In the previous post, we discussed the design and construction technique for a generic Continental-style boarded chest. Today we’ll get into some more detail of how to orient the boards in the chest to make the most of the natural attributes of the lumber. By carefully arranging the boards, the natural movement of the material will improve the strength and durability of the chest.
Lets first have a look at “bad” grain orientation. The image above is an end-view of a boarded chest. The arcs we see are the growth rings of the wood. The growth rings will ‘flatten’ as moisture changes within the wood. The arcs drawn around the chest show the direction the boards will ‘flatten’. As the growth rings flatten, the top and bottom ends of the face boards will bow out and away from the end boards. Though cut nails work to hold things together more securely by mitigating the flex, the boards will still be consistently pushing against the grip of the nails. The highest problem with this orientation is the lid. The lid will eventually form a cup, as it has nothing for secondary support. Should water directly fall on a lid like this, it will pool in the middle of the bow. This will contribute to rot over time and significantly reduce the functional lifetime of the chest.
From the same view, we’re now seeing the boards with the “cup” of the growth rings closing toward the center of the box. In this orientation the ‘flattening’ of the growth rings will push the face and back boards into the case of the chest at the ends. This puts the least strain on the cut nails and supports them holding the chest together. Again, the lid has the greatest improvement in this orientation. Instead of ‘cupping’, the lid will bow, creating a peak along the centerline of the growth rings. This is a natural semi-coopering that can be taken advantage of for a better chest. In this orientation, as the graphic shows, the lid will create an arched top which will shed water, rather than retain it on the surface.
Finally, lets have a good look at the orientation of the end boards. While the other three boards have the best orientation with the “cup” of the grain facing outward, the end boards benefit from having the cup facing inward. When the wood flexes, the center pushes into the body of the chest. While the ends will attempt to flex “out”, the nails that hold the face and back to the end boards will keep that movement in check. Were the cup oriented to flex the other direction, the center of the end boards would pull the nails out of the bottom board. While the square cross section of a cut nail is superior to all other kinds of mechanical fastener for this use-case, going into the end grain of the bottom board is the least structurally sound connection. This is why it is important to have the board flex “into” the floor board, rather than away, it allows the wood to assist mechanical fastener.
These subtle details provide the difference between an acceptable boarded chest which will survive a couple years, and a good one which will last decades or centuries.