I'm printing for the first times on my new Sovol SV04, using their PLA @ 210 °C (after printing a temp tower).
The walls and top layers are almost perfect, but the infill has a lot of gaps between layers:
I'm not sure which parameter needs to be tuned, since the walls are ok and I'm afraid to make a mess...
What could cause this behavior?
The infill speed might be set too high, but it's possible this is just some of the normal badness of self-intersecting infill like "grid" and "triangles". If you notice, these patterns have the extrusion path cross back over itself once or twice at the same points. Hitting this barrier of material already being there when the nozzle gets to it causes a rapid spike then drop in backpressure in the nozzle, and tends to make material push upward around the sides, and then underextrude right after the intersection point. This could be the cause of what you're seeing.
If so, there are several possible ways to improve the situation:
Use a non-self-intersecting infill pattern like gyroid.
Print the infill slower. The effect is lessened by slower motion.
Print hotter. I'm not sure why this works, but it does. It might help re-melt the intersection point when slamming through it, or it might just make flow more consistent and less susceptible to the pressure swing.
If this isn't the issue, other things to check for:
That flow % for infill hasn't been turned down in slicing settings.
That your infill speed times line width times layer height (in units if mm³/s) is within the flow capabilities of your hotend and extruder.
