After reading this article I’d like to know more about the used components:
belt type (GT2/2mm?)
pulley - #tooth
stepper - resolution (0.9 / 1.8?)
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@SusisStrolch Again an interesting thread you found! 
From the firmware I got 116.36 steps/mm.
From the BC part I measured the belt pitch is 2.5mm
by trying here:
I assume the Pulley has 22 teeth, if the motor is 1.8° per step, which I think it is.
The decay of drv8825 is according to the schematics at +5V.
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If I didn’t make a mistake best should be 0.17mm (0.1699593) layer height 0.1375 or 0.275 are exact multiples of an half or full motor rotation 0.1385 should give a fishy result?
This is a very interesting topic. Thanks for sharing the link!
I am reminded of a problem I had on my K8200. When the belts/pulleys were out of alignment, I would get stepping patterns in my prints, but when the pulleys were properly aligned, these artifacts would go away.
In theory, if the belts are tensioned and aligned properly then the number of teeth will be irrelevant. The belt should mesh with the teeth, and no positional errors should ever occur as a result of the teeth. Before masking the problem by optimizing the layer height, I would first make every effort to align and tension the belts. The better you get the machine adjusted, the better a baseline you will have for subsequent optimizations. (NOTE: Having the belts either too tight or too loose will cause problems.)
I am also reminded of a discussion in the K8200 forum about using DRV8255 stepper drivers, in which someone posted a diode fix for the stepper asymmetry. Here is the link to that discussion:
I tried to print the vase mode cubes at 0.14, 0.1375 0.17 0.2 0.2225 mm layer height. The patterns are hardly to see and as expected 0.17 is almost pattern free but 0.2 is almost as good. I conclude: Velleman did a very good job here in designing this printer. 
The belts are T2,5 profile 5mm width 1300mm length loops. According to this.
The steppers I bet are typical 1.8°/step NEMA 17’s. In the firmware the steps/unit is set to 116.36 which means 1/32 microstepping if the pulleys have 22 teeth.
As to the patterns I print @ 0.15mm layer heights and see no patterns at all. I would love to put Trinamic drivers into this printer but I guess that would require ordering a new PCB altogether maybe with typical step stick headers or with TMC drivers soldered during assembly.
Thank you @shelxle for the values, they are implemented in the latest 1.1.9 firmware (don’t know who’s who from here to github 
)
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