Cool Drying

[Mike Gibson]

It appears the most common way to dry rough turnings is to keep them cool (on the floor). My question is why would a refrigerator not work as modern ones extract the moisture as well. Wouldn't this speed up the process Is my thinking wrong?

 

[john lucas]

Mike cool is not what we are trying to do necessarily. Air movement also matters. Slow even drying is what helps keep a bowl from checking. I think some have done some playing with freezing. I believe freezing would dehydrate the bowl over time. I don't know what happens when you thaw it out.

 

[GeorgeH]

Mike, for about a hundred bucks you could add a hygrometer and wood moisture meter to your collection of gadgets. Then cut three pieces of wood, from the same wood source (preferably green) and try drying them in three different environments. When you get the scientific results from your experiment you can share the info. with the rest of us. :cool2:
Well, maybe that's wishful thinking. But I had to try.
Part of the cooling process (refrigeration, air conditioning, etc.) involves drying the air in a given environment. So refrigeration should (should) dry the wood faster. How much faster and how evenly remains to be seen.
But I'd give it a try if I had the frig. space. Freeze drying, as I understand it, requires a "flash" freeze process to be effective.

 

[Jake Debski]

Every so often I run into a situation that my current skills can't handle, or I've run out of time, etc. I put the rough turned piece, partially turned piece, etc. into a plastic bag, close it tight and toss it in our freezer. My homeland C.E.O. sometimes complains about all the lost space but my wood is safe. It dries, it warps, it needs to be trued up to finish but I've only has one hollow form crack. When you remove the item from the freezer and open the bag the bag is loaded with heavy frost crystals. You know like the fish you caught 3 summers ago and forgot they were still in the freezer.The dry time varies, I often forget its in there and leave it for several months and it is really dry. The only down side so far is some of the pieces don't seem to finish as nice as the slow ambient air pieces do. David Ellsworth, during one of his demos, made mention of the cell walls being ruptured during freezing or boiling and therefore would lack that nice glow that wood has when properly finished. He referred to it as chatoyance(sp?)

 

[Bob Hadley]

At the Pasadena AAW symposium (what year was that?) Vic Wood recommended a process that applied tung oil first, and then freeze-thaw-freeze-thaw (and so on) to dehydrate finished turned bowls to a stable EMC.

Because this takes up freezer space, I don’t do it that often, just with pieces that may be prone to major distortion. The theory is the freezing affects the cell structure and reduces drying stresses. It seems to work. As to any affect on the chatoyance (changing or shimmering luster of the surface), I would not bet against David Ellsworth. Not all woods have chatoyant characteristics though. The odd macadamia bowls I’ve been freezing finish fine.

 

[Joe Greiner]

US patent no. 5,852,880 (http://www.uspto.gov/patft/html) teaches a process for freeze-drying lumber. The specification asserts no damage to the wood, but this may or may not be valid at the microscopic level. Note that any commercial use of unexpired patent material will need a license from the patent holder. The patent was issued Dec. 29, 1998 and is probably still in effect.

Joe

 

[MichaelMouse]

Wow! It's relative humidity that counts. The water in the wood has to have a place to go, and the air obligingly dilutes and carries away as much as it can, depending on what burden it already has on board. http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr113.htm Is a good reference, especially chapter three. Even has the equivalent moisture contents for given relative humidities.

Means if you warm the air/wood, you increase the amount of water the air is capable of carrying, and supply extra energy to help break the bound water away from the cellulose. Lowering temperature does the opposite.

If you want to slow the rate of moisture loss to ensure the surface never gets too far ahead of the interior, go for higher relative humidity by lowering the temperature. Controls degrade. Frozen wood dries very slowly. Got more than a few cords out there as demonstration right now.

Second part of drying is the "away" business. Restricting the airflow eventually results in higher relative humidity around the piece, which is why we bag.

Get that hygrometer and monitor your relative humidity. The rest is all in the literature.

 

[tdrice]

Freeze drying

I had a piece of fresh cut apple that I rough turned into a bowl with the inside off center, meaning I had one side much thicker than the other. (1/2" and 2 1/2") I knew that is I just let it dry it was sure to crack. I put it in the freezer (chest type) unwrapped where it soon migrated to the very bottom. I pulled it out 3 years later. It was completely dry with no checks or cracks.
Just my experience for what it is worth.

 

[Jake Debski]

MM,

I have no doubt that your science is correct. It is just that for me the freezer allows me to be less than conscientious about taking care a project that I want to salvage when and if I figure out how to overcome a technique short coming. Once its in the cold I can forget it till I'm confident enough to tackle it again.

 

[MichaelMouse]

I use the same philosophy, with the outdoors as my freezer. Frost-free freezers dehumidify periodically, so you're more or less stepping down if you have the space to spend. Considering that you could use a big box and a dehumidifier with decreasing settings without disturbing the salmon and broccoli, hardly seems worth it.

Yes, the science is sound.

 

[Jake Debski]

I use the same philosophy, with the outdoors as my freezer. Frost-free freezers dehumidify periodically, so you're more or less stepping down if you have the space to spend. Considering that you could use a big box and a dehumidifier with decreasing settings without disturbing the salmon and broccoli, hardly seems worth it.

Yes, the science is sound.

Frost free? Naw, cost to much to run, and winter keeps the food frozen while we thaw the frost build up. The broccoli and salmon have a legitimate issue with me though.