Aluminium neck relief question

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Aluminium neck relief question

Postby Ross Amor » Thu Mar 01, 2012 3:20 am

I've been reading the MIMF for about 10 years on and off but this is my first real post (maybe second - I think I had one on the old forum in the late 1990s), so hello everyone. I'm in the early stages of designing an aluminium neck to retrofit to one of my guitars. I've come to wonder about relief: obviously aluminium is a lot stiffer than any wood I might use and I won't have a truss rod, so it's not going to react the same way to string tension. I've done a lot of reading about this sort of neck, and there doesn't seem to be any information on how exactly it will react. I wonder if anyone here has any experience with this sort of thing? I can't work out whether I'm going to want to design the thing with some relief built in (fettling post-build won't be easy because I'm going to have it fabricated by a pro - my flat is small, I have no tools, so anything will have to be included in my CAD files or drawings), design it dead straight and deal with the relief issue when it comes to fretboard installation time (as in remove some material from the middle of the board or dress the frets a tinch lower in the middle), or if string tension will have some effect and pull a little relief in. Any ideas would be much appreciated. It's a 25 inch scale and I run 10-52 strings, if anyone cares to know.
Last edited by Greg Robinson on Thu Mar 01, 2012 11:54 am, edited 1 time in total.
Reason: Correcting tags.
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Re: Aluminium neck relief question

Postby Mark Swanson » Thu Mar 01, 2012 9:45 am

The deal with aluminum necks is that they are sensitive to temperature changes. Every guitar I've ever heard of that had one wouldn't stay in tune because just the act of playing it warms it up and the tuning changes. Stage lights, and the seasons make that worse.
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Re: Aluminium neck relief question

Postby Leon Van Bommel » Thu Mar 01, 2012 4:07 pm

I don't know a lot about about aluminum necks, but I do know a good deal about aluminum. I am a machinist by trade and if I turn a 1" aluminum pin at room temperature it could grow by as much as 2-3 thousandths of an inch. if your guitar neck is 18-20 inches from nut to heel then your looking at a good bit of growth as mark said. But you didn't ask about that so to answer your question I believe an aluminum neck would never bend under string tension. Think of a wooden neck with one of those non-adjustable truss rods in it (Martin). I bet you could bend that truss rod quicker than you could bend a piece of aluminum the size of the neck. There's no science in my reply just experience. also google "aluminum and wood guitar neck" and click the first link. The shapes of those necks wouldn't leave room for a truss rod and I've just read on forums from people with the Kramer guitars that their necks stayed straight. It's just hear say tho I guess. One more thing and I'll stop rambling, these people were saying they found the aluminum necks very neck heavy, they corrected this by putting the forward srap button on the heel and the hind one up 2 or so inches.

hope this helped a bit.

i even looked up the linear coefficient of aluminum for you. 12.3x10^-6 in/in degF

24 fret neck =18.75 inches x 12.3x10^-6 = .00023 in/degree F. 10 degrees .0023 inches, 20 degrees .0046 inches. perhaps some one can add if that's enough to change your tuning, I'm not saying Mark is wrong, just it doesn't seem like enough to me.
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Re: Aluminium neck relief question

Postby Ross Amor » Thu Mar 01, 2012 4:33 pm

Thanks Mark and Leon for your responses.

Mark - I know that aluminium behaves badly with temparature changes and I'm fine with that. I believe people get by by making sure the guitar is at a stable temparature before it's played - I'll never have to worry about arrays of stage lights, either, 'cause I'm not very good.

Leon - I've read that site before, but thanks all the same for the legwork. You're coming down on the same side of this as I'm inclined to, that string tension isn't going to shift this neck at all, so I guess I'll draw it up with that in mind.

The tuning thing is going to be a pain, but I'm happy to deal with it for the sake of the noise these things make. I will be adding wood inserts to the back of the neck a la Kramer, which should help isolate the aluminium from hand heat and help deal with the issue, although it's hardly going to cure it. Any bright ideas on that front?
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Re: Aluminium neck relief question

Postby Peter Wilcox » Thu Mar 01, 2012 6:36 pm

A quick, probably ignorant reply.

There are tuning difficulties with temperature changes with wooden necks also. How much is due to the neck and how much due to the strings? Steel has a coefficient greater than half that of aluminum which would be partially compensatory with an aluminum neck.
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Re: Aluminium neck relief question

Postby David Schwab » Fri Mar 02, 2012 8:21 pm

I had a Kramer "The Duke" bass back in the 80s. I have to say it was one of the most stable necks on a bass I ever had. It never went out of tune, and unlike my Ric and Ibanez didn't need adjusting. it was however a lousy sounding bass, mostly due to the tiny body. The full size Kramer basses sounded better.
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Re: Aluminium neck relief question

Postby Mark Wybierala » Sun Mar 04, 2012 10:57 am

I have never encountered and aluminum neck guitar that was friendly on the bench. But then, only the guitars that have problems end up on my bench. I would imagine that the specific alloy used would have a significant impact to its character. There are way too many unknowns for me to ever take such an adventure.
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Re: Aluminium neck relief question

Postby Ross Amor » Mon Mar 05, 2012 4:28 am

Most of the companies who have built aluminium neck guitars used either 6061 or 7075 (from memory), although one of the higher-end firms used a proprietary alloy called Alumag (which I now can't seem to find any evidence of), which is reportedly almost impossible to get. 6061 and 7075 can be got from most aluminium supply places. I guess the tuning stability issue is probably influenced by the alloy - I'll look into what brands had the most tuning issues and what alloy they used.

From what David said (that his Kramer had a stable neck), I can't help thinking that the wood inserts used by Kramer might have helped keep things steady with regard to the transfer of hand heat - this is something I'm planning on emulating.

Does anyone still have one of these instruments? What I really want to know is whether the strings pull any relief into the neck or if they're dead straight all the time or if they have relief built in. Although I suppose, as I'm not afraid of tinkering, I can just build it straight and then modify the fretboard if it needs it to play well. In fact, I imagine that'll be obligatory anyhow.

As for these being a pain on the bench, I have to say I'm not looking forward to fretting this - I'm planning on a one piece aluminium neck and board a la Electrical Guitar Company, which is likely going to mean filing fret tangs, superglue and who knows what else. Fortunately this is for me, so it's not a problem if things take a while to do right.
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Re: Aluminium neck relief question

Postby Patrick Kirkham » Wed Mar 07, 2012 2:12 pm

My reply will reek of my relative perspective, but, for what it's worth...
A couple years ago my (late) entry to the $100 challenge was a headless Tele with a 1"x1" aluminum channel running the length of the center of the neck. Walnut sides were screwed to it and a fingerboard glued to that.
Image
After a string change breaks in, I don't have much more trouble with tuning, than had I an ordinary instrument with an unused vibrato bridge. I actually decided on a bridge design free of springs in order to stay in tune, but whadda you want for under $100? Rubber biscuit?

I managed a truss rod using a stack of formed shims in the fretboard side inside the channel for the all-thread to bear against. This has quite a bit of tension and I consider it overbuilt compared to anything I would do to a poor tender wooden neck. It's a freak, but I tune less than a Floyd Rose, but more than a Bigsby. (see, relative, like I said)
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