Truss rods were developed to help wooden guitar necks withstand the constant tension of steel guitar strings. They are also adjustable, allowing players to change the curvature of their neck for the best playing action. There is always ongoing refinement, but truss rods generally fall into two categories: the Vintage Single style and the Double-Expanding style. Both are available from Warmoth.
The first and oldest design we call "vintage." This is the style of rod used by both Fender® and Gibson®. It consists of a single steel rod, typically 3/16" in diameter, inset into a concave trench below the fretboard. It is anchored to the neck at both ends. One end is a fixed anchor, the other end is an threaded, adjustable anchor (threaded 10-32).
Key to the function of this rod is the concave slot or trench in which it is installed. Tightening the adjusting nut causes the rod
to pull upwards towards a straight line, thereby exerting upward pressure in the middle of the arc.
The blue arrows indicate the compression forces exerted lengthwise upon the neck. The brown arrows indicate the forces bearing up on
the center of the neck. The green arrows indicate the resulting neck movement, which helps determine string action height and corresponding relief.
Benefits of the vintage truss rod
- Light weight and minimum mass
- Closest to vintage tone
- Less torque required for adjustment
- Adjusts at the headstock on Warmoth Vintage/Modern necks
- Requires frequent adjustments with seasonal humidity changes
- Inward compression of the wood causes eventual neck distortions (lumps and bumps in the fretboard)
- More difficult installation with fitted skunk stripe
The Double-Expanding Truss Rod
The second design is a double rod made of two steel shafts welded together at one end. A long threaded nut at the other end provides adjustment and focuses the truss action away from the unmovable heel joint. This design is used by Rickenbacker®. The double rod is installed in a straight trench below the fretboard, approximately 3/8" deep. It is anchored only to itself, and not the neck wood.
When flexed in the neck, resulting pressures are shown above. The blue arrows show the inward compression, which is absorbed by the rod itself and not the neck wood. The brown arrows show the two rod ends exerting strong downward forces while the middle pushes up uniformly. The resulting neck movements shown with the green arrows, determines string action height and corresponding relief.
The force exerted by the tail end of the double rod is considerable. There must be a minimum 1/8" of wood below the rod end to prevent wood failure in this area. This becomes a concern only when thinning a neck beyond factory engineered dimensions. All Modern necks exceed this engineering requirement.
Benefits of the double expanding truss rod
- Extremely stable, no seasonal adjustments are necessary
- Increased mass for longer sustain, cleaner and clearer tones
- No end to end wood compression to eventually distort the neck
- Heel adjusting on most necks
- Adjusts at the headstock on Warmoth Tiltback necks
- Weighs 3 ounces more than a vintage rod
- More torque required for adjustment
- More expensive to manufacture
A third design now enjoying some popularity is a variation of the vintage single rod which is adjustable in two directions. While
this design is touted to be superior, it is our opinion that well designed necks built from carefully selected and cured woods exhibit
none of the problems this design is proported to solve. Warmoth does not offer this style.
Which design is right for you? This is a personal choice with no wrong answer. To precisely replicate vintage tone, only the vintage rod will do. For stability and better sustain, only the double rod delivers.