under-extrusion problem

[jbishop 0]

I'm getting an under-extrusion print failure at a similar place in a particular piece, while other pieces have printed normally. I understand that two primary reasons for under-extrusion are clogging in the printhead or deformation of the ptfe coupler, but the way this print job fails only after over an hour of correct printing, but always before two hours, doesn't seem to match up with either possibility.

https://www.dropbox.com/s/ig5tdwh308g1lnd/20160615_120430.jpg?dl=0

Ultimaker2

Cura 15.04.5

I'm using pretty standard settings for PLA 210/70 degrees and rather slowly 40 mm/sec, 0.1 mm layer and 0.4 mm nozzle.

Any thoughts appreciated, thanks.

[IRobertI 521]

Is the fan at the back of the print head running properly?

[jbishop 0]

Well I can say I hadn't even noticed that little fan back there before, but I see that yes it is running. Another problem with this piece is that I was getting stringing on the one side of it, and wondered if something like that could mess up the flow of the plastic. I think I managed to get rid the stringing by turning the Enable Combing off, am printing again now to see what that does.

[gr5 2,230]

Is it hot where you are? sometimes the heat from the extruder motor combined with unusually warm weather will heat PLA enough that it softens at the knurled sleeve and grinds to dust at the feeder. So if room with printer is unusually warm try a desk fan blowing on the feeder.

Also I don't know if your part has tons of retractions - it doesn't look like it - but who knows - if it has say 10 retractions for every spot of filament (same filament goes back and forth 10x thorugh feeder) then that can also grind up the filament at the feeder.

As the feeder driver chip on the PCB under your printer heats up it gets weaker. That might also be getting too hot. Consider removing the cover and printing on a tilt with a fan blowing air under there. If for nothing else then as a test. The UM2 can print just fine upside-down or sideways.

Still, don't rule out "bad ptfe". You have minor underextrusion on some of the lower levels of the part so I would also change the ptfe to the new kind of teflon. Try shop3d.ca.

[jbishop 0]

Interesting. It is certainly warm in our building as the management has continued to chip away at costs and every year the thermostat setting for the air conditioning inches up. The printer is sitting in a corner of the lab where the air circulation might be expected to be lower. So I'll definitely look into that, as well as the altenate ptfe material.