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 Post subject: Cooking Hardwood
PostPosted: Sun Jun 21, 2009 5:51 pm 
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Koa
Koa

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I often see threads on cooking tops. Anyone cooking their back/side sets? How about Koa?


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 Post subject: Re: Cooking Hardwood
PostPosted: Sun Jun 21, 2009 6:23 pm 
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Koa
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One builder told me that he heats his BRW in a hot press before using it. He felt that he had less cracking as a result. I think that most side bending heats the wood somewhat equivalent to cooking.


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 Post subject: Re: Cooking Hardwood
PostPosted: Sun Jun 21, 2009 7:33 pm 
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I have done this, but to backs and tops. But it is not something I have done at all in past few years. You don't need to do sides as they get pretty cooked in the bending process. You can make a box or put them in the oven. I had at one time a locker with basically a space heater. I know JJ just posted a box he built.


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 Post subject: Re: Cooking Hardwood
PostPosted: Sun Jun 21, 2009 8:52 pm 
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Mahogany
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I've had pretty much the same question on my mind Rich.

To add to it I know some may leave their sides in the bender to cook but does anyone leave them in for a whole hour? For tops seemed like it was mostly an hour or more so I assume it should probably be that long for back and sides too?

Matt


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 Post subject: Re: Cooking Hardwood
PostPosted: Mon Jun 22, 2009 8:11 am 
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Brazilian Rosewood
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The 2 main reasons for cooking tops seem to be:
1. "Setting the sap" -- so that any sap in the wood is crystallized or hardened and doesn't go gooey on you. This is normally an important part of the kiln cycles for any Pine.

2. Driving out humidity to lessen future cracking problems. From what I can tell, the general consensus is that cooking the top wood drives the moisture down close to 0%. Then, it partially re-humidifies itself over the next several weeks... but doesn't really come back up to the past high levels.

3.... Raising the temperature to kill stuff doesn't really seem to be part of why folks do this.

So.... expanding that to backs and sides....

1. Do you have a type of wood that is sappy and would benefit from "setting the sap."

2. This one may be the real benefit for woods that want to split with humidity changes.... I could see this being a real benefit on species with large reactions to humidity... maybe Oak, Maple, Osage, etc... BRW may fall into this camp as well. It probably wouldn't have much benefit on things like Mahogany or Mesquite.

The only concern I might have is speed.... I have noticed the commercial kiln facilities that do this sort of thing go slow slow slow... as in over weeks... and fast temp and humidity changes could cause more trouble than good.

Carrying this through, our heat/wet bending sides may do the opposite... cook additional water into the wood rather than drive it out.

Good luck

John


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 Post subject: Re: Cooking Hardwood
PostPosted: Mon Jun 22, 2009 9:03 am 
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Brazilian Rosewood
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Ditto for all the same reasons that TruckJohn states.

One question I have...has anyone cooked cedar tops? If so, what differences/similarities compared to spruce?

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 Post subject: Re: Cooking Hardwood
PostPosted: Mon Jun 22, 2009 1:00 pm 
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Koa
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It`s my understanding that cedar doesn`t retain much moisture.I`ve had tons of experience using it in construction,decks etc, and it seems it`s pretty dry ,and doesn`t seem to shrink.The last guitar I did had a WRC top and I didn`t cook it and it seems fine.I don`t think I would cook Cedar,or Redwood.
James

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 Post subject: Re: Cooking Hardwood
PostPosted: Mon Jun 22, 2009 1:17 pm 
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Brazilian Rosewood
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James W B wrote:
It`s my understanding that cedar doesn`t retain much moisture.I`ve had tons of experience using it in construction,decks etc, and it seems it`s pretty dry ,and doesn`t seem to shrink.The last guitar I did had a WRC top and I didn`t cook it and it seems fine.I don`t think I would cook Cedar,or Redwood.
James


What about sap content...and any change from cooking?

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 Post subject: Re: Cooking Hardwood
PostPosted: Mon Jun 22, 2009 5:28 pm 
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Brazilian Rosewood
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Just be aware of the term "caseharding"
This happens when the outside fibers of a piece of wood dry out much faster than the rest of the piece.
It will look as your cooking was a success until you plane or sand the piece and expose the inner fibers that still have moisture in them and the piece warps .
The case cells are dry-but the inside cells are not.

The reasons for this condition are -to high a heat-to low a humidity in the chamber where this process is taking place.
To long an exposure in this inviroment for the woods.

mike

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 Post subject: Re: Cooking Hardwood
PostPosted: Mon Jun 22, 2009 11:00 pm 
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Brazilian Rosewood
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Case hardening is a giant problem on certain species.... like Oak.

Pro kiln facilities go through all sorts of gyrations to prevent Oak from case hardening during kiln cycles....

My understanding is that air drying susceptible species of wood thoroughly before kiln drying them mostly takes care of this problem...

As Mike mentioned... put a Plane to it or cut it.... and it can twist and warp like crazy. I resawed an Oak board that was case hardened.... the thing was straight as an arrow, flat, and beautiful before sawing... and curled like a Christmas gift ribbon directly behind the blade while resawing.... It was 8" wide and 6' long and formed into 2 counter-rotating spirals... A total loss... In hind sight, I could probably have pitched it out in the rain for a couple months and it may have flattened... but I was a little aggravated.

Good luck

John


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 Post subject: Re: Cooking Hardwood
PostPosted: Mon Jun 22, 2009 11:16 pm 
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Koa
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Regarding cooking hardwoods, and case hardening.

Yup oak is a nasty for case hardening... the other thing we really don't hear too much about is that oak has something referred to as "dynamic tension" which sometimes can turn a thicknessed and jointed plank into two spaghetti sticks when ripped in half....even if that plank was air dried. Learned this one the hard way... So is best to buy oak as close to the final dimensions you need, then thickness and or joint to final dimensions.

Regarding cooking spruce...good idea...sets the pitch. Cedar don't gotts much pitch...so cooking not needed. Hardwoods don't really need to be cooked unless you wanna eat them, and well I never found a hardwood that tasted any good cooked or raw other than bamboo and then only the part closes to the roots.

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Padma

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 Post subject: Re: Cooking Hardwood
PostPosted: Tue Jun 23, 2009 6:25 am 
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Cocobolo
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I have cooked cedar, in the same way as spruce with no problems. I can't really comment on whether or not it is needed.

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 Post subject: Re: Cooking Hardwood
PostPosted: Tue Jun 23, 2009 11:00 am 
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I hope this isn't too far off topic to discuss in this thread. The humidity is very high in our area now. Could one "warm" a joined top, back, and braces in the oven on very low heat to reduce moisture before gluing? Curious as I don't have a humidity controlled environment.

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