A part of it is dimensional accuracy from my end as well. M2x6s are small and fragile, so if the holes aren't very accurate and you have to force it through then they can strip more easily, and can even break.I have found a little time to work on the 40 build. It’s moving along pretty good. I must say the m2x6 screws are a real challenge. Apparently there isn’t much quality control on the heads of these screws. My bit fits all of the other m2 screws very well but those 6’s are not so good.
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If something becomes too problematic, we can consider using heatset inserts. I use those in their M3 variant to secure printed printer parts to the printers, and they work quite well. Example in photos of how i used them to secure my heavy hotend assembly to my 3dpringed linear rail adapters.
There's tuning and then there's fine tuning, which is what I have been working on and will always try to improve on. Last photo is the first 40s part I printed on the updated motion system, and i can see through the smaller holes more easily. Hopefully that will translate into easier assembly.