Made of aluminum, Made for aluminum: Would love design critique!

[Zeeflyboy]

Significantly better in most regards, nice job.

Consider going one step further and putting the rails on the top of the side extrusions, you can quite literally get rid of all unsupported gantry side arms and it is certainly easier for alignment purposes than side mount.

larger extrusion on X is a good decision, I would still go for heavy profile though if that's an option in that size.

Also consider flipping the Z-axis around so the router mounts to a plate with the rails and the carriages are fixed to the gantry side... 'tis what all the cool kids are doing these days. Gives better rigidity. I'd also say just upgrade those to 20mm rail too for simplicity's sake.