Flat die-cutting is the primary method of producing folding-carton packaging: a flat die (form) cuts, creases, and cold-embosses the cardboard blank in a single stroke. This invention concerns the construction of the flat die-cutting die itself. The arrangement of its cutting and creasing rules and of the plywood base is designed to raise the accuracy and stability of cutting, creasing, and embossing of sheet cardboard, to keep the rules rigidly positioned under load, and to simplify the removal of finished blanks. The result is higher quality and repeatability of the die-cut carton blanks.