This feels like a slight pivot, but I will do my best to keep the project true to its roots, affordable and 3d printed. 

I dug up an old anet a8 metal frame, AM8.  Initially I thought extrusion wouldn't be good for this, but it was merely the 8mm rods that were insufficient.  I plan to use the 1/2 and 3/4 steel tubes (*are tubes suitable or must it be rod?) and bronze bushings.  I found inexpensive $1.50 tube holders that will work as shaft holders and bearing holders.  Another idea is to do a press fit for the shaft into the aluminum, but I don't think I can drill that accurately.  I'll still drill the frame a bit, but it'll likely just be to extend the rods and be held with a 3d printed rod holder.  There is also a possibility of brazing everything rigid.  One thing I noticed about aluminum extrusion is barely anyone is using an anchor fasteners.  Mostly through holes and 90* fasteners and I suspect the anchor makes it a much more sold structure.  Avid CNC uses anchor fasteners for their machines.  I'm going to use them on this.  Perhaps even test the difference between anchor fasteners and other options.