After building the AM8 MGN12, I realized that the Z motors and the X axis carrier were far too close to each other. This happened I have removed the spring from the bed and used fixed screws to fix the bed.
Even if the X Axis carrier was still fine, the x axis carrier is far too close to the Z motor, only few millimeters above. Even if at first I though it was pretty cool as I was increasing the Z print volume, I realized really quickly that it was not a good idea.
All the printed parts and bought parts have some tolerances and all these tolerances put together are generating an offset in the X and Y direction of the X carrier bold and the linear rod. This generates that the Z axis rod no longer perfectly aligned with the axis of the z motors. Of course the closer to the Z motors, the worse the influence of this miss alignment is visible. On top of that, I realized that the screw was no longer vertical. This generates that, during a Z movement, the x axis carrier was not moving the same way between the two motors.
The error is minimal, but still there. I decided to build the AM8 MGN12 to get the maximum accuracy possible, I just can not leave this problem there and lose accuracy just of a miss alignment of the rod and the Z motors ! It is also clear to me that it will be almost impossible to get a perfect alignment, so I decided to try to minimize the effect.
The first and easy solution was to drop the Z motor holder at the bottom of the Z axis profile is an easy one. This simply increase the distance between the Z motors and the nut, reducing the effect of the miss alignment. Immediately, the rod is no longer wobbling and that is good. It is not perfect, but that is an easy first step.
I only lose a few millimeter of printing height as the X carrier can not go right to the top anyway. The MGN12 axis are still kept in place, just so that when the X axis carrier is touching the bed, the bottom of the Z linear axis are at their end.
The next step will be to reprint some parts to correct the misalignment and to adjust some positions. But that will be another post…