Hi Maso
In regard to enlarging the hole in the top vertex to take an M8 bolt for your 608 bearing you may run into an issue. My design uses an M5 bolt through the hole and into a T nut in the tower to fix the top vertex to the tower. You will need to fix it some other way if you go with M8. This bolt also carries my two flanged 16mm bearings to form the top idler.
Andy
In regard to enlarging the hole in the top vertex to take an M8 bolt for your 608 bearing you may run into an issue. My design uses an M5 bolt through the hole and into a T nut in the tower to fix the top vertex to the tower. You will need to fix it some other way if you go with M8. This bolt also carries my two flanged 16mm bearings to form the top idler.
Andy