I make a lot of trays, boxes and frames, and gluing them up can be tricky. My method is to lay them out in a straight line, flat on a table, and tape each miter. I then fold the frame up and tape the fourth corner so I can accurately measure for the bottom. After cutting this to size, I put glue on the miters (one at a time), fold up three sides of the frame, insert the bottom, then glue the last miter. The final step is to clamp up the assembly and apply moderate pressure with a band clamp.
– Robert Collins
Snyder, New York