Nozzle off, hard to push filament

[jmengel 0]

After a print that failed mid-print, I noticed that the extruder was pushing filament until the pressure built up and it slipped backwards in the bowden. Then I undid the tightening bolt on the extruder and attempted to push filament by hand. It was difficult and the stream of extruded PLA did not appear to be commensurate with the applied pressure. After some reading on the forums, ramping temp up to 250 and pushing, and other incantations I decided to unscrew the nozzle to see if it was clogged with some dirt or similar. Upon removing the nozzle while hot, I found that simply pushing filament through the hot end without the nozzle was difficult. If I managed to push it through, and kept pushing the filament moved through fairly well, but any dwell caused the filament to "jam" or "stick" in the hot end. Any ideas? Is this normal?

FYI this is a v2 hotend with ghagen (http://www.thingiverse.com/thing:15897

) style extruder.

-J

 

[illuminarti 17]

With the nozzle attached, it's deceptively hard to push the filament by hand, except when first pushing a fresh piece of filament into an already hot pool of filament in the nozzle. Once that has squirted out, it can be really hard to keep making forward progress my hand. But with the nozzle off, there's really nothing to impede the filament and I'd expect it to move very easily, to the point of coming out the end un-melted if pushed fast enough (not that I've ever tried it).

So, it seems like there's some sort of blockage in your hot end. My best guess would be some damage or stray solidified plastic, either at the junction of the teflon piece and the PEEK, or the Bowden and the teflon piece.

 

[jmengel 0]

If I push the filament through the hotend quickly, it moves easily. If I let the filament sit in the hotend for a few seconds, with the nozzle off, then it becomes stuck. This is what is happening when printing I believe. The extruder is pushing hard, but the filament is not transferring that pressure to the pool and very little extrusion is resulting due to the filament sticking in the hot end. Prints are thus impossible to complete.

I did not have this problem with the v1 hotend. I did have the problem of the v1 extruder grinding the filament and failing to feed however. Upgrading both has led to the current situation. I'm fairly familiar with the hand pressure on the filament required to generate a given amount of extrusion, at least with the v1 hotend, and the current pressure required is too much. Such that you can easily kink the filament if you are not careful.