Have you ever wondered why tabletops often have perpendicular end boards? Is it structural? Is it purely design?
Well the end boards are called “Breadboards” and they are both for design and structure.
Structurally, they are designed to help prevent the tabletop cupping. As wood expands and contracts with the passage of time and the moisture content acclimatises to the environment the perfectly milled boards may warp, cup, twist, and do all sorts of things. Similarly to attaching an underlying brace Rigid breadboards hel
p to reduce cupping by keeping the boards in line. (Although this is what most people would say I’ve heard Christopher Schwartz teach that he’s doubtful as to how important this is. Youtube Link.)
You can attack breadboard in a number of ways. The most important point to remember is the direction of wood movement. Throughout the year as the moisture content changes solid timber expands and contracts. Different timbers expand at different percentages. The majority of expansion occurs in the plan perpendicular to the long grain. When you design your joinery it must allow the main boards to expand and slide and it must remain attached to the end.
Tongue and Groove
The simpliest joinerty is to use a tongue and groove. This can be down with a router or saw and cleaned up with a shoulder plane and sandpaper.
Stopped Tongue and Groove
Often its preferred to hide the joinery. Simply stopping before the end achieves this with little hassle. The groove cannot be cut on a tablesaw but a plunge router, drill press or hollow chisle mortiser will be effective. This is the plan for the shaker table.