In a previous design tip, we used the example of a house-shaped box with a “mousehole” doorway (See Figure 1). The outside of the house was formed by the A-side of a simple straight-pull mold; the inside was formed by the B-side of the mold. A shutoff, a raised pad on the surface of the B-side mold, formed the doorway. In this tip we’re going to complicate the process by turning the door shown in Figure 1 into a window (See Figure 2). By adding material below the bottom of the feature, we’ve created an undercut feature that cannot be produced in a two-part mold.