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Bonding aluminum to wood.

Benjamin Strange

Benjamin Strange

Commercial User
Dec 25, 2002
9,737
310
49
New Orleans, LA
www.ufodeathcult.com
Disclosures
Owner / Tech: Strange Guitarworks
#1
Hi guys,

I'm working on building a maple neck with an aluminum fretless fretboard. I did a little research on getting the aluminum to stick to the neck blank, and used a very expensive marine grade epoxy to glue it up. It seemed really strong, at least at first - but as I was cutting the nut slot the entire fretboard just fell right off! Back to the drawing board...

Upon further research I've discovered that many say the aluminum needs to be chemically treated before gluing, while others say some metal specific epoxies can be used - but none say anything about actually bonding aluminum to wood, only metal to metal bonding. Have any of you guys tried such a thing? How should I go about getting my fretboard to stay bonded to a maple neck? Any ideas?
 
#3
Yup, did that already.

The more I read, the more I realize that is going to require some chemical treating. Any oxygen getting to the aluminum will cause it to oxidize, and will slowly kill the bond. I don't have the chemistry knowledge to do this correctly - I may have to abandon this project if I don't find a simple solution.
 
#5
When you look at the failure, did the epoxy stay on the aluminum, or the wood? What kind of wood is the neck blank?

If the epoxy didn't stick to the aluminum, West System's guide says use 80 grit to provide a surface for the epoxy to "key" into, and use a solvent prior to bonding. Invalid Link Removed
 
#6
First, unless you intend to use nylon tapewounds only, you need to get the aluminum hard anodized (not just plain anodized). Any nickel or SS strings will tear up bare aluminum.

Next, you need to look up the manufacturers' tech data for any potential adhesive. For industrial marketplace product, you can also call the company and ask to speak to a tech support person or engineer, who can give recommendations for you intended substrates.

They may tell you about something that's perfect, or may lead you to something such as having (at least simple) anodizing done. Though I haven't had it done for that purpose, I know anodizing is done to promote paint adhesion, and is sometimes referred to by some process brand names such as Alodine.
 
#9
Hi.

If You want to have at least some adjustability on the neck, You can't use glues that harden solid.

The proportions and cross sections of the materials on wood/aluminium sandwich neck'd Kramers were reversed, but they got it working somehow.

Flexible epoxies might work, and an acetone soak just before gluing will get rid of the oxide layer.

If I were You, I'd use a mechanical fastening method as well though.

Regards
Sam
 
#10
I like the idea of cutting grooves into both materials so they lock together. As far as glues, I have had fantastic results using PC7 to bond wood to metal, but I can't say for sure that bare aluminum was one of the metals I bonded...
 
#12
I'm going to second a mechanical fastener. Countersunk screws out of the normal paths of the strings should help. It would also allow you a lot of adjustment and replacemet possibilities if you use only the screws.
 
#14
On aircraft we give the aluminum an alodine treatment. It's (at least) one of the conversion coatings you've been told you need. The most common formulation we use is "Alodine 1201" which is more or less chromic acid. Not something you want to absorb too much of. There is also an alodine pen - "Alodine 1132 Touch N Prep" that you can use, but I have had varying success with them depending on the flavor of aluminum.
You can get ahold of these through places like Aircraft Spruce, Sky Geek, et al. A simple google search ought to get you a handful of options.
One problem - Appearance. Alodine is great if you're going to put some paint or powdercoat on top, or if it's going inside another panel, but it can give blotchy/streaky patterns no matter how careful you can try to be on application.

I think the hard anodizing mentioned earlier might be your best option when considering appearance, unless you only want to treat the bottom where you'll be bonding to the neck.
 
#15
You should also consider that aluminum has a thermal expansion coefficient that is very different from the longitudinal coefficient for wood. With an aluminum fingerboard out front, you can expect the neck to bow forwards if you play an outdoor winter gig, and to bow backwards if you play out in the summer sun.

This is not just theoretical. Kramer owners have reported these effect with their hybrid necks, which have a moderate imbalance of materials about the neutral axis. For your construction, with is greater imbalance, it would be expected to be worse.
 
#16
grisezd said:
I'm going to second a mechanical fastener. Countersunk screws out of the normal paths of the strings should help. It would also allow you a lot of adjustment and replacemet possibilities if you use only the screws.
Click to expand...

I was thinking along this line as well. The only variant I have in mind is to have the screws under the dot markers. The dot markers might have to be positioned offset (or offset in alternating intervals) of the fretboard center line to avoid hitting the truss rod.
 
#17
I've glued Al to Al by "wet" sanding the aluminum while the epoxy is on it(if that makes sense). Worked damn well for me. I have worked with Alodine before but that was strictly for paint/primer adhesion. I've also seen studies where the type of wood had a drastic effect on, not only the bond to the aluminum, but also had serious corrosion complications as well.
Here is a link to a confusing description of some of those tests.
Handbook of aluminum bonding ... - Google Books
 
#18
pilotjones said:
You should also consider that aluminum has a thermal expansion coefficient that is very different from the longitudinal coefficient for wood. With an aluminum fingerboard out front, you can expect the neck to bow forwards if you play an outdoor winter gig, and to bow backwards if you play out in the summer sun.

This is not just theoretical. Kramer owners have reported these effect with their hybrid necks, which have a moderate imbalance of materials about the neutral axis. For your construction, with is greater imbalance, it would be expected to be worse.
Click to expand...

Glad you mentioned the Kramers, as it's true--for all the stability that a metal neck was supposed to offer. the reality is their intonation and action changed dramatically with temperature changes.
 
#19
Yeah, I've worked on some Kramers before - and they most certainly don't stay straight! This instrument I'm building is actually a guitar, not a bass, so there's less neck to move, plus only the fretboard is aluminum, while the neck is 1" thick quartersawn maple. I'm not terribly concerned about it moving on me much.

As for anodizing or chemically treating the board, the trouble is that it has to be DEAD flat - and there's no way to make sure it's flat before it goes on the neck under string tension. I do all my leveling work on a custom built neck jig, which simulates string tension and allows me to make sure everything is super accurate. However, if if were to anodize the aluminum before it goes on the neck, all that anodizing will be removed once I start leveling the fingerboard. Yes, this may help with bonding to the wood, but from most accounts it seems that adhesives just ain't going to cut it anyway.

I'm starting to think along the lines of a mechanical approach. Right now I'm thinking of screwing it down, using screws in between the outermost strings, right at the typical places fingerboard markers are. Perhaps a countersunk screw, and then cover the screw top with a round aluminum inlay, which would then almost disappear when I level the board. Hmmm...
 
#20
I'm starting to think along the lines of a mechanical approach. Right now I'm thinking of screwing it down, using screws in between the outermost strings, right at the typical places fingerboard markers are. Perhaps a countersunk screw, and then cover the screw top with a round aluminum inlay, which would then almost disappear when I level the board. Hmmm...[/QUOTE]

if you screw it down to the wood the expansion of the metal will bent the whole neck, somehow the one edge of the metal must be free (near to the pick ups), the screws must have some kind of bigger holes also for the same reason. very interesting thread by the way :hyper:
 

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