Soundboard: Edge jointing

Last weekend, after jointing one edge of my soundboard material at the router table, I took each board to the table saw and sawed defects from the edges. This shrank the widths of each board somewhat, but it was necessary to get rid of large knots and pitch pockets, which might have weakened the board and could have been torn out during planing or jointing.

Next I set up the planer and started planing each board face until roughness and oxidized wood vanished. I removed only enough to clean up each face. When this was done the material was from 6-7.5 mm thick, so I continued planing all the boards in sequence on the same planer setting to get their thicknesses to match. Since the material is quite thin, I rode each soundboard piece on top of an 8-foot long pine backer board: this is safer than trying to send something very thin through a planer on its own.

The boards are now about 5 mm thick, and I'm aiming for a starting thickness of 3.5 mm. My friendly harpsichord maker advised a thickness of a "heavy eighth inch", an even eighth being about 3.2 mm.

I jointed the sawn edges of each board to clean them up, and as an experiment I tried laying boards edge-to-edge to see how well they fit. Even after several light jointing passes, the boards wouldn't quite come together. It appeared that the length of the jointer fence was insufficient to remove a very subtle bow from the edges.

I thought I might have to invest in a good-quality large hand plane such as a jack plane, which together with a shooting board is usually what is used for jointing soundboard planks. But, after consultation with my father, we decided to adapt the shooting board principle to the router table and save the expense of the plane, which would easily be over $200.

A traditional shooting board is a long wide board to which a second narrower board is fastened. The step between the boards receives a long hand plane laid on its side, and the material to be jointed is placed atop the narrower board with the edge slightly overhanging it. The plane is pushed forwards and, guided by the edge of the narrower board, planes the edge of the desired board straight. Using a long plane ensures that any minor defects on the narrow board's edge are bridged by the plane's long sole.

We came up with a shooting board made of a 12" wide piece of medium-density fiberboard (MDF). MDF is flat, straight, stable, heavy and cheap. Atop this went a narrower piece of MDF with five slots at right angles to the long edge. Five carriage bolts were inserted through the large piece from below, with the heads countersunk, and hand knobs were screwed onto the opposite ends to hold the narrow piece down.

The slotted narrow piece acts as an adjustable fence. A piece of soundboard wood is laid against it and the fence is adjusted until the soundboard material just slightly overhangs the edge of the bottom board. Then the knobs are tightened to hold the fence in place. The entire package is pushed through the router table with the bottom edge running against a piloted router bit. This shaves the soundboard plank flush with the MDF edge.

In action the shooting board looks like this:


It's "incredibly ugly", as my father put it, but it cost $20 to make and it works. The bricks weigh down the soundboard plank and keep it from shifting around as the assembly is pushed forward.

This router bit


takes care of the trimming. You can see the pilot bearing running against the MDF edge.

After jointing each edge once and trying planks side-by-side, the fit is pretty much perfect.