In sand casting, complex patterns with undercuts or multiple parting lines require more than a simple two-part mold. The cheek provides one or more middle layers that can be drawn away laterally or lifted off separately to remove the pattern without tearing the sand. It allows founders to cast intricate geometries that would otherwise be impossible in a standard split flask.
Heard on the job
Ram up the drag first, then carefully set the cheek in place before you start packing the middle section of the pattern.