Official Luthiers Forum!

Hey guys, I'm new the forums and about to start my first acoustic build.

I got the wood from stewmac (Walnut back/side, spruce top), but within a couple hours of opening the box the back and side wood started warping, pretty severely.

I've got the wood between two sheets of mdf with weights on top, but is this something that is fixable?

Any ideas why it would happen in the first place? I live in Florida, so I was thinking humidity maybe.

You're probably right. Do you have a gage?

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Pat

Yeah, that's pretty normal. You might want to "sticker"(google images) the wood rather than putting it between MDF. this allows the air to circulate on both sides and equalize the moisture with the environment.

(P.S. the relative humidity you want to -build- the guitar at is about 50%)

50% seems a bit high to me, and most of us shoot for closer to 40%...

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"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

Agree ---- sticker for air flow and also agree that near 40% rh is a good target.

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Ken Cierp

http://www.kennethmichaelguitars.com/

Thanks guys,

I assume you mean a gauge for humidity. I don't, but will get one (and most likely a dehumidifier).

So this is something that can be fixed? These boards aren't a lost cause?

Not necessarily a lost cause. Sticker the materials and let everything acclimate.

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George :-)

Normal. Welcome to the humidity club. The goal is to manage exposure to abnormal humidity.

There is a good chance his first guitar will live in Florida, 50% relative humidity would then be fine. Over the years I've seen the suggested R.H. go from 50% to 45% and now people are saying 40%. Give me a break! If you are building in Michigan or Massachusetts where you don't have summer humidity levels that approach a rain forests at times, then 40% might be the right target, but building in relative humidity that is too low can also cause problems.

It depends on the woods you're using. Walnut has a pretty high expansion rate, so it is prone to high humidity problems. It's also very tough, so it can take a pretty big humidity drop without cracking. Bracing around 45%, I'd guesstimate its total tolerable range at 15% to 90%, with 30% to 80% being preferable.

Redwood, western redcedar, Indian rosewood, and cocobolo all have very low expansion rates. African blackwood and Honduran mahogany aren't far behind (plus mahogany has high toughness like walnut, so it can be nearly invincible to humidity). So if you brace a walnut guitar in 45% and Indian rosewood in 30%, the walnut will be the one under more stress in a rainforest.

And I'm talking about all quartersawn woods here. Flatsawn expansion rates are usually about 1.5 to 2x as high. So if you think a flatsawn walnut guitar braced in 50% will survive in a 90% rainforest, then it should be no problem to brace quartersawn rosewood in more like 20%.

Thin woods can move rather quickly. Warping can happen if the wood is laid on a flat surface, exposing the top side only. The exposed side will gain or lose moisture faster than the bottom side, causing the warp. Concave on the top side means that the wood is losing moisture to the air, and convex means it is gaining moisture. If you flip the pieces over, they should warp the other way. If you keep flipping until the movement stops, the wood is in equilibrium with the air.
This is why placing the wood on dry sticks ('stickering') is so important....especially if you are wanting to build right away.

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John

If it is just cupping, thats pretty normal and it will flatten out in awhile. I have bought wood from lots of vendors from the U.S. and Canada. Some wood cups for years then it just magically comes to equilibrium. I live in Wisconsin, I let all my tonewood rest for at least 2 years before I build with it regardless. The RH here changes all the time outside. In my shop in the winter I heat my shop with wood pellet fuel and in the summer I run an A/C unit. I get between 35 and 50%. Sometimes it goes down to 30% if we haven't had snow and its really cold. I dump water on the floors and hang wet towels in my wood room. I normally build around 40%. I know builders in FL have a hard time keeping RH down. The opposite for builders in places like Arizona, where its really dry all the time.

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Jason Moe
LaCrosse WI 54601

Update!

I got the humidity sensor, so far it has been reading between 45-60%, averaging out around 50%....

Here are some photos of the back blanks after a couple days of stickering:

https://www.dropbox.com/s/gpe0h395f36rx ... 9.jpg?dl=0

https://www.dropbox.com/s/vrtejdi91nlmx ... 2.jpg?dl=0

Still a fair amount of warping, and they aren't really rectangles anymore, kind of parallelograms...

I'm following Cumpaino, so i'm going to build the neck first. Hopefully the extra acclimation and stickering time will flatten things out.

However... there is also a not insignificant S-curve in my neck blank as well, seen here:

https://www.dropbox.com/s/xpf7ofv1swcz7 ... 6.jpg?dl=0

Does that just need to be planed straight before I start on the head piece and heel block cuts?

You can try either wiping the concave side of each piece with a damp towel or lightly sanding both sides then stickering if they don't seem to be flattening out with stickering alone.
And, yes-you need to square up your neck blank before you start cutting.

Oh, and for best results you're really gonna want your humidity to be a bit more stable if a all possible-preferably in the 42-45% range.
Seeing that your in FL and this guitar might live it's whole life in a more humid than average area you might be able to get away with building at a little higher humidity than that (I'd still opt for mid-40's if possible, though: better to build a little low than too high) but I'd at least want it fairly stable (a 15% swing in a short amount of time is enough to make these wide/thin plates move noticeably).

Wood usually warps when it goes through humidity or heat changes during shipping. Stickering does not always fix that. I have to wet all the sets I sell with H2O to show the color when I photograph them. Alcohol or other chemicals dry too fast to get good photos. By the time I've photographed a few sets, which only takes minutes, every piece of wood will be starting to warp. The best fix is to spray some H2O on both sides and then dead stack it under a weight overnight. Don't need to be sparing with the spray. You want the wood wet. It will dry out immediately due to the difference between inter cellular and intracellular water You can dead stack 4 or 5 sets like that with no problem. The top weight, usually a board with additional weight on top, has to cover the entire piece of wood you are tying to flatten. I just stack the wood on my shop cement floor. Bt the next day, all the wood will be flat, and then you can sticker it and it will stay flat unless you have bad wood. You can do this with new wood, or old wood. Works with everything thin.

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“ The meaning of life is to find your gift and the purpose of life is to give it away” Pablo Picasso