One of the most important steps in guitar making is sealing the body. On the body, there should only be one place where air can escape, and that’s the soundhole. As you assemble the sides and the plates, sealing the body well means a better sounding instrument. Here is how you do it.
Guitar Making Tip No. 12 – Sealing the Body
Thankfully, getting a really good build on the body is not terribly hard.
It does require some prep work on your end, and probably at least a few dry clamping runs without any glue. I explain why it’s harder to fix Glue Covered Problems in another article.
The better you prepare the plates, and more specifically the brace ends, the easier it will be to get a good seal on the guitar body. As with most things, the details are what counts. You are going to have to spend some time fitting the plates to the sides in order to get the easy gluing seal that you are looking for.
Prep Work for Gluing the Body Together
You can get the hard part out of the way, and then the back plate will be easier.
Decide whether your braces are going to go under the kerfing, or if they are going to terminate at the kerfing. This will determine how you are going to handle the fitting. If you are running the braces under the kerfing, you need to mark where they cross. Then, use a Dremel or a chisel to remove some of the kerfing so they fit underneath.
If you are butting them up to the kerfing, then look inside the body mold and mark where the braces touch the kerfing. After that, saw the excess, and chisel it off.
I recommend running the braces under the kerfing. This helps hold them in place because the kerfing will become a physical barrier to them lifting. It does take more time, but I believe the reasons are worth the effort.
If you like guitar making, check out Acoustic Guitar Making for Beginners, which highlights the best parts of my massive 508 page acoustic guitar making book.
Attaching the Back Plate to the Body
Decide on your method, and make the cuts to create clearance when the pate is placed against the sides.
As you are fitting the plates, be sure to check that the pieces fit against each other flush. The wood should touch without any gaps, and it should not require a ton of force to seal. If you really have to press or force the pieces, then you need to look at where they are missing and make some adjustments. This could be as simple as taking a little off a brace, or removing a little more kerfing.
Gluing the Plates and Sealing the Body
After all the clamps are in place, look around the body for gaps. If you find any, address them. If you do not, you are ready for glue.
Apply glue to one side of the guitar, along the kerfing and the edge of the sides. Spread it evenly with a finger or glue roller. Then, attach the plate. Make sure it presses into place correctly, and start adding clamps. Make sure to use a ton of clamps, and space them as close as you can for even pressure.
After you have them all in place, tighten them down enough to seal the box. Check for gaps again, and wipe off any large amounts of glue squeeze out. Allow the guitar to dry and then do the same thing with the other plate.
Now, you have a good seal on your acoustic guitar soundbox. This is important for the way the guitar functions, and will ensure that you are not losing air through gaps in the body.
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