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I bought a stack of spruce recently. Ten out of twelve sets are flat as a, well... board.

However, two panels, of separate tops, mysteriously bent profanely. Kept in the same environment with the rest, stickered like the rest as well.

I've tried wetting the concave sides and weighing it down to dry, they stayed flat for five minutes and then promptly returned to their former shape. I've encountered panels that would cup, but as soon as they equalize they flatten again. I hate to waste good wood, but these pieces sketch me out, and I'm not sure if I want to risk putting it on a guitar.

Anyone encountered anything this extreme?

I assume they are QS, can you show a picture from the top? I would try wetting it again and leaving it pressed between two thick boards for a night or two.

Not an expert opinion btw.

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久保
美智え

Heat may be a possibility.
Not a top, but I last year bought a Zircote set and one of the backs was quite badly cupped. Tried water, no luck. Supplier recommended heat, he'd had problems with a couple of tops himself, and "cooked" them weighted down on an oven, left them to cool between the metal plates he used in the oven to weight them. That worked well.
I didn't have access to an oven big enough.
So I soaked the Zircote in SS11 for several days sealed in clingfilm and alum foil, and then ironed it flat, both sides, 2/3 times each side, good and hot with a domestic iron (heat blanket wasn't big enough) Did it between sheets of alum foil, then stickered it and clamped it, and left it for a month.
It's very well behaved now.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Sorry to see that. I have seen it on some nice claro walnut. I heated them with a heat gun, sprayed hot water on them then pressed between some plywood. They flatted okay but after a week or so out of the plywood they bowed again. I did it all over again and as soon as I took them out I joined them and then added the back bracing.

I put them aside for a few months and they still look good. I will probably use them in a build soon.

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Joe Beaver
Maker of Sawdust

I wouldn't use them. I had an englemann top that had cupping and I returned it for a cheerfully supplied replacement. It looked good, but must have been cut from the same board because it cupped in a similar fashion, but only after installing rosette and fully bracing it! I still have it, because I didn't want to use it on a guitar, but somehow have trouble throwing it away! BTW, I control humidity, so it wasn't a humidity issue,

My redundant, nagging refrain.

If there is wax anywhere on the wood, do not heat it.

I have a back set that is cupped. I was told my the supplier that wet the cupped sides and press them together between 2 pieces of wood. I have not done that yet.

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EddieLee

This generally occurs in quartered spruce when one side is exposed differently than the other. For example, if the top plate in a stickered stack is uncovered, the exposed side will gain or lose moisture faster than the rest of the pieces. For that reason, I put sticks on top of the stack, and use a cover sheet.
Instead of wetting the concave side, try drying the convex side with a hair dryer.

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John

Correct.

Another way this happens is when a segment of tree is faced up for quarter sawing and then, for whatever reason, is left for a while. The exposed face dries and can also micro check and then curls when it is eventually resawn. These are the pieces that the good guys use for packing...

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

These have been at 40% RH for over a month. I've seen lots of pieces from the top of the stack do this and then settle down, but I've never seen them just stay that way perpetually.

Just expose the the convex side to the air and leave the concave side down over night. See what happens. These boards will react quickly Ed and they will indeed lay flat for you soon.

Shane

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Canada

No dice on that I'm afraid. They've had both sides exposed equally for a month now, they ain't budging...

Many time this as John Arnold points out is from improper storage . I keep my wood stacked and pressed and use stickers on wood less than 2 yr old. Wood will move because of the RH . As surface cells gain or loose moisture the outer layer will pull or push on the under layer and movement occurs. Open ended grain will not hurt a thing. Martin stores a lot more wood than any one of use and they don't wax ends but they do sticker and stack wood in a constant RH.
Wood needs to be well aclimated. Learn to store wood properly.

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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

Recently is the prime word.
However, once in a great while, I run into an outside cut of a board that I am resawing that cups badly. Usually not well dried wood and is an indicator that the rest of the cuts must be stickered a very long time...several years. I usually throw that piece away, or use it for other things.
You probably could just sticker them, weigh them down, and leave them for a few years in your shop. You could use the others first, leave those. I see they are from different sets, however there is nothing wrong with "mismatched" sets for a top. Done it a few times.

Surely a panel barely 4mm thick needn't be stored for several years before use? Even following the 1 year per inch rule, a brand new fresh off the saw top should only need stickering for a few months? The wood came off a pallet shipping to china when I snagged it, so I assume it must have been at least somewhat dry and previously stickered for at least some time. I don't believe you can just grab it off the saw, strap it, and ship it, but mind you, I don't sell top wood so I don't really know.

I just find it curious that these two panels, out of 24, have done this. I expect they'll never be used, just in case...

Shane, if you don't mind chiming in...

How long do you need to leave tops stickered off the saw before they can be shipped?

I get that Ed, try only exposing the convex side and see what happens. They are cupped, that is ONLY a moisture disparity issue and nothing else. If it was wood tension or twist or anything else they wouldn't be so uniformly cupped. Have faith Buddy, you will get them flat. Please don't add any more moisture as has been recommended, that is just a bad practice for top wood. You don't need weight or anything else either, they came off the saw flat and will go flat again. I know it was not my saw that cut them but I have done enough of this to know what is involved. You will succeed!

Shane

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Canada

Sure wasn't Shane, this is Sitka.

But I'm curious. If this is a moisture disparity issue, shouldn't having both sides exposed for some time in the RH room balance it out? I've certainly seen it enough times where the top panel in a stack cups or bows, but then flattens within a matter of hours/days when the RH returns to target. That used to be an indicator in the shop. If you came in in the morning and all the top prices of the stacks were cupped, it meant the humidifier tripped off overnight. It would always be back to normal in a few hours.

In this case, these pieces have been exposed both sides at 40% RH for about a month, and they haven't moved a bit. If I were to lay them flat and expose only one side, should it be concave side up, or down?

And I'm still curious, how long does a top need to be stickered after coming off the saw before it's ready to ship?

The board should be concave side down. That is the side that has the lesser amount of moisture. If you lay it on the ground on a sunny day it should move even faster. The sun will dry out the convex side and the ground will add moisture to the concave side. I've done this with one by lumber, never needed to do it with guitar tops.

If the tops were being shipped by a slow boat to China they may have sent them a little green.

It dependss on how many sets they are processing and how much space they have. I know that these guys used to throw the wood in the kiln for a few days but since they have restructured I am not sure of their process.

I think the issue with your particular set is just a moisture differential almost like a micro climate where there was something that contributed to one side of those sets being drier than the other, especially during this time of then year where the seasons are changing.

In most cases I leave the concave side down, so the outer edges of the top set are touching the bench. Try doing that but leave the set on the floor for a couple of days and see what happens.

Shane

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Canada

No harm trying!

I think what Trevor says about micro checks is so true. I have re-sawn a board and had the outer pieces curl and nothing will fix them, where the others are fine. I believe what he says just might be the cause.

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Joe Beaver
Maker of Sawdust

If your supplier threw the blanks in a kiln at all this could be case hardening or reverse case hardening. If that's the case the deformation is permanent, caused by unrelieved stress introduced during the (improper) kilning.

I never went by rules. Never assumed much either.
As you wish...

Use your wife's hand iron, just don't get caught. It will take about 5 minutes and you will be good to go.

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Michael F Smith
Goat Rock Ukulele
http://goatrockukulele.com