Originally Posted by
dmalicky
Very nice work! If you want more rigidity for cutting aluminum, I'd suggest closing up the slot in the gantry tube. For x loads at the tool, the gantry is put in torsion, and a fully closed section makes a huge difference for torsional stiffness (polar moment of inertia, J). For example, roll a piece of paper into a tube, then twist it -- no resistance. Then tape the seam -- stiff. Yeah, sorry for the late info! Here's a way to "tape that seam" (close the cross-section) while still keeping your slot and y-screw configuration inside the gantry tube: weld a hefty C-channel to the inside of the tube, so the slot is bridged by the channel. If you could find a channel that ~just bridges the slot, the welding could be easily done from the outside. That size may not exist; alternately, weld up a custom sized channel from flat stock. Ideally, the legs of the channel would be short, just enough to squeeze the acme nut in there.
Also for stiffness, and to minimize post-weld distortion over time, I would add a pair of ~45 degree diagonal members from the gantry/uprights down to the main frame. With only the uprights, any relaxation in the weld beads at their base will pull the gantry fore/aft by quite a bit. A pair of diagonal braces would fix most of that, and add a lot of fore/aft stiffness.