Skipped layers

[Reaping miner]

I don't see the problem at the place where holes start at all. If it is the steppers then you will just see a repeated pattern that is related to the steps per mm and you layer height.

Print a 10 mm square 50 mm high without any holes or sticky out bits or anything, see how that looks.

Print it solid then hollow then with say 15% infill. Do it as three separate prints, not all on the same print.

Here are the testprints that show the skipped layers, but not show the most obvious flaw present in the extruder, which i believe is an unrelated issue.



I am now printing a 15x15x50mm bar at the same settings as before, except for the infill, only 15% instead of 30%. (10x10 is too small, that will print too hot. A nice stepping effect is seen as the area of the layers get smaller, especially in the negative control "pyramid". Again this is why i was printing the extruder body in the first place.)

It looks like the corners of the objects are curved, this is an artefact of the camera, the corners are straight, only a little bit of elephants foot is present. This is caused by the overextrusion at the start i mentioned before.

Also one arrow in the right "pyramid" points at a line in the Z axis at an area transition layer.

Some thoughts...
To eliminate one possible issue, try a print without heating the bed. I realize you have an aluminum heatbed and it might make a difference, but multiple people have demonstrated print artifacts being caused by flexing of the bed heater as it cycles on and off using the normal Marlin bang-bang heater control loop. Migrating to SSR and PWM control of the bed heater is the solution for those artifacts.

What are you using for a filament spool mount? The filament spool needs to unwind very smoothly. If it doesn't (like if you are using the MakerFarm scheme where the filament spool sits on a fixed bar), the filament might be tugging on the extruder until the spool springs free and rotates a bit to relieve the tension in the filament. IMO, the extruder mount on these printers isn't rigid enough to not be displaced by this tugging. Is your hot end a snug fit in the extruder body? A loose fitting hot end would make this worse. Many people have added a thin spacer above the hot end to provide a more solid fit.

I will give printing without a heated bed a try as well. I do want to add that i am actually printing on a piece of glass clamped on the aluminium heatbed (MUCH better adhesion of PLA). Also i do think i am using the fancy mathematical kind of BANG-BANG temperature control (PID?), not the dumb heat ON if its under and heat off when it reaches the temperature. I did notice wobbling/ribbing in the prints of extruder gears. This wobbling/ribbing is entirely different from the problem described in this topic though. That wobbling is much smoother and very regular. (Remarkably this wobbling seems to only be present on the gear surface and not the central structural bit holds the hobbed bolt and the nut.)

I am using a threaded rod with 2 nuts to lock it in place as a filament holder, mounted on top of the printer. The issues are not caused by the filament spool, i have had that problem before (filament unwound and got tangled), that causes more serious and irregular faults, it is also very audible when sitting next to the printer when it untangles or if it stays tangled the print will fail entirely and the filament will obviously be stuck when you look at it later. The hotend is fairly snugly fit. However the extruder (+carriage) itself is not as rigid as i would like. This will be replaced together with the extruder. I plan to print or design a carriage that can better clamp the IGUS RJ4Jp bearings. (I really dislike the zipties.....)