Better Z-stage for Ultimaker

The Z-stage for the Ultimaker 3D printer is made up of layered pieces of plywood that clamp around LMU12LUU linear bearings. That construction results in an unstable Z-stage, either due to movement of the bearings in their seats, or movement due to moisture content levels in the wood itself.
This design does away with the LMU12LUU bearings and replaces them with LMK12LUU bearings that offer a flange to attach the (perpendicular) platform. Furthermore, the plywood is replaced by 10mm acrylic,