How long should my truss rod be, and what is keeping it in place?

[NR2021]

Hi all,

I'm planning on building my first guitar, but I got some questions. How long should my truss rod be, and what is keeping it in place? My fretboard will be (from nut to fret 24) 504,75 mm long.

I hope you can help me with my questions.

Kind regards,

Niels

[Bizman62]

Hi and welcome to the addiction!

The length of the truss rod depends on several variables but it's no rocket science.

• A double action truss rod with the adjusting nut at the headstock should be from the nut to the heel
• A double action rod adjusted from the body end of the neck should end at about the first fret
• A single action traditional rod adjusted from the headstock has the other end anchored in the heel inside the neck pocket area
• A single action traditional rod adjusted from the heel can be a bit tricky to make as the anchor takes quite a lot of space right in the thinnest part of the neck
• But there's single action aluminium rods without an anchor so they can be put at either end.

Obviously the heel adjusted rods should be a couple of inches longer to reach the end of the neck. And obviously the ends of the rod are solid, most of the action happens around at the 5th - 7th fret. The traditional rods do that with a curved channel, dual action rods have two rods and adjusting the length of one makes the other curve. The aluminium and other straight channel single action rods rely on tension which counteracts the string pull.

The rods are held in place mostly with friction. For dual action and aluminium rods the channel can be snug, the tradional rods can even be put inside a straw for smoother action and they also have an anchor fastened at the other end so they can't be pulled out from the other end no matter what. Anyhow, when you tighten the rod at least the amount it won't rattle it also cant slide back and forth as both the ends and the middle are snug against the channel.

The sketch shows the approximate lengths of various rods and their positioning. The headstock adjusted dual action rod is the most forgiving regarding length, that's why I've coloured the end light blue as that's optional. And of course the trad. single action anchor is right under the fretboard.

Keep on asking!

[NR2021]

1 hour ago, Bizman62 said:

Hi and welcome to the addiction!

The length of the truss rod depends on several variables but it's no rocket science.

• A double action truss rod with the adjusting nut at the headstock should be from the nut to the heel
• A double action rod adjusted from the body end of the neck should end at about the first fret
• A single action traditional rod adjusted from the headstock has the other end anchored in the heel inside the neck pocket area
• A single action traditional rod adjusted from the heel can be a bit tricky to make as the anchor takes quite a lot of space right in the thinnest part of the neck
• But there's single action aluminium rods without an anchor so they can be put at either end.

Obviously the heel adjusted rods should be a couple of inches longer to reach the end of the neck. And obviously the ends of the rod are solid, most of the action happens around at the 5th - 7th fret. The traditional rods do that with a curved channel, dual action rods have two rods and adjusting the length of one makes the other curve. The aluminium and other straight channel single action rods rely on tension which counteracts the string pull.

The rods are held in place mostly with friction. For dual action and aluminium rods the channel can be snug, the tradional rods can even be put inside a straw for smoother action and they also have an anchor fastened at the other end so they can't be pulled out from the other end no matter what. Anyhow, when you tighten the rod at least the amount it won't rattle it also cant slide back and forth as both the ends and the middle are snug against the channel.

The sketch shows the approximate lengths of various rods and their positioning. The headstock adjusted dual action rod is the most forgiving regarding length, that's why I've coloured the end light blue as that's optional. And of course the trad. single action anchor is right under the fretboard.

Keep on asking!

Thank you so much for the detailed explanation, it really helped me a lot! I think I will go for a 460mm dual action truss rod

[Bizman62]

460 mm sounds very familiar although I guess I've used even 420 mm short ones without issues. Then again most of my builds have the 24.75" (630 mm) scale length like in most Gibsons instead of the 25.5" (650 mm) of Fender Strats.

BTW the length of your fingerboard is of less importance to know than the scale length. In case you don't know what that means, it's the shortest distance from nut to bridge and the 12th fret has to be right in the middle of the scale. In theory you can join the body anywhere, even at the first fret with a loooooong cutaway. Such a long neck pocket would be quite thick so playing such an instrument would be awkward. But as long as the scale is right it's a working concept. Lap steel guitars actually are just like that, all body and no neck!

[NR2021]

53 minutes ago, Bizman62 said:

460 mm sounds very familiar although I guess I've used even 420 mm short ones without issues. Then again most of my builds have the 24.75" (630 mm) scale length like in most Gibsons instead of the 25.5" (650 mm) of Fender Strats.

BTW the length of your fingerboard is of less importance to know than the scale length. In case you don't know what that means, it's the shortest distance from nut to bridge and the 12th fret has to be right in the middle of the scale. In theory you can join the body anywhere, even at the first fret with a loooooong cutaway. Such a long neck pocket would be quite thick so playing such an instrument would be awkward. But as long as the scale is right it's a working concept. Lap steel guitars actually are just like that, all body and no neck!

For my build I will use a 26.5" (763mm) scale length. A bit longer than usual so it can hold lower tunings better with normal string tension. I've got to see my exact measurements to see if 460mm is the right size from nut to heel, but I think it's about the right length. My computer is at home so unfortunately I can't check it right now.

Thanks for the additional information!

[NR2021]

2 minutes ago, NR2021 said:

For my build I will use a 26.5" (763mm) scale length.

Oops, I meant 26.5" (673mm)

[Bizman62]

Even for that scale length 460 mm might suffice. After all the 673 mm scale length is only 43 mm longer than the 630 mm where I've been using the 420 mm long rods.

That said, there's variables that can matter somewhat. One is the free length of the neck, i.e. at which fret the neck pocket starts, another is how long the transition area to the heel is. A Gibson SG may look like there's no support at the neck joint but there's a four frets long lip underneath plus the two fret long heel and the neck may extend under the neck pickup. A double cut Les Paul looks more frightening, especially the thinner JR version: There's just the small heel leaning to the body and the two smallest frets on the body before the pickup! I've built one but that was a multi laminated neck-thru... And of course the neck profile matters. A baseball bat has lots of strength even without a truss rod, a V is almost as stiff but much nicer to play. A low C or D may require additional support like carbon rods or at least a laminated design.

When I was buying an electro acoustic I tried an Ibanez Talman. The neck was thin and slick but it bent with every chord I strummed!