Need help withe z axis video aatached

the z axis works fine it the bottom bot when he rise above 6 cm from surface he start to do problem like in the video.
whats the problem?

Z-axis is loosing steps.
May be friction or current limiter for motor set too low?

I try to play with the limiter it didnt help.
And if this is rhe problem why it works good at bottom?

I am not able to determine exactly what is going on, except the losing step thing.
If you take out the Dewalt, making the axis lighter - how does it perform then?

The only reason I can think of causing the axis to fail at the top is that the mechanical resistance is greater at this point, to great for the motor to overcome. Increasing the motor current limit may only cure the symptom, my advice would be to dismantle the Z-axis mechanics and check for foul play.

There have also been reports of the top ballbearing not seated fully on that axis, bent ACME rod/too tight Delrin block

What is the ambient temp inside the room the carve reside in? Colder temps make the Delrin block tighter. Dry lube/graphite might improve the situation if that is the case.

Do you have proper spacers? Is your acme rod straight from bottom to top?

make sure that you acme rod is not bent

I would put a touch of lubricant on the acme rod

but something is binding for sure

I would power down the machine and turn the belt by hand and see if you can locate tight spots and then loosen things up a bit until the binding stops then you will have located your problem