CNC Mini Mill made from Steel Tubing

I was kicking around the idea of an affordable way to build a steel framed CNC Mini Milling machine. The best way to do this is to build your machine form standard sized available steel. I chose steel tubing covered with some sheet metal to protect the round linear guides from contaminants. The trick is getting your steel cut square. Most steel supply places will not guarantee any cuts being square. The most guaranteed way of getting the ends of your square tubing cut perpendicular is to take it to a machinist and have the one end milled square. You really only need to do this with one piece of your "L" shaped frame because the others ends don;t have anything mounting to it. The other challenges associated with using large steel tubing is bolting things to it. You can try and use thick walled tubing and tap it but thick walled tubing is more expensive. If you use thin walled tubing, it will be plenty strong but you may have to bolt through which presents accessibility issues with bolts, screws and nuts. Either way you choose to pursue this will be a good learning experience for you. Here is a picture of what I had designed.