Acornhouseworkshop

One aspect of guitar making that most woodworkers will never deal with is the challenge of joining very thin boards, less than 3/32″  of an inch thick. Traditionally – and practically – the top and back of acoustic guitars are made from two bookmatched boards edge glued together. When making furniture, you would glue the two boards together, then apply clamps all along the edges to bring the joint tight together. With the thin boards for the guitar, especially the soft spruce or cedar used for the soundboard, this would not work. It would, at best, bow the boards up, opening the joint; and, at worst, crush the wood. So the whole thing gets flipped around. The clamps are set in place first; either two long boards or straight edge clamps, or, very traditionally, a series of nails along the edge. These clamps are set slightly narrower than the width of the two boards; just enough so that, after apply glue along the seam, you can press the two boards flat, tightening up the joint. Then paper is put over the seam, and finally something heavy so that it doesn’t spring back up. If the setup is done carefully, the result is a very strong, very flat, joint that practically disappears, especially in the spruce. By the way, the spruce that I am using is a special, rare, figured sitka spruce commonly called “bearclaw,” for the markings that look as if a bear had drug its claws through it.

The back, made from curly moabi (African pearwood), is done the same way. With the bonus step, as I discovered, that moabi, being a very hard, dense, wood, is not fun to resaw. (It made me pine for the days of resawing White Oak.) I initially wanted to resaw three or four pieces from the 1/2″ boards for the back and sides. After some complaining (smoking, drifting, stalling) from my bandsaw, I ended up with two pieces, and a lot of time at the drum sander. Oh yeah, while the moabi is lovely straightgrained, quatersawn stock, the curls make planing a strict no-no. 

After the glue cured, and the final thicknessing is done, its time for some critical drafting. Even though guitars are made from very thin wood, the final product is incredibly strong, thanks to the bracing of the top and back. Remember, the strings exert a huge amount of force on the bridge and top, and, without the bracing, they would rip the top off the guitar. Yet, they still need to allow for the vibrations of the strings to transmit the sound through the wood. This type of X-bracing was developed by C.F. Martin in the 1840’s, and is still the preferred design for steel strings today. I just transfer the layout lines from the plan. The first guitar has an amazingly big sound for such a small instrument, so no need to try anything different.

This entry was posted on August 1, 2009 at 1:53 am and is filed under Acorn House. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.