1.) You appear to be on to something here, though, I am not sure if its the whole thing. When I did a test print with the fan turned off the under extrusion seems to be reduced. Still present, but reduced. It occurs to me that a difference between the working UM1 at home and this one is that I printed new fan shroud for that one. Is there one you would recommend specifically? 2.) I just replaced the thermocouple so it seems unlikely. If it is the thermocouple it is at the very least consistent. I have watched the temp reading during the print and it never varies more than a degree (Except when the fan kicks on but that is quickly recovered). How can I tell if it is boiling? Just heat it up and listen and watch for bubbles in the filament as it oozes out of the nozzle? 3.) I have never printed ABS, and as I mentioned the nozzle, brass insert and peak tube are all brand new from UM, so clogging in there from gunk seems unlikely. 4.) I will have to gather some equipment to perform the test you suggested, but I will say that in the past when cleaning the nozzle I haven't ever found any wood debris.
I have had this UM1 for a year and things have gone well. Lately however I have been having problems with sporadic under extrusion. I was compensating by printing hotter and hotter, but once it got to 255 I finally ordered some replacement parts and started trying to get under control. Between my fully functional UM1 at home's parts and replacement parts I have replaced the Nozzle, the brass insert, the brown peak tube, the thermocouple, the wooden feeder gear and knurled bolt thing inside. I am using brand new silver filament from Ultimaker. I have measured it with calipers to be 2.85mm. I print at the Cura default speed of 50 mm/s and a layer height of .2. I have examined the roller wheel on the feeder and I don't see any dents or damage to it. The filament in the bowden tube does show signs of stripping when the under extrusion happens I have been printing at a temp of 220c for as long as I can remember, on this printer and the one at home. The one at home still works just fine at 220. Right now it seems like 230 is the magic number on this one. Anything less and I get sporadic spots in the print where their will be dotted lines where filament didnt properly extrude. 230 isnt terribly hot but it doesnt cause subtle drooping in some prints and I worry that if I let it go I will be back up to 255-260 before I know it. Any ideas as to what is going on? How can I get this thing working smoothly at 220 again? Snapshots -------------------------------------- Mid print snapshots while printing at 220c: https://www.dropbox.com/s/7pmg3s1pfbb2czr/2014-05-27%2015.56.07.jpg https://www.dropbox.com/s/kst5pzqvl3hf3zw/2014-05-27%2015.56.23.jpg The cube on the left was printed at 230 while the one on the right at 220. https://www.dropbox.com/s/s15jf97t7mf1pho/2014-05-27%2016.02.28.jpg https://www.dropbox.com/s/i2x3oiwsf4awpna/2014-05-27%2016.03.06.jpg