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Hey All -
Would Weldbond work well for carbon reinforcement rods in the neck? In the past Ive used 5 min epoxy, but its so so messy --

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Lance@LuthiersForum.com

Unless you're physically stopping the rod solidly at each end, you need to use a glue that does not creep, if you want to gain all the stiffness the CF offers(or any reinforcement, in fact). Weldbond, if it's the PVA type I think it is, is out. 5 minute Epoxy also creeps plenty.

My first(and 2nd, and 3rd...) choice would be polyurethane glue. Elemer's ProBond polyurethane is great, as is Excel One. Avoid Gorila Glue.

Since the matrix of the cf is epoxy, there must be epoxies that would work.

What's wrong with gorilla glue?

Yes, the better structural epoxies will work well, but they're messy, and only available in pretty large quantities. They are also touchy about the mix ratio being spot on, which is hard to do with the tiny amounts we'd need for inlaying a single rod.

Don't forget that -good- quality CF is made under pressure, too. There's more to it than just fibers in epoxy.

Poly glues don't show any creep, don't need mixing, and are available in small bottles(best, too, since you want to use fresh poly glue...)

A few of the tests I've read all rated Gorila lower than all other poly glues for some reason. Since the others are readily available and reliable, why bother with the one that could be the weaker one?

I use good quality 45 minute epoxy, I know it's messy but it's stable and works very well, I also use it when laminating CF into my braces. Mario's right about the mixing, I use a digital scale to measure mine out.

It's worked well so far.

-Paul-

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-Paul-

Patriot Guitars

When I used to make kayaks, we overcame the problems with accurately measuring small volumes of epoxy by using syringes. Works well and gets less messy the more you do it. You can buy smaller quantities of good quality marine epoxy ~1/2 pint at your local boating accessory store / chandlery.

I've just remembered that system three brand epoxy used to have a trial kit for $10. I checked their website and see that they've expanded the kit, it now costs $25 and includes :

"The Epoxy Book, plus 6 ounces of SilverTip Laminating Resin and Hardener, 3 ounces of GelMagic, 6 ounces of EZ Fillet, 6 ounces of QuikFair, 4 ounces of Metlweld along with fiberglass cloth, cups, sticks, gloves and a plastic squeegee...
And a coupon good for $20 off on your first $100 purchase"

It's aimed at boat builders, so some of this stuff is probably surplus to requirements for a guitar builder, but this stuff is handy to have around none the less.

Their website is [URL=http://www.systemthree.com]here[/URL] the kit is called the SilverTip Trial Kit.

[QUOTE=EricKeller] What's wrong with gorilla glue?[/QUOTE]

Based on my own personal testing, Gorilla glue has the cross sectional matrix of an extremely porous sponge. It's hardness was the softest of all glues that I have measured. I wouldn't use it if it was the last available glue on the planet. Just my $.02

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tim...
http://www.mcknightguitars.com

Lance: Visit Golfsmith and purchase their golf club shafting epoxy. It doesn't creep, has exceptional holding power, high temperature release and has an inherant design characteristic that is well suited for our applications ... an abnormally high high shear strength.

Here's the link - http://www.golfsmith.com/products/9095?fcst=GSI_WEB

It also works great for fingerboards and inlays. They have it in syringes and also sell handy mixing cups too. I have been building golf clubs for 20+ years and have yet had a club and shaft separate using this product!

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tim...
http://www.mcknightguitars.com

Thanks Tim! --

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Lance@LuthiersForum.com

I always use JB Weld. I do not recommend quick set epoxies because they do not get nearly hard enough. JB weld can be used to repair cracks in engine blocks, is structurally very hard and stiff when it sets up but its slow. Allow several days for full cure but you could work it after 24 hours. It is also very heat resistant so if the fingerboard ever has to be removed for any reason the heat used in that process will not effect the bond between the carbon fiber rods and the neck.

JB Weld comes in small tubes and in cans. I get the tubes. About 5 bucks worth will do about 3 necks.

[QUOTE=John Kinnaird] I always use JB Weld. I do not recommend quick set epoxies because they do not get nearly hard enough. JB weld can be used to repair cracks in engine blocks, is structurally very hard and stiff when it sets up but its slow. Allow several days for full cure but you could work it after 24 hours. It is also very heat resistant so if the fingerboard ever has to be removed for any reason the heat used in that process will not effect the bond between the carbon fiber rods and the neck.

JB Weld comes in small tubes and in cans. I get the tubes. About 5 bucks worth will do about 3 necks.[/QUOTE]
Just the standard JB Weld? I will have to try that.

John:
I agree that quick set epoxies just don't have the holding power that overnight cure epoxies have. The golf club shafting epoxy is a 24 hour cure as well. I have used JB Weld and it is an excellent epoxy but the down side is the grey color. Golfsmith epoxy is cream colored and can be mixed with powdered dyes or sawdust for a close color match. It doesn't have near the heat resistance as JB Weld but FB's can be easily removed with a hot clothes iron or heating blanket.

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tim...
http://www.mcknightguitars.com

Thanks for the tip, Tim! Any epoxy that can stand up to a 125 MPH Tiger Woods swing speed should be OK for a guitar neck.

Out of curiosity, when you re-shaft a club, what's your technique for de-bonding the head from the shaft?

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JJ
Napa, CA
http://www.DonohueGuitars.com

Gorilla glue has the cross sectional matrix of an extremely porous sponge. It's hardness was the softest of all glues that I have measured

Tim, you are aware that all polyurethane gleus foam, right? And you know that they require great clamping and a tight fit? The foam itself has no strength, but if you clamp the pieces together tightly, the resulting bond is among the strongest we can attain. The foaming action tried to seperate the two pieces, so we need some serious clamping to get the most from it. In my brace laminating jig, I'm getting around a 1/2 ton of pressure...

If you tried it for your golf clubs, I can understand your comment, as you'd have no way to clamp it at all. If all you did was spread some on a table and measured its hardness, shame on you <g>

That said, JB Weld may be the perfect one for the neck reinforcement, as the gray glue line and extra weight won't matter much there. If you enjoy mixing stuff....

[QUOTE=JJ Donohue] Thanks for the tip, Tim! Any epoxy that can stand up to a 125 MPH Tiger Woods swing speed should be OK for a guitar neck.

Out of curiosity, when you re-shaft a club, what's your technique for de-bonding the head from the shaft?[/QUOTE]
I have a hydraulic puller and use an electric heat gun for wood heads and a propane torch for iron heads.

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tim...
http://www.mcknightguitars.com

[QUOTE=Mario]
Tim, you are aware that all polyurethane gleus foam, right? And you know that they require great clamping and a tight fit? The foam itself has no strength, but if you clamp the pieces together tightly, the resulting bond is among the strongest we can attain. The foaming action tried to seperate the two pieces, so we need some serious clamping to get the most from it. In my brace laminating jig, I'm getting around a 1/2 ton of pressure...[/QUOTE]

Mario:
Yes, I am aware of the foaming action as the glue is chemically reacting with the moisture in the opposing wood joint face. The foaming action will try to hydraulically separate the joint if it isn't clamped sufficiently. Yes, it's possible to achieve a decent bond but when I measured the glues hardness [read ... not joint strength] it was still the softest glue of the test group.

How do you measure hardness, and why is this relevant to joint strength? I'm lost....

Mario:

I think I am taking this thread off on a tangent. I should have said that "I would prefer to use a glue that is harder than Gorilla Glue".

Glue hardness is not relevant to joint strength (see my message above). I don't have any test data to support which glue is stronger. My testing has lead me down a differnet path as I asked a different question to drive my experimentation. I wanted to understand glues hardness and it's affect on tone.

Hardness is commonly referred to as a durometer metric or measurement and is measured using the various Shore (A, B, C, D, E) scales. A durometer test instrument is a spring loaded, hand held device, that uses a unique spring which is calibrated for each specific scale (A, B, C, D, E) .

The instrument is pressed against the surface and the spring loaded [indenter] deflects or compresses the surface (or material) being measured. After a brief amount of time the instrument displays the deflection as a measurement on the scale which is a scientifically accepted metric.

Why is this important to our community? My theory is that harder glues yield lower dampening. Imagine an X brace was glued to the top but a dense sponge rubber gasket was inserted between the brace and the top (pretend the gasket is soft glue). Essentially you have increased the dampening in that joint. Try to tap test this and it will go thud.

Now hypothetically, remove the gasket (or soft glue) from the joint and attach the X brace with (hard) hide glue. You have lowered the dampening in the joint just by using a harder glue. Tap on this joint and it will go ping.

Is this a huge deal? Well, it's just one more factor in the game that we play to bring the sum of all the small parts together to yield the very best instrument that we can build.
             

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tim...
http://www.mcknightguitars.com

That's exactly how I see it.

John

Yes Tim, but here's where you lose me. In a tight fitting joint, there is no foaming, and the glue is indeed hard. Very hard. I'm just asking how you tested it. Did yuo make little globs on a table and test those, or did you take a joint apart, clean it down to the dried glue line, and test that? I'm assuming you did the former, not the latter, because my testing showed it to be a very hard glue line.


I agree about the soft gasket effect, I'm just wondering how you came to the conclusion that this glue is soft and that one isn't. Little globs dried out on a table don't matter. It only matters what a cured joint is like, right?

"Yes Tim, but here's where you lose me. In a tight fitting joint, there is no foaming, and the glue is indeed hard. Very hard."

"Very Hard" is a subjective term that could have a wide variance among a group of people. That is why I let the test data determine what is soft and what is very hard.

I originally tried to test a disassembled joint but the problem is there is so little glue film thickness that it's impossible for the durometer to test it. The drumometer requires a minimum thickness in which to depress the indenter into and the joint film is just too thin.

Next I tried building a film on glass but the glass broke due to the sharp indenter tip pressure against the glass.

I settled on milling identical [1" length x .125" depth] pockets in Ash using a ball nose end mill on a CNC mill. The glue was poured into the pockets in three successive pours and allowed to cure one week per pour. The last pour was just proud of the surface and allowed to cure 30 days for the first test and 3 months for the second test. All test coupons were milled flush so the test thickness was identical for all specimins. Then 5 tests were performed across the surface and plotted on an X bar chart. Standard deviation was calculated as well upper and lower control limits established.

The milling process revealed some startling results as some glues chipped, some were smooth on the surface but quite porous after they were milled while some separated in chunks at the glue pour line. This indicated that some glues will not adhere to them selves well.

It was a very time consuming process but one in which I learned a great deal and the data revealed the answer that my experiment question asked.

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tim...
http://www.mcknightguitars.com

Tim, your test approach seems fine for testing hardness for all but polyurethane glues given that they function so differently, as Mario pointed out.

I use epoxy for this application and it works well. Poly glues would likely work as well, but for me they are PITA. Nasty, foamy crap that turns my skin black! Ack!