My 6040 is a standard eBay example with unsupported rails on the cross axis. It's quite flexible. I haven't tried aluminium yet but I'm sure I will want to in future. It is now working OK and seller has just given me a refund to buy a new spindle, but I am keeping the machine so I don't need a 3040 now. In future I think I will want a 3040 for plastic and Al, and a larger wood router.