PCB Mill mount for Vert-X axis

Designed for Vertical X-axis competition.

PCB manufacture needs to be easier for reprap; countless numbers of printed parts can be made, but I see electronics as a real bottleneck. Just like 3D printing, the more accessible it is, the better the take up. To this end, I have started designing a milling carriage for the Vertical X-axis standard.

The idea is that the normal x-carriage can be unclipped from the x-axis, leaving LM8UU bearings on the linear rods, then this one can be clipped on to mill PCBs or other small parts.

Basic reprap PCB milling page here: http://reprap.org/wiki/PCB_Milling
Linear mounts are 70mm apart, as per the standard http://reprap.org/wiki/Vertical_X_Axis_Standard.
The LM8UU Linear bearing mounts were taken from Josef Průša/Greg Frost's X-end holders, which I think have the best grip on the bearings: http://github.com/prusajr/PrusaMendel. I guess my idea is that it could be swapped, not that you'd be doing it every day. I have found Greg's other d