With a frame of 500x500x520 mm has a build volume of 340x340x420 mm.

Detailed Album

The provided here gantry carriage is only for OpenBuilds VSlot.
Needed only 4 rails of OpenBuilds - the rest can be any cheaper 2020 profiles. Close to Spain this one is perfect.
Take the columns 20 mm longer than the screws to get the max of the vertical travel.

The three screws need to be straight: if one does not roll fine on a flat surface then do not use it: Pure Screw Z Stage!
Mount the screws to the lower rails, not like in my photo (to the upper rails).

For the cross carriage take a cheap but very good hotend:
Dual DeerArc or Solo TurtleArc

The file TJoint2020.stl needed if not using slot profiles for the Z stage, otherwise can use regular corner items and save on printing.

The best, IMHO, open source extruder SaintFlint

Except the extruder I print all my printer and robot parts wit a 0.8 nozzle out of PETG and the screenshots of the settings are provided.