What is the largest recommended size with out added support?


If you are milling, then the larger you build it, the lighter your cuts will need to be in order to keep the router bit from chattering. I built my first at 32"x32" and I had a usable cutting area of over 18"x18" and I was pretty happy with it. The nice thing about smaller builds is that you will be able to cut faster and you will need less tuning of your CAM settings. It’s easier to start smaller and get the hang of it, then extend the size of the rails later after you have the hang of the CAM programming.