There is a round coined slot just off the inside corners that prevents the frame from aligning 45 degree cuts. One of the boards in the corner slides into the relief, but the other cannot. There may be a reason for this relief, but it makes the tool very difficult for me. I cut out four pieces of very thin cutting board mat and folded them at the corners to hide the relief, it worked well. In addition, it is very durable. I cut four sticks in half because I collect smaller boxes.