Extrusion stops during first layers

Controllers Smoothie
#1

I have a stock Kingroon KP3s (the one with the linear rails) which runs on Smoothieware. The first dozen prints or so came out fine, but then I noticed ocassionally the print would fail with the extruder simply stopping mid way through the first few layers. No nozzle clog (extruded fine after resetting machine), no skipping steps, no loss of power to the extruder motor (extruder would still be energized and could not be turned by hand), just no movement from the extruder motor. All other axes would continue on just fine. After resetting the machine and restarting the print, everything would behave normally.

This problem became more and more frequent, until now every print has this issue. The extruder always stops mid way through the first layer, meaning I cannot complete any print.

Any ideas what the issue might be, or how to go about debugging?

#2

More information:
This happens with all gcode files, including gcode files that previously printed fine.
I attempted to print through Pronterface as well, while sending M114 commands to report XYZE positions. It appears that even after the extruder stops turning, the controller board is reporting increasing E position values, suggesting that the board thinks it is driving the motor but the motor is not turning.

#3

More information:

  • Printing via Pronterface: extruder has stopped already -> hit “Pause” on the pronterface GUI -> send G0 E15 -> extruder moves! -> hit “Resume” -> print continues but with extruder still stopped -> hit “Pause” again, G0 E20, extruder moves fine -> hit “Resume” print continues with extruder still stopped
  • Swap out extruder motors, same thing
#4

I had a symptom like this once when I had a slightly loose part in my extruder that occasionally jammed, but it was subtle and moving the extruder by hand would free the jam before I could see what was wrong. It became more frequent over time as it slightly loosened, until I couldn’t get a working print. I eventually discovered that (in my case) it was the set screw in the gear driving the hobbed bolt catching when it moved slightly, and moving it almost imperceptibly away from where it jammed, and tightening it securely in the new location, solved my problem.

The fact that it “is reporting increasing E position values” just means that the software is telling the motor to turn; that is, it doesn’t sound like a software problem. It’s more likely either the stepper motor driver chip or something getting jammed like I ran into.

Since it’s running smoothieware, you can swap drivers for two axes by changing the configuration file and see whether the problem follows the driver. If you, say swap X and E channels and find that now the X axis binds, you probably have a bad stepper driver chip on E. I expect, though, that the problem will stay with the extruder and that you have a subtle physical problem, like what I had.

Best of luck!

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#5

Turns out, bad stepper driver. I swapped the Z and E drivers and the problem shifted from the E axis to the Z axis.

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#6

Huh, I guessed wrong. But glad you know now!

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