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Extrusion issues UM2+

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I have been having nothing but trouble with my UM2+ recently.

First, 9 times out of 10 the extruder will grind the filament when I change materials.  I have to pull on the filament when its reversing to change materials (and then cut off the part that it started to grind away).

Second, I am having what I can only surmise is under extrusion.

The sides of the model sometimes look like this:


This one is more pronounced (its not the common case)


I also end up with weak infill and walls that do not touch (almost always).


The end result are ugly prints that are very weak and brittle.

Clearly the extruder is not up to the task of pushing the filament through the system (in either direction!).  There are only a few things I could imagine would cause this:

1. The extruder is broken.

(I have taken it apart and cleaned it many times, it looks to be in perfect working order)

2. The Bowden tube is causing a jam of some sort.

(I can easily slide filament through the Bowden tube, with no effort, when I remove it from the machine.  It is also a 3rd party "slick" Bowden tube.)

3.  The PTFE coupler has some material in a "cold zone" that is making it more difficult to push the filament through.

(I have replaced the PTFE coupler a few times because this seems to be the go-to solution to a problem like this, but I would think that ~100 hours of print time at 210c on a TFN coupler from the gr5store would not damage the coupler.)

4.  The Nozzle is clogged.

(The Nozzle is clean, I have done atomic pulls and I can hold it up to the light and see that its empty and the hole is free of obstructions)

5. The filament has gone bad.

(I have tried many different filaments, new and old, from different manufacturers, and this problem persists. Also I try the same filament on my UM3 and it works perfectly.)

6. The Heater isn't heating it up to the temperature that the thermistor says it is so its trying to push  filament out at too low of a temperature.

(Not sure how to test this one without specialized equipment.  I have manually set the temperature to 15c more than I normally print at, and while it helps just a little bit, its not enough to make a difference.)

I did have a situation awhile back when trying to use a Magigoo sample.  Nothing stuck to it and I ended up with a huge glob of melted filament stuck in every place it possible could be stuck in on the hot end.  I cleaned this up as well as humanly possible, but there was filament everywhere, even in the holes in the Olsen block where the heater and thermistor go.

Does anyone have any ideas?  If it is the PTFE coupler again, why do they seem to go bad so often?  What could cause this?

Edited by Guest

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