Single action truss rod vs double action

[Rosewood99]

Which one do you prefer and why?

[Rodger Knox]

The Blanchard design double action rod. https://alliedlutherie.com/collectio...nt=27705611654
If you need to use a truss rod, it makes sense to me to use a double action rod. It's a big advantage, especially for newer builders, to be able to dial out a little back bow. I needed it on my first few, the necks were too stiff for the strings to pull in ANY relief. I still use them, but I haven't had to adjust the last three or four to get the relief correct, the strings pull in about 0.005" relief with the rod just snug enough that it doesn't rattle.
Single action rods are usually a little lighter, but if weight is a concern, non-adjustable reinforcement (as in vintage Martins) would be my choice.

I'm not a fan of the 2-way rods. IME they are more touchy, as in a little change sometimes makes no difference, or more than you expect. They also tend to affect relief a bit unevenly compared to the 1-way rod in an aluminum channel. I won't turn down a guitar that has a 2-way rod, but I certainly don't prefer it.

FWIW, Martin's old 1/2" T-bar was the heaviest neck reinforcement they ever used - right at 5 ounces. The new 2-way bar weighs 4.6 ounces. If you want to save weight and can live with fixed reinforcement, carbon fiber is probably the best choice.

[murrmac123]

Todd, I just had an epiphany while reading your post ... it suddenly dawned on me how it would be possible to incorporate the exact amount of relief required into a neck with fixed reinforcement.... (post-build)

This would however involve both a neck jig (not the Stewmac one) and a system for sanding frets with the neck under string tension.

I cannot visualize how a builder could make a guitar, ab initio, with a non-adjustable reinforcement rod ( btw they are only truss rods if they are adjustable IMO) and guarantee the required amount of relief without subsequent sanding of the frets.

[Mr Fingers]

Since I've never had a problem with string tension being too low, the double action of a double-action rod has never been necessary for me. I agree with the comment that a single-action rod in a truly well-designed channel is the most precise setup for probably 95% or more of truss rod adjustments (I never get backbow) so that's what I prefer. I have had double-action rods fail (fiddly adjustment socket) and that's the kiss of death as far as I'm concerned.

Originally Posted by murrmac123

Todd, I just had an epiphany while reading your post ... it suddenly dawned on me how it would be possible to incorporate the exact amount of relief required into a neck with fixed reinforcement.... (post-build)

This would however involve both a neck jig (not the Stewmac one) and a system for sanding frets with the neck under string tension.

There are a number of ways to do it without taking it out of the frets - which would not be my first, second, or third choice if it involved more than 0.002"-0.003" difference in fret height. Experience helps in all of those. By judging the stiffness of the neck, some back bow can be built in with a couple different methods. If building with traditional frets, compression fretting can be used on the finished guitar. If the fretboard and inlays are sufficiently thick, the frets can be pulled and the board planed.

It should be noted that compression fretting cannot be used with EVO or stainless frets. To my knowledge they are not available with different tang thicknesses. This means Howard had to nail it some other way.

Originally Posted by murrmac123

I cannot visualize how a builder could make a guitar, ab initio, with a non-adjustable reinforcement rod ( btw they are only truss rods if they are adjustable IMO) and guarantee the required amount of relief without subsequent sanding of the frets.

While the definition does not require that a "rod" be round, that is the way I picture it. So I tend to phrase it similar to you - either non-adjustable or fixed neck reinforcement.

[leeplaysblues]

Here is a video clearly explaining how the different truss rods work

Any tips on how to get the best results with a double action truss rod?


http://https://www.youtube.com/watch?v=Ad8nqm5qP6A

[Christopher Cozad]

Originally Posted by leeplaysblues

Sorry if I sound naive, but I am sure others would love this explanation...

I wrote a short article a while back, contrasting rods and stiffeners. It may prove informative and/or helpful.

Neck "adjustment" is a relative term, and provides for a means to deviate from dead flat or an undesirable over-bowing. If you wish to create a very, very slight forward bow in an otherwise dead flat neck, creating what is known as relief (extra space for the string to vibrate without inducing string buzz against the frets), you would loosen a compression rod, allowing the string tension to bow the neck forward, or tighten the dual-action truss rod by turning clockwise, deliberately bowing the neck forward.

Never in all the acoustics I have owned have I never had a problem with a single-action truss rod. It's reliable, what more ya want?

[Monsoon1]

Originally Posted by murrmac123

Todd, I just had an epiphany while reading your post ... it suddenly dawned on me how it would be possible to incorporate the exact amount of relief required into a neck with fixed reinforcement.... (post-build)

This would however involve both a neck jig (not the Stewmac one) and a system for sanding frets with the neck under string tension.

I cannot visualize how a builder could make a guitar, ab initio, with a non-adjustable reinforcement rod ( btw they are only truss rods if they are adjustable IMO) and guarantee the required amount of relief without subsequent sanding of the frets.

Plek machines grind the frets while the neck is under tension.

[fnesnor]

Originally Posted by Todd Yates

...FWIW, Martin's old 1/2" T-bar was the heaviest neck reinforcement they ever used - right at 5 ounces...

For those with old Matins and other non adjustable necks, I use a custom built fixture and system designed and taught by Dan Erlewine to dial in a proper relief with the instrument in playing position. It allows the fretting technician to remove back bow on older, non truss rod instruments, if needed. I use two way truss rods in my builds these days but may try carbon in a future build.

[Long Jon]

Originally Posted by Monsoon1

Plek machines grind the frets while the neck is under tension.

A Plek machine makes an ideal gift for any millionaire hobby builders.

Originally Posted by Monsoon1

Plek machines grind the frets while the neck is under tension.

I'm not sure that's correct, at least not the way Murray is envisioning the solution. Typical use of the PLEK involves the operator adjusting the truss rod after the initial PLEK measurements, then the PLEK works on the frets. Not sure what others do, but Martin does not use the PLEK on any guitar with fixed reinforcement.

Originally Posted by Christopher Cozad

I wrote a short article a while back, contrasting rods and stiffeners. It may prove informative and/or helpful.

Neck "adjustment" is a relative term, and provides for a means to deviate from dead flat or an undesirable over-bowing. If you wish to create a very, very slight back bow in an otherwise dead flat neck, creating what is known as relief (extra space for the string to vibrate without inducing string buzz against the frets), you would loosen a compression rod, allowing the string tension to bow the neck forward, or tighten the dual-action truss rod by turning clockwise, deliberately bowing the neck forward.

I believe you meant to say "forward bow" in the bolded section.

Originally Posted by fnesnor

For those with old Matins and other non adjustable necks, I use a custom built fixture and system designed and taught by Dan Erlewine to dial in a proper relief with the instrument in playing position. It allows the fretting technician to remove back bow on older, non truss rod instruments, if needed. I use two way truss rods in my builds these days but may try carbon in a future build.

Like the quote above, don't you mean "forward bow" since excessive relief is a more commonly encountered problem than back bow?

[Christopher Cozad]

Originally Posted by Todd Yates

...I believe you meant to say "forward bow" in the bolded section...

Indeed. Thanks for catching that, Todd. I know better than to write as I'm falling asleep, and yet I insist on doing it anyway. I should go re-read my own posts. ;~}

[Rodger Knox]

Originally Posted by murrmac123

Todd, I just had an epiphany while reading your post ... it suddenly dawned on me how it would be possible to incorporate the exact amount of relief required into a neck with fixed reinforcement.... (post-build)

This would however involve both a neck jig (not the Stewmac one) and a system for sanding frets with the neck under string tension.

I cannot visualize how a builder could make a guitar, ab initio, with a non-adjustable reinforcement rod ( btw they are only truss rods if they are adjustable IMO) and guarantee the required amount of relief without subsequent sanding of the frets.

The relief can be built into the fretboard, but that has to be taken into consideration when leveling the frets. I typically sand in .003" more relief on the bass side, and strings pull in .003", so that gives me the .003"/.006" relief I'm looking for. With a little carbon fiber, it would be easy to build a neck stiff enough that string tension would not measurably deflect it, and whatever relief is desired could be sanded into the fretboard.