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I baked a top yesterday for my 12 string & will bring it down to .125 how long do I wait before glue up & bracing?
Mike

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Mike McNerney

I wait until the top becomes stable. It should returned to pretty much the same flatness as before it was baked. I like to sticker it top and bottom and apply some weight just incase it forgets what it should look like.

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Joe Beaver
Maker of Sawdust

Bring it to your climate control/build area and weigh it. Once the weight remains constant it should be acclimated.

That's what I do too. I just weigh it and write down the weight right on the top. Then the next day weigh it again and so on. It's always nice to have plenty of time but it will probably be stable in a week.

I've only done this once and it was with a top resawn (1/4" thick) from a board at the big box store. No telling how wet it was when it started. I baked it a few times clamped down with stickers. I let it set in the shop for about a week and it never moved. Thinner stock may take less time to acclimate but why rush it? It is going to be really dry when it comes out of the oven.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

I'm curious. Talking about tops, what happens with the weight after baking? Does it lose or gain going from the bake
to room condition. I 'm assuming it"s not green just before baking. My thinking is that baking would remove all residual
moisture and what's left would be immeasurable. I haven't done any baking, so gimmie the low down please and thanks.
Ken

IME, specific gravity (density) goes up, as does stiffness.
(Edit to clarify - Wood acclimatised to 43% RH, then baked, and then re-acclimatised to the same 43% RH)

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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.

I am, by no means, an authority on this but. . . I think your question is will the wood gain weight after you bake it. I think the answer is yes. Baking will drive out most of the water and that wood will have to acclimate to normal conditions so it should gain weight as it gains water. My understanding is that wood that acclimates to a given RH will have slightly less water if it is gaining moisture to acclimate than if it is losing water (I'm not sure how much). But, you should be able to say that if it is no longer gaining weight, it has stabilized to the shop RH.

If your question is more about what happens to the wood due to the baking process, that is a more complicated answer and I KNOW I shouldn't be tackling that one. . . I'll be interested to read the responses from those who know though!

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

"IME, specific gravity (density) goes up, as does stiffness.
(Edit to clarify - Wood acclimatised to 43% RH, then baked, and then re-acclimatised to the same 43% RH)"

So... if I bake a top panel that's weighs 200 grams it will weigh more once returned to 43% RH. Or do the dimensional
quantities change? I guess the question I'm asking is, what is the variable that causes density to go up?

Shrinkage.

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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.

"I was in the pool! I was in the pool!" ~George Costanza

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Good judgement comes from experience. Experience comes from poor judgement.

From my deflection testing the stiffness didn't appreciably go up after baking. I have not measured density but I could see that going up. It will shrink but then it will come back too. In theory it will never come back to the size it was prior to going in the oven. My understanding of baking tops is that it's not so much a tonal thing but rather a structural or stability thing. It might make the wood more stable. It certainly does drive out the resins because you can see them bubble up to the surface. But it's nothing like torrafaction for example.

That's a good point about the resin. It sure did drive a bunch up to the surface the one time I did it. That alone should make the stiffness to weight ratio go up, I would think.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

I agree. Basically I have baked tops to stabilise them as they were recently harvested. Brian Burns did extensive testing and found that baking improved Q, a measure of the resonant qualities of wood, but it seems to have vanished from the net. Any improvement in stiffness is small.
I believe that Collins and Taylor bake their tops, for stability.

_________________
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.