Flattening curls in wide cocobolo (and other valuable woods)

[btberlin]

I recently bought a Cocobolo set from Global Woodsource (http://www.globalwoodsource.com/), in Santa Clara, CA while visiting my son. The set I picked was rough off the resaw bandsaw,and unfortunately had a potato-chip curl in one piece of the back, and a slight twist in the other. The wood is too valuable to let it go though, so, when I got it home, i tried a few ways to flatten it. The way suggested by Eric Jacobson, co-owner (?) with his dad, was to put weights on it and let it rest for a few months. After a while, seeing that not working, I tried a vacuum storage bag - which, with the wood enclosed and against a flat board for support, puts about 3000 lbs of weight (15 lbs per square inch) on the wood. No luck there either. So, it hit me that i could use the heated bending blanket and some plywood to flatten the potato chip curl. I set up the blanket, and the metal slats, and some Kraft paper as i would have for bending sides, put that over the curled back piece, but the whole thing between two pieces of 3/4 plywood, and used C-clamps to squeeze once the blanket reached temperature. Then i let it cool as usual and opened up. That worked extremely well. The only downside i saw was that the heating caused a tremendous amount of oozing of resin, which appears black - making large areas of the piece look charred (but it isn't). The ooze comes off, slowly, with paint thinner, but, since the piece is way too thick, a cabinet scraper and a drum sander is taking care of removal, while getting the piece to the right thickness. So, I wouldn't hesitate to purchase a set that looks hopelessly curled if it were the wood species i wanted, and the appearance i loved.

BTW - http://www.globalwoodsource.com/ -- their site, shows that they have just gotten in some wide cocobolo, as well as some other interesting woods.

bert

[tippie53]

Often this happens on fresh cut wood. Best advice is to sticker it and lay weight on it. Flipping it once a week or so. After a while it will acclimate to the environment. If you have a few clamps you can also just clamp it flat . When I store wood that I just resaw I use a 3/4 in sitcker and clamp the pile together. Once every few weeks I open them and flip the side so I can expose all sides to the air.
The clamps keep them from cupping.

[btberlin]

Yeah - that would work with a wood that absorbs or loses moisture readily. Have a look at the Wood Database site, http://www.wood-database.com/lumber-ide ... /cocobolo/, especially in relation to coco's resistance to wet/dry cycles because of its high oil content. Cocobolo is described as having an "incredibly high density" and in fact sinks in water. And that ain't because it becomes waterlogged! Stickering is of course common practice for storage of wood, for the purpose you mention. It didn't work to well for coco for me though.

b

Bert,
Would you happen to have a photo documentary of the procedure? If not, maybe
you could photograph the procedure next time you employ it.

-tommy

[tippie53]

All wood will move in accordance to the moisture content of the cells. The surface cells will gain or loose moisture rapidly compared to the deeper cells ,, this is what makes the cupping . By flipping . you allow the cells to slowly let the excess moisture out. Without a kiln to dry the wood , you will have to rely on air .
This can take a while , about 1 year or longer. Woods like Cocobolo and other rosewood have a higher oil content but the moisture leaving and being absorbed will highly influence the outer layer and often the top layer first. This is why stickering helps to expose both surfaces to the air.
Wood is always in flux and it takes a long time for it to become perfectly acclimated . Kiln drying starts first with air exchange to lower the relative humidity in the room so you can control the amount of moisture loss. Often green wood can be as high as 80%. We had a saw mill and used to run the wood in air for about a week to pull the wood to about 30%. Then at this point we could apply heat and control the loss of moisture for about a 30 day cycle. We took the RH down slowly by controlling the heat and air flow. By the end of the 30 days we wanted to be at 6% in the wood.
Drying by air takes longer and you have to control air flow. Modern kilns also use radio waves to help heat wood. Most kilns are just large dryers. Martin will actually add steam and take the wood up to a high moisture content then bring it down to 6%.

[tippie53]

I have cut and worked with my share of Cocobolo. In all cases , my high end wood is always stickered and clamped.
Honduran Brazilian and cocobolo