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The Guitar Medic

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Repair and Restoration
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Yamaha FD01S Broken Neck
The only purpose in showing this repair in progress is to demonstrate clamping. When gluing and clamping a neck it is important to follow a sequence to insure you can achieve the best results. The sequence and process to insure success are as follows:
1) Clean out the crack as best as possible. If nothing has entered the crack, this step is not necessary. However, consider that if several people (or even just one person with dirty hands) has run their finger over a crack, skin oil enters and inhibits good adhesion of glue. Surface preparation (cleanliness) of the joint is everything! So first, go wash your hands.
2) Secure the instrument so that you can push the neck downward to "open" up the crack. This will allow you to work glue into the crack. This can be done in many ways. I have a method I've used with great success. First put a glob of glue at the crack opening.  Begin "pushing" the glue into the crack. Keep wiping the excess and forcing it into the crack until none remains on the surface (except of course residue). Apply more and repeat.  Now take a thin sheet of plastic (like used for a sheet protector; credit card material is too thick) and cut into a wedge shape with a point. Use this to slip into the crack--pushing in and out to further work glue into the joint.
3) Dampen a paper towel and wipe away the excess glue. Dampen another paper towel and put it aside.
4) Begin clamping at the innermost part of the crack first. The goal is to push as much glue out of the joint as possible. WHAT??? I thought I was supposed to get a lot of glue in there!!!?? Now you want it out???!!!  The reason is this: Glue is water based. Wood absorbs water into its cells and expands. If you don't push out the excess glue from the inside out, you will end up with a VERY uneven joint and a horrible-looking repair. So take my word for it and do it this way.
5) Use LOTS of clamps, and be sure you put them where they're doing the most good. See my photos...they illustrate this very well. All clamping in these photos followed the outside perimeter of the crack to insure I have a seamless joint when dry. Note that this was AFTER I had done the necessary clamping to remove excess glue.
6) Allow the joint to dry for at least 2-3 hours before removing any clamps. Although wood glue manufacturers tell you that you can unclamp in 30 minutes to an hour, I always proceed cautiously with this. Reason is, that when you cap up your glue, it does not dry out. Same goes for putting glue into a closed space and then clamping it so no air can get to it. Although there is sufficient air in the wood for the glue to set up, I prefer to err on the side of caution. It really doesn't hurt to leave it for the extra time.
7) Adjust clamps if needed while the glue is setting up.  After removing the clamps, you can easily clean away the excess glue with a damp paper towel or cloth. However, be careful to not oversaturate the rag or towel--you do not want to introduce water back into the crack joint again. After removing excess dried glue, you can lightly sand with 600-grit paper. Sanding lightly will not usually remove material enough to go through the color.  You need to then simply scrub out sanding dust with an old toothbrush. Apply shellac into the crack edges to seal them.  Wait about 30 minutes, then lighly dampen a rag with alcohol, and run over the crack to remove excess shellac. Again--do not allow alcohol to get into the crack, or it will dissolve the shellac.  Final touches should be buffing--using a commercial automotive scratch remover.