Wednesday, May 20, 2009

The Soundboard

The jointer is a bit of a pain to set up, so while I had it out to work on the neck I figured I would go ahead with a couple of other tasks that need it. Both the back and the top (I know, if the back is the back, then why isn't the top called the front? But it's not. It's the top, also known as the soundboard), which are in two pieces, need to be jointed and glued into one piece. For reasons I'll explain later, I couldn't do the back, so I went ahead and started on the top.

The edges to be glued together are only about 1/8" thick. If you put the two edges together and hold them up to a light, you can see gaps. These gaps need to be eliminated so the there is a good glue joint.

I fold the bookmatched pieces together, lining up the end grain, and use some painters tape to hold the pieces in place, and run the edge over the jointer a couple of times.

The result is a pretty good fit, but pretty good isn't good enough. There's going to be a lot of forces trying to separate these pieces, so they need to mate perfectly.

I then lay two pieces of plywood on the work bench, one 3/4" and one 1/2". I lay the pieces down on the 3/4" piece with the edge to be jointed overhanging the edge slightly, and clamp them down. The 1/2" plywood goes under the overhanging spruce top, and on top of that I place a carpenter's level. Using spray adhesive I glue narrow strips of 220-grit sandpaper onto on edge of the level, and lay the level on it's side so that the sandpaper faces the edge of the spruce.

This enables me to sand the entire length of the edge, removing any imperfections left from the jointer.

After a few minutes, the edge is nice and smooth. I hold them together toward the light and behold! No light can be seen through the edge. It's now ready to be glued.

As you can imagine, clamping two long boards together on their thin edges can be challenging, but there is an ingenius way to do it. (Obviously I didn't come up with it.)

I lay two 1 x 2 sticks on the bench top, and place three more such sticks on top, perpendicular to them.

The soundboard goes on top of these three sticks, and three more sticks are laid on top of the soundboard directly above the three sticks that are under the soundboard.

I take a 100 ft. length of cord that has a loop on one end and loop it around the far left bottom stick.

I then begin to wrap the soundboard with the cord in a figure-8 that goes around both of the far left sticks, crossing over the top one.

I do this about six times, then move to the center set of sticks, and finally to the right set, winding the cord snug but not too snug.

I then take three long 1" wide wooden wedges and one at a time place then on each top rung, with the point slipping under the crossed cords on top. Once each wedge is in place, I gently push them farther under the cords. This causes the cords to tighten, pulling the soundboard halves together tightly. The top rungs prevent the boards from buckling under the clamping pressure.

I do all of this dry--no glue. With every glueing procedure it's best to do a dry run to make sure that everything is working and fitting correctly. I'm actually able to pick up this entire mousetrap and hold it up to a light to make sure there is a good fit. There is, so I undo it all, get out the Tite-Bond, spread glue on both edges, and do it all over again.

After cleaning up any glue squeeze-out, I leave it to dry over night. The next day, I have a soundboard!

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