I'm new to 3D printing, so please forgive a noob question. I've tried a few different settings in Cura slicer and the walls of my prints consistently have gaps between them. I checked all the suggestions in How to fix wall separation in 3D prints (gaps in between wall perimeters)? and I do not see an improvement. Printing plain PLA at 220 °C on an Ender 3 Neo with a direct drive and 0.4 mm nozzle.
From the underside, the bottom layer is nicely merged
The result looks fine externally, but the gap between the walls looks huge (relatively speaking)
Here are my slicer settings. I increased the line width, infill overlap percentage, and wall line width. I slowed down the wall speed. and I get the same result. From what I've read, this is under-extrusion but I don't know what else to try.
I watched a video about tuning the flow rate using a 20 mm cube and measuring the wall thickness. This confirmed the under-extrusion. I increased the flow rate on the Ender 3 settings, which definitely improved things. I also tried increasing the Wall Flow rate in the slicer. This worked too.
I went from 100% to 127% based on the ratio of the actual wall thickness to the expected wall thickness
I'd like to understand why only the walls are under-extruding
