Ultimaker 2 optical Z-Endstop (UM2 plus extended)

2017/02/20 Update:
Sorry, I put the wrong EndStopHolder-Front.stl, please re-download it.

[Summary]
This is an optical Z-Endstop upgrade kit for Ultimaker 2 series.
It can improve the repeatability of Z height.
Also add some extra build space(about 1.5mm) at Z direction.
A step by step instruction in PDF format is included in the download area,
please read PDF before build it.

Firmware rebuild is required (just 1 line change, stated in the instruction PDF),
DO NOT use it with the