Baked not fried! Cooking tops

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Alain
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Baked not fried! Cooking tops

Post by Alain » Sat Oct 27, 2007 4:01 am

Members of the board,

I was thinking of cooking up some nice spruce tops. It seems the general consensus is around 200 degrees farenheit for about an hour...is that correct?

I also remember reading that Mario Proulx also likes to keep the oven door slightly ajar to let the humidity escape, should there be any...

Thoughts, tips, tricks or considerations?
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Post by Hesh1956 » Sat Oct 27, 2007 4:07 am

Yep that is what I do, 200 degrees F for one hour but I don't keep the oven door open not that this is a bad idea, I just never do it.

Be set up to weight the plates flat after baking because they will at times try to curl on you. I would suggest doing one top first to get your methodology down.

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Post by Hesh1956 » Sat Oct 27, 2007 4:07 am

Oh and a dry run to be sure your oven is big enough is helpful too. I have a large oven but some tops have to be trimmed to fit in it.

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Dennis Leahy
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Post by Dennis Leahy » Sat Oct 27, 2007 8:16 am

My first 2 bakers worked perfectly, and left me with 2 flat sets. (I used the recipe that Alain mentions.)

The third time I tried, I stacked all the wood from a resawn Lutz billet (about 5 or 6 top sets) with 1/4" x 1/4" stickers between them and baked the whole cluster. All of the wood now has a twist. I won't do it like that again. I would recommend stickers between (like I did) PLUS stickers above the stack and stickers below the stack, and some method of clamping (rope?) that pulls the outer stickers together. Might not be a bad idea to rotate the stack after a half hour. Or, it might not be a bad idea to put the stack in the oven sideways, so the heat would travel straight up through the spaces between the boards.

Oddly, the individual boards have quite different tap tones, from resonant to rather dead. Though I lost track of which boards were on top, I suspect that the lower boards (nearest the heat) got the driest and are the most resonant, and the upper boards re-absorbed moisture as the moist heat rose.

That reminds me that I need to contact Mario DaCosta and ask if he knows what I should do about the twisted boards. Do I soak them in water and just sticker them with weights on top? Or, soak them, sticker them, and cook them again? Or what?

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Post by TimS » Sat Oct 27, 2007 9:55 am

Does any one know what actually happens and what benefits are derived from the elevated heating process besides the obvious that there is accelerated moisture loss?

regards

Tim
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Kim
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Post by Kim » Sat Oct 27, 2007 10:19 am

Tim,

Taylor guitars, among others, bake their tops in order to stabilize the wood. The theory is that by taking the wood to extremes before it is constricted to braces and glued, you offer some resistance to future splitting during exposure to dramatic changes in temperature and RH such as may be experienced inside a vehicle on a hot day. This is in-line with the theory that as wood expands and contracts with changes in temp and RH, it does so to a lesser degree each time as it begins to relaxes or season into it's cut form.

Still others suggest that this process enhances and sets the tone by turning sap more crystalline sort of like accelerated ageing if you will. In this vein of thought, it is also suggested that in exposing the wood to a period of high temperature, the sap is forced to express, or gas out those volatile elements which normally leach gradually from the wood after the guitar is complete and can cause the finish to sink back slightly.

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Post by TimS » Sat Oct 27, 2007 10:56 am

Thank you Kim for that explanation.
I wonder whether anyone has built two guitar with tops from the same log: one with untreated and the other "baked".
regards

Tim
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Post by kiwigeo » Sat Oct 27, 2007 12:10 pm

Some people just love a barbequed look for their tops :lol:

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Post by graham mcdonald » Sat Oct 27, 2007 12:22 pm

I don't think you are actually getting rid of much free moisture, rather as Kim suggested getting rid of some moisture that allows the crystalization of some resins in the wood. A 5mm soundboard gets to an equilibrium moisture content within a few weeks of being sliced up, or at least the wieght and width stabilises out after that period. Cooking them in the oven drops another 1-2% in mass and does bring up the tap-tone a little. I measured a couple of soundboards which I had cut quite wet from a billet of Sitka from Alaska, let then sit in the shed for a couple of months in summer, which is quite dry in Canberra and then cooked them. I wrote the measurements down somewhere, but I now , of course, can't find them. I don't think this should be done as a way to dry wet timber, but as a final stage before using, if you can't let them sit around for a few years.

For the twisted ones, try wetting them and clamping them flat. If that doesn't work, soak them, seal them inside an oven bag and cook them at around 250-300F until they soften up (15-20 mins) and then clamp them flat and take the oven bags off once they cool down. Leave to dry for a couple of weeks. Perhaps a last resort, but if they can't be used for anything else...

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Post by Lillian » Sat Oct 27, 2007 1:37 pm

What I took away from the rather lengthy discussion over at the OLF was that baking tops was akin to washing fabric before you sewed something with it, preshrinking it, if you will. The intent was to stabilize the wood. Actually it did two things at once, stabilize the wood as well as let you know sooner if there was any issues, internal stress that you didn't know about before hand.

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Post by BillyT » Sat Oct 27, 2007 4:53 pm

Carruth mentioned something about the conversion of cellulose in the wood to another form, I believe named hemi cellulose!

One thing that is done with steel is the rapid, repeated, cycling of temp from like -200º F then back up to 600º depending on the steel itself. Sress relieveing is the common named used.

I always wanted to try this with wood and see if this is a case of releasing stress in the wood.

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Post by Bob Connor » Sat Oct 27, 2007 6:06 pm

The Maton factory is kiln drying their woods down to 5-6% and then they will let it stabilise back to 8% for building.

Similar theory I guess but not as dramatic as the oven job.

They have recently lowered the RH in the factory to 41-42%.

I was talking to Pat Evans a couple of weeks ago about this. Seems they were having problems with some of their instruments up in Queensland.

He was also telling me that their standard soundboard thickness was 3.2mm for Sitka. Fairly beefy soundboard considering Matons aren't exactly braced lightly.

Bob

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Alain
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Post by Alain » Sun Oct 28, 2007 3:27 am

Thanks for your thoughts and input folks.

Also, I remember someone mentioning that cooking a top had exposed a 'pitch' pocket that had been otherwise undetectable...

I'm about to do it (possibly Monday), I'll take pictures, of course!
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Post by Hesh1956 » Sun Oct 28, 2007 4:21 am

I was just handling a top that I cooked a week ago and I wanted to give you some impressions.

I used a micrometer on the top and there is no difference in thickness from before to after I cooked it. In this case the possible pitch pockets look the same to me too.

But.... the bear claw figure that was supposed to be in the top and I could not see prior to cooking it I can now see. The top feels differently too to me more like a potato chip in texture and less "soft" and fuzzy.

I'll know the stiffness when I start working with it but I suspect that baking does not change that.

The top does smell like roast beef though so perhaps I should clean my oven...... :D

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Ron Wisdom
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Post by Ron Wisdom » Sun Oct 28, 2007 4:40 am

I believe in the book "Luthier Woods"(?) put out GAL, they say to use only air dried wood and not kiln dried. The forced drying changes the cell structure making it less suitable and perhaps more brittle. I certainly don't know and, so far, haven't cooked any.

Ron

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Serge
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Post by Serge » Sun Oct 28, 2007 6:37 am

Ron Wisdom wrote:I believe in the book "Luthier Woods"(?) put out GAL, they say to use only air dried wood and not kiln dried. The forced drying changes the cell structure making it less suitable and perhaps more brittle. I certainly don't know and, so far, haven't cooked any.

Ron
I kind of agree with that even though many experienced luthiers would have convincing arguments on how the resins would harden after baking their tops and for one reason.

Bought a plank of kiln dried purple heart at Adams and Kennedy a couple of years ago and this plank has twisted beyond belief compared to the air seasoned wood that i had in my shop.

But i'm no expert so i guess it's what your experience tells you but when i see that a top sounds great without baking, i'd rather keep proceeding the same way and not play with the fibers of the wood or elasticity of the resins of certain conifers, some fibers are long and narrow and could easily facilitate cracking in the long run, to me, it's just a wild guess that i'm not ready to take.
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Kim
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Post by Kim » Sun Oct 28, 2007 8:11 am

Serge and Ron,

I think when discussing this topic it is important to maintain a clear divide between hard and soft woods. I too steer clear of kiln dried hardwood, I feel that the density or more compact cell structure in hardwoods does not lend itself to the process of baking either.

I am no botanist and I am sure there is a more correct way to explain this, but I see trees as just being great big pumps. They suck nutrient rich water into their root system via capillary action triggered by the effects of sunlight. If a tree grows in an area with abundant sunlight but only limited available water, it simply does not need large capillaries as growth is generally slow and steady the year round. As a result, the cells are smaller and more compact making the wood heavy and more dense, and less incline to give up any stored moisture.

On the other hand, if a tree is growing in an area with plenty of nutrient rich water around, but only a relatively small window of sunlight per year to produce a growth period (think any of the picea family in situ) Then that tree is in a race against time and, all the other species growing around it seeking to compete for the lions share of that sunlight. In order to win this race each year, a spruce tree needs to produce large cells very quickly and to do this it requires big snorting capillaries to feed that rapid expansion during that growth period.

As I said, I am no scientist, but I just get the feeling that softwood, being more sponge like due to these large cells, is capable of expelling moisture more rapidly, and therefore, in wood that has already been dried out ready for use, little if any pressure would be created within those cells during the baking process to cause any adverse effect to the overall structure of that wood.

On the other hand, I think that the increased density and smaller structure of the cells found in hardwoods, by their very design, restrict the loss of any moisture. I therefore remain concerned about microscopic damage occurring and compromising the structural integrity of the wood from the rapid expansion of moisture within those tightly packed cells and the effects of the compounded pressure which would ultimately occur, even in a board which had a relatively low moisture content to begin with, during the baking process.

But, that's just a hunch. 8)

Cheers

Kim

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Serge
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Post by Serge » Sun Oct 28, 2007 2:19 pm

Thanks Kim, great post!

Thanks for separating the hardwoods from the soft ones, i had forgotten i guess! :lol:

Good points and i'm not gonna encourage someone not to bake their tops, after all, if the experience worked well for others, it should go just as fine for us but i'd rather have sweet sugar pies coming out of that oven for now! :lol: :lol: :lol:
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