# Partial underextrusion in walls

I'm facing weird "pillars" of underextrusion on outer walls of my XYZ test cube.

On the pictures below Ive printed PLA test cubes with a 0.4 mm nozzle, 0.2 mm height and 210/50 °C hotends/bed temperature.

Gaps are appearing in walls parallel to both X and Y sides. The pictured side is parallel to Y face.

I'm slicing with Cura, my printer is a homebuilt around Anycubic Kossel with Marlin 2.0 onboard.

1. Temperature from 190 to 210 °C
2. Retraction from none to 6 mm 60 mm/sec
3. Tuning down Jerk in Marlin from [10,10,0.3] to [5,5,0.3]
4. Tuning down acceleration from 3000 to 1000
5. Tuning print speed from 60 to 30 mm/sec 6. Checking belts, nozzle and extruder.

Now I just ran out of ideas. Delta is calibrated by G33` autotune. Mechanics looks just fine. What am I missing?

UPD1: tried removing combing - it did not help. But I noticed that my printer accelerates strangely at this parts

UPD2: could it be stuttering? I have 320 segments per second with block buffer size of 8 bytes(?)

UPD3: lowering segments count to 120 and raising block size to 32

• Welcome to 3dPrinting.SE! Could you help us out here and orient the print for us? What side exactly are we looking at in the images? Being specific about which direction the print is printed in (ie: X/Y/Z axes) will help in the diagnosis. Feb 17 '20 at 23:02
• Are you sure it's actually underextrusion? It looks like the bulges in your walls coincide with where the infill lines hit. Is it possible that you have too much play in the delta mechanisms such that these lines overshoot from momentum of the head? Feb 18 '20 at 14:43
• Not sure about the extrusion, actually. I've checked the play and the head stands still. Feb 18 '20 at 15:06