When you are gluing box joints, here's a tip that will help make this already strong woodworking joint even stronger. After you have glued and assembled the joint, apply glue to the exposed end grains of the joint. Normally, you never want glue on your wood. But in this case the end grain will absorb the glue that you put on which will cause the wood to expand slightly. This makes your box joint stronger and tighter. Once the glue is dry, sand away any excess.