Question is what is your budget? Just spent 10 mins knocking up a quick design on Sketchup and I reckon you can build the base out of one 7.5m length of 100x50x4mm, one 7.5m length of 50x50x4 steel and one 3m length (chopped into 2 x 1.5m lengths) of 100x50x6mm Ali plus a spoil board of either MDF or Ply. With a length of 1.6m you could just get away (I'm sure Jazz or someone else will confirm) RM1610 ballscrews and 3Nm Nema 23 steppers. If you were frugal it could be done for approx. £2k with half decent electronics (like AM882 drivers, PDMX126 BOB, home made PSU etc.) and second hand (from fleabay) THK or NSK linear rails.

I've not drawn everything in, but it should give you an idea. The frame/bed will need more bracing and supporting but you'll get the idea from the sketch...

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