Knowing what types of glues are available—and when to use each one—is a fundamental guitar-tech skill.
Neck joints are under constant pressure, compression, and draw. As a result, eventually the angle of the neck needs to be reset for the guitar to play well. This can be as easy as changing shims on a bolt-on or as complex as removing a set neck and re-carving its heel and tenon. Understanding the physics of the guitar you’re working on is the key to planning the project. There are different categories of neck joints. Here are six types you’ll typically encounter:
• Bolt-on, no glue.
• Bolt-on with glued mortise and tenon.
• Glued mortise and tenon without bolts.
• Dovetail with shims and glue.
• Bayoneted with glue.
• Neck through body.
Neck resets are a common repair that all professional guitar techs should learn and master. Not only is it part of restoring a guitar, but it’s a critical factor that determines whether the guitar will be playable or merely a wall hanger. To get a sense of what’s involved in a basic reset, check out my Guitar Shop 101 column “How to Shim a Bolt-On Neck.”
Repairing Body Cracks
In an acoustic, body cracks are typically caused by low humidity or impact. Unfortunately, body cracks diminish an instrument’s value. However, you can limit the amount it’s devalued if you treat the crack correctly.
To repair top cracks, techs use deep throat clamps and specialized cauls to ensure the crack closes flush when glued. Repairing side cracks involves powerful rare-earth magnets, spool clamps, and cauls. Back cracks are little more complicated because you can’t use any clamps. In this case, you’d use rare-earth magnets and cauls to close up the crack.
When repairing top and back cracks, you need to be aware of the braces. If the crack crosses a brace, it’s best to reglue the brace at the same time. You’ll need some custom cauls to do this, especially for the back.
Mastering soldering is an essential skill, as is knowing how to interpret a wiring schematic.
Tip: Never rub a bare finger on a crack. This will allow dirt, oil, and sweat to discolor the wood, which can result in poor glue joints and an ugly stain.
Bridges and Bridge Plates
Bridge repairs are another bread-and-butter job for the qualified tech. Often you can address a playability issue with a good setup, but in some cases a bridge has to be replaced. With electric guitars, this typically involves putting new saddles on a fixed or tremolo-style bridge, or replacing a Tune-o-matic-style bridge that has collapsed from years of downward pressure. I describe the latter in “How to Install a New Tune-o-matic Bridge.”
For acoustic instruments, you either reglue the original bridge—if it’s not cracked or warped—or carve a new one. Carving a bridge is complicated because it involves matching the height, outline, and string spacing of the original, and matching the new bridge’s base to the contours of the top. This process takes several hours when you begin with a raw piece of wood. For details on this operation, read John Brown’s “Replacing the Bridge on a ’74 Gibson Flattop.”
The bridge plate plays an important role in the structural integrity of the guitar’s top. Over time it wears out and eventually cracks. If the plate is simply worn out, there are ways to restore it. However, if the plate is cracked, it must be replaced. Otherwise, it will eventually crack the bridge and cause braces to fail.
Many repairs, such as regluing a bridge that has lifted on a flattop, requires an intimate knowledge of the guitar’s interior, the principles of intonation, and advanced woodworking techniques.
Replacing the bridge plate can take hours, and just removing it requires several specialized tools, cauls, and equipment. Bridges and bridge plate repairs are fairly common in vintage guitars. I recommend you practice these repairs on several inexpensive guitars to develop your skills before attempting to work on a customer’s prized instrument.
When a brace fails in an acoustic guitar, it can cause significant damage. Loose or cracked braces can create body cracks, bridge and bridge plate failure, and a dramatic change in the action. In many cases, this can give the false impression that the guitar has a poor neck angle, when the real issue is brace failure that’s causing the top to either collapse or belly up. A loose brace can be reglued, but a cracked brace may have to be replaced. Repairing top braces requires deep throat clamps with brace and top cauls. Never over-clamp a brace. This can damage both it and the soundboard.
Broken headstocks are a sad reality. Usually they can be repaired, but occasionally it’s a lost cause. If there’s enough wood to reglue the headstock, it can be a very successful project. But if the break is too shear, the project may not be cost-effective. When repairing a broken headstock, you need to have enough wood on both the headstock and the neck to hold them together.
Guitarists have a knack for breaking headstocks. If you know how to undo the damage done, word will travel.
At my shop, we first saturate the wood with a 50/50 mix of TiteBond II and water. After cleaning up any excess, we then apply full-strength TiteBond II and clamp the two pieces together. This repair requires custom cauls to prevent damaging the finish and to ensure a solid glue joint. To let the glue completely dry, you’ll need to wait 24 to 72 hours before stringing up the guitar.
Build or Repair?
I’ll leave you with one final thought. In the world of lutherie, there are two directions you can follow: guitar building and guitar repair. I can tell you from personal experience that it’s very difficult to do both. Building requires a lot of equipment, tools, materials, and money. Repair and restoration doesn’t require nearly as much to get started. Building guitars can be very satisfying, but it’s tough to make a living, especially given the competition. However, as I mentioned at the start of this article, repair and restoration are always in demand. Well-trained professional guitar technicians can make a great living if they work efficiently, effectively, and intelligently. If the idea of becoming a guitar tech resonates with you, your first step is to acquire hands-on training. Tools and materials will flow from there. Good luck!