Thank you for your reply. I saw the videos as well. Also, I assembled this several times. However, it is locked when I screwed the (8) M6 X 14 socket head cap screws. I think the spindle dimensions, especially its height and J1 turret platform are not very accurate. I bought the aluminum kits from Annin Robotics. The only way is to put the (4) M4 x 10 set at a special distance from the bearing and not tighten (8) M6 X 14 socket head cap screws. However, in this way, the (8) M6 X 14 socket head cap screws can be rotated by hand. What is your opinion?