Ermmm I've just down loaded your drawing and can see that your using 12mm round rail.!! . . . This would concern me and would seriously consider selling and upgrading to supported rail.

It's a lot of work and expensive aluminium to potentially waste and I'm confident to say it will significantly reduce your depths and feed rate in aluminium..:sad:

So times it's less painfull and expensive to cut your loss's and start a fresh.! . . . If you have a fully working Z axis now why not sell it complete to someone who doesn't need the strength or abilty to cut harder materials. Then treat your self to supported rails and ballscrew from china.? . . . Think you'll be surprised how cheap you can build a great Z axis for with supported rails and ballscrews.!!