Official Luthiers Forum!

Anything wrong with using 1/8" x 1/2" aluminium bars in a neck instead of CF? There must be as I haven't seen anybody do it. I am curious to read opinions on this.

_________________
Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

I read once that the original Selmers had aluminum reinforcements but I am not positive it was accurate. I can't think of why it would be bad.

_________________
Burton
http://www.legeytinstruments.com
Brookline, MA.

Laurent,

I would suspect that standard grade aluminum is not nearly strong enough to resist the force of the strings. I do know of at least one luthier who has used aircraft grade aluminum with good success.

_________________
Jimmy Caldwell
http://www.caldwellguitars.com

Aluminum will bend over time, while CF will always try to remain strait, thus providing a better support over time. And although I'm not sure, but I believe aluminum is heavier than CF.

_________________
Alain Moisan
Former full time builder of Acoustics, Classicals and Flamencos.
(Now building just for fun!)

How about Titanium?

Titanium is almost twice as dense as aluminum, and both are denser than carbon fiber composite.

Laurent,

Overall Carbon Fiber will be lighter and stiffer than Aluminum. CF doesnt really deform much and will hit a point where it just snaps. Aluminum will deform more before it fails. I would think that CF would have greater rebound under a working load while most Aluminum may not come back all the way. That would be the biggest problem. There may be something that retains an acceptable shape under the loads needed. Problem is there is a lot of different grades and tempers in aluminum and priced according to how much is made in that grade. I can look through the ASME Reference books tomorrow if you know what the strength and elongation factors are for CF to compare or what you are looking for in stiffness/load factor? My experience is that the harder Aluminums will have a bit of ring to them, especially in thin shapes, CF is dead.

Tim

Hi Laurent,

If you want to research this then understand that "modulus of elasticity" is the mechanical property that most clearly indicates the ability of a material to withstand a bending load...provided that when you are considering carbon fiber, you are applying that load against fiber that is oriented lengthwise along the neck. With the better aluminum alloys like 6061 T651 this is about 10 million lb-in2. Titanium is about 16 million lb-in2. The weakest carbon fiber is 32 million lb-in2. Carbon fiber can also be produced to get upwards of 120 million lb-in2.

These published properties are usually guaranteed with aluminum because of the way it is processed. With carbon fiber, however, there is no guarantee that a company selling cured rods has used a process that will have maximized the potential of carbon fiber. Chances are pretty good that a carbon fiber rod that you have obtained is not coming very close to the theoretical potential of carbon fiber. Essentially, a molding process has to control each individual fiber so that it lays PERFECTLY parallel to all other fibers and that they all cure under equal tension. This can't ever be done in manufacturing but with trainloads of technology, some aerospace companies get fairly close. It isn't likey that a manufacturing process used to make bars for the purpose of being a truss rods is even remotely contolled in this way.

That's a long way of saying that it's hard to say what you're getting with carbon fiber truss rods. I will say that a halfway decent molding process will likely yield a bar that is at least twice the strength of an aluminum bar of the same dimensions. I will also say the the geometrical shape of the bar plays a VERY significant role in the load bearing ability of the bar. The difference between a depth of 3/4" and 1/2" for a carbon fiber truss rod would about double its bending strength assuming the width was the same on both bars..

_________________
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

I seem to recall that Irving Sloane recommended some sort of fancy aluminum as a truss rod material in his steel string book... I've never tried it, and couldn't tell you if it works.

_________________
Rian Gitar og Mandolin

I used aluminum (1/4 x 1/2 deep) in the necks of some guitars I built back in the 70s, when the David Russell Young book was 'the latest word'. I must have read something about using Al in the GAL DataSheets, because Young recommends a steel bar in the book.
The necks are doing fine, as far as I know (I've checked a couple of them in the past year or two.)

I doubt that the load in a guitar neck would bend a 1/2" deep Al beam very much.
CF (with some cleaning and scuffing to make sure there's a good bonding surface) is a lot better to glue than Al, if that matters.
Since a neck-sized chunk of CF only costs a few dollars, probably the 'high-tech' factor - good for impressing buyers/owners- counts more than function.

Cheers
John

CF is superior to Aluminum. A Tee bar would be best for stifiness. I prefer the CF and have used it. I would use steel before Aluminium.

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Thanks much for the replies.
John, I think Collings uses 2 x spring steel slats as reinforcement in their necks, and that may be the better solution.
The T-bar is out of question because I still want to use a truss-rod, weight is also an issue.
I am asking because I have some 1/8" aluminium stock, and it seems as light and strong as CF… to my hands…
I understand it needs to be cleaned before gluing. Also I truly despise CF dust…

_________________
Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

There's plenty of necks out there with nothing but a truss rod. Since you've got some aluminum I'd say use it.

_________________
I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

I ment: "Aluminum will deform over time, while CF will always try to remain strait...". (Excuse my english, as they say!) But, that said, it seems I was wrong even then. I don't know where I got the information, but I was sure that aluminum would deform if it was bent over a long period of time.

_________________
Alain Moisan
Former full time builder of Acoustics, Classicals and Flamencos.
(Now building just for fun!)

To be clear, I am not too concerned about "deformation" over time as I use a double-acting rod. I am asking about the validity (if any) of replacing CF rods with aluminium rods. I dado the rods in the neck and FB and what I am looking for is rigidity, stiffness and stability.

_________________
Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

Laurent, your idea seems valid to me.
And especially if your bars are proud of the neck, and run in matching slots of the fretboard. (I think I read you correctly?)
Seems like a very stiff sandwich to me.
Might try it myself. Do you know what type alloy you have on hand?

Steve

_________________
From Nacogdoches...the oldest town in Texas.

http://www.stephenkinnaird.com

6061-T6 is at 69 or 70Gpa and it's the stuff off the shelf at pretty much any metal supplier selling aluminum bar. All things considered, particularly that you can make the rods pretty deep, I think it'll work just fine. 6061 to CF requires twice the depth and half the width to get the same Youngs Modulus to weight ratio compared to good pultruded CF. At that dimension, it'll most likely be doing better than the stuff we have access to, since I'm pretty sure the guys selling rods to us aren't investing in aerospace grade pultruders. Aluminum's still over twice as stiff as wood per mass.

The aluminum degrading and other stuff is a little knowledge being a dangerous thing. Aircraft parts are switched out after 20,000 hours of active stress at which point they've got a virtually zero chance of failure. Under a small static load like a guitar neck, I'd feel fine with warranteeing the aluminum rods until the wood crumbles to dust around them.

I'll probably end up using CF, but I also have an in to get nice pultruded rods that'll go as deep as I want in the neck.

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Well, if I ever find out from who I got the information, I'll tell him that. In the mean time I'll let others comment when thread involves aluminum...

_________________
Alain Moisan
Former full time builder of Acoustics, Classicals and Flamencos.
(Now building just for fun!)

Sorry if that came off wrong, I definitely didn't want to demean sharing knowledge. Writing is not my medium

The information is right, it's just that the order of magnitude means it's not applicable here. Unlike steel and titanium, which have a certain range of motion over which they can be continually deformed without degradation, aluminum gets 'damaged' by every little bit of motion. But it could take a million cycles for it to fail. An aluminum spring will die in short order, but an aluminum airplane wing can be whipped back and forth for three years straight without failing.

There's a lot of talk in bike frames about this property of aluminum, and it sells a decent number of titanium frames in some sectors. At the end of the day, though, there's nobody who's going to do enough riding on one frame in their lifetime to have their aluminum frame fail due to actual aluminum fatigue.

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

No worries Bob!

_________________
Alain Moisan
Former full time builder of Acoustics, Classicals and Flamencos.
(Now building just for fun!)

Laurent: Have used both steel and aluminum rods 1/4 by 1/2.I had to build in back bow to counter act for string tension.Only used AL once as the relief crept up too high,forget what it was but I was not happy. Used the steel about 15 times or so and was happy with that,if you hit the relief right on it generally stayed.That's over a period going back to the 70's.Steel made a heavy off balanced guitar but think it helped sustain and volume.Using light tuners and wooden buttons helps by taking weight off the end of the cantilever beam called a neck. I now use a two way rod with two CF 1/8 by 3/8 rods and find that the best yet. I really like the idea of the spring steel and think that would be a worthwhile experiment. Keep us all informed of what you do and how it works out. Good luck.
Tom

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

Very informative replies, thanks again.
Bob, I was hoping you'd chime in!
I think I'll go ahead since it's a guitar I build for myself (me) as I still haven't a personal guitar, and it's going to be an interesting build.
Woody, agreed: I rarely use rods in the neck. So far when I did, I've used 2x 1/8" x 3/8" CF for customers who desired a very rigid neck for the usual reasons (medium strings, constant change of open tunings etc.).
Steve, you read me correctly. I did this a couple of times for the Turner/Stauffer tilt-neck, but with CF. I think aluminum will work fine.

_________________
Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

Wouldn't the aluminum be expensive? Also how does it adhere and which glue would you use?

_________________
Greg
http://garibaldiinstruments.com/

Bob, I take exception to this. It's kind of like saying guys who machine parts for guitar makers can't hold real tolerances, which we both know is not true.

For those of you who are reading this and have purchased carbon fiber rods in the past from Los Alamos Composites I would like you to know;

1) I produce all of the rods we sell in house. I do not buy from a pultruder and resell.

2) I use only prepreg material from Toray, same as the aircraft industry. Prepreg materials have a precisely controlled resin content, 35% in my case which has a huge impact on the stiffness of the final composite. Composite pieces produced from prepreg are the highest quality of composite parts due to the control of the resin. Prepreg parts are made by laying down layers .005 at a time and curing the part under heat and pressure. This is not slopping resin onto dry fibers and letting it cure.

3) Pultruded product which is the most readily available form of rods is an inferior product to pieces made from prepreg due to pultrusion’s high resin content, assuming the same fibers. It does look better however if that’s important to you.

4) As far as stiffness goes, the rods from Los Alamos Composites are almost 2x as stiff as aluminum while being lighter.

I saw this post earlier and I was really annoyed by it, so I felt like I needed to get this off my mind.
I’m not producing any more rods in the near future, partly because a prepreg type product can’t compete price wise with a pultruded product, and the customer base doesn’t understand the difference. Pultruded product is obviously good enough, in fact nothing is obviously good enough, they made lot’s of guitars without carbon fiber, it does stiffen the neck though which I think is a good thing.

Now to try and contribute something to laurents question. I think aluminum could work great. The only potential problem I see would be it’s coefficient of thermal expansion. I’m sure that it’s a non issue for 99% of the time. High temperatures could move the neck around changing the relief. It’s kind of hard to imagine that happening however. Just a thought.

_________________
Jim Watts
http://jameswattsguitars.com

Your analogy was excellent, apt, and appreciated. I should have specified that there's a pretty small difference between what they can pull off and what a good non-unlimited-budget operation can. I can't hold a tenth, and those guys can, because I didn't have $450,000 to spend on my mill and they do. That little distinction, though, is both invisible and irrelevant to 99.5% of my clients getting precision work.

My last phrase didn't come out right, and I sincerely apologize for the oversight. I'll clear that one up: If I didn't this particular friend, I would absolutely be using rods from Los Alamos, without a second thought. I think that it wouldn't be difficult to make a completely unmovable neck using them. The reason I believe the aluminum will work fine is that CF exceeds the requirements by such a margin that significantly less stiff materials can still do the job, even though they might not be in it's class.

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services