I'm trying to glue-up a frame that is 35 x 20 x 3 (inches) The joinery is dovetails. I put clamps on the length first, then the sides, so the pins and tails are proud and tight. Now for squareness. This is the problem. I put a clamp on diagonally and square opposite corners, but the other two are not. So, I switch corners and the opposite happens. Going back and forth to square all four corners. There must be an easier way? I have one more to do, but this one is 5" high. The glue I'm using has a long open time. Any suggestion would be geatly appreciated. Thanks