I'm considering re-designing my gantry to something more suited to self build. The hassle and cost of machining it all from ali plate is putting me off the current design. My only worry is the hassle I had with the out of square/bowed/twisted 80 x 80 I used for the frame, would make building a gantry nice and square very difficult indeed.

Any thoughts on using a heavy duty ali extrusion, say 160 x 80, instead of RHS/SHS? Would it be possible to build a gantry from extrusion strong enough for machining mostly aluminium?