Weird intermittent print quality problem - any suggestions?

  • My mini-Kossel+Duet is suffering from a weird problem inasmuch that while it will often print extremely well, sometimes it produces poor results that look like it has expanded a layer. As far as I can tell, the layers are not shifted, the're expanded (or shrunk). Like all of us, it seems to have good days and bad days! Here's an example:


    Often, but not always the effect happens on every other layer.

    The rod ends are a little worn but I have rubber bands across the rods which takes out the slack and I don't think the effector has any more backlash/wobble than previous.

    I guess the question is, apart from mechanical slop, what else could cause this effect on an intermittent basis?

  • Binding caused by temperature fluctuations?

  • Mechanical issues due to backlash?

    Is each layer printed in the same direction or does the head go clockwise for one layer and counterclockwise for the next layer?

    That what it looks like to me, just my opinion of course.

    Test it by printing something in vase mode to keep the head moving in the same direction all the time. See if the problem still exists.

  • Belated thanks to those who replied.

    I now think that the issue was caused by an unreliable hotend thermistor. It finally went so bad that the temperature would change sufficiently (and quickly enough) to produce heater faults.

    Since changing the thermistor, the problem has not yet occurred again.

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