Reinforced Mendel X Carriage with Slim LM8UU Holder

This is a modified version of the carriage by Jonas Kuehling for use on a RepRap Mendel.

**Changes:**

* As the Mendel uses a horizontal belt path, the belt attachment has been rotated 90 degrees
* Added reinforment bars to the ends of the carriage to improve rigidity
* Added mounting holes to attach things like an opto flag, fan holder, lights etc.
* Still supports the original fan mounting (see source)

This design is much lighter compared to the original carriage and the use