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Freeze Drying

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Freeze Drying

Postby Barry Guest » Mon Jul 29, 2013 6:46 am

I searched the forum to see if this topic had been mentioned previously, but didn't find a single mention. My question is: has anyone tried drying timber by freezing? Seems that you freeze a piece in a plastic bag for three days, then remove the crystalizations that form, freeze it again repeating the process until forced removal of the moisture content is reduced to the local atmospheric moisture content.

Any comments? Knowledge? Pros and cons?
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Re: Freeze Drying

Postby Chuck Tweedy » Mon Jul 29, 2013 9:43 am

Interesting idea.
I don't know how much ice you would get inside the bag. I would think the water would pretty much just stay frozen in the wood.

True freeze drying (or lyophilisation), uses vacuum to remove the water directly by sublimation (ice -> gas). So you could put the wood in a vacuum bag while frozen.
Seems like a lot of work :-)
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Re: Freeze Drying

Postby David King » Mon Jul 29, 2013 8:12 pm

Why the plastic bag? Seems like that would prevent normal sublimation from taking place. A modern frost free freezer stays pretty dry. I might be worried about the wood picking up off odors. I'd include some baking soda in a tray.
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Re: Freeze Drying

Postby Mark Swanson » Mon Jul 29, 2013 10:53 pm

I think I'd be worried about the same thing that happens to wood in a natural setting. When it is wet, and it goes through cycles of freezing/thawing, it cracks. The water in the wood expands as it freezes, something that doesn't happen when drying it normally. The freezing seems like something that could cause cracking in a thin piece of wood.
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Re: Freeze Drying

Postby Barry Guest » Tue Jul 30, 2013 5:47 am

I posted this topic after talking to a woodworker at my local market day on Sunday, selling his beautiful work from a stall.

His specialty is bowl turning. He told me he turns the bowl green, then "cures" the finished product by freezing as above until the wood is stabilized. I questioned him about splits, warps etc and he said that his success rate is above 90%. When the item comes out after freeze drying, he puts it back on the lathe to sand and finish.

He said he does it this way because he has a network of local tree loppers who supply him. By turning the item green, he sidesteps the process of natural drying or kiln drying.

Some of his work is turned down to less than a 1/4" thick, so I was amazed at this process and wanted to know more about it. Think I'll need to go back next month and have another chat.
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Re: Freeze Drying

Postby Jason Rodgers » Tue Jul 30, 2013 10:29 am

That's interesting, especially since bowl turners usually prefer burls and spalts that we'd consider less stable.
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Re: Freeze Drying

Postby Barry Daniels » Tue Jul 30, 2013 3:13 pm

Bowl turning involves different issues than guitar wood. Turners like to turn green wood because getting a large block of wood dried without cracking is difficult. Also, green wood turns more easily. Neither of those are factors for us.
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Re: Freeze Drying

Postby David King » Tue Jul 30, 2013 6:33 pm

Most domestic trees go down to -40º with no issues at all out in nature. The sap acts as a natural anti-freeze. As soon as the wood is cut it will usually drop excess moisture saturation until it gets to 20%. At that point a hard freeze will likely have some effect on individual cell walls but it's unlikely to cause the wood to fail completely as there's some space for the water to expand into.
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Re: Freeze Drying

Postby Mario Proulx » Tue Jul 30, 2013 9:53 pm

I played around with various "tricks" early-on, and one thing I did was to soak a few raw guitar tops for a week or more, then tossed them out in my unheated garage. In January. In temps passed minus 40. Left them out there for months.... All told, the wood was neither better or worse than the sister sets that didn't get the treatment. So, it won't break, crack or split, but it also won't do anything "special" to the wood.

I have some raw spruce billets that have been in my shed for 10-12 years now, and have seen temps nearing +100°F and -54°. Nicely seasoned, but not special otherwise.
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