A new hope: Epoxy granite and steel.

[hardenum]

The Z looks complex. I assume you have a complete machine shop to build it. Ideally it should be as wide as the gantry carriage.

I would go fixed gantry for the relatively small working area you planned.

Maybe also consider simplifying the shape of the columns, but in the end you'll be the one to build the molds :)

I do not, all I have is a hand drill and a dremel, I'm outsourcing it. The sheet metal cutting and welding. It's not more complex then a straight or a C plate. It's just a square steel tubing in the end. I've actually received a quote for the whole piece from the local shop EUR600 total for the thing.

Besides the Z, nothing is final yet. I'd go with a fixed gantry but I haven't got a clue yet as to how I'd deal with the bed. What I mean by that is I want to be able to mount the 640x320 work piece vertically. With a moving bed, I don't have any ideas how to do that though.