have a bit of a bizarre theory that I am still verifying:
    I am thinking that every so often the actively printing nozzle drops a tiny bit of extra material, maybe it was hanging on the outside of the nozzle, who knows. The second nozzle which sits at the same height as the first nozzle comes along and bumps into this tiny blob causing the whole carriage to lift ever so slightly which in turn causes the active print head to bump up which makes a small bump which the second nozzle bumps against and so on and so on until something interrupts the chain of events.
    If I turn the model a bit, the second print head no longer traverses the same path as the first print head and magically these artifacts go away !!!!

    Has anyone run into this with a dual print head? Does my theory sound plausible? Other than turning the model so that walls are not aligned strictly in the y direction, has anyone managed to fix this kind of an issue?

    My next print test will be done with the second nozzle heated which may or may not flatted out the bump rather than forcing the nozzle to ride over the bump.

    BTW, the little bumps shed are generally less than the layer height so in regular use, where the second print head doesn't follow in exactly the same track as the first head, or in single head setup, the next level seamlessly prints over the bump and absorbs it in the new layer.

  • that looks like a mechanical issue. like broken bearing.

  • @jens55 I'd say you could be on to something. I've seen something similar on my chimera. You might also see something where the unused nozzle crosses a diagonal perimeter.

    If I'm not gonna be using the second nozzle for a while, I adjust the heights so the unused one is 1mm higher and won't hit anything. If I'm using both nozzles, then I make sure they are 'as level as a level thing' and run them both hot, maybe with the inactive one 10deg cooler to avoid any oozing.

    I found it all gets worse if you have something that causes a bump in the first place (e.g. your ringing), so you'll probably get the best improvement by tackling that too.

  • It's confirmed - the same print with the same orientation printed just fine when I heated up the second nozzle.
    engikeneer, I also use the chimera! The ringing is caused (in my opinion) by the large and heavy bed and bed slinger technology. I suspect the only way to maintain the 500 by 500 work envelope and reduce ringing is by going to a different movement technology where the head(s) travel in x and y and the bed is limited to z motion.
    I had avoided messing with the height of the nozzles because I find it really tricky to hit just the right height with both and being off by 0.05 mm is enough to cause issues.
    I am really getting disenchanted with a two nozzle setup and am thinking of converting back to a single nozzle. The reason I am reluctant is because in a single nozzle setup you still need to adjust the offset between probe and nozzle unless you happen to run a piezo head where the nozzle and probe are one and the same. I had all kinds of problems with consistent probing with a piezo setup where it was working exceptionally well in one spot and would end up pushing the bed down in another spot. Way too finicky!

    I was hoping to wait a bit for the tool head changing technology to get sorted out a bit more but this is getting very frustrating. I do not trust the accuracy claimed in positioning tool head height between two different head assemblies. Even with a single head and probe offset dialed in just right, I find that I tweak the baby step height here and there for the best first layer even though repeatability of the probe is very good. Once the height is perfect, I do not ever release holding current on the steppers in order to avoid having to re-probe and re-adjust between prints.
    I have already given up printing two material prints but was hanging on to the two nozzle configuration in order to easily switch between two different nozzle diameters (0.4 and 0.8 mm).

    Some heavy soul searching will be required!

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