Design Help Pt2 Required for CNC design/Build

[JAZZCNC]

However, I urge you to consider not having gantry sides and using the style, like mine and Jazz's bigger machine where the cutter operates below the level of the X-axis rails. That eliminates the flexing of the gantry sides, as there aren't any, and puts the X-axis ballnut(s) in a much more optimal location in terms of the forces they receive.

Y-axis of 750mm sounds a bit much for just one ballscrew on X, especially considering you want to cut aluminium.

Seen as Jonathan agree'd with me I'll agree with him. . Lol . . . . Thou Ive actually built the same type machine as shown, it was with the specific intension of cutting just Wood which it does very very well and not to disagree with jonathan it also cutts Ali ok.
That said If building an allround machine then I'd go with what Jonathan says and actually I will be building just such a machine over the next few months ounce I've got other commitments out the way.
I've attached the first ruff models thou it may change in dimensions before it's built with ballscrews covered and rear of gantry enclosed along with Cable chain etc. The bed will be adjustable because a forth axis will be needed at some point also allows for milling vises etc.

Edit: Oh by the way It's going to sit on a bench not floor mounted.!