A key thing to know is that the cap iron (chipbreaker) must be undercut. This happens when you are sharpening/flattening the edge. As shown in Mr. Duffield’s photo, the cap iron is positioned on the stone in a way which will undercut the edge. Thus, the cap iron will meet the iron, not flush, but on a knife edge. The undercutting of the knife edge allows for some flexing of the cap iron when it is tightened.