Inconsistent under-extrusion

General Discussion
1

Basic Information:

Printer Model: Custom i3 style
MCU / Printerboard: BTT SKR 1.4
Host / SBC: Acer N281G mini-desktop
printer.log (1.3 MB), heattest.txt (22.0 KB)

Describe your issue:

I’ve recently started having under-extrusion issues on one of my printers and I can’t seem to find a fix. It’s an old extruder from an Anet A8 clone, but it worked just fine until now.

Solid infill @ 45 degrees

photo_2024-09-24_18-48-01
photo_2024-09-24_18-48-01576×1280 229 KB

Solid infill @ 0 degrees

photo_2024-09-24_20-20-01
photo_2024-09-24_20-20-01720×1280 272 KB

And this is a photo of a few weeks old print from the same printer, it didn’t have the under-extrusion issues:

photo_2024-09-24_20-51-22
photo_2024-09-24_20-51-221280×720 150 KB

I’ve tried everything I could think of

  • tuned rotation_distance - it extrudes in 50mm when asked to do so and it’s 98.22% of the value based on physical measurements, at 100% it under extrudes about 2mm of filament when asked for 50mm.
  • verified the extruder. The gear looks brand new, the pulley seems good.
  • changed the heat break to an all-metal one, then back to one with a PTFE tube
  • ran PID_CALIBRATE a bajillion times for all the different changes I’ve made.
  • added a MOSFET and tried it on an extra power supply, tried 2 different extra power supplies, just for the hotend, a 12V one and a 24V one (in the logs you see the 24V one with a 0.6 max_power, but I’ve tested most prints at the default value)
  • reverted all slicer settings to the built-in values as provided by PrusaSlicer.
  • reduced the printer speed, increased it.
  • I’ve tested 3 different brands of filament (they worked fine in the past).
  • changed the extruder motor driver and cable – didn’t change the motor
  • tried different temperatures, the temperature seems stable enough, even at 24V with 0.6 max_power.
  • I even played with the belt tension and stepper current (1.5A) for both the extruder and the X&Y axes
  • printed different shapes and at different sizes, but I couldn’t find a consistent pattern

Does anyone have any ideas on what else I should check?

Thank you!

2

The template asked for the klippy.log.
Deleting the requesting lines does not free you from posting that log.

1 Like
3

It’s there, but it’s printer.log, sorry about that.

4

I gave up after a couple of days of trying various things, and I’ve decided to cannibalize a working printer.

Took half of the X gantry and the issue on the problematic printer is gone:

photo_2024-09-25_00-07-17
photo_2024-09-25_00-07-17720×1280 208 KB

It’s a bit under-extruded, but it’s constant, no more bands, so this can be fixed by doing a “measure and trim procedure”, the “new” extruder probably has a slightly different gear.

So I’ve narrowed the problem down to these:

  • extruder
  • extruder motor
  • heatbreak
  • heater block
  • nozzle

I’ve reused the heater and thermistor and I didn’t have to touch the X gantry belt because the gantry is made out 2 printed parts with heat-set inserts that wrap around the rods and a metal plate that holds the parts listed above.

I wasn’t expecting this change to fix the issue.

It’s late now, I’ll continue tomorrow.

5

Have you checked the motor driver - swapped with another one?

6

Yes, I’ve changed it with a brand new one, and tuned the current to 1.5A as per manufacturer specifications, it didn’t seem to make a difference.

7

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