drying wood in a freezer

[Raul McCai]

Just, thought I'd try it. You know, one of those wacky ideas with no down side in the event of failure.

Freeze drying is an old thing. Moisture loss in the freezer is real. Real slow, but real
I tossed a chunk of very green wood in the freezer 24 days ago.
At the time it weighed 399 grams
24 days later it weighs 360 grams
It is definitely losing water.
Comparable hunks of the same log left in the open air of my shop are much drier (but still wet) and much more warped and checked.
This piece in the freezer has experienced no checking or warping.
It's back in the freezer. This may be a game changer if the drying progress is linear; that is if the zero checking and zero warping continues on down to 8 or 6 % moisture. I may end up with a couple of used chest freezers.

I ain't the first person to try this, but I've not seen any one tracking the moisture loss.
http://www.woodturningonline.com/forum/viewtopic.php?t=1010&f=5

 

[hockenbery]

I use the freezer for the opposite: to keep wood wet. It has to be in plastic bags to prevent the drying in frost free freezers. Keeps wood in good condition for turning wet later.

A frost free freezer will dry wood over time. Not sure how controlled the drying would be.

 

[Zach LaPerriere]

Good experiment.

I'll be curious to see if the moisture moves from the inside of the bowl to the outside. If it doesn't, you'd think there may be checking. I see that a lot when it gets super cold here. I'm a big fan of drying bowls a bit above freezing, since things slow a little and cracks become rare.

 

[Bill Boehme]

Did you put a rough turned piece in the freezer or was it a solid block. For the sake of efficiency it would be better to rough turn the piece before freezing it.

Freshly cut very wet wood loses moisture very fast. After collecting a lot of drying data on rough turned green wood bowls and plotting the results in Excel, it was clear that essentially all of the free water was gone in less than a month for average size bowls. The remainder of the drying process was losing the bound water which took an additional two to six months depending on the size and species of the piece. Maybe I'm just lucky, but I haven't had any cracked bowls by just coating them completely with Anchorseal and letting them dry in our air conditioned garage.

 

[Joe Greiner]

US Patent No. 5,852,880, by Jack Harrison of Wasilla AK, relates to freeze-drying wood.

from the Abstract:

A method for drying wood by placing the wood in a dehydration chamber in which the temperature, humidity and pressure are controlled. Air and or gasses are circulated in the chamber to wick away moisture while the wood remains frozen. Both the internal temperature and the circulating air are kept below freezing during the drying process. Atmospheric pressure is manipulated to enhance drying and may be either increased or reduced. Exposure to the volume of dry air (air with zero percent humidity) varies with the drying process and depends on the species, the quantity of wood to be dried and the initial moisture content of the material.

 

[Pete Blair]

I've been using a freezer to keep some special pieces that I got wet and didn't have time to turn with mixed success. My testing was anything but scientific. My wood freezer is outside and is shared by food overflow. My wife believes I could buy any dry wood I want cheaper than keeping this thing cold even our mild summers!!!!

 

[hockenbery]

I mostly keep pieces in the freezer for demos coming up.

I have blanks in the freezer now I prepared a couple of months ago for two demos I will do in January. The blanks are ready to mount Shrink wrapped then in the a couple of plastic grocery bags and then in a thick gargage bag, taped, & labeled. The layers of plastic provide the moisture barrier to prevent freez drying.
The day before the demo I take them out of the freezer to thaw. Leave the shrink wrap on until the demo. The blanks are in the same condition they were when I put them in the freezer.

 

[Paul Gilbert]

this sounds like a good topic for a kids science project. The kid would have to anticipate the upcoming assignment as the project would run for 6 mo. or more.

Technically the process of "freeze drying" is called sublimation which is a chemical process where a solid turns into a gas without going through a liquid stage. An example of sublimiation is when you get freezer burn on an improperly wrapped piece of meat. The interesting part of the above experiment would be to determine if the frozen water moved through the bulk of the specimen, or if all drying was occurring at, or very near, the surface. I also wonder about the effect of freeze drying would remove bound water, given enough time. I know that freeze drying completely dehydrates food without loss of nutrient value, but this industrial process is done under high vacuum and low temp.

 

[Raul McCai]

Well if any one wants to build a big enough vacuum chamber and send it to me along with a huge chest freezer big enough to take it; I have a Sergeant Welsh Twin Stage Rotary Vein Vacuum pump that will suck the snot out of anything. Send it to the address on the back of My Screwball Avatar

 

[Paul Gilbert]

For the man who has a 7K lathe, what better to set beside it than a 3K freeze dryer.
https://harvestright.com/store/

of course you could build one of these

View: https://www.youtube.com/watch?v=1qckdVa_UF4

but you would use up a lot of dry ice if you dried very many bowls.

 

[DON FRANK]

The basic idea of freeze drying its that Water boils at a much lower temperature when in a full or partial vacuum. The idea is that the water leaves the cells without rupturing them so that you don't have the normal shrinkage that occurs from just dehydration. If you take a piece of steak and freeze dry it until all the moisture is gone it will hold it's shape fairly well depending on the fat content of the meat. If you air dry the same piece of meat it looks like beef jerky.
A friend in Colorado who owns several commercial freeze dry machines (and is also a wood turner) has been experimenting with drying once turned bowls with varying success. We have had several discussions about what has worked and what has not. The process is fairly slow an far from certain.
Also, there is a book available on the subject of making a vacuum kiln. Companies make industrial vacuum kilns for drying long dimensional lumber. The book is more concerned with drying bowls and smaller turnings using a large (12-20") PVC pipe for the chamber and an electric pad heater to maintain a certain temperature while pulling a vacuum on the chamber. It sounds like a once turned bowl can be dried to 8-10% in 3-5 days. If someone is in a hurry it might be worth the effort but it's a lot of work and expense.
Coming full circle, the freezer sounds like a great solution for maintaining the moisture level of a blank without checking and perhaps for slow drying of once turned bowls. Any version of a home freeze dryer or vacuum kiln is going to be a project.