Seems to me that if you are going to make one with twin vertical screws you could do a lot better than just copying a single screw machine twice. Those screws should be on the ends of the table to remove the cantilever problem of having them at the back, better still would be one screw at each front corner and one screw in the middle at the back, that is the way Stratasys did it initially, before they went through their "make it cheaper" phase