Mini underextruding after a while


I have a relatively new Mini (a few weeks old) and yesterday it started under-extruding partway through a print. It first happened a couple hours into a fairly complex print. After that it was under-extruding on simple prints too.

This morning, I switch cura over to the default settings and tried again. About fifteen minutes into a relatively simple print is started happening again. But for the first 15 minutes, I had no trouble.

If I have the Hotend heated to 200 and I manually extrude some filament (10), the mechanism seems to lock up periodically (I can see the large gear stop temporarily). If I release the tension holding the filament to the extruder wheel, the mechanism no longer binds. But there is some clicking noise in at some points (not motor noise).

I’m printing with 3mm PLA Filament from ic3d and removed about a foot of material to no effect. I’ve gone through the nozzle clearing process a few times and get the expected shape at the end of the filament with the exception of the tiny 1mm extruded bit at the tip.

If the gear mechanism does need oil, do I just apply it to the bearing on the front of the mechanism? If it needs cleaning, do you have a guide taking it apart?

Any other ideas?

Don’t oil anything – there are no extruder parts that need lubrication.

If the large gear is stopping/starting during a manual 10mm extrusion, that sounds like a loose set screw on the small gear of the extruder – which is allowing the motor to intermittently turn inside the small gear. Check/tighten that set screw (there is a “flat” on the motor shaft, so make sure that is aligned properly when tightening the set screw).

The other typical cause for extrusion stopping mid-print is “heat creep”, where the filament softens in the heat break (the finned area above the nozzle and melt chamber). But that back-pressure isn’t enough to stop the extruder from turning, so the gear continues to turn and the hobbed bolt chews a half-moon shape into the filament. If the gear is actually stopping, then either the set screw is loose/missing or (less likely) there is a problem with the motor or motor driver.

Is there a guide or diagram for doing this?

Ah, never-mind, I think I figured out the setscrew. So far it looks to have fixed things.


Great! For future reference, the entire extruder assembly instructions are here (small gear / set screw starts at 21):

Of course that addresses initial assembly rather than “in place repair” – but still provides a good starting point.