Prusa i3 rework (pcb) milling system

The system is made to switch back and forth between 3d-printing and milling as fast as possible.
It consists of the holder for the proxxon flexishaft micromot 110/P (can be attached to a dremel too) and an attachable z-axis pushdown system.
The problem with the Prusa i3 is that the z-axis loosely sits on the m5-nuts and only moves down through it's own weight. To mill and especially drill pcb's for example some more force is needed. The pushdown-system can easily be attached without demount