Thank you for the reply.
I haven't tried the "unencumbered" extrusion yet. How can I check the amperage?
I had thought it might be the bolts circumference as well, but it didn't line up.
I checked and cleaned it again, printed slow again. Worked relatively well but the problem came back.
I've had the problem with different filament types.
I haven't noticed anything major wrong with the temp. But to be sure I increased it a fair bit.
The filament feeds quite easily into the bowden/hot end when I feed it by hand, I can't see an particular reason for it to be binding or anything.
It's a fresh nozzle and I've done cold pulls to be sure.
One thing that's been quite consistent is that I am always able to get a really good start to a print, and then after a little while it will have this underextrusion problem. Sometimes it's after 5 or 6 layers. Last print it took an hour (~50 layers). I checked the filament and everything that had passed through the bowden and extruder looked great up until when it started to grind.
Everything but the extruder has been, I believe, eliminated from my troubleshooting.
I know the motors always run a bit hot, but is it possible that the extruder motor is running so hot the hobbled bolt is slipping because it's too warm? The extruder motor is super hot to the touch. Even when going at 20mm/s.