Ok here’s what I did to fix the problem I was having. I drilled a 5mm hole in the new threaded rods. And I know its time to switch to leadscrews. You can see in the pic how it looks. The hole is used to locate the stepper motor so it’s perfectly center. The flexible coupler is now just there to hold it in place. The 2 video’s show the dial indicator as the bed moves up the movement is now 0.01mm other pic is the first print with that done. You can see the improvement over the previous prints.
Nice work. How did you center the rod bore, lathe?
It’s not even really time to switch to leadscrews. Instead of using that 8mm allthread, drop down to 6mm…it doesn’t have enough stiffness to force things around like that.