Several months ago, we were commissioned to build a 48″ x 144″ maple parsons table for the breakroom of a Detroit advertising company. The table was designed to seat 12 people comfortably, and would be bar height at 42″.
The material chosen was maple veneer for the table top surface and solid maple for the table top sides and legs. The legs would sit in square cut outs in the corners of the table top, allowing the end grain of the legs to contrast nicely with the face grain of the surface.
The thickness of the table top was 4″ and the legs were 4″ square.
There were two engineering issues that had to be tackled during the construction of this table. The first was how to keep the 144″ span of the table top from sagging. The second issue was how to securely fasten the legs to the corners of the top in order to minimize side-to-side racking and to withstand the downward force of gravity and pressure exerted by the users.
Originally, we thought the best way to minimize the sagging of the top would be to install two steel “I” beams under the table top, but at the last minute, we decided that the increased weight and the difficulty in attaching those “I” beams to the underside of the table top was not worth it.
Instead, we decided that we would just use 1″ thick Euro-Ply to create the underside bracing.
To create the 12′ long top, we started with three sheets of 1/2″ thick 4’x8′ baltic birch. Why baltic birch you ask? My rational was to make the table top as stiff as possible during every step of the construction process. Baltic birch is stiffer and denser than normal plywood, and once the two layers were glued and stapled together, the 1″ thick top would be pretty stable, even without any framework underneath it.
We constructed the top by gluing and nailing together two sheets of 4×8 material and two sheets of 4×4 material. The layers were connected by spreading glue over the entire surface, staggering the joints, and stapling every 8″ or so.
Once the glue had cured overnight, we filled and sanded the top seam, ensuring the joint would not telegraph through the maple veneer.
With the top to its final size, it was time to create the notches for the four legs. We cut away most of the material with a jig saw and, using a corner jig, a flush trim bit, and a router, we sized each corner perfectly.
The rounded inside corner, left over by the router bit, was easily squared up using a chisel and each leg was fitted to ensure a perfect fit.
Next, we began adding the framework to the underside, which would be the key to the table tops overall stiffness and rigidity. We started out by gluing and pocket screwing the framework to the perimeter.
Each length of bracing in the middle was a double layer of Euro-Ply. The joints were staggered along the length and glued and screwed to the underside of the top. Once we had all the framework installed, we milled and installed the solid Maple trim around the perimeter of the table. The Maple trim was 3/4″ thick and, once glued and screwed to the Euro-Ply bracing and the Baltic birch top, helped to make the entire assembly one rigid structure.
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