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Guitar Shop 101: How to Shim a Bolt-On Neck


Recently a client brought an older Fender Telecaster into the shop for a setup. The action was really high, but the saddles had run out of adjustment and couldn’t drop any lower. After careful inspection, I determined that the neck needed a shim to fix the problem. Fortunately, shimming a bolt-on neck isn’t too hard. In fact, if you’re handy with basic tools you can do this yourself, but you need to understand the process and know what mistakes to avoid. Let’s investigate.

Understanding neck angle. Our journey begins with neck angle, which is the pitch of the neck relative to the guitar’s body and bridge. When the neck angle is set correctly, an electric guitar’s saddles can be raised or lowered to create comfortable playing action and optimum tone and sustain.

Fig. 1. This neck angle is too low, so even dropping the saddles flush to the bridge plate won’t bring the strings close enough to the fretboard to play comfortably.

But when the neck angle is too low (Fig. 1), the saddles can’t be moved down enough to bring the strings close to the frets. The guitar is hard to play and the intonation suffers. Conversely, when the neck angle is too high (Fig. 2), you can’t raise the strings enough to prevent fretting out or buzzing—even when the saddles are adjusted to their maximum height.

Fig. 2. This neck angle is too high. The guitar is unplayable even with the saddles raised to their maximum height.

In this column, we’ll learn how to fix a neck angle that’s too low. Typically, this problem can be resolved using a shim (Fig. 3).

Fig. 3. A full-pocket neck shim can correct a neck angle that’s too low.

What causes a neck angle that’s too low? Most players don’t realize that an electric guitar can compress over time. As an instrument ages, constant string tension can cause the body to become slightly concave, and this changes the neck angle. This doesn’t occur with every guitar, but it is common.

Many experts say that the angle for a bolt-on neck should be between zero and five degrees. From my experience, this is correct in most cases. But what I find even more important is how you adjust the neck to its optimal angle. When this is done properly, your guitar will play and sound at its best. When the neck angle is adjusted improperly, it can ruin a perfectly good neck.

If your guitar plays well and the saddles offer enough adjustment range for you to set the action correctly, you don’t need to change anything. However, if the angle is too low and you can’t move the saddles down any further, the neck needs a shim.

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