Slight change to design, working on my KISS principle (Keep it simple stupid) I have removed the longitudinal extrusion between the Y axis plates, the 10 mm plate supporting the machine and Y axis ballscrews will be of sufficient strength.

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8 fewer holes, reduced cutting and plate, removed 2 pieces of extrusion.

I was hoping to have two Y axis plates across the whole width of the machine but I cannot cut this length and to buy them will be too expensive so I have opted for a '4 feet' design.