Thanks for the feedback. Twin Y axis (I assume you mean Y?) ballscrews was on my list, I will probably add the mounting holes in so I can add them in the future. All plate will be 20mm thick I think.

Been doing some more work...

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At the moment I only have 2x Hiwin carriages on the X axis. Would there be much benefit/need to double up on these? I.e. two carriages per rail? If so then I will need to increase the X axis length to get a decent travel. I am leading towards this anyway...

Dave