Acoustic Guitar Neck Angle

Acoustic guitars may require a neck angle reset once the action (string height) has risen and methods to lower it have been exhausted.

Does My Guitar Need A Neck Reset?

Increased String Height Above Frets

Rising action can make an instrument difficult, even painful to fret. It also plays havoc with intonation.

Normally string height is lowered by performing a set up which makes adjustments to the truss rod, nut and saddle height. Eventually, however, some instruments arrive at a point to which no further adjustments are available.

Low Saddle

Guitars that are in need of a neck reset often have a very low saddle.

As the arch (belly) of the top rises thru years of string tension, the saddle is lowered to counteract it. Eventually the saddle is shaved as low as possible and the neck's angle must be reset to accommodate the new arch of the top.

Very low saddles can diminish the volume and tone of the instrument.

Insufficient Angle


Plane of fingerboard passes below the top of the bridge
indicating the need for neck resetting.

To assess the neck angle a long straight edge can be used. It is placed down the center of the fingerboard to the bridge.

As seen in the picture above, the arch of the top has risen and the bottom of the straight edge now falls below the top of the bridge, literally running into it.

Ideally the a straightedge, sitting atop the frets, should pass over the top of the bridge slightly when no string tension is on the instrument.

changed neck angle

It's also important to note that, when possible, the neck relief (bow) is removed to provide a more accurate measurement of neck angle.

Causes

Many are under the impression that neck resets are necessary because the neck moves, in actuality that is rarely the case.

While necks do bow under tension, a properly working truss rod can adjust the amount of bow (relief) in the neck. Neck resets are performed because the top's arch has increased, raising the string height. We often call this "top belly".

Neck resets are most often necessary because tension has caused the top to belly, which raises the bridge and string height.

Neck angle and neck relief are two entirely different things though both affect string height.

Neck Angle is the pitch (angle) at which the neck is set in the body and requires neck removal to change.
Neck Relief is the amount of curvature (bow/relief) in the neck itself and is controlled by the truss rod.

A neck with excessive relief can also create high action. When checking neck angle with a straightedge the neck should be adjusted straight if possible.

Other Considerations

Loose Necks

Guitar necks are normally bolted or glued to the neck block. If the neck should come loose from the block, string tension could pull it's heel out of the neck block, effectively changing it's angle. This condition would be readily apparent as a gap beneath the heel would be visible with tension is placed on the neck.

Loose Neck Block

A more difficult (and far more rare) issue to spot is a loose neck block. Because the neck is glued to the neck block it too must be securely glued to the top, back and sides. (Note some mortise style neck blocks may not touch the back.)

A neck block that has shifted can cause the neck angle to change when tension is applied and it moves within the body. This can occur when an instrument is left in a hot environment and the glue has softened. A thin feeler gauge can be used to check for gaps between the body and neck block.


Loose neck block
Under tension the neck angle would shift as a result.

I have also seen this on inexpensive instruments with neck blocks that have limited contact with the top and back. Epiphone's® FT series guitars with bolt on necks are notorious for loose neck blocks (as well as other issues).

Loose or Broken X-Brace & Worn Bridge Plates

Though rare, I have also seen a significantly loose X-brace's cause high action due to excessive bellying of the top.

The X-brace supports and stiffens the top as does the bridge plate. When a large section is loose it can permit excessive bellying, which raises the action.

Cost

Neck resets are generally only performed on relatively valuable instruments due to the cost. Along with resetting the neck angle, most instruments will require a complete refret so the fingerboard can be planed.

A neck reset with refret starts at $650.

See Also: Neck Resetting

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