Best metal bar that resists bending for guitar truss rod.

[Moab]

I'm looking for suggestions on the best square metal bar stock or t bar stock that would resist bending the most while being used as a truss rod in a guitar neck. This would be a non adjustable guitar truss rod of course and the ultimate material would keep the neck perfectly flat under the pressure from the guitar strings. The material would be glued inside of the guitar neck to keep it flat.

Size of the material would have to be no bigger than 1/4" x 1/4" square for bar stock. A smaller size would be better of course due to weight concerns, but stiffness and strength is the primary concern.

What material will resist bending the most?

 

[arunmrao]

THere are different grades of steel with high stiffness which could be helpful. However, I wonder if this would not add weight to the guitar( I have never handled one just imagining). Perhaps a carbon fibre composite like the ones used in tennis racquets will be useful.

 

[Guest102023]

If stiffness only is required, all steels are more or less equal. Stiffness will then be primarily a function of the cross-sectional shape and how effectively it is bonded to the neck.

But I suspect by 'stiffness' you really mean 'strength'.

Permanent deformation is one problem to be avoided, so you will want to have a reasonably good yield strength, say 48 ksi or greater. You would need to do some calculations to determine what strength might be required - but it is probably best to find out what is 'standard practice' in the guitar building world rather than have an engineer try to figure it out from first principles. That approach might produce an instrument too heavy to lift!

I am wondering now if corrosion might be an issue? In that case stainless steel would be recommended.

 

[CoryPad]

If stiffness is the limiting factor, then the best likely would be beryllium: E = 303 GPa and [ρ] = 1.8 [·] 10[sup]3[/sup] kg m[sup]-3[/sup].

If cost is any kind of a concern, then steel will be hard to beat: E = 207 GPa and [ρ] = 7.9 [·] 10[sup]3[/sup] kg m[sup]-3[/sup].

If a nonmetallic material may be considered, Arun's suggestion of a long-fiber carbon-fiber reinforced polymeric composite would work well.

 

[SnTMan]

Moab, I am going to go out on a limb and guess that many of the members of this forum have no idea what a "non adjustable guitar truss rod" is or where within the guitar it lives. A picture could really sharpen the discussion.

I will say that at 1/4" x 1/4" you are not going to gain a lot of bending resistance, whatever material is used. Oh, and nothing is perfectly flat.

Regards,

Mike

 

[EdStainless]

Another option that would available would be a tungsten rod. This metal is used as welding electrodes and EDM electrodes and is commonly available as round rod. It is about twice as stiff as steel. This would help limit deflection of the neck.

One caution, W is brittle. If you overload it you will not bend the rod, it will snap.

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[Moab]

Thanks for all of the above posts and I will explain what a guitar truss rod is and what it does.

Electric Guitar strings place around 180 pounds of string pull on the wood guitar neck which will bend the guitar neck and make it unplayable. Different styles of truss rods have been used over the years to keep the guitar neck from bending and to keep it flat. Vintage Martin acoustic guitars had a non adjustable straight metal T-bar truss rod glued into the neck of the guitar to help keep it straight and this style worked very well. In later years Martin switched to a hollow square metal tube truss rod that was glued into the neck, but it was not a stiff as the t-bar design and many people do not like this style of truss rod.

Fender electric guitars have an adjustable metal truss rod in the neck of the guitar that is basically a round piece of steel with a threaded adjustment bolt on one end that is placed in a slightly curved or "U" shaped route of the guitar neck. This truss rod design can be tightened which will straighten the neck when the guitar strings are on the guitar.

Vigier electric guitars have some kind of flat carbon fiber bar placed into the wood necks of their guitars and it keeps the neck perfectly flat under the pressure of the guitar strings. A friend of mine owns one of those and whatever they are using works extremely well. This is a non adjustable design and I'm trying to accomplish something similar.

Every 18 inch long steel bar material I have tried bends. I have bought 18 inch long square carbon fiber bar and square carbon fiber hollow tube, but all of the material I have tried bends, is not stiff or strong enough and does not stay flat under the string pull of the guitar strings.

The ultimate material would be light, not too big and stay perfectly flat under the pull of the guitar strings once glued into the guitar neck.

 

[SnTMan]

Moab, the deeper section the better. The ultimate probably would be a carbon fiber section (unidirectional ply along the neck length) nearly as deep as the neck is thick. Can you take one of your Vigiers and cut thru the neck to see the dimension of the bar? [I didn't think so]

I'm betting it is nearly as deep as the neck is thick, and could even be a variable depth to follow the neck. It may not be a simple rectangular section either, but a T or something.

Can you make the whole neck carbon fiber?

Regards,

Mike

 

[EdStainless]

What do you mean by saying that what you have tried bends? Do they flex too much? or take a permanent set? or both?
The amount of flex is a function of the material's modulus and geometry, the taking a permanent bend is a function of strength.

The more material that there is further away from the load the more it will help. A "T" with the wide end to the outside will have about the same stiffness as a square or round tube or bar of the same width. The "T" adds the most stiffness with the least material.
It would make sense to have the leg of the "T" get shorter as it ran up the neck since the greatest load is near the bottom.

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Plymouth Tube

 

[IRstuff]

Steel, which is presumably what you purchased, comes in a ton of different alloys, with differing properties. Seems to me you could dismantle an existing guitar neck and compare its truss bar with the stuff you bought.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[tr1ntx]

There are a few other tricks to the trade, such as pre-stressing and asymtric heat treatment.

Have you tried a Martin style T-bar? Those guys really knew their craft.

For any of your steel prototypes, bend it to put a slight bow into the truss bar. Install it so that it bows down, i.e., opposite the direction the strings will pull it. When you tighten the strings and bend the bar straight, it will exhibit a higher stiffness from that point onward. The amount of pre-bend can be calculated pretty closely, but might still require some trial & error.

More complicatedly, you could have a bar hard-tempered just from one side, trying not to get all the way through. That will be difficult for such a small cross-section, so you might have to do a larger piece then have it milled down. With a T-bar, it might be easier. You could heat from the ends of the flat and not get so much into the vertical. (Or am I thinking backwards and you would want to heat to end of the vertical?) Hmmm . . . .

Like IRStuff said, there are tons of steels and steel alloys and many specialty, little publicized ones for niche applications and heat treatments. Just in terms of carbon steel, I would guesstimate that 1045 or 1050, maybe even 1060, is what you would want and those are available in small squares & rounds. You can have a T milled from a square bar. Try one of those with the bending method of prestressing and see how close you are.

 

[Compositepro]

"Every 18 inch long steel bar material I have tried bends. I have bought 18 inch long square carbon fiber bar and square carbon fiber hollow tube, but all of the material I have tried bends, is not stiff or strong enough and does not stay flat under the string pull of the guitar strings."

Truss rods are not intended to be flexurally stiff. They carry only tensile loads which balance with the string tension. The neck of the guitar is under compression. Truss rods allow the use of less stiff (cheaper) materials for the neck. If the neck is made very stiff to begin with then a truss rod is not needed. But no material is infinitely stiff and string tension will always tend to bend the neck. Increasing tension on the truss rod bends the neck in the opposite direction to string tension.

A bend in the neck is undesirable because it changes the distance between the strings and the frets.

Carbon fiber for the neck and truss rod is the ultimate solution but few people can afford it. Carbon composite has very high modulus, tensile and compressive strength, and it is almost unaffected by changes in temperature and humidity.

 

[unclesyd]

Off the wall approach.

You might want to look at the higher modulus woods especially Pau Lope for the neck.. This wood could be used as a composite or stand alone. There are several varieties of this wood so look around.
It is also known as Brazilian walnut or Brazilian ironwood among others..

This comparison is for the diamond decking product, the wood.

http://www.diamonddecking.com/compare.htm

 

[Moab]

SnTMan, it would be fun to see the Vigier neck construction, and it would cost around $1,400.00 to cut one up. Vigier is most likely doing exactly what you are suggesting with carbon fiber.

My problem has been finding carbon fiber material that is incredibly stiff. A guitar building supply company I buy products from does sell carbon fiber bar stock, but the material they sell is not stiff enough. I bought some carbon fiber bar stock from one of the best custom kite makers who uses it and what he sent me was not stiff enough. I have not tried carbon fiber t-bar shaped material and that may be the perfect solution. Where can I find a supplier for it? If anyone has suggestions of carbon fiber suppliers I should consider buying from please let me know.

 

[Moab]

EdStainless

I'm just bending the steel and carbon fiber square bar stock by placing the ends up on blocks and then pushing down on the bar stock at the half way point by hand. When the material I'm testing bends too easily then it just will not work.

I have not bought any steel or carbon fiber t-bar stock yet. I will keep searching for the best metal and carbon fiber material that will work.

 

[Moab]

IRstuff

Almost all of the American made guitars are using the traditional adjustable round truss rod which works great. I have been building guitars for over twenty years, so I'm very familiar with it. What I'm not familiar with is having a square bar or t-bar that is so stiff that once you glue it into a guitar neck it will keep the guitar neck perfectly straight no matter what humidity changes take place or what the string pull is on the guitar neck.

The Vigier guitars are made in France and they are doing something the American guitar companies are not. They simply have come up with a way of constructing a wood guitar neck with carbon fiber placed inside of it that always stays flat and you can not adjust this truss rod. This is something new. My friend who owns a Vigier says it works perfectly.

 

[Moab]

Tr1ntx

Bending the bar is not something I want to do. Too many variables considering the construction and it would be much harder to do.

The easier approach is to use flat/straight stable seasoned quarter-sawn wood that is already very stiff and glue a straight metal or carbon fiber bar/t-bar into the neck that keeps it flat under the string pressure and humidity changes.

 

[Moab]

Compositepro

You know exactly what I'm talking about. Carbon fiber is most likely the ultimate solution. Finding an already made bar stock or t-bar stock made out of carbon fiber that will work for my application has not been easy. I have not found the perfect material yet and you can definitely suggest a supplier who might have the material I need.

 

[SnTMan]

Maob,

http://www.aircraftspruce.com/menus/me/carbonfiber.html

 

[Moab]

Unclesyd

Good suggestion on Pau Lope.

A wood I was very interested in trying was mesquite which grows like weeds in Texas. Mesquite has some superior properties when it comes to shrinkage, hardness, strength and humidity changes. A Janka hardness test is 2350 on Brazilian cherry, 2345 on mesquite and 1450 on hard maple as an example.

The problem is Mesquite trees do not grow very straight and many grow with twists in the wood. Finding a supplier who would sell me guitar grade mesquite which was straight grained was almost impossible. Mesquite is a fantastic flooring material.