Double trussrod to prevent twisting, overkill?

[Big B.]

Everyone has already covered the dubious usefulness of having 2 truss rods in most bass necks. Another problem with 2 truss rods is that it will severely limit how much wood you can carve away from the back of the neck. Having a truss rod in the center with a smaller carbon fiber rod on each side allows for a nice round neck profile. With two truss rods spaced apart you'll be forced into a more square profile to make sure you are leaving enough material behind them.

I've built a lot of 6 string basses and one truss rod has always been enough. Seven strings with a high F on the other hand seem to straddle the line of considering another rod. The tension of the upper strings will sometimes pull that side of the neck just a bit more than the bass side which can cause setup issues.

 

[4string5string]

5 strings? 6 Strings? 35+ scale length? I’ll take two trussrods, please.

 

[DriftyOmega]

I've built a few crazy wide necks, 7 and 8-string unison monsters, that were 3" wide at the nut. In that case, I did use two truss rods that were spaced about 1 1/2" apart. They were necessary to counteract the load from all those strings. And it was helpful to be able to bias their loading a little bit, to even out the relief on either side of the neck. Not fixing serious neck twist, but fine adjustments to the relief.

My general rule is: single truss rod for necks up to 2 1/4" wide.

Thank you for the info you share.

Do you still epoxy the CF TOW strands under the 2 truss rods, or do you just keep the single stripe down the middle between the 2 rods? Also curious if you increase the laminates?

Planning an 8 string build (F#-F) now. Considered a 7pc laminate neck plus CF and 2 truss rods but i came across your CF TOW recommendation and wasnt sure how i should proceed. This response was gold because the nut is at least 3".

 

[Bruce Johnson]

Thank you for the info you share.

Do you still epoxy the CF TOW strands under the 2 truss rods, or do you just keep the single stripe down the middle between the 2 rods? Also curious if you increase the laminates?

Planning an 8 string build (F#-F) now. Considered a 7pc laminate neck plus CF and 2 truss rods but i came across your CF TOW recommendation and wasnt sure how i should proceed. This response was gold because the nut is at least 3".

If I were building it, yes, I'd put the CF TOW backstraps under both truss rods. That's to prevent the ski jump condition, and you have to cut those two slots anyway.

The reason for building the neck multi-lam is for stability. Get all the rings all opposing and symmetrical, with the V facing upward. If you do that, 3 lams is all you really need. Going to 5 or 7 or more doesn't add much more strength or stability. But on a wide neck like this, you may want to use more lams for looks, or the width of wood strips you have available. Likewise, adding thin ribbon strips between the laminations is mostly decoration. Nothing wrong with making the bass prettier, but they're not necessary for structural reasons.

If I were building that neck to be strong and clean looking, I'd probably go with 5-piece maple. Two truss rods, two carbon fiber backstraps. That's all it really needs.

 

[DriftyOmega]

If I were building it, yes, I'd put the CF TOW backstraps under both truss rods. That's to prevent the ski jump condition, and you have to cut those two slots anyway.

The reason for building the neck multi-lam is for stability. Get all the rings all opposing and symmetrical, with the V facing upward. If you do that, 3 lams is all you really need. Going to 5 or 7 or more doesn't add much more strength or stability. But on a wide neck like this, you may want to use more lams for looks, or the width of wood strips you have available. Likewise, adding thin ribbon strips between the laminations is mostly decoration. Nothing wrong with making the bass prettier, but they're not necessary for structural reasons.

If I were building that neck to be strong and clean looking, I'd probably go with 5-piece maple. Two truss rods, two carbon fiber backstraps. That's all it really needs.

Awesome, thanks so much Bruce for setting me straight.
Im looking forward to trying those backstraps. Also happy to know 5 is a good base so i can decide on the aesthetic strips or not.
I have a lot data on 6 string basses but the extra size makes me question my judgement and i have a tendency for overkill so much appreciated!

 

[Videojunkie]

Awesome, thanks so much Bruce for setting me straight.
Im looking forward to trying those backstraps. Also happy to know 5 is a good base so i can decide on the aesthetic strips or not.
I have a lot data on 6 string basses but the extra size makes me question my judgement and i have a tendency for overkill so much appreciated!

If you haven't, you should look up @Rôckhewer 's builds. I think at least one of them is a 7 string.

 

[DriftyOmega]

Does it matter if the truss rods are parallel to each other or the neck/fingerboard sides?

 

[TerribleTim68]

Awesome, thanks so much Bruce for setting me straight.
Im looking forward to trying those backstraps. Also happy to know 5 is a good base so i can decide on the aesthetic strips or not.
I have a lot data on 6 string basses but the extra size makes me question my judgement and i have a tendency for overkill so much appreciated!

If you haven't, you should look up @Rôckhewer 's builds. I think at least one of them is a 7 string.

You could also look up @Triad 's builds, he just finished this one up (posted on his FB page) -

I don't think he knows how to build a "normal" bass. And yeah, 2 truss rods.

 

[Bruce Johnson]

Does it matter if the truss rods are parallel to each other or the neck/fingerboard sides?

It doesn't matter too much. Unless the neck has a really dramatic taper. Just be careful how you position the rods at the nut end. Don't get them too far apart, where they are in danger of poking down through when you shape the back.

 

[DriftyOmega]

Don't get them too far apart, where they are in danger of poking down through when you shape the back.

Thank you, good point. Ill check that when estimating the TOW channels' depth.

How far from the end of the neck should the truss rods extend?
DA hot rods from SM would be about 3/4" from the end, and LMIs longest stock would be 1". Not sure if i should go custom length to be safe, or if just extending into the heel is sufficient.

 

[Bruce Johnson]

Thank you, good point. Ill check that when estimating the TOW channels' depth.

How far from the end of the neck should the truss rods extend?
DA hot rods from SM would be about 3/4" from the end, and LMIs longest stock would be 1". Not sure if i should go custom length to be safe, or if just extending into the heel is sufficient.

General good practice is to have the working length of the truss rod 1" shorter than the fingerboard, 1/2" at each end. On a heel access TR, the actuating nut should end up about flush with the end of the heel.

 

[DriftyOmega]

General good practice is to have the working length of the truss rod 1" shorter than the fingerboard, 1/2" at each end. On a heel access TR, the actuating nut should end up about flush with the end of the heel.

Ah perfect, that makes sense. Helps distribute the pressure more evenly.

Thanks again Mr Johnson!