Sunday, October 31, 2010

Joining the Back and Top Plates

Preparing the back and soundboard halves for gluing is a relatively easy but critical step in guitar construction. Many luthiers use a traditional shooting board similar to the one pictured below. The back or soundboard halves are placed flat, one on top of the other, with the edges to be joined overhanging the ledge slightly; the plane is pushed along the length of the overhanging plate edges.

My own take on this has been to build a shooting board in such a way that the plates to be joined are held vertically between two cork-lined jaws as the picture below shows. The top or back plates are clamped lightly and accurately aligned before the jaws are fully tightened. Truing the edges then takes place with the plane guided by the vertical fence, with pressure applied from above and the plane held in the familiar and more controllable upright position. The advantage of this configuration for me is that, once they're firmly clamped, the plates are immobilised and I feel I'm able to apply more even pressure than a more typical shooting board would permit. To ensure an accurate cut, my trusty old wooden plane has been fed through the drum sander to true up the side which bears against the fence.

A few judicious strokes with a sharp plane blade are generally all that's required to achieve the perfect joint, after which, the halves are glued together using the jig shown below. As you can see, wedges are tapped into place to apply the necessary clamping pressure. The underside of the blocks is faced with 80-grit sandpaper which reduces slippage once the wing nuts are tightened and the wedges are tapped home.