So I bought myself a used Vellemann Vertex K8400 3d printer. While it looks cool and I found quite positive reviews, I have to admit, that this printer was a false investment. Too many things are just not right with it (I’ll give you some keywords, there is enough info on the web: Loud, Threads on the Pulleys, uncommon Belt type, Hotend, Stepper drivers).
Anyway, I had a problem with massively shifted layers mid print (1-2cm). At first I thought, this would have to be the Stepper driver. As it only happened on the X-Axis, I swapped the X and Y driver, to see if I can move the problem to the other Axis – wrong.
General Advice on shifted layers is checking Alignment – you can read a lot on the web about it. Alignment was fine.
Next easy step was to mark the pulleys, Axles and stepper Axle, to be sure that there is no belt slippage or pulley slipping. Unfortunately, everything was tight.
So I continued, as I was sure, that it is not an alignment Issue, I swapped the Stepper Motor from the Extruder with the one of the X-Axis. Problem still happened on X, so I could rule that out as well.
I got to a point where I was sure that this must be a problem with the Mainboard, which costs more than I want to invest into that printer. So I asked myself, what can I do without buying a new Mainboard. This was the moment when Software came into my mind. The K8400 uses the Marvin firmware, and this is open source. So it was easy to configure the X-Axis Pins with the Y-Axis pins and vice versa in pins.h of the marlin firmware, Swap the Stepper motor connectors and Test. With this, I was able to rule out the Mainboard, and stepper driver. In case it would be the Mainboard, I could use the Stepper Pins from the secondary extruder that I don’t have.
It all sounded so good, but the shifted Layers didn’t disappear. I measured the motor Cable, 0 Ohms on all leads.
To sum up, I had ruled out:
– Belts / Pulleys.
What was left? I removed the stepper Motor again, and this time I also removed the X Belts. While moving the axis, it got stuck without the belts, but when I had the belts on, it didn’t get stuck.
Turned out, that one of the “bushings” on the X-Axis had two loose hex screws, it seems that under some circumstances it tilted when changing directions.
Two loose hex screws that cost me about 300g of PLA and I don’t want to know how many hours of troubleshooting.
I hope this helps someone else when troubleshooting a K8400 or other 3d Printer.