I already have build momus CNC and is cutting good, but recently I got good deal on THK linear rails and I was thinking of building new one since the rails are longer than are needed to replace on momus.
but my question is .. what material is better to build it out of. Momus is half aluminum half plywood. I'll be mostly cutting wood and soft materials and once in a while I may cut aluminum. Also I like that same design as momus is (bridge cnc) So I'm not sure if to use 80/20 profiles or just build it out of plywood and use aluminum on the Y axis or go all 80/20.

I'll will be using THK rails for X and Y and THK KR33 actuator for Z which has 4.5" travel. I already have controller board and steppers.