Hello all,
I recently purchased a 3D printer, and it seems there are some issues. There is a connection between the Z motor and the threaded rod using a beam coupling. The issue is that the stepper spins alright, except the rod doesn't start spinning, and then suddenly starts spinning and moves off the stepper and starts moving up off the 3D printer.

https://www.youtube.com/watch?v=TtlYJFSl_pY

Please help!

Thanks