Randomly underextruding/overextruding small part on CR-10

Question

I am printing fairly cheap, but highly rated, PLA and not sure whether this is underextrusion or overextrusion; but it just looks bumpy and not clean. My settings:

• 195 °C at 60 mm/s bed temp 50 °C
• 0.4 mm nozzle at 90 % extrusion
• 0.1 mm layer height
• 6 mm retraction at 60 mm/s with 0.50 mm coasting

I tried at 190 °C and it severely underextruded halfway through, but the outside looks much smoother; I also tried with and without coasting with no difference and tried adding -0.2 mm extra restart distance which didn't change much either. Could this be because I am just printing a rather small part (25 mm diameter)? I think this because I tried printing a much larger 100 mm diameter hemisphere just before, which printed perfectly using the exact same filament.

I've switched out to a new 0.4 mm nozzle, tried a 0.6 mm nozzle, but the only complete print I got had this rough and bumpy outside. It is printed in the orientation shown as removing support from those thin legs lead to them snapping.

I also had moderate stringing throughout, which I thought coasting and restart distance would fix.

Any ideas would be much appreciated.

Edit 12/04:

I have since reinstalled one of my all metal hotends, as I wasn't using them due to clogging issues, installed a brand new 0.4 mm nozzle, set the extrusion multiplier to 1.0 and disabled coasting. I also calibrated my e-steps, which means I needed to buy an arduino and burn new firmware.

Sadly I didn't print in between fixed, but these are the results I got.

The prints are much better but there is some pretty serious stringing and zits due to me needing to reduce the retraction distance for the hotend to 2 mm, as the 6 mm distance I was using before would make it clog; but since I'm using a bowden extruder it creates stringing. How could I go about fixing this? I feel like I'm playing a game of whack-a-mole.

Answer 1

The first one has major extrusion problems going on, possibly combined with issues caused by things you did to compensate for it or other issues. You should not see "bubbly" surfaces like that. There are a lot of things it could be, but my best guesses are wet filament, clogged nozzle or damage in the ptfe tube (if your printer uses one), and your 90% flow rate. If it was really printed "right after" the successful hemisphere that probably rules out wet filament and indicates a clog of some sort or your changes to settings.

Your retraction amount is probably good if you have a bowden printer but excessive and likely to clog with direct drive. Coasting and extra unretract are always wrong; they were a hack from a long time ago trying to simulate what linear advance feature in firmware does, but with a fixed hardcoded offset. Flow rate as low as 90% is also wrong unless your steps per mm were miscalculated. You can only go up/down by a few % without messing things up badly; there just isn't that much room for error.

Answer 2

I just saw your update so I'm adding a new answer to address it specifically. Your print looks much better, and all the remaining problems are likely caused by Cura's bad default Limit Support Retractions option. It causes Cura to skip retracting when moving from one support structure to another, producing heavy oozing/stringing there and leaving insufficient material in the hotend for whatever is supposed to be printed next. This will result in underextrusion and other problems. So, turn of off.

If you have any additional weird options like Coasting or extra unretract after travel, disable them too. These intentionally do the wrong thing trying to compensate for other things being wrong, rather than fixing the core problem. Depending on whether you tuned your retraction to settings like this you'd changed, you might need to re-tune retraction too.