I am posting this, still a newb with the X-Carve and machine carving in general. I wanted to share though. I was cutting a 30" x 30" sign and noticed that the bottom of the sign was being cut deeper than the top. I first dismissed this as I thought maybe it was the wood, and the difference was less than 1/16 of an inch or so.
I starting doing halftone carvings and then notices all my pictures were darker at the top than the bottom, and I had been having a lot of trouble tying to tune the settings of the halftoner carvings.
Finally, I zeroed the z: axis to the waste board in one corner and the manually moved the spindle to all 4 corners. I found that it was scratching halfway across the waste board.
Looking at the frame, I realized that while the rails of the y-axis are precisely drilled and aligned , the frame of the waste board had some play when the bolts were loosened.
I loosened all four corners, and used a medium pry bar at each corner to lift the y-axis rails as high as they would go, and tightened each corner. Now I can move the spindle from corner to corner and have the same depth.
I have though noticed that the x-axis rails bow slightly in the middle with very little pressure. This is not a problem yet, but as I carve more, it my start bothering me.