3mm PLA grinding

I have seen the previous topics and it’s not heat creep (laser thermometer tested), it appears to be either the PTFE tube is too small, or the idler is just loose enough to grind away at it slowly if it slips. also, it only happens after a retraction, we printed a cube with no retraction and it came out perfect, but we tried printing the MAKE torture test from the 2013 printer roundup, and it failed on the 3rd layer. we printed a 20mm cube, more fillament went into that than the 3 sucessful torture test layers (at least based on cura’s estimate)
printer: TAZ 4 (guava in the devel files)
Extruder/hotend: stock 0.5mm
Fillament: 3mm blue PLA from lulzbot
temp: 195-205 (tried 3 times)
bed: 50
slicer: cura and slic3r
host: repetier-host/server on an imac/rpi (imac with host and pi with server)

I know the default settings for retraction in Cura are 40 mm/s and 4.5 mm. These are too high for the TAZ, as it is carriage mounted extruder (as opposed to a bowden setup like the ultimaker). I would recommend anything between 10mm/s and 30mm/s for the retraction speed, and .5mm to 1.5mm retraction length, depending on material.

I doubt the PTFE is too small, unless you are running some oversize filament. Is it easy to feed through the extruder manually or does it require quite a bit of force?

Is there any chance you can post some pictures? Seeing the failed part helps a lot with diagnosis.

sorry, don’t have any pictures to post as of now, but I did turn down cura’s retract settings quite a bit (30 and 1mm) and both cura and slic3r have had problems, so I doubt it’s my configs. if you know the few blobs that come out of the hot end when just starting the brim, that’s what’s happening here, just midway through the print. as for fillament feed, after taking a closer look at it, it seems to be just fine for the PTFE tubing size. I’ll see if I can get a picture of the fillament next time this happens

Now I have pictures, they can be found here: http://imgur.com/a/QkLdl
the octopus had no problems (no retractions were heard)
and I just realized something, it clicks really loudly when it starts skipping, it also is really hard to extract the filament after it grinds it down
distance from clamp screws to plastic part: 10.5mm top, 7.5 bottom
the sides of the tardis are fine, but the problems start when the retractions start

Are you sure the nozzle diameter is 0.5? Our stock TAZ ships with a 0.35mm hot end. Your retraction settings seem fine for Cura. What is the size of the compressed spring on the two extruder screws?

yep, it looks like a 0.35 nozzle, don’t know where I got 0.5, will check BoM when I get the chance to see if it came with a 0.35 or 0.5 nozzle (the printer is in a different class)
EDIT: BoM says it’s 0.35 mm, facedesk
EDIT: still happening, will try adjusting filament diameter and flow rate