Neck reinforcement rods vs truss rod

[abarson]

I understand the purpose of neck reinforcement rods (carbon fiber, titanium, etc.) to be a method to stiffen an instrument's neck, making it more stable.
I understand the purpose of the truss rod to be a mechanism to alter the straightness of an instrument's neck, where changes are usually attributed to temperature changes, etc.
It just seems to me that a truss rod might end up fighting against the reinforcement rods if neck relief is called for. As I'm sure I"m not accounting for something, I'm hoping that a builder can explain what is actually going on in this situation.

 

[Bruce Johnson]

You aren't missing anything. The stiffer the neck is built, whether by lumber, laminations or stiffening rods, the harder the truss rod has to work to make the neck bend a small amount.

Stiffness and stability are two different things. Generally, a stiff neck will be more stable, but not always. A stiff neck, built poorly, can still develop a long-term warp or be unstable when the weather changes. And, when a stiff neck warps, the truss rod probably can't help it.

 

[StuStu]

You aren't missing anything. The stiffer the neck is built, whether by lumber, laminations or stiffening rods, the harder the truss rod has to work to make the neck bend a small amount.

Stiffness and stability are two different things. Generally, a stiff neck will be more stable, but not always. A stiff neck, built poorly, can still develop a long-term warp or be unstable when the weather changes. And, when a stiff neck warps, the truss rod probably can't help it.

Hey Bruce,
So I'm starting my first build and am planning on using both graphite rods with a truss rod in between. Neck will be laminated as well. Is this a bad plan? Does one method actually negate the other(s)? TIA.
Stu

 

[Bruce Johnson]

I'll say it again: Stiffness and stability are two different things.

If you build the neck correctly, you won't have a problem with stability. It won't warp or twist over time (long term stability) and it won't move much with changes in the weather (short term stability). The neck can be built to be stiff or to be soft. If it's built carefully, it will be stable.

Reinforcing rods or bars of graphite, steel, whatever, add stiffness to the neck. That is, it will take more pounds of force to bend it the same amount. So, if you built the neck poorly and the wood tries to warp or bend with the weather, the graphite rods will resist against that bending. The rods can't completely stop the bending, but they will reduce the amount.

The truss rod is an adjustable stiffener. It can add no stiffness, if it's loose, or a lot of stiffness, if it's tight. Tightening it adds stiffness and forces the neck to bend backwards. A double-acting truss rod can force the neck to bend backwards or forwards.

The truss rod only has a limited amount of force that it can apply. The stiffer the neck is overall, the less range of movement you can get from tightening the truss rod. If the neck is really stiff, the truss rod is useless. If a really stiff neck warps, you are out of luck. The truss rod can't help it.

If the neck is built well, and doesn't have a stability problem, then the reinforcing rods aren't necessary. They are just added weight and stiffness, and they are restricting the capability of the truss rod.

How stiff or soft you decide to build the neck will have an effect on the overall sound of the bass. That's a complicated subject by itself, but in general, a stiff neck makes the bass colder, clearer, with a flatter attack curve and minimal background coloration. A softer neck makes the bass warmer sounding, more percussive, and with more background coloration. But there are many overlaps and other factors in there. So, you may want to build the neck really stiff, or not. It depends what kind of bass you are building.

Building a neck correctly, so it doesn't have stability problems, is also a big topic by itself, but it comes down to three things:

1.) Making sure that the wood is properly dried and free of internal stresses.
2.) Cutting the wood and any lamination strips to put the growth rings and grain lines in the best orientation along the neck axis.
3.) Sealing up the wood, so that moisture from the air doesn't soak in and out as the humidity changes.

I hope this answers your question? When you get into the details, building a "good" bass neck is more complicated than it appears. There isn't any single best way; there are tradeoffs and many different approaches.

 

[Gilmourisgod]

A subject of great interest to me, having put two 1/8" x 3/8" graphite stiffeners and a DA rod in my neck-through build! I did this in pure uninformed copycat mode based on current Warmouth neck designs. I've always had good luck with Warmouth necks, so I figured....... yeah, hoping for the best! The neck developed a tiny backbow during construction, which I found I could easily fix with a 1/4 turn of the rod, so I'm hopeful that the neck won't be too stiff to easily adjust under string tension. The sheer number of opinions on every conceivable aspect of luthiery, along with all the assorted gadgets and products for sale, is pretty hard to navigate for amateurs. On TB the watchword is WWBD, What Would Bruce Do?

 

[Jisch]

I have a Kiesel Icon 5 bass, I've had it for about 3 months now. It has a one piece maple neck (non-laminated) but has 2 carbon bars embedded (according to the Kiesel website). I have never seen a neck move as much as this one does. I swear it's a different bass every time I pick it up. It's not unmanageable - I can adjust the neck with small adjustments to the truss rod, but the number of times I'm doing those adjustments is a bit bizarre. I'll bet I've made 5 or 6 adjustments in 3 months. When I make a neck it I usually adjust it a few times over the course of a few weeks then it's set and I don't touch it much after that.

 

[StuStu]

I'll say it again: Stiffness and stability are two different things.

If you build the neck correctly, you won't have a problem with stability. It won't warp or twist over time (long term stability) and it won't move much with changes in the weather (short term stability). The neck can be built to be stiff or to be soft. If it's built carefully, it will be stable.

Reinforcing rods or bars of graphite, steel, whatever, add stiffness to the neck. That is, it will take more pounds of force to bend it the same amount. So, if you built the neck poorly and the wood tries to warp or bend with the weather, the graphite rods will resist against that bending. The rods can't completely stop the bending, but they will reduce the amount.

The truss rod is an adjustable stiffener. It can add no stiffness, if it's loose, or a lot of stiffness, if it's tight. Tightening it adds stiffness and forces the neck to bend backwards. A double-acting truss rod can force the neck to bend backwards or forwards.

The truss rod only has a limited amount of force that it can apply. The stiffer the neck is overall, the less range of movement you can get from tightening the truss rod. If the neck is really stiff, the truss rod is useless. If a really stiff neck warps, you are out of luck. The truss rod can't help it.

If the neck is built well, and doesn't have a stability problem, then the reinforcing rods aren't necessary. They are just added weight and stiffness, and they are restricting the capability of the truss rod.

How stiff or soft you decide to build the neck will have an effect on the overall sound of the bass. That's a complicated subject by itself, but in general, a stiff neck makes the bass colder, clearer, with a flatter attack curve and minimal background coloration. A softer neck makes the bass warmer sounding, more percussive, and with more background coloration. But there are many overlaps and other factors in there. So, you may want to build the neck really stiff, or not. It depends what kind of bass you are building.

Building a neck correctly, so it doesn't have stability problems, is also a big topic by itself, but it comes down to three things:

1.) Making sure that the wood is properly dried and free of internal stresses.
2.) Cutting the wood and any lamination strips to put the growth rings and grain lines in the best orientation along the neck axis.
3.) Sealing up the wood, so that moisture from the air doesn't soak in and out as the humidity changes.

I hope this answers your question? When you get into the details, building a "good" bass neck is more complicated than it appears. There isn't any single best way; there are tradeoffs and many different approaches.

I appreciate the excellent, detailed response. Thanks, Bruce.

 

[Gilmourisgod]

Here's a link to the Warmouth neck page showing the "super-bass" construction, which is a single DA trussrod and two stiffener bars, either steel or graphite. If its just hype, it worked on me, though as I said, I've had zero problems with my Warmouth necks. YMMV. One downside to adding stiffeners is how thin you can shave the neck.With graphite rods, I havent seen anyone using less than 3/8" deep, which effectively sets how thin you can make the neck under the bars. The minimum wood cover under bars or trussrod I keep reading is 3/16", but that may be a matter of opinion.
Invalid Link Removed

 

[Dadagoboi]

Here's a link to the Warmouth neck page showing the "super-bass" construction, which is a single DA trussrod and two stiffener bars, either steel or graphite.
Invalid Link Removed

That's a double expanding SINGLE ACTION trussrod, it ONLY works against front bow. It's similar to this rod used by Harmony and others in the 60s. Much better design than Fender or Gibson's single rods but NOT DA.

Here's the proof: You can remove the adjusting nut on a Warmoth rod. You can't do that with a typical DA rod.

Video showing DA vs SA:


I just used a Warmoth wenge/ ebony neck on a build...believe me I wish the rod had been a DA. The neck was so stiff I could barely get minimal relief with a set of 45-130 flats on it and no tension on the truss rod nut. Luckily the customer likes his action super low.

 

[saved]

I have build a DA with welded one side.As you can see the DA has more threads under the screw.If the welded has more it would act like DA but there is no threads to work from the other direction

 

[40Hz]

If the neck is built well, and doesn't have a stability problem, then the reinforcing rods aren't necessary. They are just added weight and stiffness, and they are restricting the capability of the truss rod.

I've been told by another professional luthier that she felt the reinforcing rods were in there more as a CYA for the neck supplier than they were for addressing any real need. She said the same as you that if the wood or woods being used were properly selected, dried, and tooled when building a neck, such supplemental stiffeners were an unnecessary addition.

Does that ring true with you as well?

 

[Bruce Johnson]

I've been told by another professional luthier that she felt the reinforcing rods were in there more as a CYA for the neck supplier than they were for addressing any real need. She said the same as you that if the wood or woods being used were properly selected, dried, and tooled when building a neck, such supplemental stiffeners were an unnecessary addition.

Does that ring true with you as well?

Yes, I agree. But, the carbon fiber reinforcing rods aren't snake oil. They do stiffen the neck, and they will resist warpage and instability. To a degree. For a large scale manufacturer, adding the bars means that they can be sloppier in their selection of wood, which can result in big cost savings, with fewer rejects and returns. Plus there's the marketing bonus of having Carbon Fiber Bars for Increased Stability. Everyone wants Increased Stability, right?

Aftermarket neck builders like Warmoth put in the reinforcing rods mostly to stiffen up Fender-style necks. These days, everyone wants super-low action. The classic simple Fender design necks aren't real stable. Back in the old days, when bassists played with higher action, nobody noticed or cared. Now, it matters. Customers know about Carbon Fiber Bars and demand Increased Stability! So, Warmoth puts them in to satisfy their customers. But Warmoth also knows how to build necks right, and they do. From what I hear, very few customers have problems with unstable Warmoth necks, whether they have the reinforcing rods or not.

That's the point. Carbon Fiber Bars aren't a guaranteed preventor of instability, which allows you to ignore good construction technique. And, the contrary applies: If a neck doesn't have the bars, it doesn't mean that it will be unstable.

 

[GMC]

I really would advise aganst tightening a dual action truss rod to counter act a bow. I would find the rod's bite point...lossen it off a tad, bend the neck to the desired bow and then re-tighten the rod to the bite point or a bit beyond. The modern 2 way rods don't have a lot of strength to curve a neck, but are designed to lock a curve in place. I've seen a number of broken rods due to severer over tightening. This is not a Fender style rod...so...loosen....make bow and lock...don't keep turning thinking that the neck will bow more...it won't and it'll snap.

 

[reverendrally]

I've just reread this thread and I'm thinking about some new mahogany (type local timber) neck blanks I've just put together.

I'm planning a 32-33"-ish scale 5 string. Should I bother with graphite bars or not?

P.s. they're a 4 piece laminate.

 

[buldog5151bass]

@Bruce Johnson Do you ever use split (rather than sawn) wood when making necks? I make baseball bats, and that is how the wood billets are prepared, to ensure the orientation of the grain is as parallel to the neck as possible.

 

[D-Smith]

@Bruce Johnson Do you ever use split (rather than sawn) wood when making necks? I make baseball bats, and that is how the wood billets are prepared, to ensure the orientation of the grain is as parallel to the neck as possible.

If you can read the grain it's six of one, half dozen of the other.

 

[HaMMerHeD]

...If its just hype, it worked on me, though as I said, I've had zero problems with With graphite rods, I havent seen anyone using less than 3/8" deep, which effectively sets how thin you can make the neck under the bars.

I use 1/4" pultruded carbon fiber tubes from LMII. I think they get them from DragonPlate. They are inexpensive and very stiff, and I can route for them with the same bit I use for truss rod slots. I use System Three T-88 structural epoxy to bed them in.

It's a good system with a shallow route.

 

[Bruce Johnson]

@Bruce Johnson Do you ever use split (rather than sawn) wood when making necks? I make baseball bats, and that is how the wood billets are prepared, to ensure the orientation of the grain is as parallel to the neck as possible.

No, I never have. But, splitting the wood certainly is an old traditional way to find the grain lines. I align the grain lines in a neck by looking at them on surfaced boards, and adjusting the template or drawn lines. Then I saw it.

 

[Gilmourisgod]

I have what’s probably a stupid question:
When gluing in carbon rods, is there any reason NOT to have the neck beam dead flat? I suppose you could “bake in” a very slight forward or back bow by bending the neck prior to epoxying in the bars? I’ve been combining (2) Carbon bars with a single DA trussrod on my builds, basically copying Warmouth neck construction.

 

[reverendrally]

I have what’s probably a stupid question:
When gluing in carbon rods, is there any reason NOT to have the neck beam dead flat? I suppose you could “bake in” a very slight forward or back bow by bending the neck prior to epoxying in the bars? I’ve been combining (2) Carbon bars with a single DA trussrod on my builds, basically copying Warmouth neck construction.

Seems like a good idea. No so much in practice. I didn't do it on purpose, but don't ask me how I know this.

Now, should I put rods in medium scale mahogany necks or not?