Thats an unusual one. It definitly looks like a bit of underextruding, but that shouldn’t be causing the extra plastic loops. From the print image I can see it’s entering the new layers right around those 4 points, so it probably is some sort of nozzle ooze related issue, which would make sense that retraction affects it. Thats a fairly large amount of material error right at that spot not to show up as effects anywhere else in the print though.
The amount of material shown here is about the least I can get it down to before it starts skipping. I watched it print many time and it’s a bit of ooze that’s is indeed getting wiped onto the walls. As the print progresses, the hotend passes through the “gunk” and eventually starts dragging it around and making a big mess…
Check the extruder out really well. Is the small gear on the extruder motor locked down and tight on the motor shaft? Is the large gear excessivly worn and or able to move on the hobbed bolt without actually rotating the hobbed bolt? A Taz 1 had unsealed 608zz bearings in the extruder itself, check the idler arm bearing and the two bearings on the hobbed bolt and make sure they are still turning correctly and smoothly. It wouldn’t be unusuall at all for any of those bearings to be putting excess resistance on the hobbed bolt.
I recently printed new gears and there isn’t much slack I can feel between the gears and nothing turns that shouldn’t. I’ll check out the bearings.
Maybe check the hotend too. make sure the peek isolator is not melted or out of true in the bore, that everything is alligned and fillament isn’t binding at the junction between the extruder and the hot end. You may also want to run some extruder calibrations and see if your e-steps is off at all. (http://www.instructables.com/id/How-to-calibrate-the-Extruder-on-your-3d-Printer/)
I just swapped the hotend out and the problem lessened but it didn’t go away. The hotend that was on the printer had
what looked like a longer barrel (part between the heat sync and actual hotend) and I theorized it was heating up extra material and therefore increasing ooze. As mentioned it helped but didn’t completely fix the problem. I also checked the e-steps but the Taz1 doesn’t have a display and I didn’t have the time/energy today to reflash. FWIW, one extrusion measured 94mm, the other 98mm. Both should have been 100. I measured 120mm from the top of the extruder, marked with tape, extruded 100mm and measured from the top of the extruder to the tape. Should have been 20mm, right? One was 26, the other 22.
You might also try upgrading the Slic3r version you are using. if you are using the stock taz 1 software, that would have came with an older version that had some circle issues.
I’m using Simplify3D. I’m going to try both Cura and Slicer to see if either make a difference. If it does then I’ll dissect the settings.
It also looks like your belts might be slightly loose. It could just be the STL file, but the round area of the inside of what I am assuming is some sort of fan bracket looks slightly flat in segments, which can be an indication of a slightly loose belt.
I’ve checked the belts but they also may be worn, I’ll give them a recheck and/or replace them, thanks!
Thanks for the feedback, I’ll give this a look next week when I get back to work!