Prints suddenly fail after hours of succesful printing



  • Hi

    My printer screws up every single print. I try to print these quite big parts (800 grams) and everything goes smooth usually for quite some time. Then suddenly X loses it completely and spaghetti follows. The print takes 35 hours and this time around 20 hrs it had failed. Sometimes it happens earlier. There happens a layer shift either positive or negative direction on X. Then later on there is usually some more layer shifts. They come totally randomly what makes it so difficult to hunt down the reason.

    There is nothing tricky in the piece, I have lowered the speeds , jerks and accelerations into very reasonable (even ridiculously slow) levels but nothing seems to save it. The files are fine, I check them always in gcode.ws. I assume there is a hardware issue but after working days on it I only can suspect the motor being somehow bad, allthough it has often been running half a day flawlessly before the torture begins again.

    The prints look absolutely great before they get completely destroyed - devastatingly frustrating.

    The printer is a big boy with dual Y nema23 and one on X running a belt loop of almost 2 meters (950mm X). There is a linear rail for the extruders and the belt is clamped on the extruders. Pretty straight forward.

    Oh yes, everything was going smooth on Duet 0.8.5 before I shorted some driver chips on it and had to get a new controller, Duet ethernet.

    Any advise very welcome

    Thanks!


  • administrators

    Some common causes of layer shifts:

    • Nozzle hitting a blob or curl up on the print and not getting past or through it without skipping steps. Using Z lift on travel moves may help, although on a Cartesian or CoreXY printer this will slow down travel moves and cause a lot more wear on the Z axis. Increasing motor current may also help. What is the rated current of your Nema 23 motors, and what current are you running them at?

    • Driver overheating, causing the driver to go into thermal shutdown. On the Duet Ethernet with 1.19 firmware you will get an over-temperature warning some time before this happens.

    • Loose pulley on motor shaft

    • Binding in the mechanics, perhaps temperature-dependent. This could even be in the motor, especially if the motor is getting hot.

    • Power brownouts. But these would affect the Y axis as well as the X axis.



  • I have been searching signs of mechanical hit but not found any evidence. Also there is a bit flex in the machine because of the dimensions and it not being made out of cast iron so in these speeds and with these forces the conical nozzle should be able to climb a bit if meeting a blob. I have been manually testing how much force there has to be applied to make the X and Y skip steps and it is considerable.

    The current is around 2 amps, I have been playing on both sides of that in search of well running settings with my external DM542A and DQ542MA drivers. The motors are separated from the build chamber, enclosed and cooled. Drivers stay nice and cool.

    I was earlier not able to get the Zhop working (using Cura) but now will put more effort on that. It may have been caused by the short signal width that I now have changed into 3 microseconds.

    The pulleys and belts and shafts are tight and playfree.

    Temperature related binding in the linear rail has been under consideration but they are from a quality manufacturer and I would expect the error then continuing from a certain timepoint on or at least be more frequent. Instead the layer shift happens only every now and then, and after a shift the print continues beautifully untill the next shift that comes randomly at some point.

    Power related issues have been thought too, but they're not probable with the UPS (and surely would be weird affecting only X as you said.)


 

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