Official Luthiers Forum!

Does anyone use aluminium neck inserts instead of graphite or carbon fibre?
If so, what thickness and depth?
If not, why not?

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We are all in the gutter but some of us are looking at guitars.

In lieu of a truss rod or in addition too? I suppose a T-bar of a decent alloy would work fine.

Graphite and carbon fiber are stiffer and maybe even lighter then aluminum. Aluminum can bend and lose it's original form. The carbon fiber and graphite can flex slightly but will maintain its form.

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Another day, another dollar.

There is nothing about Al that is superior to CF.

A .125 x .3 x 18" CF can be had for less than $3.

It's a no brainer.

Yes! Ovation!

Abomovations have a great big aluminum frame around the truss rod that goes up the neck and they epoxy the CRAP outta it! Not pretty!

CF is lighter, but even more, it's much stiffer than aluminum. The stiffer the neck the less energy is sucked up by the neck, in making the neck wobble back and forth without making sound. In sitars they put a gourd on the end of the neck called a tumba to take advantage of this energy loss.

I've heard a couple of times, people using CF for the first time after making guitars without CF reinforcement, how much sustain and clarity their guitars have in doing such.

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Billy Dean Thomas
Covina, CA

"Multi famam, conscientiam, pauci verentur."
(Many fear their reputation, few their conscience)

Aluminum is the truss rod in the Sloane guitar that is being worked on by Todd Stock. It's .250" by .5" 2024 T3 aluminum. Back when I first started I first used the David Russell Young book and that used a .250" X .5" steel bar. You had to build in a back bend to allow for the pull of the strings, if you got that right they were generally quite stable and stiff neck and I think it added to the sound. Only did one using the Sloane Aluminum type. Did not see much difference if I recall correctly but went back to the steel bar for a while before switching to ajustable rods. The point I am trying to make is that one uses what one knows at the time. At the present time it is very easy to look back at that type of thing and ask what was that person thinking. There was not an internet with it all laid out on a platter like it is today. Young, Sloane and folks like them made it possible for us less talented folks to get a foot hold and find some of the skills to be able to make guitars.
Tom

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A person who has never made a mistake has never made anything!!!

The primary mechanical property that opposes string tension in any reinforcing material that might be used in guitar necks is modulus of elasticity...or basically...stiffness. The cheapest, weakest carbon fiber (probably the only kind you're going to find in truss rod reinforcement sticks) is trypically three times stiffer than aluminum. Advanced carbon fibers can get up to ten times stiffer than aluminum but they are not commonly used.

There's little point in using aluminum as a reinforcement when carbon is available...unless the aluminum imparts a tonal improvement...which I doubt.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

It could work. While not as favorable as carbon fiber, aluminum alloys are roughly equivalent to steel alloys in stiffness to weight, very generally speaking.

It isn't a good idea IMHO for an entirely different reason. The coefficient of thermal expansion isn't particularly good. IOW it expands and contracts more than steel as the temperature changes. This could cause tuning issues.

I can think of a one case where aluminum or steel would be preferable over CF for a neck reinforcement: a neck that's meant to last a long time (50+ years). CFRP has many wonderful properties, but as with all fiber-reinforced polymer composites, longevity is not one of them. Pretty much anything causes them to degrade over time: vibration, oxidation, moisture, fatigue, chemicals, etc. Degradation affects both strength and stiffness. As environments go, the inside of a neck is a relatively good one for CFRP, except for vibrations and possibly wood tannin leaching. Still, oxidation, moisture, temp cycling, etc will probably degrade it with time, especially if the epoxy and processing are of the bargain variety.

Metals like steel and aluminum also lose strength with fatigue, but more slowly and predictably, and their stiffness remains unchanged. CFRP also creeps more than steel or aluminum, though of course much less than wood. Lightweight and stiff neck reinforcements out of metal could be done -- Modulus * Moment_of_inertia (E*I) is the important quantity for bending stiffness. The lower modulus of alum means a taller section is needed for the same E*I as CFRP. Hollow, C, and I sections have the best moment of inertia per weight. In aluminum, a heat-treated alloy would be best for strength (6061-T6, 2024-T4), but it may be tough to fit the equivalent E*I of, say, 1/4"x3/8" tall CFRP. For higher-tech marketing, 4130 or titanium sheet could be bent into a C. Or mild steel and stainless. Al, Ti, and all steels all have the same ratio of modulus/density; with thin-wall sections, vary the wall thickness to get the ~same E*I and mass.

Bottom line: a 50-year CFRP neck reinforcement is a difficult problem to model, we don't have the field data, and CFRP doesn't have a good track record for longevity. It might last just fine for 100+ years, but there's no way to have confidence. Metals are predictable and reliable.

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David Malicky

Didn't the Selmer /Macaferri's use a aluminium bar?

Thanks for the replies.
A general downer on Aluminum, although David makes an interesting, positive case for it.
I've never used neck inserts before, just truss rods and I want to use both now.
Anyone in the UK know where I can buy suitable CF or graphite for this?

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We are all in the gutter but some of us are looking at guitars.

Dragonplate Rectangle

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Billy Dean Thomas
Covina, CA

"Multi famam, conscientiam, pauci verentur."
(Many fear their reputation, few their conscience)