Even when a container has good folds, seams, and overall proportions, the blank could still be slightly twisted. This squareness defines how well adjacent panels intersect at their edges and whether opposite panels are parallel to each other. For a practice container, squareness is important because even minor misalignments can impact flap fit, stacking, closure location, and weight distribution on the container walls.
The simplest method to test squareness is to place the container on a flat surface without forcing it to lie in place and see whether all panels that should be contacting the surface actually do. If one corner is elevated or if the container rocks on any of the sides, then the blank was not properly folded and/or one panel of the container was not aligned properly during construction. Examine multiple sides of the container when testing and don’t rely on a single side alone.
To test individual corners, use a square and carefully hold it against the panels that form the corner to verify that the square contacts both panels along the same line. Any space between the square and the container could indicate a fold that is too far from the score line, panels that are not the correct size, or panels that were joined at an incorrect angle. Do not press the walls together when you test; the goal is to assess the shape of the container as it exists after being built.
Squareness can also be checked by examining opposite dimensions. Measure the distance between opposite panels to see whether the width of the panels matches the specified or designed width. If the container is supposed to be rectangular, the corresponding panels should be about the same length. You can also check diagonal lengths. A rectangular container should have equal diagonals; if the diagonals differ significantly, then the container is out of square. This method is best used as a general guide for beginner projects instead of as an actual measurement check.
Errors in squareness typically occur during earlier steps, such as cutting, scoring, or gluing. If a cut line isn’t straight, it changes the edge of that panel. If a score line is not straight, then the fold will not go in the right direction. If a container wall was constructed out of materials that are too thick or too thin, the panels may bind as the container closes. If glue was applied too early in the construction process, it can pull the container walls out of alignment. It is much easier to correct errors in the earlier steps than to try and force a finished container to square.
As a simple project, build two small containers from the same simple blank. For the first container, just build as usual. For the second, pay special attention to making sure the blanks are marked correctly, scored correctly, folded correctly, and the seams glued correctly. Once both containers are complete, set them side-by-side on a flat surface and look at the corners, opposite panels, flaps, and other dimensions. You should be able to easily see which aspects of the blank construction most affect the final squareness of the container.
Don’t think that your work is only improved when the container looks pretty. A much better indicator is whether your containers stand up well, have parallel sides, square corners, and flaps that close properly without being forced into place. When all these things come together, your work will look good as well!
