Summary: I solved under extrusion problems by raising nozzle temperature to 220°C.
My first test print came out pretty good. So I moved the printer to my office so I could run some more test prints while I work. Using the same exact settings as the first print, I printed another Ultimaker Robot. The results were horrible!
I did some reading on the internets and figured the problem looked like under extrusion. The nozzle was not putting out enough PLA, leaving all of those ugly gaps. Under extrusion could be caused by a variety of things: clogged nozzle, slipping filament feeder, incorrect filament diameter setting, etc. So I reached out for some advice on the Ultimaker forum. I was directed to some useful posts on print quality and troubleshooting. Incorrect temperature can also affect print quality. If the filament is too cool, it will flow more slowly through the nozzle. Following Occam's Razor (the simplest answer is most often correct) I decided to increase the temperature setting. The default setting for PLA was 210°C. So I bumped it up to 215°C and tried again.
|printed at 215°C. getting better|
|back view at 215°C|
The resulting print was immensely better and maybe just a little better than my first print. But there were still some minor signs of under extrusion. So I changed the PLA setting to 220°C and tried again.
|printed at 220°C|
I noticed that the prints stick to the glass much tighter at the higher temperatures. At 210°C the prints pull off pretty easy. At 215°C the prints stick really tight. I think the gluestick might be overkill for PLA prints on a heated build plate. Looks like the higher temperature pretty much eliminated the under extrusion problem. No more visible pits in the walls of the print. The overhangs still need some work, but that's a different problem for another day. I'm loving this printer.