The previous heated bed design used a single RP part as z-switch-holder, which could not be
attached directly to the aluminium sheet for obvious reason.
Many people had problem with it, and also it could easily turn a little, so the M5 bolthead could not push the switch.
Also I modified the aluminium sheet, now it contains 3 additional threaded M3 holes. Note to my previous buyers: you need to drill by hand this holes, and use nut at the other side.
Step by step mounting tutorial
The final setup also needs two RP parts, just like the stock Rapman machine.
Here are some more photos from the every possible angle of the final mounted z-switch.