This is an alternative arrangement for positioning and adjusting the Z-stop on a QU-BD RXL 3-D printer.
**Update: 10/27/13: I replaced the STL files with lower-res versions, oriented to lie flat in the X/Y plane for easier slicing and printing.**
I found that the homing repeatability on my RXL printer was very poor, with a variability of at least 0.5mm, which I attributed in part to the very obvious flex in the corner of the frame that held the bed. Furthermore, the tight positioning of the Z end-stop switch behind the front right frame pillar made it very difficult to adjust the z=0 position.
To fix this, I decided to move the z-stop over by the Z-axis, where the stability of the platform is maximized, and use an easily adjusted screw to trigger it. I needed to keep the assembly as rigid and firmly fixed as possible, so I added a built-in 'banana block' clamp (inspired by Jeremie Francois' design for sliding blocks that I am using on my Ultimaker).
With this in place, I am getting perfect z-homing every time, compared to the the 20% or less first-layer success rate I was seeing originally.