Prints Failing Midway Through While Topping Infill (Stops Extruding)

[willjtucker 0]

Hi folks!

Been working with some his UM2 for about two months now. It's in a student lab in our University and is getting quite a bit of use. It was working fine up until about 3 weeks ago, when it started having major underextrusion issues. These issues were mostly quelled with @iroberti 's feeder and spool holder, and Steckdosentier's filament guide pulleys, as well as tempered speeds. However, then a new problem sprang up: prints started failing midway through for no apparent reason!

After a number of prints and experiments, I determined that this occurred as the print was transitioning from infill to a solid top, or shortly thereafter. Here are a number of pictures of failed prints. As you can see they are at different heights with different geometries. The main commonality is the topping operation. The filament seems to get caught in the hotend, because nothing comes out but the feeder still feeds (and either grinds away filament or skips away depending on the tensioner setting).

Standard Black PLA/PHA filament from colorFabb, most at 230C, layers ranging 0.12 - 0.18mm, general speed 50mm/s with more speeds in picture, with retraction unless noted

     

Here are some images of the filament tips removed after the failed prints. Even after heating up the hotend to 260C, I was unable to retract the filament via the motor or manually. I ended up pulling the bowden tube out of the head, which removed the filament with it. This showed that the filament had mushroomed and could not be pulled back through the bowden. Inbetween each failed print I did a number of atomic cleanings, the results of one are seen below.

 

I've double-checked the diamenter of the filament on the spool (2.80-2.82mm) and the extrudate diamenter (.36 -.47mm). Here is a photo of the extrusion test cylinder sans retraction (could not find retraction version -- @illuminarti could you please upload those gcodes [retraction & no retraction] somewhere? -- they no longer are attached to the forum thread). All good except for some slight underextrusion on 10mm3/s. Same material, 230C.

After reading through the entirety of this thread and many others, printing test cylinders, and generally banging my head against the wall, I have some hypothesis and some questions and I think the community might be able to help:

Hypothesis #1: The PTFE coupler is shot. Why? The printer ran for a few weeks with the fan cables switched, so the right fan was always on and the back fan only came on into the 2nd layer. From what I've read, this could mean that the PTFE piece is damaged from the heat. This might also explain the strange looking filament tips upon removal. I don't want to disassemble the hotend until I have another coupler in hand in case it breaks.

Hypothesis #2:  The stepper motor is faulty. Why? It recently started making a lot more noise. Besides the occasional skip back, there is often a constant clicking, as can be heard in this video. This corresponded roughly to the point at which I switched from the stock feeder to Robert's, but I don't have any evidence on causality there.

http://youtu.be/pDSEcBNTj28

Hypothesis #3:  Something is wrong in my Cura settings. Why? The problem only occurs during this one type of operation, which is heavily dependent on the speeds and movements of the head.

Questions

 

• Is the stepper motor OK to be making those noises?
  
• What do you think about this behavior and these hypothesis?
  
• What are my first steps in further troubleshooting or remedying the problem?.
  

 

Thanks so much in advance for your help! We've got a lot of students trying to use this machine and it's killing me to not have it meeting, let alone exceeding expectations. I also can't afford to babysit it any longer..

Will

Edited May 26, 2015 by Guest