I'm just curious why you aren't going with a gantry design? If you ever plan on cutting any large aluminum sheets, the consistency of the cut will vary a great deal depending on where in the y-axis you are. I am also going through the metal struggles of designing a machine, and I'm consistenty coming up with a gantry style machine driven by a center located ballscrew underneath the table. The ballscrew will be fixed at the ends with a spinning nut. The only problem i may have is skewing. But a very stout gantry should prevent that.
Also consider the loads on your linear bearings when making a cut way out at the end of the y-travel. If you're worried about a lack of z-range with a gantry design, then make the y-axis movable. So when cutting large foam blocks the gantry height can be raised, but then when cutting aluminum everything can be lowered to increase stiffness by a large amount. Does that make sense?
Edit: I didn't see your dimension up top, I think at that size it should be fine. If you scale up you may want to go with the proven gantry style machine.  |