fixed my mid-print failure  

Re: fixed my mid-print failure

You could have short-circuited this entire process by applying generous amounts of alcohol to the operator after the 6th try.

Good job, and a good lesson. If "it used to work", make sure you're replicating the scenario is worked under.

RE: fixed my mid-print failure

Posted by: @sam-h7

I recently had a two day working session with my mk3 to fix mid-print failures, and thought I would share to maybe save someone else some time:

Situation:
1. tried a new iridescent filament at 50 um layer height
2. print failed mid-print due to hobbed gears stripping the filament
3. all subsequent prints failed mid-print for the same reason

First Try:
Hypothesis:
If I increase the nozzle temperature, then it will will not fail, because the filament will be less viscous and will require less force to push through the hot end and so the hobbed gears will not strip the filament.
Test:
print something at 210 °C, 215 °C, 220 °C, and 225 °C, and observe failure
Results:
Filament stripped mid-print at all temperatures

Second try:
Hypothesis:
If I change the filaments to the filament that shipped with the printer, then it will not fail, because the iridescent has particles in it to produce the iridescent effect and they clogged the printer at least partially
Test:
try printing the same object with filament that was shipped with the printer
Results:
Filament stripped mid-print

Third try:
Hypothesis:
If I clean the hobbed gears, then it won't fail, because now the filament is able to get a good grip on the filament
Test:
clean the hobbed gear and idler and print the same object again.
Results:
Filament stripped mid-print

Fourth try:
Hypothesis:
If I screw in the screws that hold the idler to the hobbed gear more, then the print won't fail mid-print, because when i cleaned the hobbed gear/idler i didn't screw them in far enough so the hobbed gear/idler were not properly engaged causing damage to the filament
Test:
Put additional pressure between the hobbed gear and idler, and print the same object
Results:
filament stripped mid-print

Fifth try:
If i run the self-test, i will see a a problem with the fans, because https://help.prusa3d.com/l/en/article/WWVRzOY1dX-clogged-nozzle#_ga=2.190637481.368874594.1530841254-838878222.1512856119 told me i would because i am seeing failures mid-print
Test:
Run the self test.
Results:
Everything is fine.

at this point, it didn't feel like a clogged nozzle...

Sixth try:
Hypothesis:
If i cry long enough, then the printer will magically work, because reasons
Test:
Cry deeply, then print the same object
Results:
Filament stripped mid-print

Seventh try:
Hypothesis:
If I inspect the idler, i will see a physical problem with it, because i checked the low hanging fruit problems with the filament, hot end, and process settings, so the problem has to be with how the extruder axis is interacting with the filament.
Test:
Remove the idler holder and closely visually inspect.
Results:
The shaft that supported the idler had been pushed out to one side, so only one side of the idler was actually supported

Eighth try:
Hypothesis:
If i reset the shaft into both sides to correctly support the idler, then the print will not fail, because the idler will now correctly interact with the hobbed gear and the filament
Test:
Reset the shaft for the idler and print the same object
Results:
The filament did not strip mid print! Horray! However there was a layer shift. Boo.

Ninth try:
Hypothesis:
If i print a 3d benchy and compare it to one that i printed when I first got the printer, then they will look the same, because dnd minatures are hard to print and this particualar one of a grick had attached a piece of the model do the underside of the heater block, which catch on the model and produced the layer shift.
Test:
Print the 3d benchy instead of the grick.
Results:
Confirmed! my fresh 3d benchy looks identical to the 3d benchy i printed when i first got the printer.

Summary
If you are having mid-print extrusion failures...
1. make sure you are printing models of known performance when troubleshooting, e.g., a 3d benchy
2. check to see if your idler is seated correctly

Countermeasure:
simple: routinely check the idler shaft seating whenever one oils the guide rods
cooler: Design and print a replacement part for the printer. One that does not have through holes for the shaft, but rather two pockets that the shaft can load into securely from the front of the piece instead of sliding in sideways.

Hi THere,

that sounds exactly like my frustrating situation and I´m unable to solve it.

I have some trouble to understand your fix (maybe because I´m not a native speaker)what is the "Idler shaft" and how can I check the correct seating ... do you have pics to show it correctly?

Regards in advance

Peter