Quote:
The 18th century brought significant improvements to the wood plane. Handles began to evolve which made the plane much easier to use. The installation process of the iron evolved as well. The iron was wedged into place in tapered grooves which were cut into the sides of the body rather than being wedged against a cross-bar. Wedging the iron in tapered grooves with a more thinly shaped wedge allowed the plane to clog less often, and hence, increasing the work time. Much later in the century another improvement was made to the plane’s design, the use of double iron. A slightly curved cap iron, or chipbreaker, screwed to the cutting iron greatly improved the plane’s ability to cut difficult wood. This made the entire plane heavier, more rigid and more stable, and it allowed the shavings to curl and break apart as they pass through the mouth. This simple mechanical advantage reduced tear out and left smoother surfaces.
Could it have been that Leonard Bailey (Stanley Rule & Level) couldn't patent something already part of common practice and in wide use? In the design of things Bailey/Stanley, the cap iron is what connected the blade to the Bailey adjuster.