Evenly spaced sections of alternating thin and thick filamen

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Re: Evenly spaced sections of alternating thin and thick fil

Post by ednisley » Wed May 07, 2014 5:07 pm

format13 wrote:stripes of perfectly normal layers, and stripes where no filament is extruded...
It looks like alternating bands, each with precisely 16 threads: one set normal, one set under-filled. That suggests a problem connected to the extruder motor rotation, rather than anything in the hot end.

If the tiny grub screw that locks the drive gear to the gearbox output shaft comes loose, you'll get terrible retraction (which we can't see in that single layer) and weird extrusion effects. But the relentless regularity suggests the reduction gearing between the extrusion stepper and the drive gear is going bad.

Draw a line across the stepper shaft (on the back of the motor), mark both the drive gear and the output shaft (on the front of the motor, hidden by the fan), and mark the filament every 10 mm. Print another wrench and watch what happens:
  • If the stepper shaft stops turning, I'll be surprised
  • If the output shaft keeps turning and the drive gear stops, tighten the grub screw
  • If both the output shaft and the drive gear stop, the gearbox is bad
  • If only the filament stops, check for crud in the drive gear teeth
If everything keeps turning & moving the way it should, but no plastic comes out the nozzle, the extruder has a hyperspace shunt in full effect!

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