A3 Router Build

[GTJim]

Hi Jazz, I completely understand the issue with the position of the Y axis ballscrew, but these side plates have been cut. It was done in haste as a friend was leaving his job and offered, if I could get a sketch to him quickly.
Initially these side plates would have been 20mm aluminium but 12mm steel was available so the design is evolving already. So I think I’m stuck with this configuration until its made, and hopefully then make a better Y axis.
I am hoping to use 80x80 aluminium extrusion with 20mm rails.
My first question is regarding mounting of the extrusion to the side plates. Currently the design relies on 4off M16 cap head screws with 4 location pins/studs on each side, will this work or are there better ways, such as threaded rod going through the extrusion. See Sketch.