El Beast - Initial design phase, comments and critique welcomed!

[Zeeflyboy]

No, they would be aligned in the vertical plane too... ecocast bed plate could be fastened to the top and then I would insert a shim of 2.5mm between carriage and bed with the carriage at one end, clamp it in place and tighten end screw. Move carriage to other end, insert same shim again and clamp. Tighten that end screw... If required you could repeat that at several points along the length.

Repeat on the other side and both rails are aligned vertically using the eco cast bed plate as a reference.

The parallelism and squareness of the Y-rails would be taken care of to acceptable tolerances by the captive ecocast end plates, milled extrusions and thorlabs corner brackets, while the vertical alignment (both in X axis rotation and Z plane height) would be done in reference to an ecocast bed plate.

What am I missing? In my head that ends up with the rails fully aligned in all axis to within the tolerance of the milled surfaces which should be sufficient for a pretty accurate machine all said and done.