Thanks @Walter_Hsiao this is highly appreciated. Independent from your answer i investigated a bit more yesterday when continuing the build with my friend. I think there are multiple problems. One for sure is that the quality of my print isn’t really good. The holes aren’t as good/round as they should be - especially the one that is printed horizontally. That is mostly due to the missing cooling fan on the ordbot. I’m in the process of designing an extruder for the printrbot gearheads. This will be a direct drive and hopefully Filaflex (like ninjaflex) should print well there. Also i have ordered some adjustable reamers to be able to ream the wholes to a constant diameter and make sure they’re round. The shorter flex rings are a good idea - maybe i’ll give that a try.