Hobby project

[DIYSwede]

Thanks, Tony for sharing your thoughts on your project and the tip to the interesting mechatronics site.

FWIW: Given that an epoxy-granite filled gantry will be more rigid than a single vertical support of any design,
one remaining problem will be the gantry-to-spindle overhang distance (for the given precision of the linear rails).
Humble tip: You could mount the vertical rails on the outside of the gantry, to:
1) utilize the rail's inherent rigidity from their greater width (rather than their height, and perhaps even wider distance between the top and bottom bearing) and
2) thus improving overall rigidity by reducing the spindle overhang with app 30 mm.

In Leibnitz' perfect world - one could perhaps imagine a rigid, high rectangular box around the gantry,
with the horizontal rails inside and spindle centre at the centre of the gantry's footprint?
Unwieldy, heavy and cumbersome of course, but optimized rigidity given the components involved.

Just my two cents...
ATB and good luck!
Johan